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Bigger engine - buy or bore?

  • Thread starter Thread starter 80GS1000
  • Start date Start date
Mike_H said:
I haven't seen this mentioned yet, so I'll throw my 0.02 in. You need to consider your usage. It sounds like your looking for a quick revving engine, mid range grunt, and durability. Yet you keep mentioning the 1150 because of its drag prowess. Road racing, and drag racing are completely different animals, and as such entail completely different builds.

Personally, I would keep the engine stock. I don't know how your trackday event work, but when I used to autocross cages, they seperated cars out based on modifications. I think you'll have a better chance with a torquey, dependible engine in a stockish class (you've already bumped yourself with suspension mods) rather than a full-blown heavily modified class, where you'll be racing with GSX-R 1000's and the like that have been heavily modified. You'll get whoomped.
Click to expand...

All very good points.

By roadrace trackdays I mean just for fun - not serious competition. Get out there and learn how to drag a knee on the GS1000 Wes Cooley style.

For serious competition you need serious artillery, which these days are bikes like the GSXR 1000 (175 HP stock :shock:) and Yamaha R1s. I'd get lapped if I tried to take the GS1000 against that kind of hardware.

I love riding the twisties and I think going to the roadrace track is the next logical step to learn how to really ride well and know what the bike can do - no cops, no speed limit, no opposing traffic, good instructors, and smooth, debris-free pavement.

The bike will probably spend 10-15% of its time on the track, the rest on the street.

I mentioned the GS1150 motor because it makes so much horsepower - the most out of the GS series. How would you describe the motor in terms of revving speed, torque, top end speed etc? Never ridden one, but the fact they won so many drag races before the 'Busa came out says a lot about the engine.

You're right on the money that I couldn't race this bike in its class by the suspension mods that have been done, but that's OK by me. I think the better brakes, tires and handling will be worth it.

So yeah, I'd love to have a quick revving, reliable engine with lots of middle and top end grunt, from about 4000 RPM to redline in all gears. I really like the way the 1000 dishes out the power now, with a very broad, very linear torque curve. If I could just get some more top end speed and torque, and a taller rev range (the Yoshi GS1000 redlined at 10500 RPM vs. the stock 8500 RPM) I'd be a happy camper. The local track has a 7/10th mile main straight, and I don't want to get left in the dust for lack of top end speed.

Which, if any, mods should be done to get there?
 
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80GS1000 said:
All very good points.

So yeah, I'd love to have a quick revving, reliable engine with lots of middle and top end grunt, from about 4000 RPM to redline in all gears. I really like the way the 1000 dishes out the power now, with a very broad, very linear torque curve. If I could just get some more top end speed and torque, and a taller rev range (the Yoshi GS1000 redlined at 10500 RPM vs. the stock 8500 RPM) I'd be a happy camper. Which, if any, mods should be done to get there?
Click to expand...

A couple of points:

1. based upon your mod list, and your mechanical ability, you're probably looking at $3,000 for the package
2. your bike would be less fun on the street
3. The Yosh race engines get rebuilt every other race, contain parts you'll never find and require constant service
4. I think you'd be better off getting something 5-8 years old for track days (maybe the SV 1000 with the bars on the top of the triple clamp) 2003? for just a bit more money

The 1100/1150 motor gets its power increase from its 4 valves and other changes more than just the displacement.

It's not so much a lack of horsepower, but wind resistance, that slows you over 100 mph. A good, large fairing would be helpful
 
If you go to a 4 valve GS, stick with an 1100 motor, they are considerably cheaper and easier to find than 1150s and have the same potential for performance when being modified.
 
Thanks for all the tips and advice guys - much appreciated.

Let's go down the engine swap road for a minute.

I have a line on a 1980 GS1100E parts bike for cheap ($150). It's complete, minus the headlight, carbs, and airbox. The guy says it makes 120 psi dry, 140 wet on a compression test. The motor appears to be leaking some oil, but so does my GS1000 motor. It's unknown how long it's been since it ran. What kind of questions should I be asking from the seller?

Who knows, maybe the 1100 will turn into a restoration project.

The GS1000 is my first project bike and first effort at motorcycle mechanics - it's been a lot of fun and very educational so far but I've barely scratched the surface. You guys are the gurus. :-D

Here's some pics of the parts bike and engine:

Picture-054.jpg


 
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So yeah, I'd love to have a quick revving, reliable engine with lots of middle and top end grunt, from about 4000 RPM to redline in all gears. I really like the way the 1000 dishes out the power now, with a very broad, very linear torque curve. If I could just get some more top end speed and torque, and a taller rev range (the Yoshi GS1000 redlined at 10500 RPM vs. the stock 8500 RPM) I'd be a happy camper. The local track has a 7/10th mile main straight, and I don't want to get left in the dust for lack of top end speed.

Which, if any, mods should be done to get there?
Click to expand...
Boy, You wanna be able to rev higher too!! Basically, how quick the engine will "spool up" is a function of recipricating mass. How heavy is the stuff that moves in an engine (crank, flywheel, etc). The lighter it is, the greater the rotational acceleration of the crank can be. Stroke is also a big part of the equation. Ever notice how quick a modern bikes (esp 600 class) will spool? They have very short stroke lengths, which keeps maximum piston accel down. Lower acceleration values means the pistons can change direction more quickly, and with less strain on the conn rods, and crank. All of this in turn keeps the engine from becoming a grenade. Maximum RPM is basically a function of how fast the valvetrain can rotate, and not have the valves "float" off the camshaft. Heavier (more spring pressure) valvesprings and lighter valves help out here.

