I have a 312 with stock heads with some porting  runs around 140 # of compression per CLY and some cam not sure how much. I have a Paxttion for it I think they only put out about 6# of boost so I think I will be OK. Or do you think I need to blow off some compression?  

Stock heads doesn't tell us much.  Have a look here to identify what you have, http://www.ford-y-block.com/cylinderheadchart.htm 

If the engine had never been apart, then compression should be low enough to get by,

Since the heads have been ported, then we know the heads have been off and the engine is therefore not original.  If you know exactly what has been done to the engine, then you can calculate the compression.  If you do not know, then you cannot be sure without taking the heads off for some measurements of the block, pistons, heads and head gaskets.


Lawrenceville, GA

The Paxton makes whatever boost you set the pulleys for. Opinions differ about reliability at high boost levels, but the SN series I used, with later model internals, were supposedly reliable to 7-8lbs. At say 5500 rpm, maybe a bit higher.

I ran an older version of Mummert's stroker kit in a 40 over 292,with ported, posted, 113 heads. That motor was 9:1 static with composition head gaskets. It had an older version of his 270 cam. I had my reasons for the 9:1 base. The blower pulleys showed just under 5 lbs at 5000rpm. It didn't show any boost on a 2 1/16" gauge until about 3000rpm. With premium 92 fuel, warm weather, ethanol content 10% or less, it would detonate at 3500-4000rpm. 10-12 degrees initial, and 36 degrees all the way in at 2500rpm or thereabouts.

I used a 2 degree retard, triggered at 3lbs boost. That solved it except on a hot day and a hot motor, say, blowing off (pun intended) frustration after being stuck in traffic. Every engine will vary, temperature and density altitude, etc. If I had raced it, and been on it for a full 1/4 mile, I'm sure I'd have needed more retard or better fuel. But on the street that's what worked. Octane booster helped, but just barely.

Send me a pm, I can provide more details on the installation.

miker
55 bird, 32 cabrio F code
Kent, WA
Tucson, AZ

Thanks  Your right it is hard to know when I did not do the Engine I may hold of until this winter and tare it down