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Discussion Starter #1
Hello. I have tried seaching with no luck. Does anyone know what flywheel you would use on a 8.1 when using a SM465??

Thanks,

Eric
 

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If it is the 8.1 liter big block, I think that you can use one out of a 454, or a 402. I don't know if the 8.1 is externally balanced or not. The 454 is for externally balanced, and the 402/396 is internally balanced.
 

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Bump... I've got the same question. Just picked up an '01 Vortec 8.1 and I'd like to mate it to my SM465.
 

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I would recommend using an 8.1L flywheel. You know the flywheel that was intended for that engine……. There is very limited commonality between the 8.1L and other big blocks of the past so I certainly would not assume a 454 flywheel would work. Maybe a Gen VI 454 flywheel with the one piece rear main seal….maybe.

A SM465 should work fine with an 8.1L if you use the original 8.1L flywheel. I guess you will be one of the first on the block to know for sure.

I used a 14096987 flywheel on my Gen VI 454. You might be able to research that part number and see if it is compatible with the 8.1L. I kind of doubt it.

Keep us posted. I have two 8.1’s sitting in my garage now. Both are broke but fixable. I also have an 8.1 in a Silverado with a 6 speed manual that I bough new in 2001. It is certainly not fast but has gobs of torque and barely gets fuel mileage numbers in the double digits. Burns a qt of oil every 1200 miles like clock work though. I am not complaining….that is just the way big blocks are.
 

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I would recommend using an 8.1L flywheel. You know the flywheel that was intended for that engine…….
Around here you can't find newer chevies with a stick shift. They all have an auto behind them. I was hoping there would be something else I could find in a wreckers somewhere that would work. Time to visit the parts counter I guess. :D

Now the question is will a standard 11" clutch for a SM465 bolt up to a stock 8.1 flywheel?
 

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Discussion Starter #8
Here is the 8.1L flywheel part number....... 12582964
Larry,

Thanks. I had heard somewhere that a flywheel off of a 396/427 would work. The 8.1 is internally balanced, so I know one from a 454 won't work. I could not think of any 396/427s that had a one piece rear seal and did not know if they really had a different bolt pattern.

The only problem I had with using an 8.1 flywheel was the clutch setup to go with it. I was going to try to run a mechanical clutch linkage, instead of a hydraulic. I guess I will just have to try it and see. I definately don't want to be cheap and fu$% up the balance on my new engine.

Thanks again.
 

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Around here you can't find newer chevies with a stick shift. They all have an auto behind them. I was hoping there would be something else I could find in a wreckers somewhere that would work. Time to visit the parts counter I guess. :D

Now the question is will a standard 11" clutch for a SM465 bolt up to a stock 8.1 flywheel?

Same problem I was finding. I was also concerned about the clutch. I will know in a couple weeks, once I get started on this. I have the 8.1, with an auto flexplate, a SM 465 with bellhousing (mechanical clutch) a 203 mated to the 465, and a 32 spline 205 I am planning on mating to the 203. I just need to get the flywheel/clutch setup figured out.

I just don't know if the depth on my current bellhousing would allow me to use the older clutch with an 8.1. I am going to find out in a couple weeks though. Once my boat work slows down in January, I'll have an answer and post up. Maybe it will help someone else out.
 

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I would not put to much concern on the hydro clutch problem..


that one is easy,


make a bracket from angle iron or plate.

use a wilwood master and a cnc slave cylender with or use stock chevy parts from the counter. When I converted my old 86 k5 I went this route, after finding the throw I needed and getting it set up it worked out great!







I got all my parts from a local circle track shop for about 150.00 for everything even the lines and a fitting or two.

they also have trick unit that incorperated it into the throw out bearing its self!
 

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Sheepdog,

I agree…..doubt the 396/427 flywheels would work due to the one piece rear main seal that require a unique flywheel. However, I believe there was a GEN VI 427 tall block in late model medium duty trucks. Might want to look into that.

At the end of the day, the 8.1L flywheel is a little over a hundred bucks at the GM stealer. Might as well just go with a new one. The worse thing I can think of is you may have to use a Silverado HD clutch. I believe the Silverado ZF S-650 and SM465 manual trans still use the same spline count.

I wouldn’t think using a hydraulic or manual linkage would matter as you would be using the SM465 bell housing anyway. I am collecting parts now to convert my 78 K10 to a hydraulic set up when I yank the engine out in a few weeks for my EFI swap.

In hindsight, I wish I had built one of these 8.1’s for my K10 rather than spend the money to EFI my Gen VI 454HO. EFI story linky.... http://67-72chevytrucks.com/vboard/showthread.php?t=263323

Keep us posted man…..
 

