[webfoot]

Should I plan on getting these things dished, or will it run on premium fuel OK? Car will be street only. Cam is a lil comp cams 268H (218/218 @ .050). Pistons are forged flat top speed pros with 4 valve reliefs.

Also, with this mild build (will be using RA manifolds) would it even be worth the investment to get Ferrea SS valves?

[OINK 1]

The duration is way too short. Get either an Ultra-Dyne ( the best) cam with 280/288 gross duration, @.050 223/231, lift w/1.5's .463"/.485".
Comp:XE268H, 268/280 gross,224/230@ .050, lift w 1.5's .477"/ .480"
Both of these will run on pump gas, power brakes will work too !
The UD will make more power though, + 30 horse.

You can get the cams from me if you like.

Pontiac Gregg
1-303-776-0877
web site: http://www.pontiacengines.net

[chiphead]

I agree the cam is too small for the car in your sig. I assume you will have 9.5-10 compression and non-ported heads and stock rods? A Crower or UD cam with intake duration in the 220-228 range and 112-115 LSA would be a good choice for a strong street application.

I would replace the valves and exhaust seats with quality parts. The valves are 35+ years old, seats may be pitted/recessed. As I recall, about $10-12 a valve should be a fair price for a street motor.

[Mr. P-Body]

In answer to your question, yes, the pistons should be "dished". If chambers measure between 72 and 74 CCs, a 3" diameter, .080" deep dish will get the compression down to a manageable level.

The 268H is an antique. A similar (parametrically) cam with "modern design" would be the XE268H. We prefer the XE grinds in the lower compression engines, as nothing else has shown us the real performance they have.

Jim

[HWYSTR455]

Ditto on the dish, you'll be sorry if you don't. Also agree in regards to the cam, go bigger, as well as the XE grind (if you're going Comp).

Valves, yes, go SS, and the Ferreas are 'the' choice in my opinion. Do the heads right now and save yourself grief later.

I say leave the seats alone unless they're damaged. Clean-up/cut is fine.


.

[webfoot]

Originally Posted by chiphead

I agree the cam is too small for the car in your sig. I assume you will have 9.5-10 compression and non-ported heads and stock rods?

Correct on the non-ported heads but I have tomahawk forged rods for this motor.

[chiphead]

My thinking was that you wouldnt want a cam that pulled over 5200 RPM if you had stock rods. Since you'll have good rods, you can spin that sucker to 6 grand if you've got a halfway decent oiling system without hurting the motor.

I'd set the compression for 9.5 and run a crower cam. The idea is with unported heads, you'll have to make the power with compression and not with RPM (unported heads won't support making power over 5500). That calls for a cam with a wider LSA to spread the powerband out where you can use it with higher compression.

See, the only drawback with seriously dishing the pistons is stepping up HP later. You'd have to have your iron heads ported, or go aluminum. You'd want the compression you lost to dishing back if you went to aluminum heads. So point is, carefully consider present and future goals and RPM range of the engine.

[Cliff R]

The forged TRW's typically end up WAY below the deck at TDC, so you may want to look at correcting that situation along with making a better cam choice.

The type of transmission, converter stall speed, manual trans, gear ratio, etc must be considered along with the engine cid and static compression ratio when choosing camshafts. Since you are in the street section, I'd look at larger cams on wider LSA's.....Cliff

PS: one would have to "assume" the vehicle in the signature is getting the engine we are talking about here???"

[OINK 1]

You DO NOT need dished pistons ! The heads are open chambered.
I've done 100's of 400's with the same set up you have.
It's all in the ignition curve !! BTW run Auto lite # 85 plugs, gap @ .030.

Pontiac Gregg

[HWYSTR455]

You can't curve 'out' det on a street iron head 10.8 engine on 92 pump gas, not likely on a 10.3 engine, and it's a fine line on a 9.8 engine. Once you back it off so it doesn't ping, not only do you loose power, but you run into overheating issues, for one.

