ok guys just curious here
friend has a car that is going to have stock heads, maybe just some MILD port work... like removing casting flash and port match the heads.
should have a 4bbl (came with a 2)
possible stock converter
275/60/15 tires with 3.08 gears


just curious as to some ideas for for possible cam ideas
doesn't want anything huge
wants to have something that will give mild performance upgrade and good gas milage



what can he expect for gas milage anyway?


also what are the hp/torque numbers at what rpm?

thanx guys






just wish he could put that 428 he has in the bird

 

Rx,

The Poncho V-8s had some pretty good head/port designs - usually a little better than the "average" Chevy SBC heads. Matching the ports and a little cleanup should help a little, but they probably aren't as restrictive unless you have a very late Pontiac (mid-'70s) head. Most of them came with nicely sized valves and decent ports. As always, core shift can throw off the port locations, so matching and blending aren't a bad idea.

One thing to remember is that Pontiacs like a LOT of timing advance to make power. They also have a very heavy bottom end, so spinning up to RPM may seem a bit sluggish.

 

I know these things are torque monster... well compared to most cars of same displacement


350 = 3.75 inch stroke and small bore


what is the valve size?


and any idea for the combo listed above a good cam duration?

 

Pontiac 350 = same torque as about any other brand of 350

The gasoline molecules do not wake up as they burn, and look around themselves, and check who cast the cast iron, and declare to each other "this brand of cast iron shall be known henceforth as 'torque monster' so I shall release more energy!!" That whole idea is just laughable.

Pontiac heads have very similar flow characteristics to small block Chevy heads, except for the major design flaw of the center 2 exhaust ports being one port instead of 2, which limits the scavenging effect that headers will produce. So half the cylinders end up with much poorer evacuation than the other half. They respond very similarly to cam properties to how SBCs do, subject to that particular flaw.

The old Comp 268H was what I used to stick in Pontiac 350s for people back in the 80s, seemed to work OK at the time with a slightly loosened-up converter or a stick shift plus a decent gear. I'd suggest their XE262 since you're stuck with such a crappy gear.

HP & torque numbers will depend on the heads and I'm no expert on Pontiac heads by casting #. Peak torque will be around 400-420 ft-lbs at the crank at some RPM, depending on the heads. If they're typical stock Pontiac heads with minimal work as you describe, I'd expect that peak torque will occur at around 3800 RPM, and peak HP will be at about 290-320 at around 4700 RPM.

 

Valve size depends on the head. Sizes and chamber volumes varied widely depending on the intended engine.

Do you have the short casting number?

 

hehe

sure vader make me look like fool

I know it's not in the iron
but I was assuming through the longer stroke of the pontiac motors that generally for the same displacement they are going to produce a little more torque

3.75 pontiac vs 3.48 for chevy

and whats this I hear with pontiac heads not working so well with higher valve lifts?

I just keep hearing from a friend that they work better with a lower valve lift and a higher lobe seperation angle




think the head numbers were something like 47 or 47h
not sure though

 

Get a set of Ram Air IV's for it.

 

Torque is the same as a Chevy 350, for a similar buildup; the stroke may be longer, but the bore is smaller.

It's all numbers. You have the same cyl pressure as you would at any bore/stroke ratio, i.e. some particular psi that depends on how much gasoline you burn in that cyl; torque = psi x area of piston (directly proportional to bore) x stroke; so for any given CID, peak torque will pretty much be a constant regardless of bore/stroke ratio as well as the cast-iron foundry, assuming approximately equal levels of cylinder fill (volumetric efficiency). The RPM at which that peak cyl fill is achieved may vary, depending on things like the camshaft profile and exhaust flow, but the actual peak torque is always just about the same. However, a lower bore/stroke ratio will typically lower the RPM at which the peak occurs; a handy thing to do, when putting 2.something gears into a car for gas mileage.

Pontiac motors have an extremely stupid non-adjustable rocker system, and so are very unforgiving of changes in valve train geometry. You just stick the rockers on, tighten the nut down until it hits a shoulder on the stud, and pray that it comes out somewhere within the lifter's tolerance. That's where the "don't work well at higher lift" thing comes from. People who build them seriously do away with the dumb adjustment-challenged shouldered rocker studs and put SBC studs and adjustable rockers on them.

 

ok

about high lift

I don't know
wish I could for sure not my motor
also this is second hand info I have heard from a friend who is a pontiac guy right now

but he is saying that flowbench numbers with high lift cause low cfm. and that a two angle valve job works better then a three and so on

how would you go about putting SBC rockers on there though?
what would it cost and how hard?

how would a higher piston area create more torque?....
other then more CID?
and by what I was saying with higher torque for pontiac
didn't mean huge big difference
but it seems that they are low end grunt motors for sure... but also typicly seem to have about 20-30 more torque then something of the same build for other motors.... but then again that comes just from my findings nothing from first hand experience or anything of the sort


the only real experience I have with a pontiac motor is a 301..... and we all might as well laugh at that car

 

i have a lot of things to adress here, so be patient.

they heads are what i'm assuminmg to be 47-h??? i looked on the center exhaust port and there is a 47 and on the rear port there is an h.

the valves are something similer to most sbc heads (1.94 intake etc...) not exact bu tclose if i remember right.

i dunno about the non adjustable rockers. but i know that with some heads all you need to do is screw in new studs (6x came with screw in studs and to can put bbc studs right in.

i dunno about these heads tho.

i would love to find a set of ram air heads period, but that sort of thing just doesn't happen here, i looked for a year to find a 400... (then i found a 428, turned out to actually be a 400 then i changed it for a real 428....)

as far as cams go, i am confused. every board i have been to says that ponchos dislike single pattern cams, then i read in a pontiac mag that they in fact do better with single patern cams because they have better flow on the exhaust than thet intake... so i dunno??? an dfrom certian dyno pulls it shows that they don't really do much better with higher lift cams and sometimes worse, so i think that it is something to blame other than the rocker design, not saying that that plays no part however.... but i do know that they like cams with wider lsa's so a lot of comp grinds aren't always the besy choice.

but here is a question for you guys to ponder. advancing a cam puts the power lower in the rmp band righ? and more duration puts the power higer in the rpm band right? so could one take a higer duration cam and advance it and in effect "stretch" the powerband out a little wider?

thanks guys......

 

oh, and thanks for the help, rx