Built auto 8k rev

Cmiggz

Private
Jun 4, 2017
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2008 ST 335i
Has anyone figured out how to increase rev limit on 6hp21?
I have a built auto with PD clutches but trans hits a rev limit at 7200. I have spoken to both Terry @ BMS and Semin @ XHP, unfortunally car wont go past 7200 no matter what setting are changed.
 

ShocknAwe

Captain
Jan 24, 2018
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Charleston, SC
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N54/3 1er ///Mutt
Has anyone figured out how to increase rev limit on 6hp21?
I have a built auto with PD clutches but trans hits a rev limit at 7200. I have spoken to both Terry @ BMS and Semin @ XHP, unfortunally car wont go past 7200 no matter what setting are changed.

Ouch. 7800 is my favorite part.
 

Torgus

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Nov 6, 2016
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Were you able to get your auto to 7800?
If so how? Thanks

He is a manual unless things have changed.

A higher rev range is key to this platform evolving. While 7200 is nice, without displacement you NEED revs. Another 1k of revs is huge as you obviously know.

Hope there is a solution for you!
 

RuskiRacer

Captain
Jul 17, 2019
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2009 e93 335i
Yeah I agree 2js, rbs, alot of them are revving to 9k 10k rpms some even more.
 

Cmiggz

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Jun 4, 2017
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2008 ST 335i
He is a manual unless things have changed.

A higher rev range is key to this platform evolving. While 7200 is nice, without displacement you NEED revs. Another 1k of revs is huge as you obviously know.

Hope there is a solution for you!
Yes deffenlty would be nice to rev this thing out but i have yet yo see someone do it with an auto
 

ShocknAwe

Captain
Jan 24, 2018
1,577
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Charleston, SC
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N54/3 1er ///Mutt
I don't think 9-10k will ever be feasible on stock DME or even a good idea with our architecture. From what I recall it's a hard limit at 8200.
 

RuskiRacer

Captain
Jul 17, 2019
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2009 e93 335i
You rev to 8 k ? thats something I wanna start doing. Why from an architecture standpoint do you think its not a good idea?
 

Torgus

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Nov 6, 2016
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You rev to 8 k ? thats something I wanna start doing. Why from an architecture standpoint do you think its not a good idea?

The N54 is an undersquare design. It is not square or over square. It will never be a 'high' reving motor because of that. The head is also a limitation with the valves but that is a different issue. That being said 8160 is still decent. 8160rpm limit comes from the DME hard limit. I don't think most have pushed much past that with standalones. If they have they don't talk about it. Regardless it will always be a rev limited motor.

Some reading:


An oversquare engine allows for more and larger valves in the head of the cylinder, higher possible rpm by lowering maximum piston speed, and lower crank stress due to the lower peak piston acceleration for the same engine (rotational) speed. Because these characteristics favor higher engine speeds, oversquare engines are often tuned to develop peak torque at a relatively high speed.

An undersquare engine at a given engine speed, a longer stroke increases engine friction and increases stress on the crankshaft due to the higher peak piston acceleration. The smaller bore also reduces the area available for valves in the cylinder head, requiring them to be smaller or fewer in number. Undersquare engines exhibit peak torque at lower rpm than an oversquare engine due to their longer crank throw and high piston speed. Undersquare engines have become more common lately, as manufacturers push for more and more efficient engines and higher fuel economy.




Here is a list of the top 5 highest production piston speeds:

1. Honda S2000:
Engine Code: F20C1
Bore/Stroke: 3.43" X 3.31"
Redline: 9000rpm
Piston Speed: 4965 Ft/min

2. Lamborghini Gallardo
Engine Code: N/A
Bore/Stroke: 3.25" X 3.65"
Redline: 8000rpm
Piston Speed: 4866.67 Ft/min

3. Acura Integra Type R
Engine Code: B18C5
Bore/Stroke: 3.19" X 3.43"
Redline: 8400rpm
Piston Speed: 4802 Ft/min

4. BMW M3 (Germany)
Engine Code: S54
Bore/Stroke: 3.43" X 3.58"
Redline: 8000rpm
Piston Speed: 4773.33 Ft/min

5. Honda S2000 2004
Engine Code: F22C
Bore/Stroke: 3.43" X 3.57"
Redline: 8000rpm
Piston Speed: 4760 Ft/min


The n54 piston speed reaches 4708 at 8k


There is plenty you can read up on about piston speed, rod angle, etc.



An n54 making 750whp is making 250whp per liter of displacement at 7200 rpm. That is pretty damn good and doable with stock cam and head. Something most other 3l powerplants can't do. At least not 3Ls back in 2006 when the n54 was released.
 

Milan

Sergeant
Dec 24, 2016
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your mom
Are you sure you can’t shift higher than 7200? I mean mine is also at 7200 so I haven’t tried but why not change your shift points higher in xHP and then raise your fuel cut in the tune?
 

Terry@BMS

Sergeant
Platinum Vendor
Jan 23, 2017
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Yes your BEF is set to 8000rpm, it's something on the trans side holding it back. I've taking our built motor to 8k but we also did an MT swap so it was no problem. :)
 
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zomski101

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Dec 28, 2019
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335i
Did you try talking to Rod Sutphin? I had his trans tune without the proper dme adjustments and my car randomly downshifted to 7.9k after a pull. Had something to do with the dme tq limiters idk this is beyond my knowledge.
 
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nyt

Sergeant
Sep 15, 2019
335
1
292
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2010 335xi
Has anyone figured out how to increase rev limit on 6hp21?
I have a built auto with PD clutches but trans hits a rev limit at 7200. I have spoken to both Terry @ BMS and Semin @ XHP, unfortunally car wont go past 7200 no matter what setting are changed.

What did XHP say?
 

Cmiggz

Private
Jun 4, 2017
42
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2008 ST 335i
What did XHP say?
They werent able to help me much , besides telling me to switch shift points.
I ended up going with sutphin tuning and he ended up getting everything yo work. Trans shifts way better now, driveability is way better aswell. Car shifts at 7500 right now, due to missfire up top.
 

Dennis

Specialist
Nov 5, 2016
65
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Bay
hm, I've been revving my built N54 to 7.5k for a while now with a stock 6HP19.. Haven't had any trans rev limit issue. I do have an xhp stage 3 flash on the trans.