67mustang302

Remember, that 570 comes with a 8.5 power valve and some lean primary jetting for high horsepower applications. Holley reccomends that carb for "under 300 horsepower." Pfeh. I had to jet my primaries up from 54's to 58's. 4 stages.

my77stang

differences between the 570 cfm Street Avenger and the Model 4160 600 cfm Holleys
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cfm Main Jets Secondary Jets Power Valve Secondary Spring
570 54 65 85 Silver
600 64 70 65 Black

Holley paperwork says you shouldn't have to go more than 4 jet sizes up. I want to go 10 sizes, but I have concerns that it will be too damn much for the 570. On the other hand, they are *almost* the same cfm rating so WTF.

I'm looking at 64/70 jets and a 50 or 55 Power Valve, something tells me it will run alot better because right now its a friggen pig.

Baxsom, what condition is your 600 and is it stock? what do you want for it if its in decent shape? I'd like to have one for "troubleshooting"

67mustang302

Yeah, and you don't have that much vacuum either, so I'm sure that power valve in it now is making it really fat rolling out from a stop. [&:]Who knows though, maybe the SA's are better at metering fuel and you won't need as much jetting? Check the plugs, like usual. In the end though, I just ignore a lot of that stuff from the engineers about "no more than 4 sizes up" and "For applications over 300hp use 670." Use whatever size carb you need with whatever jetting gives the correct a/f ratio, that's the way I see it.

my77stang

i always thought the power valve took vacuum to make it work, but from what i have been reading it sounds like it takes vacuum to close it?

how exactly does that friggen thing work?

67mustang302

It'sbasically a vacuum diaphragm with a pathway for the fuel to get into the metering system through a valve, and a spring that tries to keep the valve open, the spring being on one side, and the diaphragm on the other, with the diaphragm attached to the valve so the intake vacuumcan pullit closed. The spring itself is what determines the valve's rating, 8.5" 6.5" etc. The spring is always trying to open the valve, and it's the intake vacuum that overcomes the spring to keep it closed. When you open the throttle enough and the vacuum drops to the spring's rate, the valve opens. So when you're at enoughload to have less vacuum(numerically lower, or closer to 0")than the valve is rated at, it opens, when there's more vacuum(numerically higher)than the valve is rated, the vacuum pulls on the diaphragm which is attached to the valve, and compresses the spring so it closes. That's why if you have a power valve with a higher rating than your idle vacuum, the power valve is open at idle and floods the carb, cuz there's not enough force from the vacuum to overcome the springrate. In your case, you have relatively low idle vacuum at around 10", and a valve that's only rated at like 1.5" less than that, so when you try to roll out from a stop under load, or give it some throttle at low rpm, the vacuum drops to the valve's rate quickly and kicks it open sooner than you need it, and makes you run pig rich.

So it's a tug of war, with the manifold vacuum trying to close the valve, and the spring trying to open it. With your's, I wouldn't go any bigger than a 65, a 50 or 55 may run better. That 85 is just too high though, and I wouldn't be suprised if you're fouling plugs.

my77stang

i'll be checking those plugs soon enough, heads are coming off to drill steam holes in the block[:@]

67mustang302

Time for some alum heads methinks.

my77stang

joo got some money to loan me indefinately?

67mustang302

I spent all mine building the 302 I have now.

my77stang