building ahrma middleweight superbike--need advice

why r u going back the the 650 head? r the 750 chambers bigger?

I'm a little lazy.took a look at the 750 intake and exhaust runners why port a 650 when its already done.I went backwards on compression.Don't know what a 750 cc's at but I'll bet its bigger.Get out the die grinder let the alum fly.p.s homemade head gskt..022 thick

I'm he same way and had the exact same thought. My attempts to cc the head without a plate seemed pretty similar, but I guess I better get ahold of that plate and double check things. Might change my maths some.

I use to play with the 750/650 stuff a few yrs ago and we found a little more power in the 650 head with 750 valves than by just using a 750 head, both being ported. Quench seem to be a little different. I believe the 750 turbo head is alot like the 650 head in chamber design but already has the bigger valves.

Les

Thanks, guys. Guess I'll start saving to have the 650 head done up right in the future. Will have to compensate for the 750 head in the interim.

looks good indeed RS!

Racing for my 3rd year, and have learned a lot in the changes I've done to my '85 GPz550, and I'm still learning, and modifying.

I have measured and scaled the stock 2.50 18" rear wheel and a 4.50 2006-2010 EX650 Rear Wheel, and both weigh the same. Front going from a stock 2.15 to a 3.50 17" EX650, and still scales about the same.

Do the math on the tires. AM23 130/650-18 (24.65") and 160/60-17(24.55") and they are just about the same height, so no rear difference in ride height. 17" will give you more options, but the Avons are a great for DOT Race Tires. The Avon DOT Race Tires on my bike last more than a full season (7 race weekends a season).

You can be fast in the corners, but remember the finish line is always on a long straight, so I have found having more power up top will keep those from coming around you on the last lap. You still need to be fast in the corners. All of this in time. If you can't race a lot of rounds, do track days in between, and get some coaching too.

Build the bike according to the rules and if it doesn't say you can do it, don't assume you can.

AHRMA Middleweight has a CC Limit? If so, punch out the stock 553cc to 615cc, and go to town on everything else. I have been told by many who raced a GPz550 that these faster than the GPz750. There is a guy racing in VRRA, Paul Brubaker, that makes his own +1mm high compression 550 pistons, because VRRA has a +1mm piston limit, and is getting close to the 80 rear wheel hp from it. I am only at 66/39.

Not deterring you from the 650 of choice, but you have a lot of options out there to start with.

I look forward to reading more about your build.