gsx400 upping power

[Guest]

so I did some calculations between classes today, and I figure I am making somewhere between 54 and 56 horse power on my 400cc engine. anyone else tried to crunch the numbers on their performance mods? did i screw up my math?
I have pod filters and a jet kit that is running may be just a touch lean on some days.
The testing:
pior to any changes from the stock condition, my gs was topping out at 138kph to 143kph depending on the day, rpm in the 8500 range, with me crouched behind the guages. Stock top speed is lists as 141, with 44hp at the 9500rpm, and 3.7kg*m at 8000rpm.

Post changes, with a stiffer suspention, I topped out somewhere between 175kph and 180kph, again with rpm in the 8500 area.

I will be doing more fluid flow calculations, but as it stands i count 55hp or so.


Comments?

[Nessism]

Pods and a jet kit are worth about 3 hp max on a small bike like a 400. Don't understand how you have come up with 10-12 hp increase. Based on your numbers you changed the gearing since you claim the bike went faster at the same top rpm; very strange that you are pulling 37kph more at the same rpm considering the minor changes to the bike.

[robertob]

That's not even possible, dude! If you're turning the same RPM you're going the same speed unless you changed the gearing or tire size significantly. Plus it's impossible to have increased power by 25% with only pods & jet kit!

[derwood]

same rpm is same speed in same gear no matter what the horse power changes are, unless you've change sprocket sizes. your speedo could be wonky. My old 81 gs 400 tscc 4 valve twin would do about 155km/hr indicated (5th gear) on her best day, riding like Rollie Free but with clothes on. only mod was no air box lid and rejet accordingly but I don't think that made any difference although at the time i thought it sounded meaner.

[Nessism]

My old 81 gs 400 tscc 4 valve twin would do about 155km/hr indicated (5th gear) on her best day, riding like Rollie Free but with clothes on.

[BentRod]

when the bike was topping out at 140, I had to use 5th gear. in 6th, the bike would have nothing to do with going above 120 or so, the torque just isn't there.

Once the carbs were properly jetted and the pod filters were on, I was able to accelerate in 6th gear happily past 140.

again... the results that I calculated seem off to me as well, but I can tell you I saw that needle pass 175 and keep on going... I couldn't really look at the speedo after that.

I checked the gearing ratios and it seems to be possible, although my RPM at 175 would have been closer to 9000 to 9500.



It has also occured to me that if the air friction losses are less than i originally thought, that it could be that a lack of torque in the original configuration could have prevented the engine from reaching max power output.
Pods and jet kit could have boosted the torque enough that the engine was able to reach a higher RPM, and make max horse power, which should have been bosted, by increase fuel and air rate, by about 8% to 10%

I'm going to see if I can find a Dyno at the university that I can use... its slim, but I can try.

[tkent02]

I could see if it just barely wouldn't pull sixth into the power band, it could take a tiny nudge more power to get it where it would pull sixth and once in the power it could go a fair bit more.
Could be conditions were better that second day too, tailwind, temp, humidity.

My old 550 would not pull sixth up to top speed from just rolling on the throttle in the mid RPM range, but if you redlined fourth and fifth and then shifted into sixth it would sometimes pull it on out from there. No idea what sprockets were on it at the time.

[derwood]

you must be doing something right, on my 400 6th gear was a joke. like 5th in the old 2.0l ford ranger

[zig06]

Back in the day, I bought my first new bike when I was in the army. It was a '83 GS-450e.

I had to work several long days during my first summer at Fort Hood Texas. On more than one occasion when I was heading back to my apartment (off post!!), I "opened it up". And it was very predictable, I could hit 70 mph (113 km/h) at 6,000 rpm. Problem is the speedo ended at 85 mph. But being late at night and all alone on the freeway, more than once I could top it out at 9,000 rpm ~ consistantly.

And that calculates to 105 mph or 169 km/h. And that bike was totally stock, topped out in 6th gear.

[Nessism]

Back in the day, I bought my first new bike when I was in the army. It was a '83 GS-450e.

I had to work several long days during my first summer at Fort Hood Texas. On more than one occasion when I was heading back to my apartment (off post!!), I "opened it up". And it was very predictable, I could hit 70 mph (113 km/h) at 6,000 rpm. Problem is the speedo ended at 85 mph. But being late at night and all alone on the freeway, more than once I could top it out at 9,000 rpm ~ consistantly.

And that calculates to 105 mph or 169 km/h. And that bike was totally stock, topped out in 6th gear.

Not bad! :-D Rode a bunch of different 400's back in the GS era: Honda CB360, Yamaha RD400, Honda Hawk CB400T2, Honda 400-4, Yamaha XS400. Not sure any of them could top 100 mph (RD didn't run well enough to try). Loved every one.:-D:-D:-D

[BentRod]

in any event, I'm still pondering as to how i reached 175-180 on a bike that is supposed to do 141... and L model no less...

I'm going to see if i can track down a gps unit to calibrate my speedo this spring... I'll get back to this thread at that point

Thanks everyone!

[tkent02]

in any event, I'm still pondering as to how i reached 175-180 on a bike that is supposed to do 141... and L model no less...

I'm going to see if i can track down a gps unit to calibrate my speedo this spring... I'll get back to this thread at that point

Thanks everyone!

Before GPS was invented people used to use stopwatches for this.