LocostUSA.com

It is not a Subaru part.
It comes from the Datsun/ Nissan Racing
It was used in the 240/260/280/300 Z's
The WRX from the UK had a 3.545 some others had 3.9.
The one I have is a JDM Sti with 4.18.

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American 7 5.0 T5
Lotus 15 ish?
914/H6

I have zero experience with that particular pcm. It comes down to how close you are to the design load and how flexible the tables are in the oem pcm.

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Miata UBJ: ES-2074R('70s maz pickup)
Ford IFS viewtopic.php?f=5&t=13225&p=134742
Simple Spring select viewtopic.php?f=5&t=11815
LxWxHt
360LA 442E: 134.5x46x15
Lotus7:115x39x7.25
Tiger Avon:114x40x13.3-12.6
Champion/Book:114x42x11
Gibbs/Haynes:122x42x14
VoDou:113x44x14
McSorley 442:122x46x14
Collins 241:127x46x12

This post takes into account many things I didn't even consider when choosing rear end ratios. Interesting.

Tires were 225 not 255. I wish I could put that big tire on this car but????


I have been relooking at the tires for this build. Looks like my 225/50/15's are goimg away. Oh well. And they were to big for the body. Thinking of going with 205/55/15. This will work with the wheels I have and should help with the load on the bike trans? Also I can use the Sti rear end I have with the 4.18 in it. What do you think?And thanks for the input!

Numbers would come out something like this.This is with a 11,500 readline!

1= 3.9525=49 mph
2= 2.9122=67
3=2.3715=82
4=2.1074=92
5=1.8972=102
6=1.7628= 110 faster,faster,faster?

This all tells me,short tracks+ , lost of turns+ , and this all for a little Lotus/Locost? 11/15.

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American 7 5.0 T5
Lotus 15 ish?
914/H6

Sounds reasonable to me. Are you sure the rear you have is an STi? I read that STi R180 ratios are 4.44, 3.9, and 3.54 while the standard subbie R160 is closest to a 4.18 at 4.11. It is much narrower than the R180 but probably still adequate with a low curb weight.

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Miata UBJ: ES-2074R('70s maz pickup)
Ford IFS viewtopic.php?f=5&t=13225&p=134742
Simple Spring select viewtopic.php?f=5&t=11815
LxWxHt
360LA 442E: 134.5x46x15
Lotus7:115x39x7.25
Tiger Avon:114x40x13.3-12.6
Champion/Book:114x42x11
Gibbs/Haynes:122x42x14
VoDou:113x44x14
McSorley 442:122x46x14
Collins 241:127x46x12

Was hopping you would chime in! Thanks. My parts are from the way back. The car was a 1994,a JDM.

After thinking about what you posted, the load made me think I needed to rethink the rear end. And the tire size's are close at 24".
Also made me wonder how the the 3+ gears are working on the other Bike/cars? Would give then the high top end but??
the clutch?

So 110 mph will need to work for the 11/15R1.
Thanks again. Randy

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American 7 5.0 T5
Lotus 15 ish?
914/H6

It's not so much the 110 mph top end that will kill you but the fact you'll be turning 50% of redline at 55 mph and 64% of redline at about 70 mph. Constantly running revs that high will reduce the life of the bike engine over an extended period of time. It will also punish you in the fuel mileage department. And the constant higher RPM state can be grinding on the ears and nerves from an NVH standpoint.

You may want to look at gear ratios closer to 3.0 for the diff even if it means adding a few pounds to the car simply to improve fuel mileage, engine life and overall driving pleasure.

For my R1 build, I've sourced a lightweight 3.27 diff and running 13" 205 tires it looks like I should be able to manage a 147 mph top end. Far more importantly, my 70 mph cruise rpm is down to about 50% of max revs (past redline). I'd much prefer a gear ratio in the 2.xx range for "around town" use, but plan to use the car largely as a track toy as well.

Odd thought: It may be remotely possible that the 5th and 6th gears from an '08 FZ1 (or others with the same gearing) might be a possible swap into an R1 gearbox. 1st through 4th are the same ratios as an R1, but 5th and 6th are slightly taller and keep the same relative spacing as 1st through 4th. I have done zero serious investigation into this, but may eventually. However it may also not be worth the effort involved; in my situation when cruising at 75 mph it only reduces the rpms by roughly 330.

In general, it looks like bike transmissions have been standing up to BEC use, but I'm not sure about actual transmission life. I'm not aware of any BECs that have logged more than a few thousand miles.

I've added my gear ratios spreadsheet as an attachment. It's an Open Office / Libre Office file (.ods). It looks like MS office can open it, but the calculations get turned into static values. Useful if you want the data but not much use if you want to use the auto-calc features and formulas. I'll try to find time to port the formulas over this weekend.

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.. in the world

It's true that lower revs at a given speed will result in reduced piston travel per mile.
It's also true that lower cruising revs can result in better mpg and less noise.

