89 Gsxr 750 Roadrace Engine Build Advice

[Wcrracing221]

Hi all,

Preparing to build a new motor for the race bike.  2 hour endurance plus 4 sprint races 20 and 30 minutes each per weekend.

looking for 130 hp on premium pump gas and reliable.

Bike has 2 aftermarket oil coolers, dual venting etc.

I have an 89 short stroke and a California 92 longstroke as donor motors.

i cannot use the 92 as it is not legal for my vintage.

The plan is to undercut the gears and do a 771 Wiseco kit which keeps me legal.

Question:  Can I and should I use the bottom of the long stroke and the jugs head etc from the short stroke to make a frankenmotor?

In theory this could increase the volume and open options for 4 into 1 exhaust over the rarer 4 into 2 into 1.

Comments and advice appreciated.

 

[riversbikes]

Hey fellow hoser, where are you located.  I can offer no other advice other than typical polite Canadian encouragement.

Thanks, and sorry.

[Wcrracing221]

Sudbury, Ont.  Thanks Eh!

[Swiss Toni]

Hey Bud! Welcome to OSS. That bike is the business!!! 

[Oilyspanner]

Hi - the two types of 750 engine have different sized big ends and small ends, so you can't swap cranks/rods/pistons. The short stroke heads fits 1052/1127/1157  block, but cam chain tunnel is wrong for the long stroke 750. Perhaps with machining, specially made rods etc you can put the parts together, but as standard they won't match up. Maybe someone has done the alterations and will see your post, I haven't heard anything though - good luck though.

[Wcrracing221]

Read the frankenstein posts and although can be done, sounds like the work does not support the benefits.

I’m going to build the short stroke and if I need to change the oil pan and pickups, I can do that.

The new motor will have Mikuni RS38SS carbs with matched ports and velocity stacks same as the current engine.

Any other tricks?

[Kurf]

Nice bike! And welcome

[dupersunc]

I'd go long stroke, the 89-92 bottom ends are the same. not sure what the cut off date is for you.  I'd also go 4-2-1 if you can, gives you a fatter torque curve.

130bhp, will mean lots of compression, and lots of heat.   Go big on the oil coolers, then bigger, and pay attention to the ducting.

Pay attention to the crank case breathing too.

 

Cool Bike

Edited November 9, 2018 by dupersunc

[Lachie04]

I have a 816 short longstroke motor have only done about 800k on it so far and taking it somewhat easy as was all blueprinted and just run back in for road use. was not a lot of work you have to bore the small end out to 19mm make or buy a spacing plate we used 5mm 6061 swap the cam sprockets over for the hyvo chain (we took a link out) I don't know if you'd get 130 a guy in the states reckoned he got 128 doesn't feel like it to me but nice and torquey I have a custom built 421 the curve is nice and smooth exhaust cam at 106 inlt 104 and still pulling hard at 1150 rpm very happy with motor in about a month I'm going to through it on the dyno will be interested to see what it turns note this uses the longstroke case and gearbox ss the main bearings are smaller bigger (cant remember)than the short stroke motor so not able to swap crank in

Edited November 9, 2018 by Lachie04

[Wcrracing221]

Oil coolers and venting.

[manden]

Mine was a slingshot with an shortstroke engine from Suzuki's Motorsport department in Germany. It had 13.5 comp on the outer cylinders and 12.8 comp on the two center cylinders. A friend of mine had 113hp on the wheel on his slingshot and weighed 10 kg less than me and his was a bit slower than mine. Both had -2 on the front sprocket

[Slabbyruss712]

Watching this as I'm building a longstroke 750 for the earlystocks es, and I'm looking for ideas, 

[FJD]

On 11/10/2018 at 9:24 PM, manden said:

Mine was a slingshot with an shortstroke engine from Suzuki's Motorsport department in Germany. It had 13.5 comp on the outer cylinders and 12.8 comp on the two center cylinders. A friend of mine had 113hp on the wheel on his slingshot and weighed 10 kg less than me and his was a bit slower than mine. Both had -2 on the front sprocket

?? what do you mean  - the engine had different compression ratios on the cylinders ?

 

[dupersunc]

53 minutes ago, FJD said:

?? what do you mean  - the engine had different compression ratios on the cylinders ?

 

Makes sense. The inner cylinders will run hotter, so can only get away with lower compression.

[FJD]

i´m no engine building expert - but that sounds nonsens to me !

on a multi cyclinder engine, you try to have equal power output of each cylinder, which you will not have if running different compresion ratios.

The heat is controlled through carb jetting

[dupersunc]

2 hours ago, FJD said:

i´m no engine building expert - but that sounds nonsens to me !

on a multi cyclinder engine, you try to have equal power output of each cylinder, which you will not have if running different compresion ratios.

The heat is controlled through carb jetting

I'm guess Suzuki had an Idea of what they were doing.

Yes you can cool the cylinders by running rich, but they won't produce the power.  

If you can extra power out of the outer 2 cylinders by bumping the cr up on them a couple more points why wouldn't you?

[jonny1bump]

Im sure I remember way back it was proved curved cooler works better then straight cooler.

Running different compression ratios crazy idea. All sorts of experiments are carried out on track does not mean it's good idea.