Raising the rev limiter on a stock S54

[Anri]

You make a good point. I could downshift into 2nd but

By going to 2nd your revs will be near the rev limiter which is not good this
will make the car very slow because it won't accelerate. From 2nd to 3rd
the gap is way too much (look at the chart I made for you)

Study race boxes. 1st gear is in low 3.00 and the rest are low
and also spaced very close to each other.

Like I said the 5spd/6spd is a grocery gather gear box and to get
the good out of it you need to use 3rd for very slow corners and 4th will
be on the mid straight and then 5th to top speed.

You need to understand the idea and it will be easier for you to make
a comfortable choice without doubts otherwise no progress towards
Podium. I feel like you never looked at the charts I made for you ?
Note the RPM drop and you will see the rpm's the engine is at.


Regards,
Anri

[bigjae46]

You make a good point. I could downshift into 2nd but if I had a 4.27 then I’d be at least closer to the sweet spot for the rev range in 3rd. Then I don’t have the mostly useless revs above 135mph.

Interesting.

Part of the reason I was debating a 3.91 or a 4.10 is I can get them cheap. I might try out a 4.27 at some point.

EDIT: A 4.27 is very interesting. I will have to look into sourcing one and an extra ZF clutch LSD.


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[Anri]

just too short in 5th gear at one track…I have a 5 speed.

Hi,

You are confused, if its 5 spd does not mean its too short.

ZF E36M3 5spd ratios are the same ratio as the G420 6spd. ZF minus the
6th gear which is used for cruise and to achieve 170-180mph as of bonus the ZF
is almost 27pounds lighter...

ZF 5spd ratios bellow:

4:20
2:49
1:67
1:24
1:00

Getrag G420:

4:23
2:53
1:67
1:23
1:00
0:83


So when you say I have a 5spd that does no mean you are shorter than
the OEM 6spd for your intended use.


Note the Graph when shifting at 7500rpm and when you upshift you are
not falling in the higher HP range window and till the engine reaches those
revs its too late...the straight is gone.

I will not sacrifice revs for neglected loss of 2-3-4-5 hp never they wont
make you any faster....But proper gearing will make you faster. I have tested a
set up where the car has less HP but better gearing and over takes the
more HP package. Proven not a theory...

I watched the videos several times and it confirms my point I am making.

Your average RPM you are staying is around ~3800-5700rpm and at that
range S54 ain't pulling hard.....I mean listen to the engine just simple as
that. It spends more time in the mid range and very little time up top...the
gearing is way to long. On several corner exit when I see your throttle at wot
and you demand the engine "Go" you are not in hi window range...


At Laguna Seca LeMans cars are barely making 140mph cars that pull almost
3pound per hp and M3 GTR is making 142mph in the range of around 6pounds
per hp that is just because the gearing is fucked up for Laguna Seca.

Maybe about 30-40 times per year

Not sure how eager you are to Win the race or all is for fun...? There is big
difference. When one is out there to fight for podium no sacrifices are made.

Remember Racing is not Cheap in absolute by any mean!!!!

For the track revs are needed for exact reason I have mentioned and yes
if the revs are raised to say 8500rpm is better but engine will ware out faster
and something will let go sooner or later. Is why those racers who have the mind
to win the Race do sacrificed reliability and have a spare engine sitting it in their
garage and ready to be swapped...pass say 30hours the engine is pulled and
the New is in and the old one is all apart for inspection and parts replacement...

Rule book is what it is. If one is after a podium things must be done outside
of the rule book so that you have something others don't other wise it becomes
"club-racing" I have solutions which are not described by the rule book and it is
legal and will make the car faster compared to those who are strictly by rule book.
When Toyota won the World Rally they did something that was outside of the rule
book and they won the race. Later they changed the book rules for that exact
event.....

Again, your operating % range of RPM per lap is sort of mid range and away from
pick HP which makes the car accelerate slower under wot off a corner.

I likely think you are going to remain on this set-up as is.


Regards,
Anri

[bigjae46]

That’s some interesting analysis and makes sense to me.

It’s really only 2 straights where I will likely get over 8000rpms top speed and just want to hold it in 4th a little longer. This is for cooler conditions and during practice and competition. Maybe about 30-40 times per year?

It’s the section between 2:15 to 2:30 in this video…

https://youtu.be/2Vhh0iJDNT0

In that case I’m willing to accept more wear.

I typically shift at 7500. Even if I drop in a 3.91, won’t affect the number of shifts excepts in a few places where I’m not really too concerned.

I thought about a 4.27 or a 4.44 but it’s just too short in 5th gear at one track…I have a 5 speed.

