KZ810 or GPZ 810 specs or dyno results...

Hi,

Has anybody had done a dyno run with a KZ 810 or GPZ 810 (810cc bore & piston kit)?

I'm getting it installed in my GPZ 750 and i'm curious what the new specs would be....

How much torque and hp approx. it will have more?

btw, stock gpz cams (all the head is stock), no porting but a 4 into 1 free flow pipe.

Thank you very much!

best regards,
laurent

It's not the size that matters, but how much air you can get atop of those pistons. Headwork will produce the greatest amount of results. If you are only increasing the displacement you can figure that your HP gain will be about 90% of the % of displacement increase. so about 5-7HP increase. You can triple that with good headwork and a good cam.

Kz810 -82, stock head, keihin cv34 carbs, gpz cams=> 75rwhp.

90 rwhp in race tune: 12:1 CR, 29mm Keihin's, mildly cleaned ports, full open pipe.

According to cycle magazine from 83' stock was 68 rwhp BTW.

TG

Those are nice engine power gain.

Btw turboguzzi how do you calculate the real compression ratio for an engine ?

have a nice day!

laurent

ELCouz wrote: Those are nice engine power gain.

Btw turboguzzi how do you calculate the real compression ratio for an engine ?

have a nice day!

laurent

I suppose that depends on what you mean by "real" compression ratio. Typically, it is merely the ratio of the measured volume of the cylinder + combustion chamber at bottom dead center divided by the volume at top dead center. If you want to get fancier, then valve timing will need to be considered. If you want to talk about actual compression, I suppose one could divide peak measured cylinder pressure (using a compression gauge) by atmospheric pressure.

Cranking pressure will mean a lot more as cam/valve selection and adjustment will affect this greatly. TG - do you have a cranking PSI number ( or EU equivelant :S ) for your cylinders?

Sorry guys, disagree on cranking pressure meaning a lot more simply because at cranking speeds the charge inertia effects are non existing.

or in other words, agree that cam timing will change trapped volume but same could be said about cranking speed... You'll get high trapped volume (as well as highest "real CR") at the peak of torque rpm, say 9000 rpm, so cant see how cranking a motor with the starter at 200 rpm can be relevant. And i dont even have a e-starter in my bike, i use rollers...so no psi numbers and it doesnt interest me either.

all i care for is if in hard race conditions, i do get pinging or not.

so guys, lets not confuse this Elcouz guy who's just finding his way around.... the only reasonable starting point is therefore calculated CR, i.e. measured combustion chamber volume + displacement divided by CC volume.

in every book, spec sheet, technical analysis that's the number you'll see. there is no way to calculate "real" CR as a function of valve timing or psi at cranking speeds, as far as i know.

TG

Thank you for these replies guys!

From what I've learned ... CR is just a marketing thing there is no real way to know it.

Maybe if you can tap in the head , put a pressure sensor , keep the engine hot and make the crankshaft spin externally at 9000 rpm that could give you a guess...

But then you have the fuel issue, i guess that fuel/air mixture change it's compressibility so running the engine with air only would be inaccurate....

In short, forget about CR !


regards,
laurent

dont agree with that either

CR is actually very important as it is one of most crucial parameters for efficiency, i.e. higher CR = higher power from the same X amount of fuel.

that's why you seek the highest possibile CR you can live with in a tuned engine, it will give more power.

What ratio is "OK to live with" in terms of CR is an open discussion and depends also on fuel available to you. Here in Italy, finding 98 octane at a station is quite easy, so living with a 10.5:1 or even 11:1 air cooled street motor is doable. If what you can get at the pump is only 92, then these numbers will be lower.

For my race motors with 12:1 - 13:1 i use 98 pump gas + octane additives that take it to around 100-102 octane

Sorry to ask you another question... you just woke up my curiosity again ! damn it

so living with a 10.5:1 or even 11:1 air cooled street motor is doable

Does it means that air cooled engines are more prone to detonation (pinging) than water cooled ones ?


have a nice day!

laurent

Yes, mostly because of the limited ability to cool. Overheating an air cooled motor *can* be easier to do than a water cooled engine that has a near-constant flow (or regulated by thermostat) of coolant removing heat from the engine combustion area.

This and combustion chamber design, electronic fuel injection, and other improvements are what allow modern bikes to run 11:1 and higher compression ratios without danger of detonation.