Forcus

Hey guys, I was wondering what the lowest (numerically) gear ratio I can get in a GSL-SE, stock or aftermarket, would be.

I am building a Lotus replica with an R1 bike engine. I believe most GSL-SE's came with the 4.11 gear ratio. I want to use this axle because it is the right width and has rear disc brakes, LSD, and desirable bolt pattern.

I have heard you can use a truck gearset. Is that true?

Any help would be great. I am looking for around 2.73 gearing, but lower numerically would even be better. 2.73 gearing would enable 140 mph at 10000 rpm.

Thanks
Brian

rx7gslse

lower? hmm... those may be hard to come by because most of the aftermarket goes for the higher 4.44's, 4.88's or even 5.12's

I would check mazdacomp's website and see if that list anything.

A truck gear? I beleive the 86-88 B2200 (or what it 2600) had a interchangeable one, but my understanding was that it has a higher ratio (same deal with the Kia sportage front diff *rumor* )

lemme dig and see what I can come up with.

Forcus

Thanks. The alternative is an expensive aftermarket overdrive - adds weight and cost.

Cloud

Well, I'm sure there are plenty of non -SE owners here who would trade you their 3.90 gears straight up, but that isn't quite enough of a drop for you, I guess.

Check the V8 guys out - many of them have worked hard on finding lower (numerically) gears - v8rx7.com or rx7v8.com - I can never remember which one is the torquecentral forums.

rotor vs. piston

Look for a '82 diesel B2000 pickup, they have 3.308 ring and pinions, and are the lowest gears that can enterchange that are known

rotor vs. piston

Also check out this site so you can get a figure of what ratio you'll really need.

If you only want to go 140mph at 10000rpm you don't need a lower gear.

In forth gear (a 1 to 1 ratio) at 10000rpm you'll be doing 172mph WITH the 4.10 and the stock size tires and rims

j9fd3s

iTrader: (3)

i was gonna say you need a piston gear set.

mike

Forcus

I have a spreadsheet for gear ratios. I'm checking to make sure it's accurate but top gear (6) in the R1 trans is 1.115. If my calcs are right, with a 4.10 rear end gear, 225/50/16 rear tires, in 6th gear at 60 MPH I'll be at 6000 RPM. Top speed will only be around 117 MPH.

Let me check on this some more as the sheet I got from someone else factored in the "primary ratio" which may not be applicable in my case.

Forcus

Ok, Primary Ratio is between the engine and trans. Secondary Ratio is between trans and tire (sprocket). Primary applies, secondary doesnt.

With 225/50/16 rear tires, 4.10 rear gear, 1.581 primary ratio, 1.115 6th gear, I'm looking at a top speed of 117.82 (bad, but I never really would use it probably unless it was the track) and cruise at 60 MPH is about 6000 RPM and 75 MPH is about 7500. In my opinion way too high for road trips.

With all of the above the same, and the diesel 3.308 gear, the numbers are better at 146 MPH at the rev limit (likely would be aerodynamically limited), 60 mph cruise at 4800 RPM and 75 mph at around 6000. Might still be too high (60 MPH cruise is for country driving, 75 for interstate).

How rare is a 3.308 gearset? Can I get one from a dealer for a reasonable price? Will it still work with the LSD and carrier? Thanks for all the info.

Brian

j9fd3s

iTrader: (3)

you could prolly still get it from a dealer. the diesel trucks are 81-84?

mike

rotor vs. piston

If I remember right, the diesel gear sets are not avilible new anymore. I did a salvage yard search on the internet and found one for 150+ if I remember right. I'll have to look back threw my emails.

Even with the 1.115 ratio I'm getting 167mph, mabey I'm just not relizing something.

Forcus

I don't think you are including the primary ratio - this is between the engine and transmission.

Forcus

bump

Cloud

Off-topic, but at least it keeps your post at the top...

How are you planning on connecting the bike tranny to the standard rear diff? On SAE cars I have been involved in, and other projects utilizing bike engines and 4 wheels (like a Cub Cadet lawn tractor with a 1200cc bike motor), there was still always a chain drive.

Sounds like an interesting project. What'll it weigh? Any links to something similar so I can check the suspension specs, etc? Good luck!

Cloud

TTT for an answer.

Forcus

Sorry about that - I typed a big long answer before and then something happened and my post didnt go through - so I said screw it

The bike engine functions by being rotated 90 degrees from its orientation in the bike frame. The cylinders face longitudinally in the car. The trans output, which is a sprocket, is then converted for bike engineed car use by welding a U joint holder to the sprocket (these are available for sale from companies, not a recommended shadetree operation). A conventional driveshaft can then be run back to a conventional differential.

With a bike engine, weight is around 900 lbs. 1200 lbs with a car engine and conventional transmission.

The suspension is pretty simple, 5 link rear and double wishbone front, coilovers all around. There is alot of room for small changes in design if you wish.

Here are some links:

http://www.championmotorcars.com/
http://www.striker1.plus.com/
http://biketransplant.tripod.com

Forcus

another

Cloud

Very, very nice...thanks for the links, I will be pouring over them for quite awhile. Nice solution to the tranny and d/s problem, sounds excellent.

Thanks again, and good luck - that will be a LOT of fun when you're done. Did you find the gears you were looking for yet?

Forcus

No, but now I know what gears I need to find. I should be able to just use the 3.308's and it will provide a good combination of cruising RPM, top speed, and fuel economy.

I have more links and if I think about it a little later I'll post them. There are quite a few yahoo groups devoted to them (locost, lowcost, lotus, striker, caterham, westfield, etc).

You might want to check out the caterham site for more pics. You can make a Lotus ugly but functional or nice like the blue one I posted.

Have fun. It's a cool project.