Cam questions for my 86 gt

[Desperado]

ok guys and gals. i believe the pistons in my 86 gt are factory. I also have a set of E7 heads on it. can i run a cam since i believe that the stock flat top pistons with no valve reliefs are still in there?

the car is all stock except the E7's on it and the roller rockers.

 

[stockhatch]

I would think a low lift cam like the B-303 would be fine, but who knows for sure until you check clearances.

AC

 

[N8Miller]

yeah, it would have to be a very small cam. the other thing is that your speed density doesnt like a whole lot of cams. there are a few that it will work with though.

 

[tjm73]

It would have to be a small lift increase over stock. B303 might work physically, but the Speed Density computer control will not like it at idle. It will hunt and surge.

 

[Desperado]

it has been converted to mass air. i am running a a9p computer and stock maf on my 5 speed car. just don't want to have to rebuild a motor that runs great just to have a cam.

 

[Michael Yount]

Each combo is different - you'll have to measure p to v clearance on yours to know what you've got and what you can get away with. I've helped a buddy with his combo - ported e7 heads, stock size valves, and 86 flat tops. There was no clearance at all on the intake, and insufficient clearance on the exhaust with a TFS stage II cam. With the stock later pistons with reliefs, he thinks he'll be ok.

Peak lift is a non-issue - you can run as much lift as your springs/valve train will handle (although those stock heads won't be able to use much more than .500"). At peak valve lift, the pistons are way down the cylinder - so peak lift has no clearance impact. Duration, overlap and LSA are the issue from the cam's perspective. As duration increases, overlap increases, and/or LSA decreases, during overlap the intake valve opens earlier and the exhaust valve opens later (as the piston's passing through tdc) - that's what reduces clearance.

So, if you don't want to replace or cut the pistons, then look for cams with closer to stock duration and greater than stock lift. And as others said, the speed density system is based on manifold vacuum, and any cam that is aggressive enough to significantly impact idle vacuum levels is gonna give the speed density system fits.