Jetting with a Blower
 

I'm new to having Blowers! I'm in the proces of rebuilding carbs. The motor's are 468ci, Dart heads, Stainless Marine GENIII's, dry pipes, with 420 Mega Blowers. Each motor has dual 850 Holley's. The plugs were black! I'm thinking that they were set up way "Fat", 88s primaries with 6.5 PV and 96s with 8.5PV secondaries. Frankly I was surprised to find the big differences in jets between the primary and secondaries given that there were powervalves in each? Looking for some knowledgable feedback.

Unless the plugs were brand new, run at wot and then the motors shut off I wouldn't change anything without running with an air/fuel ratio meter. Too many variables that can contribute to black plugs. Could be way fat at idle but lean on the top end, just didn't run there long enough to clean off or burn up the plugs or pistons.

i think because of the power valves in the secondary,s you are rich.your engines sound a lot like mild thunder,s so hopefully he will see this thread and chime in.

You gotta lose the secondary PV and jet down. A power valve is close to 10 jet sizes worth of fuel. Its like having 106 jets in there. Way too much fuel.
Originally the geniuses that set up my boat put close to the same set up in my 540`s including the secondary power valves and my AFR meter was showing 9.0AFR.
Cylinders were probably getting a good wash down.
Get a AFR meter it`ll make things a lot faster and easier to figure out where you need to be jet wise, I`d say 84/92

dyno dyno dyno,no other accurate solution

AFR meter in real world conditions seems pretty accurate to me. Dyno to get you started.

danialson,you are a fast lerner.

I have good teacher, wax on wax off. I even have my own tackle box of jets and carb parts just like Mr. Miyagi :D

I agree. I was just trying to get an idea from someone with a similar setup if the 8.5 PV on the secondaries with such a large jet sounds unusual? My experience has me of the school of thought that if you have 2 power valves that the jetting is usually close in all four corners.

Are the carbs boost referenced? It does sound like way too much jet, but who knows. The motors are out right? $500 on the dyno could be money well spent. If you want to run out of fairhaven in the spring and do some plug readings let me know

They are not boost referenced. I'm thinking this is something I should do!

Remove the rear powervalves asap for a starting point. Your dumping fuel for sure. Then work your way down on jets from there. I have 84P/92S with 8.5PV in primary only. 468's, Dart heads, B&M 420's at 6psi. Holley 850 carbs.

Not necessary. I prefer it, but not totally necessary. Your best friend on these setups is a wideband 02 sensor setup. Have a bung welded in your dry tail, and you can get a NGK Powerdex wideband. They are great quality and affordable compared to some others.

http://www.amazon.com/NGK-Powerdex-A.../dp/B0018MUNTM

We have tuned quite a few carbed blower setups using widebands, and its amazing the ''holes" you can find in the fuel systems from idle to wot. Its really an invaluable tool, that will not only help keep the engines in a better state of tune fuel wise, but also save money on fuel consumption. You probably wouldn't believe the amount of blower engines out there with AFR's in the 9's running way rich, or in the 12's borderline hurting things. Plus it really helps speed up the tuning process.

Thankyou. I'll order four power valve plugs tonight.

Hey Tom, I get all my carb stuff from these guys. Fantastic pricing and good shipping.

http://www.allcarbs.com/detail.php?p...&ctgn=39&stt=5

http://www.summitracing.com/parts/hly-26-36/overview/

Hey mild just a question . But do you have to run power valves on blowers or just even jets all corners? Also I have cmi headers how would I put a wide band meter bung in those. The water comes out right on the ends. Or can it be done?

You can run powervalves. Whether or not you boost reference them is up to you. Is it mandatory, no. You can tune around them. The reason a lot of guys boost reference is in fear of the vacuum on top of blower/under carb, can suck the PV closed shut. This is really not an issue on a marine setup running low boost. Mercury did not boost reference their carbs on their supercharged engines.

The problem not running powervalves, is you'll have to run large main jets. For example, lets say you were running a jetting combo of 82/92 with a pv in the primary. To remove and plug the PV, you would have to step the primary main jets up from 82, to say, 88 to as much as maybe 96, depending on the size of the power valve channel restriction. I've seen some aftermarket carbs with huge power valve channel restrictions, which is basically like a jet size. Also, you lose some tuneabilty as by not being able to tune for a light load situation where the power valve is closed, keeping the air fuel ratio in a leaner state. The only time i would consider plugging all the PV's is for a drag car or drag boat for the most part, where there are two throttle positions, idle and WOT. IMO i would leave at least a primary power valve in on a typical progressive linkage carb. If using 1:1 linkage, I would use front and rear pv.

