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Hey ladies and gentlemen,
My name is Roger. I’m new to the group. So I’m building a Pontiac 400. The car is a 1975 Formula Firebird. The engine I’m building is a 1969 YS code 400. (Yes I know I will have to buy the motor mount adapters) the bottom end is done and I’ve actually already put the cam in the block. I decided to go with Spotts Performance and I bought his HCP01 cam and lifter set. Here’s the basics of the cam. Operating range is 1800-5500. It has a 103 “N” crank, factory rods, that’s been fully floated, spiral locked, and resized with arp fasteners. (I wish I would’ve just bought an aftermarket set) KB forged flat tops. The block has been 0 decked, line honed, and of course punched 30. So the cam I chose I felt would be a great decision for this setup. The car weighs almost 3250. It has a th400 with a shift kit, it’s a 10bolt with Richmond 4.56’s. It’s an 1/8th mile car. I WILL be switching to 3.42’s hoping I can run an 1/8th in 1st and go through the lights wound tight in 2nd, then still have high gear to drive it home. It is a street car. There’s a 2200 rpm stall going in place of the old 1800 rpm stall that was in it. I have an edelbrock performer (clearance issues using a performer rpm with the hood, and the hood is 100% staying) the performer has a old school Holley 800cfm spreadbore on top. So the HCP01 with my comp cams full 1.52 roller rockers produces @.050 224* and 234* lift is .466” int and .487” exh. Lobe separation of 114. I can easily elongate the pushrod holes in the heads to accommodate 1.65’s if need be. Paul advertised the cam as having a noticeable lope, good idle, and great vacuum. Which is important……street car with power breaks. I do have a tiny shot of nitrous I was planning on hittin it with eventually. Like a small 100-125 shot. The car has a set of 6x-4 heads on it that’s been cleaned up, not truly ported, just the intake runners cleaned up very nicely. Really wanting Marty Warden to get them for me, but anyways, this is the one and only iron headed Pontiac I will be building. The next engine I’m hoping will be an MR1 with Kauffman high ports. The car was my Dads, well he passed 2 years ago and sold the car about 5 months before passing, well I tracked the car down and bought it back. I have a set of 28”x10.5 slicks that will be on the car if anybody needs that information as well. The car is super light! About the same as a gt fox body. I was REALLY thinking about throwing a set of Rhoades in it and just going with the ole glory “041” RA4 cam honestly. Or the Comp cams xtreme energy 268H. It’s a 1600-5800 rpm range, and Dur @.050 is 224* int and 230* exh. With a lsa of 110* I need some help with this seriously! This was my Dads car when I was a kid and this car meant the world to us! Oh yeah, Pertronix flamethrower HEI distributor. Also has longtubes with 2 mufflers turned down as soon as they exit the muffler. I want this car to make my Dad proud up there. That’s all. Thanks for any help y’all can give me very much!!!
Tire Wheel Car Vehicle Sky
 

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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
 

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1979 Chevrolet Malibu 496-TH400-9" (cruiser). 1992 Chevrolet S10 355-700r4-7.625" (daily driver).
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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?
 

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Race it, Don't rice it!
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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.
 

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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
 

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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
 
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