hmm i took mine out to this weekend with 30+ mph cross winds out on the water i couldnt go for it.well actually i did and it started dancing REAL bad chine walking and i backed out.but i also noticed that if i hammer down on it i feels like the motor flatens out around 5000rpms.then if pull back to about 3/4 throttle it seems to pick back up and pull real hard.maybe the blower belt is slipping and when i back off a little it catches up and grabs? anybody else have this problem with a procharger? i have the nickerson carb on and did a few plug checks and they look good so far(DIDNT GET A FULL THROTTLE PLUG CHOP YET THOUGH)and all i needed to do was adjust the idle screw about 1/8 turn.

I had that rev limit feel one time and had the timing way high,,blew a hole in the piston. Also the dieseling doen't sound good. Can you get a timing light with built in advance?Are you sure you are rich at WOT and not just after coming in? I'm probably less knowledgable than you, but that's my 02.

Hardcore how big is your boat, what brand? Just curious as Im running a similar setup. Greg

My experience with carburated procharger is that it tends to lean out on top, keep in mind that if plugs are rich in midrange, a short blast at WOT is not going to clean them up, although you may be lean on top end. Are you using the power valves, there was a good thread regarding this subject some time back, regarding the power valves and the correct opening under boost. Basically it reads the difference in pressures. You may want to investigate this issue.

yeah hardcore you need a timming lite with a advane knob so you can set it at 30 or whatever you want and rev it up and dial in toal advance.no need to take the balancer off and degree it a good timming lite will do the job.

Thanks for the reply guys. I don't have a "dial-back" timing light so I have to rev it up in neutral till the timing stops (like 3500 RPMs or so) and check the max advance on the balancer. I don't really like the dial-back lights because from my (albeit limited) experience and from what I've read, no two give the same reading (usually like a few degrees off).
I don't think it has a hole in the piston though because I would probably have noticed that by now (I hope!).
I think I'm gonna go way rich and try it again. It might be high speed lean out.
I idled down and shut it down quick (but didn't kill it at WOT) and checked the plugs in the water. I don't think just idling down like that for a few seconds would change the look of the plugs that much, though. The plugs have a light brown/tan discolouration on the center insulator/electrode and black soot on the threaded part. I'm currently running 12 jet sizes bigger than the carb came with and I have two power valves (6.5 HG) so I thought that would be enough fuel. But, better safe than sorry!
I'll jet it up to like #99's and work my way down.
As for marking the balancer all I'll do is measure the circumference of the balancer (with like a cloth tape), (or you can calculate it from the diameter (pi x radius (1/2 dia.) squared - I think) divide it by 360 (as in 360 degrees) and then multiply that figure by 30 to get the measurement from 0 (TDC) to 30 deg. advance.
BTW: HP Junkie, I have a 1995 American Offshore 2600. I'm running a stock B-1 L/U with nosecone.

I jetted the carb up this weekend to #94's all round and now the motor is running way rich. I checked the timing and it's definitely at 28deg. BTC. I also reinstalled the fuel inlets that came with the carb since they have bigger orfices than the .110" inlets that came in the Holley Trick Kit. This is something to look out for because when you have positive displacement of air through the carb ("blow through") the carb will need to flow fuel like it was a Dominator and the bowls can only fill as fast as the inlets will let them. The larger the mains (and the higher the air pressure in the bowls) the quicker the bowls will empty out so you need to keep up the flow. This is quite possibly why some P/Charger (and other blower) setups lean out at high RPM. I'm still not certain that the inlets I have in the carb are big enough so I'm going to order some .150" steel or Titanium ones to make sure.
I also installed the anti-pullover ("butterfly") squirters to prevent fuel enrichment through the accel. circuit.
I ran the boat with two other people and a bunch of gear on board and it ran easily up to 96MPH on the GPS but then it gets to 5600 RPM and starts to lay down - like it's flooding or running way lean. I think if it was lean I would have hurt the motor by now and the plugs are telling me that I'm drowning them (the whole end is black and wet). I have never seen over 5600 RPM and I'm even starting to wonder whether my 6000RPM chip is off by 400 rpm because the thing pulls like a freight train up to that point. (I mean 60 to 95 MPH feels like my old Drag-Motor Mirage did with a 24" Yamaha prop!)
Also, I am getting over 15lbs of fuel pressure at full boost (5lbs) so I'm wondering, is it flooding up there because the seats can't handle that kind of pressure (effectively 10 lbs of equivalent atmospheric pressure)?. I have the Aeromotive regulator referenced off of the carb box and have it set at 7.5 lbs static (about 5.5 to 6 lbs with idle vacuum). I guess I'll go back down to the #90 jets and gradually drop the pressure. I'm also ordering a labbed 32 Bravo 1 prop because I'm convinced the one I have is not the prop for my application. Stay tuned for next week's episode...:D

