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2G Setting a target PSI for an EVO III 16g

Gwaihir

Proven Member
62
9
Jun 18, 2018
CHELMSFORD, Massachusetts
Reading through the threads about evo iii 16g. I've prepared my car for a tune (my profile is up to date) with new fuel system and all the other supporting mods needed to up the boost on my 16g past stock PSI of 12. My question is how do I know what I should be selecting as a target PSI for a tune?

I would like to think there is some math to the madness that can at least point me in the right direction. So below I have some rudimentary thoughts on how the PSI, turbo and fuel system relate. Let me know if I'm on the right track.

I know that flow rates of the turbo are piece in the puzzle and from what I have read in these threads:
https://www.dsmtuners.com/threads/the-difference-between-a-small-16g-and-a-big-16g.318980/
https://www.dsmtuners.com/threads/16g-flow-rates.375030/
https://www.dsmtuners.com/threads/evoiii-16g-lbs-min.208897/

15PSI on an evo 16g is going to be mid 20slbs/min. 20 PSI will start to show high 30s.

From this thread https://www.dsmtuners.com/threads/injectors-and-fuel-pumps.244522/ I found that 750 injectors at 80% are going to flow about 43lbs/min so I know that is my max limit I want to hit. Does PSI effect this at all or is PSI only going to impact the fuel pump?

My pump is currently without a rewire and according to the same injector/pump thread it looks like the Walbro 190 is going to support 43lbs/min of flow at 15PSI. I don't expect that my injectors would need to be open at 80% at this point though correct (due to the output of the 16g at 15PSI)? So I could go to a higher PSI, knowing the fuel pump will flow less than 43, but that will be ok because my injectors aren't near 80% DC and the turbo isn't close to flowing 43lbs/min yet?

20PSI shows the walbro 190 at about 38lbs/min. That should be in the ballpark of where the output of the evo 16g is at that PSI.


So based on maths (with the assumption that all the above makes sense) my max target for my fuel system without a rewire on the pump should be 20PSI? Do I need to back that off a bit to compensate for creep and maybe target 18PSI?

I'm running 93 Octane if that matters at all.
 

rEclipserGST

Supporting Member
1,704
55
Nov 17, 2007
Columbus, Ohio
Are you attempting to do this on 450 injectors? Because you never stated which.

Also, why aren't you rewiring the fuel pump?

Such a beautiful car, why the halfassery?
 

Gwaihir

Proven Member
62
9
Jun 18, 2018
CHELMSFORD, Massachusetts
Are you attempting to do this on 450 injectors? Because you never stated which.

Also, why aren't you rewiring the fuel pump?

Such a beautiful car, why the halfassery?


If you read my profile like I mentioned in my post you would see I have FIC 750s installed. I haven’t had the chance to rewire and it’s cold in MA right now so I won’t be doing it for at least a couple of months. I don’t have anywhere heated to work on the car.

So what half assery are you accusing me of? If you can’t bother to read the details I provide and have an attitude don’t bother posting. You literally added zero value to the conversation and don’t even come close to answering any of the questions. You just came in here posting judgement.
 

rEclipserGST

Supporting Member
1,704
55
Nov 17, 2007
Columbus, Ohio
You are right. I should of went out of my way to click 3 more buttons, instead of you just posting that missing info. You literally posted everything else.

Rewire the fuel pump or you it won't last. That is a broad statement. Think outside the box.

On an internal wastegate, you will be fighting boost creep.

Should be no issues running 20 psi on a 16g with 750's. Evo injectors are 560 with a 16g.... do the math.

I've run 21 psi on 14b. Had around 83% IDC before swapping in my 1000cc injectors. My 190 was rewired. Enjoy.
 

stillrunning

Proven Member
135
68
Oct 10, 2013
brandon, Florida
For reference I'm running a stock engine, 14b, ~17-19psi on average, fic 750cc, 250lph pump not rewired, larger side mount intercooler.
I see a max of just under 70% duty cycle at 10.5 afr.
At this pressure ratio the 14b & 16g should be relatively comparable.
 

Stapl3

Proven Member
1,548
119
Oct 27, 2004
MI, Michigan
You're thinking about it too much. You'll get a ballpark answer here but the answer is to just do it and end up where you end up. Most people get their setup together and go to get a tune with a preset psi in mind. "I want to run 20psi, I want to do 25psi". The reality is this. You turn the boost up slowly until you hit a limitation. For your case, it's going to be fuel. Tighten the plug gap down, up the boost, and with 93 you're going to be lowering timing until it all jives and you find a happy medium of timing not at zero and boost as high as can be. Then you'll mod from there to get more power correctly.

Boost is an arbitrary number. Where it ends up is where it ends up. Set your psi around the tune, not the other way around.
 

1cleangsx

Proven Member
680
554
Sep 28, 2013
Cheyenne, Wyoming
Go e85! My evo 3 16g was beast when I was able to add some timing with e85. I was on fic 650’s with a non rewired 255. I started with a 50/50 mix and monitored my idc’s. Even on a 50% mix I was running like 23 degrees timing up top and the car pulled like a freight train, super fun on the street! Most boost I ever ran was 27 to 28 psi, flowing around 36-37 lb/per min, that was on a totally high mileage stock 6 bolt at 6000ft.
 

