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Twin Engine GSXR Land Speed Racer

55764 Views 337 Replies 83 Participants Last post by  Beairsto Racing
Hi everyone,
This my first post. I was slacking off and surfing the net hoping to find race parts for early GSXR's and ended up on this site and then was surprised to see a recent thread on one of my race bikes. I just enjoyed my 8th year competing at the Bonneville Salt Flats, I've had some success with very large displacement Hayabusa's. I still own my first race bike, a 1986 GSXR 1100 built as a period endurance racer.

One of my mentors, Larry Forstall built my twin engine GSXR back in the early 90's. Larry built it to run in the "naked" classes without any bodywork. Other than a couple of shake down passes which were aborted due to vision problems and salt conditions, the bike has never run. The Double sat for over a decade in Pennsylvania. I met Larry in 2002, the year that I got inducted into the Bonneville 200 MPH Club and he mentioned having a twin engine GSXR in storage. I was after Larry for several years to either sell it to me or let me fix it up and race it. Bonneville has such a rich history of multi-engine vehicles, I thought the Double was very cool. I was teased with pictures at first but Larry finally agreed to sell it to me and I had it shipped up to Alberta, Canada. I will always run it as a "Beairsto & Forstall" entry. Larry is an innovator and I'm proud to own a piece of his work.

The Double uses a pair of 1986 GSXR 1100 engines, they are now 1255cc with Cosworth pistons, ported heads, Carrillo rods, Falicon cranks, Megacycle cams, 40mm flat slide Mikuni's, all the good stuff that was available at the time. Older technology for sure but horsepower is horsepower. The engines are coupled together, both transmissions are engaged.

I work overseas in the middle east and Africa, I'm not home much and it was hard trying to get 3 other race bikes ready for Bonneville. As anyone who has run at Bonneville knows, corrosion is a bitch. It doesn't seem to matter how much you clean up afterwards, it ruins everything. Having sat for so long, the bike needed some attention. I also wanted to be able to run the bike with bodywork and decided that an early GSXR competition fairing was the right choice. We replaced the wiring harness, spark plug wires, cleaned the carbs and got the front engine running fairly quickly. The rear engine gave us a little more grief but we sorted through the electrical gremlins. A seized rear custom clutch slave cylinder almost kept the bike at home, we fixed that the night before we left.

I had never driven the bike until I let the clutch out for the first time on the salt. Its very stable at speed but it is a bit of a stretch even laid out over it and the gear shift pattern is backwards.
The front engine is started using a battery cart, with the bike on a stand, I shift into 1st gear, rev it up a little and drop the clutch. The rear engine fires up and the bike gets alot of attention. I put it back into neutral, the stand is removed and I wait for the starter to give me the ok to run on the course.

I did a couple of passes on the short course to get familiar with the bike but we soon discovered a weak link in the engine's coupler. I knew with the weak idler gear that I would only be able to make a few runs. My top speed was 203mph @ only 7000rpm, the bike has alot of potential in it. I like it because its different, my Hayabusa disappears in a sea of other 'Busas at Bonneville. On my last run, we actually broke the coupler's idler gear and the loose chain caused a bit of damage but nothing that can't be repaired. There's nothing like running 200 mph and hearing bad crunchy noises coming from the coupler.

I hope to be able to run it again this year at Bonneville or El Mirage, work permitting. The bike is in a shop right now getting the coupler modified. I also need to improve the rear suspension and add some ballast for traction. It just spins the tire hopelessly at anything over 3/4 throttle. Over the winter I'd like to throw some more power at it and upgrade the 1255's, its a shame they stopped making the big blocks. We are entertaining the idea of adding fuel injection as well.

Well I should get back to work.



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Oh I think you will also want to make sure the front engine is always the lead engine. Otherwise, you may be putting way too much force on your idler gear and it's support
First just want to say this is an impressive bit of machinery. I really like it especially since I also have an 86 GSXR 1100. :punk

OK so I played around with Power point and did a quick spreadsheet (the problem was intriguing :dunno). I attached a somewhat more complicated design, but it is certainly more balanced.

