Holley Carb set up / tune
 

G'day all,

Here's a situation for you to ponder.
I am no expert on Holley or any other brand of carb for that matter. I can rebuild one, tune one and fix most things but whether or not I'm right is a different matter.

I am running a Gen VI BBC, 468ci 10.5:1 comp, RPM Air Gap intake, Vortec heads, Crower (for now...) 01404LM cam - 292/303 Dur, .585 / .612 Lift and a holley 850 HP D/P carb.

I get about 4-5 inches of manifold vacuum from the vac port on the carb base plate and I think my power valve is a 35 but I'm going to check tomorrow.

All that asside, I now live in Darwin, Australia, which is hot all the time and more humid than a hippo's armpit during mating season. It is however; at sea level.

Anyone with any good advice as to what jets I should be looking at and any thoughts on the merits of dropping to a 25 power valve?

The boat is a Stinger 222 and I've got a B1 24P, a P5 23P and a Mir+ 25P, so far I've only really tested the 5 Blade and it was slower to get up on a plane than I expected and topped out at (GPS) 62mph at ~4250 rpm.

Any advice or input would be greatly appreciated! :drink:

Cheers,
John

4-5 inches at idle ?? if so you have a problem, should have twice that...fix that first...Rob

I would think you would at least twice that also. With your cam it would seem like you'd have 10 - 12 inches of vac. You sure your vacuum port isn't pinced or do you perhaps have a leak somewhere. Sounds like your on the right track with lowering down to a 25 though based on your vac numbers. Half the vac is typically a good starting point. There was a thread here not long ago and an individual on the board was really helpful on the subject. It's a good idea to also have the vac gauge visable when running at various RPM's to know for certain when your PV is opened and closed.

Good luck Mate!

PS I would also check it in and out of gear at an idle.

I thought about running the gauge up the inside of the scoop so it's visible with the hatch down for the next time I take her out for a test. I might have used the wrong port on the carb for vacuum, I checked the manual and it referred to it as the 'timing / vac adv port' which has limited vac at idle so as not to advance the dist (if used). :lolhit:
I'll try today on the other port and see how that measures up.

Cheers,
John

You got it. Just make sure you use one on the bottom of the base plate and not one on your intake runners. Pull the carb off and look at the bottom to be certain you have the right one. What rpm does it idle at?

you got to put a smaller prop mirage is the way to go prop it so the rpm are higher that motor needs to see 5200 to 5500rpm you are way off at 4250rpm the motor is dogging !!!!

Okay, so I tested again today...

Managed 8-9 inches vac (on the correct port this time!) I tried all sorts of adjustment of idle an mixture but 9 is the best I could do while still having the motor at idle.

I then pulled the carb off and tore it down, here is what I learned:
Jets: #86 on all four corners (I'm hoping their not #98s but they look too small!)
Power Valves: 65 on both ends.

Now with my way of thinking, to get a boat out of the water and up on plane, you'd need large primary jets right?

Given that I managed to only muster 9" vac, I'm planning on going with 45 PVs and then trying a set of 92 primary, 90 Secondaries then doing a plug check run to see how that feels.

Any thoughts on that idea?

You are getting close to the right idea. Generally for a a marine carb you go up 2 jet sizes on all 4 jets. If you want to be real safe, go up 4 jet sizes to start. No matter what, do all 4 jets the same. Say if it came with 86 squared go to 90 squared. If it came with 82 in the fronts and 86 in the rears go to 86 in the fronts and 90 in the rears. On the power valves, you go down 4 sizes from the low vacuum level. You say 8-9 inches, its calling for a 4 or 3.5 power valve. A 4.5 might work. A power valve adds about 8 jet sizes of fuel when it drops below its rating. they generally start opening about 2 sizes above its rating. The vacuum keeps it shut. The valve should never open at idle, only WOT. Set the idle screws no more than 1 turn out then adjust the idle.

The cam seems a little large for that size engine. I would suggest you only time the engine at 32 with that compression unless running good fuel(92+) You will need premium at minimum. You should also not install over a 140 thermostat. Good Luck

Thanks Linster, that advice seems solid to me.

