decoupe
(deceased)
Google has failed me so I will ask - what is the maximum (redline) for a m90 engine? Same as m30?
Thanks
Thanks
Redline for m90
- Thread starter decoupe
- Start date
I will be very interested to see what the collected wisdom of this forum brings forth as we are considering using an M90 block in my Luigi CSL when we rebuild the motor.
decoupe
(deceased)
Can we get a volume discount for two of them? Just kidding.
I have a m90 block with a b35 head and 284/284 cam EFI and it wants to wind past the 6200 cut off I programmed as a limit.
I have a m90 block with a b35 head and 284/284 cam EFI and it wants to wind past the 6200 cut off I programmed as a limit.
I don't know what the redline is, but in theory it should be lower than a 2.8 and 3.0, and higher than the B32/B33/B35. The first two engines have a short stroke of 80mm, the M90 is 84mm, and the later engines are 86mm.
Honolulu
Well-Known Member
Are you looking for the highest physical rpm without expensive noises, or approaching this from the other direction via a dyno sheet, and building your engine to withstand the forces you'll encounter at a few hundred rpm past peak torque?
Physically: identify the weak link and use it as the limiting factor. Calculate the dynamic forces on the main bearing and rod caps, bolt strength, pistons, rods, valves and springs etc. based on their mass, elasticity and material strength plus a safety factor. Use a higher safety factor for mission critical components and those which one wouldn't/can't find replacements for. I imagine a competent race engine builder would have tools for redline calculation based on the above.
Seat of the pants: compare engines with similar rods, caps, bolts, pistons, etc.
Alternatively, google "calculate engine redline" (which I assume you have done) and all sorts of links come up.
Physically: identify the weak link and use it as the limiting factor. Calculate the dynamic forces on the main bearing and rod caps, bolt strength, pistons, rods, valves and springs etc. based on their mass, elasticity and material strength plus a safety factor. Use a higher safety factor for mission critical components and those which one wouldn't/can't find replacements for. I imagine a competent race engine builder would have tools for redline calculation based on the above.
Seat of the pants: compare engines with similar rods, caps, bolts, pistons, etc.
Alternatively, google "calculate engine redline" (which I assume you have done) and all sorts of links come up.
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BMW M90 redline spec is 6200 rpm +/_ 40, constant speed limit 6000 rpm The M88, on the same bottom end has a 6900rpm redline, 6500 constant speed. I've just started my M90 build.
decoupe
(deceased)
Thank you for this - both Ian and Don.
2275xxx
Well-Known Member
On the 84mm crank the works cars of 1973 were producing 375ps @7800rpm, and the Schnitzer car even 385ps @7900 (but the latter was not reliable at all).
With the appropriate preparation work, you should be able to regularly pull a race M90 to 7200-7300 without reliability issues (and get something like 350ps with loads of torque).
With the proper springs (double) and a good after market set of rocker arms I would go to 7000.
Rocker arms are where you usually get a failure.
After market arms are hard to find and some I saw last year were something like $2k.
I went through a good set of stock arms and reduced their weight and smoothed all the edges and seams where they are the weakest and prone to breaking.
Also used titanium retainers which save weight.
If you knife edge the crank and lighten it and get some non steel rods that are lighter then all this mass reduction makes running at 7000 a lot easier.
I took something like 10 ounces out of my steel rods and used a very accurate scale to weigh each one so they matched. I also had my crank balanced.
I usually don't go over 6500 with my motor but the Webers seem to limit it anyhow.
Rocker arms are where you usually get a failure.
After market arms are hard to find and some I saw last year were something like $2k.
I went through a good set of stock arms and reduced their weight and smoothed all the edges and seams where they are the weakest and prone to breaking.
Also used titanium retainers which save weight.
If you knife edge the crank and lighten it and get some non steel rods that are lighter then all this mass reduction makes running at 7000 a lot easier.
I took something like 10 ounces out of my steel rods and used a very accurate scale to weigh each one so they matched. I also had my crank balanced.
I usually don't go over 6500 with my motor but the Webers seem to limit it anyhow.