Dumb Idea of the Day(TM)?: removing a compression ring to mimic the XFi 1-ring piston

[MetroMPG]

Really? I was at TeamSwift yesterday re-reading your head-shave reports, and they seemed positive to me! You should go back and update that thread. :P

The pinging's no huge surprise, but I'd like to hear about the "general trouble".

You took Mike's advice and went for the .040 reduction, right? If you could put some back, would you? Or would you only go right back to stock?

[Daox]

Well, .040 is a lot to take off a head. I took .025 off my Paseo's head and I got no problems at all. If I knew what I know now about head design I'd go a bit further.

[MetroMPG]

Tim, are you running timing advance too with that shaved head? All on regular gas?

Kind of straying from the topic of piston ring-ectomy, but whatever.

[Coyote X]

I would say most of the gain I got was from fixing the burnt valve and doing a mild porting and polishing of the head. After running with the audio knock sensor for a while after doing it I pretty much figured that shaving the head caused more tuning issues than the gain it gave me. It will also take a lot of your bottom end power away and make it suck under 1500rpms if you want to keep the knock halfway under control.

With a stock computer and no knock sensor it might not be apparent but I bet the engine won't last as long with a shaved head. It would have a much higher chance of bottom end failure from the knock. I would guess 75-100k miles. My setup has a pretty good bit of information available to help tune out the knock and even with 93 octane it cant take more than 1/4 throttle under 2000rpm. That was with the timing at -10 degrees so it is mainly compression causing the knock and not spark timing. 020 might be ok to try but really with a year of messing with a shaved head I am pretty much ready to give up on it. Unless I can get a reliable water injection system working then I will want to shave a bit more off

[Frank Lee]

Burn E85 in it

[Bicycle Bob]

I think that you want a special ring with overlapping ends if you are only going to use one.

[ncs]

You mean gapless pison rings.

Total Seal Rings Top-End Performance

Another fun idea is getting the piston skirts coated with anti-friction material, and the tops with ceramic. I don't think anyone has done it for mileage and documented the results.

[Daox]

The Paseo uses a distributorless ignition system. There is no easy way to alter ignition timing as the computer handles it completely. I just let the computer advance it as much as it feels it should. It is possible that it retarded timing a bit when I shaved the head. I unfortunately have no way of knowing for sure.

[guudasitgets]

Originally Posted by MetroMPG

OK, so the obvious question: why didn't you do it on the racing motors as well?

See the post below

[guudasitgets]

Originally Posted by guudasitgets

you can either collapse the second ring or leave it out. We did this on qualifying motors where we didn't want as much drag on internal parts, racing oil filters are another trick (i.e. NASCAR restrictor plate tracks, less filter media to push through, less horsepower)loss

see bold type