84TAProject

A friend of mine has a 350 pontiac in his 68 le mans (yeah not third gen i know, but you guys seem to know everything about cars) with 4.11 rear gears, long tubes and flows, 265/60/r15's on the back, th350, rpm intake, and an edelbrock carb. He wants to upgrade the cam in it, the motor is a 10.25:1 compression HO pontiac 350. What cam do you recommend for a 5500rpm and below pontiac motor. I figured the same kind of cam like in my car (218/224 @ .050) but figured I should check, not knowing about breathing characteristic on a pontiac motor vs. a chevy motor.

RB83L69

Pontiac head flow characteristics are fairly similar to SBC heads. The same general types of cams that work well in the one, also do well in the other.

We used to run the old Comp HE268 and 280 in Pontiacs alot. I'd bet that a XE268 would be great in it.

ME Leigh

Yeah the XE268 would run nice just like in a SBC.

Damon

ALWAYS ALWAYS ALWAYS install new springs when you swap a Pontiac cam. You will NOT like the results if it's got stock valvesprings in it. Even a stock cam will float the vavles at only 5200 on NEW stock springs. With an aggressive can you won't make it over 4500. With worn out 30 year old springs I've seen valve-on-seat spring pressures as low as 42 lbs!!

It's even a bit more of a PITA than it sounds since Pontiac used about 5 different length valves in various heads so you MUST measure the height of the spring pocket with the valve closed and make sure it's close to the spring's installed height spec or bad things can hapen. Many times the installed height will be pretty close but not always. It's been off enough times that even in limited expereince with Ponchos I've run across it twice.

Pontiac valve trains are real PITA. But properly set up they work just fine.

Vader

You aren't by some chance running Ram Air heads, are you? The port sizes on those are fairly generous to compliment the larger valve sizes.

Damon is right on. All I can add is that you'll almost surely need new push rods as well as springs. The lash theory on Ponchos is quite different, so push rod length is more critical.

As for cam selection, make sure you know what size valves you are using first. Some of the larger valve engines are not very friendly to high ramp cams without some serious springs and studs. I had a 326 in my '67 and used a .452/.452 grind with RA-IV heads. That was maybe a little too much for the street. Of course, the Powerglide and 2.56 rear gears didn't help, but 80 MPH in first gear was never a question - breaking the tires loose from a dead stop was.

bob8748

The Pontiacs prefer a dual pattern cam... check out www.performanceyears.com great Pontiac info there.:hail:

bob8748

Another thing to remember... anytime you change the valve geometery on a Pontiac engine you can no longer just tighten the valves down to 20 lbs to set lash. You will have to use polylocs or a locking nut to set the valves.I take out the 3/8-7/16 bottleneck studs and use BBC 7/16 studs. Then use roller rockers.

Air_Adam

Ram Air motors were only the 400ci and up motors i think... and wouldn't that be a bad thing for a Pontiac 350, since the bores are almost microscopic, you would have a much lower compression ratio? Correct me if i'm wrong.

Vader

Yes. The Pontiac V-8s shared the same 3-3/4" stroke (except the 455) and bore sizes varied the displacement. The RA-IV heads used to be a popular 350 modification. Many of the factory 350s had static compression ratios as low as 7.6:1,and 8.2:1 wasn't uncommon either, so the heads didn't hurt at all. (I think most Pontiac chambers were about the same size.) Anyone building them typically shaved either the original or replacement heads to bump compression. Even the small bore 326 I had ran much better with the 400 heads and just a little cam.

bob8748

'You arent by chance using ram air heads, are you"

Man... if you can find a set of ram air heads let me know... I will buy all of them...