Any difference in the shortblock of a 86 and 90GT?

[nisreo]

Did a search but couldn't find anything. Just need to know if theres anything different about 86GT shortblock and a 90GT shortblock? I don't think there is but I want to make sure.

Thanks
Brian

 

[NIKwoaC]

'86 has true flat top pistons, '90 has valve relief notches in the pistons (due to different cylinder head geometry for the '86 model year only). Cam profiles also may be slightly different, IIRC, but not extremely. Other than that, the short blocks are identical.

 

[nisreo]

ok cool, so if I use the 86 block only and the rest 90 stuff (including pistons and heads). Ill be good.

 

[85_SS_302_Coupe]

ok cool, so if I use the 86 block only and the rest 90 stuff (including pistons and heads). Ill be good.

Yep...also if memory serves me right i think the '85 cams were a slight (and i mean slight) bit more aggressive if that makes a difference.

Something i've always wanted to see is if someone took '86 pistons and notched them for valve relief and then ran'em. They would yield a higher compression ratio than '85/87+ pistons.

 

[tiptop]

yep

 

[skunk21]

some would say no way you need to cut reliefs into the pistons when using E7 heads, I have seen this swap go in no problem with .090" of clearance, though some have had clearance issues. remember with the old e6 heads no reliefs where needed. I would clay the pistons and make sure you have the clearance needed has a safe guard, chances are you will okay. but if you don't, and you are not clear...well you can guess what then.

also too the 86 had forged pistons with thicker ring lands & ring grooves and use a low tension ring set(vs the 85 design.) this same design carried over for the 87-92 pistons but they machined in a .030 dish and the 4 valve reliefs displacing 5.5cc, now with the e7's the compression dropped from 9.2:1 to 9.0:1, if anyone cared to know .

 

[Mustang5L5]

I beleive the 87+ blocks are stronger than the 86 blocks....i think

 

[85_SS_302_Coupe]

The PTV clearance on my engine with the X303 was very small, like less than 1/32 of an inch, and the pistons are the same in the '85 as the '87+. I wouldn't waste my time trying to put them in an '86.

 

[skunk21]

I beleive the 87+ blocks are stronger than the 86 blocks....i think

They started in 86, they stiffened the block with thicker decks, cylinder walls and semi-siamesed water jacketing around the cylinder bores.

The PTV clearance on my engine with the X303 was very small, like less than 1/32 of an inch, and the pistons are the same in the '85 as the '87+. I wouldn't waste my time trying to put them in an '86.

I wasn't saying to swap pistons if that is what you thought but on some swaps the ptv clearance has been close using E7's or GT40's with 86 pistons. I was just suggesting claying for safety. The 85 piston is a different casting # is lighter than the 87+ pistons.