Go back to 3.73 from 4.10?

[10/10ths]

So I switched to the 4.10 about 4 years ago for my autox car, it was one of the best upgrades for my car back then. The courses I ran on in western WA were tight to medium sized and I would rarely hit the rev limiter, 7000. Except for one site where a shift to 3rd was justified because I could stay in it for 3-4 seconds.

Well now I'm in Indiana and looking at videos of the all local sites, I might be hitting the limiter a lot more here, the sites are big with long corners/slaloms. I dont want to ride the limiter for obvious reasons so I'm thinking of switching back to the 3.73. My car is pretty well set-up and I run slicks so I'm able to carry a decent amount of speed on course. The last time I was on the 3.73 I was still on street tires and stock springs, not to mention my driving skill wasn't as high. I'm thinking of going back to the 3.73 to potentially help my overall times and reduce the "work" of shifting up and down in autocross, also reducing engine and tranny wear.

Anybody made this switch and then switched back? Anyone swap the diffs depending on the site they are running?

Thanks for your replys,
Justin

[Hick]

what car?

swapping my m42 to a 3.73 was the best mod ive done so far. way more driveable around town, and great for the autocross... still hit the limiter in 2nd from time to time

[10/10ths]

what car?

Sorry, a DSP 325i

[lennon]

me and a few friends have all tried 3.73 and 4.10s in our 325i's, and i think we're all of the opinion that the 3.73 is better because of the longer 2nd, like you're thinking. 3.73 matches the motor just fine for me. my buddy has a 3.91 (i think) from an auto 325is in his car now and he claims it is a nice compromise.

[nando]

personally I'd rather have the 4.10s and a higher redline, but in DSP you can't really do a whole lot about that.

[kamotors]

4.27 ftw:)

[gearheadE30]

I'll be making the switch soon as well, I believe. Second gear is too short when the M42 effectively runs out of power by 6500 revs. Perhaps the M20 is a little different, but I bet that you'd be able to use more of the torque of the engine with a 3.73. And first gear might actually by useable for something, heh

[10/10ths]

personally I'd rather have the 4.10s and a higher redline, but in DSP you can't really do a whole lot about that.

I would love a higher redline as well, but I'm nervous going to 7k as it is. I avoid it pretty much, never on the street, and at the track I would usually shift around 6k. Autocross is really the only situation where I need the extra revs.

I bet The motor would keep pulling past 7k though, after I did the exhaust overhaul (headers, straight pipe, tri-flo) and the miller ecu the power didn't "fall off" anymore.

[nando]

it probably still falls off just not as bad. I wouldn't rev past 7k with a stock cam and valve springs either, there's no point. You would need headwork to have useable power above 7k which isn't legal in DSP, so you're probably best off going with the 3.73. Plus you can always swap it back later, it isn't your only car and it's not that hard right? :p

[10/10ths]

Plus you can always swap it back later, it isn't your only car and it's not that hard right? :p

Besides being heavy, it looks easy enough. But honestly Ron swapped it for me last time, my car was already there for something else so I just had him do it.

I thought about taking the 3.73 out of Jenna's car and putting the 4.10 in that...see how long it takes her to notice :grin: Seriously though, I wish I could but the 4.10 for the street isnt a good idea, especially for her car at 220k miles.