I won't claim to understand all (any) of the issues with trying to couple the two motors but assume the crank to crank spacing is required to get an integral number of links within that spacing. The idea is that the front lead motor will pull the most and the straight section of chain will establish the relative timing (I realized this just before I posted the pic :sad). The motors are spaced exactly N links apart and with N links on the sprockets they are in sync (nominally at least). If the chain stretches you have to slide the motors further apart.

That must be the reason for trying to pull out all the chain slack on the bottom. Of course is this is very unbalanced . Additionally the adjuster is pushing "in" and so the small idler has to spin so much faster as well as the increased chain deflection angle.

Here are some highlights:

1.) Lower chain deflection angles on the chain adjusters because there are two adjusters. Slight increase on the lead drive sides with a decrease on the follower drive side

2.) Idlers have reduced load because the chain is wanting to fly out away from the idler rather than pushing against it (this might be a minimal effect).

3.) I believe that there is sufficient adjustment to get 1 full 530 link of slack adjustment on the leader drive side with less chain deflection. Then the lower follower side can be set for slack adjustment. Depending upon the symmetry of the idlers, it may be close to identical.

4.) Since there is more space inside the chain, larger idlers can be used reducing the idler RPM in proportion to the chain in #of teeth

5.) The adjusters are angled for improved fit as well as to better oppose the drive side chain tension even though the angles are reduced.

6.) By simply using the timing marks on both motors, the tensions can be set to synchronize the motors without moving (crank shaft spacing) either motor as required in the current version.

I also threw in some guides (inside and outside in blue). Also little squirter's for an oiler would be easy to add as show rather than going to a full bath.

I have now way of knowing, but I would certainly think that this configuration would be much more stable and once the engines were synced (using timing marks and tensioning) that the bike would run longer in sync as there is likely to be less chain wear and stretch and even the chain wear and stretch will be symmetrical and nominally not change the timing (as the existing will if there is any stretch). It is easy to do a quick after run alignment adjust if required and you are off and running again. :burnout

Nice bike what ever you happen to decide.


P.S I'm just looking at the pic again, It seems now you might have enough room to sync the cranks instead of the transmission and then run a separate chain and gearing for the tranies if you think a single transmission will handle the power.


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I may have missed something but it seems the bikes setup is running with clutches linked on both motors and I am guessing both shifters linked toghter as well. If that is the case it doesnt matter if the motors are timed together seeing as its not coming from the engine output shaft.
To answer some of your comments...

Yes it has both clutches and transmissions, they are both shifted together, it is the countershafts that are coupled together.

As shown, yes there is a cover for the coupler, with a bit of work, it could be made oil tight.

Its too long to fit on a dyno. I would estimate the previous 1255cc engines were each capable of an honest 175 rear wheel hp in a conventional bike. I'm sure we lose a bit through the coupler and probably lots when we are frying it.

No, it didn't need more hp considering the wheel spin and the weak coupler but I consider big blocks to be the "holy grail" of oil coolers so I was happy that I scored 2 new ones. We'll also add some ballast and improve the rear suspension in hopes of helping it hook up.

Thanks again for your suggestions!



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If you keep that chain well oiled and can keep the salt out, your set up will probably serve you well for your purposes. Chains seldom break catastrophically so most likely you will probably only see a reduction in performance. So if you would check the chain stretch and sprockets periodically, it would give you early warning.

The idler is there only to take up excessive slack due to chain stretch (since the engines can't be moved) - you really don't need it for anything else. Actually if you have plenty of replacement chain (to replace when it stretches), you could eliminate the idler altogether if it keeps giving you problems. Don't over tighten the chain either, allow it to move some. Chains will move up and down on the tension side (top in your case) - they are supposed to. If you start seeing excessive wear on the front sprocket (assuming it is the lead engine) you may want to remove chain guides or at least widen them allowing alittle chain movement. Good luck
Ohhh what was I thinking?...this is what it looked like when it showed up at my local Suzuki dealer after having it shipped to Alberta from Pennsylvania. I was stuck on a rig in Mexico and they sent me this teaser shot.

It had not run in over 15 years. I was happy to score a Performance Machine "Chicane" front rim that matched the rear. I wan't really feeling the old spoked top fuel rim. It had drag slicks on it, which is odd because they are illegal at Bonneville and the bike had passed tech there a couple times.

