The idea that there is some "magic" bore/stroke may actually have some validity, but probably not as applied to a typical SBC. The case of a displacement limited racing class is where it might apply. Something like F1, where displacement is limited and there are megabucks available to truly optimize EVERYTHING about the engine within the rules of the class. Even basic technical info such as B/S numbers aren't readily available, but the specs I have seen do indicate that they are all pretty close. The rules mandate a V-10, and all of the engines except the Renault have 72 degree V. The Renault is 110 degrees. They end up very, very similar in basic architecture.

It would be with engines that highly developed that things like conecting rod length and other subtleties make a measurable difference. It's nutty to spend much time discussing things like that for a street or street/strip motor. Small differences are just not going to matter. The power advantage is going to go to the engine with more displacement, better heads and induction system, better exhaust, and an optimized cam.

Rich

 

well, so far anybody where i live i have raced and beat. Mustang with 406, and was built beat him. 88 pickup 383 built, beat him too. Im not tring to brag but the 377 is just a motor that is underestimated.

 

There is no "magic number" as you said, but diaplacement per cylinder and operating rpm and all its limitations may push a design toward certain numbers.

Late in 2003 BMW published some performance specs for their 2003 F1 engine. From these, if they were true, some interesting dimensional specs can be calculated.

BMW said 19,200 max rpm, 10,000g max piston acceleration and 25 m/s (4921 ft/min) average piston speed. With some calculation a stroke of 39.065 mm (1.538 in.) results, and a bore of 98.75 mm (3.888 in.) gives about 3.0L. The piston gs allow one to calculate rod length also, which I got to be about 80.25 mm (3.159 in.), and a rod/stroke ratio of 2.05. None of these numbers seemed out of line with other things I've read, and the relatively sane average piston speed surprised me. My guess is that the rod was about the shortest they could fit into an engine with that stroke and large piston diameter.I'll bet it's titanium and VERY light!

V-angles of F1 engines seem very strange to me. Renault gave up the wide angle in 2004, I believe, and 72 to maybe 90 degrees is used. Personally I don't care for "odd-fire" v-angles like 90 on a V6 or V10, but that's evidently less important than other things like packaging in F1.



My $.02

 

well i was thinking about this in class today. and can you image how crappy this would make motorsport? engines wouldn't rev, they would just have the same hum. and for spectators hearing that it would get dull. not to mention various teams would be trying to find the max hp/tq at the exact rpm. like making 675.45hp @ 6547.547 rpms
and alot of the smaller teams probably wouldn't be able to afford the changes in research.

 

That avg. piston speed surprises me as well. I have been using 4,500fps for the amateur level drag race and street/stip engines I'm involved with. And these aren't using anything exotic in terms of materials.

Rich

 

About the shortest legal stroke in s 358 Cup engine is 3.25 or maybe 3.27. That gives the same avg. piston speed as the F1 BMW at about 9100 rpm, and we are seeing 9500+ on telemetry. That's approaching 5200 ft/min for an endurance engine. Hey, that's only 5000 piston gs. Piece of cake!

Cup shortblocks see practice, qualifying and the race. That's a lot of revs in anger (10^6 minimum). Next year that will decrease maybe 10-15% in about half the races with Sat qualifying and no happy hour. Won't save much money, IMO.