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86 is likely a large cap hei distributor. 87 was the switch over year as I recall. But they can be converted from one to the other, which maybe a previous owner has done. (Not super likely but very plausible)
All you have to do is look at it. They are distinctly different. The small cap has a ign coil separate, large cap holds the coil in the top of the cap. The photo with wires attached is the large cap
Iirc 85-86 was identical to 85-91 c4 but with a non melonized gear. Unlike 74 style hei the tpi large cab used screws instead of latches to hold on coil/cap. Can probably pick one from cardone on Amazon.
Both are clamp down. I'm not exactly sure what Tuned is referring to. I'm not aware of any screw down large cap. I took a very quick glance and the parts called for a 86 call for a normal large distributor cap.
The only difference I know of is a melonized gear for roller cam. Your 86 would've been a flat tappet cam from the factory.
I see, Tuned. I took a longer look. The listing for 86 shows both types. Which one that is on the OP's car remains to be seen. The function would be identical, I'd imagine.
Odd that I've never ran into a screw type before. Even on the 86 I owned. Interesting.
Maybe a case of one on TPI and one on carb?
Last edited by aliceempire; Apr 16, 2022 at 07:11 PM.
Oh, okay - and from what I read, melonizing is just a hardening process, so I’d be okay using it also on a flat tappet?
I do have a comp cam in it, but from recollection, it is not a roller (it’s been a couple of decades, and this is certainly not my expertise )
Melonized distributor gears are fine on flat tappet camshafts.
what is exactly wrong with your current distributor?
Well, honestly Im not sure if anything is wrong with it.. But I’’ve been battling this problem seen in the thread below, and the distributor parts, ecu/prom and fuel pump are pretty much the last things not replaced.
I do not believe it is the fuel pump, and it appears less expensive to buy the whole distributor than all the parts for it..
It probably doesn’t make sense to you guys do it like this, but Im at a loss here for figuring this thing out - and since I live in Norway, it isn’t just to run down to Autozone to grab the parts one by one I have to order from the US and the shipping is killer - so that must be factored in as well..
The large cap distributor for the '86 TPI is also lower than the later versions. Switching may prevent the installation of the trim piece at the rear of the plenum. I believe that's same reason why the later Y-bodies kept the large cap to survive with reduced hood clearance.
86 is likely a large cap hei distributor. 87 was the switch over year as I recall. But they can be converted from one to the other, which maybe a previous owner has done. (Not super likely but very plausible)
All you have to do is look at it. They are distinctly different. The small cap has a ign coil separate, large cap holds the coil in the top of the cap. The photo with wires attached is the large cap
Would a Small Cap Distributor be able to fit a 86 305 TPI? I found one from DUI that is intended for an 87 but has the same engine. Wondering if that is able to just drop in or if it needs modifications.
Would a Small Cap Distributor be able to fit a 86 305 TPI? I found one from DUI that is intended for an 87 but has the same engine. Wondering if that is able to just drop in or if it needs modifications.
)
I have to order from the US and the shipping is killer - so that must be factored in as well..
