gsxr 750 valvetrain

[manden]

hey guys

 

how did suzuki make the 750 reliable with the 13.5 rev limit? the 2 ive had never skipped a beat? i now have an 1100 with shims head that im going to install nice cams in over the winter.

 

thanks

[Gixer1460]

Short stroke oversquare engines will rev - the 1100 comparatively is long stroke............in 1100 terms. The internals of a 750 weigh considerably less which helps! 

[manden]

it was more if there was any difference in the oiling or or pressures to keep it reliable. my limit is now at 11.950 rpm and i plan to raise it to 13.500 if its safe to do so

[dupersunc]

13500 on an 1100?

[manden]

the cam grinder said they where good to 14000, and the 750 ive had ran 13.500 so i figured that it would be the safe limit. i have busa rods and modern light weight spitons in, so it should be ok

[manden]

i hope

[manden]

slabside 1100 with a built 78mm bore motor

[dupersunc]

So some calcs on piston speed. not that the valves will flow enough air to produce power at that rpm.

[dupersunc]

13500 rpm on a 58mm stroke, Gives a mean Piston speed of 13.1 m/s. basically the same as a Motogp bike.

Most production super bike engines have a mean piston speed of 10 m/s at max rpm.

Good luck.

[Oilyspanner]

If you're using a standard tacho they lie crazily, especially higher up - if you do a dyno run, or fit a good digital tacho, you'll see a big difference between real revs and those indicated on the standard unit (over 1000 revs).  The standard cranks don't like to be over revved, even specially prepped ones crack through when asked to rev much beyond 11000 revs on a regular basis.

These engines were raced a lot in the past and still are in classic classes, these engine's strengths and weaknesses are known - head design, crank strength and cooling will prevent what you're proposing. Modern engines are very different in design, port design is very different - there's loads to consider. Cams have to work as part of a package, you have to know the abilities of the other parts in order to design a cam that gets the best out of what you've got.

I don't want to pee on your bonfire, but doing what you're proposing will just end up as a liability, engine failure isn't good... expensive and sometimes painful yes !

[canamant]

5200 feet per minute mean piston speed will end in tears. That, plus the weight of the 100 piston compared to the 750 one will give the rod a really hard time at the top of the exhaust stroke.  One thing I have noted is that the short stroke 750s might not rev as hard as the tacho suggests.  I've run longstroke 750 race bikes on standard ignition systems  to the revlimiter using 11000 12000 and 13000 rpm tachos and they all passed the redline before the revlimiter cut in. 

 

[Oilyspanner]

Our engines have wide angled valves, unlike the latest stuff, this compromises chamber shape and piston crown shape, flatter is better  - they use this to good advantage and run tight clearances . Modern heads are downdraught to help with cylinder filling, it also allows the whole valve circumference to be used, something that is much harder on  a pretty horizontal inlet port. The cranks on modern stuff are much more compact and all components are reduced in weight...… you get the idea, there is a' BUT' though.... unlike modern stuff our old engines can be increased in capacity by levels far beyond hyper revving rockets - so the best way is to make the most of what you've got, or what can be more easily achieved. Our engines can make big torque and can be very entertaining on roads, even tracks -  our bikes are like a big boned lass, they won't be good at marathons, but they're powerful over the shorter distances and have big ……..overhead cams ! (always nice)

I'm pretty sure old GSXRs used an over reading tacho as part of the racy image thing Canamant !

[canamant]

I agree !  gear train ratios are similar on both engines as is final drive.  Wheel size accounts for 4 or 5% so the top speed should have been 15% higher on short strokes.  

 

Edited September 11, 2018 by canamant
clarity

[manden]

On 9/9/2018 at 10:39 PM, Oilyspanner said:

If you're using a standard tacho they lie crazily, especially higher up - if you do a dyno run, or fit a good digital tacho, you'll see a big difference between real revs and those indicated on the standard unit (over 1000 revs).  The standard cranks don't like to be over revved, even specially prepped ones crack through when asked to rev much beyond 11000 revs on a regular basis.

These engines were raced a lot in the past and still are in classic classes, these engine's strengths and weaknesses are known - head design, crank strength and cooling will prevent what you're proposing. Modern engines are very different in design, port design is very different - there's loads to consider. Cams have to work as part of a package, you have to know the abilities of the other parts in order to design a cam that gets the best out of what you've got.

I don't want to pee on your bonfire, but doing what you're proposing will just end up as a liability, engine failure isn't good... expensive and sometimes painful yes !

Thanks for your reply m8. It's apreciated

[manden]

On 9/11/2018 at 5:11 PM, Oilyspanner said:

Our engines have wide angled valves, unlike the latest stuff, this compromises chamber shape and piston crown shape, flatter is better  - they use this to good advantage and run tight clearances . Modern heads are downdraught to help with cylinder filling, it also allows the whole valve circumference to be used, something that is much harder on  a pretty horizontal inlet port. The cranks on modern stuff are much more compact and all components are reduced in weight...… you get the idea, there is a' BUT' though.... unlike modern stuff our old engines can be increased in capacity by levels far beyond hyper revving rockets - so the best way is to make the most of what you've got, or what can be more easily achieved. Our engines can make big torque and can be very entertaining on roads, even tracks -  our bikes are like a big boned lass, they won't be good at marathons, but they're powerful over the shorter distances and have big ……..overhead cams ! (always nice)

I'm pretty sure old GSXRs used an over reading tacho as part of the racy image thing Canamant !

Anyone wanna trade an 1500cc engine for race cams?