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      09-22-2015, 11:21 PM   #1
Loboost
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Stock linear power vs JB4 Big Block Torque

I want to make this clear off the bat, this thread Is not to bash the JB4 it makes awesome power and transforms the car into a beast and has times lips and dyno#s to prove it.

Now to the point of this thread I removed my JB4 and sold it since I am planning on selling my M3 shortly to get a X5M.

What I noticed is that since returning my car to stock it is obviously slower but what is interesting is it still seems faster at least from 6k to redline. Let me explain with the JB4 and additional torque traction was non existent so trying to leave from a stop aggresively was usually met with spinning tires or DTC stopping all of the fun too early. With the stock tune the car just takes off with minimal wheel spin and the power builds nicely all the way to redline and the engine seems to rev quite freely and without excess wheel spin in real world driving the car just seems faster.

With the JB 4 on various maps including a linear based map 6 the power seemed to come on too quickly to maintain traction and 1st and 2nd are pretty much useless. Once in 3rd the car hooks up and pulls hard but the power band seems to be done at around 6500rpm. I am not saying it would not continue to pull to redline but it just seemed that the engine was laboring and wanted to be shifted at 6500 rpm and the car is probably faster if driven that way.

I know that the small turbos are creating to much back pressure and choking the engine at the higher Rpm's. I know bigger turbos would solve this issue as long as the fuel system is also able to keep up with demand.

So do you guys enjoy having all the torque early with a shorter power band and short shifting or would you prefer to keep a similar to stock power band up to around 5K then have the hp ramp up all the way to redline instead of nosing over?

I personally feel after having tried both the stock power band seems to be more appropriate for the car. I think these cars with larger turbos and a improved fuel system would be very fun to drive and would really be a game changer in 1/4 miles and roll races.

It will be interesting to see how some of these new turbo offerings will do from 5k to redline!

Just thinking out loud.

Last edited by Loboost; 09-22-2015 at 11:47 PM..
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      09-23-2015, 06:06 AM   #2
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When I want a more linear feel I use the //M map 5. But while the OEM tune may feel "stronger" to redline it's just your butt dyno not calibrated At the dragstrip the cars run ~116mph stock and ~123mph+ tuned pretty regularly with no other mods.

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      09-23-2015, 06:13 AM   #3
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Also gonna attach a baseline dyno for you (no tune) and you can see that power is pretty much flat from 6500+ with a slight taper even on OEM tuning. Its just the nature of the Turbos. It think BMW did a phenomenal job in actually keeping the power steady to redline.

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Last edited by Mike@N54Tuning.com; 09-24-2015 at 08:00 AM..
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      09-23-2015, 11:51 AM   #4
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Jb4 map is not linear in power, but it's a linear increase in boost with rpm but that unfortunately creates almost an exponential swell in power. You can create custom maps though with jb4 and make a more linear power band if so desired
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      09-23-2015, 12:04 PM   #5
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I think you hit the nail on the head regarding bigger turbos and more fuel. The car is probably violent in 1st and 2nd and thus 3rd gear feels tame once the car hooks up. As stated, the car is clearly faster on the strip and making more power on the dyno.
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      09-23-2015, 01:17 PM   #6
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Interesting post.

I prefer the instant power that the JB4 offers. You can always keep stock boost up to 4500 rpm using map 6 then add more power after that range.
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      09-23-2015, 07:28 PM   #7
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Wow I at no point in my post tried to bash the JB4 I stated that from the beginning! I also stated there are dyno #s and time slips to prove it works.

I am only talking about power delivery. Mark my words when Pure turbo's and some others are fully supported everyone will say how awesome it is to be able to make power all the way to redline.

The whole point of my post was about the stock linear power band, I think the thing that is most prevalent is how the torque drops off significantly at the higher rpms and hp does not really rise. This gives the sensation of power falling off even if it makes more power than stock. This sensation seems to be worse with the higher stages and as you stated the turbo,s are out of steam and the car is faster if you shift at 6500rpms! I already stated that in my original post as well.

I was just trying see what everyone thought about the power band.

Regardless currently with the exception of few actual tunes JB 4 is the best way to tune for larger turbo's etc. But to maximize everything the vehicle still needs a larger fuel system and bigger turbo's, and upgraded clutch paks or a beefier clutch.
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      09-23-2015, 10:46 PM   #8
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Quote:
Originally Posted by Loboost View Post

I personally feel after having tried both the stock power band seems to be more appropriate for the car. I think these cars with larger turbos and a improved fuel system would be very fun to drive and would really be a game changer in 1/4 miles and roll races.

It will be interesting to see how some of these new turbo offerings will do from 5k to redline!

Just thinking out loud.
because BMW spent time and money making a appropriate system. All the JB4 does is add power, and change the way power comes.
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      09-24-2015, 12:12 AM   #9
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+1 - to everything you have said about the power band. The nature of a turbo is to be efficient in a range of 3-4000rpm. A car manufacturer can then decide where in the rev range he would like to put that effiency matching a given car type.
With a "high reving" engine like the S55 this becomes a difficult compromise between good everyday torque and actually utilizing the full rev range.
Installing the JB4 increasing the boost this experienced effective rev range is narrowed, hence it will be slower to reach full power and run out sooner. All of the sudden its not so fun to rev the car anymore... Car will be faster - of course, but more fun to drive - maybe not.
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      09-24-2015, 12:43 AM   #10
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Quote:
Originally Posted by harkes View Post
+1 - to everything you have said about the power band. The nature of a turbo is to be efficient in a range of 3-4000rpm. A car manufacturer can then decide where in the rev range he would like to put that effiency matching a given car type.
With a "high reving" engine like the S55 this becomes a difficult compromise between good everyday torque and actually utilizing the full rev range.
Installing the JB4 increasing the boost this experienced effective rev range is narrowed, hence it will be slower to reach full power and run out sooner. All of the sudden its not so fun to rev the car anymore... Car will be faster - of course, but more fun to drive - maybe not.
Thank you for Clarifying what I was trying to say!

