OW31 Top End

[JR]

OK All, I do have 2 rd400 complete engines and 2 r5 engines. One of the r5's is setup as a real TR3 top end with 34mm mikuni's, TR3 CDI, and factory chambers. The rules at the drag strip state that motorcycles must use motorcycle engines. Technically, a Banshee engine is a quad engine. Not sure which way to go A/C or L/C?

[m in sc]

id go aircooled 400. simpler. no chance of blowing coolant all over the track either. also longer stroke = more torque

[teazer]

Banshee is just an RZ350 without powervalves and with different gear ratios, so I wouldn't worry too much about that, but you already have RD400 cores to work with, so it seems to me that's the logical approach.

Now work out how much HP you want and if the RD400 cylinders will get you there or if the TZ750 top end can be made to work for your application with a spacer plate.  Both approaches will require a fair amount of time on the porting bench, so start calculating.

[Jspooner]

I'd go water cooled. I'd take your R5 cases and put one of your RD400 transmissions in it and then I'd port the shit out of that OW31 cylinder you mentioned, get some giant carbs like I mentioned before and have some pipes built that give you the power delivery you need for drag racing. The reason I'd use the R5 cases is because that TZ cylinder will bolt right on and no rod or stroke change is needed and no spacer plate needed. Blaster reed cages fit the TZ cylinders perfectly.

[JR]

So, one of the rd400 engines that I have came all apart when I purchased a complete rd400 barn find with that extra engine. The parts are all there, but the crank has a bad rod bearing. Assuming that the crank needs rebuilt,
If 110mm rods are used instead of 115mm rods, could we then use the OW31 top end without a spacer?

[m in sc]

wont the pistons hit the crank? also the different stoke? why not just either use the other r5 bottom if you insist on using that top end?

[Jspooner]

So, one of the rd400 engines that I have came all apart when I purchased a complete rd400 barn find with that extra engine. The parts are all there, but the crank has a bad rod bearing. Assuming that the crank needs rebuilt,
If 110mm rods are used instead of 115mm rods, could we then use the OW31 top end without a spacer?

The 400 crank still has a different stroke regardless of rod length. Why not use the R5 bottom end? I'm sure the 400 bottom end could be made to work with the correct spacer plate, porting changes, etc, but why? It works perfectly on an air cooled 350 bottom end. It works even better on an LC bottom end because then you have the built in water pump you don't have to think about.

[John Ritter]

JR, last year when we discussed this if I remember correctly you were adamant about using the R5 bottom and exactly 410cc and finishing in 2nd place was out of the question, this required bore/stroke/rod changes, dyno time, crank balancing etc making for a costly build. Now that I see you are allowing a 400 into the mix a much more logical build is possible, by the way, do not short rod the 400, go 120 or maybe 122 to 125. You are running in the dirt and a short rod might cause wheel spin, you need to hook up right out of the hole. My first thoughts without studying it would be 2R9 cylinders @ 64.75mm bore, crank build, porting, 40 Lectrons, 6 petal reeds etc.

[JR]

John, I didn't think that you were still interested in building this motor for me. I would be happy to have you do this project! As far as the 2R9 cylinders, I was having problems locating a set for sale last year. Joe

[John Ritter]

Joe, I was only suggesting a possible build combination, I have to pass, I'm finishing up odds and end customer jobs, not taking on anything new. I have several personal projects of my own I'd like to see completed. One is a stroked GT80 for our RD60, a very intense 175 drag engine, revamp the current 175 drag engine for nitrous, reassemble our RD400 land speed engine and dyno build pipes for it, finish the land speed FJ1100 chassis and build a 400 bottom with sleeved and injected R5 with a  Procharger engine and my son reminded me Monday I promised him a 522cc build for our street RD400, I better live to be 100 because at the rate I'm going it will take until then.