Still playing with numbers. It’s a trade off. I’m pretty sure if I raise the rev limiter, I’ll be increasing my NASA avg HP. As the car sits, I’m right at 11. I want to pull more weight out of the car and I need to lose some weight. At that point, I’d be right on the edge of 10 (TT3) without having to add ballast (want to avoid). In the end, might have to stick with the 8000rpm limiter anyway…making this effort pointless. At least I walk away learning something.


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[Anri]

BigJae46,

First I would like to apologize for the long post because there so much to
consider. Easy to add 300rpm but not so easy to consider the actual facts.

If I were you I would do the following based on the data you have provided.
I put together some numbers for you perhaps you will like my suggestion
something that works well from my end.

On the rev limiter: Do not raise your rev limiter pass 8100rpm-(8200rpm pushing it)....
on a std S54 is darn drought to the limit from the factory at 7900rpm.

On a production line engines as S54 is the Balancing on the parts is
not "Race-Balanced" The pistons from factory I have measure are very
close between each other but the piston is not so light for you to increase
the revs by 600rpm, rods are also not exactly light for its length at 139mm.

One should understand that every 100rpm pass 7900rpm as the factory
rev limiter the ware of the engine at 8500 increases by almost 20-30%
the 1.52rod ratio wants to rape the side wall and cog it.

Those who have tune and share "Bro on my daily I rev to 8500rpm bro and
no problem"... sure you are doing it ones twice and for very short time...track
engine do stay a lot of time in hi Harmonics...window....and the stress of the
parts are quadruple compared to the "Bro" cruising in NY City at 2am from idle to
8500 and next light slow down because cop is behind us....

So the 600rpm does not sound by much but you will
ware out the engine more than if keeping at around std rev limiter.

The abused S54s I have seen apart which were revved pass 7900rpm, most have
shredded damper aligning pin which is pressed inside at the nose of the frank.
This is because the Second Order Harmonics are going so violent back and
forth that the 4 torx bolts can not hold the damper in place and the damper
slip so little that holds on the pin and then the pin brakes till the damper rests
on the 4 bolts.

The damper itself from heat cycles the Elastomer dries out and its changing
the wide Frequency which has been tune from the factory and no longer support
that.

BMW MS and PTG Team never ever revved more than 8400 on a soft cut and
hard is at max 8500rpm.

When you push anything pass 7900rpm- 8500rpm-9000rpm Dynamics balancing
is absolute critical,pistons, rods, small end big end etc...must be as light as possible
and balanced.

There is a single downside of having oil squirters is that they spray so much oil
under the piston crown to cool it down that the oil gets stuck there as a film on the
rods pours because they are cast...that this makes the parts little off balance. Part
reason why Dry-Sump system is very helpful on this part and pulling the oil from the
parts via suction and also the vacuum and sucking the oil which is splashing all over
the crank, rods, pistons..etc...

Every New Sachs Kits I install on engines I always sent for balancing and always comes
somewhere between 10-18grams off that is a lot...18here, 4 there, 1 elsewhere.....and
when you combine it becomes one rattle box of parts.

When we had the track E46M3 I installed solid (delrin) engine mounts and tranny
and pass 7900rpm to 8300rpm the engine vibrations were so loud in the tranny tunnel
it felt like the guts are all falling on pieces....then had to back up the revs 8000rpm

I would not pass 8100rpm on std S54 max if you want to have long lasting engine.




Gearing: I know exactly what are you asking from the engine at the track when you
want say need the rev higher so that you will hold on one gear and avoid shifting.

Note, the charts I made for you and take this numbers and compare it to your telemetry
track info.

By rising the rev limiter as you aim so that you don't shift you are going to gain very
little...1mph here 1mph there....

If I were you I would put 4.27 ring and pinion. Why ? sounds absurd but in real world
your car will be faster because the 4 and 5th gap is very nice and close. 3rd gear will
be used in low speed corners which is great because it will act like tall 1st gear as on
all race gear boxes and ones you accelerate 4th gear rpm drop will be small and then
on 5th gear the rpm drop will be right closer to Pick-HP and then at the end of the straight
you will reach your top speed right bro the rev limiter.

Hi speed like 100mph-120mhp+ one needs power to fight the air drag. Look at Dodge Viper
ACR at the curb weight as the E46M3 std can't reach 300km/h-180mph due to its massive
aero, an engine that is almost 2.5 times the size of an S54 and massive 650hp or so.

Our BMW engines are hi revving and one need relatively short gearing and very little rpm
drop so that to fight the drag.

Don't forget in race gear box all the gears are used at the track. Not sure if you have driven
Laguna Seca but the GTRs were filling up 5th gear at this given short straight....


