Calculating rev limit
Calculating rev limit
(OP)
I'm in the process of stroking my 4G63 from 2.0l into approx. 2.2l New billet steel crank, forged steel rods, uprated rod bolts, forged pistons. I'm going from a standard 88mm stroke to 94mm. I've gone to the extent recently of calculating the max force on the rods/rod bolts at TDC exhaust stroke. What I find is that the lighter pistons and rods of my new configuration make up for the increased acceleration due to the increased stroke.
My question is :- assuming a correctly preloaded rod bolt, what is the accepted max. force (% of the bolts yield force) in a high performance application? ie. what is the maximum force that I can allow the bolts to experience (considering cyclic/fatigue loading, temperature expansion, etc.) and hold up?
My question is :- assuming a correctly preloaded rod bolt, what is the accepted max. force (% of the bolts yield force) in a high performance application? ie. what is the maximum force that I can allow the bolts to experience (considering cyclic/fatigue loading, temperature expansion, etc.) and hold up?





RE: Calculating rev limit
You'll have to look up the proof stress yourself (easy enough to find that online, given the bolt grade), and look up or calculate the load-carrying area of the bolts (inside the thread root). Multiply 85% * proof stress * tensile load area to get force per bolt. Subtract from that your bearing crush force per bolt. Compare the force you end up with to the external tensile load applied to the joint, and what you have is a big-end joint separation cover factor. 1.0 is too low. 1.5 is a bit more cozy. Use judgement.
RE: Calculating rev limit
RE: Calculating rev limit
I have always thought that bolt stretch was the most accurate was to preload a bolt, but angle gauge is better than a toque wrench.
Regards
pat pprimmer@acay.com.au
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: Calculating rev limit
RE: Calculating rev limit
RE: Calculating rev limit
The good aftermarket bolts used in many "hot rodded" engines come with the dimples in each end. Most rods have the cap bolt holes all the way through, but as you say, very few people (including myself) bother with the bolt stretch method. If I had doubtful bolt strength, or a few bolt failures it might change my habits though.
Regards
pat pprimmer@acay.com.au
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: Calculating rev limit
Thanks.
RE: Calculating rev limit
RE: Calculating rev limit
Maybe I'm thinking about this wrong. If so, please clarify.
RE: Calculating rev limit
Cheers
Greg Locock
RE: Calculating rev limit
More reliable: 28 m/s (5500 f/s) max piston speed = 8935 RPM.
RE: Calculating rev limit
for a rough cut, which is all you'd probably use for a hand calculation of large-end joint separation, use 215 MPa * bearing shell (backing) thickness * bearing shell backing width * 2
If you want to get fancy, add 0.5 * bearing lining thickness to the backing thickness.