[dzenno]

Something that bothers me in the datalogs is how the actual boost vs. boost set point show against each other. I know that at this point there's no boost leaks on the car and the car is really running great, BUT, how is it that actual boost in 2-3-4th gears sometimes doesn't follow target (setpoint) and is lower by even 2psi in certain cases. Mind you this was a really hot day (~85F) and the car didn't get proper cooldowns at the strip but still, is this ok to be like that in some circumstances? Attached is a datalog of one of the 1/4 runs..100% meth...100%UT, 0%ign corr..any ideas?

[jpsimon]

It just looks like the stock turbos can't handle 20psi through multiple gears. That's a ton of boost man, are you just trying to kill the stock turbos before getting the RB's?

[supracg]

I think this was a track run for him so he was running the highest settings.. but i think jp is right, the stock turbos are just runnin out of air

[dzenno]

Originally Posted by jpsimon

It just looks like the stock turbos can't handle 20psi through multiple gears. That's a ton of boost man, are you just trying to kill the stock turbos before getting the RB's?

not trying to kill them, just really don't care too much at this point at the same time this is what shiv is recommending these days to run with race gas and meth (UT: 100%)...only at the 1/4 though not for a DD setup..i run UT at 75 with meth daily, 55 without meth..100 is for only a couple pulls down the quarter...really i think there seems to be no point/benefit in going above 80-85 UT as turbos just won't hold that much..

supracg, you're right, this was at the 1/4 strip..

[forza1976]

Wow, what did you run on that run. I bet it was a good time from what that log shows. Looks pretty darn strong!

[dzenno]

that was a 12.2@119.8...ran faster on the same setup before 12.3@121 just this run was on a much more humid/hot day that the 121mph run..street tires 19'' rims 2.0 60'

[OpenFlash]

Yep.. Turbo limitation. No way stock turbos are going to support 20psi at high rpm. And in low gears, the engine outruns the turbo so there is no way it will make full boost in 1st and 2nd gears. Very typical.

Shiv

[dzenno]

Originally Posted by shiv@vishnu

Yep.. Turbo limitation. No way stock turbos are going to support 20psi at high rpm. And in low gears, the engine outruns the turbo so there is no way it will make full boost in 1st and 2nd gears. Very typical.

Shiv

sounds reasonable but your advice is to run 100 UT on race gas and meth at the 1/4 to squeeze out max numbers...but if most of the time we're running above 4.5k rpm and given they won't hold that boost there, is there really any advantage in raising this beyond 80-85? i guess doing a few runs can tell but given the above graph what do you suggest to be the most optimum settings for 1/4 racing with all boltons, meth and race gas?

the only reason I can see to run this high of a boost target is to get a higher avg boost value in the upper rpms then you'd typically get with a lower setting...for example, setting 100 UT, by 6200rpm you'll be at around 17.5 psi or something...with a 75 UT setting you'll be pushing around 14-15 psi at 6200rpm..is this why you're recommending 100 UT??

[OpenFlash]

Short answer: yes

[MFKN3]

Will the stockers hold 17.5psi (75% UT) reliably with meth for daily driving? How do I know when too much is too much - will the autotune start raising Debug 2 (IC)?

[rbaldwin28]

Originally Posted by xsboost

Will the stockers hold 17.5psi (75% UT) reliably with meth for daily driving? How do I know when too much is too much - will the autotune start raising Debug 2 (IC)?

Its not going to hurt anything if your turbos can't hold boost up high in the rpm band its just that the normal vacuum that the engine produces is raising faster than you can spin the turbos and create boost. If you can make 20 psi of boost at 6000rpm and the motor is creating a strong vacuum robbing you of 3psi but your turbos are already at 200,000rpm and just can't spin any faster with out destroying them. Getting a larger compressor turbine and housing would help. You might also check to see that your waste-gates are not leaking as this would make your pressure drop worse and begin earlier in the rpm range.

[dzenno]

from what i've seen in the procede datalogs these turbos can hold up to 18.5 in the datalogs which is about 17.5 at the manifold...obviously you have to be running with meth and/or race gas to keep it safe...higher boost targets on these turbos are reachable (20psi, 19 at the mani) but they won't hold for more than a couple hundred engine rpms...

[Trojan4evr]

always something to learn. Thanks OP and Shiv and others for helping me understand

[jpsimon]

just a simple compressor upgrade/clipped turbine and you can run that no problemo. once you get your fully upgraded turbos in your mind is gonna be blown!

[MFKN3]

Originally Posted by rbaldwin28

Its not going to hurt anything if your turbos can't hold boost up high in the rpm band its just that the normal vacuum that the engine produces is raising faster than you can spin the turbos and create boost. If you can make 20 psi of boost at 6000rpm and the motor is creating a strong vacuum robbing you of 3psi but your turbos are already at 200,000rpm and just can't spin any faster with out destroying them. Getting a larger compressor turbine and housing would help. You might also check to see that your waste-gates are not leaking as this would make your pressure drop worse and begin earlier in the rpm range.

Thanks mate. Pumped it up to 75% UT under meth and 10% IC (simply because I haven't data logged yet - but I bet it has auto tuned to 0% IC anyway. Without meth I run 55% UT and auto tune drops debug 2(IC) down to 0% and agression stays around 1.5

My car hits approx 17.2psi under boost and feels great - hasn't missed a beat, no missfire, etc. Will datalog tonight to check debug 7, 2 and 6, etc and do some fine tuning.

I've taken a few buddies for a spin and they shit their pants. Well done to Shiv, the tune and meth kit is great