Welcome to Hotrodders.. You posted to a few very old threads where the members have not logged in for many years. Post engine questions in the Engine forum. Very helpful people here.

I moved your thread from Introduction forum over to here in the Engine forum... Thanks

 

do you have any flow info on your heads? We have a few poncho guys here.

 

I'm not too familiar with the Pontiac 400 but the numbers I get for a 6x-4 cylinder head show a pretty large combustion chamber. Flat top pistons with those heads would yield a low compression ratio. Did you happen to measure the combustion chamber?

What are the heads with the 1969 engine?

 

Yes, I had them shaved 28 thousandths to bump compression to around 9.2-9.5:1 with a zero deck and flat top pistons.

 

I think youll be happy with the original cam you chose. It's in the ball park.
After all, there lots of room for chassis tuning that'll net you more than a cam change.

 

Well this was my Dad’s street/strip car. Suspension, trans (th400 that been heavily gone through) and a lot of old school suspension tricks. My Dad was born in 52. All he did was race. He passed about 2 years after selling the car and i absolutely HAD to buy this car back. Well I did, original 557 (trash Pontiac block) dad slung a rod through the side of it. So I found a 1969 YS code 400 that I punched 30 over. My real big concern is the factory rods, even though they’ve had some killer tricks done to help improve life, but still, they’re factory cast rods. They have been resized with arp bolts, smoothed all over, and also free floating wrist pins with small holes in the top of the small end of the rod to provide oiling to the eel rust pins. 6x-4’s shaved 28 thousandths, 5 angle valve job, nice intake port runners porting, cleaned up then bowls, had every single out of place casting mark in the in intake ports and exh ports cleaned up. Id say they have to flow at minimum 215, I’d say closer to 225 maybe 230. They’ve been port matched to felpro 1233 intake gaskets, along with the edelbrock performer port matched to the heads after the porting to 1233 intake port size. Set of Hedman longtubes, with Pypes 3” x pipe going under the seats of the car with a set of welded ultra flo thrush mufflers. Supposedly best flowing mufflers from Jim Hands Pontiac book. 8.5” 10 bolt with Richmond 4.56 gears….. 1/8th mile car, but also a street car that driven to the track, so the 4.56’s will be chunked in favor of 3.42’s. Hoping with a 28” tall tire I can run the 1/8th like a powerglide, and still have high gear for the cruise home. That’s the plan anyway.

 

HPE01 is an old time cam profile that uses more ramp duration between what passes as starting on the lobe ramp profile and the .050 point compared to the XE268H. The difference is for comparable performance at the crankshaft flange the HPE01 will want about .5 to 1 ratio increase possibly as much as a full ratio more. The point is getting the most torque and power as related to the tolerable compression ratio on the highest octane fuel available.

Neither cam is particularly idealized for a boosted engine regardless of that being mechanical or nitrous. The issue here is power adders greatly increase the volume of exhaust to be eliminated which falls back on adding a bit more duration and lift on the exhaust valve side of the cam.

These values are probably more nits than anything on the street where drivability, even of a performance motor, is often a bigger issue than hitting the highest numbers possible on a dyno. Your biggest constraint with a Pontic is the rods as Pontiac was a big user of cast steel rather than forged rods. The cast rods are failure prone under high power and RPM, so unless you know for sure this engine has forged rods the rods are going to set the limits as to what you can do with adding power. I always sweat rods, they are the highest loaded part in the engine and their failure is almost always a total loss of the engine and the money you put into it. Pretty much my minimum naturally aspirated street street engine not to exceed 6000 RPM would be rods that are 5140 forgings. For any kind of serious performance including boosted from street on up through the track my bottom choice is 4340 with its grade qualities going up with the beating they are expected to take. This is more important than the choice of cast to forged crank and more important than 4 bolt mains. Actually tge Pontiac cast crank will take an amazing beating.

Pistons are another critical point especially with todays octane fuels. Forgings are way more tolerant to detonation than casting including hypereutectic castings which are a long way ahead of ordinary castings.

Bogie

 

You need to get your static CR up to 9.5 to one

Smaller chambered heads, flat tops. 82-85 CC will get you there.Zero deck the block. Use the quench built in to fend off detonation
You need to know the compression height of the pistons

Stock rods are not ideal
I would put in some forged ones
You could get a butler stroker kit and run the heads you have.The increased stroke would make the heads about right for 9.5 to one
Plus all those extra cubic inches more power,more fun

 

Currently at this moment with then6x-4’s shaved 28 thousandths, the zero decked block, and forged Keith Black flat tops I’m at the 9.2 to 9.5:1 range.

 

Great car, i am glad that you tracked it down and got a hold of it. When you get something like that you know it's a gift. Try Lunati 10510702. It did pretty good in a stock all iron 455 with rods and pistons had a great average powerband. Made 500 tq at 3000 rpm! Made 380hp at 4600 rpm. you probably make yours higher in rpm. And try a performer EPS for intake with 1.75" or 2" headers. Other than that have fun with the 268. Another cam the comp# BP6014 SP it works higher in the rpm band a little bit from this cam. 510 lb. ft. @ 3400 rpm! And a super powerband. Hitting 396 hp @ 4900 rpm. Keep in mind this is the 455. The 400 may work really good with these or a step down in size cam. You may even have close to similar hp results but not as much torque. i am guessing 350 hp and 450 torque. Put in some butler performance even if it is just rods and pistons, you won't be sorry. If you figure the 455 heads what they flow, then you can make similar results just a little less since your down on cubes. The best thing would be heads i think. But the 268 is a great daily driver cam in this thing as long as it has some more compression the results shall be good.

 

Note, no thought is given to budget constraints respectively here on this list. If you shall, if i am may, it is suggestion or recommendation of combination of making this work better than expected.
The highest quality torque convertor you can afford. Slinging any crank with inertia more than a small block you need better convertors. 3000 stall with your cam and cams mentioned above. Tight nitrous style internals can offer more grip for highway and be able to use higher stalls at part throttle more efficiently let builder know.
A gear vendors unit would be awesome. Along with 2.10, 1.40 second gear set. then keep the 4.56. A 3.90 does pretty good at 3200 rpm or so. Right near peak torque as well.
Also PRW 1.65:1 ratio roller rockers have 1.82:1 measured off the seat ratio, exaggerating your ramp rates and duration/ lift timing respectively. So do not be discouraged at your 268 or so camshaft. It shall have more impact.
Some weld racing wheels are in order.
A carb to help this get the most MPG and Power down at the track would be a Dominator 1050 dual circuit. Some others are Pro Systems carburetors The SV1 single throat can snap a cast crank in half with it's throttle response so careful. Also their King Cobra is another good one. 850 cfm shall be perfect for you setup. And the alternative 4150 that is a cut above the standard 4150 the edelbrock VRS 850 cfm'er. Yes an edelbrock single plane or Performer RPM would work. Just use a tapered HVH spacer / adapter for the Dominator. Dyno tests and driving have shown MPG increase of 4mpg on a nova with 11mpg and with 1050 dual circuit dominator got 15 mpg. That means power is up also. Of course if your going for MPG and no one admits it, just keep your foot out of it and feather it at peak torque. Some shoot for the lowest rpm possible, i don't. And your LSA should be a 108* on a 106*ICL.
Well some biggest valves you can fit and/ or aluminum heads would really up your power and performance more significantly more than anything, well and a stroker kit with it. Check out butler performance, and edelbrock may have some good heads as well for the pontiac.
Oh yeah, you could just slap on a blower and run it at 5PSI.
Laters.