Bmw 6 Speed to Ls1
05-15-2011, 09:53 PM
#1
Staging Lane
Thread Starter
Join Date: Feb 2009
Posts: 58
Likes: 0
Received 0 Likes
on
0 Posts
Bmw 6 Speed to Ls1 I'm not sure in which forum I should post this.. conversion or here but I guess it's tranny related!
I want to fit a BMW 6 speed transmission to an LS1 block for a swap. I'm toying with a few different options, etc with pros/cons and wanted some opinons on them. I have a BMW block and auto transmission on hand only atm.
Some specs to start with (which are part of the problems mostly).
Ls1 flywheel diameter : 14in
Bmw flywheel diameter : ~9.5in
So there's 3 options that came to my mind.
1) Use complete BMW flywheel/clutch kit with an adapter plate. Sounds like easiest way... if I can find a spot to fit a starter. Since the diameter is much smaller (and I don't have a block to mock-up) I think it will be "inside" to block almost all around. Could maybe get away with mounting it inverted with little modification to bellhousing and adapter plate. Flywheel would need to be spaced out to make up for adapter plate thickness.
2) Same as option one, but use a custom bellhousing. Could integrated starter in the design and won't need to space flywheel. I'd definitly would like to avoid going that route if possible tho.
3) Use a modified/custom LS1 flywheel and starter, mated with a BMW clutch kit. Since flywheel would be larger than BMW bellhousing opening it would either need a weird adapter plate (and would space out the tranny quite a bit) or a custom bellhousing. No starter issues, no flywheel bolt pattern issue. A huge surface or the flywheel would be going to waste and results in wasted weight/inertie.
I can do all the machining myself for all the options mentionned. An adapter plate would be much easier than a full bellhousing tho.
I'd like to hear your inputs on that... and people who got more experience/a block close how possible would it be to stick a starter on a 9.5in flywheel on the block side on an LS1
I want to fit a BMW 6 speed transmission to an LS1 block for a swap. I'm toying with a few different options, etc with pros/cons and wanted some opinons on them. I have a BMW block and auto transmission on hand only atm.
Some specs to start with (which are part of the problems mostly).
Ls1 flywheel diameter : 14in
Bmw flywheel diameter : ~9.5in
So there's 3 options that came to my mind.
1) Use complete BMW flywheel/clutch kit with an adapter plate. Sounds like easiest way... if I can find a spot to fit a starter. Since the diameter is much smaller (and I don't have a block to mock-up) I think it will be "inside" to block almost all around. Could maybe get away with mounting it inverted with little modification to bellhousing and adapter plate. Flywheel would need to be spaced out to make up for adapter plate thickness.
2) Same as option one, but use a custom bellhousing. Could integrated starter in the design and won't need to space flywheel. I'd definitly would like to avoid going that route if possible tho.
3) Use a modified/custom LS1 flywheel and starter, mated with a BMW clutch kit. Since flywheel would be larger than BMW bellhousing opening it would either need a weird adapter plate (and would space out the tranny quite a bit) or a custom bellhousing. No starter issues, no flywheel bolt pattern issue. A huge surface or the flywheel would be going to waste and results in wasted weight/inertie.
I can do all the machining myself for all the options mentionned. An adapter plate would be much easier than a full bellhousing tho.
I'd like to hear your inputs on that... and people who got more experience/a block close how possible would it be to stick a starter on a 9.5in flywheel on the block side on an LS1
05-15-2011, 10:43 PM
#2
Before getting too far into a project like this, you should make sure the drivetrain gear ratios are well suited to the engine's powerband. BMW like many euro brands goes for a lower (2.xx) differential ratio and less of an overdrive ratio (0.8x) whereas GM as you know usually has a higher diff. ratio and more OD. You may have thought this through already, but a poorly geared car is an inefficient and less fun to drive car. /soapbox
With a swap like this, you should do a cost analysis before doing it too. A good T56 is not cheap, but if you put hours of your own time and have to buy custom parts every time you replace the clutch, you've destroyed the purpose of the swap. (I have a "push" clutch in front of an LT1 T56 & bellhousing; my parts are cheaper and can be bought anywhere.)
That said, keep it simple. You haven't addressed all dimensions of the transmission and related bellhousings yet. The BMW trans. input shaft might be long enough to make the swap simple and it might be short enough to make the swap a nightmare, given the adapter plate you plan on.
In general,
If the BMW input is long enough, your simplest swap might be LS1 block/flywheel/clutch/starter/bellhousing and adapt the bellhousing to the BMW trans. There are two production pilot bearing/bushing depths to choose from and a few extended pilot bushing options as well. Machine the pilot of the input or bushing to match, obviously.
