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Message started by Super Thumper on 12/17/12 at 15:08:58

Title: Bore & stroke the engine
Post by Super Thumper on 12/17/12 at 15:08:58

Well, I have my bike all apart and removed the engine from the frame today. Going to do the big bore / high comp kit from lancer and was wondering this: Has anybody tried to stroke one of these engines?? If so, what is needed to do this? I am looking to enhance the performance as much as possible...looking to make it a true "Super Thumper" hence my handle ;D P.S. I had a dream about my bike the other night....my "Super Thumper" specs from the dream......750cc, 75hp, 80 ft. Lb Torgue. 1/4 mile....12.8 @ 115mph [smiley=vrolijk_26.gif]

Title: Re: Bore & stroke the engine
Post by Serowbot on 12/17/12 at 17:30:59

Was ya' wearin' a cape?... ;D...

Title: Re: Bore & stroke the engine
Post by Charon on 12/17/12 at 19:07:51

750 cc is 45 cubic inches, implying about 45 ft-lbs of torque unless you use a serious blower and some mighty high-octane fuel. Based on the Savage engine, probably 7000 or so rpm and lower if you stroke it. If you can get the high torque at max rpm (unlikely) you might be looking at 60 horsepower. I'd bet for more like 50 hp. But, I wish you luck.

Title: Re: Bore & stroke the engine
Post by LANCER on 12/18/12 at 01:44:57

The LS650 engine has a stock redline at 6500 rpm now, which makes for a piston speed of ....... ???? I don't recall the specific numbers but it seems to be near the reasonable range. I'm not sure I would want to move that up any higher. The cost would be substantial too. I'm comfortable with improving air flow, bore and bumping the CR up to make the extra ponies, and that does quite a bit.
Keep in mind that the 97mm piston/bore brings it up to 695cc.

Title: Re: Bore & stroke the engine
Post by Charon on 12/18/12 at 06:49:31

The old rule of thumb says piston speed should be kept under about 4500 feet per minute for reasonable engine life. With a 94 mm stroke that comes to about 7300 rpm, about 15% above Suzuki's red line of 6500. Suzuki may have other reasons for the lower red line, or they could just be a little conservative on an engine simply not designed for maximum power.

Title: Re: Bore & stroke the engine
Post by arteacher on 12/18/12 at 08:16:47

Seems to me it would be a lot cheaper to work on the breathing (turbo or supercharge) than it would to bore it to 750cc and stroke it, to get that kind of performance. And don't forget, if you stroke it you are reducing displacement. Also the brakes and suspension are not up to the task of that much power, so you are building a whole new bike.

Title: Re: Bore & stroke the engine
Post by verslagen1 on 12/18/12 at 09:03:48

707B7B727E71706A6B1F0 wrote:

if you stroke it you are reducing displacement.

Stroke usually means additional i.e., 94mm increased to 97mm
De-stroke means less i.e., 94mm reduced to 91mm

longer stroke means more displacement.

Title: Re: Bore & stroke the engine
Post by arteacher on 12/18/12 at 16:21:55

I stand corrected.
That would mean turning a whole new crank then....and a taller jug. $$$$$$$!

Title: Re: Bore & stroke the engine
Post by Charon on 12/18/12 at 17:13:11

I've never been that involved in engine modifications, but I understand that a crank throw can have metal added to it on the outside by some variation of welding, and then the throw can be turned or ground with its center slightly further out, thus increasing the crank throw and the stroke. I would guess the cylinder could then be moved out by, perhaps, adding a brass spacer to the cylinder base gasket. Other factors would no doubt crop up, including cam chain length. Sounds like an interesting, and expensive, project.

Title: Re: Bore & stroke the engine
Post by Dave on 12/18/12 at 17:16:41

535858515D525349483C0 wrote:

I stand corrected.
That would mean turning a whole new crank then....and a taller jug. $$$$$$$!

Some adventurous people can stroke these cranks by making an offset crank pin. You then would have to get a longer cylinder, or a shorter rod and figure out how to keep the piston from hitting the counterweight and crank, or a piston with a relocated pin location. I doubt any of this would be worth the effort.

Put in a bigger Wiseco piston, a cam, do some porting and intake/exhaust work.....and you will be pleased. It will run nicely....but you are not going to be chasing down any sport bikes!

Title: Re: Bore & stroke the engine
Post by houstonbofh on 12/18/12 at 18:04:45

725950435E5F310 wrote:

That is an offset grind of the same size. You can also go with an offset grind at a smaller size if you are willing to change the rods. (Which you may have to do anyway.)

I was looking at doing this on a Marauder. Now I have not been deep inside a Savage motor, so this may not apply, but the same guys designed both so...

With more throw, you have the rod going down into the case more. There was insufficient clearance in the Marauder case to do this without clearanceing the case. And the case walls are kind thin, so that made me nervous.

Also, with more throw, you have sharper rod angles. I was looking at potentially having clearance problems with the side of the rod and the bottom of the jug.

And if you solve all that, you had best calculate the deck height right. Shorter desk heights mean more cam chain to take up... And it also retards the cam as it takes it up...

I decided to look at other places than displacement. Specifically raising compression, cam advance and timing advance.

Title: Re: Bore & stroke the engine
Post by Super Thumper on 12/23/12 at 20:30:14

WOW....it was a dream after all and I realize stroking the engine and whatever else would be necessary to achieve what was in the dream would take buckets of $$$....and YES I was wearing my cape in the dream! ;D