sounds like your getting pretty close.mine is laying down at 5000 then if i back down to 3/4 throttle it starts pulling hard and you having to slowly inch the throttle up.full msd 30 total advance 5600 chip with a new nickerson blow through procharger set up carb (hp 500).the plugs look perfect doing a midrange plug chop a little rich after idling in the harbor and flushing it.i havnt been able to just give it a full run and plug chop as its been to windy so im planning on it this week.i also have the aeromotive pump/reg boosted of the box set as low as possible at around still 7+psi at idle and up around 13 under boost.im think my belt might be slipping up top end causing it to lay down around 5000 after doing a search on some old posts. so i put about 4 to 5 turns on the tensioner and its ready for another try also.

I think you need to put 2 more degrees of timing in it for total of 30.

On fuel pressure, if the regulator is refrencing the carb box the pressure is going to be the lowest when the engine is off & go up from there. I thought that the Aeromotive regulator was a 1 for 1, that means as pressure goes up the fuel pressure goes up equal amount. As motor off 5 psi, motor running pressure in box say at 3 psi, then fuel pressure is 8psi. In effect the carb is only seeing 5 psi, since pressure around it is at 3 psi. If your pressure is going down when the engine is running you may have a fuel pump or supply problem. That could explain the laydown @ 5600rpm

I thought the carb setup used a 1:1 regulator and the EFIs the 3:1 to up the injector capacity. Is it possible you have an EFI regulator?

Thanks for the input guys.
I haven't been able to do a full throttle chop yet either so it may be lean right up on top (!!). I will definitely check this weekend.
Turbojack - on the regulator issue I have to admit that I f@cked up there because I was thinking about when I initially had the boost referenced off a port UNDER the carb. (this is where I have my boost gauge now). Because that location actually generates vacuum at idle, I was getting a drop in fuel pressure with the engine idling (since the Aeromotive Reg. actually works both ways), but I realize now that the pressure is now at 7.5 lbs at idle (since I'm now referencing the reg off the box).
It is definitely pegging the 15lb. fuel pressure gauge at full boost though (and doesn't fluctuate at all), so I still think it might be flooding.
Thanks for the advice on the timing. Seems the general consensus is 30 deg. timing advance.
Later...

nordicheat hey this is james from jax. FL. just finshed up with my fast system i would like too look at your base and send you what i have thanks james [email protected]

Update:
Changed jetting back to #90s on all 4 corners.
Checked float level & set at slightly above (1/6-1/8") bottom of hole for both bowls.
Turned fuel pressure down to 6 lbs. at idle.
Left max. timing @ 28 degrees BTC.
Installed a 34pitch labbed Bravo 1.
Ran it and noticed a lean sneeze during part throttle acceleration so changed secondary squirter to a # 42 (which cured the problem).
Ran it up to 100mph in about 3/4 mile and had to chop throttle because was running into a cross-wind and trimmed up and boat started to lift too much. Still felt like it was laying down on top so I decided to change prop to really see what was going on.
Changed fuel press. back to 7.5 @ idle to be safe and installed 29" "Accelerator".
Ran it again for about a mile and held it down and the GPS wouldn't't go over 94mph and it kept "bucking" like it was running out of fuel - like stalling for a few seconds
and then catching back. I finally shut it down just cut it off and checked the plugs - and they are LEAN! Like bleach-white insulator lean. I had my brother in the boat and he kept his eye on the fuel press and says it was pegged - steady- at 15+lbs. I think this all confirms my suspicions - the carb is drying out the bowls and the motor goes so lean it stalls momentarily (thankfully, too lean, too suddenly to "lean out!).
The reason it's more noticeable with the smaller prop is because it's accelerating and revving harder. I think it's the needle and seat assembly (.110" - I believe) not being able to keep up with the flow of two #90 jets (each has a .1055" orifice) as well as the two Power Valve orifices which look like around .080 ". Even though the fuel is flowing at 15 lbs (10lbs effectively @5lbs of boost) at the needle, it still can't flow enough.
I'm ordering some .150" needles and seats shortly. This is the biggest they make so hopefully it will be enough.
I keep you all posted.

i like the aeromotive set up better for a procharger.but what your saying makes sence hopefully your fuel pump can keep up with the big needle and seat.man that motor is thirsty.

