Yes; another 390 build....
 

I have a '66 F100 LWB with C-O-M tranny and 3:55 gears. I'm looking to build a 390 with good torque and acceleration. I won't be towing as it's a show truck but I do daily drive it. I'm concerned with quench and proper cylinder pressures. I bought a fresh 390 with a stock build. I'd like to add a cam and Edelbrock F427 intake. Heads are C8AE-H with adjustable rockers. I run full length headers and true 2-1/2" duals. Dizzy is recurved and Pertronix installed. The 390 is bored .060 and the pistons are H304P. I suspect I may need to run metal shim gaskets to get optimal quench. I would like to run 87 octane if possible. I have yet to measure deck height as the receipts show the block and heads have been milled. I'm considering the Comp 268H cam recommended by a friend. I need to stay automatic tranny friendly with the cam duration. Truck runs a/c but no power brakes. Carb is the Autolite 4100 1.12 venturis.

Ideas or recommendations? I am by no means an experienced engine builder but am mechanically inclined.
Thanks and fire away!!!

Come on folks....
 

63 views and no takers. Yes I've researched 390 builds until I'm blue in the face but very few talk about the use of H304P pistons with their .080" dish and quench using C8AE-H heads. Do a search here for "H304P" here and you get one page of results. I'm hoping not to end up with a gutless pig with no torque.

I would love to give you some advice here but your questions are way over my experiance and knowledge level. Sorry man, wish i knew everything so i could help.

Thank you and I wish I knew everything as well.

According to this, and from what you post, those the low compression truck pistons. I tried to look them up earlier and it lists everything with a 390 as the application.

https://www.ford-trucks.com/forums/9...er-racing.html

The 360 pistons as referenced in that thread are basically the same as the pistons used in '60s "regular fuel" 390s, which were said to have 9.5 compression. I would guess the ones you have are in the 8s. Is that what you want?

Cam looks decent, certainly better than stock:

33-224-3 - High Energy

Headers: check

Intake: Page 1, post 37, and for entertainment, post 46:

https://www.ford-trucks.com/forums/1...um-intake.html

A little more cam, but similar:

https://www.ford-trucks.com/forums/1...e-i-order.html

More solid info:

https://www.ford-trucks.com/forums/1...r-upgrade.html


You probably hit a little "repetitive question fatigue" in this forum. No big deal, but it happens. (trans forum has a bunch of -0- response threads all the time....

Sounds like you are on your way to a proper motor. Good luck with it.

FWIW, I've been told here that I know nothing, and just repeat what I've seen on the internet. That's not 100% true, but at least I post the links to the stuff I find....:D

Thanks and that's definately a start. My next question would be:
Should I use a .020" metal shim gasket to raise CR? I don't want to run premium fuel if I can get away with it.

Edit: Seems I got my numbers mixed up. Those are the pistons you want. 1.76 is the compression distance of the higher CR pistons and the lower CR are 1.66. I would use a standard .041 gasket.

The 268H is a good choice and seems to make a lot of people happy. I personally like the XE line better on an FE with unported heads as it gives the exhaust a bit more duration and lift to compensate for the low flow of the exhaust port. The XE262H outperforms the 268H on their online dyno and puts your dynamic CR at exactly 8:1 (9.5:1 static CR). Which is just about right for 87 pump in a heavy vehicle.

Is it that the dished pistons, the ones he has, are the "9.5" spec, and the flat tops with the same CH are the 10 or 10.5 CR pistons?

From that post I linked:

noticed that these were 360 pistons, so I called Flatlander and they sent me H304P .040 390 Hyp pistons.They both have 1.75 pin heights. The 360 is a flat top with 4-valve releifs the 390 is a 4- valve releif with a .080 x3.23 dish in it.

OP can figure his piston height vs. deck, and put the numbers in here:

RSR Static Compression Ratio Calculator

A few cc's in that dish, or in the combustion chamber make a lot of difference.

Did you cc the heads to see what they really are? Supposed to be 71cc, but they vary, and according to a recent post, they trend towards the high side of the spec, like 74.

Yeah, that's right. The dished are the 9.5:1 and the flat tops are 10.5:1. Depending on the tolerances in the stack those can vary a bit, many times coming in under the advertised CR.

This is the calculator that I use United Engine & Machine Co. Incorporated. It also calculates DCR if you know the IVC° of the cam. Which is crucial for determining what grade of gas you can run on.
Their little formula of adding 15 degrees doesn't come out correct. Assuming you have a symmetrical cam profile (most flat tappets except the Lunati Voodoo line, for FEs) the formula for figuring IVC is:

Int. Adv.dur./2 + ICL(intake center line) - 180= IVC°
Insert this number in the calc.

Some cam companies list it at seat to seat which is what you want(.006 is close enough), and some list it at .050 which won't do.

From what I've seen people post the C8s tend to be one of the smaller cc chambers ranging from 69-72cc usually, but of course there are always exceptions. The D2 are also supposed to be small chambered but then you see someone cc one at 76 so you never know until you measure.

My C8s all came in at about 71cc's with a .010 shave.

I see in another post OP says those pistons sit .030 down the hole.

The dish, .080 x 3.23 = 6.23 cc's, roughly, if I figured it right. Add 4 cc's for the valve reliefs, give or take, round it to 10cc's.

So, if you put those numbers in with a 74cc combustion chamber, the .041 gasket, .030 down the hole, 10cc piston top, and 4.11 bore, you get 9.27 CR with the calculator above. IF the heads are 71cc's, 9.53 CR.

That would be bingo, methinks.....

Yassir, seems like it to me. :-X22

Thanks guys! Here's what I found out today:

The pistons sit .028" down the hole in front and .025" in the rear. Pistons seemed to be cocked front to rear???

The dish is another .080" from the top of piston.

1.759 compression distance

Dish is 3.220 in diameter.

I haven't cc'd the heads.

I've been considering porting the heads but I'm up for suggestions.

I haven't chosen a cam as of yet.

Something to keep in mind is detonation from heat. I live in the heart of AZ. and we see up to 120* days. The hot air charge can't help.