Why are there holes in V6 pistons tops ? (Page 3/3)
fieroguru AUG 16, 07:02 AM
Here is a set of 6 NOS 2.8L pistons. Notice 2 have the side notch, 2 have the hole, and 2 have both.


This tells me that GM used multiple castings and/or suppliers over the years and the notch, the hole or both we all acceptable means of noting for the forward side of the piston. We see this all the time with engines having multiple part #s and slight design changes even with the same make/model/year (like LS4s came from the factory with 243 and 799 cylinder heads within the same year).

The ones in the picture have 3 different part #s, but I don't know which is which.
(2) 14020518
(2) 14091814
(2) 14033225

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[This message has been edited by fieroguru (edited 08-16-2023).]

fierogt28 AUG 17, 12:21 AM
Patrick is correct, and Guru is correct also.
I have a stock 88 V6 here with the notch on the side of the piston. The need for it was to insure the piston is installed correctly pointing towards the front of the engine. Facing the waterpump.

Like Guru mentioned, it’s very possible GM changed suppliers, and there was a design change. We know GM has been good for that. As well, some parts like the lower intake manifold on the V6. Different part number on the 85-87 LIM, and different part number on the 88 LIM.
Unless there was an improvement, or casting update, why would GM change the part number. Might have been used on another GM car in that era just before 1988, or in 1988.
I still would like to know if there is a difference in that LIM.
But that’s getting off topic, but my point is the same.
I would only install the 6 “same” pistons on and engine due to balancing issues. Being a few grams off, can be a lot at higher RPMs.
That’s why like Patrick said, for perfect piston balance, some have filed the piston skirts to get the perfect piston weight. Then use a precise scale to get the piston weight to perfection.
It’s been documented that the 88V6 Fiero pistons were lighter than the pre-88 V6 pistons. But I have never checked this on a scale if it’s the facts or truth.

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fierogt28

88 GT, Loaded, 5-speed.
88 GT, 5-speed. Beechwood interior, All original.

fierogt28 AUG 17, 12:32 AM
And the picture that Guru posted, my 88V6 pistons are
flat top pistons like on the far right.
GM did also document the V6 engines at 8.5:1 CR, and 8.9:1 CR.
So why?
Is it the same reason they changed or confused us with the 140hp rating in the early production of the GT, and in 1987-88 the were claiming 135hp to get more buyers to purchase a Fiero because it would lower insurance for drivers?

It’s sad why some automotive companies can’t be consistent on info or specs regarding their own products

Not trying to badmouth GM, but more get an answer.
It can lead to confusion, and that’s why we are talking about it.

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fierogt28

88 GT, Loaded, 5-speed.
88 GT, 5-speed. Beechwood interior, All original.