I have the Aeromotive A1000 Pump plumbed with -8 hose and I have a Aeromotive Carb Bypass Regulator w/ boost reference port. According to what I've read, this pump is good for between 1,000 and 1,300 hp depending on whether you're injected or carbed. I'm pretty sure it'll keep up with the biggest needle and seat. BTW: I've just ordered a set of .150" Titanium needle assemblies from Summit Racing. Hopefully I'll get them this week so I can test again this weekend.

Is your pressure gauge on the regulator or at the carb? Are you running 1 or 2 lines from the regulator to the carb? If gauge is at regulator & only single line to carb maybe you do have 15lbs at the regulator but not at the carb.

Opps sorry for some reason i thought you had a mallory pump.

My pressure gauge reads off the Regulator which is connected via a single 8" long -8AN hose to the connector on the Vortech box (yep - that's my bastard setup!) which then tees inside the box to 2 -6AN hard lines into the carb inlets (this is all part of the Vortech box setup). I don't see how the pressure could be dropping there though, because there is really no restriction between the regulator and the box and the carb inlets and, after all, all of the fuel is still only going through those tiny little .110" needles into the carb. I can move the gauge fitting from the Reg. to the fitting on the carb box and that would move it downstream about 8 inches so that if there is a restriction between the reg. and the bulkhead fitting on the box, I would know.
BTW: Has anybody tested the difference between the Vortech and the Procharger box? (The Vortech box looks like it might have a restriction where the tube flows into the box) Or either one and a carb hat or pipe? I'm starting to think that this whole carb box deal is more trouble than it's worth. It's certainly a pain in the A$$ to change jets! Why don't they make them so that the lid is deeper than the bottom so you can easily get at the float bowls without pulling the carb out of the box?
:mad:

I flow tested a Vortech carb box when I started designing the supercooler. For comparison I flowed a 750 carb on a Superflow 600 flow bench. All numbers are reported at 28" H2O.

1000 CFM - carb in box without lid
643 CFM - carb in box with lid and pipes (2@90s)
545 CFM - carb in box with lid, pipes and intercooler

That's right, the plumbing to connect the blower to the intercooler and carb costs you that much airflow, more if you are using more than 2@90s. We never think about this because the blower overcomes the restriction and we get a overall increase in performance.

The supercooler carb/ intercooler box flows 735 CFM as opposed to 545 CFM and this adds about 90 HP without touching the blower pulley.

I haven't tested the Procharger box but based on the similar geometry I wouldn't expect it to be any better.

I also don't like the fuel line plumbing on the Vortech box. Every fitting increases restriction and reduces the max flow available. I think it makes sense to keep the two lines provided out of the regulator separate all the way to the fuel bowls. I tried to use the Vortech fittings in the supercooler but they interefered with air flow.

I am looking at a Holley book by Mike Urich and it says 110 seat with a window(not holes)flows 295 lb /hr @ 6 psi. I've read elsewhere it takes .7 lb/hp for supercharged setup. That's support for 842 HP if you have 6 psi at the carb. As fast as you are you are prob right there.

Thanks for your input, guys.
Tomcat:
If I knew what I know now when I was buying the Vortech box, I would have definitely bought your Supercooler setup. It certainly looks a lot nicer. So does the dyno sheet, from what I've seen;)
I agree that Vortech box plumbing has too many tees and 90 deg. turns, but I still can't see it being that much of a restriction to cause the problem I'm having.
Cooltoys: Thanks. Thats the kind of info I was looking for. If Mike Urick is right, then I don't see how the .110 seat assm. could be the problem. I don't know if I'm at 840+ HP. I don't think so, but I would like to be.