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Same problem I was finding. I was also concerned about the clutch. I will know in a couple weeks, once I get started on this. I have the 8.1, with an auto flexplate, a SM 465 with bellhousing (mechanical clutch) a 203 mated to the 465, and a 32 spline 205 I am planning on mating to the 203. I just need to get the flywheel/clutch setup figured out.
I've got my choice of a SM465 manual clutch or a factory hydraulic clutch bellhousing. I'll see if I can get a stock 8.1 flywheel and try bolting stuff together. If it works I'll report back. No idea how long it will take to get the 8.1 flywheel though.

BTW - I've got the same combo going in. Replacing my NP203/D300 with a NP203/NP205 combo. Even with the 32 spline outputs on the D300 I think the torque from the 8.1 will have it begging for mercy. :D
 

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Some initial poking around on some online parts websites leads me to believe we may need to mix and match clutch parts to make this work.

Apparently the stock 8.1L clutch is a 10 spline 1 3/8" input. An SM465 has a 10 spline 1 1/8" input I believe. I haven't been able to check if the pressure plate bolt pattern is the same or not. Assuming it is then we can run a SM465 clutch kit (standard 11" stuff). If it isn't I guess the next step is to try an 8.1L pressure plate with an SM465 clutch disc.

Hmm again assuming the SM465 pressure plate won't bolt up to an 8.1L flywheel I wonder if it's possible to drill and tap the 8.1L flywheel for it?

I'll also need to check the distance from the bellhousing mounting surface to the face of the flywheel on both setups.

Sorry.. Thinking out loud here :emb3:
 

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Discussion Starter #14
I think I am going to get an 8.1 flywheel and try out the older clutch on it. I will let everyone know how it goes.

Larry, I was thinking of putting EFI on a big block I currently have. I bought the complete drop out 8.1 for $2100 with 60K miles on it. I just could not justify not doing it.

FWIW, I have a 8.1 in my Dually and I love it. Tons of power and at 130K miles, still going strong.

Supersize, that looks like a nice setup. I may look into that. Never really thought about just making a bracket like you did. I did not want to deal with the goofy plumbing on a stock slave cylinder, but your looks nice and simple.

See, it helps to think out loud.:)
 

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I found a picture of an 8.1L flywheel. It does look quite different from my 454HO flywheel in the center area.

I bet you guys are right…you will need to mix and match clutch disks to pressure plates.

Aside from figuring out the clutch dealeo, what your all of your plans for wiring harnesses and ECM’s. I am pretty fond of the MEFI-4 controllers over stock OBDII controllers from GM trucks, etc. The MEFI-4 controllers are non-emissions controlled and have a lot more freedom for custom calibrations. The MEFI controllers are usually found in marine applications and with GM Performance Parts crate engines (Ramjet, etc) The wiring is easier to deal with and less complex. A lot cleaner looking too over dealing with a take out harness from a Silverado.

The hot ticket on an 8.1 is to use a marine manual throttle body so you can use a manual throttle cable, custom harness from Arizona Speed and Marine and run it on a MEFI-4 controller. A new MEFI-5 controller was introduced last year but I am not all that up to speed on benefits of that controller.






14096987 Gen. V & Gen VI 1991 through current year,
14" diameter.
3.58" Crank flange bolt pattern.
For 11" clutch.
168 Gear teeth.
 

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I found a picture of an 8.1L flywheel. It does look quite different from my 454HO flywheel in the center area.
Weren't the 454's externally balanced? Thats probably the difference.

Aside from figuring out the clutch dealeo, what your all of your plans for wiring harnesses and ECM’s.
I think the stock stuff is good enough for me. I'm going to rework the stock harness and use as much of the factory stuff as possible. Partly to keep costs down and partly to make diagnosing problems easier. I may get the ECM reflashed with a hotter setup but I'll wait until it's in and running (mostly because I want to see how much difference it makes). I'm also going to try and stick with the factory drive-by-wire setup.

I've swapped a few TBI motors and a Vortec V6 before so I'm not too worried about the wiring. I've also got a factory manual for an '02 Chev Truck (my daily driver is an '02 Duramax).

The hot ticket on an 8.1 is to use a marine manual throttle body so you can use a manual throttle cable, custom harness from Arizona Speed and Marine and run it on a MEFI-4 controller. A new MEFI-5 controller was introduced last year but I am not all that up to speed on benefits of that controller.
Any hp/torque specs from that combo? What are the perks besides easier to calibrate and install (not that those aren't reasons enough to use it).
 

