Engine Recommendations Page
Bateman Racing recommendations on basic engine specifications for 160 and 175 based roadracers.
As more and more bikes get built, I have been getting a lot of questions about what modifications are worthwhile. These are my suggestions based on experience and on the development potential of the engines.
There are three basic variants - the 160 engine, the sloper 175 engine and the vertical 175 engine. Vertical and sloper 175 engines have basically the same development potential and can share pretty much all top end parts. You can hotrod any engine of course, but the 175 had way more power potential, so if it's power you're after you should build a 175 variant.
Fowler Formula spec 160 engine
I suggest that if you're building a 160, you keep pretty close to the original "Fowler Formula." The 160 engines are good solid inexpensive engines when built to this spec. That means: Stock 1st through 4th oversize pistons, stock camshaft (degreed), light porting in the head, good valve job, race valve springs, stock carbs. You should go through the transmission, and if you can afford it you should switch to good racing stainless valves, keepers and Ti caps, and Pertronix ignition. You could also consider a lightened clutch basket. You could also consider copper head and base gaskets to help with setting piston to head clearances. That's about it. An engine built to this spec will make about 14 hp and will be a good solid performer that will last for several seasons without issues if cared for.
BRE spec 175 engine
If you're after more power in a solid engine, start with a 175. For a sloper chassis you'll need a sloper bottom end, for a vertical chassis you'll need a vertical bottom end. You should go through the transmission, but it's not as critical as it is in a 160 as they're quite a bit better from stock. Use stock pistons in 1st through 4th oversize, copper head and base gaskets, cylinder head decked 0.020", Kibblewhite stainless valves in stock diameters, race springs, Ti caps and the appropriate keepers, good 3 angle valve jobs, light porting and cleaned/smoothed ports, stock camshaft (degreed), Keihin PE24 carburetors and Pertronix ignition. I would also suggest a lightened clutch basket, Ampco-45 valve guides and valve guide seals if you can afford the extra expense. An engine built to this will make about 18.5hp and will last for at least a full season if cared for. You'll need to freshen it after a season of racing, with a disassembly/inspection and light valve job at least. There are 4 bikes built to this spec now and they are proving to be reliable and fast.
If you want to go beyond these engine specs and build a world beater it will get expensive and you will likely blow things up in the development of your engine. I suggest you contact me for advice and parts suggestions.
Copyright © 2008 Michael Bateman
Email: michael at batemanracing dot com