need help with cam selection for Propane

fatnlow · Feb 23, 2016

I am working on an older small block Chevy 350 we put Vortec heads on it. they have had the machining done for the screw in studs and to accept bigger valve springs. Now we are trying to figure out what cam to run? it is a 40 over motor and I am trying to keep building power from 5000 to 7000 rpms wanting to stay in the 500 to 5:25 lift

muddinmetal · Feb 23, 2016

fatnlow said:
I am working on an older small block Chevy 350 we put Vortec heads on it. they have had the machining done for the screw in studs and to accept bigger valve springs. Now we are trying to figure out what cam to run? it is a 40 over motor and I am trying to keep building power from 5000 to 7000 rpms wanting to stay in the 500 to 5:25 lift

a 425 mixer will NOT feed a 350 at 7000rpms!!!!! Propane likes cams with less overlap anyways....

Klutch · Feb 23, 2016

Just my 2cents - I have an older 350 bored 40 over with flat top Pistons 305 heads and a rv cam on propane
And it's just bout rite , pulls good revs good , quick to respond I like it a lot,,,,,,, jus sayin

muddinmetal · Feb 23, 2016

Klutch said:
Just my 2cents - I have an older 350 bored 40 over with flat top Pistons 305 heads and a rv cam on propane
And it's just bout rite , pulls good revs good , quick to respond I like it a lot,,,,,,, jus sayin

He ain't hearing that, he want's a big donkey **** cam that wastes horsepower and sounds good

Elliott · Feb 23, 2016

A 500 inch cam doesn't need to rev anywhere near that high, neither do those heads.

altfuel1991 · Feb 24, 2016

A few years ago I supplied a dual mixer setup to an engine builder in Atlanta that was putting together a 383 stroker for use in a competition buggy in the XTERRA series. He had a cam ground specifically for that combination. It had a strong idle, not loping, and had a torque curve of over 500lb.ft of torque from 1800 rpm through 6500rpm. He would not give out the specs on the cam. My suggestion is to contact a cam grinder and tell them what you are going to run and let them make the proper suggestion. Horsepower on comes into play at high rpm, torque is what gets you there. You can run a higher lift but you do not want a lot of duration. The cam needs to keep the vacuum signal high. The cam grinder needs to know all the critical info on the engine. And as was poster earlier, a single mixer will not feed a small block above 5000 rpm properly. It is like running a two barrel carb, simply can't flow enough air and fuel.

Elliott · Feb 24, 2016

I bet a hydraulic roller ground similar to a 2 barrel round track car would wake up a propane motor, especially if it was a 4 pattern cam.

95yj · Feb 24, 2016

Comp 305H cam

mrdrinksalil · Feb 24, 2016

I just got a 350 back from the machine shop that is being built for a single mixer setup. 10.5:1 and Aluminum 180cc intake heads. goal was to maximize HP/Torque from 1000 up to 5000 RPM. Went with an X4262H from COMP CAMS. Anything bigger was going to sacrifice bottom end power for RPM's you just can't hit with a single mixer. Going in a trail truck, not a bouncer. Motor wont be together for a couple more weeks.

Pumpkin · Feb 24, 2016

Re:

I have the 262/270 4x4 extreme cam from Comp. I'm happy with it for a single mixer on a completely stock crank and heads in a 406 SBC. Has plenty of torque but in not a fast revving set up. Not what I wanted anyways, but it is dependable.

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BPetty · Feb 25, 2016

I just went threw all of this, to save money in the long run have some one grind you a cam for propane, making all the hp and torque that you can under 6 grand. Like the guy above said, they must pull a lot of vacuum to start properly. But you can have a rough idle and a lot of lift. I have pretty much the same set up, mine is 12 to 1 compression with vortec heads. Hyd roller cam 545 lift 1.6 rockers on exit side 1.5 on intake. But yes it runs out of fuel at about 6 grand.