All of this means that your basically constrained to what the engine designers gave you, within say 10 percent increase. It can be done, and I know a lot of people on the boards have installed big bore kits (pretty much the easiest way to add power, after a free flowing exhaust and high perf air filter), but there will be tradeoffs. If you insist on more power (and who doesn't :) ?) I would say try to find an 1150, and shoehorn that in. If you still want more, go buy a 'busa, chip it, and put a wet NOS system in it. That oughta blow your hair back! Keep the GS for everyday riding and nostalgia.

Oh one other thing, You mentioned an 8500 RPM redline. Is that the published figure, or just what you indicate at top speed? If its just what is indicated at terminal velocity, you could try dropping a tooth on the wheel sprocket. That will make the bike easier to "push" through the wind, and should allow the engine to spin a tad faster. Wind resistance increases exponentially as speed increases, so at 100 mph, your aerodynamic drag is holding you back more that engine power. Put a 1/4 fairing on, I bet you pick up 5-10 mph in top speed. I was reading Cycle World, and they had a side bar about a guy who took an old WW2 bomb housing, and designed a motorcycle around it. The bike made about 70HP, and his top speed was over 200 MPH. Food for thought.
 
Wonder if it would fit in the frame...? Looks like they peak out at about 145 HP (at least the air/oil cooled versions), which would make the bike a wee bit on the fast side. :D

But it's not a GS engine - would look funny with that huge radiator on the front, and not period correct either.

But it would make it easier to find parts, especially exhausts....

NoBars said:
go balls out and swap in a oil cooled GSXR 1100
Click to expand...
 
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I shoe-horned a 16 valve 1100 engine into a 750 frame a few years back. The 750 engine was blown beyond recognition and it was an easy job to fit the 1100 engine. It went real well for an old 750.
 
terbang said:
I shoe-horned a 16 valve 1100 engine into a 750 frame a few years back. The 750 engine was blown beyond recognition and it was an easy job to fit the 1100 engine. It went real well for an old 750.
Click to expand...

Got any pics of that GS 7/11? Sounds great.
 
Sorry it was a while back so no pickkies.
I had to fab up a couple of bottom mounting brackets and fit the 1100 airbox outlets into the 750 airbox. Changed the front sprocket and all the rest was the same. Only those that knew GSes could tell the difference.
Ping, a 100HP Sevenfiddy..!
 
The GS1150 is a gooder engine. If you're spending that much money and don't care about the classic looks of the old two-valve engine, buy an 1150 motor. You're rebuilding it anyways, so you're ending up with a new engine regardless - so it doesn't matter what the condition of the engine is (to an extent).
 
Diggin' on this GS(XR)1000 with an early oilcooled GSXR 1100 motor installed. Bet the thing accelerates like a beast, has the handling to match, and love the classic GS styling.

200620002_bearbeitet.jpg
 
Yes, lighter and better ground clearance too. If you're willing to forego a GS series engine, the GSXR1100 is definitely the right choice.
 
Seems to be for sure.

The early (86-92) oil boiler GSXR 1100 motors are 128-145 HP stock. They look like a late model GS engine. Performance pipes are available. Would be cheaper and easier to buy a complete, reliable Gixxer 1100 engine than build up the stock GS motor. Even with the GS engine hopped up, it'd still make less HP than the Gixxer motor and be more prone to breaking down from the extra stress. My GS engine leaks oil pretty bad, so it's either rebuild or get another engine. From a performance and reliability perspective, the Gixxer motor seems to be the way to go.
 
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80GS1000 said:
Thanks for all the tips and advice guys - much appreciated.

Let's go down the engine swap road for a minute.

I have a line on a 1980 GS1100E parts bike for cheap ($150). It's complete, minus the headlight, carbs, and airbox. The guy says it makes 120 psi dry, 140 wet on a compression test. The motor appears to be leaking some oil, but so does my GS1000 motor. It's unknown how long it's been since it ran. What kind of questions should I be asking from the seller?

Who knows, maybe the 1100 will turn into a restoration project.

The GS1000 is my first project bike and first effort at motorcycle mechanics - it's been a lot of fun and very educational so far but I've barely scratched the surface. You guys are the gurus. :-D

Here's some pics of the parts bike and engine:

Picture-054.jpg


Click to expand...


Okay, remove everything not necessary to have it function, get one of those racy seats off Ebay, rebuild that motor, and make it a track only bike, You'd have the best of both worlds.
 
That R motor 1000s is what I am talking 'bout. It looks right and makes good power. Notice how the motor is pushed to the front, leaving the gap in the back to weight the front tire (R engine is a couple inches shorter).
Even the oil coller looks good.
 
NoBars said:
That R motor 1000s is what I am talking 'bout. It looks right and makes good power. Notice how the motor is pushed to the front, leaving the gap in the back to weight the front tire (R engine is a couple inches shorter).
Even the oil coller looks good.
Click to expand...

Agreed on the looks of the motor matching and complementing the bike. Is weighting the front tire a good thing?
 
Weighting up the front end gives a more secure feeling and allows higher corner speeds, notice that sports bikes are all hunched up over the front?

Dink
 
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