Gk73A Power Output

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Hawktre
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Bike owned: GSXR 400 GK73
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Gk73A Power Output

Post by Hawktre » Sat Jan 14, 2017 12:12 pm

Does anybody know what is the maximum potential power/torque output i could get out of a GK73 engine? Lets assume i can go ballistic on mods, etc....

moforockband
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Re: Gk73A Power Output

Post by moforockband » Sat Jan 14, 2017 2:35 pm

They're reliable as std, but can be fragile when tuned, unless you get it spot on.
Approx 55hp at wheel totally std depending on engine health. 60hp with induction/exhaust. 70hp est with 442 kit and induction/exhaust. All rwhp dynojet readings.

With proper parts and a professional tuner more likely higher.

Edit: remember there is limitations to the valve running gear on the 73 engine, so 15000 rpm should be ceiling revs.
Last edited by moforockband on Sun Apr 19, 2020 11:43 am, edited 1 time in total.

Hawktre
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Re: Gk73A Power Output

Post by Hawktre » Sun Jan 15, 2017 2:15 pm

Thanks for the info... I was thinking about the TTS BIG BORE kit and stroking the crank to give me about 500cc. But will do all the calculations and see what is possible. I am quite adept in Engineering and have played around with a few single cylinder engines with varied success. I have the entire motor stripped at the moment and going throught the tedious task of cleaning components. Then its time to make my decision on the way forward. Will post pics and updates as i progress. Maybe it all ends up been a big blow up and i end up taking on a new hobby!! Hopefully not though... :grin:

moforockband
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Re: Gk73A Power Output

Post by moforockband » Thu Jan 19, 2017 8:42 pm

One thing to note about the tts kit, is that they weigh 15% more than the std Suzuki piston assy. That's 52 grams (someone else's measurements, not mine) across all 4 pots.
If you factor that in to the build you could get around it. But you may have to lower the revs, (maybe use a bandit 400 cdi which has 1000 less revs, but I have never tried this cdi myself).
Do not open up the ports on the gsxr400 as they seem to be quite large as std (29mm). I had my cylinder head ported and triple angled the valve seats professionally and lost 7 hp. I think the air velocity suffered, and did not cram the cylinder with mixture as well as std. The cam timing is also married to the port size, change one and you have to modify the other. With a 442 kit you may be able to open them up slightly and keep the power.

The same power should be possible with std 399cc pistons by having the ports modified professionally, ie welded and re-formed. There is a company on the web who have gains of 10hp on modern 600's using this ideology. I had 78 rwhp out of my zxr400 with 0.5 over pistons and cams and ramair, so 70rwhp should be possible out of the Suzuki with a cam regrind, degreed wheels and modded ports, and keep the 15000 rpm ceiling.

On 400's it's all about keeping the gas speed up, and filling the chamber as much as poss, that's where the power is. Extra cc's help, but a pro tune will cost the same as the TTS kit. :peace:
Last edited by moforockband on Sun Apr 19, 2020 11:46 am, edited 3 times in total.

Hawktre
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Re: Gk73A Power Output

Post by Hawktre » Sat Jan 21, 2017 9:03 pm

Thanks. You have been a great help and certainly have got me thinking abit more in depth about this project.

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Re: Gk73A Power Output

Post by Variablevalves suck » Thu Jan 26, 2017 9:07 pm

Quick way to lighten the tts kit is use the fzr6 rods, tts rods are serious lumps of metal, yam are internally tapered and much lighter.
If you going do crank work go over to 76a crank and clutch as it has straight cut gears.
You have to watch the top end as the old style pin adjusters used for valve clearance are not the best for high revs, you can certainly get them to go but as said they can get a little fragile BUT that said a lot a blow ups have been people just going for massive power and not getting everything spot on, you see people bore them out etc and not check any oil clearances etc.

Id say the biggest problem is getting enough air into them, the standard air box doesn't flow very well, yoshimira use to dump the air box on their bikes and run open carbs.

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Re: Gk73A Power Output

Post by moforockband » Sat Jan 28, 2017 9:38 pm

What do you mean by the TTS rods Chris? OEM or aftermarket?

I'm assuming Yoshi used non CV carbs on their bikes also?

Cheers Nick.

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Re: Gk73A Power Output

Post by Variablevalves suck » Mon Jan 30, 2017 8:33 am

Sorry i should have said pins!

the Gudgeon pin (wrist pin) supplied with the kit is heavy, yam 600 one is machined out same as oe GSXR400 one.


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