clevoxt

Need some advice on jets and power valve sizes for my 600vs holley,or would i benefit more from say a 650dp.My specs are,
Cam-@50 219/219 525/525
Manifold-performer
Ignition-procomp
Exhaust-extractors,twin 21/2
Heads-std
Trans-c10
Diff-3.50 gears

brenx

I think it very borderline 650dp. My mates 302 doesn't have much more cam than that yet runs a 650DP.

Brenden

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Racer

Jetting is one of the least understood things. The jetting should initially match the carby. The carb should be jetted to to give the right balance of air/fuel for the paticular carb size (CFM). Jetting is merely to fine tune the whole engine assembly as one. If you need to change more than say 4 jet sizes, something is wrong with the carby, or the carby is the wrong size for the engine.

Contrary to popular belief, a engine with an oversized carby may need larger jets, and an undersized carby may need smaller. This is the reverse to what most people think. The reason is that an undersized carby has a stronger signal on the boosters and pulls more fuel. The reverse is true of an oversized carby.

Get the list number off the choke housing and go to the Holley site and put the baseline jetting back in it. A 600 should be fine. The standard GT351 carby is smaller than that.

XECLEVO

I'm running a 650 vac sec on a near standard 351 and it works a treat. All i have is a mild cam and twin 2 1/4 exhausts.

northiam

Your idle vac would be 15+ inches with that mild setup so a standard 6.5 pv would be sweet. Jetting would be also very close as your carb size is good too.

TTNOS8

northiam, I doubt idle vacuum would be that high.

clevoxt, If you want to see what is best and you've got time and tools to play around then try both.

Get your timing right, idle mixtures right, and run your engine up to oper temp. auto or manual?

Put a vacuum gauge on the engine and read the idle vacuum.

record reading and fit power valves up to around 2 inches lower than reading.

fit air/fuel ratio meter to engine, monitor all readings throughout rpm range under different load situations and jet, adjust carb, timing, etc to suit.

I usually try and get a/f to around the 13.2 mark under power.

Or spend around $120 and take to a dyno shop

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northiam

My F238 with a performer manifold run at 11 inch of vaccum! My old XC 351 with a 214-219@0.050 run @ 17inches. I reckon it will be close!

Nod

I must have a problem, I run a 208-208@.50 and get 14inches :(