The only way to tell, and I mean the ONLY way to tell, is to measure the stroke. Some say you can tell by the casting number on the block but that isn't true. I have a 400 that has what some say are 351M casting numbers. And valve covers and other parts are easily swapped between the two.

So you must measure the stoke, and that is almost impossible without pulling the engine apart. But, you could flood a cylinder with something like oil when at BDC and then capture the oil pushed out via the spark plug hole when you turn it over slowing. Measuring the oil would tell you. And even if some leaked by the rings or out a valve it would still be over a 351 if a 400.

 

Thanks for the information, I can easily see how it can be difficult to identify a 400 motor. For now I will assume it's a 400 based on the label and who I purchased it from.

I guess I will also wait for additional feedback from other users on what my next steps should be.

Thanks again Gary!

 

Just a little update, I called CompCams and they recommended the following Cam kits for my 400 motor:

Xtreme Energy™, XE256H: Cam & Kit

Xtreme Energy™, XE262H: Cam & Kit

Just adding more options to the table. They stated that I could use these and leave the motor as is as long as I buy the kit.

 

.
. Unless someone swapped the valve covers, it should be a 400"... neither Ford nor Chevy liked to admit the actual compression ratio on their engines back then was actually in the 7's:1... if you read the entire thread that Gary linked to above it answers all your other questions... Comp wants to sell you a cam, so not going to tell you that you need decent pistons first... going bigger cam on low compression engine just makes it soggier and even worse on MPG...

 

What you're saying makes sense after reading through the article. In regards to pistons, what would you recommend? The link for Dynagear in the 351/400 Bronco article no longer works.

Thanks!

 

.
. There's only one source for reasonably priced off-the-shelf pistons, and that's TMI who has KB 351C pistons factory modified to fit 400's...

http://www.tmeyerinc.com

. After pistons, what you mainly want to use the truck for will determine which cam is best... I just picked up the Summit K5201 for mine... for hot street/off road use

http://www.summitracing.com/parts/sum-k5201

 

Thanks again guys, I will look into getting new pistons and a decent cam.

If I can't afford pistons though, I may just get a lower end cam like you recommended earlier.

 

.
. I think DynaGear made the 'Ohio' pistons, some of which weren't too bad, like the rare 1971-only 400" pistons, but I think they are out of business now... all other general 'rebuilder' pistons sit way too far down in the cylinders...

. You can call TMI and discuss your plans with Tim...

. Only other choice is get pistons and have them modified somewhere's or modify the rods to fit the smaller 351C piston pins... I want about 11:1 compression, willing to use octane booster all the time, so may modify these domed top pistons:

KB149 Ford 351C Hypereutectic Piston
.

 

I would do a leak-down test to understand how worn the engine is before jumping in to completely rebuild it. You won't be able to have it bored and install new pistons and rings for much less than $1500. But if the rings are ok then advancing the existing cam will give more performance for very little money.

 

I would go with the 255 DEH - folks here seem to have very good success with that cam.

 

Since I have a 400 motor, would it be more economical to revert the 8 degree timing chain issue instead of adding a cam? Thoughts?

 

. Yes, fixing the retarded timing helps power and MPG some... not much use going bigger cam unless adding pistons to increase the compression ratio... if not, even stock cam too big...

 

Just to confirm, this would be the issue with a 1978 400 6.6 engine?

 

Buzz will confirm in a bit, I'm sure, but that's a big YES. BY 78 the factory cam timing was badly retarded and the engines ran poorly.

 

Thanks! I will wait for a response from Buzz. It may make sense for me to replace just the intake and carb if I fix the retarded timing chain.