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View Full Version : XB - Short stroke with big bore???


xl1200r
1st March 2007, 19:56
Anybody done this?

I have an XB12R and someday (maybe next year???) I'd like to do the motor internally. I'd like to put in an XB9 flywheel assembly for the shorter with the big bore kit. I believe this basically stays 1200cc.

So, if I do this, throw on a Micron exhaust, a strip/street/race cam, and a stage 2 or 3 headjob, what kind of power can I expect and where? I dig the tourqie of the 12, but would like to add the revs of the 9. I basically don't want to have any less power than with the stock motor at any place in the rev range.

I think I'd like to shoot for 120-125rwhp. Is this going to be realistic and reliable?

I haven't been able to find any good dyno numbers on a big-bore XB9 that didn't have the 12 crank installed.

Gone
11th March 2007, 06:51
The Mopar guys were all hot and bothered for years at shoving 440" cranks into 400" blocks as the "hot set-up". It turned out to be a fad that is mostly dead these days. If you are street riding, I'd suggest staying with the longer stroke for the edge in bottom end torque. Surely there can't be anything about an 88" Buell that won't keep you excited?

racerwill
11th March 2007, 07:14
The Mopar guys were all hot and bothered for years at shoving 440" cranks into 400" blocks as the "hot set-up". It turned out to be a fad that is mostly dead these days. If you are street riding, I'd suggest staying with the longer stroke for the edge in bottom end torque. Surely there can't be anything about an 88" Buell that won't keep you excited?

a 440 crank in a .030 400 block with big block Chevy rods and a little ofset gring on the crank makes something like 572 cid.....agreed about keeping the longer stroke for much better driveability and lots more low RPM power

Ww

Rocker59
11th March 2007, 07:27
Anybody done this?

I have an XB12R and someday (maybe next year???) I'd like to do the motor internally. I'd like to put in an XB9 flywheel assembly for the shorter with the big bore kit. I believe this basically stays 1200cc.

So, if I do this, throw on a Micron exhaust, a strip/street/race cam, and a stage 2 or 3 headjob, what kind of power can I expect and where? I dig the tourqie of the 12, but would like to add the revs of the 9. I basically don't want to have any less power than with the stock motor at any place in the rev range.

I think I'd like to shoot for 120-125rwhp. Is this going to be realistic and reliable?

I haven't been able to find any good dyno numbers on a big-bore XB9 that didn't have the 12 crank installed.

Go for it !!! Sounds like a great project !!!

I love the revvy characteristic of the 984cc Buell engine. Your idea of short stroke + big pistons to keep it 1200 sounds like a good recipe.

Should be a screamer !!! (If you're into that sort of thing)

Will be sorta like a Chevy 302 !!!

Gone
11th March 2007, 09:49
a 440 crank in a .030 400 block with big block Chevy rods and a little ofset gring on the crank makes something like 572 cid.....agreed about keeping the longer stroke for much better driveability and lots more low RPM power
Ww

I was referring to the stock 440" stroke (3.75") conversion so they could "fool" people into thinking they still had low-deck 400's. There was no power advantage over a 440" so it was a fad that quickly went away. Grinding the crank journals undersized to fit the 400" block was a waste of money.
Usually, outfitting motors with "odd" combinations has far less return of hp per dollar.

xl1200r
11th March 2007, 09:58
Will be sorta like a Chevy 302 !!!

My thoughts exactly - I'm a HUGE DZ-302 fan.

Still no concrete numbers, but it seems some other folks have done the same recipie with good success on another Buell forum.

As far as keeping the long stroke for street riding - I agree this is better for the lower-end torque, but I'd be curious to see if this engine combination woudl really be lacking down low. My guess is not.

Trust me, 88" would be tons of fun, but 1200cc is just a magic number for me, and like I said before - I really dig the idea of big cube engines with slightly undersquare proportions.

aswracing
11th March 2007, 16:49
How do you plan to raise the rev limit?

The 12's injectors and ecm are different. The 12's ecm controls the servo valve in the muffler as well.

xl1200r
15th March 2007, 05:01
How do you plan to raise the rev limit?

The 12's injectors and ecm are different. The 12's ecm controls the servo valve in the muffler as well.

I would probably go for a Micron exhaust which elimiates the exhuast servo, and use an emulator to fool the ECM into thinking it was still there.

Or, just use the ECM from a 9 which already has the higher rev limit and no exhaust servo.

In either case, could direct link tuning not make this engine combination work?

Rigpa
18th March 2007, 03:31
Or get an ECM from a XBRR ;) Just joking...though it's using the 3.125 stroke and just over a 4 inch bore for about 82 inches. If the claimed > 150hp is correct that's quite impressive. Looks like they took a page from the XR750 design but though if claims of 100hp for the XR-750's are correct, it's hp/in3 ratio is still tops.

xl1200r
18th March 2007, 18:47
Or get an ECM from a XBRR ;) Just joking...though it's using the 3.125 stroke and just over a 4 inch bore for about 82 inches. If the claimed > 150hp is correct that's quite impressive. Looks like they took a page from the XR750 design but though if claims of 100hp for the XR-750's are correct, it's hp/in3 ratio is still tops.

No need to joke - from what I understand, you can order XBRR parts right from your dealer now! I think that ECM might run a tad rich though... ;)

citified
23rd March 2007, 03:14
xb9 and xb12 are the same bore, putting a 9r crank in a 12r would get you a 9r. Sorry to burst your bubble.

rottenralph
23rd March 2007, 03:23
Are the heads between the two different xb bikes the same. Valve sizes the same between the two xb bikes.

xl1200r
26th March 2007, 00:00
xb9 and xb12 are the same bore, putting a 9r crank in a 12r would get you a 9r. Sorry to burst your bubble.

Read my first post again. I want to put in the shorter stroke 9 crank with the big-bore cylinders. Hence "short stroke with big bore".:doh

No bubbles bursted.:D

Are the heads between the two different xb bikes the same. Valve sizes the same between the two xb bikes.

Heads are identical between the 2 engines.

2003xb9R
26th March 2007, 23:08
Well I got at 2003 xb9r and want to put a 12 crank in it, do u want to just swap engines and ecm's lol?

citified
30th March 2007, 04:03
Read my first post again. I want to put in the shorter stroke 9 crank with the big-bore cylinders. Hence "short stroke with big bore".:doh

No bubbles bursted.:D



Heads are identical between the 2 engines.



sorry, I thought wrong.:o I too would like to do the 1050 kit, some day, After I blow it up anyway:)

xl1200r
7th April 2007, 20:18
sorry, I thought wrong.:o I too would like to do the 1050 kit, some day, After I blow it up anyway:)

Kind of my boat - part of me wants an excuse to have to tear the whole thing down.:frownthre

Sleeper
7th April 2007, 20:40
I considered that build also, but most of the professional builders I talked to, said the valve train is the limiting factor. To reach the HP levels you want would take reving the hell out of it. :frownone
Even so it would be cool to get a HD motor to rev like a NASCAR motor.:)

Streetpro
6th January 2008, 18:25
I know guys from the Hillbilly-racing-team here in Germany combined an XB9 crank with a big bore set from Millenium tech. It turned out to be an 1170 cc "short-attack" bike with 100+ rwhp. Anyway I would guess 120+ rwhp out of 1200 cc is not good for all-around street-use.
I got these numbers from a 1430 cc = 87 ci square engine with radical cams and 11:1 CR.

Martin

Stephen Lowry
22nd April 2009, 22:02
If you had heads and ECM to support it, it would make a good race motor for AHRMA Pro twins formula 2.