I run 98 PULP in the boat just to be sure, my current timing is set to 34deg (total.) I run the Crane HI-6M and use advance curve 6 (NA motors). Setting 6 has my base timing at 14 deg BTDC with 20 Deg advance in the curve. I am going to try adv curve 8 (high HP NA Motors - High idle advance) next time out which has a base of 24 BTDC and 10 Deg adv curve. We'll see how that goes.

I'm not running a thermo at the moment as I'm worried about my cast alloy exhaust. I have a 140deg which I've drilled out but because the water here is so warm all the time, I don't seem to have trouble getting engine temp up a bit and steady.

I'm going to get a pair of 35 and 45 PVs to see how they go. I'll also get a set of #90 jets to try and see if they work any better.

How would you know if a set up should / shouldn't have different / offset jet sizes in it (ie: 92 & 90)? What difference would it make in a marine engine? How will I be able to tell if that may work for me?

Thanks for all your help so far, sorry to hit back with more questions but I'd like to tget this right!

Cheers,
John

try advancing the base timing and watch the vac gauge, 9 still to low, see if that raises it ? also do you have another carb you can try ? what idle speed are you at ? but you should be in the low-mid teen in vac at idle..so something no right...Rob

Okay, Tried again today. Lovely day on the water mind you!

I put the Mirage Plus 25P on and re-built the carb with new #65 PVs and left the #86 Jets in to see what it would do.

With the base vacuum tuned to around 10 - 11 inches, the screws are about 1 1/2 turns out. Motor ran a lot better with the new PVs and an oil change!

Best I could muster was 68.7mph (GPS) at around 4850rpm. Engine felt like it wanted to go better but seemed to lack fuel?

The plugs were a bit blackened and there was some black residue on the transom so that leads me to think it's too rich?

Base timing is 14 Deg BTDC with 20 Deg adv curve on a HI-6M.

Next test I'll leave the Mirage on and lean it out a touch. Anything else anyone can think of or any other suggestions?

Cheers,
John

ok i think your getting there . my late motor was close to your this is wt i would do . 1 run your motor at 3000rpm set the timing at 34degrees then lock it in ! then run it on the water . you got 68.7 last speed at 4850you need to go down on the pitch more ! it is 200rpm for i pitch size . i would try a 23mirage plus that will give you 5250rpm was your motor dyno????.i last year i had same thing go wrong on my boat i put smaller prop on my boat ! 4900rpm my boat ran 75mph ,but it was a dog ,i went down pitch now 5500rpm now going over 80mph .if you have a dyno sheet look to see where your highes tq number is . lets say your is 4400rpm then you add 1000rpm to that ,that will give you max rpm to prop your boat. good luck

I have a Bravo 1 24P I'll be testing next but for now I just want to get the carb / fueling issues sorted out and make sure I've got the right jets etc in before I put too much emphasis on anything else.

Any thoughts on the Jet sizes?

that 24 prop will be almost the same as the 25 pitch . 3 blade props are faster ! . i ran 84 jets in pri. 88 jets in sec. with a850 holley on my motor .you say your runnig 86 all 4 . do the timming then put the prop that give you the rigth rpm . then run the boat at 3000 rpm for a few miles trun key of and pull 2 spark plugs see wt they look like hoping tan color if they are the pri. jets are rigth! then you got to go full throttle and do the same thing trun key off and pull some plugs .your timming has to be rigth and the motor need to be pro at the rigth rpm . the motor has to be in the power band. that y you are runnig rich. once you get your boat runnig 5200 to 5500 range then you can see wt jets you need . the only other way is put it on a dyno !