When it comes to tuning in the boat, the primary main jet should be sized for low speed light load cruise AFR. The PV circuit should engage when the load is increased as to when you start getting into boost. Heavy boats will want a PV that opens sooner, light boats will want it later from a rpm standpoint. Secondary main jet should be tuned from when secondarys begin to open and to wot. If you carbs are boost referenced, the pv circuit will almost always be into play unless you have a really light efficient boat that will cruise in vacuum. For a boost ref pv to stay closed while on plane, your gonna need a low number, like a 2.5. pretty much your primary main jet tuning will be from low rpm to where the secondarys open, for desired afr. If AFR needs to be adjusted above the point of when the secondarys are open, add or remove secondary main jet, so you can keep your cruise afr where you want it. A 800HP supercharged engine in a 38 Cigarette might need a different setup than a 26ft cat.

Yes, you can install bungs in your exhaust tails esp if they are dry. Many of us have them installed. I would probably skip the boost referencing, run a PV in the primary only. Start with a high number PV like a 10.5 and go out and start tuning. Install a vacuum gauge in the baseplate of the carb adapter (most have a 1/8Th NPT plug you can replace with a nipple). Record RPM/AFR/Vacuum readings throughout the curve. The vacuum readings will tell you what your power valve will be seeing. Adjust from there.

This kind of tuning is nearly impossible on a dyno. While i don't think it replaces the need to dyno by any means, I think it is a useful and valuable tool, that will pay for itself. Most engines are dyno'd in a full state steady wot pull, and cannot duplicate different load/rpm scenerios in the boat. While its also a good idea to evaluate spark plugs, tuning off them alone, imo, is 1980 stuff. Todays unleaded fuels can make reading a plug difficult. I may be inexperienced in that area, but i cannot tell a difference between a plug held at WOT at 11.7 AFR and another one held at 11.3AFR. Some experts look at porcelain for jetting, some look at the base ring on the threaded body. Some look at heat marks on the ground strap for ignition lead, some look at it for plug heat range. Who is correct? I mean i can look at a plug and say "that's rich", or "that's too lean", but i cant pinpoint it to where i can say, 'yup, that plug there was running at 12.5 AFR, and that one over there, ya, that one was at 12.2"

Some may look at this kind of tuning as a waste of time and unneccesary. The way i look at it is this. If I put an engine package together, and spec a cam with .650 lift, i want .650 lift, not .620 lift. If I order cylinder heads with 2.25 valves, i want 2.25 valves, not 2.19. I want 8.5:1 compression not 8.25:1 compression. My thoughts are by guesstimating at your fuel curve, will leave performance results on the table, no more or less than the examples i gave. We don't cut corners on engine specs, but are willing to cut corners on tuning the engine?

More good solid advice. Thanks MT for taking the time to provide VALUABLE insight and staying on point as usual.

Eliminatorshane - We installed bungs in all four of my CMI tailpipes right after the joint. So far no issues with the O2's getting wet and they have provided great information.

Quick question, I had bungs welded in my tails at the end of last season, I want to set my carbs up. Everything is working well but I'd like to dial in my Afr, what's a good ratio to shoot for on some mild blower motors? From what I've been told 12.5 is the gold standard for n/a motors, but blowers should run richer than that? Just asking because I've never got a straight answer on that. If it helps, carbed hp 500 with 177 blowers and sport tube exhaust and aed boost referenced 850's

I would keep that thing as rich as possible with those tiny blowers on a 9:1 502 with iron heads with a single carb. Prob like high 10's and hope it lives . I would not try running more than about 4psi with it . Do u have intercoolers?

Cool jamonte I am sitting down tonight and ordering an afr after dinner. I hope they have the ones to kinda match my gauges. Thx a lot . Also thanks mild and others for the advice. I'm still up in the air of using stock block or go dart. Realistically I'm gonna have 750- 800.hp. The 502 block is 4 bolt main. My Malibu I've sprayed dual stage nitrous through it before and never had problem but the way my luck goes this marine stuff would break my stuff. Just rather know if it will hold up.

You can always do a handheld one, tune it, unplug it and be done.

You'll be fine with a gen 6 GM block at that power level.

