85 vs 86 TI differences

[Xtrempickup]

Am in process of putting a 85 t1 motor back together. Im missing some things and have a 86 t1 engine complete im taking parts off of. I pulled the head off the 86 and it has dished pistons with valve reliefs. The 85 has just dished pistons, no reliefs. Did they change piston styles 85 to 86? The 85 i know is non rebuilt and bone stock. The 86 im not sure about. Just trying to figure out if whats in this 86 donor is correct for what it is.

[turismolover22]

84-85 will be a G-Head, so the pistons will have different dishes on them/compression. The block is drilled for 10mm headbolts. The G-Head has a smaller combustion area in the head, so the larger dish was required to make the compression target

[Xtrempickup]

Ok. Would running a 782 head on the 85 be any issue?

[black86glhs]

The 782 head will raise the compression ratio a little. Not sure if it will cause a big problem. Guess it depends on how much oooomph your looking to make.

[Xtrempickup]

Looking for 250hp max, likely not gonna see it with the stock t2 garrett turbo. i think in a light 85 turbo z will be more than enough.

[black86glhs]

Are you running an 86 computer? If so, you might have to drop the timing back a couple degrees to keep it from detonating. I think I have that right.

[4 l-bodies]

85 will also probably have 6 bolt crank vs. 86 8 bolt crank. 85 rods are stronger than 86. If it were me, I would just find a good g-head and forget all the mixing and matching. Your opening up a can-o-worms. You will have about 8.5-8.6:1 compression using the swirl head on the 85 shortblock. Even more if block or head gets resurfaced. Also the valve reliefs are there for a reason Tom. Hope you don't break a timing belt, or you'll have yet another problem.

[4 l-bodies]

84-85 will be a G-Head, so the pistons will have different dishes on them/compression. The block is drilled for 10mm headbolts. The G-Head has a smaller combustion area in the head, so the larger dish was required to make the compression target

Either you got part of that reversed or I'm reading this wrong. A g-head has a bigger 56cc head, hense uses smaller dish 9cc pistons. Swirl uses larger 14.5cc dish pistons combined with smaller 50cc head. Both had 8.1:1 CR.
Tom, the end result using a swirl head on a 85 shortblock is your chamber volume is -6cc which will raise compression close to half a point.
Todd

[Xtrempickup]

The 782 i have needs a cut. Guess i should hit the yard for ghead. Car is gonna run on a glhs computer, it had been run before that way and the motor before i got it had a 88 top end on it. I received the car with just the bottomend, the owner sold the top end.

[turismolover22]

Yea, I did have that backwards, long day, my appologies.

[GLHS60]

You sure are complicating things!!
The GLHS computer is programmed to run with the swirl, or fast burn head.
A swirl head on 1985 pistons and G computer is more detonation prone.
A swirl head on 1985 pistons and GLHS computer somewhat less.
A swirl head on 1986 pistons and GLHS computer is obviously preferred.

Thanks
Randy

[black86glhs]

You sure are complicating things!!
The GLHS computer is programmed to run with the swirl, or fast burn head.
A swirl head on 1985 pistons and G computer is more detonation prone.
A swirl head on 1985 pistons and GLHS computer somewhat less.
A swirl head on 1986 pistons and GLHS computer is obviously preferred.

Thanks
Randy

Thanks Randy. I couldn't remember which way it went.

[Xtrempickup]

Well thats what i got to work with, the guy ran it that way for years on a stage 3 glhs comp with 17psi boost. Pistons are good, said leak down test of motor was good also. Figured id set it up the same way he had it if it worked for him.