Gsxr 750 91 907cc kit

[Quist]

Planning to do some engine work on the 750 later this year or next year. So better start saving and slowly collecting parts.

Who got experience with an 907cc kit? 

What numbers are we looking at? stock carburators or flat slides?

Any info is welcome.

[p4ddy]

Didn't realise there was a 907 kit, I thought it only went up to 800 and something. Is it cost effective over just 7/11 ??

[Quist]

I don't know if it's cost effective.

My 750 got 112whp now and a 1100 130-145whp. 1100 got a 5 speed, 750 a 6 speed gearbox etc. 750 got a better cilinderhead etc. Each engine got his benefits. Make a 7/11 is an easy job but still don't know the condition of the engine.

The bike got 50000km on it, runs perfect but want to do an overhaul in the future and bore it.

@Rene EFE told me that there was a bored 750 which made big numbers and rode like an idiot. So looking for people with experience with boring a 750.

[Rene EFE]

 @gsxr884 is the man to speak to. 

[Oilyspanner]

The long stroke 750 heads have smaller valves than the 1100s, so aren't better. The 750J/K has the larger valves like the 1100 motor and when fitted to an 1052/1127/1156 engine produces a decent gain in power, most of the gain is due to the smaller combustion chamber/higher compression. The 1127 and 1156 heads aren't bad, with equal compression these heads would be very close to the short stroke head. I don't think you can fit the short stroke head to the long stroke 750 barrels due to valves and proximity to liners. As you will fit different liners for the 907 engine you probably could - I haven't done this on an oil cooled motor.

What I did have was a water cooled GSXR907 WR SP - JE pistons and carried out by Performoto, this was in 1995. The SP version of the WR had 40mm TMR carbs, close ratio gearbox among other things, the close ratio gearbox wasn't necessary on the 907 engine. I had a full race Termignoni exhaust system and was jetted by the mechanic that set-up Paul Denning's 884cc version. When first run in it was brilliant, even with the largest gearbox sprocket fitted it revved out in top and ate ZZR1100s. Revving out as easily as the 750 engine made it break gudgeon pins after a couple thousand miles or so. The compression was gradually reduced and the engine not so eager to rip through the upper mid range. The bike made close to 140 hp - Paul Dennings' , with some head work ,made around 150hp. I sold it after a year and a couple of g.pin failures. The conversion utterly changed the power delivery, if the bike didn't rev to 13500 so easily it would've lasted longer. Even the carbs worked really well, it was so much quicker than my mates' near standard 750WR it was embarrassing (for him !).

[gsxr884]

It depends which 750 you are talking about , its not just valve sizes , it is also port shape, Jack Valentine of V&M reckon'd the 750M had the best port shape of any oil cooled engine , my 2 884 one is an M the other an RK are both bonkers , both on flat slides and full race 4-1s , M never been dyno'd RK last time on was making 125 bhp , cant remember torque figure but it was running rich so there is more to come .I have a 750 WN waiting for a 907 kit and TMRs to be fitted when I get time

 

 

Edited June 12, 2016 by gsxr884

[MeanBean49]

Short stroke motor can be bored to 837cc, pistons are bit like rocking horse poo though, my old race bike 837cc, ported and flowed head and full race exhaust, running on gsxr 36mm carbs, was good for 125bhp but you had to really work the motor hard, didn't have a lot of mid range, cracking fun to ride though.

I prefer big bore 1216 motors every time though, even on track, similar money to do but more go everywhere, but I am lazy and have been corrupted by power.

[Del]

On 21/03/2016 at 7:01 PM, p4ddy said:

Didn't realise there was a 907 kit, I thought it only went up to 800 and something. Is it cost effective over just 7/11 ??

JE do a 955cc kit for the long stroke 600/750's
http://www.jepistons.com/Catalogs/Powersports/Street-Cycle/Suzuki/gsxr_750-90-92.aspx

[AsaNZ]

I have a JE 907 kit fitted to my old '86 slabby. Its a lot of money to spend on an old engine, but there are definitely power gains. 

Its done about 20,000km without a problem. 36mmCVs from the '88 worked much better than the stock flat slides.I did loose the top end rush but it pulls great from about 5k on, like my old TL1000R.

.....if I was to do it again though I would probably do the 7/11, as then there's more scope for upgrades.

[canamant]

It's not just the pistons, it's liners which means 4 additional bore jobs to the block.  My 861s ran be to about 175 quid in boring costs for the block and the liners to be bored and matches to the pistons.