Where can I get handheld and what's a good one? Thx mild

No coolers, low boost, motors have been together for years. Thanks for the help

I would install an 02 and see what you have for a current tune as far as AFR numbers. Since they have been together with no issues, that should tell ya something. You may just wanna "fine" tune it a bit

Post number 13 in this thread I put a link to the NGK one. I also had a FAST efi one. It had dual channels to read both banks at same time. But that one is around 400 bucks. Both worked well. The NGK on is simpler, and doesn't record a log like the fast one. Innovate makes a nice one too that can be used with a data logger I believe. For the average guy I think the NGK one is hard to beat. You can calibrate it easily before use also

Joe. Awesome insight man. I have a question. What is boost referencing a carb? I've read the term on here but have no clue what it is.

Basically the powervalves open when in boost instead of a specific vacuum.

Basically what Icdedppl said. On a N/A aspirated engine, the carb is mounted on the intake manifold, and the power valve reads this intake manifold vacuum. When throttle is opened, manifold vacuum drops, power valve opens.

With roots supercharger, the carb sits on top of the blower. It no longer can read intake manifold vacuum. It reads whatever the vacuum is at the top of the supercharger. In certain scenerios, your intake manifold will see boost psi, but your power valve is still seeing vacuum.

Boost referencing is simply modifying the carb so that you can hook an external vacuum line from the carbs PV circuit, to the intake manifold. This way the power valve only sees manifold vacuum/boost.

joe very good info ive got the 02 bungs in my tail pipes ill be doing some testing this spring good seeing you on my b day

It was a great time!

I have to share an experience with you on the boost ref, carb set up. back in the mid 80s I put together a non intercooled blower motor, with water/meth injection at 2lbs of boost. Never having any experience with superchargers I called B&M tech for tuning tips long story short I drilled a port through the throttle plate to intersect with the power valve port, next took a bigger bit and went in 1/4 inch so I could pound in a slosh tube (with Loctite) for a vacuum hose hook up to Manifold. Next I tapped the port in the bottom of the TP and inserted a allen set screw (Loctite) to seal of the manifold vacuum. proceed to tune the carb via jetting. the motor ran great and for it's time was quite a sleeper. Here's the real story, when I sold it the guy took it to (his) mechanic and was told " who in the hell F!!d up this carb? and what is this water tank on here for? The mechanic removed both and installed a stock carb with who knows what jetting, and within a week the motor burned down!! buyer came to me pissed off, I seen what was done and told him to pound sand!! He never did find anyone to get it to run right again! Asked me twice to help but with his bad attitude I just answered "don't think I know how to do that technical ****" LOL Besides that I was busy helping my boat dealer friend put together a set of twin turbo intercooled motors. for his 30 ft Cat. That's my Sunday afternoon contribution.

Was the mechanic who worked on it named pslonaker by any chance ??? :party-smiley-004:

Maybe related, but couldn't be pslonaker because this guy actually had a shop registered with the state, and worked on bread and butter motors, not one off custom beasty mills. I don't think he had a state of the art "Magic Room" filled with specialty tools and climate controlled as our "YouTube video instructor" pslonaker !!

lol. Seriously though, some guys just don't get custom engines or supercharged stuff, etc. They can be great at dealing with stock engines. Like your local tech at the chevy dealer. He can fix about anything on a Chevy impala, but that doesn't mean he's the guy you want working on your 900hp blown boat engines.

I remember when I was about 16 years old. A friend of mine had a 75 Buick Lesabre with a 455. I was young and still experimenting with carbs and tuning them. His car wouldn't run right, so I got in there and did some adjusting, modifying, etc. It ran worse. We brought it to his family's mechanic, and old timer who was a great mechanic, but grumpy and cranky as all hell. He took the air cleaner lid off, started poking around the carb. He looked at my buddy who owned the car, and said "did you have someone mess with this carb", my buddy said "ya, a friend of mine tried adjusting it". Not knowing I was the friend who was standing right there, the grumpy old mechanic said "well, whoever it was, needs to have his fukin hands chopped off so he never touches another carb again". You could def hear crickets after that, and I went back to reading up on carburetors. lol.

Very true on the custom engines!

As far as the carb on the Buick, that is how we learned the back in the day, just jump in and see how it works turn this bend that, and then research afterwards, I would hang out as a kid at the corner Sinclair gas station and work for free sweeping, cleaning and all the time absorbing as much knowledge as I could. They finally hired me at 15 years old and started to teach me hands on stuff.. What a great way to learn the basic stuff. I made a lot of mistakes but learned on every one!! Not much of that going on these days.

I do hire one intern every summer and try to teach them the basics and encourage them in automotive restoration field.

Definitely some great info in here.. Mild Thunder great posts....

