L98boy

Hello,

Do the early 1986 l98 engines have forged pistons or just all of the 85's ?? Thanks!

dgoodhue

Early Iron headed 86's have cast pistons. If you do search on my users name I looked up the part number in the last few months.

Storz

what does the 87 have...forged??

Juliet

All 1987 vettes had the aluminum heads so I believe they also had the forged pistons. 1986 was the transition year. The early coupes had cast pistons and iron heads. 1986 convertible production was held up until the Al heads were ready for production so all 86 convertibles had the forged pistons with it. late 1986 coupes had Al / forged. I don't know what the VIN transition number is, but the NCRS C4 manuals (soon to be out) will probably have an estimate of the transition point based on C4 survey data. ~Juliet

MrNuke

Actually it is reversed..

'85 had the forged bottom end,
86+ had the weaker cast bottom end.

vader86

Your car doesnt have forged pistons.

L98boy

Thank you for the replies :)

lead foot 85 vet

Mr. Nuke we've been going back and forth on this subject for years I have a supercharged 85 and am real interested .where did you get the spec on the 85 engine. thanks :chevy

CarAteMyMoney

I also have an early '86... build date 10/85.. I didn't think ANY of those 80s motors have forged internals.. so do I have cast or forged?

I remember my old '88 Iroc had cast

Rich B.

Juliet -

AFAIK, I've never submitted any data based on VIN to any survey. Who has been surveying C4 owners???

Juliet

Now you guys got me all confused. The head transition was definately during 1986. Did a change in pistons happen at the same time? I was under the impression based on stuff I've read in this thread an other similar ones in the past that they changed at the same time. But I honestly have no info to substantiate that. :eek:

Vito Cimilluca is the C4 Team leader for the NCRS. He's got an ongoing C4 survey. There's one for 84-86 and a second for 87-89. I put the survey forms into PDF format and loaded them on my NCRS chapter website here: http://www.ncrs.org/masondixon/c4/C4TechPhotos.htm If you would like to contribute, you can fill them out and snail them to Vito at the address on the forms. :yesnod: Sorry to hijack the thread with this. :crazy:

Back to the original question - did the pistons change at the same time as the heads or was that a different and completely unrelated transition? NCRS won't probably have info in the TIN&JG about pistons since they aren't visible and a judged item. They'll definately have info about the iron vs. Alum. heads though. :flag Sorry if I got things boogered up here guys. :p:


[Modified by Juliet, 2:04 PM 12/22/2002]

dgoodhue

The Forged piston were a model year change between and 85 and 86. The pistons were changed with the Aluminum heads, but both are cast and it was just for compression ratio.

dgoodhue

It came from the factory with cast. Even though your car was built in 85, production typically starts in Late June or early July of previous year. So your car would be already 1/4 the way into 86 production.


[Modified by dgoodhue, 6:06 PM 12/22/2002]

CarAteMyMoney

I took a magnet to it before, and I have iron heads, so i'm guessing I have the cast pistons?

Is there a book or website that has all this information? I also need to figure out which top I have


[Modified by CarAteMyMoney, 11:06 PM 12/22/2002]

dgoodhue

Cast piston is correct, the head changeover happen early in 1986 (calendar year) From what I have seen all 86 came with cast piston (Juliet was mistaken), I don't think any leftover 85 blocks would have been used since 86 was different block (1 piece rear main seals) I think you would have the early top as I suspect the change over happen when the factory retooled for convertible in March 86, but that is just my educated opinion, I am not 100% sure. Their is a measurement for early and late tops but I don't know the numbers.


[Modified by dgoodhue, 10:58 AM 12/23/2002]

vader86

the change in tops was at the same time as the head changes as far as i can tell, my VIN is 16,000-something and the head change was around 18,000 and i know i have the earlier top.