What would be the compression ratio be with C4AE-G heads on a stock block 1971 390 truck motor.....? I haven't bought head gaskets yet.....
thanks.

 

Well If your trying to pick up CR.. your going to have to either Deck the block, Change piston's, Mill the heads,

C4 Heads are 71.2 to 74.2 cc chambered heads, So average that to 72.7cc's

Ok with .041" head Gasket- Piston .030 in the hole= 7.80 to 1 CR

with a .018" shim gasket = 8.15 to 1 CR..

Stock CR is about 8.3 to 8.5 to 1....

Hope this helps,

Russ

 

yikes......I lost compression by not using c8ae-h heads.....

The c4 heads were milled .007".... how much more should be milled or decked... and what are some piston options...?

 

Use 360 pistons. The tops are flat with only the valve reliefs...the stock 390 truck pistons have a lower relief in them for low compression. Also pin to piston top dimension is different on the 360 piston putting the piston top closer to the deck. You have to measure everything to get an accurate compression ratio for your build. With the 360 pistons, 73 cc heads and a standard head gasket I think you'll be around 9.5 to 1...the steel shim head gasket will put you closer to 10 to 1.

 

With the heads Milled .007" saying you picked up a CC to 71.7cc's

with the .041" gasket = 7.86 cr

and with the .018" shim your at 8.23 cr

with you stock truck pistons...

Russ

 

[QUOTE=zsir]yikes......I lost compression by not using c8ae-h heads.....
QUOTE]

Yep...stick with them.

--Mike

 

Thanks for the replies...

I thought the chamber volume was virtually the same between the two heads, but it seems I've lost about 1/2 point of compression... The C8ae-h head had a mangled ex manifold bolt boss, I didn't notice it till I tore the motor down. I got a good price on the c4ae-g heads...

So I can get some 1970-1971 360 pistons and install them without having to worry about any valve clearence issues (.500" lift) or anything, and be somewhere between 9.2 and 10.0-1....?

Is the .041 head gasket a standard fel-pro gasket...?

 

yes, standard fel-pro head gasket is .041 thick compressed. After much research in this forum, I put the 360 pistons in my 390. There is a thread from a few months back that discusses the piston/compression ratio issue in great detail...search for threads started by me and you should find it...I think it was Feb or March of this year. It's not completely cut and dried as I've heard in this forum that a couple of times that after assembly someone's pistons ended up slightly higher than the deck and they compensated with a copper shim. I think their blocks must have been surfaced a lot. As I understand it, a 360 piston with 390 crank and rods should leave the piston about .012 below the deck, which is exactly where mine came out. The really big difference is the fact that the 390 truck has low compression pistons and the 360 piston is not. Search the web for compression ratio calculators and you'll quickly see how this is calculated...you can play around with the #'s and see the differences. Basically the stock 390 truck was low compression and less than 200 hp...upping the compression, along with a decent cam, intake, carb, headers, port and polish the heads, and you'll be pushing 400 hp. and still be very streetable.

 

OK Z.... here's what I have with your heads being averaged stock 72.7cc's with .007" shaved off= about 1cc less 71.7cc's and a Felpro .041 gasket,Pistons with a -10cc Valve relief, sitting .012" in the hole= 9.57 to 1 CR..

And with a Mr. Gasket .032" Head gasket its 9.78 CR...

And with a .018" shim gasket at 4.250" its 10.17 to 1 CR

I hope this gives you an Idea of the different combo's that are out there..

Russ

 

Thanks Russ,

I just ordered some pistons and rings......

Does anyone know what the victor head gaskets spec @ when compressed..?

 

Sorry, I don't know the answer to that. I've heard here that the Felpro head gaskets are the best. If you want to bump the compression higher than you'll get with just the piston change then the steel shim gaskets obviously give you the most. You can purchase these from www.dscmotorsports.com. Dennis there is very knowledgeable about the FE engines. You may want to look at his solid spacer adjustable rocker arm sets as well. I used the steel shim gaskets...I sprayed them with coppercoat and installed. If you use the steel shim gaskets you need to make sure the block deck and head surfaces are good and flat. For the Felpro's I've heard it's best to install them without using a sealant...I've apparently been incorrectly using coppercoat on most everything for years now...lol.

Good Luck!

Tracy

 

Nope I couldnt help ya there either....I have always used Felpro..and this will be my first time using Mr. Gasket (head Gaskets) I have used other Mr. Gasket stuff over the years with no complaints.. knock on wood!!

Russ

 

DSC has been a good source of parts for this build. So far I bought:
adjustable rocker set up, push rods, stainless int and ex valves, valve spring kit, lifters, windage tray...

Here's some of the other parts I picked up:
DUI distributor, hedman hedders, edelbrock intake and carb, edelbrock water pump, arp dist drive, ..............

 

I was questioning DSC at first, but now i highly recommend DSC. He was very helpful and got parts shipped out very quickly.


I got the 427 HD pushrods. now iam good to go.

 

Update:

I got some silv-o-lite pistons\hastings rings and took them to the machine shop....I compared them to the original pistons..... The valve reliefs looked identical, but I could see where the oval dish in the center of the pistons was not in the 360 pistons....

I ordered 360 truck pistons but the box said Ford 390.... I guess as was stated 360 pistons = 390 car pistons.....

Thanks everyone for your help....