[Sniz]

Went out tonight and did some runs to see what my boost was looking like. the car has felt great recently and 3rd and 4th gear just rip . the one thing I have noticed is that if I start in 3rd gear and floor it, there seems to be dip in power in the midrange in 3rd gear. If I start in 2nd gear 3rd gear feels strong the whole way. It made me curious.

I was able to capture the drop in boost in this datalog. The ambient temps were 28 degrees. Keep in mind I have never been able to get boost logs in the 14's like most people. I have a much larger intercooler than stock which is the most likely cause.

SHIV - we need an intercooler map please

You can see the dip in 3rd gear here....it actually went below 8psi! Thats lower than it will boost stock sometimes.....weird.



I immediately turned around and ran 2nd thru 4th and the boost was good and stable. It hit 13psi in the beginning of 4th but dropped all the way back down by the end of 4th. Honestly the car feels great.



I did dyno the car and on a dynojet it hit 350whp w V2, the intercooler, and forge DV....no other mods, and that was w/ no fan running into the intercooler.

[andrewflk]

If you want to feel better check out my last logs…

I’ve done logs two separate days in cold weather (~32F) with similar dips. I can’t imagine what the cold weather has to do with it but after seeing your log I think it might be worth some more cold vs.warm weather testing. Only time I ever had decent logs was when we had warm weather a couple weeks ago (~60F).

By the way I’m completely stock except for V2, I always warm the car up before logging, and I have no reason to believe I have a boost leak other than these crazy dips in my logs.

Anyone else have a similar problem?

All of these pulls were full throttle 3rd gear.



Sine wave or boost log?:



Best one but still a dip:

[OpenFlash]

There's always going to be a boost dip around 4000-4500rpm. This is caused by a valve timing phase shift at often occurs right here. Totally normal. And the colder it gets, the lower boost you will see. Especially during the first (of several) runs when intake temp readings are the lowest. It never really gets below 50F here so I can't speak from firsthand experience when temps drop to freezing levels.

shiv

[Sniz]

Originally Posted by shiv@vishnu

There's always going to be a boost dip around 4000-4500rpm. This is caused by a valve timing phase shift at often occurs right here. Totally normal. And the colder it gets, the lower boost you will see. Especially during the first (of several) runs when intake temp readings are the lowest. It never really gets below 50F here so I can't speak from firsthand experience when temps drop to freezing levels.

shiv

I 100% understand that....I was just surprised to see a dip below 8psi at full throttle. I COULD feel that dip in psi.....it lost steam for a bit then picked it back up as the boost rose in the higher rpms.

[OpenFlash]

Originally Posted by Sniz

I 100% understand that....I was just surprised to see a dip below 8psi at full throttle. I COULD feel that dip in psi.....it lost steam for a bit then picked it back up as the boost rose in the higher rpms.

If the dip is consistent and able to be felt, go ahead and bump up User TQ in that rpm range by 2-3%. With a higher volume intercooler, this would make sense.

Shiv

[Sniz]

Originally Posted by shiv@vishnu

If the dip is consistent and able to be felt, go ahead and bump up User TQ in that rpm range by 2-3%. With a higher volume intercooler, this would make sense.

Shiv

so you think I could go to 96-98% in those ranges? I'm already at 95% on 93 octane.

[jpsimon]

Shiv, just sent you a PM. I'm wondering the same thing

[cn555ic]

Wow...To change the intercooler to make the engine cooler gets you better performance, but if temps outside is too, too cold, it takes away performance...that is totally a oxymoron!!

[Sniz]

Originally Posted by cn555ic

Wow...To change the intercooler to make the engine cooler gets you better performance, but if temps outside is too, too cold, it takes away performance...that is totally a oxymoron!!

its not really taking away performance, I think its just allowing for more

[WilyB]

Originally Posted by Sniz

its not really taking away performance, I think its just allowing for more

Yes, the way I understand it, the BMW ECu is trying to deliver a constant 300HP/300TQ whatever the conditions, which is pretty cool AND leaves a lot on the table for good tuners.

[Sniz]

Originally Posted by WilyB

Yes, the way I understand it, the BMW ECu is trying to deliver a constant 300HP/300TQ whatever the conditions, which is pretty cool AND leaves a lot on the table for good tuners.

thats my understanding as well....as the ECU sees it, it can hit xpsi and make the horsepower. If the new intercooler is delivering a much cooler intake charge then the ECU decides that xpsi - 3 can do the same thing. Of course I'm making up the "3", but thats the logic that I'm seeing in it.

