Balancing the 928 Engine - some surprises
04-25-2005, 10:33 AM
#46
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Greg,
I admire your goal (100 hp per liter) and I wish you well. I've always wanted to try a similar build-up but I'm a little discouraged as I think Sterling has done a very (if not one of the most) thorough jobs on his engine including variable valve timing, decking the block and stroking. I know his Dyno numbers are likely understated but the last time I looked, he was mid 300 RWHP for 6.4 liters.
I know higher RPM will boost the HP numbers but to get to 100 hp per liter normally aspirated would be quite the feat!
I admire your goal (100 hp per liter) and I wish you well. I've always wanted to try a similar build-up but I'm a little discouraged as I think Sterling has done a very (if not one of the most) thorough jobs on his engine including variable valve timing, decking the block and stroking. I know his Dyno numbers are likely understated but the last time I looked, he was mid 300 RWHP for 6.4 liters.
I know higher RPM will boost the HP numbers but to get to 100 hp per liter normally aspirated would be quite the feat!
04-25-2005, 05:28 PM
#47
Correct John, the 100 hp mark is a hard thing to do. You can only try, if I come up short so be it. Yes there are differences between mine and Sterling's, his will have a nicer disposition, mine will be a bit rortier. The revs make the difference. I think you need at least 7200 rpm to make 100 hp per liter and strokers don't like revs. Also I will have solid lifters, for valve control this should be good. Also the dry sump should add some extra power.
Just found some bolts for the rods, this should now solve my problem as far as the bottom end goes. The ARP bolts are good for 215,000 PSI and the standard Porsche ones are only 156,000 PSI So this in association with a little metal removal and cleaning up of the rods and balancing of the rest of the assembly should be o.k for the high revs. I worked out my mass force calculations and they are quite conservative, especially given this isn't a race motor that will be constantly thrashed.
Cheers Greg
Just found some bolts for the rods, this should now solve my problem as far as the bottom end goes. The ARP bolts are good for 215,000 PSI and the standard Porsche ones are only 156,000 PSI So this in association with a little metal removal and cleaning up of the rods and balancing of the rest of the assembly should be o.k for the high revs. I worked out my mass force calculations and they are quite conservative, especially given this isn't a race motor that will be constantly thrashed.
Cheers Greg
04-25-2005, 05:57 PM
#48
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Greg,
not to hijack this thread but I had spoken to a crank expert here a few months ago about grinding the 928 cranks rod journals to accept 1.888 rod bearings. Apparently this size (which is a standard thats been employed in many high performance engines) is all the rage in many circles for the reduction of reciprocating and spinning weight.
I wasn't looking at it from that point of view but from a low cost stroker standpoint, as our cranks could be offset ground to gain around 5mm of additional stroke. I don't know how much weight reduction it buys you but I would expect that it may be substantial as the rod journals, counterweights and rods could all be lighter. It would mean custom rods but at that time, I had looked at machining my own out of 6061 aluminum. Just a thought.
not to hijack this thread but I had spoken to a crank expert here a few months ago about grinding the 928 cranks rod journals to accept 1.888 rod bearings. Apparently this size (which is a standard thats been employed in many high performance engines) is all the rage in many circles for the reduction of reciprocating and spinning weight.
I wasn't looking at it from that point of view but from a low cost stroker standpoint, as our cranks could be offset ground to gain around 5mm of additional stroke. I don't know how much weight reduction it buys you but I would expect that it may be substantial as the rod journals, counterweights and rods could all be lighter. It would mean custom rods but at that time, I had looked at machining my own out of 6061 aluminum. Just a thought.
04-25-2005, 09:15 PM
#49
Hi John when I was going to do my big engine, Oliver racing advised those rods are for racing only. They have a limited life, they suggested the 2 inch ones, which sounded reasonable.
Cheers Greg
Cheers Greg
