Compression Ratio
Thread Starter
|
Cross-Country
Joined: Aug 2012
Posts: 53
Likes: 2
From: Sioux Falls
Compression Ratio
I have a 390 with that, I think, has 9.5 comp pistons and stoc heads. I wanted to know what compression will be with cj 428 heads on it. I have done quite a bit of looking on the internet and the cj heads have a 69 cc chamber and the stock heads have a 72 cc chamber. I'm looking to get around 10.5 compression when I'm done. Should I keep these pistons or get flat tops or will that be too much compression with the cj heads?
Super Moderator
Joined: Apr 2004
Posts: 34,466
Likes: 2,798
This here says the CJ heads are 72.8 to 75.8 cc.
FE Series Engine Specification Chart
Why do you think you have 9.5 pistons? Was this a car engine or was it rebuilt with the car "Regular Fuel" (or 360 spec) dished piston with valve reliefs?
FE Series Engine Specification Chart
Why do you think you have 9.5 pistons? Was this a car engine or was it rebuilt with the car "Regular Fuel" (or 360 spec) dished piston with valve reliefs?
Hotshot
Joined: Jul 2005
Posts: 13,834
Likes: 25
From: Middle Tn.
This here says the CJ heads are 72.8 to 75.8 cc.
FE Series Engine Specification Chart
Why do you think you have 9.5 pistons? Was this a car engine or was it rebuilt with the car "Regular Fuel" (or 360 spec) dished piston with valve reliefs?
FE Series Engine Specification Chart
Why do you think you have 9.5 pistons? Was this a car engine or was it rebuilt with the car "Regular Fuel" (or 360 spec) dished piston with valve reliefs?
Thread Starter
|
Cross-Country
Joined: Aug 2012
Posts: 53
Likes: 2
From: Sioux Falls
It was a car enging that started as a 352 and the pistons I got have a small dish in them.
I got the cheacked the cc with a casting number and the mechine shop here in town called to somewhere and thats what they told me from it. Thi casting number is C8AEH.
I got the cheacked the cc with a casting number and the mechine shop here in town called to somewhere and thats what they told me from it. Thi casting number is C8AEH.
Mountain Pass
Joined: May 2013
Posts: 131
Likes: 0
From: Spanish Springs
Maybe this will help. The hard part is getting accurate numbers to plug in.
http://www.summitracing.com/popup/ca...ion-calculator
http://www.summitracing.com/popup/ca...ion-calculator
Freshman User
Joined: Feb 2014
Posts: 41
Likes: 0
C8aeh heads did have the smaller chamber, I had to surface mine and ended up at 70cc , but if you have an opportunity to get a set of cj heads jump at it, the runners and ports are where the FE's power is bound. The best heads in my opinion were either the 58 machined heads or the 64 large runner castings, both flow much better than the c8. The 58's are hard to find but most have the 30° intake seats that the cj heads have , as do some of the 64's. My experience is that a 9.0cr with a great set of heads will outrun most 10.0+ motors with unported c8 heads. Oh and the whole pump gas vs race gas thing too.
Trending Topics
Thread Starter
|
Cross-Country
Joined: Aug 2012
Posts: 53
Likes: 2
From: Sioux Falls
Well you guys are right they are a 72 cc head.
Can I get better flow out of the heads I have with a port and pollish?
Can I get better flow out of the heads I have with a port and pollish?
FTE Stories
Ford Trucks for Ford Truck Enthusiasts
10 Best Ford Truck Engines We Miss the Most!
Joe Kucinski
2026 Shelby F-150 Off-Road: Better Than a Raptor R?
Brett Foote
2027 Super Duty Carhartt Package First Look: 12 Things You NEED to Know!
Michael S. Palmer
10 Most Surprising 2026 Ford Truck Features!
Joe Kucinski
Top 10 Ford Trucks Coming to Mecum Indy 2026
Brett Foote
5 Best / 5 Worst Ford Truck Wheels of All Time
Joe Kucinski
Ford Super Duty: 5 Things Owners LOVE, 5 Things They LOATHE!
Joe Kucinski
Every 2026 Ford Truck Engine RANKED from WORST to FIRST!
Michael S. Palmer
The Best F-150 Deal of Every Trim Level (XL through Raptor)
Joe Kucinski
Thread Starter
|
Cross-Country
Joined: Aug 2012
Posts: 53
Likes: 2
From: Sioux Falls
Ok I said that badly. Will they out run the other heads talked about? I have a cousin who works in a mechineshop and can do it for a case of beer.
Freshman User
Joined: Feb 2014
Posts: 41
Likes: 0
Don't let your cousin do a case of beer job on them, heads are the key to a potent motor, if you get them done get someone to flow bench them , and be sure to bowl blend the chamber. And yes *if *they are ported well and you put the bigger valves they will perform with the other heads.
Freshman User
Joined: Feb 2014
Posts: 41
Likes: 0
Also, did you go over bore? The 352 had a 4.0 inch bore and the 390 is 4.050, if you run the 352 piston on the 390 rotating assembly it may well hang out of the deck a fair bit, definitely not going to run on the c8 head. What is the height from the center of the piston pin to the top? Has the block been decked or machined at all?
Thread Starter
|
Cross-Country
Joined: Aug 2012
Posts: 53
Likes: 2
From: Sioux Falls
I have 390 pistons. The block has not been decked yet its in the plans tho same with a balance, port and polish, line hone and I'm still decideing on cam a lifters. Would you folks have any suggestions?
Super Moderator
Joined: Apr 2004
Posts: 34,466
Likes: 2,798
Flat top? Compression height? Dish? Sit below deck or flush?
Freshman User
Joined: Feb 2014
Posts: 41
Likes: 0
The pin height changes in quite a few of them. Find out what your pistons measure at and we can help you figure out how much you can or can't take out of the block. I have had good luck with lunati , also had a really mild comp that lasted about 150k miles. How crazy you go depends on the rest of the build (converter and gearing) as well as the intended use...