A shop that re-builds clutches can change the disc hub to another. Usually, it's one that works with big truck brake and clutch relining. This is another critical area where the input shaft spline location matters.
I don't know of a starter where the pinion is that far inboard relative to the main starter body so that's probably not a great direction to go with this swap. As well, a 9.5 clutch probably won't offer legitimate performance or cost gains.
Based on your post, you have a lot more measuring and documentation to do.
With a swap like this, you should do a cost analysis before doing it too. A good T56 is not cheap, but if you put hours of your own time and have to buy custom parts every time you replace the clutch, you've destroyed the purpose of the swap. (I have a "push" clutch in front of an LT1 T56 & bellhousing; my parts are cheaper and can be bought anywhere.)
That said, keep it simple. You haven't addressed all dimensions of the transmission and related bellhousings yet. The BMW trans. input shaft might be long enough to make the swap simple and it might be short enough to make the swap a nightmare, given the adapter plate you plan on.
In general,
If the BMW input is long enough, your simplest swap might be LS1 block/flywheel/clutch/starter/bellhousing and adapt the bellhousing to the BMW trans. There are two production pilot bearing/bushing depths to choose from and a few extended pilot bushing options as well. Machine the pilot of the input or bushing to match, obviously.
A shop that re-builds clutches can change the disc hub to another. Usually, it's one that works with big truck brake and clutch relining. This is another critical area where the input shaft spline location matters.
I don't know of a starter where the pinion is that far inboard relative to the main starter body so that's probably not a great direction to go with this swap. As well, a 9.5 clutch probably won't offer legitimate performance or cost gains.
Based on your post, you have a lot more measuring and documentation to do.
05-16-2011, 07:01 AM
#3
Staging Lane
Thread Starter
Join Date: Feb 2009
Posts: 58
Likes: 0
Received 0 Likes
on
0 Posts
Actually the bmw transmission is perfectly geared for my application (track car) compared to a to long geared T56. It's the only reason I'm considering all this stuff!
I know I need more info to get everything working, but I'm brainstorming at the moment and I don't want to buy parts to soon.
Thank for your input just reminded me I can use the T56 bellhousing to. That's the kind of stuff I'm looking for.. ideas and possibilities.
I know I need more info to get everything working, but I'm brainstorming at the moment and I don't want to buy parts to soon.
Thank for your input just reminded me I can use the T56 bellhousing to. That's the kind of stuff I'm looking for.. ideas and possibilities.
05-16-2011, 08:54 AM
#4
I would probably use the T56 cable clutch bellhousing, LS series flywheel, and adapter plate AFTER the bellhousing. Then you'd just need to set depth of the BMW input shaft, re-spline the LS series clutch for the BMW spline count, and probably install a custom pilot bearing. This guy has a pretty sweet cable setup (using a Cobra T56 that could be made to work with any transmission, really.
05-16-2011, 09:39 PM
#5
Staging Lane
Thread Starter
Join Date: Feb 2009
Posts: 58
Likes: 0
Received 0 Likes
on
0 Posts
After looking at several flywheel setup and mixing ideas with bellhousings and stuff I really think a custom flywheel would be easier and solve alot of problems with this setup. Use a ring gear that fits LS1, machine a custom center to fit BMW off the shelf clutch kit, use T56 bellhousing and adapter plate. Every parts stays off the shelf or in house produced.
The smaller clutch may not give any "advantages" but it's lighter, gets the job done and is already fitting the input shaft. I'd rather mess with what I know (machining) than with clutch disks and such which I'm not as much familiar with.
Thanks for inputs though it made me realize a few things! I think to get more stuff figured out now I will need parts in hands.
The smaller clutch may not give any "advantages" but it's lighter, gets the job done and is already fitting the input shaft. I'd rather mess with what I know (machining) than with clutch disks and such which I'm not as much familiar with.
Thanks for inputs though it made me realize a few things! I think to get more stuff figured out now I will need parts in hands.
05-21-2011, 04:54 PM
#7
Staging Lane
Thread Starter
Join Date: Feb 2009
Posts: 58
Likes: 0
Received 0 Likes
on
0 Posts
Well I guess I won't need all that problem anymore! I just found about a sweet setup using a TKO 600 Road Race and reverse starter setup with a 5.5" 3 disc clutch! TKO ratio are spot on.. kinda like a 5 speed bmw transmission that I wanted to use but couldnt (to weak). It's barely more expensive and saves me tons of trouble!