Good catch Cliff, yeah, someone should have mentioned the zero deck thing, especially on the the TRW/SpeedPros. They do end up in the hole, seen as much as .24 before!

What many don't realize is the fact that you don't loose hardly ANY HP going from say 10.75 to 9.25 SCR, like what, maybe 5% - 7%? I don't think even that much. If you pull off a 440HP 400, 5% is what, max, 25HP? You can make that up somewhere else, and it's certainly better to run a on-tune 9.25 engine than a 'crutched' 10.5 engine.

Real issue with running lower than say 9.5-9.25 is the cam selections. That's where people 'think' they loose power by dropping SCR.

I don't feel there's much of a drawback to dishing, even if later you choose a aluminum head. Just get the 72cc, could even run a thin gasket if you want more. Use a profile that builds pressure too if you want.

.

[webfoot]

Wow, lots of great info to ponder. Thanks guys!

Sounds like I am in the market for a new cam, at the very least. I am not opposed to getting some Kemco additive as I doubt the car will get driven more than a couple thousand miles a year. (It will be my 2nd "toy" car.)

I should change my sig, because I have found out that my trans is actually a 1967 M-20 (was orig an M-21) and the pontiac 10-bolt was long gone. May run something like a 3:31 gear instead. (original equipment is listed.)

[Tiberius]

Hi Webfoot,

I'm going against consensus here but I know this combo should be fine as I have the exact same combo on Two motors.


I have the L2262 and #62 heads
Same CC and compression... and I have the Comp Cam 268H

I had two motors built exactly the same one with #62 & #13 heads also.

The combo has power galore, and absolutely NO issues with pinging of using 91 octane

I say go for it. I've had this motor now for ove 2 yrs and no issues.

Back then I asked the same question and my engine builder didn't bat an eye.

[Skip Fix]

If there is no pinging go to the track,chassis dyno make a reading/run. Dump in half a tank of race gas and see if your times pick up. If they do yes you have detonation going on even if you can't hear it. When we dynoed my very open chamber RAIV 400 zero decked TRW piston motor no audible detonation standing next to the motor. Race gas picked up almost 10 hp.

[sixt8bird]

Non ported heads #16s, TRWs, stock rods. Rev it to 6,200 rpm every time I drive it. Dyno'd it and the power never dropped even at 6200+ rpm. Pump gas.


http://www.youtube.com/watch?v=6dTfM...e=channel_page

[Skip Fix]

"Dyno'd it and the power never dropped even at 6200+ rpm. Pump gas."--- But did you try race gas??? My power never dropped either on the RAIV, just made more. My pump gas 455 at 10.25 aluminum heads did NOT change power with race gas over pump gas.

I think my 78 virgin block is 0.012-0.015 down with it's TRWs

[webfoot]

One other question, what is a good piston ring compressor? I like the idea of the non-adjustable ones such as summit sells, but the closest they have is 4.155, will this work or do I need another type?

[sixt8bird]

I actually used race gas once at the track and it was the worst day I have had as far as times. I now just use piss water gas.

[Skip Fix]

A friend with a lower compression SBC in his Canadian Pontiac Acadian had the same experience with race gas, Ran out of gas at the track and all they had was race gas, car ran alot slower than earlier runs with pump gas.

[chiphead]

I use a set of ring compressors like the one in the link. It'll do most any size and works well. I build a lot of different stuff, so I need more than 1 size.

http://www.sjdiscounttools.com/kd850.html

Zero decking, balancing, setting bearing clearance, setting ring gaps and the other typical performance work to the long block will result in a very strong and reliable powerplant. I agree that 9.2-9.5 is a perfectly fine CR if you're not trying to press the ragged edge of horsepower on pump gas.

[webfoot]

I've got Mr. Hand's good book and will take my time. Already checked ring gaps, they are .025 which I think is within tolerance. (?)

Bearings are clevite 77s.