4.5 Allante flywheel balance (Page 1/1)
V8 Formula MAR 11, 09:37 PM
I'm putting a 1990 Allante 4.5 and a Getrag in my Formula. When I ordered my flywheel, I was planning on installing a 4.9 but I found an Allante engine instead. I know the 4.5 Allante block is the same as the 4.9 so I am going to use the same LSC flywheel on my Allante 4.5. But then I read that the Allante 4.5 has a different crank balance than the 4.9 somehow. Should I take the 4.9 flywheel along with the 4.5 Allante flexplate and have the flywheel balanced? Or can I just use the 4.9 LSC flywheel on my Allante 4.5 as-is? Thanks!
Raydar MAR 12, 07:10 AM
Send a message to Johns 4.9. He will likely know the particulars. Pretty sure the balance is different from the 4.9. Maybe even different from the other 4.5s, depending upon which block it's based on. (There were at least two different 4.5s. One was the 90-only PFI, from which the 4.9 was derived. The only difference between that one and the 4.9 is the stroke. The earlier 4.5 was even different from that. I'm not sure which one of these the Allante 4.5 was more similar to.)

[This message has been edited by Raydar (edited 03-12-2021).]

Dennis LaGrua MAR 12, 08:45 AM
I would think a factor to consider would be if the 4.5L needs a neutrally balanced flywheel or one balanced to the crank. If you have the flexplate a flywheel could be matched to provide the same balance. I would still check with Johns4.9 as he is the resident wiz on these engines.

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" THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite.
"THE COLUSSUS"
87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H
" ON THE LOOSE WITHOUT THE JUICE "

Johns 4.9 MAR 12, 12:29 PM
Hi,
The Cadillac and Allante 4.5 engine is internally balanced on the front half and externally balanced on the back half. I found this out while building a 4.5 for a customer with an aluminum flywheel. You can tell this by looking at the 4.5 flexplate compared to the 4.9 flexplate. The aluminum flywheel was too light to balance so we ended up adding heavy metal to the rear of the crankshaft to get it to balance.
If you are using a steel flywheel, you wont have a balance problem to where you need to add weight to the crank. Just take your 4.5 flexplate and your new flywheel and have it "matched balanced" at your local machine shop. Then you are good to go.
It will look something like this.
Cheers
John
Dennis LaGrua MAR 12, 12:39 PM
John provided quite a proven detailed and complex answer. Easier than I thought.

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" THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite.
"THE COLUSSUS"
87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H
" ON THE LOOSE WITHOUT THE JUICE "

[This message has been edited by Dennis LaGrua (edited 03-12-2021).]

Johns 4.9 MAR 12, 01:01 PM
Thanks, Dennis.
Cheers
Spadesluck MAR 12, 04:55 PM
The LSC flywheel will work with either motor.

Side note...Anything 4.5/4.9 related go to John!
V8 Formula MAR 12, 05:29 PM
Here's what I have. I put a magnet on the flywheel and it's definitely steel and heavy AF like a street flywheel should be. I'll take them up to a machine shop and have them balance matched. Thanks John.



Thanks Raydar, Dennis, and Spadesluck. for your thoughts. I've texted John a couple times on FaceBook but I'm in FB jail at the moment.

[This message has been edited by V8 Formula (edited 03-12-2021).]