Stroke rod ratio
Stroke rod ratio
(OP)
I have been asked to build a BMW performance engine (low boost turbocharged) using the M10 block and the crank from the 87mm stroked 2.5 liter M3. This is a little out of the ordinary for me and have been doing some research on the Bimmer engines. With the 135mm M10 rods, the standard r:s ratio is 1.69:1. The 87mm stroker has a r:s ratio of 1.55:1. Ugh!
Using the 144mm M3 rods, the ratio is 1:66:1. Better, but hardly optimum.
I note that the old school M30s had a r:s ratio of 1.57:1 (135mm rods - same as the M10 and 86mm stroke).
Rather than source custom or M3 rods, as this is a budget build up, the owner wants to use M30 pistons and standard rods with the 87mm crank. I'm a little wary. I'd appreciate views.
Using the 144mm M3 rods, the ratio is 1:66:1. Better, but hardly optimum.
I note that the old school M30s had a r:s ratio of 1.57:1 (135mm rods - same as the M10 and 86mm stroke).
Rather than source custom or M3 rods, as this is a budget build up, the owner wants to use M30 pistons and standard rods with the 87mm crank. I'm a little wary. I'd appreciate views.





RE: Stroke rod ratio
RE: Stroke rod ratio
RE: Stroke rod ratio
I believe Top Fuel Dragsters run shorter rod ratios than this and they run very big engines at 8000 rpm at huge boost and up to 6000 hp, but they only last 4 or 5 seconds between top end overhauls and inspection.
I think 1.8 would be ideal for an M3 that needed long term durability at higher rpm's, but 1.55 will still work OK
Regards
pat
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: Stroke rod ratio
Cheers
RE: Stroke rod ratio
RE: Stroke rod ratio
Thread71-86266
Regards
pat
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: Stroke rod ratio
I made the same mistake for quite a while before it was pointed out to me
Regards
pat
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.