R&M Racing BMW M20 Adjustable Camshaft Gear

[briansjacobs]

theoretically I could do 155 with my 4.10s. You can make reliable peak power at 6500-7000 without sacraficing too much. But it's a system, as you know. I'm ending up redoing a lot of things after realizing how it works together..

maybe in theory, but you better rev to 10,000 RPM.

making 165 RWHP with 11:1 compression with 4.10 gears and Getrag 260 all I could was 136 on the revlimiter at 8000RPM. This was running Daytona, I was on the limiter from nascar 4 all the way to 1. That sucked, next time back will be with a 3.43 as I am making more power but new motor only goes to 7000

[nando]

maybe in theory, but you better rev to 10,000 RPM.

making 165 RWHP with 11:1 compression with 4.10 gears and Getrag 260 all I could was 136 on the revlimiter at 8000RPM. This was running Daytona, I was on the limiter from nascar 4 all the way to 1. That sucked, next time back will be with a 3.43 as I am making more power but new motor only goes to 7000

that's not right, your tires must have been really short, or your limiter wasn't really 8000rpm. at 7400rpm, I could definitely do 155 in 5th gear, and my limiter is set at 7500 now. if I set it to 8000 I could d 140 in 4th.

10000rpm in 5th would be over 200 ;)

http://www.enormouslysideways.net/calc.html

tire width: 235
sidewall: 50
wheel size: 15
rev limit: 7500
over drive gear ratio: .83 (G260 - 1 for 4th gear)
final drive: 4.10

theoretical top speed: 159mph

no way you topped out at 136mph at 8000rpm with a G260 and a 4.10 unless your tires were way undersized.

[briansjacobs]

have you done this in real life or just playing with the calculator?

tires 225/45/15

[nando]

Nice to see you already got it installed! When you get your motor all running, we would appreciate any feedback you can give us :)

-Riley Alexander
R-M Racing

it's running, I still haven't toyed with it yet, I just set it to 0 which I think is a degree or so retarded from where I had it before. The plan is to go to the dyno and find the best overall powerband.

the only thing I had a problem with was getting a timing belt on. The teeth on the gear are just a *tiny* bit wider than the stock (and probably somewhat worn) gear. I'm hoping it wears in a bit until I change the belt again.

[briansjacobs]

note the disclaimer at the top of the page, it does not take into consideration rolling resistance, aero, drag....

I would venture to say if I put the car on the dyno and simulate a downhill run to reduce resistance with no aerodynamic drag I may be able to hit 160. However the E30 is shaped like a brick and creates a shit ton of drag (yes that is a unit of measure) and according to my speedometer (this was before I ran GPS data) my top speed was 136 (maybe 138 but not 140)

[nando]

note the disclaimer at the top of the page, it does not take into consideration rolling resistance, aero, drag....

I would venture to say if I put the car on the dyno and simulate a downhill run to reduce resistance with no aerodynamic drag I may be able to hit 160. However the E30 is shaped like a brick and creates a shit ton of drag (yes that is a unit of measure) and according to my speedometer (this was before I ran GPS data) my top speed was 136 (maybe 138 but not 140)

of course it doesn't, but you said you were on the 8000rpm limiter at 136mph, which is just not possible with a G260 and 4.10s. I know my car won't do 159, but theoretically I could if I hit the limiter in 5th. Therefore the 4.10 is not too short. Hell it might even be too tall. ;)

[briansjacobs]

I'll tell you what, I have raced the car at Daytona and that was all I could pull out of it. at Homestead with the new motor a little short of 7000 I hit 131, and the speed is verified on GPS data, not the RPM. The old motor stopped making power at 6300 so the 1700 RPMs up to redline really did not accelerate alot. It takes alot more power to get through the air.

my new E36 style mirrors are supposed to improve top speed by 1mph. LOL

[briansjacobs]

I want to move to theory, everything seems to work there!

[nando]

I want to move to theory, everything seems to work there!

okay, tell me what tire diameter you would require to hit the redline at 136mph in 5th gear, at 8000rpm, with a 4.10 and a getrag 260?

it's not possible. you should have shifted up from 4th, because that's probably what happened, or you never actually hit redline. ;)

edit: I'll tell you. You'd need tires almost 5" shorter than stock for that to happen. I can also tell you I can definitely hit over 130 in 4th gear.

[briansjacobs]

BMW's claim was 131mph with at 6500 with a 3.46, how are you going to get to 159 with a 4.10? more power does not give you more speed, it gets you to speed quicker. The extra RPM will give you some more MPH, but you still need to overcome the drag. Hoosier racing tires create some drag, would go faster on the straight with narrower tires but then could not slow for turn 1, or turn when you get there.

You can play with your silly calculator till you are blue in the face, do it in real life and tell me how it worked out for you. I am on a race track either driving or running data 2-3 weekends a month every month for the past 11 years.

[nando]

ugh are you not understanding what I'm saying?

You said you hit redline, which was set at 8000rpm, at 136mph with a Getrag 260 and a 4.10. That isn't possible, unless you were running 13" wheels with 19" diamter tires.

How do you hit 159 with 4.10s? 7500rpm (with 235/50-15 tires), that's how. Now, I'm not saying my car will *actually* go 159mph (I know it won't), but I'm not going to hit redline before I top the car out. *that* was my point.

You couldn't have redlined the car at 136mph, if your redline was 8000rpm. It's simple math!

tire diameter: ~24"
final drive ratio: 4.10
5th gear ratio: .83:1
redline: 8000rpm

=136mph

does not compute

[nando]

have you done this in real life or just playing with the calculator?

tires 225/45/15

and to quote myself, since you apparently can't read

theoretical top speed: 159mph

no way you topped out at 136mph at 8000rpm with a G260 and a 4.10 unless your tires were way undersized.

unless your clutch was slipping, in 5th gear you would have REDLINED at 160mph. So either you weren't redlining the car, you were in 4th gear, or you're lying. I'm not saying it's the last one, either.

[briansjacobs]

God damn it, you made me go out to the garage and check my log book from September 25/26 2005. That was the last time this car ran Daytona. RPM was set at 7000, we later moved the redline to 8000 RPM but could not get enough air into the motor to achieve 8000 rpms with the stock cam and 11+:1 compression.

now running 288 shrick but with the stroke can get air to run past 7000rpm, i now shift at 6200

[nando]

there we go :D

I think you just misread when I said theoretical top speed of 159mph, and thought I said I could *really* go that fast. I'm thinking I'd top out at 140-145, but I've never tried. I do rather enjoy hitting 94mph in 3rd though :)

[briansjacobs]

what motor/work do you have done?