Tomcat: I know you and Dean Nickerson are the Gurus of Centrifugal setups - so, do you think it might simply be just too lean? Could it be that I might be rich at mid- range but way lean at full boost/high RPM? :confused:

I guess if I don't sort it out this weekend, I'm just gonna have to give up and give Dean a call.
Thanks again guys.

cooltoys61:

We have seen 1000 HP with 0.6 lb/hr, so that's in line with your calculation.

Hardcore:

Thanks for the detailed test results. I reread the whole thread and this is what the tech section is all about.

I am not a carb expert but if you have two power valves and the channel restriction size is 0.080" that's a lot of fuel. What are your power valve numbers and what are your manifold vacuum and fuel pressure when cruising on the primaries only? What I'm trying to get at is the differential pressure acting on the power valve.

I'm not sure about the P/V orifices because I didn't measure them, but I can see that they are quite a bit bigger than what I have seen in other 850's. I'll measure them this weekend. I have a bunch of very small drill-bits (from my former Nitrous-jetting days) so I might open up a bit so I don't have to go so big on the mains.
I also haven't really studied the boost/vacuum gauge at cruise (I know I should have) but from what I have seen the motor normally pulls around 7 - 3 " of vac. at cruise. This is why I believe it runs real rich at 1/4 throttle or so - because the Power Valves(6.5") are tipping in. I have a couple each of 4.5" and 10.5" P/V's on order that I'm going to play with.
Also, I have like 8-10lbs of fuel pressure at cruise and 15+ under full boost.
I have seen that I can cruise at about 2/3 to 3/4 throttle at 85mph with the vacuum/boost gauge @ 0" boost, so I figure with even just 5lbs. of boost 105+ should be no problem.
(BTW: The boost gauge is referenced off the Vortech box base plate BELOW the carb, and the Regulator is referenced out of the box.)

Too bad I have to frickin work for a living or I could be testing now. (Well I guess if I didn't have to work, I would have had a Skater 46' w/ Turbines!! and my own pit crew!)

At least if I don't sort it out I should have some data for Nickerson to work with:D

Oh, I forgot to mention that this problem is more noticeable when the motor is at a warmer temp, like 140+ deg water temp. I was almost tempted to think it might be vapor-lock, but I'm sure the carb doesn't get that hot - I think :eek:

I'm the air flow guy, Nickerson's the fuel flow guy, but I can share some of my thoughts on the blowthrough carb issue, maybe it will help you. By the way, I don't think I would have the nerve to tackle the carb, and my hat's off to you because you obviously have a lot of experience and seem to be taking things one at a time.

OK, this may be long-winded so I apologize in advance if you already know it. I just need to start at the beginning to keep it straight in my own head.

Let's say an engine makes 500 HP naturally aspirated and the carb is jetted for that. Then we add a blower and intercooler and WOT air density is increased by 50%. Now there's 750 HP worth of air and the carb needs to add 50% more fuel. However, actual CFM through the venturis has not changed, since the engine is a positive displacement pump. So air velocity is the same and the signal to the fuel metering passages is the same.

This is the problem. We have made a huge density change, but the carb doesn't know it. This isn't quite true since venturis do respond somewhat to the density increase, meaning the signal to the fuel metering passages does increase a bit with density, but let's ignore that to be on the rich side.

This problem is the reason you have to richen the jets when you move a carb to sea level. But that's easy; there the higher atmospheric pressure is constant. A blowthrough carb sees a range of pressures. So we have to start thinking about the different operating points.

The easiest is WOT. Let's say that the naturally aspirated carb had 78 primaries, a 6.5 primary power valve and a power valve channel restriction (PVCR) of 0.040" which would add 25% enrichment on the primary side, 94 secondaries and no secondary power valve. We can calculate the total metering area of this combination, and the additional metering area needed to make up for the 50% increase in density.

I did this calculation for the example above, and if we added all the additional metering area to the secondary side, we would need 130 jets. Procharger used to tell people to drill their secondary jets out to 140.

So now we are covered for WOT, and we have the original primary jets so off plane and docking should be fine. What about cruising on the primaries?

If there was 9 psi fuel pressure at cruise on a 6 psi base, we would have 3 psi boost in the box. That's about a 20% density increase, so if we were cruising on the 78 primaries, we'd be lean.

What is the power valve doing? If we had 5" of vacuum at the same time as the 3 psi in the carb box then the total pressure difference across the power valve is:

(3 psi X 2) + 5 " Hg = 11 " Hg

The 6.5 power valve is closed. It will only open when the combination of carb box boost and intake manifold vacuum fall below 6.5" Hg.

