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Tuning Boost for Quarter Mile Only

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4gfun

Supporting VIP
2,009
55
Dec 10, 2007
Ask Me, Virginia
Alrighty, well I have finally got my Big 16g running where I want it. I plan on running 21 psi on 93 psi and then forgetting about it. If all I care about is 1/4 and could care less about how much boost I am running after it, what gear/speed etc should I set my 21 psi at?

I would expect that ultimately my car should trap anywhere between 104-112 mph. This is all hypothetical though.

I am aware that there are other aspects to tuning, I just want to get the boost part out of the way so that I can move on to the other parts.

P.S. I haven't noticed any boost creep either, this is probably attributable to the external wastegate. I do notice that the higher the gear I am in, the more boost I am getting.
 
Are you trying to set up some sort of electronic boost control?
With a MBC it's simple, you just set the boost pressure and that's as high as it will go as long as the exhaust isn't causing boost creep.
 
Are you trying to set up some sort of electronic boost control?
With a MBC it's simple, you just set the boost pressure and that's as high as it will go as long as the exhaust isn't causing boost creep.

No, I am using a MBC. I am noticing that the boost is higher in each gear. Wouldn't that be normal as air pressure (sorry don't know if that is the right term) increases when I go down the highway?

I thought creep is only when you watch the boost go up while in a given gear.

Sorry if I am not conveying the message properly.

So what you are saying is that if I have my MBC set, I can set it to 21 psi in 2nd gear and it should remain that way regardless of how fast I go or what gear I am in?

Thanks

P.S. I am doing some research and boost is supposed to increase in each gear due to "load". This is along the lines of what I am trying to say.
 
Alrighty, well I have finally got my Big 16g running where I want it. I plan on running 21 psi on 93 psi and then forgetting about it. If all I care about is 1/4 and could care less about how much boost I am running after it, what gear/speed etc should I set my 21 psi at?

I would expect that ultimately my car should trap anywhere between 104-112 mph. This is all hypothetical though.

I am aware that there are other aspects to tuning, I just want to get the boost part out of the way so that I can move on to the other parts.

P.S. I haven't noticed any boost creep either, this is probably attributable to the external wastegate. I do notice that the higher the gear I am in, the more boost I am getting.

Sounds good. Are you runninng stock fuel system and stock internals?:hmm:
 
You should only see strange issues like that if the turbo is way too big and laggy or if the wg is leaking a little bit. What rpm do you see 21psi at?
 
Look at my mod list.

I'm running a External gate as well, turbo ported to hell. I have a 1 Bar spring aka 14.7psi. Because of the porting my lowest possible boost is 16-17psi.

Lower your boost controller to "zero" or "no addition", you should be at wastegate spring pressure now.
Now do a WOT pull, don't worry about re-tuning as you should be rich anyway. See what your boost is at.
Do you know what wastegate spring is in your external gate? Say it's a 1Bar like mine.

Hypothetically if you have a 1Bar(14.7psi) and under WOT your loosing/dropping boost lower then 14.7 you have a leak in the charge piping/ injector seals,TB seals,etc.,etc.

Now if that's your case do a BLT!

Sounds good. Are you runninng stock fuel system and stock internals?:hmm:

Look at his mod list, internals shouldn't be a problem at the power his setup is capable of making.
 
If the wastegate is functioning correctly the boost shouldn't go any higher than what you set the MBC to.

PLEASE don't take this as a sign of disrespect because I know that you know your stuff. It is probably just ME not getting my point across.

If you google this issue it seems like this applies to almost any vehicle. I have been on the EVO forums and it seems that they encourage you to setup your boost in 3rd gear because you will build more boost in higher gears due to engine load. I have read this OVER and OVER and OVER.

Are you saying that I could just set my boost in 1st or 2nd gear and boost will NEVER EVER go any higher than I set it in 1st or 2nd gear and if it EVER goes higher than I set it in 1st or 2nd then something is DEFINITELY wrong?

Please let me know. You have always helped me out and I trust what you are saying, but I want to make sure that you are absolutely sure what I am saying.

Thanks

Sounds good. Are you runninng stock fuel system and stock internals?:hmm:
Yes and thanks, not sure what you are thinking though! :D

You should only see strange issues like that if the turbo is way too big and laggy or if the wg is leaking a little bit. What rpm do you see 21psi at?

I don't see the issues as being strange based upon what I see above. Please don't take this personal. Again, it may be the way that I am conveying information.

Thank you

Look at my mod list.

I'm running a External gate as well, turbo ported to hell. I have a 1 Bar spring aka 14.7psi. Because of the porting my lowest possible boost is 16-17psi.

Lower your boost controller to "zero" or "no addition", you should be at wastegate spring pressure now.
Now do a WOT pull, don't worry about re-tuning as you should be rich anyway. See what your boost is at.
Do you know what wastegate spring is in your external gate? Say it's a 1Bar like mine.

Hypothetically if you have a 1Bar(14.7psi) and under WOT your loosing/dropping boost lower then 14.7 you have a leak in the charge piping/ injector seals,TB seals,etc.,etc.

Now if that's your case do a BLT!

Look at his mod list, internals shouldn't be a problem at the power his setup is capable of making.