Measure your vacuum while running....you will need an assistant. :drink: My guess is your PV may be opening too soon. Try a PV that is at the vacuum level at 80% of WOT.

what holley carb are you using anyway? I have an opinion however would like to know what model/size holley you have or did I miss that in another post?
John

Fixx
 

What everybody said! just throwing out my o2 here,with a Holley you need to get the carb to operating temps first to make then idle correctly..Also your primary throttle blades shouldn't be touched from the factory spec's to turn the idle up because it throws off the idle circuit and the fuel going into the motor puddles instead of spraying..if you need to raise the idle adjust the secondary stop screw to achieve the correct idle.if its loading up at idle you need to turn in the idle enrichment screws,like stated no more then one turn out,most of my boat engines end up at a half of a turn..you want the front throttle blade as closed as possible..if its open to far then you will get a stumble off idle..somtimes it can be corrected with a bigger squirter in the throat of the carb...

Back to running no thermostats! run a restrict or plate,i make my own out of 316 ss with hole punches in various sizes to get the proper engine temps,you will never have to worry about a thermostat sticking this way from some of the crappy water we run in..

Sounds good to me!
I've checked and re-checked the timing. I'm now set at 14 BTDC (start) running a 20 deg Adv Curve for total timing of 34 BTDC. My other option is to run an initial advance of 24 deg BTDC and run 10 deg adv curve, which might help me at idle / docking speeds? Running the HI-6M makes adjustment easy!

My last test, when coming up onto a plane (or trying to), the engine seemed to stumble around 3600-4000 rpm when on full throttle. If I tried to get it up using less throttle, there was no stumble but it takes longer (obviously).

I'll check the primary idle and try adjusting using the secondary. I didn't know about that one, thanks!

John: My Carb is a Holley 850 D/P HP (4 corner idle, PV protection circuit, no choke, less vacuum ports on the base). I'd be keen to hear your thoughts too!

Thanks all.
John (the other one)

ok john it sound like you on the rigth track . think about when you drive a car you put it in the wrong gear . you have it in 3 gear . you take off the motor slowly pick up power til it hits the higher rpm . you give it gas and it bogs and feel like it has no power. how about you try 2 gear to start out in ? it will bog , but it will pick up better. . well that wt your prop is doing! i beleive if you put a smaller pitch prop so the rpm is higher up in 5200 to 5500 you will not get that stummble at3600 to 4000rpm !4850 is to low for your motor.my boat did the same thing !i put a smaller prop on . i run 5500and the boat is very fast no stummble .once you get the rigth prop on then see wt it runs like

Hey guys,
Sometimes you just have to get to back to basics.
First by my caclulations the motor / carb combo is good to 6276 RPM.
Now with that in mind you are either running to much carb or to much prop.
Now concerning the vacuum issue. A camshaft of this type has a certain amount of overlap / valve timing.
This always creates a less than ideal amount (10-12 inches) of vacuum.
First you must make sure you are measuring manifold vacuum. Most ports on the carb are NOT manifold vacuum.
Once you have determined optimum vacuum at idle, with a Holley carb you take that number and divide it by 2 and that will give you the size power valve you need.
The real trick is to establish baseline numbers. Then make 1 maybe 2 changes then go make the same test run. Record the gains or losses and adjust accordingly.

How are you coming along. Are you still running rich and have the stumble? I really don't think your over carbed. You could perhaps get away with the 9022 - 800 cfm however I don't think the 850 if properly tuned would give you the trouble your having. I can't remember at the moment if you rebuilt it or not. If not I would get a kit and do it. Make sure you soak the entire carb/parts in cleaner over night and blow threw everything extremely well. Did you buy the carb new? Perhaps a previous owner has changed out the plastic cams to taylor their needs. What are you using for ignition? Also any test you do especially pertaining to jetting always do it with a new plug in number 8 cylinder at the very least and check it every time. That's most often your hotest cylinder on a BBC. What size squirters do you have in the front and rear. Also you'll want both front and rear plates cracked at an idle. try and keep both the same. There is a lot of info on holley carbs when you google it. Information from experts to help you tune as well as holleys site. Just a thought. I would imagine you have a lot of boater friends around the area. See if you can borrow a couple of different carbs to help diagnose any problems you may have. The carb calculators are OK however I have ended anywhere close to the number it gives you. That's kind of an old time theory. Marine engines always like carbs a tad on the larger size. Believe it or not to large of a carb can actually lean out at WOT. They get lazy a little lazy so to speak and tend to not pull is much fuel through. As mentioned above I would also try and prop it for 5400 to 5600. Your duration @.050 - 236/245 will like the higher rpm. It will seem like a whole different boat.

