Anyone running a 1238 GS1000 on the street?

[Paul]

At 1238 cc you have to machine out crankcase mouth to accept the oversize cylinder liners. To go bigger bore requires, (I think) bigger liners, which then means that the standard Suzuki cylinder block is to thin. ie: the liners are through to the fins! Plus the liners are bigger the crankcase mouth has to be opened up more, so the sealing surface at the is getting thin, & closer to the oil-way gallery. Also the cylinder/cylinder head bolts may be too close to the liner.
Can you use a 4-valve GS crankcase & block, & fit a 2-valve top end?
I've just remembered - - You can fit the 4-valve GS crank into a 2-valve engine, that gives you a longer stroke which takes the capacity to (I think) just above 1300cc. You have to fit spacers under the cylinder block & chamfer the liners to clear the rods.
Saying all that wasn't there a top-fuel Suzuki in the late '80s that was the first bike to pass the 200mph terminal speed. I think that was a 2-valve engine - I've got a feeling that it was Terry Kizer, or was it Larry McBride? I can't remember now. I'm sure that somebody else will!
Peppermint Patti - where are you?

[Paul]

At 1238 cc you have to machine out crankcase mouth to accept the oversize cylinder liners. To go bigger bore requires, (I think) bigger liners, which then means that the standard Suzuki cylinder block is to thin. ie: the liners are through to the fins! Plus the liners are bigger the crankcase mouth has to be opened up more, so the sealing surface at the is getting thin, & closer to the oil-way gallery. Also the cylinder/cylinder head bolts may be too close to the liner.
Can you use a 4-valve GS crankcase & block, & fit a 2-valve top end?
I've just remembered - - You can fit the 4-valve GS crank into a 2-valve engine, that gives you a longer stroke which takes the capacity to (I think) just above 1300cc. You have to fit spacers under the cylinder block & chamfer the liners to clear the rods.
Saying all that wasn't there a top-fuel Suzuki in the late '80s that was the first bike to pass the 200mph terminal speed. I think that was a 2-valve engine - I've got a feeling that it was Terry Kizer, or was it Larry McBride? I can't remember now. I'm sure that somebody else will!
Peppermint Patti - where are you?

[Paul]

Sorry about the double post, but I'm getting message

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But obviously message has got through!

[Hoomgar]

I don't claim to know a lot about that but I do know that the GS1000 (the 78, 79 at least) transmission is a popular choice for GS drag bikes and that these guys will bolt up larger cylinder jugs and heads onto them to accomplish what your asking without boring out the original one to dangerous levels.

More details I don't know, only that they do it so it can be done.

[Hap Call]

In Pro Stock, almost all the bikes are running 1500cc with 2 valve heads. If you are running a four valve head you are limited to 1200cc displacement.

The problem with 1500cc displacement is that there are no cooling passages between the cylinders, thus over heating becomes a major problem when you ride these bikes on the street.

Hap

[Paul]

I don't claim to know a lot about that but I do know that the GS1000 (the 78, 79 at least) transmission is a popular choice for GS drag bikes and that these guys will bolt up larger cylinder jugs and heads onto them to accomplish what your asking without boring out the original one to dangerous levels.

More details I don't know, only that they do it so it can be done.

GS1000 transmission will NOT take the power of a seriously tuned engine. The gearbox will burst, it is the limiting factor in a GS1000 engine, unless you go to heavily modified crankcases etc.

[Paul]

In Pro Stock, almost all the bikes are running 1500cc with 2 valve heads. If you are running a four valve head you are limited to 1200cc displacement.

The problem with 1500cc displacement is that there are no cooling passages between the cylinders, thus over heating becomes a major problem when you ride these bikes on the street.

Hap

Are these running stroker cranks? I suppose they must be to get that capacity.

[Anonymous]

GS1000 transmission will NOT take the power of a seriously tuned engine. The gearbox will burst, it is the limiting factor in a GS1000 engine, unless you go to heavily modified crankcases etc.

I understand the GSX1100 gearbox will go in with little or no modification. And therefore any race box suitable for the 1100.

[Anonymous]

I've just remembered - - You can fit the 4-valve GS crank into a 2-valve engine, that gives you a longer stroke which takes the capacity to (I think) just above 1300cc.?