This is where I am right now, major major tuning issues... 516ci BBC, entirely re-done from top to bottom with all quality stuff. B&M 420 sent out for a full retro update to 3 Lobe Helix rotors. Scrapped the old Holley 750's and got brand new QFT 750 Boost Reference Carbs... That was the first mistake... Family friend's brother in law is a big wig over at QFT, so we were promised the world with these carbs to be angels from heaven... Yea... NO....

Started with 8.2psi boost on the dyno, spend 3/4ths of the day chasing the carbs and a tune... They were doing crazy things on the dyno after air bleed changes and jetting, but not really following suit as to what they should have been doing with the changes... after the first pull, made an air bleed change, picked up 26hp, after that, air bleeds didn't do any, no response on the dyno with additional changes. Called it a day, and overnighted a smaller pulley...

Running 10.2psi boost....Same dyno reults... Gained nothing after adding 2 PSI... Still chasing the carbs for a tune... I cant even begin to tell you how many times we had the bowls off... Finally throw our hands up and call QFT... Explain what is going on, and from the looks of the data sheets, we have a Flow issue and a metering block issue... So we are told that the jets in the Metering Blocks should be .028, Blank, .028, .028 on each side... They tell us to swap the blank to the 3 spot, and still the 4th spot to .033... Scratch our head and say, OK... Start measuring the jets in the metering blocks, and 1 spot is .029, 2 spot is a blank, 3 spot is .030, 4th spot is .031... Look at the opposite side and the Blank is in the 3 spot instead of the 2 spot... Now we are getting really ticked.. Nevertheless, we put them the way they want, though we didn't have jets to make them .028 like they should have been, but get the blanks in their 3 spot and the bottom jet to .033... Put them back on, and it makes it worse....

Go back to 8.2psi and try dialing in some distributor advance, get a little better... Start measuring vacuum under the carbs... 1.2" @ 6500rpm.. Well, they don't flow that's for sure.... Finally decide on the 10.2psi setup cause the motor liked the early boost, took a reading with 10.2psi and its 2" @ 6500rpm... Shoot me now!!

With no time left, 2 weeks before DS, and 2 days on the dyno, 20 pulls later, we try to get a somewhat usable tune for DS... Find a rich jetting set to be safe, air bleeds weren't responding to anything.... so we went back through all the pulls and came up with a tune...

Even did Back to Back pulls and both pulls weren't even remotely close to each other...

So don't know if both carbs are the issue or 1 carbs has major issues, but they definitely didn't flow for crap....

End up heading out to DS.... not a ton of running around or pushing the motor, but for whatever reason the left side of the transom was 2x as black as the right... Obviously plugs were black... Only thing we could think of is the progressive throttle linkage opens up the secondary's at cruising speed and is dumping way too much fuel in....

Needless to say, these carbs are going back, getting my money and coming up with a better solution....

As far as the AFR meter and water headers, I have a bung spot where the 4 goes into 1 on the Lightening Headers, is there anything special I have to do or worry about running the Sensor with Water through the exhaust, or will that not affect it?

According to the carb CFM calculator from BDS website, a 516CI spinning 6500 RPM, with 10lbs of boost, would require 1630CFM. A pair of 750's would be undersized, and not the size carbs I would have chosen for that combo. BDS says you can go up to 30% larger, which would be 2120CFM. My little blown engines in my boat require 1150 CFM according to that calculator, however, I have a pair of 850's on top of my B&M 420 blower. They made great power for what they are, and there is no lack of response, or any negatives I've seen from the size of the carbs. I think a pair of 950 or 1050 carbs would have been my choice on your setup. Not only from a fuel curve standpoint, but it has been proven, that going to larger, properly sized carbs, will also lower IAT temps. When you start seeing 2" of vaccum at WOT under the carbs, and basically see they are undersized, the metering goes out the window on them. I've seen this on a blow thru setup also. Carbs worked great at low boost. Crank the boost up past their comfort level, and the metering goes to $hit. They cant handle the turbulence.

I've seen the quick fuel 1050-B2 blower carbs work very well first hand, almost right out of the box, with minor jetting changes. I am no carb expert or guru by any means, but my recommendation, would be lose the 750's, and go bigger. Do NOT get the standard 950 holleys that are based on the 750 body. They dont flow anywhere near 950CFM. The Holley ULTRA HP 950 is a much better carb. To sum it up, I recommend error'ing to the large size on carbs with roots blowers.

