1G 1990 4G63T Piston to cylinder wall clearance?

[May1989TalonTSiAWDst]

Hey tuners,
Putting some piston in, ported heads, exhaust, intake, the works. Have a piston to cylinder gap question. #1 piston had a valve tap with extensive scaring. Had to hone and now have a measurement of 85.10 and the max gap is suppose to be .0012" - .002" = 85.03 - 85.05mm from what I read.

What is the ideal piston to cylinder gap?

You can check out the measurements at the bottom of my youtube post to get an idea of where I'm at with it at about 9.01 minutes in. Wanted to return to stock piston but they measure 84.97mm on 3 and an 84.95 on one.

89 Eagle Talon 2.0L DOHC 4G63 turbo Engine Work 2

What would work best? re-sleeve, bore out, custom piston?

Thanks, Ty

 

[May1989TalonTSiAWDst]

I've been doing some research. Piston to cylinder bore gap for a 4G63 my year is .03 - 05mm. I cross referenced this with a Nissan gtr which has 86mm piston, they say to use .035 - .055mm which is almost the same.

I'm pretty sure that I have to bore out to 85.5mm, my #1 being at 85.10, dang. Since I have to do some machining, I've been studying up on some engine dynamics. I just don't like using forged aluminium as a piston. Forging Al temps are from 600 - 900 degrees F. Header temps on a turbo car can easily reach 1200 F. When a material forges it slightly turns to liquid reforming itself. I just don't think a liquid piston is a good idea, forged or not. So what to do? The tensile strength of forged aluminium is about 50,000 psi at best.

What I'm going to do to fix this problem. Grade 1 titanium has a tensile strength is 270 000 psi which is the same as tool steel. Grade 5 has a tensile strength approaching 900 000 psi but can not be worked with easily. Also, titanium is 60% the mass of Al but 6 times the strength. So if I went with half the weight, a titanium piston would still be 3 times stronger. Also thermal expansion of titanium 8.6 micro/K Al is 23.1 micro/K, which means the piston taper from top to bottom could be less too with a tighter fit. Another benefit is titanium is forged around 1250 to 1650 F which is over normal operating high boosted temp. Think I'm going to recycle my pepsi cans for something that is going to last. I'll be back after I get off the lathe, might be a while. The cost of titanium round bar stock is the cost of a finished Al piston but I do not plan on doing this again. Next time a valve taps my piston I change the valve. Back in a bit.

 

[steve]

High coolness factor having titanium pistons but quite unneeded.
People are running forged AL pistons in 4G63's upwards to 1000hp.
At more reasonable power levels they have proven to be daily driver reliable.

I didn't know there was a Vancouver in Ontario so I'm confused.
If you in Vancouver, BC talk to the guys at English Racing http://englishracing.net/
If you are in Ontario go to Magnus Motorsports http://magnusmotorsports.com/

Those are both first rate Old School DSM experts.

 

[zedicus]

you absolutely should NOT use titanium pistons in an iron block/sleeve. the engine will not live 10 miles before nuclear destruction.

.003" PTW (ive always hear ptw talked about in inches, so convert that to mm if you want) is fine on forged pistons but the skirts are not identical. if your engine is cut for .003 wisecos it will be TITE and your break in should be meticulous. if cut for .003 on JE its going to sound like your motor is full of ball bearings until the motor is warm and broken in (ive always found JE to be loose like a middle aged blonde)