304 head swap?

[caspermj]

I've got a '75 CJ5 304 that I want to install a pair of '70 high compression heads (got them already). I know I need new rockers, but what else will I need? I've heard depending on head gasket choice, I'll get 9:2 or 9:5. Has anyone done this swap and could give me some pointers? I'm planning stock cam and 2bbl carb as well, but open to suggestions. I'm not looking to lift the front wheels, just a bit more punch :t: Thanks.

~Roy

[tufcj]

Are they the 3199517 or the 3196291 casting? If they're the 517 casting (304), you've got it covered. If they're 291 casting (360-401), you're going to have problems with valve to cylinder wall clearance. The big valves of the 291 heads can hit the cylinder wall of an un-bored 304 when they open. The valves being so close to the cylinder wall can actually cause a loss of performance because the air doesn't flow smoothly around the valves.

An engine is a big air pump. Compression alone won't gain you much in performance. You need to get more air in-thru-out. That means a bigger carb, better flowing intake, bigger cam, free flowing exhaust, and possibly port work to the heads. Keep it reasonable, bigger isn't always better. Watch your tach (you do have one don't you?), and buy a cam/manifold that work in the RPM range you're in the most. Carb no bigger than 600 CFM on a mild 304. Think about headers, or at least a 2.5" free flowing exhaust.

Bob
tufcj

[caspermj]

Thanks for the reply. I'm at work right now (offshore) so I can't check the casting numbers, but I do know they were off a 1970 police car w/ a 304, and have the smaller combustion chambers. I think I'm ok there. I've heard different things regarding the 304, and I'm not looking for alot more power, I just thought it might be a more efficient running motor with a more "modern" cr. Most companies in the '70's and early 80's figured dropping the cr would burn less fuel....didn't work! I'm also not looking for great gas mileage :wink: Do I need to worry about running temps? How does the 304 react to a hotter combustion with a stock 3 core rad, wp, etc.? I've also heard the 304 is better for offroad, low rpm's if left pretty much stock (exh manifolds, MC2100, cam, etc). Any truth to that?

~Roy

[tufcj]

The low CRs were actually for emissions. Lower CRs produced less Nox emissions. The bump certainly won't hurt. I ran the factory 304 in my CJ for years with a .030 bore, 10.5:1 forged pistons, mild cam (268 duration, .488 lift), Torker intake (not the best choice), and 600 carb. With the whole thing balanced, I ran it regularly to 6500 RPM at the mud bogs. Surprised a lot of people who expected to see a SBC when I opened the hood. It is a surprisingly torquey little engine, and can make a lot of HP with a little work.

The Motorcraft carb and factory intake work well, you can use them for now. I'd think cam, exhaust, and ignition upgrades to make it breathe a little better, and intake and carb down the line. I think the 75 still has points, I'd go electronic. I run a Mallory unilite, it works well for me. There are also GM style HEI distributors out there for AMCs.

Bob
tufcj

[caspermj]

Sounds good. I was planning a DUI distributor, cast exh manifolds down into a single 2 1/2" exhaust (maybe 3"???) with a flowmaster. I wasn't sure on a cam, but would do it now since I'm tearing the motor down anyway. Can you recommend one for good torque that will still be good if I upgrade the intake and carb in the future? I've heard Edelbrock isn't that great??? I have no experience with the AMC's, thus don't want to assume anything. I don't need a power monster, otherwise I'd probably grab "at least" a 360 to build. It's just seems that so many people put the 304 down...gives me even more reason to want to run one :t:

~Roy

[caspermj]

I've been doing some reading in the older posts and found a lot of people like the Edelbrock performer series stuff for the 304. That's good to know. I'll probably try to find a cam that comes well recommended, and add to the "outside" later as I can (intake, exhaust, etc.). This really is the best site I've found for tech info! Lot's of "hands on" experience, not just speculation.

[tufcj]

I run a Performer cam and manifold on my 360. I have Howell EFI on it (GM TBI), stock exhaust manifolds and 3" single exhaust. The heads are 1970 291C heads with roller rockers and some mild port/polish work. Pistons are factory. It has plenty of torque for the rock crawling I do. With the 4.27 gears in the diff, T-18 trans and Dana 300 t-case, it has about a 72:1 crawl ratio. It will sit at idle in low/low and spin all 4 tires if it can't find traction.

The Summit 8600 or 8601 are also good cams for torque.

Bob
tufcj

[caspermj]

It will sit at idle in low/low and spin all 4 tires if it can't find traction.

Sounds nice :) I've got a T18 w/granny 1st but with 3:73's and a D20 t/c. I'm looking for the pieces to do the "cheapy" low gears in the D20. I'll look into the Summit cams too. Thanks.