Machining cylinder head for more compression?

[Diseazd]

You are creating a lot of unavoidable work by using the E88 from a 260Z. That just isn’t the best head for performance. It will be cheaper to buy an early E31 or E88 and just bolt it on IMO. The 260 has a longer stroke, so not sure what the CR would be, but would be up there. I’ve never built that combo, but assume the parts would work together to provide 10:1 or so compression. Anyone done that?

Edited January 9, 2021 by Diseazd

[grannyknot]

The F54 block/N42 head L28 engine I use to own had a compression ratio of 10.5:1 The head had been ported, polished and decked.  The engine was carburated and no matter what I did I could not get rid of a bad ping on acceleration even though I was running 94 octane.

Eventually I had to install an expensive Kameari 2.0mm steel head gasket to bring down the comp. ratio.  Now I know others run 10.5 and sometimes higher ratios and say they have no problems so I just mention this as a cautionary tale.  I can't remember what the final comp. ratio ended up at but that .08mm extra solved the ping problem and the engine felt no less powerful than it did before.

Edited January 9, 2021 by grannyknot

[Diseazd]

Good point grannyknot. I’m one of those that run 10.5 to 1 in my strokers, but a high duration, higher lift cam is supposed to solve that problem. I can’t make mine knock. I’m running Isky Stage III .490 lift with 20 degrees more than stock duration.

[grannyknot]

1 minute ago, Diseazd said:

Good point grannyknot. I’m one of those that run 10.5 to 1 in my strokers, but a high duration, higher lift cam is supposed to solve that problem. I can’t make mine knock. I’m running Isky Stage III .490 lift with 20 degrees more than stock duration.

Ahh! you've  jogged the old memory banks and I do remember a longer duration cam was the other option for trying to solve the ping problem but the cost of the Kameari HG was less than the cost of a new cam, new lash pads and reconditioned rockers.

Thanks

[Diseazd]

6 minutes ago, grannyknot said:

Ahh! you've  jogged the old memory banks and I do remember a longer duration cam was the other option for trying to solve the ping problem but the cost of the Kameari HG was less than the cost of a new cam, new lash pads and reconditioned rockers.

Thanks

Ahhh, but by buying a thicker gasket, you are defeating your purpose. By buying a Stage III cam, you are improving the package. Why God created money!!! 😳

Edited January 9, 2021 by Diseazd

[z shredder]

1 hour ago, Diseazd said:

You are creating a lot of unavoidable work by using the E88 from a 260Z. That just isn’t the best head for performance. It will be cheaper to buy an early E31 or E88 and just bolt it on IMO. The 260 has a longer stroke, so not sure what the CR would be, but would be up there. I’ve never built that combo, but assume the parts would work together to provide 10:1 or so compression. Anyone done that?

Well I have 2 options using the E88 head from the l26 or using the E88 head from my l24 I heard that the l26 had bigger valves and that's why I wanted to go with this. 

The thing about the E31 heads is that they are extremely hard to find in Germany so I think machining down an E88 to get the same compression is the best option. 

[jonbill]

I've got an e88 skimmed to 36cc chambers on a "big bore l26" and 10.5:1 CR I built recently. There's no problem with chain tension or cam timing. It hasn't run yet but it won't ping on decent fuel I'm sure. 

[240260280]

4 hours ago, z shredder said:

Did you move the link over one spot on the sprocket or did you mean to say removed a link? 

I just rotated the cam 1 link.  I believe there are 42 links between the marks when set up. I had to go to 41 to make up the change.  The tensioner takes up the slack.

[siteunseen]

Or you could start straight off in #3 hole on the cam sprocket. It advances the valve train components action. Intake valves open sooner as well as exhaust valves. 8 degrees if I remember right.

Read it in the Racer Brown article. I lost some top end, maybe 500 rpm but they're street cars. Red light to red light, no top speed racing around here

Edit

Hole #2 would be better. A happy middle. I've thought about going back one but that's it, just a thought. They pull hard from about 2,000 to 6,000 or a little more. They're loud that high and I live in fairly small town.

Edited January 9, 2021 by siteunseen

[Zed Head]

9 hours ago, grannyknot said:

The F54 block/N42 head L28 engine I use to own had a compression ratio of 10.5:1 The head had been ported, polished and decked.  The engine was carburated and no matter what I did I could not get rid of a bad ping on acceleration even though I was running 94 octane.

Did you ever measure cylinder pressure?  Compression ratio is a really simple number, just )combustion chamber plus swept volume)/(combustion chamber).  It doesn't tell you what the cylinder pressures are, which is what causes detonation.  Pressure.

Funny, but I went out to be sure I had my definition of CR correct and found some sources that define it incorrectly.  People forget the combustion chamber volume in some of them.  Anyway, pressure is the key, calculating CR is just a starting point.

https://www.britannica.com/technology/compression-ratio

[grannyknot]

 

9 hours ago, Diseazd said:

Ahhh, but by buying a thicker gasket, you are defeating your purpose. By buying a Stage III cam, you are improving the package. Why God created money!!! 😳

OR, you sell that engine a drop a bigger one in.

 

34 minutes ago, Zed Head said:

Did you ever measure cylinder pressure?  Compression ratio is a really simple number, just )combustion chamber plus swept volume)/(combustion chamber).  It doesn't tell you what the cylinder pressures are, which is what causes detonation.  Pressure.

Funny, but I went out to be sure I had my definition of CR correct and found some sources that define it incorrectly.  People forget the combustion chamber volume in some of them.  Anyway, pressure is the key, calculating CR is just a starting point.

https://www.britannica.com/technology/compression-ratio

No I never did, that was 4 engines ago.

[Jeff G 78]

I cut 0.050" off a P79 head on my race car engine.  I slotted the chain guides to take up the slack and then I used the eccentric bushing method from the "How to Modify Your Datsun..." book to dial in the cam timing.  It works great and pulls strong.  I like the P79 for this because the chamber shape is better for knock resistance compared to the E88, and N47.