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
Twin Engine GSXR Land Speed Racer
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.
-Scott
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.
-Scott
Attachments
41 - 60 of 338 Posts
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. 
unk
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.
Posplayr
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.
unkOK 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.
Posplayr
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.
Attachments
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!
Scott
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!
Scott
Attachments
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.
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.
Attachments
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!
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!
Attachments
41 - 60 of 338 Posts
