How fast is is your old GS?

[KEITH KRAUSE]

I have had the Tractor out to 10 500 rpm in top gear 8O luckily this is only 1000 rpm past redline

This is what I find interesting. :?
These bikes make their peak HP before redline. IN TOP GEAR, STOCK GEARING, LEVEL GROUND, STOCK OR MINOR MOD'S, how can the engine pull more rpm's past redline when the HP is dropping off?
I can believe reaching/passing redline in a lower gear, but top gear?
Not trying to cause trouble here Dink, or anyone else. This just has me scratching my head.

[earlfor]

That would be because although the engine has passed its peak hp rating, the hp output while declining, is still greater than the sum of the resistances of parasitic, induced and mechanical drags. Where the drag and hp curves intersect beyond the peak hp level is where the top speed will be. Depending on gearing, top speed may be almost anywhere on the hp curve.

Earl

how can the engine pull more rpm's past redline when the HP is dropping off?
I can believe reaching/passing redline in a lower gear, but top gear?
Not trying to cause trouble here Dink, or anyone else. This just has me scratching my head.

[Anonymous]

i can go roughly 220mph on my 1982 GS 650

I actually find that statement very interesting, as I have an '83 GS650GLD, and my speedo tops out at 160mph. I have had it up to 108mph with the RPM's at ~6800 and a redline of 9500.

I'd like to know how you can get to 220mph. Serious engine mods?

[Dink]

I have had the Tractor out to 10 500 rpm in top gear 8O luckily this is only 1000 rpm past redline

This is what I find interesting. :?
These bikes make their peak HP before redline. IN TOP GEAR, STOCK GEARING, LEVEL GROUND, STOCK OR MINOR MOD'S, how can the engine pull more rpm's past redline when the HP is dropping off?
I can believe reaching/passing redline in a lower gear, but top gear?
Not trying to cause trouble here Dink, or anyone else. This just has me scratching my head.

No problem Keith, allow me to qualify it by adding I had 30 miles of road to play with, uphill downhill and all
Dink

[saaz]

Mine was on the Hay plain...long flat and boring, but it did not take much to get up to speed. I was thinking about police, but I suppose 200...220...not much different on a ticket really

[earlfor]

Lets try a different perspective. If I remember correctly from my rambling around the net and reading specs on various GS models, a 650 is about 60 hp and I think top end spec'd by Suzuki was 115 mph. Its an aerodynamic fact that drag increases as the square of the speed. Or, said differently, if you double the speed, then drag will increase fourfold. Since top speed is reached when hp is in balance with drag, then drag controls speed. Without drag, we could go 1000 mph with 1 hp. So, to accelerate your 650 to 230 mph, the hp required will be 4 x 60 or 240 hp. This only accounts for induced drag or drag from air flow. I havent included parasitic drag ( drag from form factor), or mechanical drag values such as internal engine parts, tire contact patch, etc. The reality is that for an open bike, it probably will require something in the range of 280 to 300 hp to reach a speed of 230-240 mph.

As a rule of thumb, for low drag, aerodynamically efficient bikes such as the Hayabusa, you can figure that as speeds of 200 mph are approached, it will require aproximately 1 hp per mile per hour. You want to break 200 mph on your busa, then youre going to need about 200 hp.

Earl

i can go roughly 220mph on my 1982 GS 650

I actually find that statement very interesting, as I have an '83 GS650GLD, and my speedo tops out at 160mph. I have had it up to 108mph with the RPM's at ~6800 and a redline of 9500.

I'd like to know how you can get to 220mph. Serious engine mods?

[lartross]

I've had every bike I owned topped out...the '78 gs1000 I had had no speedo...my 850 only goes to 85...past that easily in third gear...a '71 cb750 I had went 135 on the speedo...oh, I take that back...I never had my xs1100 wide open...it just didn't feel secure over 130. I go much nearer the speed limit most of the time, but, there are occasions...

[kevin gs1100e]

145mph at 9500 rpm too scared to push her further


Kevin

[oldschoolGS]

[quote="earlfor"]Lets try a different perspective. If I remember correctly from my rambling around the net and reading specs on various GS models, a 650 is about 60 hp and I think top end spec'd by Suzuki was 115 mph. Its an aerodynamic fact that drag increases as the square of the speed. Or, said differently, if you double the speed, then drag will increase fourfold. Since top speed is reached when hp is in balance with drag, then drag controls speed. Without drag, we could go 1000 mph with 1 hp. So, to accelerate your 650 to 230 mph, the hp required will be 4 x 60 or 240 hp. This only accounts for induced drag or drag from air flow. I havent included parasitic drag ( drag from form factor), or mechanical drag values such as internal engine parts, tire contact patch, etc. The reality is that for an open bike, it probably will require something in the range of 280 to 300 hp to reach a speed of 230-240 mph.

As a rule of thumb, for low aerydynamically efficient bikes such as the Hayabusa, you can figure that as speeds of 200 mph are approached, it will require aproximately 1 hp per mile per hour. You want to break 200 mph on your busa, then youre going to need about 200 hp.

Earl






Well put Earl.

[KEITH KRAUSE]

a '71 cb750 I had went 135 on the speedo.

With what mod's?

[lartross]

nary a one [mod] I just twisted the throttle and left it there at 1 am on the freeway. I see what the engineer says, I'm telling you what I saw on my speedometer. Take it or leave it.

[KEITH KRAUSE]

nary a one [mod] I just twisted the throttle and left it there at 1 am on the freeway. I see what the engineer says, I'm telling you what I saw on my speedometer. Take it or leave it.

Something was wrong with the speedo then. No stock CB750 can go anywhere near 135. In fact, the '69 and '70 models were infamous for going faster in 4th than in 5th. About 110 on level ground. A decade later in '81, they still wouldn't go past 110. My best friend had a '81, freshly broken in. We both tried top speed runs on it. He hit 108 according to my GS1000's speedo. Then I tried it and hit 110.
There's been a lot of speedo errors in this thread I think.

[Anonymous]

1982 GS750EZ

Rejetted carburator and pipe - 1982 GS750EZ would redline in top gear....figure 128 + . The dyno'd rear wheel horsies were about 65 at the time.

Later - modified it to 77 rear wheel horsies - so not sure what it would have done then. - Dieter

[Jethro]

After about 8 Budwisers and a couple of hits of meth, I have gotten my pocket bike up to 1300mph. Or maybe it was 13, one or the other.

[Anonymous]

198Km/h or 123mp/h whichever way you like to look at it....

Slightly up-hill, long straight, on my 1977 GS750. I had to back off for an almost right angle bend (taken at 85Km/h), but on the straight there was still heaps more left in it.

a few mods:
15/36 (530) sprokets
K&N pod filters
bigger (125) jets
Unknown single alloy muffler on 4-1 system
Retshal bikini fairing