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| Early (85-87) vs 88 V6. Pistons have different compression height?! (Page 2/2) |
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pmbrunelle
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NOV 25, 12:57 PM
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If there really is a difference, it would take a difference of 0.016" of compression height (or something else such as gasket thickness) to explain the 0.4 CR difference.
On my Fiero engine rebuild, there was maybe about 0.005" of head gasket crush IIRC, but that was with MLS gaskets.
With a vernier caliper, you get an measurement from the uppermost edge of the hole to the piston top. Then, measure the diameter of the hole, and subtract its radius from the first measurement to obtain compression height.
It's also bizarre that compression ratio would increase, but that power ratings would decrease over V6 Fiero production; something doesn't add up.
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Gall757
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NOV 25, 02:37 PM
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| quote | Originally posted by pmbrunelle:
It's also bizarre that compression ratio would increase, but that power ratings would decrease over V6 Fiero production; something doesn't add up. |
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The US federal government's test calculation for emissions changed in model year 87, lowering the hp rating to 135. Earlier it was 140. Apparently they used a lower RPM to get better results.[This message has been edited by Gall757 (edited 11-25-2020).]
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fierofool
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NOV 25, 05:04 PM
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Weren't those HP ratings at different rpm? That could account for it.
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Will
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NOV 28, 09:30 AM
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| quote | Originally posted by fierogt28:
Thanks Will... 
What I meant was the stock 88V6 pistons where 14.8mm shorter than the 85-87V6 pistons.
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Umm... try again? Even 1.48mm would be quite a large amount of compression height difference.
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Gall757
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NOV 28, 09:41 AM
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| quote | Originally posted by Will:
Umm... try again? Even 1.48mm would be quite a large amount of compression height difference. |
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Overall piston height does not change the compression ratio. Wrist pin center to top of piston does.
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fierogt28
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NOV 28, 07:29 PM
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I'm talking about the piston from top to bottom. (piston top, to lower skirt) ------------------
fierogt28
88 GT, Loaded, 5-speed.
88 GT, 5-speed. Beechwood interior, All original.
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Will
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NOV 30, 09:37 AM
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Ahh, ok. That is not compression height.
I thought you were referring to difference in compression height.[This message has been edited by Will (edited 12-01-2020).]
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