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      07-17-2020, 06:19 PM   #1
bluemsp4
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N54 or n55 for Autocross?

Looking to buy a 135i and trying to figure out which is best for both daily driving and the occasional autocross?
Wife says it has to be auto, so couple of things I was wondering - what would be better, n54 or n55. I know the n55 has the dct, so out of box it would probably be quicker shifts, but I've seen a lot of good things on the xHP flash for the n54. From everything I've read seems like the n54 is better to mod but both are good. Also read the n55 tends to be more reliable.
Not trying to do crazy mods so something around 350-400whp(max). Would be doing full bolt-ons, tune, coilovers, wheels and tires.

What does everyone think is the best balance between reliability and performance for daily and autoX. What transmission would be best?

Also if anyone has any buying tips or things to look out for other than the big ones let me know.
Thanks!
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      07-17-2020, 06:49 PM   #2
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Only here suggesting you keep the 'occasional' auto-x expectations grounded....a bit of an underdog in either F Street or STU (likely landing spot if going full bolt on). It's a great car to daily - good luck with your shopping.
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      07-18-2020, 07:50 PM   #3
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Thanks for the suggestions. Just looking to have some fun and spirited driving. Was wondering which auto trans would be the better option and more durable.
Also if the n55 was worth spending a couple more thousand dollars to get the reliability?
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      07-19-2020, 09:48 PM   #4
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The N55 develops torque quicker down low in the rev range, so that might help in an autox. The old auto in the N54 is probably "stronger" if you were going to build big power, but that's hard to use in an autox situation.

I would spend the extra little bit to get the reliability to be honest...
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      07-20-2020, 08:42 PM   #5
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N55/DCT is more fun than N54/6HP.
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      07-22-2020, 12:48 PM   #6
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My first hand experience driving cars with both engines is that the N55 is more responsive. N54 will make more power tuned though. Not sure how that impacts the stopwatch in an autocross. The only N54's I ever see are either novice drivers or in 1M cars so not much of a real-world comparison can be made. I have heard people complaining about overheating in N54's at autocross. I don't see how that is possible but it's just something anecdotal I've come across.

The engine will have less to do with your success in autocross than your driving will that's for sure.
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      07-23-2020, 12:52 PM   #7
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N55/DCT is more fun than N54/6HP.
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      07-25-2020, 02:15 PM   #8
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Quote:
Originally Posted by SKI-R View Post
Only here suggesting you keep the 'occasional' auto-x expectations grounded....a bit of an underdog in either F Street or STU (likely landing spot if going full bolt on). It's a great car to daily - good luck with your shopping.

This post is spot on. The 135 is a great daily driver but outgunned when put against the cars in its class. If you do decide to get more competitive you will have to figure out a way to contain the roll up front and keep the front tires from rolling over. Honestly I would go with a 3er for a/x just because you can put more tire on that car.
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      07-26-2020, 05:38 PM   #9
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The better turbo engine for autox is the one with less lag, a lower boost threshold, and and a broader power band. It's mostly about area under the curve and throttle response. Peak power is largely irrelevant.
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      07-28-2020, 11:22 AM   #10
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N54 + 6MT is much more fun, hard to get these cars competitive thankfully they now have a class for those that modify and want to stay on 200TW
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      10-18-2020, 07:09 PM   #11
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just came across this thread - I have a 2012 135i/DCT M-Sport (64Kmiles) and I auto-x, errrr at least I did before covid. Anyway here's a few thoughts.
135i N55/DCT is fun and works as a daily driver (i needed a rear seat for my 5 yr old) and weekend auto-x very well but needs help on both fronts. With fold down rear seats I can make costco runs, load my bike (less front wheel) and even get my 8'10" surfboard inside.
My car already had the MPP installed so it makes 135is power ~320 HP/Torque. Feels plenty fast. I'll add a Dinan tune because at only $600 why not get >350hp and 400 torque? Also the Dinan tune doesn't write over the MPP which improves the exhaust note vs. stock.
The DCT works well in sport mode with sport shifting for both driving situations here in SOCAL where traffic gets stupid and there are lots of mountain/canyon runs.
My first Auto-X mod: I went out and bought Style 68 E46 M-sport wheels on CL for <$300 and wrapped them in Federal 595RS RR tires <$450, combined about the cost of a set of Bridgestone RE-71's alone. Auto-X ruins street tires. I also run Firestone Firehawk 500 street tires at +1 all around for both street and auto-x no problem.
The question you have ask yourself is: are doing auto-x for fun or to be fastest in the field? 135i = fun but the base suspension has so much understeer that its impossible to win overall. Gotta know that answer going in. There are improvements however.
After competing here in San Diego and winning in my small class a couple times I decided to improve the breathability and handling as I had more than enough power. The understeer/front wheel roll of the 135i even with MSport suspension cannot be understated.
I installed a Mishimoto FMIC because it required zero modification and I could do it in about an hour. I'm pleased.
Next I tackled the suspension in Mar 2020 so I haven't been able to AutoX on it but as a dd its been great.
I installed 1M/M3 front control arms and Power Flex black rear bushing inserts along with Dinan fixed camber plates, and Koni yellow and Eibach Cup Kit. Totally transformed the driving experience. I'm running -2 degrees camber up front and almost that much in the rear. The Power Flex blacks are inexpensive and worth the money. The rear end of these cars are super flexible and almost unstable at high breaking loads stock. Inserts are a fraction of the cost and effort of replacing bushings.
Everyone wants to modify the engine and body on these cars and that's cool (i plan to as well) but the 135i weakness are in the suspension and interior. So I modified both and now I love my car. My car had the sensatec interior that was in perfect condition but oh boy was it drab! And the inside is where we spend the majority of our time. I re-upholstered mine in a scottish tartan/leather with red stitching also covering all 5 arm rests in padded leather. What a huge improvement on the enjoyment scale. I also wanted a car that didn't have nav as the systems are old tech and the big screen on the dash looks awful long term. That's why we all have a smart phones, right?

anyway hope this helps and that auto-x returns asap.
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      01-18-2021, 03:44 PM   #12
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Sure N55 DCT, but as others have said, 135i is not the best BMW nor STU car for its class. I would say that it is a better street car than the STU competition though (M3, 350z, STI). If you want a competitive autocross car get a e36/46/92 M3. FWIW the only cars I lose in Autocross to are e92 M3 and M2 with good drivers, but I have all the suspension mods. If I wanted to widen the front to be more competitive, it would kick me into SCCA ASP or BMW SS.
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      01-23-2021, 01:00 AM   #13
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The 135i is not a great autoX car as the suspension needs a lot of work and it's relatively heavy.

That said, the N55 DCT will be the best choice for autoX. N55 torque curve starts earlier and is more linear.

But the biggest advantage is the DCT. You will get perfect shifts as they will be lightning fast and perfectly rev matched. That means you minimize time losses (compared to manual transmission) due to sloppy shifts and mismatched rpm which both cause unnecessary weight transfer.

Consult the rule book to optimize your 135i for the best class to run in. You do not need engine mods or tune to run in autoX

Last edited by PcarDefector; 01-23-2021 at 09:25 AM..
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