If we get into the secondaries from this part throttle position we will initially be way too rich since we put all of our extra metering into the secondary jets. As RPM and boost climb we eventually get to the point where the mixture is right.

Richening the primary jets will help the lean cruising condition, but we would need 85 jets to add 20% more metering area. The limit here is how much this affects low speed operations like docking. It might be better to add some of this 20% by enlarging the primary PVCRs and playing with power valves to get it synchronized with the load and boost curve.

Leaning out the secondaries would help the overly rich condition just above part throttle cruising, but whatever we take out of the jets has to go into the primary PVCRs to maintain a safe WOT mixture. If we use a secondary power valve, we could add it too the secondary PVCRs.

That's my theory and what it is too!:rolleyes: :D

An additional proble that I always noticed is with the carbs sideways, fuel from the secondaries did not like to cross over to 2,4,6,8 when it was stepped up for WOT. The primaries would feed 1,3,5,7 and didn't seem to cross over during cruising. The end result was always having one side of the motor richer or leaner and not a happy medium. I ended up cutting the divider out of the manifold to the floor and still had this issue to a degree. I gave up and bought fuel injection.

Just a bit more about the hypothetical described above. If we decided to add all the extra metering area to the primary PVCRs we would have to drill them out to about 0.100". If we split the extra metering area between the primary and secondary PVCRs, then we would have to drill them out to about 0.075".

I have been thinking about your testing procedure and I wondered if it would make sense to first determine what primary jet will support your cruising speed on primaries only, no power valve enrichment. This should end up with a smaller primary jet than 90s. Then do your WOT testing to select the secondary jets. This will satisfy the two extremes and probably result in too rich in the midrange. Then you can start playing with power valves and the PVCRs.

PVCRs come anywhere from 0.030" to 0.120". If yours look like 0.080" then your current metering area with the 90s is 75% more than my naturally aspirated carb example. Without knowing charge air temperature and pressure I can't calculate air density, but I doubt if it is 75% higher so you sound rich to me.

We too have experienced the lugging at WOT throttle and Nickerson tells us to decrease secondary jet size. I must admit it is hard to take his advice when we see the white plugs.

One thing that complicates matters is the fact that you have a 100+MPH jet of air blowing across the top of the carb venturis. This probably does some weird things to venturi operation, making your tuning job tougher. Procharger tells people to run a small brass flame arrestor inside their box to address this turbulence, but we have gained 75 HP on the dyno by taking them out.

Good luck with your testing!

Tom

Whew! Dammnn Tomcat, it's a good thing you're not the "carb guy"! I'm going to have to read all of that over again for it to sink in! Thanks for taking the time to help a poor fool like me out!!:crazy:

I'm starting to think that it's just that the motor wants a ton of fuel at full boost/W.O.T. and when I fatten the mains up it runs too fat in the middle. So, I think I'm going to install the new inlets (just to be safe) and I'm going to measure and increase (drill out) the Power Valve orifices by about 10-15%. What the hell - if I screw up I'll just have to buy two new metering blocks is all.
I'm going to go a bit bigger on the secondary main jets as well.
I didn't realize that Procharger used to tell you to drill out to #140 jets- Sh!t! that's big! Alcohol-jet territory, even. (the biggest jets I have are #99s)
Hmmnn, I wonder if anyone ever tried using/ tuning an alcohol calibrated carb for a blow-through setup... Big jets, big fuel calibration all round, seems like the perfect candidate for an "artificial atmosphere" setup!

As for the power valves, I take it then that I need to increase the opening point # (say to 10.5") to ensure that they come in earlier? BTW: if I have my boost reference for the gauge below the carb where the power valve is also referenced from, isn't what I'm seeing effectively the same vacuum reading as the P/V?
Thanks again for all your help.

Tomcat, I've just seen your most recent post about what Nickerson recommends with the lugging- Do you think it could be possible that I'm too rich? I wonder if this is why the motor lugs more when it is hotter than when it is relatively cold? Colder engine, colder air charge, denser singlet air, leaner mixture, right?
If this is so, I have to say that I'm kinda worried about leaning the jetting down because the insulator is white. The threads are black (sooty) though and the Procharger manual says that you must ignore everything else about the plug and concentrate on the threads. They say that once the first two threads are nice and black/sooty then the jetting is right on. It may be then, that regular plug reading technique doesn't apply to blown applications since we are definitely generating higher combustion temperatures.
Man, what a dilemma! I guess I'll have to check the PVCRs first and that should give me an idea of whether I'm rich or not.

