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George Bryce: V-Twin vs. 4-Cylinder

Explanation of Horsepower Differences between

these two Pro Stock Motorcycle Engines


Note: This conversation was copied from a Facebook conversation between Star Racing owner George Bryce and one of the team's fans.

The fan's name was omitted for privacy reasons.

Race Fan

Hey George, a curiosity question about the rules and the Suzuki CI limit........ HOW BIG can you make a Suzuki engine and can it safely LIVE at that size? I have been curious about the 107 CI vs the 160 CI on the v twins?

George

We make almost the same power with each. That is why the best Buell and best Suzuki go within .05 hundredths of each other. In order for a big Vtwin to run with a small 4 cylinder you will have to have them come close to the same power output. We make about 3.5 to 3.6 HP per cubic inch with the Suzuki … and that is with a TON of RPM ... 14000.

The 160 cube Vtwin only makes 2.3 or 2.4 HP per cubic inch because there is low RPM, only 9500 and only 2 cylinders to make the crank rotate ... bang, coast, coast, coast, BANG, coast, coast, etc. The inline 4 has 4 cylinders to share the load and to help the crank to rotate with half of the coast time.

The big Vtwin has pushrods, rocker arms and long flexible moving parts. The Suzuki has "cam on valve" short, light parts. Our job is to build both at the same time to see which combo has the best chance to win.

We think 107 and maybe a 110 would be reliable enough to race at max effort.

Race Fan YOU da man! I always wondered what kind of power was at hand for each type of engine. ITS kind of a “big bang VS machine gun” type of HP. I knew the Suzuki's was “wringing the cat’s tail," HOW is the crank bearings (original was roller and you have the same in the PSB engine)? WONDERFUL explanation, I was always curious WHY there was NO Yamaha PSB motorcycles when they HAD the FZ engines, 5 valves and STOCK was a 14,000 rpm, tiny valves 3 intake and 2 exhaust.

WOW roughly 368 HP for a vtwin and 374 for a Suzuki under IDEAL conditions at the crank?
George There is no OTHER engine that has the architecture or "footprint" to make an engine big enough to make 350 hp AND turn enough RPM to run that quick. Just like a V 8, the bore centers on every engine out there are too small to run "with the big dawgs."

We are going to try and make the same with both

As you can "see" they are within 4 or 5 HP, and they both run close to the same E.T. as well.
Race Fan

HEHE I’m a rooting for ya all the way no matter which you run! GOOD to see you working with both! BEST of luck and MO POWER for you!

It is pretty amazing, that close in HP. I’m pleased to be able to ask questions and get a real answer and I’m humbled, TY George!




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