19gsx91

Proven Member
1,201
294
Apr 20, 2011
Walworth, New_York
I agree with @Stapl3 you can have an idea of a ballpark of where the car will be happy but until you start dialing everything in it's a guessing game.. on my evoIII 16g with 850s behind a 5spd with just minor bolt ons I managed 350awhp @24psi.... on 93 octane. on a non-rewired 255. everyone has their reasons for why they don't do something so I'm not going to get into that with the OP nor reclipse. I held off for the longest time on doing certain things because I always wanted to be able to "put it back" quickly if the need arose.
 

Gwaihir

Proven Member
62
9
Jun 18, 2018
CHELMSFORD, Massachusetts
Thank you for everyone’s feedback. Sounds like 20PSI is pretty standard to run on the evo 16g. It’s only a few PSI above stock evo settings.

Just to close/clear this up my original question was supposed to be: What is the max safe PSI I can set my 16g to given my setup and is there a mathematical way to know that it is safe?

As PSI rises the fuel pump supports less and less air flow. The injectors don’t seem to care what the PSI is, and as we all know you increase PSI the turbo will flow more air. So the pump and turbo have inverse relations as you crank boost. Somewhere those lines cross on a graph and that’s the max target that I think would be safe to run as PSI. The catch is where they cross also has to be below the flow rate that the injectors can support which for 750s is 43 lbs/min. Which is close to the 16gs limits.

So as others have pointed out my pump is my limiting factor which I already knew. My question was what was safe PSI and it seems everyone agrees as is 20 is ok and I can go higher with a rewire.
 

stillrunning

Proven Member
135
68
Oct 10, 2013
brandon, Florida
Of course there are mathematical models, the ecm is doing just that but overall that's beyond me.
Things you can keep in mind are, as mentioned before, psi is not everything.
The MAF measures air volume entering the turbo where it is compressed and then psi can be measured.
PSI is generally going to be the product of a flow restriction of some sort.
An engine with an efficient intake tract & good VE will make more power with less psi because more air makes it to the cylinder.
Compressed air is hot and less dense and hot air has a lower threshold for self ignition which affects potential "psi" you run
The compressor maps are not going to take into account engine VE or restrictions after air leaves the turbo.
The fuel pressure the engine sees should be static, meaning at the injector tip it should always be effectively ~43.5psi constant, the fuel pressure regulator compensates for differential pressure at the tip from vacuum to positive manifold pressure to maintain that constant.
So if you have 20psi of boost at the intake manifold to maintain the effective 43.5psi constant the fuel pump will now have to be able to deliver flow at 63.5psi at the injector tip. As fuel pump pressure is increase flow is generally reduced, you can figure this out by looking at the fuel pump flow chart.
On 93 octane you will probably have to reduce timing at torque peak/point of highest cylinder pressure.

There's just allot to break down and for me it's beyond breaking it down in a short post.

Anyways, not sure if any of that helps at all but it's a relatively huge topic with allot of variables.

As mentioned don't over think it unless you really want to understand everything which can be a very deep topic.
 

lasthope05

Proven Member
1,163
271
Mar 31, 2006
Philadelphia, Pennsylvania
To put it simply. The pump is limited by flow rate and pressure. The injectors are limited by size, airflow and afr. You can stretch out 750cc injectors by running leaner AFRs but nobody is going to be able to tell you anything relative to your setup. Two cars with identical mods can have vastly different IDCs can fueling demands while running the same 20psi.

Honestly, just run it and the car will tell you what it likes. The pump and injectors are a perfect match for the 16g. You're over thinking things.
 
Last edited:

JusMX141

Moderator
15,087
1,130
Dec 13, 2005
Greensburg, Pennsylvania
Just to close/clear this up my original question was supposed to be: What is the max safe PSI I can set my 16g to given my setup and is there a mathematical way to know that it is safe?
Impossible to know for sure because there are literally a million variables. Fuel type, tune, air temp/density, intercooler efficiency, air intake type/size, exhaust flow, injector size and flow rate...even spark plug heat range can effect how an engine's max safe boost level before knock is seen on a given setup. We have a dead-end thread where such discussions have been open-ended for years:

https://www.dsmtuners.com/threads/max-safe-boost-merged-10-6.143197/
 

Gwaihir

Proven Member
62
9
Jun 18, 2018
CHELMSFORD, Massachusetts
That thread is interesting. There sure is a lot to account for. Makes me wonder if Mitsu actually figures all of that out ahead of time, or if they just pieced stuff together and tested at different psi intervals until they found one that made the car run the way they liked given other fixed components like injectors and pump.
 

19gsx91

Proven Member
1,201
294
Apr 20, 2011
Walworth, New_York
Mistu overbuilt everything on the 1g, stressed parts a touch more on the 2g. you have to remember what the stock boost pressure was originally meant to be on our cars. anything beyond that and it's pretty much rule of thumb.. that's why people are saying don't kill yourself trying to do the math just go by the conventional knowledge.. dsms have been around a long time, and people have been modding for 2+ decades now. tried and true methods are just that. tried. and true.
 

Gwaihir

Proven Member
62
9
Jun 18, 2018
CHELMSFORD, Massachusetts
Are you attempting to do this on 450 injectors? Because you never stated which.

Also, why aren't you rewiring the fuel pump?

Such a beautiful car, why the halfassery?


I was able to get my rewire done this weekend. I have the car in for tuning now at Racetek NH. I’m doing what I can to keep it healthy.
 
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