After fighting the above jetting problem along with what you are fighting for 2 years I also went with fuel injection.

Hardcore. Your power valve needs to be smaller 4.5 or so to come in earler. Bigger to come in latter. Remeber the power valve is seeing the difference between top & bottom of carb. When I was crusing @ 2500 rpms I had 3+ lbs of boost in box & had 6-5inches of vacuum in maifold.

Tom- You are the man.

Here's another theory:
Carbs are designed to be "sucked" through and so the venturis are designed to cause a pressure differential (a drop in pressure, or Vacuum) so as to pull fuel from through the jets and out of boosters. The vacuum comes from the air being displaced through the engine and this causes a pressure drop in the manifold plenum and so forth.
So, when we "pressurize" the whole intake tract with a positive displacement of air through the carb, we adversely affect the pressure differential at the venturi/booster. The booster therefore produces a much weaker signal and (everything else remaining equal) less fuel is pulled through the same jet.
However, air is still flowing through the carb throat so there is still enough of a pressure drop at the booster to pull fuel through it and the engine still runs, albeit seemingly lean for the size jetting it has.
This is why I think a smaller venturi and perhaps an annular booster is needed to generate enough fuel flow through the carb to keep up with the air. This might be why Nickerson (and some others) changes to a 750 main body on some applications (or so I've heard), so as to speed up the air flow at the venturis and thereby provide better signal to the boosters.
Has anybody tried changing to annular boosters and/or a smaller main body and if so what were the results?

Hardcore:

Yes, I think it is possible that you are too rich. I know those insulators are white, we've seen that too. But I've seen Nickerson's personal boat engine on the dyno deliver 900 - 1000 HP with BSFC numbers of 0.6 and the plugs look white to me. He doesn't seem concerned and I realize I don't know anything about reading plugs!!

The other way I look at it is the total metering area. For example, the jets and single power valve in an HP500 carb have a total metering area of 0.0251 in2. Although this is an 800 CFM carb not the 850 you have, I would expect it too work just fine on your 509.

Now if you had a 50% increase in air density, you would need a total metering area of 0.0251 X 1.5 = 0.0376 in2. Your carb with 90s and 0.080" PVCRs would have a total metering area of 0.0456 in2: way too much. If it has 0.060:"PVCRs then the total metering area would be 0.0368 in2, which is almost a 50% increase, just about right.

Once you measure the PVCRs you will know what your total metering area is, and be in a much better position to know what to do next.

Air flows through the carb because the pressure above is greater than the pressure below. It doesn't matter if it is atmospheric above vacuum, or boost above vacuum or even boost above less boost. At WOT, when you see 5 psi on the boost gauge, you probably have no more than 6 psi in the carb box. This 1 psi differential is plenty to flow the required actual CFM. Four barrel carbs are rated at 1.5" Hg which is about 3/4 psi.

As discussed above it is the increase of velocity (or to be more exact - the velocity pressure) inside the venturi that results in the reduction in static pressure which at the nozzles. The greater static pressure in the fuel bowl pushes the fuel through the metering passages. This happens whether the engine is supercharged or not.

The real problem is the increase in the density of the air rushing through the carb. It has more oxygen molecules and it needs more fuel molecules! No wait, that isn't a problem, it's a good thing! The problem is deciding which passages to put the extra fuel through; how much and when. :D

Tomcat:

Thanks for once again taking the time to point me in the right direction. It is certainly a huge help (and a great relief!) to know that the white insulators might not indicate a lean mixture.
This forum certainly benefits immensely from having knowledgeable people like yourself take such an active part in these types of threads.

I agree with you that I need to measure my PVCR's before I guess anymore and I am grateful for the expertise on calculating total metering area. As soon as I have some more info/testing data I will let you know whats up.
Thanks again.:)

Hardcore:

The reason I say I'm not the carb guy is because my knowledge is mostly theoretical. When it comes to the practical application I'm learning too. But you've got practical experience and can apply the theory.