Hopefully Shiv can shed some light on this for us mortals....and at the same time show me how to squeeze some more hp out of my car safely. It looks like a downpipe and intercooler map may be in order. If I'm already tuning up to 98% or so on 93 octane and still only seeing 14psi.......what am I going to do when I'm running 104 octane at the strip.....tune to 105%?


Note - I'm going to need to wait until we have some 50-60 degree ambient temps before I can really see what the boost is doing. Unfortunately the road I test on is only really safe and deserted in the evening, which recently has meant 20-35 degree temps.

[jpsimon]

same here, this 15-30 degree weather at 2am probably isn't the greatest for tuning

i'm gunna be back out there tonight

Originally Posted by Sniz

Note - I'm going to need to wait until we have some 50-60 degree ambient temps before I can really see what the boost is doing. Unfortunately the road I test on is only really safe and deserted in the evening, which recently has meant 20-35 degree temps.

[Sniz]

Originally Posted by jpsimon

same here, this 15-30 degree weather at 2am probably isn't the greatest for tuning

i'm gunna be back out there tonight

[jpsimon]

I'm headed to the dyno on saturday, so i just want to get things 100% in order and adapted by then

[roller84]

Originally Posted by Sniz

one thing I have noticed is that if I start in 3rd gear and floor it, there seems to be dip in power in the midrange in 3rd gear. If I start in 2nd gear 3rd gear feels strong the whole way.

I have noticed the same thing since I upgraded to V2. With V1.4x I did not have this issue. I have a spearco intercooler installed.

[Sniz]

Originally Posted by roller84

I have noticed the same thing since I upgraded to V2. With V1.4x I did not have this issue. I have a spearco intercooler installed.

my guess is that it has something to do with our larger intercoolers. Shiv recommended that I try bumping the tq values up in this range by 2-3%, but that would put me at 97-98% still running 93 octane. Im going to try it and see how it feels....listening reallllly closely for any knock.

[roller84]

Originally Posted by Sniz

my guess is that it has something to do with our larger intercoolers. Shiv recommended that I try bumping the tq values up in this range by 2-3%, but that would put me at 97-98% still running 93 octane. Im going to try it and see how it feels....listening reallllly closely for any knock.

But 3rd gear feels good after shifting from 2nd while going WOT. If you punch it in 3rd gear then I get a power dip. I have to produce some datalogs myself to see whats happening. If I read corrrectly, you are experiencing the same thing. I don't understand how raising the tq values resolves this issue. Infact, I would think that the PSI would be too high when going WOT making a shift from 2nd to 3rd. Maybe Shiv can chime in.

[Sniz]

Originally Posted by roller84

But 3rd gear feels good after shifting from 2nd while going WOT. If you punch it in 3rd gear then I get a power dip. I have to produce some datalogs myself to see whats happening. If I read corrrectly, you are experiencing the same thing. I don't understand how raising the tq values resolves this issue. Infact, I would think that the PSI would be too high when going WOT making a shift from 2nd to 3rd. Maybe Shiv can chime in.

could you post a few datalogs in this thread? What are you tq settings now? I'm at 95% across the board. If you are not at too high a psi at that settings could you try 95% as well so we can compare?

[andrewflk]

Originally Posted by Sniz

my guess is that it has something to do with our larger intercoolers. Shiv recommended that I try bumping the tq values up in this range by 2-3%, but that would put me at 97-98% still running 93 octane. Im going to try it and see how it feels....listening reallllly closely for any knock.

I’ve got the exact same problem without an intercooler. If I start from 3rd gear I get a boost curve with a big dip down to 10 PSI. If I start in 2nd it pulls hard to 14.5psi with no problem. I specifically tested for this tonight and was able to duplicate every time. At least now I figured out how to reproduce my problem.

[Sniz]

Originally Posted by andrewflk

I’ve got the exact same problem without an intercooler. If I start from 3rd gear I get a boost curve with a big dip down to 10 PSI. If I start in 2nd it pulls hard to 14.5psi with no problem. I specifically tested for this tonight and was able to duplicate every time. At least now I figured out how to reproduce my problem.

maybe its just Maryland

[roller84]

Originally Posted by Sniz

could you post a few datalogs in this thread? What are you tq settings now? I'm at 95% across the board. If you are not at too high a psi at that settings could you try 95% as well so we can compare?

Currently at 94% across the board. I did multiple 2nd-4th gear runs and the highest peak I've read so far is 14.6psi.

I won't be able to datalog until this weekend.

[andrewflk]

FWIW - Here are my logs from tonight...

3rd gear start with dip:



2-3-4 they look great.