Milled 915 combustion chamber pics

[68-500]

Looking for pics of 915 cylinder head combustion chamber pics. Please tell how much was milled off along with the pic. I wondering how much needs milled off to get them closer to a heart shaped chamber. As cast they have a ridge between chamber and flat part.

 

[65CopCar]

Not what you are looking for, but my 67 383 heads were 81cc and I milled 0.045" and got to 72cc.

 

[QuickBpBp]

If planning on milling a lot from the head I would make sure that you get the intake surface of the head cut too. That way you can use any intake on that head verses cutting every intake that ever gets bolted to that head...

 

[65CopCar]

If planning on milling a lot from the head I would make sure that you get the intake surface of the head cut too. That way you can use any intake on that head verses cutting every intake that ever gets bolted to that head...

Totally agree. It's what I did.

 

[padam]

I don’t know what a 915 looks like, but I milled a set of 906s.
I took .090” off, and also .120 off the intake surface.
I did this many years ago to increase my compression ratio. I didn’t cc the chambers, but mathematically figured it raised cr from 9:1 to 10:1.
(I had a clean up cut a couple years ago, probably another .010”. )

It made a huge improvement, I believe I picked up at least .80 seconds in the 1/4. I figured it was good for close to 100 hp. The car ran better, I guess I would say this “woke it up.”

I would NOT do this again. I had to cut my intake several times to get it to fit, now it is one of a kind, and I can’t bolt a new manifold on it. Valves are closer to pistons, I had to notch them when I put a bigger dam in.

Also, the pushrods are have to be custom.

I was on a non existent budget at the time though.

The photo has a head gasket so it’s a little hard to see. The flat part of the chamber is mostly flush with the mounting surface.

 

[68-500]

I don’t know what a 915 looks like, but I milled a set of 906s.
I took .090” off, and also .120 off the intake surface.
I did this many years ago to increase my compression ratio. I didn’t cc the chambers, but mathematically figured it raised cr from 9:1 to 10:1.
(I had a clean up cut a couple years ago, probably another .010”. )

It made a huge improvement, I believe I picked up at least .80 seconds in the 1/4. I figured it was good for close to 100 hp. The car ran better, I guess I would say this “woke it up.”

I would NOT do this again. I had to cut my intake several times to get it to fit, now it is one of a kind, and I can’t bolt a new manifold on it. Valves are closer to pistons, I had to notch them when I put a bigger dam in.

Also, the pushrods are have to be custom.

I was on a non existent budget at the time though.

The photo has a head gasket so it’s a little hard to see. The flat part of the chamber is mostly flush with the mounting surface.

View attachment 1796904

Looks like you just about milled the open chamber into a closed chamber.

If planning on milling a lot from the head I would make sure that you get the intake surface of the head cut too. That way you can use any intake on that head verses cutting every intake that ever gets bolted to that head...

For sure. Id like to be able to use a different intake in the future.

 

[padam]

Yes that’s what I was trying to do.

The inside valve cover rail is very thin.

Probably for the cost of machine work these days, it wouldn’t be too much more to buy new pistons

 

[BSB67]

Not really sure what the OP is trying to accomplish. There is no amount of milling of the deck surface of 915 head to get a heart shaped combustion chamber.

To the OP, do you think there is something to be gained from eliminating the relatively sharp transition from the machined surface to the cast chamber?

 

[1968rt]

Started out at 79ccs .030 milled I believe it was around 72ccs, with final prep about 74ccs

 

[68-500]

Not really sure what the OP is trying to accomplish. There is no amount of milling of the deck surface of 915 head to get a heart shaped combustion chamber.

To the OP, do you think there is something to be gained from eliminating the relatively sharp transition from the machined surface to the cast chamber?

I agree I couldn’t mill enough to get a heart shaped chamber. But I strongly believe a well shaped chamber is very effective against detention and would promote a more efficient burn and it would help unshrud the valves a little bit. And removing the ridge is 1 step closer to each.

Started out at 79ccs .030 milled I believe it was around 72ccs, with final prep about 74ccs

View attachment 1796988

View attachment 1796998

Thanks for the pic and information. That helps. Maybe softening that edge would be effective.