The reason I refer people to Nickerson is pretty simple. Nickerson has a supercooler, so I know that anyone I send his way will get the carb calibration that Nickerson has worked out on the dyno and in the water for his own boat engine. That way I can relax!

There is a good discussion of metering area and changing the ratio of metering area between main jets and PVCRs on page 65 of the S-A Design book "Super Tuning and Modifying Holley Carburetors". They also talk briefly about blowthrough carb jetting on page 71, but they don't go into using the PVCRs.

Thanks. I don't think have that book. I have one by Alex Warlordy that I need to read over again. As far as I can recall he has quite a bit of material on tuning with power valves, but the book is like circa 1980s. (although Holley Carbs haven't really changed that much in the last forty years or so...)

Hey guys,
Man, I knew if I kept hangin around here somebody would tune my Prochargers for me :). I have decided to let my tired 454 mags rest thru the summer and blow them up late fall with the M 3's. I am just now getting my new/old '29 Fountain in the water and changed to Aeromotive pump and reg,built return lines,repositioned hatch lift,bad outdrives,upholstery, etc, planning on having it blown&tuned by now but multiple delays and ignorance and learning has slowed me down to much,,,AND I'm tired,just want to drink a cold beer on my boat,away from the ramp. Don't want to risk it this time of year:( I hate being practical but could not stand being boatless after all the time and $$ I have spent since Jan.
I have to say again the incredible amount of experience combined with a common interest and just plain helpfulness on this site has made what was once almost impossible( getting useful info about high perf boats) a click away. I have decided to join up as a paying member. This is cheap and easy compared to what I have saved and been able to do myself.
Keep tuning HARDCORE. Maybe you can help when I get ready around Oct. Where do you live in the Caymans? We were down there for our honeymoon in '02 and loved it. Georgetown on a cruise stop.
TOMCAT, I'm saving all your "theory" and going to send to a publisher soon. May I just say,,WOW !!!
My wife is getting her PHD in Finance(she can do hypersurface calculus(I can't even spell it)) and she thinks I'm a genius because I can build a mtr or whatever and it usually works. I told her to read a few of these post and she'll see I know nothing compared to you guys,,but I'm learning,and always doing,so maybe I can help some poor sap find his #1 cyl or oil filter and do my part here:)

Hey Cooltoys. Like I had indicated in my earlier post, without the expertise AND willingness to be helpful on the part of Tomcat (and quite a number of others on this site) this forum in particular would be quite useless. I too am going to sign up as a paying member (as soon as I can stop kicking myself in the A$$ for not buying a Supercooler setup!). I feel obliged to say that if this is an indication of the kind of dedication that Tom shows his customers, I wouldn't hesitate for a second to recommend buying his product (even if it didn't make a sh!tload more power, to boot!)
I'm going to find out what this problem is this weekend (or blow my motor trying!)
Sounds like you have a sound understanding of these things yourself. My last boat was a light weight Mirage River Racer w/ a Merc Drag motor (ran 109mph in the 1/4 mile) and before that it had a Nitroused OMC so the whole setup of my boat has been a new experience for me. I basically bought the hull w/out motor and tore it apart and started from scratch. Believe me, without help from this forum and friends like "Cayformula" I wouldn't have known where to start.
As soon as I sign up I'll post some photos of the rig.
BTW: I live in the central part of Grand Cayman and work in George Town (attorney) but I spend most of my weekends in the water (since we are, after all, surrounded by it here). Later.
:D

Hey cooltoys61:

The fact that you're waiting until fall to install the blowers makes you smarter than me. Have a good season!

Hardcore:

I checked my books on the equation for venturis. What it boils down to is the signal or "suction" generated at the fuel nozzle increases in proportion to velocity SQUARED, but that signal only increases in direct proportion to density.

So if you increase the amount of air entering a naturally aspirated engine, by using better heads and more RPM, such that the air velocity in the venturis goes up by 1.5, the signal on the fuel nozzle goes up by 2.25. Due to similiar laws of physics, you need this 2.25 increase in signal to get the fuel passage to flow 1.5 times more fuel. So carbs can do a good job of metering fuel flow according to air flow, as long as density doesn't change.

