Cobra Jet Crank In 390

[Cayenne06 10]

I have searched this forum but can't find a thread on this topic. I have a 69 Mach 1 S code and would like to install a 428 CJ crank, intake, and carb. Also want to add headers. Has anyone else tried this on their 390?

[LiLMike 42]

That was how we stroked a 390 back in the day. here is a link that will help you get the idea of what is required. Hope this helps.

 

http://www.woodyg.com/fairlane/finfo/390intro.html

[Cayenne06 10]

Excuse my ignorance, but I have been told that you can install the cobra jet crank without having to change the pistons, connecting rods, flywheel, and vibration damper. Is this correct? My engine does not need a rebuild, just looking for a little more power.

[Jimjific 23]

I want to do the same thing to my 68 "S" code Cougar. It makes the engine a 410 c.i. which Mercury offered, but never in a Cougar. The only thing that is kind of a pain is that a 428 is externally balanced vs. a 390 in internally balanced. So, you have to find a 428 balancer, which from my experience, people thing is worth their weight in gold. To me, the better solution is to buy a new 428 crank from Scat. They designed it to be internally balanced. they sell the whole bottom end assy for ~$1500.

 

Just my thouhts,

 

Jim

[Cayenne06 10]

Also, will cobra jet exhaust manifolds bolt up to the 390 GT heads?

[LindenBruce 27]

Also, will cobra jet exhaust manifolds bolt up to the 390 GT heads?

 

 

No, not as is. The problem with the 390GT heads is the top outer exhaust bolt holes. They were moved lower from the standard FE exhaust bolt hole positions. You must have 428cj heads to use 428cj exhaust manifolds. The holes could be drilled and tapped on your 390GT heads.

 

The 428/410 as stated are externally balanced. But the balance weight is on the flywheel. So you can use your front damper with no problems. Now, having said that, the 428SCJ damper is larger in diameter and width. Also, the 428SCJ used a hatchet weight damper spacer along with the weighted flywheel. So if you are using a 428cj crank make sure you use a 428cj flywheel. Or pay to have a machine shop add heavy metal to the counter weights and make it internally balanced. Which might be cheaper than buying a new SCAT crank?

 

Check out survival motorsports, Barry Rabotnick's shop. They are king on the FE.

 

Headers on Mustang FE's are a total fracking PITA!! If you go with headers use FPA's for PS applications. If you don't have PS then I would use Doug's, the style that has two tubes crossing under the engine. Which ever you use here is a life saving tip. Use a button head allen bolt for the front two top boltholes on each side. They will give a little extra clearance for your shock towers.

 

Bruce

Edited May 31, 2012 by LindenBruce

[Cayenne06 10]

Thanks for the info.

[Jimjific 23]

I've posted this guys build link before. It is a great built and gives you lots of info and ideas. http://thefactoryfiveforum.com/showthread.php?1215-Engine-Build-Thread-427ci-FE-Big-Block

 

Jim

[Angel 24]

Out of curiosity, can you put a 390 crank in a 428 block?

[Jimjific 23]

Yes you can. Most of the FE stuff is interchangeable.

[BuckeyeDemon 211]

I have been told that you can install the cobra jet crank without having to change the pistons, connecting rods, flywheel, and vibration damper. Is this correct?

 

i don't see how that's possible.

 

if my numbers are right, the deck heights are the same and the stroke is different. there would be no way to simply swap to a 428 crank and keep the rods and pistons from the 390. if you did the pistons would be out of the hole by about .1".

 

someone might have been thinking of a 427 crank?

[R4K 10]

i don't see how that's possible.

 

if my numbers are right, the deck heights are the same and the stroke is different. there would be no way to simply swap to a 428 crank and keep the rods and pistons from the 390. if you did the pistons would be out of the hole by about .1".

 

someone might have been thinking of a 427 crank?

 

You'll want to use the low-compression 390 truck pistons, and its been a while, so I can't remember the numbers. Building a 410 has long been a secret desire of mine. :-)

 

EDIT -- 381P is the part number, I have a set of. 60 overs that came out of my mustang when I got it, couldn't stand myself and had to go dig them out. :-)

Edited June 4, 2012 by R4K