Big Valve Heads on 290/304 ???

[amundaza]

Hey guys,
We’re beginning the build-up of the stroker 304 and I have some questions about running the 1970 291C heads on the smaller bore block. I’m boring the 304 out to 3.83” (0.080” over stock size of 3.75”). I picked up a set of race-prepped 1970 360 heads with 2.02/1.60” SBC valves installed, because they were a good deal. The heads are about done with a new valve job, hardened seats on the exhaust and some new valves with undercut 5/16” stems. The heads have had a mild port/polish done to them by NAMDRA’s head guy (don’t recall his name … he originally built the heads).

The spacing across the SBC valves measures in at 3.73” from outside of intake to outside of exhaust valve. Does anyone know the relation of the intake to the bore and the exhaust valve to the bore on a stock AMC? If one is closer to the bore, which? Or if they are ‘evenly spaced’ it would leave 0.050” valve to bore clearance … IF … I run the 1970 360 heads on the 3.83” bore block.

Performance AM Style calls for a 0.060-0.090” valve-to-bore clearance, when running the bigger valve 1970 heads (2.02/1.625 stock) on the 290/304 blocks, and calls for notching the block for valve clearance. If this becomes too much work for a street/offroad engine, I have a set of 1970 304 heads that I can put 1.94/1.50” SBC valves into. That would measure in at 3.63” across the valves and definitely clear the 3.83” bore 304 block.

Has anyone on the forum run the big valve heads on the 290/304 or can point me to someone who has? Herman Lewis? Atkins?

Thanks all for your feedback.

Sincerely,
Greg Taylor :) <><
Rochester Hills, MI
1989 Jeep Grand Wagoneer "TRMN8R2"

[Mudrat]

80 over??? :shock:

Got any water jacket left?? :-|

[amundaza]

80 over??? :shock:

Got any water jacket left?? :-|

290/304's can be bored 0.125" over stock ... plenty of room left! :t:

[ironman_gq]

bolt one on and see how it clears. worst thing that can happen is that the valves dont clear the cylinder. I could see some performance loss due to shrouding because the valve is too close to the cylinder wall but even so it should flow more than the small vale 304 heads. I have also been thinking of doing a big valve conversion for my 304 but haven't squirreled away enough pennies to make it happen yet.

[73hatch]

I`m also interested in the big valve 304 topic since I`m in the process of building a stroked 304 too(I bought your old piston/rod combo :lo1l: ).Performance american style has a set of oversized valves for the 290/304 engines . They are 1.92" intake and 1.6" exhaust with 3/8" stems.
I have a set of edelbrock heads I would like to use but I think I cant put 1.94 intake valves in them without replacing the valve seat...

[dwg86]

I built a .030 304 years ago for my 79 cj5. I was young, dumb and just starting to learn my gearhead ways. Without any research, I used 360 heads with a 280H, 490 lift, comp cam. At that time, I didn't know about the valves hitting the cylinder walls. I ran it hard for a couple years and few thousand miles, often turning 7000 rpms smoking 302 mustangs. I replaced the 304 with a 401. I tore down the 304 to have a look at how it handled my abuse. If I can remember correctly...There were a few marks on the cylinder walls, but not all of them. Also had a few marks on top of the pistons. Probably do to valve float, and the pistons weren't notched properly for the bigger valves(I used 199 flat top 6 cylinder pistons for the 304. Same bore and comp hieght.)

So yes the bigger valves will hit the cylinder walls. I would think you would be better off with the 304 heads with some porting and some undercut SBC valves.

Oh yeah...I still own that that same 1979 CJ5. I was my first Jeep. I bought it wrecked in November 1988, after I started my career job as an aircraft mechanic. It was my first major purchase($1900.00) at 20 years old. It has recently undergone a full body off restoration and has been retired from "serious" off roading and abuse. It sits warm and dry in my garage. With a fiberglass body, powder coated frame, 36 inch super swampers on weld wheels, .040 over 401, T18, 4 wheel power disc brakes. Every nut, bolt, and washer has been replaced with stainless, except for suspension/high stress areas. There I used grade 8. Probably more info than you needed...