Are you certain? I thought the rod spacing was a good bit different on the 4 valver.

[Anonymous]

I have heard conflicting comments about the GSX cranks in GS motors, and I'm not sure if the bore centre to centre distances are the same in these motors. Anybody got spare GSX and GS blocks around and can confirm centre to centre distances???
If they aren't the same then maybe its a case of using some GSX crank parts to build up a GS crank, to give 66mm stroke instead of 64.8mm e.g. 1238cc becomes 1261cc.

Rules governing Pro-stock motors seem to vary between governing bodies(NHRA/Prostar/etc.), but apart from a few Harleys(huge motors and aftermarket cases, heads,....everything!), and a couple of modern ZX-12's and Hayabusa's, everyone uses either GSX motors or KZ/GPz 70's/80's air-cooled motors, running 1500cc, although some go up to 1640cc. Some use the original head castings, but many use aftermarket Vortex 2-valve heads.

So, can anyone measure their spare 4-v 1100 block / 2-v 1000 block for comparison?

[Hap Call]

In Pro Stock, almost all the bikes are running 1500cc with 2 valve heads. If you are running a four valve head you are limited to 1200cc displacement.

The problem with 1500cc displacement is that there are no cooling passages between the cylinders, thus over heating becomes a major problem when you ride these bikes on the street.

Hap

Are these running stroker cranks? I suppose they must be to get that capacity.

Yes, they are stroked and bored...

Hap

[Anonymous]

I thought they were bore only, stroker cranks not allowed in pro-stock...

[Paul]

I've just remembered - - You can fit the 4-valve GS crank into a 2-valve engine, that gives you a longer stroke which takes the capacity to (I think) just above 1300cc.?

Are you certain? I thought the rod spacing was a good bit different on the 4 valver.

No, not certain. But I was told that this was the way to go to get mine any bigger. I don't know if you know him, but it was Alan Jefferies who told me - used to be at TTS, then NCK before going on his own. I couldn't see the point of the expense for a very small gain, so I didn't go any further.

[Paul]

GS1000 transmission will NOT take the power of a seriously tuned engine. The gearbox will burst, it is the limiting factor in a GS1000 engine, unless you go to heavily modified crankcases etc.

I understand the GSX1100 gearbox will go in with little or no modification. And therefore any race box suitable for the 1100.

The GSX box suffers the same sort of problems as the GS.
The aftermarket 3 or 4 speed transmissions are much stronger, but I didn't think that you could fit into GS cases.
Again, I was under the impression that you could use a GSX bottom end & put on a GS top.
I have seen an aftermarket (Orient Express 3 speed) 2nd gear split on EVERY run up the quarter.

[Hap Call]

I thought they were bore only, stroker cranks not allowed in pro-stock...

Must be of a type specifically designed and manufactured for a production motorcycle. Engine manufacturer will determine make of bike. Harley-Davidson V-Twin unlimited bore and stroke; Kawasaki 2-valve roller bearing crank, unlimited bore and stroke; Suzuki 2-valve and 4-valve roller bearing crank, unlimited bore and stock stroke. 2-valve and 4-valve 1994 or newer plain bearing imports unlimited bore and stroke. Suzuki 2-valve 66.4 or smaller stroke allowed. Modification to main engine cases only permitted for repair purposes. CLUTCH: Slider clutch permitted. CYLINDER HEADS: After market cylinder heads permitted with prior approval and consent of the NMRA Technical Department (see General Regulations 1:4). Modifications to the cylinder head may not affect its appearance. All engines must be self-starting. Plug-in electric starters permitted. Push or roller starts prohibited. Snap back throttle return mandatory. TRANSMISSION: Any transmission with a maximum of 6 forward speeds, minimum 4 forward speeds permitted. It must be contained within the stock case, and shifted from gear to gear manually or by air shifter. RPM or computer-shifted gearboxes prohibited. Engine recommended to be equipped with a lower-engine-ballistic/restraint device; (unit must be NMRA accepted) or chassis should be equipped with a sealed fairing or belly pan with a minimum 1 inch raise on all edges and cutouts to cover the bottom of the engine.


Kinda confusing...

Hap