higher boost/lower timing - how far is too far?
 

At what point does raising boost (and lowering timing) to make more power becomes dangerous, assuming that you still aren't seeing any knock counts? I know that sometimes there's a point where more boost doesn't increase power, but I'm talking about where you are still seeing gains from more boost.

It seems like you see more and more people running what used to be considered "unsafe boost levels for pump gas."

Just wondering how you know when to stop...

Thanks!

it depends on the turbo being used and the corresponding efficiency

of course there are other factors at play

...good question..i think the most people are doin is 25 on pump....i guess u wont know the breakin point until something.......breaks..

What's mostly catching my attention are those running 26-30 psi on FP Red turbos with just 93 octane. Seems like a lot of boost compared to what people have traditionally run without a T3+ turbo or lowered static compression.

at some point you will run the turbo to high enough boost levels that the car will knock and/or the turbo will be out of efficiency range. knock is obvious but being out of efficiency of the turbo is as easy/hard as not making power after a certain boost level since the turbo will be blowing hot air. Once you find a boost level tune timing and fuel.

As MrFred kind of pointed out here...

https://www.evolutionm.net/forums/sh...4&postcount=11


https://www.evolutionm.net/forums/at...hmentid=124817

...on average (this is an evo8 turbo map btw) going above 23psi is really where you'd start seeing the efficiency start to drop off. Up to around 26 psi isn't all that bad, and 27-30psi seems to stay in the same efficiency range. It all boils down to how hot the IAT's are actually getting with the higher boost levels. This is generally why you'll see people with water/alcohol injection taking advantage of the very high boost levels since they are cooling the air charge a bit anyways by design.

On the stock turbo I would say its most beneficial to tune @ 23psi while trying to get as close to MBT before the onset of knock.

I've seen people running upwards of 30psi on 93 octane. I'm actually one of those morons from time to time. When the weather is cool, you have a good FMIC, and the turbo is decently efficient at that range, and you have enough fuel to support it, it works out well. The thing is boost is just a number. Even tapping different pressure sources on the manifold will yield different PSI levels, sometimes 4-5 psi different. Most gauges I see people using and quoting numbers off of also aren't very accurate.

On the "typical" evo though, running over 25psi on the stock turbo day to day probably isn't the most efficient way to get things done. Most cars run best between 20-25psi as measured by the JDM map, with a good exhaust, decent FMIC, and enough fuel on 93 octane.

Now if your running E85 or race gas, throw all that out the window...........

Interesting. I guess I ought to hurry up and get my AIT sensor bung welded onto my UICP so I can monitor those temps. I have a good FMIC and a Red. So far I've run it up to 26 psi and there is a significant gain with every pound of boost.

EDIT: I am of course tweaking the tune as I go, datalogging with EvoScan and monitoring via KnockCEL on the fly, etc.

Thats freakin awesome. I would love to figure out where the best efficiency range is on my turbo. I really wonder how the efficiency of your motor effects the math. I figure that my 2.4L is bigger displacement, but my (single overhead cam)head doesn't flow as well.

according to here
http://www.rbracing-rsr.com/turbotech.html
I need roughly 450CFM or 36 lbs/min for 300hp. Now, how the heck do I figure out whats actually getting pushed through the motor? Like say I figure out that with my airflow I'm getting the 36lbs per minute I need, how do I figure up whether I'm in the efficient zone?

First find your compressor map, then datalog your airflow in "lb./min" with evoscan (I know version 2.5 can give you rough figures). Find out the volume of air at your peak boost and make a dot representing where it is on the chart every 500rpm to make a graph similar to MrFred's above.

Is there a compressor map available for any of the stock variant turbos?

OK, so I log the air-flow in terms of lb/min. Then plot it on the graph in 500rpm increments. But the numbers that are on the left, I can read that it says pressure ratio. I just don't understand how to figure out what PSI it would equal.

according to this guy,
http://www.automotivearticles.com/Turbo_Selection.shtml
MrFred is not plotting the y-axis right. I'm not saying that he is wrong, I just would like to understand the axis before I plot my little red dots.

..... never mind I got it.
http://www.turbobygarrett.com/turbob.../acronyms.html

Just incase somebody else reads this thread I'll add the info I just searched for.
(I'll just use the evoscan's version)

this puts MrFred's numbers right on. I'll just use the number estimates he used, each line being about 3 psi.

The one I posted above is a stock Evo VIII turbo map according to MrFred.

I have run 1 bar boost held with 18* timing up top with zero knock and drives well. flat low/mid end but great top end on fpgreen.

1bar boost? Peak and held? That has to be one slow evo... ;)