hey all,

I think I know the answer to this but I though I'd ask to be sure. I've got an '83 LG4 that has a bent rod. I pulled that piston and connecting rod and would like to just replace it with another used rod and piston from another engine. I've found another user to sell me just a piston and rod from his standard bore '86 tpi engine. That piston would have valve reliefs in it though. I would imagine this means the pistons are of a different compression ratio...something I don't want to use. Can anybody answer definitively whether this piston will FUNCTIONALLY interchange (not physically) with what I've had and make my motor live a little longer. Or is it like I'm thinking, it just won't work.

Thanks for any insight

and if anyone has a standard bore LG4 piston and connecting rod to sell...I'm in the market

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Clem
SCCA TransAm Series Race Mechanic/CrewChief
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1983 Z28 with LG4, 5 speed, and (unfortunately) T-tops
1983 Z28, NO T-tops, (unfortunately) Auto Transmission (hopefully not for long)

 

Transferring to

Tech / General Engine

 

You are correct... the TPI motors have flat-top pistons, the older LG4 has dished. You would end up with one cylinder with 9.3:1 CR and 7 with 8.5:1.

Somebody on this BBS was asking the other day what his 305 TPI core in supposedly decent old used condition was worth. Maybe you could work a deal. The motor would run several horsepower better with the higher CR. All you'd need would be the 1-pc flexplate.

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"So many Mustangs, so little time..."
ICON Motorsports

 

I figured that was the case, thanks

Clem

 

here's one:

If I use all of the pisons and rods out of a later engine, does it have any chance of living? If both are standard bore with the same jornals and all, can I just throw the pistons and rods into my old block? Sould I change the rings over from the old pistons to the "new" pistons? (I would Imagine I should use the "old" bearings that are currently run in on the crank in the engine)

the reason I'm asking is because yet another board user has offered me the complete rod/piston set out of an '88 tpi engine

thanks for any insight,
Clem

 

If you do that, you should be in good shape.

I think it would be foolhardy to go to all the trouble of assembling and installing such a thing without replacing the rings and bearings though; you'd end up wasting more money in fluids and gaskets (not to mention time and trouble) re-doing it if it doesn't work than the R & B will cost in the first place, and you'd still have to buy them too. If your block is in good shape, less than .005" of ring wear, you could just hone it and run it with new soft parts, and life should be good.

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"So many Mustangs, so little time..."
ICON Motorsports