Carb Jetting Survey

[cudabob496]

I'm still trying to dial in my 12 year old 850 Holley DP, with the choke tower removed, using
my AFR meter. Holley told me my carb probably came with 80 Primary, 78 secondary side jetting.
So I'll call it 80/78.

I'm trying to support a 496 RB, that should be around 625 hp, I would guess, given all the goodies.

What jets would you guys normally see on an 850 that was trying to support 625 or so horsepower.

Right now after a week of tweaking, I'm at 78/84. Does that sound reasonable?

This is a little more difficult, getting the right air fuel ratio, because I do not have adjustable air bleeds.

Thanks

[Strawdawg]

fine stranded wire....

[Strawdawg]

Nkqjw gave you some good tips the other day on tuning a Holley.

Here is a link with some good pics with similar advice on how to set one up

http://www.corvetteactioncenter.com/tech/bbfh/big-block-from-hell-part-17.html#.UXKah7Xvvwq

[Chryco Psycho]

Typical means nothing ... i assume you have Powervalves both front & rear in that carb , most carbs would jet square [same size in every corner initially] the intake can vary fuel distbution , I usually see slightly smaller jets on the primary side due to the choke but yours is removed , you now have a better tuning tool than I have ever used so you tell us what works best .
 It sounds wrong but often larger displacement stroker engines use smaller jetting as the engine will pull the air through the carb with more velocity / signal  , the misconception is that a lrger engine requires larger jets but it is just a balance of keeping the right amount of fuel added to the air flow so more air may already mix in more fuel with better draw through the carb .
As Strawdawg said inserting wire into the bleeds can make a dramatic change especially in the idle circuit , this is why I chose more modern carbs like the Proform & new Holley HP series with removable bleeds so you can tune the carb better .
 Sounds like you mave left a lot of power out with the rear jetting 6 sizes too small , it should feel al lot stronger now .

[BS CUDA]

Typical means nothing ... i assume you have Powervalves both front & rear in that carb , most carbs would jet square [same size in every corner initially] the intake can vary fuel distbution , I usually see slightly smaller jets on the primary side due to the choke but yours is removed , you now have a better tuning tool than I have ever used so you tell us what works best .
 It sounds wrong but often larger displacement stroker engines use smaller jetting as the engine will pull the air through the carb with more velocity / signal  , the misconception is that a lrger engine requires larger jets but it is just a balance of keeping the right amount of fuel added to the air flow so more air may already mix in more fuel with better draw through the carb .
As Strawdawg said inserting wire into the bleeds can make a dramatic change especially in the idle circuit , this is why I chose more modern carbs like the Proform & new Holley HP series with removable bleeds so you can tune the carb better .

Looks reasonable and should get you down the road and run well. Way too many variables though to answer the question properly. Cruising or 1/4 mile, Air density, altitude etc.... I have never touched my bleeds - between accelerator pump tuning, power valves, vacuum setting etc I have always been able to get a good AFR reading on the street or on the track. I run a 500CI stroker w/ 1000 CFM Holley, 50CC accelerator pump, 4.10 gears, auto etc. It is perfectly streetable and very fun at the track but is consistently tuned for conditions. My 

[Strawdawg]

I think we can thank QuickFuel, Proform, and other ex-Holley guys for modernizing the carbs.  Holley seemed to be stuck in the '70's until recently and the new Ultra HP carbs have caught up with the modern features and added a few more.

In the '70's we did not worry about much other than wot performance so we looked at the plugs and tried to dial things in for quarter mile performance.  We stuck fine wire into the idle circuit to try to lean down the idle to keep from fouling the plugs at low speed but we did not worry much about gas mileage and such.

Then gas got sorry and expensive and we gradually began to try to improve drivability and gas mileage as well as optimize wot performance on daily drivers.  Holley DP's always seemed rich to me other than at wot.  These new carbs make it much easier to dial one in.  For some reason, in the '70's, I did not mind leaning over the fender and pulling the blows off 15 times on a Saturday afternoon, but neither the motivation or my back are interested in such today.  I would rather pull out my laptop and adjust the fuel curves, but if I cannot do that, then I really like the new carbs.

I am not sure what a typical Holley is because everyone I have ever worked on seemed to be a bit different-particularly after they started going to metering plates and such to cut cost.

[cudabob496]

OK, 78/84 is giving me consistent 12.5 AFR at WOT.

But cruising at 3000 rpm, I'm around 12 AFR. So maybe go 76/86?

[Chryco Psycho]

Makes sense to me , cruise uses only front jets so leaning them & adding more fuel through the secondaries should balance it out .