Im using a 750 vac sec holley. I am running vortec heads and a cam with 495/503 lift and 218/224 duration. Edelbrock RPM air-gap. Im pushing close to 375hp turning about 5300RPMs...I know some of you small block guys are running somewhat similar combo's..My question is this..I am looking for a ballpark figure on my jets. Just a place to start.....I know the carb was calibrated for a big block/electric fuel pump 3-1/2psi and I don't know how the base calibration would differ from a small block/mech fuel pump 6psi...Im running 78primarys and 80secondary jets...Not sure on the accel pump cam or vac secondary spring..Main thing is I am curious as to what everybody else is running..Since this is my first REAL go-around with a holley since running the "Brock" I wondering if I am even in the ballpark starting off....


BH

I can't tell you what jet's to use but another thing is the power valve. They make a bunch of different sizes. You'll need to see how much vacuum you've got and use the appropriate valve.
My brother just went through this with his Demon that's on a built 460 (in a car) Made a big difference in around performance.
Probably would be best to buy a book on Holley's.

I used to run 780 vac secondary, 64 primary jets 66 secondary 6.5 power valve primary side,not sure on the spring I would have to measure the wire dia. 400 small block ,ported stock heads ,comp cams 260 h cam I think it turned around 5000 rpms.
How many cu. inches?

Rob

I have almost the same exact setup. 350, Comp XM264HR (you have the 270), 1.6 ratio comp rockers, rpm airgap, IMCO risers, MSD and pro-action 220 CC heads. My compression ratio with 0.015 steel shim gaskets is 9.39:1 static with a .039 quench distance

I run a 600 vac sec dual feed (center hung float) holley (in a quest to try out a 750 - and put an O2 sensor in the pipe). I run 66 primary & 72 secondary, purple sec spring, pink cam - hole #1 w/ 31 squirter. I really need to go to a 28 squirter and drop down on the power valve... if my memory recalls correctly i have a 8.5 power valve in there and that is too high, i need to drop down an inch at least since i cruise in the 3000 - 4000 range... i average around 4 miles / gallon in that cruise range...

my vacuum curve under load is such: (all in Inches of Hg)

15 1/2 @ 750 rpm idle
11 1/2 @ 2500 rpm
10 1/2 @ 3000 rpm
9 @ 3500
8 @ 4000
7 1/2 @ 4500
5 - 5 1/2 @ WOT - 5500 rpm

The 73 primarys and 76 secondaries I gave you in those carbs were the jets that crusader had in them for their 500 horse 454...so you probably are gonna go down from there. I think I was running 80's on the secondaries and 78's on the primaries with merlin heads and the 415 horse roller cam on my 502. I think the number on the power valve was stamped into them too.....Glenn

BAD HABBIT, what kind of prop and what kind of top end do you get out of that.. I am still trying ot figure out the jets on my SBC with a Perf RPM with a Rochester carb. I can crank 5100 RPM with a 19" pitch prop. Just curious

Interesting note. Ive found out that using a bigger than usual (necessary) carb means that the carb will require more of a accelerator shot and larger jets than a bigger motor will. Ive tried to do as much reading as possible lately on the holleys and have read this several places. I guess it's because the vaccum signal is less on a smaller motor. The smaller motor will still use the same amount of fuel with a 750 as a 600. The pounds per hour are the same just the velocity will be different hence the need for a bigger shot and jets....

BH

Im running a 19" Ballistic pushing about 5200rpms. Top end is 56GPS (still inching towards 60 )Thats from a base of 47 with the stock 260hp 5.7. Im pushing about 4300lbs loaded. Im hoping of hitting 60 after I get the motor dialed in and get the prop labbed and blue-printed. Now if I go by the speedometer Im pushing 60 already!

BH

I am running a 750 holley vac secondary non marine carb.

Last years motor.

383
vortech heads
9.9:1 comp ratio
222/230 .509/.528 roller cam
air gap dual plane intake.
ran great with 72's in the primarys. This carb has no jets in the secondaies

New motor

383
afr heads
10.8:1 comp ratio with 110 octane
single plane intake
234/242 .575/.595 lift roller cam
same carb Rejetted to 74's in the primaries last weekend and plugs look great. no jets in secondaries

Traviss...Explain the no jets in the secondaries thing Whats the purpose? Just Curious

BH