I ordered a land speed front fender and early GSXR competition fairing from Air Tech. I think I bought 3 fairing mounts off ebay before I got a good one. It had a pair of rechargeable tachometers which I figured were junk from being so old, I replaced them with a couple of Trail Techs, cheap and easy.


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Its super cool and we support what you are doing,
most of us are not experts and we are only trying to help with suggestions that may have been over looked.
Please dont take us the wrong way, we all want to see this one and see what it can do.
I personally think you chain coupler issue is the small idler sprocket.
That thing has got to be turning some serious rpm with a load on it
I personally think you chain coupler issue is the small idler sprocket.
That thing has got to be turning some serious rpm with a load on it
Yes the small idler will always have a higher RPM and a higher load and is by far the weak link in the setup.

If possible pull out another link and reduce the deflection that the idler has to put into the chain.

With even more Hp planned, I would hate to see than chain break at 200MPH +
Yeah if that chain was to break, I dont think the cover will hold it in.
The new chain has one less link than the one we thrashed, it is also has a rivet master link where as the old one had a clip style which was certainly easier to install. The 2 counter sprockets and the chain are installed at the same time now, it probably doesn't show in the picture but you end up spreading the counter sprockets as far as you can to get them on and its pretty tough with the short chain. Its not possible to remove another link, I wish it was.
Yeah, we'll just stick to the short course and inspect it after every run.
The record is only 208mph in this class, obviously we are looking to shatter it, not many of these old twin engine dinosaurs left. It was last set in '79 by Tom Elrod on a twin engine Kawasaki.
Great to see this thread is alive and well.

Scott, I think Posplayr had a much improved diagram for reducing the wear and tear on your chain drive synchro setup. Have you given it any thought?
I'm stuck in sandy Saudi Arabia for the next month or so. I'm looking forward to getting back in my garage and enjoying a beer while I have a good look at the coupler.

I certainly appreciate all of the positive suggestions. I'm definitely interested in trying to run a larger idler, I'm undecided about two of them.
I've saved Posplayr's diagram (THANKS!! I don't even know how you can make something like that..very cool) and will run it by my engine builder and team mates.

Whatever I do this year depends on how much time that I get home. The engine rebuilds are dragging on, I'm told today that my new big blocks and pistons are being shipped but I've heard that every week for a month. I definitely need to get the engines back in the bike and we'll go from there, it will probably be an all night thrash as usual but thats racing. If all goes well, I'll focus on finishing up my 1693cc Busa when I get home and my engine guy can play with the Double once I do the grunt work and install the engines. We do have some ambitious long term projects for the Double, I want EFI.
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Do you plan on running at El Mirage or just Bonneville.
If you come to El Mirage, I can make the trip and assist in any way.
Thanks, I appreciate that!
I always plan on running Speed Week every year in mid August. That is put on the table immediately with who ever I work for, non-negotiable.
El Mirage is 28 hours straight from my place, there are only two 2 day events each year, one in May and another in November, its hit or miss with my schedule and its too hard to justify the travel for the 1 day events.
Here's a teaser....

This is the body that we will be running next year, this is sitting loose on a Buell but you get the idea.

Although bikes have a small frontal area, they suck aerodynamically because they are too short, the air never gets a chance to re-attach which results in drag. A long bike like the Double has the chance to be very slippery. It also helps that the SCTA has relaxed some rules concerning the rear of the bikes, length, height, amount that the wheel is covered etc.

So once we get the coupler sorted, we're planning on going fast!


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Looks awesome.I'll ship those carbs next week if that's cool.I would love to buy some spare gsxr 1100 parts grom you if have any sell?
Sure, ship the carbs next week, no problem. I'm buying up GSXR 1100 parts myself, I have a feeling the Double is going to be hard on parts.
Have you talked to my buddies at MDR?
They are big into the land speed stuff
Expect them to set a new electric record this year as well as beating the normal 500cc records they do.
I have some inside info about that electric airstream they are going to run.
Lets just say the dyno wasnt happy
I buy land speed body work from Air Tech. Kent Riches, Air Tech, MDR, same crowd.
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