mopowers
Well-Known Member
Does anyone happen to know off hand what the stock PVCR size for a 4779 (750dp) Holley is?
Holley 4779 specs?
- Thread starter mopowers
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mopowers
Well-Known Member
Unfortunately, no. All I know is it's an old one. The choke tower is milled off. How much did the PVCRs change through the various "-" numbers. I'm just curious what they came with in stock form.
Mike's working on one right now. He's got the specs of what he found in it posted
Holley - racingfuelsystems.myfunforum.org
Funny I have long term loaner 4778 here with the choke tower cut off and the body restamped 4779-2. But the venturi measurements can not be denied. LOL
Holley - racingfuelsystems.myfunforum.org
Funny I have long term loaner 4778 here with the choke tower cut off and the body restamped 4779-2. But the venturi measurements can not be denied. LOL
mopowers
Well-Known Member
Thanks, but I meant the power valve channel restrictor size, not the power valve #. I appreciate the help though.
mopowers
Well-Known Member
Thanks! It looks like his were 0.055". Exactly what I needed. Thanks again.
Pin gauges are really inexpensive...
The orfices can be all over the place.
The orfices can be all over the place.
mopowers
Well-Known Member
That's a good idea. I planned on opening it up this weekend anyway.
The reason I ask is the old 4779 I've got needs the PVCRs opened up a bit. The metering blocks on it are from a 4777, so I'm assuming the PVCRs are a bit smaller them, which is why they need to be opened up.
Any idea how much of a change in PVCR size makes much of a difference? Are they like IFRs, where a tiny change can make a big difference in AFR?
The reason I ask is the old 4779 I've got needs the PVCRs opened up a bit. The metering blocks on it are from a 4777, so I'm assuming the PVCRs are a bit smaller them, which is why they need to be opened up.
Any idea how much of a change in PVCR size makes much of a difference? Are they like IFRs, where a tiny change can make a big difference in AFR?
Send me an PM with your email.
I have a spreadsheet to help figure out the total area of jets/PVCR.
You can sort of figure out the PVCR sizing if the rear doesn't have a PV. The jet spread area sizing should be very close to the PVCR sizing.
I have a spreadsheet to help figure out the total area of jets/PVCR.
You can sort of figure out the PVCR sizing if the rear doesn't have a PV. The jet spread area sizing should be very close to the PVCR sizing.
mopowers
Well-Known Member
That's a great though. I'd hadn't though of that. Math... Whoodda thunk! lol PM coming.
mopowers
Well-Known Member
Well, I opened up the PVCRs in front from .055" to .059". I'll take it for a spin today to see how it responds. Hopefully the .004" isn't too large of an increase.
mderoy340
Well-Known Member
Every .004 increase is equal to approx 1 jet number, .059, .063, .067 etc. Don't be surprised if you need to go up to .063 or .067 I always end up dropping primary jet size to lean primary cruise and then dial in WOT with the PVCR up front and SJ.
mopowers
Well-Known Member
Good to know. Thanks! Ya know, it'd be nice if jet #'s actually reflected their respective orifice size.
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