Who converted those B&M's to the 3 lobe setup if you dont mind me asking? I'd be curious to see what , if any, was gained here from getting rid of the stripped 2 lobe deal. Did you notice any change in overdrive/boost level? The theory behind a two lobe, wasnt less air, it was more air per revolution. When the blower turns and takes a gulp of air, having more room inside the case from not having the added displacement of a third rotor taking up airspace, was the idea. The downside to the two lobe, was the issue of "carryback" at low speed, which really never became much of an issue, unless extremely low drive ratios.

As far as the fuel distribution, from seeing 02's in each collector on various blown engines, the left bank/right bank difference seemed to be worse, with a 3 lobe twisted rotor, vs my 2 lobe straight rotor. With an 02 in each bank on my engines,, the AFR readings were almost identical to each other, at most .1-.2 difference. With the GMC style twist, I've seen them as much as .5 or more difference left to right.

BTW, what is the details on the build, and what kind of power numbers are we talking about here with 8 and 10lbs of boost?

Hey MT.. Thanks for the reply.... Again, solid info and thank you... Im not going to point fingers on the original motor build being complete junk, but Ill say it started out as a Teague 720, and its seen 2 different motor shops that have touched the motor, and I am the 3rd owner... From a motor standpoint being a completely F'ed build, I dont know where to start... I guess Ill start with, the mains werent studded, nor the heads...The bearings werent coated, the line hone was off, stock GM crank, even cut for a keyway, but wasnt used, Valves were so short that they had to use special keepers and the rockers were hitting on the top. Merlin heads, nor stud girdles, intake ports went in and 90'ed straight down, an engine shop put a new cam in it, but didnt even check if the valve springs had enough pressure, lets just say the springs were only 89lbs and the cam required like 220...no screens in the oil galley, Balancer had a HUGE chunk of metal for balancing on it, valve job was just a 45, cheap rings, I know Im missing stuff, but again, a complete and utter cluster F build... Even the B&M blower hone was crooked... Go figured, fell right in line with everything else....

New build got coated bearings, line honed correctly, Dragon Slayer crank, crane springs, inconel valves, new H bean rods and pistons went from an 8.53:1 to 7.5:1 setup to run higher boost, total seal rings, stud girdles for merlin heads, guess there only 1 mfg that makes them, studded mains and heads, MLS for the heads, cleaned up intake and exhaust ports, new distributor and oil pump, blah blah... LOL

Supercharger USA did the conversion, there was some major differences that we took into account, 1 was the pre-heat packing from the air packing in and escaping out, and being packed again which ultimately resulted in higher EGTs, so the 3 lobe helix would reduce this air surge and ultimately lower the EGTs cause the intake air would be cooler, I forget what the formula was for intake temp > Exhaust temp, but any help to reduce EGT was a plus, the other was efficiency, the efficiency went up 20 points, which obviously is a plus, lastly was a more sustained boost... These were our selling points on just fixing vs converting, granted it cost more for the conversion, but we also did the heat treated gears and input shaft and billet bearing retainers too.. Might as well do it right....

On the Dyno with 8psi, we laid down after a few adjustments just under 800hp, with just under 800 ft lbs... definitely missed our mark... So we overnighted a smaller pulley the 5" cause we just didnt have the pulleys to get 10psi... Running the 16 rib 6.3" Lower and 5" upper for 10psi.. 8psi setup was 6.75" lower and 5.8" upper...

Literally saw little to nothing on the dyno... 800hp and just over 800 ftlbs with 10psi... this was at 27 degrees timing... dyno was only plotting to 6400, but if you watch the dyno it ran to 6600 and it was still building HP... Has a 7k rev chip, dont know if I would wanna see 7k too much, but its a solid build and literally sounds better spinning 6400 than it does at 3500 LOL, it just sings...

Never the less we went back to 8psi and started dialing in some timing, bumped timing to 30, and literally laid down almost the same numbers with the 10psi setup.. again shocking... At the end of the day, we left the timing at 30, went back to the 10psi setup, and found a happy medium in the various tunes we tried.... One of the biggest things aside from flow and normal tuning issue we saw with the carbs is that it kept getting fat on the top end, and not matter what we tried we couldnt get the top end lean, so it was really hurting the HP....

I was going to go the Holley Ultra HP route until I was persuaded by our long time family friend to go with QFT... We are currently in talks with Brasswell since they are local here in AZ, still waiting for a build and price, they said they know exactly what is happening...

Either way, When you say 1050's I see my debit card melting at the gas pumps... LOL Although, going through all this unburnt fuel with these crappy carbs prob isnt helping the cause either...