Thanks mate,
I've got a 23P Rev4 on the way to try and get the revs up a bit.
I'll check the squirters but I think they're good. The cams on the accel pumps are okay (I had them checked too.) The carb is virtually brand new and I just had it rebult again anyway. I then tore it all down and confirmed what was done and put all new parts & gaskets in again just to be sure.

I think from what I've read so far, I've been running it rich in an effort to compensate for a porely established base idle which I set using the primarys. I've re-adjusted using the secondarys and leaned it out a bit. I've managed to get it to idle now aroun 800rpm pulling 12 inches (at best) with about 2/3-3/4 turn out on the screws. I'll put her in the water again when my new breathers show up and give that set up a go.

Thanks all, I have learned a great deal which hopefully will help me hit my goal of 90+ mph!

what flame arrester ? seen those restrict and cause a rich condition, seems rich by what you are saying....can you crack you hatch and run the boat ? have seen boats that do not get enough air into the engine compartment..basiclly chokes the engine..would show up as rich...Rob, ps did get a intake, thanks for your offer !!

I don't think air flow is an issue.
Massive scoop and equally massive oval billet air cleaner with K&N filter. I think mixture or jet size is my bain at the moment so I'll scew with that till it's sorted and see how that goes.

90+ - I think you been chasing to many Kangaroos and drinking to much of that goofy beer you have over there. LOL... Good luck though. That was a good point made above in regards to the flame arrestor however sounds like you got that covered. I have to look back however what is your total timing?

34 BTDC Total. Start 14 Deg BTDC, 20 Deg curve. Could that be a problem?

I would say your right on. Sometimes I have seen advance curves vary even with the same modules. Just wanted to make sure you did check total advance with a timing light. The only time I check base timing is when first start up after a rebuild.

ghostrider did you do wt i told you to do run the enginge at 3000rpm then put the timming on 36deg. . when you run it at 3000 your timming will be at full . ..

I am not familiar with the crane HI 6M ignition however I am assuming that total advance is by 3,000 or is this adjustable?

Ghostrider, how do you like the Crane Ign. box? I was thinking of adding those to my merc TB 1V ign.

I've checked the engine under load at 3000 and the timing is spot on. That's the joy of the HI-6M, it set's the advance curve with the pre-selection of one of the built in curves. I have mine set to position 6, N/A motor, 14 deg BTDC start, 20 Deg curve. You can also select from 7 other curves for 525 efi, 600 - 900 SC curves and a High initial advance curve for Hihg HP N/A motors with idle issues which you pre-set to 24 Deg BTDC and run a 10 Deg curve for 34 Deg total. The HI-6M is a great box and IMO, far more robust and reliable than the MSD unit, with the addition of the built in curves just makes it better all round, it also has a built in rev limiter, adjustable to 100 rpm. It's compatible with the TBIV system, I know Fastlane40 runs two boxes on his Skater Race boat with TBIV distributors for reliability!

I've got some testing to do once I've fitted the new breathers; I'm going to try the new carb settings and try the 5 blade prop again (less pitch). I'm also going to try the LH Bravo 1 24P I just received and see if running left rotation improves handling at all.

I'll let you know how that goes!

You stated that you are running Vortec heads. These are fast burn heads and cannot support the amount of timing you are running. Generally about 28 degrees is the most advance you can run without detonation. They also can run higher compression than a traditional cylinder head.

Hardend exhaust seats. What is the chamber size? I was thinking they're just over 100cc's however his chambers could be opened up also to help the flow. He probably has flat top pistons to achieve his 10.5 to 1 comp. Not the greatest flowing heads however I'm just happy to know they offshore boat in the land down under.

You know, now that I think about it, you never do hear of to many boat engines with those heads???

