# 400 Pontiac Engine Advice



## rossph (Oct 26, 2008)

Hello,
I am building a 400 Pontiac 2 bolt mains and have #16 heads, I will have to go .30 over on the pistons, I am aiming to have 10 to 1 to 10:5 to 1 compression. I would like to have the engine idle OK, still run on pump gas. I want to use the original intake number 9799068 (not stuck on the stock intake but need the proper height to accommodate the ram air assembly would like to keep it if it works). This engine is for a 1970 GTO judge, that will come out on the weekends and not be raced, so i am not concerned that much about running premium gas or idling in traffic. I am planning on running a 2300-2500 stall with the stock turbo 400 transmission.
Can I get a recommendation on Pistons, Cam, and if i should change out the intake?
Any advice from the pros would be appreciated.
Thanks


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## Shake-N-Bake (Jun 16, 2015)

rossph said:


> Hello,
> I am building a 400 Pontiac 2 bolt mains and have #16 heads, I will have to go .30 over on the pistons, I am aiming to have 10 to 1 to 10:5 to 1 compression. I would like to have the engine idle OK, still run on pump gas. I want to use the original intake number 9799068 (not stuck on the stock intake but need the proper height to accommodate the ram air assembly would like to keep it if it works). This engine is for a 1970 GTO judge, that will come out on the weekends and not be raced, so i am not concerned that much about running premium gas or idling in traffic. I am planning on running a 2300-2500 stall with the stock turbo 400 transmission.
> Can I get a recommendation on Pistons, Cam, and if i should change out the intake?
> Any advice from the pros would be appreciated.
> Thanks


Your stall speed sounds good. What gear are you going to run? One of the best engines I ever had was a 1970 RAIII that I modified for my own use. I tried a couple of different intake manifolds and the stock part performed equally well so I'd say you can stick with your intake with no ill effects. Back in the day the cam I would run was the HC-01 cam from HO Racing Specialties. To this day it remains the best street cam that I've ever run in one of these engines. I am not sure if you can get them any more but the Summit K2801 sounds like it might be pretty close. 272/282 adv dur,. 214/[email protected], .440/.470 lift @ 1.5:1 I find that split pattern cams perform very well with Pontiac heads. The exhaust port needs a little help since they turn down so much so the split pattern cams adjust for that situation. I am sure there are dozens of good cams out there that will work. I would call the manufacturer and tell them what you are planning on building and then write down the cam they recommend. Then call someone else and do the same thing. After a few times you will get some good info and be able to make your own choice. The cam is the hardest thing to get right in my opinion. I've swapped more cams than I care to remember trying to find one that I liked. Once I found something that worked, I usually stuck with it. If you know now that you might want to turn it up later then you could consider some taller/stiffer springs (machine down the spring seats) and start with 1.5 rocker arms....then when you are ready you can try out some 1.65 and see how it runs. 

Depending on tire size, a 3:55 or 3:73 gears are what I've used with good results. The 3.73 gears were my favorite. I am not sure who makes good pistons these days but make sure you get a forged set. Stock rods will be fine if you keep it under 5500 rpm most times. I always stress relieved the rods and then used the best rod bolts I could find. Don't skimp on the rod bolts. 

This combo worked pretty well for me in the past. Others may chime in and post their preferred combos as well. There really isn't a solid answer to the question....many variables to consider. Make sure your fuel pump is able to keep the bowl(s) full. I had to run electric pumps in all my cars because I preferred Q-jet carbs and their fuel bowls were quite tiny. 

Good luck. I hope this info helps. :thumbsup:


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## oldskool (Apr 26, 2015)

A .030 over 400 with #16 heads has too much compression for pump gas.

If you plan to run them, with pump gas, you need to buy dish pistons which will give you a final CR of 9.5 max. 9:1 is safer.

http://www.wallaceracing.com/cr_test2.php

I also like the idea of the Summit 2801 cam. 

Also, the #16 heads did not have hardened valve seats, for use with unleaded gas. Many recommend having hardened seats installed, for daily use with unleaded gas.


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