Alright, this whole carb thing baffles me sometimes. I have always used fuel injection till this car.

How do I set up my holley 750DP for the fuel needs of my new 383 with a Weiand 144?

I guess I need to start at the jets, move to the squirters and continue on from there, I just don't even know of a baseline to start at.

HELP!

 

bump

 

you would need to reference the power valve for it.......search this section.it has been done and i did it to an 850 cfm carb which i run with my 144 roots blower with no issues

 

yea, I got that, but I was thinkin about not running a power valve at all.

Tho, it would be better to use one for obvious reasons.

Do you remember which jets, squirters, and power valve you used? I need some idea for a base tune.

 

Good starting point is 4 jet sizes richer than stock on both side of the carb. Don't take out the power valve- just bump it up from the stock 6.5 to about an 8.0 if you don't plan on modifying the carb to boost-reference it. If you DO boost-reference it you should put in a lower number PV- like a 3.5 or a 4.0.

The main idea is you want power valve enrichment of the mixture BEFORE the engine sees positive boost. And boost will start to build in the intake while there is still some modest amount of vacuum under the carb. On my engine (mild 383 combo with Weiand 142 blower) that crossover point is about 4-5" of vacuum under the carb when the intake just starts to pass the 0 line into boost. By opening the PV at a higher number than that you can be assured it will be open before the engine tips into boost.

If you boost reference it, you don't have to worry about that since it's directly reading vacuum/boost that the engine is seeing and you can drop the PV number much lower. This mod is not necessary on a mild combo with a small cam and plenty of vacuum while idling and cruising around at part throttle (like my engine). On wilder combos with big cams that make very little vacuum under any conditions it's pretty much required or you'll be driving around with the PV open almost all the time.

 

alright, I don't plan on boost referencing it at this point.
So this would do?
http://www.summitracing.com/parts/QFT-25-85/

UGH! So much to learn!

 

I just took my carb apart and it seems that its a proform main bod.

The jets are 76 and 84, no power valves at all, and 37 squirters. I called proform and they said without a powervalve they should be more closely jetted.

When I put a powervalve in this carb I will need to run the vacuum line under the blower, correct?

I'm thinking that based on what Damon said, that all I need to do for it to start up on a baseline tune, is throw in a 8.5 powervalve, or should I go with a 7.5? I didn't see any 8.0s on summit. thanks again!

 

Well, given that the carb is a "Frankenstein", expect to have to spend some time tuning it. You can't go just by long-distance recommendations. You can never be sure how a different/aftermarket part in the middle of your carb is going to affect the tune. Remember that the boosters and air bleeds reside in the main body, so that right there is 2 potentially big differences from the stock Holley main body right there. Might work great right off the bat, might take a lot of tuning to make it all work together well.

Agreed, the jets should probably be much closer if neither side has a power valve. A power valve is equal to about 8-10 jet size differences. (Add 8 jet sizes to those 76s and you end up at 84- the same size you already have in the secondaries.) If the previous owner decided to replace the power valve with a plug he should have gone up 8 jet sizes to compensate, otherwise it will run lean under heavy load/WOT. Obviously, that would then make it very rich at part throttle, so removing the primary side power valve is generally a bad idea for a street driven engine. That's for strip-only applications where part throttle drivability is not a concern.

Running no power valve on the secondary side is OK, generally. By the time you're deep enough into the throttle to open the secondaries you're generally at a low enough vacuum level it would be open anyway.

Try just installing a #8.0 power valve with those jets and put it back together. Might as well do a clean and rebuild with new gaskets while you're in there. Tune from that point.

 

Thanks for the response. I couldn't find an 8.0 so I ordered a 7.5 and an 8.5. The 7.5 arrived first so that went in first, lol.

I cleaned up the carb a bit, it looked pretty healthy. It was on a race only engine so I knew I had to throw in a power valve. I'm going to keep with the current jet setup, like you suggested and get a wideband, hopefully by monday.

Question there is, how do you tune with the wideband being that it has primaries and secondaries?

I'm guessing, when in wide open throttle, if its rich or lean you adjust the secondaries, where as cruising on partial throttle you adjust the primaries? And what about the squirters??? Oh man! I totally forgot about those!