Bore, stroke, and rod length

Joe, I seem to remember that Jim Bell experimented many years ago with that line of reasoning. I think he used a 455 block with a modified nail-head crank (big bore/short stroke) to be used in toilet bowl racing. I'll see if I can dig up some info on it.

 

I'm not worried about detenation. It will just be less forgiving if things get a little lean. I'm going the 470 cu in route. When the time comes, you'll know how well it works. :Brow:

 

That bore/stroke ratio is not uncommon in the unlimited classes such as NHRA Pro Stock and and Comp Elim. The last numbers I heard from Pro Stock land was 4.75 +/- bore and 3.62 +/- stroke. It comes out around 499 ci. That's using a 4.900 bore center block. They're turning 10,000 RPM's, and making 1350+ hp. They also have short deck block to keep the rods short.

I think the only thing keeping the new block Buicks from using that type of bore/stroke would be cylinder heads, I don't think even the Stage 4 stuff could feed that motor enough. Your cam specs would need much more duration. PS motors run a 65 or 70 mm cam core, making a much bigger base circle, which allows lobe ramps that would tear up a normal cam core. You're also getting into needing Ti valve springs, valves, etc., and huge pushrods.

I had planned about the same thing as you mentioned, but RPM's cost big $$$. But hey, it's only money :laugh:

Have fun.

 

I just got done reading a drag review article on PS engine set-ups. The story stated that they run a couple of different combo's, based on different tracks and alt. the longest stroke I saw was 4.61 bore with a 3.74 stroke. Refered as a low RPM torque motor peek hp came in at around 8800 and shifted at 9700 :3gears: . The other day I read a tech write-up on the net talking about the different set-up people use below is a cut and paste from that article--------------------------------------------------------------------------------

Posted by T.O.O. on June 14, 1998 at 08:06:56:
In Reply to: T.O.O. or NITRO: Higher RPM's with S/C? posted by body on June 14, 1998 at 00:31:34:

If you want to build an engine that will rev to an unlimited rpm, that's fine, but it really doesn't do you any good after a point because the spring pressures necessary to control valve timing, as well as other internal friction and parasitic losses will rise to a point that there's no torque, and you have to have to have torque and rpm to make hp.
High rpm is the single greatest cause of failure in "performance" engines. My definition of rpm is "Ruins Peoples Motors", and there's not a single program that I've been involved in for the last 30 years where one of the primary goals wasn't to lower the rpm range that the engine operated in.
We've never built an engine to see how high we could make it rev. We already use valve springs that cost $500.00 each, valves that cost $400.00 ea., and that's just a start. A competitive "domestic" normally aspirated ProStock drag racing engine will bring an easy $90,000.00, and it will need a total rebuild after 7 quarter mile runs. these engines are not to be confused with the supercharged fuel burning engines in Top Fuel and Funny Cars. They actually cost a lot less, and they don't turn the rpm either.
From an airflow stand point, if you try to flow enough air through any size orifice, you will finally reach a saturation point. It doesn't matter if the engine is pulling the air in (NA) or a blower is pushing it in, once you reach the "magic number", you're going to use more energy trying to move the air than you'll ever make in power. :Comp:

next part of the article :Smarty:

The bore / stroke combination for this rev. range will use a slightly longer stroke, and smaller bore, at first the first "look". This is where the package height starts affecting everything we do. Since I attempt to run a rod length to stroke ratio of 1.75 - 1, calculating the rod length combined with the compression height(distance from pin C/L to deck), and (.5 x stroke) will yield our block deck height once we settle on the stroke. The combination using 4.6" bore, and 3.75" stroke, with a 6.5" rod, and a piston with a 1.265" compression height will yield a deck height of 9.635"and the rod length to stroke ratio will be 1.73 -1 which is "good". As were looking for a really "fat" torque curve, were going to build another combination for this engine. Number (2) engine , combined will use a 3.80" stroke and a 4.57" bore combined with a 6.57" rod will again provide a rod to stroke ratio of 1.73 -1. In order to place each engines internals under the same deck height, the compression height on #2 will be 1.165" which is "doable".


Higher RPM's with S/C? Pro Stock drag racing engines?

 

Unless you are limited by class rules, why not go with the most cubic inches you can get? No matter the class, the racers always maximize the cubes to the limit and then start fooling with combos to get the best numbers from that engine size.

What was the number of cubes JB thought was possible from this block and a custom crank? If you stuff the biggest crank you can get in there and let the deck decide the rod-length, what rod length an r/s ratio would you have?

Does anybody have a $500 valve spring in their Buick? YIKES!