Does anyone make bolt-in lumps for a GMC 302 head? I've looked at the lumps on both Tom Lowe's and Larry's (Twisted 6) websites, but they seem to be only for the Chevy 6's.

I don't know of anything like that for the older engines. The port design is totally different. The 302 ports are huge. Lots of old timers preferred the smaller ports for street use.

The lumps would have to be T-shaped because the port is shaped similarly. This would make the insertion of them impossible because the width of the lump will be almost 3 times wider than the port opening.

Good to know. I don't have my 302 head yet, so I haven't been able to look at the port shape to see this for myself. I had thought that I read of others using lump ported 302 heads somewhere, but maybe I was mistaken.

Im not saying it cant be done, it just will take some thinking to work it out. Maybe even a 2 piece lump....

I agree that the short side radius is bad, which will (probably) be helped by a curved floor. If a lump was made in symmetrical (L&R) pairs they would look like an upside down "L". Each could be rotated 90° and inserted, then locked together.
However: there's no existing head bolt to attach either one. I don't see any easy method here?
Any insertion also decreases port area somewhat, so this may work best on the large port heads such as the H.

Quick,

I got my 302 head to flow 250+ cfm by using 2.02/1.60 SB Chevy valves. That much intake flow is enough to support 500 HP. The real problem is the sorry-ass exhaust port (end port)that only flowed 144 cfm. You need to have your cam ground with some extra exhaust duration.

The actual porting was minimul but the combustion chamber needs to be modified or you can't get the intake to flow. If you email me (goldenri@aol.com)I'll send you a picture of the combustion chamber modification.

By the way, what are you going to put the Jimmy in?

Ron

Thanks Ron. I'll shoot you an e-mail as I'm definitely interested in the pictures.

I'm going to put the Jimmy in a 1935 Ford 1/2-ton pickup that I'm building. It's a bit of a rust-bucket chopped cab right now, but I'm trying to save it and make something fun. Still on the fence between naturally aspirated and forced induction, which will really affect what I should do with the head.