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2.8 to 3.1 rebuild by TA6SPD
Started on: 02-08-2004 09:38 PM
Replies: 7
Last post by: chameleogaz on 02-09-2004 02:14 AM
TA6SPD
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Report this Post02-08-2004 09:38 PM Click Here to See the Profile for TA6SPDClick Here to Email TA6SPDSend a Private Message to TA6SPDDirect Link to This Post
I recently got a 1985 fiero GT. I got the car running today, and not to my suprise it has a rod knock. I've been in to the F-bodies for a long time and have a stack of bad 2.8 V6's out of these cars. I have a good 3.1 out of a F-body. What I need to know is what parts out of the 3.1 do I need to convert the 2.8 to a 3.1. I want to do a complete rebuild with hi-po parts.
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JazzMan
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Report this Post02-08-2004 10:34 PM Click Here to See the Profile for JazzManClick Here to Email JazzManSend a Private Message to JazzManDirect Link to This Post
It depends on what heads your donor 3.1 engines have. Basically the iron head 3.1 motors have the same block and head chamber size as the 2.8 iron head motors, the only real differences between the two are the pistons and crank, and the flywheel/flexplate on all 3.1s is neutrally balanced whereas the Fiero didn't get neutral balance flywheel/flexplates until the '88 year. To do this swap, just swap the crank and pistons into the Fiero block and get a neutrally balanced flywheel/flexplate for the '85 GT.

If the heads are aluminum it's a whole different ballgame. Nothing above the block will interchange between the two.The pistons are matched to the head and if used with the Fiero heads will yield a compression ration down in the sevens. About the only thing useful out of the aluminum head motors is the crank and rods, everything else will need to be bought. If you want to use the whole motor it's a real engine swap with ECM replacement and the whole nine yards.

JazzMan

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TA6SPD
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Report this Post02-08-2004 10:49 PM Click Here to See the Profile for TA6SPDClick Here to Email TA6SPDSend a Private Message to TA6SPDDirect Link to This Post
The 3.1 in the f-body is cast heads. I'm planning on replacing the pistons. Are the only difference in the pistons the dish?. Will the flywheel out of the f-body work in the fiero?
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Report this Post02-08-2004 11:24 PM Click Here to See the Profile for JazzManClick Here to Email JazzManSend a Private Message to JazzManDirect Link to This Post
The 3.1 is just a stroked 2.8 from GM. GM increased the stroke 8 mm, and to use the same rods GM moved the piston pin up 4mm in the piston. Since the displacement increase but the head CC didn't, GM dished the pistons to make the compression reasonable. So basically the pistons are matched to the crank in the iron-headed motors.

As far as the flywheel working, I have no idea.

JazzMan

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Earl
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Report this Post02-08-2004 11:32 PM Click Here to See the Profile for EarlSend a Private Message to EarlDirect Link to This Post
Some one corect me if I am wrong. I would use the 3.1 block just redrill the starter holes and use the fiero intake and fuel injection. It will look liek a stock fiero 2.8 and have better oiling and more power.

Please corect any information I have wrong.

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TA6SPD
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Report this Post02-09-2004 12:02 AM Click Here to See the Profile for TA6SPDClick Here to Email TA6SPDSend a Private Message to TA6SPDDirect Link to This Post
Everything that I have read says there is not enough metal to redrill the starter holes. If anyone knows that this could be done let me know. I have two more fieros comeing in the next two weeks. One is a 86 SE V6. The other I'm not sure what it is. I really don't care for $50.
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chameleogaz
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Report this Post02-09-2004 02:11 AM Click Here to See the Profile for chameleogazClick Here to Email chameleogazSend a Private Message to chameleogazDirect Link to This Post
 
quote
Originally posted by TA6SPD:

Everything that I have read says there is not enough metal to redrill the starter holes. If anyone knows that this could be done let me know. I have two more fieros comeing in the next two weeks. One is a 86 SE V6. The other I'm not sure what it is. I really don't care for $50.

my 3.1L engine (as I've stated in another thread) was a GM crate intended for an 89-91 firebird. I drilled the starter holes with Rodney Dickman's jig, and it worked great. If you're wondering if there's enough metal, give Rodney a call, I'd think if you were to take a picture of the block and email it to him he'd be able to tell you if it would work. If you don't have the $50 for the jig, you could ask around the mall for one? I'd offer you mine, but it's at home (in cleveland) and I'm at school (in cincinnati).

Goodluck, I hope you get all the information that you need.

-Jeff

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chameleogaz
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Report this Post02-09-2004 02:14 AM Click Here to See the Profile for chameleogazClick Here to Email chameleogazSend a Private Message to chameleogazDirect Link to This Post

chameleogaz

224 posts
Member since Aug 2003
as for the flywheel, as far as I know (I could be wrong) it's the engine internals such as the crank that determines if an engine is interally or externally ballanced. If you're using the 3.1L's engine internals (the 3.1L should be interally ballanced), then your resulting engine should be internally ballanced meaning you'll want to use a neutrally ballanced flywheel like the one that came with the 3.1L.

-Jeff

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