However, turning lower revs while towing extra weight does not extend engine life; it's just the opposite.

I haven't seen any bec 4 wheel locosts built for mpg. Many cars get better mpg than the donor bikes commonly used. The extra weight and drag will only make it worse, but factory gearing on most bikes is rather short for the torque you'd expect from a toy. Stretch the gearing out too far from stock on the bike (much less a heavier car) and you can expect durability issues. Just putting the stock bike gearing into the car has the same affect.

_________________
Miata UBJ: ES-2074R('70s maz pickup)
Ford IFS viewtopic.php?f=5&t=13225&p=134742
Simple Spring select viewtopic.php?f=5&t=11815
LxWxHt
360LA 442E: 134.5x46x15
Lotus7:115x39x7.25
Tiger Avon:114x40x13.3-12.6
Champion/Book:114x42x11
Gibbs/Haynes:122x42x14
VoDou:113x44x14
McSorley 442:122x46x14
Collins 241:127x46x12

Dosen,t the R1 peek torque at about 8000 rpm.

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American 7 5.0 T5
Lotus 15 ish?
914/H6

All of the above is true, but every BEC with an automotive differential I've seen has a lower effective gear ratio than the original bike. A stock R1 runs a 2.641 final drive. I know that loading the engine heavily at low rpms is bad, but I'm pretty sure that even a diff with stock R1 gearing is unlikely to be a big problem at lower speeds.

As an example my proposed 3.27 diff would yield a 1st gear rpm of 4,655 at 25 mph; a stock R1 turns about 3,440 with OE R1 gearing and a stock sized 17" tire. The stock R1 ratio would turn 3,768 rpms at 25 mph using my tire size. I suspect as long as the combination keeps the speed vs rpms below a stock bike, the engine load wouldn't be too badly affected. Of course I have no data to back up that assumption.

Also at 8K with my 3.27 diff the speed in each gear would be 43, 53, 62, 71, 80, and 86 mph .. nothing that typically represents a huge corner speed problem for a lightweight car on slicks on most tracks. It could also be a bit of a dog at very low speeds on the street. That is an inherent issue with a gearbox that has really close ratios. It can be optimized for top-end speeds, mid-range speeds, or low speeds, but it can't be an effective jack-of-all-trades.

* edited to fix a reference to stock bike gearing *

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.. in the world

You may want to look at gear ratios closer to 3.0 for the diff even if it means adding a few pounds to the car simply to improve fuel mileage, engine life and overall driving pleasure.

I can add a bit of 'real world' experience to this that might help..

I've recently regeared my Ford 7.5 IRS diff WAY down to combat the issues I'd had at highway speeds.. I'm running a VFR800 with a 1.9 reduction on 175-50-13s... I used to have a Miata diff at 3.9, and on the highway it was just not tolerable.. I know bike motors need to be revved to get up into the powerband (mine redlines at 11,750), but I had to really wind it up to 7K/8K just to keep up with traffic on the CA freeways.. I hated it!

Now I've knee-jerked and gone quite far the other way.. I've pulled the Miata diff and have accepted the wieght penalty of installing a Ford 7.5, now with 2.73 gears swapped in... I know I'm going to lose some of my down-low power, but as a DD/street car, this thing was just unusable as it was.. I don't yet have it running with the 2.73 setup, but even if I've gone too far, I figure I can step up to 3.08s or 3.27s if I must.. My experience so far tells me as so many other BECers have learned, somewhere near 3.XX seems to work well..

-ccrunner

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Dean

1972 Honda N600 Restomod "ccrunner's N600 VFR800 repower"

1963 Volvo P1800 Restomod
http://locostusa.com/forums/viewtopic.php?f=36&t=16309

1959 Berkeley SE492 Restomod...
viewtopic.php?f=36&t=19397

"ccrunner's 1960 MGA coupe Restomod" found on MGExp.com

Please keep us posted on how your swap works out.

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.. in the world

Found a 3.08 rear end. Think I need to look into it ?

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American 7 5.0 T5
Lotus 15 ish?
914/H6

I would if I were you.. as discussed, that ballpark ratio should keep your freeway RPMs tolerable

--ccrunner

_________________
Dean

1972 Honda N600 Restomod "ccrunner's N600 VFR800 repower"

1963 Volvo P1800 Restomod
http://locostusa.com/forums/viewtopic.php?f=36&t=16309

1959 Berkeley SE492 Restomod...
viewtopic.php?f=36&t=19397

"ccrunner's 1960 MGA coupe Restomod" found on MGExp.com

I'm running a Subaru 3.90 rear out of a 93 turbo wagon. I calculated all of this out and also bought a spare 3.60 just in case. The Subaru rears come in 3.54, 3.60, 3.90, 4.11, and 4.54.

The axles and stubs are slightly different. Most Subaru parts are fairly easy to swap, but rears may cause a headache - especially if you have custom axles.