High RPM (3500-3900) boost issue... not reaching target??

[GeneralTJI]

Ok...

So I built a high RPM tune (2006 LBZ). It fuels all the way to 4k (went through EVERY table that has anything to do with high rpm stuff). After doing my custom lift pump setup rail pressure holds up top now as well. But Boost is dropping off??

My tune is nothing crazy, but it makes around 25-26psi max in the 2500-3000 rpm area... and then starts dropping off... I am seeing maybe 22 at best at 3900. I played with turbo vane positioning to see what I could do there.... when opening the vanes up some (19-20 in the high rpms) I only saw 19-20 psi at 3900. When I closed them down a little tighter (around 40) I see 22psi at 3900...?

I raised my high rpm boost target tables up to around 26-27psi and that had no effect.

I used the timing calculator and targeted about a 45/55 split.

Truck seems to smoke worse up top too, especially with the vanes opened up (which makes sense) Was really hoping to see 24-25psi up top... seems like I have enough fuel, I'd like to make better use of it up there and also make a little bit more power (running this tune to keep out of 5th gear).. I aimed my tune at making more top end power and not a ton more torque (again trying to go a little easier on the trans)

Just looking for some pointers / advice?! THANKS!!!

(I am close to 7000ft elevation as well...)

[LBZoom]

Hey General,

One thing to remember is that the desired boost table values are not what the gauge will read, you have to subtract out barometric pressure. For example if the desired boost table value is 30psi and barometric pressure is 14, your actual boost is 16psi on your gauge.

Also, make sure your max allowed boost is high enough (table b2226), and your vane position max tables as well (b2222-b2224)

Also, check your intake air temp multiplers and your altitude multipliers aren't a limiting factor as well, hope this helps!

[bballer182]

Hey General,

One thing to remember is that the desired boost table values are not what the gauge will read, you have to subtract out barometric pressure. For example if the desired boost table value is 30psi and barometric pressure is 14, your actual boost is 16psi on your gauge.

Also, make sure your max allowed boost is high enough (table b2226), and your vane position max tables as well (b2222-b2224)

Also, check your intake air temp multiplers and your altitude multipliers aren't a limiting factor as well, hope this helps!

good explanation :good:

[LBZoom]

Why thank you! lol

Also, another point worth mentioning General, is that the desired boost table will overcome the vane tables to achieve the desired boost pressure as far as I know. So if you need to experiment just adjust the desired boost table and don't worry about setting your vane position yet, it'll save you some steps for now. Just be sure to disable the MIL's associated with the boost system because if the vanes position doesn't match correctly it will throw a check engine light. You can go back and "dial" in your vanes to achieve faster spoolup at a later time.

[bballer182]

Why thank you! lol

Also, another point worth mentioning General, is that the desired boost table will overcome the vane tables to achieve the desired boost pressure as far as I know. So if you need to experiment just adjust the desired boost table and don't worry about setting your vane position yet, it'll save you some steps for now. Just be sure to disable the MIL's associated with the boost system because if the vanes position doesn't match correctly it will throw a check engine light. You can go back and "dial" in your vanes to achieve faster spoolup at a later time.

setting LOW mm3 values in B2231 and B2232 will eliminate the need to turn off those DTC's. setting the values low with force the ECM to reference the boost tables and adjust the vanes to match whatever you have requested boost wise. Setting the values higher than stock (or whatever the mm3 per rpm you operate at) will force the ECM to reference the vane tables and whatever boost is made is whatever boost is made.

[GeneralTJI]

Thanks for the input. I had already adjusted all my boost tables to what I was looking for. But the truck won't meet the boost in the upper rpms??

I had it set as high as 27psi (after comp. for atmospheric pressure) and it still only reaches 21 maybe 22 up top.

Adjusting vane position did allow me to get a little or more depending on what I requested.... which is strange, I did not realize the truck will override the vane posi table! It's acting like it's not reading from the boost tables actually. I would think I wouldn't need THAT much vane posi. on the top end to make the boost. I am running about 25% more pulsewidth up top btw. I'm sure being at 7000ft just makes it that much harder for the turbo to reach those boost levels but that still seems low.

I have been over and over all tables related and I don't see anything.. I'd post the map but I'm an HP guy :( (long story) .... I do appreciated the advice though.

It's a little frustrating, I'm all about the high rpm power... (mainly because I'm trying to keep the torque numbers from getting to high on a stock trans).. but the truck does seem to make pretty good power even with the boost low.


etting LOW mm3 values in B2231 and B2232 will eliminate the need to turn off those DTC's.

What's the name of these tables since I don't have EFI live? I haven't thrown any codes so it must not be too out of whack but just curious to take a look etc.

Thanks!!!!!

