[Hawkguymo]

Hello all I am new to this site and relatively new to pontiacs. I have a 81 TA that is currently without engine,I am rebuilding a 72 400 it has std. bore and pistons(original cast)they are in pretty good shape.The crank I had turned 10/10 the rotating asmby.is together minus cam and oil pump which I ordered today.The cam I ordered is the xe274.My heads which I already had are casting #143 they came with the car and are pretty fresh.I relize that the comp. ratio may be a bit much but this is what I have to work with(ie "broke/poor") what do you think? will the ratio be way too much to get this thing to perform on the street? Thanks

[Hawkguymo]

Hello all I am new to this site and relatively new to pontiacs. I have a 81 TA that is currently without engine,I am rebuilding a 72 400 it has std. bore and pistons(original cast)they are in pretty good shape.The crank I had turned 10/10 the rotating asmby.is together minus cam and oil pump which I ordered today.The cam I ordered is the xe274.My heads which I already had are casting #143 they came with the car and are pretty fresh.I relize that the comp. ratio may be a bit much but this is what I have to work with(ie "broke/poor") what do you think? will the ratio be way too much to get this thing to perform on the street? Thanks

[b-man]

The #143 heads came on 1967 290 HP 400 engines, factory compression rated at 10.5:1. In actuality it will be about 9.75:1 or 10:1. That much compression might be pushing it for pump gas operation.

The press-in rocker studs on your heads may not be too happy with the fast-acting cam and the valve springs you have chosen.

Another problem is the '72 pistons have valve reliefs that don't match the valve location and angle on the #143 heads. In mid-'67 the head design changed, your heads were made before that change occured.

My take: Find some different heads.

Yours have too much compression, press-in studs and the wrong valve angle to match your pistons.

The press-in studs will pull out in time. The valves may hit the pistons. The engine may suffer damge running pump gas on 10:1 compression.

[BVR421]

sad but true, b-man tells the story!
might be do-able with a very mild cAm like a Summit 2800 or a Melling stock 067 replacement cam

One thing is certain, even a very mild 400 will feel like a monster compared to what was originally in that car in 1981

Even if you decide to try the early heads right now, keep your eyes open for some 70s smog era heads to install nest year, the 6X heads are popular so they cost a little more but the less popular heads are just as good and are often free or cheap.

[Hawkguymo]

Guys thanks for the info,I am probably going to have to chance it for now and go with another set of heads sometime this summer.I will check to see about the clearance issue before I do a final assembly. If I were to retard the camshaft 4 deg.would this help to bleed off some of the compression? Also do octane boosters really work?If so what would be a good one to use? Thank you for your help.

[Hawkguymo]

help anyone out there

[Bulldog]

As BVR21 said keep your eyes out for some oild smog era heads...BUT you do not have to settle for just 6X as those that might not have seen the recent flow test on 6X, 6X-8, 4X-7H and three other heads that HPP did, five out of the six heads tested did not out flow greater than the others. 4X-7H were 1 off in the INT and EXH category with the 6X-8s.

[BenBen]

Retarding the cam\timing will help, but the motor will likely run like a dog to get you to the point where you won't encounter detonation. Octane boosters supposedly do work, but only increase octane ratings by something like 0.1-0.2 per bottle. A friend of mine runs his 11.5:1 e-head '77 Trans Am on two bottles of octane boost (@ $3.50 per bottle) and puts 91 octane in and doesn't have audible detonation. He claims the octane boost is why, but he doesn't really know much about tuning, so it seems to me to be a disaster waiting to happen. I personally wouldn't trust my car to it. I'd just build the motor to run on pump gas to eliminate the worry (and have ;-) ).