Faster but not as fun anymore.
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      09-24-2015, 12:43 AM   #11
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OP tried to say 'flat power band' when he said linear. Some people misunderstood it as 'linear increase.' I too think BMW did an awesome job (nearly) keeping the max power to red line.
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      09-24-2015, 01:18 AM   #12
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An increase in acceleration must be what we experience as "thrill" (just something I though off haha). This will stop when the power increase cannot overcome the increase in drag. So from that point the car will feel like dying...

Nice theory - right?
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      09-24-2015, 07:57 AM   #13
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Quote:
Originally Posted by darge82 View Post

Second thing, no offense, but even in stock form these cars do not have a linear power curve. Horsepower Plateaus @ 5,500rpms and falls slightly by redline in stock form. TQ peaks very early, around 3,000 RPMs and starts to fall around 5,000 RPMs in stock form. This is not a linear power delivery. Even in stock form you can feel the car stop "pulling" around 5500 all the way to 7000 RPMs. I have driven and built cars with very linear power curves and the car keeps pulling HARD to redline, this car, does not. @ 5500 its done, it just kind of "maintains" from there in stock form.
+1

as demonstrated by the attached dynos above.

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      09-24-2015, 07:58 AM   #14
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Quote:
Originally Posted by 8600RPM View Post
Jb4 map is not linear in power, but it's a linear increase in boost with rpm but that unfortunately creates almost an exponential swell in power. You can create custom maps though with jb4 and make a more linear power band if so desired
I remember you created a pretty cool map. Can you post your user setting again? Did you ever dyno that map?

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      09-24-2015, 10:51 AM   #15
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Those of you running map 2 or 7...what do you limit your boost at in 1st and 2nd? Just curious
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      09-24-2015, 10:55 AM   #16
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Quote:
Originally Posted by Siciliano611 View Post
Those of you running map 2 or 7...what do you limit your boost at in 1st and 2nd? Just curious
I fully limit boost in 1 and 2 (stock boost levels)

Mike
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      09-24-2015, 11:00 AM   #17
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Quote:
Originally Posted by Mike@N54Tuning.com View Post
I remember you created a pretty cool map. Can you post your user setting again? Did you ever dyno that map?

Mike
I don't have the car or jb4 anymore. I essentially used map 6 as an additive map running a tick boost to 5500 and then adding boost from there until redline. Worked great. Never got a chance to dyno
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      09-24-2015, 06:11 PM   #18
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Quote:
Originally Posted by Mike@N54Tuning.com
Quote:
Originally Posted by Siciliano611 View Post
Those of you running map 2 or 7...what do you limit your boost at in 1st and 2nd? Just curious
I fully limit boost in 1 and 2 (stock boost levels)

Mike
What psi amount do you set those two values at to make those gears be stock
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      09-24-2015, 06:46 PM   #19
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Quote:
Originally Posted by Siciliano611 View Post
What psi amount do you set those two values at to make those gears be stock
Setting to 15 should do it.

Mike
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      09-24-2015, 06:47 PM   #20
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Quote:
Originally Posted by 8600RPM View Post
I don't have the car or jb4 anymore. I essentially used map 6 as an additive map running a tick boost to 5500 and then adding boost from there until redline. Worked great. Never got a chance to dyno
Sorry to hear that. Why did you sell your car?
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      09-24-2015, 10:50 PM   #21
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Quote:
Originally Posted by Mike@N54Tuning.com View Post
I fully limit boost in 1 and 2 (stock boost levels)

Mike
So if you need to set it to stock power levels to hook up you just confirmed what I said in my original post that the car seems faster stock in real world use because of limited traction. Just sayin now add drag radials then it is different but now it can't go around corners and a M3 is now straight line machine. There are a lot of cheaper better suited vehicles for straight line duty.

Now with that said I a know a JB 4 equipped vehicle is still faster than stock as proven with dyno graphs and time slips etc.

As I said before the car feels faster stock since it likes to rev and has better real world traction. I did not create this post to take anything away or tarnish the JB4 reputation.

I love big block torque the JB 4 creates, (this is just my opinion) but not at the cost of not allowing it to rev freely to redline takes away from the cars soul even if it is faster short shifting.

In stock form the car makes more hp than torque even stage 1 makes more torque than hp. When torque is higher than hp then it will make the engine feel sluggish at high rpm's even though it is probably faster.

That's why the guys that are looking to go fast are looking at upgraded turbos so the engine can rev more freely and continue to make power.

Last edited by Loboost; 09-24-2015 at 11:02 PM..
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      09-29-2015, 03:19 AM   #22
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Quote:
Originally Posted by darge82 View Post
Modulate throttle in 1st gear, as soon as you hit 2nd it dead hooks and its out from there. Also even from a 2nd gear roll around 2500 RPMs, just stab the throttle and BYE! No tire spin.
I agree with the premise of your entire post. People who just want to mash the throttle at any time have never driven a powerful car before. They might *think* they have, but nope.

However, I have no idea what you're talking about 2nd gear traction. If I bury the throttle in 2nd gear like you describe at 2500 rpm, the tires let go at about 3500-4000rpm. I literally just tested this to get the RPM value where I lose traction.

Since the day I picked up the car from the dealership a year ago until today, I have never had enough traction to floor it in 2nd with the stock MPSS tyres.
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