86 5.0 cans and cants

[TTop GT]

i have read and heard that the 86s came with flat top pistons, and cams will cause piston to valve contact...

does this mean every cam will, including the e303 and b303?
and if so, how about the stock cam with 1.6 or 1.72 rockers?

what exactly can you get away with?

oh and one more thing... are the heads the same as the 87-93 heads? if not, are they better or worse? :hmm:

[red95gts]

You are correct, the 1986 motors have flat-top pistons with no valve reliefs (87+ have valve reliefs). The lack of reliefs will reduce potential piston-valve-clearance. From what I've seen the stock cam + 1.72s seems to be a hit-or-miss deal depending on whether or not the heads have been milled. I do know someone running a B303 on an 86 short, but I don't know how much clearance he has. Obviously a stock cam + 1.6s (assuming cam is installed correctly) will clear as that is what came from the factory. :)

The only way to know for sure is to mock it up and measure....

The heads are E6 castings, which flow pretty terrible as compared to the E7TE heads the 87+ cars use. Although the E6 heads have the kidney-shaped chamber that makes the World Products' heads popular.....

Good Luck

[TTop GT]

dont the 86 5.0s have slightly higher compression? (9.2:1)

and if you switch from the e6 to the e7te, will you gain any power? will you lose any compression, and will there be any more of a piston to valve clearence threat?

-thanks for your time-

[red95gts]

Well...I don't know for sure, but all else being equal, no valve reliefs = more compression. It's going to depend on the copression height of the 86 piston.

If you put some ported E7s on the car, you'll definitely pick up some power. Even some unported E7s would probably pick up some...but it would be easy enough to lightly port them....

Good Luck

[Forrest]

/me cracks guru knuckles...

the HO 86 style engines (found in the 86 GT's and 86 and 87 Mark VII LSC's (the bill blass' got the non HO engines) had the E6 heads and completely flat pistons...

the E6 heads have SHORTER VALVES which means they are farther away from the piston... so you can run a decent sized cam with the E6 heads on an 86 shortblock... BUT... factory spec E7 heads are going to be sorta close on P/V clearance with even the stock cam... I wouldn't try higher ratio rockers...

now, I LIKE the 86 pistons... get a pair of box stock TFS heads and you can run the same cams you could run on an 85/87+ shortblock but you've got another half a point of compression...

the 86 HO engines had ~ the same compression as the 87+ engines... they have a larger chamber than the E7's

the chambers shroud the valves TERRIBLY and properly unshrouding them would probably yield 8.5:1 or less even with the flat pistons... not worth it...

I've always wanted to try a pair of worked E6's on a budget turbo motor... on an 87 style shortblock you'd have ~8-8.2:1 compression and MILES of piston to valve clearance with equal or better flow to ported E7's AND the E6's point the spark plug at the exhaust valve...

but I digress...

bottom line? get your hands on a piston notching tool! :D

Forrest