Fixx
 

I think he must be mistaken on the vortech heads part..i dont believe edlbrock makes a airgap intake for that head yet..He probably has the standard 088 head..

I know of a couple of guys running them. Their main advantage is the combustion chamber. I think it is a 98cc. They're happy with them, but I think its only because they had the 330hp motors and the heads provided an instant upgrade in compression ratio and really livened up the motors.

I definately have the Vortec heads (10141279...96-up...oval..CLOSED.."Vortec 7400", 100cc chambers) Technically speaking, now 105cc.

I had them openened slightly to allow better flow and I had the oval ports matched to the Felpro gaskets. I then bought the RPM Air-Gap manifold (PN 7561 - Oval Ports) and had it CNC Flowed and port matched as well. .I had the heads resurfaced / shaved 0.020" to 55Ra which will also help with the comp ratio. The combination of head chamber size and my pistons allow for about 10.5:1 Comp. They run the standard valve size (2.065" I & 1.72" E) with the large oval ports and a better exhaust port profile (which Merlin and Dart use on their heads now too.) Reason you don't see many marine engines with them (IMO) us that too many people think that all oval ports are too small and they 'must' run Rect ports to make any power in a boat! Truth is, the Vortec heads flow better than all the other ovals and the exhaust port profile makes them a far more efficient head! Only downfall is I'd like a set of 2.19" intake and 1.88" exhaust Iconel valves in there to open them up!

I'm interested to learn more about the 'fast burn heads' thoughts though from Bobl. I hadn't heard that before and it is well worth considering. So if I set the timing to 8 deg initial withthe 20 deg curve (for 28 total) and give that a go it should be safer? Or will it possibly make more power?

Cheers all. Good discussion!

Hey bud, "fast burn" I think that's claimed due to the cleaner castings and unique or different chamber design. Supposodly the fuel atomizes better than that of comparable or previous casting heads. More efficient. If he could explain perhaps it would make sense however I wouldn't change your timing yet. Be careful with to low of total advance also as valves tend heat up more than normal. Hopefully someone will chime in that knows for sure. I've always been a big fan of oval port heads myself especially for marine application. On my most recent 496 builds I was even very close to staing with oval ports as well. 496's, depending on other components etc. You can have good results with rec. or oval. With the desired power I wanted to achieve the cams I used pretty much dictated the size of my intake runners. I ended up with 310cc's. The ovals would have worked well also but would have worn out quite few carbides in the process. Very understandable for a quick fix on Comp. ratio to wake up a stock 454/330. I don't know for certain however those heads may limit your top end RPM to around the 5,300 or so however I don't think you want to run much more than that anyway. I found some stock flow numbers and it looks like they fall off much over .525-.550 lift. I would like to talk to you about some other things also so I'll send you a PM. I'm just curious as to the cam your using vs your heads. I'll talk to Valako and get his input tomorrow.

John
What's your weather like there this time of year?

From what I understand the 049 castings and the 781 casting actually both flow better than the vortec heads, despite the new casting on the exhaust profile. I know street racers that are going mid-10's on the 781 heads, and they wouldn't think of trying to get that out of vortec heads. Allegedly, according to them, it would take too much port work to get the vortec heads to flow as good as the 781 heads, if its even possible.

GhostRider,
How tall are the intake ports at the gasket? As long as everything holds together and you can boat trouble free that's not all bad either. Down the road maybe you can change your heads out. With your other components a good set of aftermarket heads would really wake that thing up. Do you have any speed shops around where you live. As much as I have always wanted to visit I have yet to do so. You pay my ticket and I will carry on a couple of heads with me for luggage and we'll get your boat really moving.

These heads have the heart shaped combustion chambers. I've built and dynod several engines very similar to this. HP is around 450 at 5500 rpm(but I don't run quite as large a cam) They will detonate with very much timing. Because of the chamber design, combustion occurs much faster, thus requiring less lead time for ignition. This information has been documented many times. Pull the timing back and give it a try. BTW I own Full Throttle Marine and build marine engines for a living(so you know my background).