[bballer182]

What's the name of these tables since I don't have EFI live? I haven't thrown any codes so it must not be too out of whack but just curious to take a look etc.

Thanks!!!!!

anything over 1800RPM you shouldn't have to worry about it as the tables in stock form are already set to 1 and 2 mm3 which is low.

[GeneralTJI]

Oh.. the boost control enable / disable tables... gotcha, yea I left those as they were.

How much vane % is in theory ok to run in the high rpms?? (with my 25% added pulsewidth) .. I was running up around 40 on my max vane posi tables from 3600 on... figured going to high would be counter productive? (choking out the motor and running really high drive pressure etc.)

[Dozerboy]

Are you using the edge for your only boost gauge? That ain't going to work neither is running your truck up to 4000RPM. There is no reason to go over 3600 with the stock turbo. you shouldn't need your vanes at much if any over 20% at high RPMs.

[GeneralTJI]

Keeping the truck out of 5th gear on a stock trans is a pretty good reason to rev the truck up close to 4k.

I am using the Edge to monitor boost.... the truck targets about 26 and up to around 32000 rpms it seems to hold pretty right on (Edge reads 26) I suppose it wouldn't hurt to install a manual gauge at some point!?

I agree I shouldn't need high vane position, but for some reason the truck won't build that kind of boost without closing them down. Maybe thats because I'm not running super high pulsewidth levels? I just don't have the fire to drive the turbo with the vanes opened up??

[JoshH]

At your altitude, you should be running pretty solidly in the medium altitude boost tables and maybe even partially into the high altitude tables. You need to make sure you are adjusting all the boost tables to match your desired boost. Also, keep in mind that when you run higher RPM, the amount of air consumed by the engine becomes increasingly larger. You may be exceeding the lbs/min of air the stock turbo can flow thus diminishing the amount of boost pressure. You may be able to get more boost out of it, but you run the risk of pushing the turbo outside its map. I'm not saying that is what is happening, but it is a possibility and something you should keep in mind. It is even more likely at your high altitude.

[GeneralTJI]

I completely agree... I did adjust all tables btw... vane tables as well etc.

I actually assumed the motor wouldn't breathe that well in the high rpms, thus allowing me to hold boost pressure to try and maintain power.. but it appears that it does breathe well enough the stock turbo may not be able to hold that kind of boost..... power wise it does feel pretty strong .... If this is the case, it's not surprised that people can make pretty big power in the high rpms with a big enough turbo(s) even with the stock cam / heads etc. .....

[killerbee]

Keep this in mind. You are challenging the choke limitations on the compressor map. Your MAF is limited by the real world air flow capacity of the turbo. Elevation is very stressful.

In my modest opinion, at that rpm, you are testing the choke limits, trying to push it further will pop the turbo. If you would like a calculator to play around with, that shows some of the REAL impact of 1. rpm and 2. altitude look here. Look at the turbo calc worksheet.

http://killerbeeperformance.com/downloads/intakes-and-induction/

When you increase elevation and rpm, the results on the bottom will start to go into infinity. These are choke limits.

If you want to see the results, put a temp sensor on the compressor output, hot CAC tube. You will see temps suddenly spike to 500 or 600F.

So my suggestion, is lower your rpm, and your expectations. Twins would be good at your elevation and air flow (maf) requirements.

[GeneralTJI]

Thanks for the link to the worksheet. According to that I am just over the limits at 22psi / 3800 rpms.

Elevation is a beotch.... been fighting with it for a long time! The difference is amazing. Times at our tracks here just don't seem very impressive when you start throwing them around online but until you come and run on a track at 5k ft in 80-90 degree weather people just don't get it. At my house I generally have about 11.43 psi of atmospheric pressure (I live at 6700ft)

The high rev aspect of the tune is nice... I can pass someone on the highway without entering 5th gear under heavy throttle etc. In fact I don't use 5th or 6th for anything but cruising.

But, I should quit screwing with this truck trying to squeeze everything I can out of it.. I bought it for a weekend driver (have a company car) and to pull my fast car to the track (not to try and make it the fast car lol).

If I had the money, I would do a built trans and at least a 4094vvt or maybe twins :) .... but I don't :doh2:

[roadkill81304]

Don't feel bad I have been fighting similar issues. I can make 37-40 lbs boost (mech guage) at part throttle in 4-6th gr with conv. locked, but at full throttle 27 is is about max. I also live at higher altitude but the strange thing is I could make better boost #s at 7000 ft or above than I can achieve @ 4700 ft. Baro usually runs about 12.3 here. I have a custom twin turbo setup but the a/rs arent quite right yet so maybe that has somn to do with it it. If i had the money I think i'd go with mpi and idaho rob's tuning. Its definitetly a battle when you don't have all the resources necassary to do the proper tuning on these things, but the challenge is rewarding.