But if you increase the amount of air entering the engine by supercharging to get a 1.5 increase in air density, and actual CFM and therefore velocity don't change, the signal on the fuel nozzle only goes up by 1.5. This is only enough signal to pull 1.225 times more fuel. So you need to add more metering area to bring the total fuel flow up to 1.5 times more fuel.

In the calculations of total metering area a few posts ago, I ignored the fact that density increases do increase the signal somewhat. I thought that this was a conservative approach, and might result in an overly rich, but safe mixture which could then be tuned down. But there is another factor to consider.

Whereas naturally aspirated engines are often tuned for a BSFC of 0.45 - 0.5, supercharged engines seem happier at 0.6 - 0.7. The exact numbers depend on lots of things but if we just consider this ratio, it means we need not 1.5 times more fuel, but

1.5 X 0.6/0.5 = 1.8 times more fuel

Based on this I feel a rule of thumb coming along. If the increase in air density is 50%, add 50% more metering area and rely on the response of the venturi to density to provide the rest. Using the numbers from above, the new fuel flow based on both metering area changes and signal increase due to density would be:

1.5 X 1.225 = 1.84 times more fuel

Once again this is theory, but it's good to know. ;)

Re: Jetting/tuning For Procharger setup
 

Hey Tom. Thanks again for the guidance. I found out that I had stupidly installed #84 jets instead of #90s!!! How it happened was simple. I took them out of the Holley box that I have them stored in and simply looked at the guide on the lid of the box. #84 is right above #90 and so I simply took them out of the wrong compartment! (If that don't get the stupid mistake of the year, I don't know what will!)Anyways, not to fear. The ENGINE is OK. The drive - well, we'll get to that.
I measured the PVCR's and found that they are in fact .080" (apparently, I can read minute measurements better than I can read writing! So, it seems that I did have adequate fuel augmentation from the P/Vs so no meltdown (WheW!)
I installed #88's in front and #90's in the rear and installed the .150" inlets. I quickly removed the inlets though because the floats just can't produce enough leverage to keep them closed once they are at higher pressure under boost. (or so I was thinking at the time)
The lugging is now more like a speed limiter, like the power just flattens out up top. Felt like it was just going way rich up top. Also, I'm now getting a lot of slip according to the speed versus RPM's (can you guess where this is going?)
After a couple of runs, I really started studying the fuel pressure and noticed that it would fluctuate and that when the problem occurred the pressure was spiking - like 17+ psi! WTF? It was obvious that something was causing a pressure spike (NOT a pressure drop).
So, pulled down the regulator. Found that the nipple for the boost reference was screwed into the body so far that it was hooking on the spring, which would obviously cause a problem and I'm thinking that at higher RPM's, when there is less flow through the bypass (more fuel being consumed by the engine) so that the diaphragm sits lower and simultaneously the boost pushed the diaphragm and spring down more into the well of the regulator, the spring would hook on the nipple and keep the bypass closed (or nearly) and consequently, increase the pressure. Quite a complex little problem isn't it?
Well I'm happy now, so I launch the boat yesterday, reversed off the trailer and WTF? No forward gear! Apparently my cone clutch has given up the ghost and gone to the big boat-boneyard in the sky! Oh well, as soon as I can cornswabble a drive off someone I'll report back with my findings on the "regulatory issues".
Thanks once again for all of your assistance.
to be continued...

Re: Jetting/tuning For Procharger setup
 

Hardcore I have been following your thread and have learned from you as well as the other intelligent post on this thread, as stated earlier several of us have faced this issue with the Prochargers and eventually gave up to buying fuel injection systems. two things I'll mention, I have a twin carb box that I'm no longer using and would love to sell- intake carbs polished box. I will give you a smoking deal on all of it, for I no longer have a need for it, but it is all excellent condition and ready to use. second after making it this far and reading admiring your mechanical ability thus far, I would encourage you to tear in to that drive and fix it yourself, I did and was amazed how easy Bravos are to work on. So amazed that I find it hard to believe that with all the mechanical ability that most of the backyard mechanics on this board exhibit that we aren't all Bravo experts by now. I will give you step by step instruction from memory and serve as a moderator to assist in taking apart or putting back together. The con clutch is a snap to fix. Good luck and let me know on either circumstance if I may be of assistance.

Re: Jetting/tuning For Procharger setup
 

Iwas reading Hardcores post and wondering if you still had that carb box and carbs for sale? How much and what else do I need to make it work ? Greg