So in your case you will same as now 3rd 4th and 5th I assume is why you are asking to rev higher
so that you don't up-shift to stay on 4th gear ? or you upshift in 5th before. I assume your engine is
tuned and your power has been shifted to the right aka up top.


With 4.27 even at low speed off a corner you will be right "In-Cam" 4500-5000rpm so your window
range will be all out usable and the S54 will be always in easy to pull hard on the revs.

Take look the charts and lets look at it together, share more info from the track telemetry.
such as what is the slowest corner at Cota let say.

Note in Blue the RPM drop between gears. 4.27 is "Win-Win"

Regards,
Anri


3,62





3.91




4.27

[bigjae46]

Hi,

Okay and one more question, you mentioned NT01. I assume
you are running 275 35 18 ? as no less tires is used in the
E46M3 world.

Anri

275/40R17 which is the same diameter as a 275/35R18


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[Anri]

Right now, top speed on my home track is 125mph which was set in the Jun when it was 90+ degrees outside, on NT01s, and some room for improvement. I figure I will be around 129-130 with some improvement, cooler weather and stickier tires. I want to stay in 4th gear to save a shift.

Fastest track I will drive at is COTA - at 139 mph lifting at the end since I had a plywood splitter causing the front end to porpoise. Probably going to be around 142-143mph if I don't have to lift. I don't see that getting much higher. With a 3.91, I should be fine at any track in the US.

Hi,

Okay and one more question, you mentioned NT01. I assume
you are running 275 35 18 ? as no less tires is used in the
E46M3 world.

Anri

[repoman89]

8400rpm would be a really nice set point if it’s actually mostly safe. That’s an even 5% increase which would mostly compensate for the 8% speed decrease in each gear with a 3.91 while still providing the 8% torque to the wheels boost. Plus it sounds like with the full set of bolt ons the car can make peak power up there.

As noted already though, would definitely have to be more careful about the limiter since it can be a couple hundred RPM off.

[bigjae46]

Hi,

Okay.

What is your home track/s top speed you are reaching out ?

Give me the top speed of the track which has the longest
straight you ever get. The lower tracks with lower top speed are
not important for what I have in mind.

Regards,
Anri

Right now, top speed on my home track is 125mph which was set in the Jun when it was 90+ degrees outside, on NT01s, and some room for improvement. I figure I will be around 129-130 with some improvement, cooler weather and stickier tires. I want to stay in 4th gear to save a shift.

Fastest track I will drive at is COTA - at 139 mph lifting at the end since I had a plywood splitter causing the front end to porpoise. Probably going to be around 142-143mph if I don't have to lift. I don't see that getting much higher. With a 3.91, I should be fine at any track in the US.

[Anri]

Trailer. Its fun to drive on the track...not so fun on the street.

Hi,

Okay.

What is your home track/s top speed you are reaching out ?

Give me the top speed of the track which has the longest
straight you ever get. The lower tracks with lower top speed are
not important for what I have in mind.

Regards,
Anri

[bigjae46]

Bigjae46,

I have a question, you mentioned that your car not street legal.
If its not how do you go the track ? via trailering the car ?

Regards,
Anri

Trailer. Its fun to drive on the track...not so fun on the street.

[Anri]

I've considered a 3.85. Its shorter but the 3.91 is more optimal by my calculations. I could very well be wrong. I am willing to take the risk. I've rebuilt 3 diffs so far so I'm getting building skills down. Not a big deal if I have to swap in a different gear ratio.

Bigjae46,

I have a question, you mentioned that your car not street legal.
If its not how do you go the track ? via trailering the car ?

Regards,
Anri

[bigjae46]

I've considered a 3.85. Its shorter but the 3.91 is more optimal by my calculations. I could very well be wrong. I am willing to take the risk. I've rebuilt 3 diffs so far so I'm getting building skills down. Not a big deal if I have to swap in a different gear ratio.

[Rudbari]

Why not go with 3.85 from e92 m3 manual

If I can get a few more revs I can use shorter gearing without an upshift. I’m on 3.73, want to go up to 3.91.

I know there is an argument that taller gears are better but data from my experiment tells a different story. If I compare data to someone with a 4.10, they have a distance time delta and speed gain advantage when the car straightens and under full throttle. 4-5mph at some points. RPMs are slightly higher, more accurate and precise throttle steerIng.

Real world, I only really catch him through turns. Most cars I run down in turns. I’ve driven E46s with 3.91s, it’s faster. Can be more of a handful but I’m OK with that.


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[SliM3]

8500 will definitely put your stock fuel injector duty cycles @ >90%. I suggest throwing in one size bigger if you go that high.