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Yeah, the 454 is externally balanced and the 8.1 is definitely internally balanced. The main part that looks different to me is the flat clutch plate surface. The 454 looks to have a bigger surface area.

Real quickly, then I need to get back to work….

There are a couple down sides of using a production vehicle OBDII (PCM 32) controller. One being the fact that it is just that….. OBDII, and you will need a special scan tool to read codes, etc. OBDII can be very temperamental. You will also need to use the Silverado TAC module and APP sensor (electronic throttle pedal) to make the drive by wire system work. That is a lot of harness to mess with inside the cab. Another downside is in 2002 or 2003 GM Powertrain changed the oxygen sensor arrangement from 2 sensors to 4. The later system places post oxygen sensors after the cats. If that is how your current PCM 32 controller is set up you will need to run cats and that sucks. Hope that is not what you guys have. The stock PCM 32 controller batch fires the injectors running on mass air flow calculations. That is fine except you have a mass air flow sensor to mount somewhere between the air intake and throttle body.

The MEFI-4 controller requires no cat converters, can use manual throttle body, batch fires the injectors on speed density calculations, which requires no mass air flow sensor. The MEFI-4 controller is also very small (about the size of two packs of cigarettes) and can be mounted right on the engine. MEFI's can be calibrated to run anything from an Ecotech 4 popper to a shag nasty 572. The wiring harness for a MEFI-4 is very unintrusive and easy to hide and route. The MEFI controller basically runs OBDI where the codes can be pulled by flash codes with a very inexpensive GM Performance Parts tool or any old OBDI scanner. The down side to the MEFI-4 is the $$$ of the controller and harness. I got my Ramjet 502 harness and MEFI-4 for $425 but usually the controller alone goes for $500 not including custom calibrations that usually cost around $300.

HP gains of MEFI-4…I don’t know for sure, but the stock 8.1L was advertised at 340 HP and 455 lbs ft of torque. I have heard internet rumors and claims from AZ Speed and Marine that a stock 8.1 running on a MEFI controller crank out well over 400 HP.

The reasons above is why I chose to go with a Ramjet 502 harness on my 454 and use the MEFI-4 controller vs a GM production vehicle PCM 32 controller. You guys got me wishing I would have sunk the money into building one of my 8.1’s now instead of this 454HO. Dang it… At least with the 454HO I will not need to use an electric fuel pump. That is a bonus right there.
 

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Discussion Starter #18
Larry,

I may look into the MEFI 4 stuff, but I m trying to do this on a budget. I appreciate your thoughts though. I have the harness and stock ecm, MAF, gas pedal and control box, everything. Couldn't beat the price.

I was planning on running O2 sims for the rear oxygen sensors, they worked well on my TA with no cats. I also have a marine throttle body for an 8.1. I have not gotten around to seeing if it will work or not. I work on boats for a living and am just slammed with winterization work right now. January will be here soon though and then I can just play with my projects for about 6 weeks.

I really would like to get away from the electronic gas pedal. It is okay in my dually, but not very precise.

As far as tuning the 8.1 with a stock ecm, you can use LS1 edit, that was my plan. Used to use it on my supercharged TA and it is not too bad to work with. I am going to look at the MEFI 4 stuff. I have a 8.1 marine harness and would just need an ECM. Do you know of any tuning software for the MEFI 4?

I ordered the 8.1 flywheel today. Maybe I can check it out sometime soon to see about which clutch setup to use.

I'll keep you posted.
 

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I forgot I saw that you work on boats. I am surprised your marine experience hasn’t sealed the deal for you to go with MEFI.

I don’t have any experience with any aftermarket tuning software for the MEFI but I did stumble across this company a while back. They also have a lot if helpful MEFI links on their page as well.

http://www.obd2allinone.com/sc/toplevel.asp?cat=32

How much was the fine for the 8.1 flywheel?
 

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I forgot I saw that you work on boats. I am surprised your marine experience hasn’t sealed the deal for you to go with MEFI.

I don’t have any experience with any aftermarket tuning software for the MEFI but I did stumble across this company a while back. They also have a lot if helpful MEFI links on their page as well.

http://www.obd2allinone.com/sc/toplevel.asp?cat=32

How much was the fine for the 8.1 flywheel?
Maybe that's why I don't have MEFI.:)

The 8.1s stall a lot idling at 650 rpm. You can't order a special tune from Mercruiser and I have not really looked into tuning them any further. I work mainly on big cruising boats, not go fast boats.

The MEFI is definately cleaner as far as wiring goes, but 8.1s in most boats have the rev limiter come in at 4800.

The GM factory ecm is actually pretty good and has lots of tuneability if you have LS1 edit. Wiring is ugly though.
 
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