Based on what I said above, I don't think that I would have the same boost in 1st, 2nd, and 3rd gear. I think that I should have more boost in the upper gears due to the reasons that I have been trying to state above. Again, please be patient with me, I am just going off of what I have googled etc and it seems to be the same story over and over again.

I will also try what you mentioned but absolute clarity as to my first question would be appreciated.

If it is ME, then sorry for not getting it!

Thanks!
 
Yes, 3rd or 4th I'd set my target boost in. Sorry to not specify. Dialing in boost in 1st and 2nd is hard as shit anyway.
For example I'll set my boost at 26psi in 3rd or 4th and in first gear I'll spike to 28-30psi! You shouldn't have to worry about spike or creep though.
When you run in the higher range of the 16G on it's internal wastegate at 30psi though, many have problems with it tapering off to 24psi-ish. You and myself being external gate rarely have as bad creep/taper issues.

So yeah, go ahead and set your minimum boost in 4th gear, report back. If its lower then designed wastegate spring threshold, it's likely there is a leak.

Your boost in each gear shouldn't vary that much either. I'd say 2-4psi max. In my situation I know why and what is going on, so I tuned for it.
Unless your experiencing:

Boost creep - Boost steadily raises without much control other then throttle input (and typically keeps climbing until you let off)
Boost spike - Boost suddenly raises with no control, in most cases then boost settles out at preset pressure.

In both of these situations we are talking about a raise of typically 5psi or more.

Oh, almost forgot. Run a single dedicated line to your boost controller - this provides better results.
Same for your BOV, no Tees.
 
Like stated set boost in 3rd gear and above. Large turbos that boost 30+psi usually only hit 15psi in 1st gear. Thats why us built 16g guys can hit 1.4 60's since we can get good boost in 1st.
 
Yes, 3rd or 4th I'd set my target boost in. Sorry to not specify. Dialing in boost in 1st and 2nd is hard as shit anyway.
For example I'll set my boost at 26psi in 3rd or 4th and in first gear I'll spike to 28-30psi! You shouldn't have to worry about spike or creep though.
When you run in the higher range of the 16G on it's internal wastegate at 30psi though, many have problems with it tapering off to 24psi-ish.

So yeah, go ahead and set your minimum boost in 4th gear, report back. If its lower then designed wastegate spring threshold, it's likely there is a like

We are almost there. Thanks for being patient with me.

What I have been reading is that you set your boost in 3rd or 4th and the boost is lower in 1st or 2nd than it would be in 3rd or 4th. This is what I am getting on my car. I guess this doesn't matter though now that we have established that each gear will run a different amount of boost even with an external wastegate right?

What I don't get is why everyone is suspecting a boost leak if what I have described seems to be normal? Unless I am confusing everyone. :D :confused:

(Don't get me wrong, I know I need to do it eventually)

So when I run it in 4th gear, what RPM do I need to be at to see if I can get boost to go below 14.5 psi. (Not sure if I mentioned that I opened the wastegate and it's the 14.5 psi spring). Do I have to go very fast in 4th or could it be at the beginning of 4th at a low rpm?

Could I try the same test in 3rd?

I am not a big fan of high speed runs to be honest since I haven't had a speeding ticket in 7+ years but for the prior 7 years to that I had (60 speeding tickets LOL).

Thanks for any other info!

Like stated set boost in 3rd gear and above. Large turbos that boost 30+psi usually only hit 15psi in 1st gear. Thats why us built 16g guys can hit 1.4 60's since we can get good boost in 1st.

Ahh viprez586 has modified his post to include more info.

I am going to go back and read his updates. You hit the nail on the head with larger turbos. What about the 16g guys? Would you expect to see more boost in higher gears like I am experiencing or what viprez586 experiences? On my Subaru Forester 2.5 XT turbo AWD I get more boost in each gear and it has been this way for every DSM I have ever had.

Thanks for contributing.

Yes, 3rd or 4th I'd set my target boost in. Sorry to not specify. Dialing in boost in 1st and 2nd is hard as shit anyway.
For example I'll set my boost at 26psi in 3rd or 4th and in first gear I'll spike to 28-30psi! You shouldn't have to worry about spike or creep though.
When you run in the higher range of the 16G on it's internal wastegate at 30psi though, many have problems with it tapering off to 24psi-ish. You and myself being external gate rarely have as bad creep/taper issues.

So yeah, go ahead and set your minimum boost in 4th gear, report back. If its lower then designed wastegate spring threshold, it's likely there is a leak.

Your boost in each gear shouldn't vary that much either. I'd say 2-4psi max. In my situation I know why and what is going on, so I tuned for it.
Unless your experiencing:

Boost creep - Boost steadily raises without much control other then throttle input (and typically keeps climbing until you let off)
Boost spike - Boost suddenly raises with no control, in most cases then boost settles out at preset pressure.

In both of these situations we are talking about a raise of typically 5psi or more.

Oh, almost forgot. Run a single dedicated line to your boost controller - this provides better results.
Same for your BOV, no Tees.

This amended post has awesome information, thanks! When you have a second, could you answer the other questions about when I can gun it in 4th for the wastegate test? What rpm? Can I do the test in 3rd? If so, then at what rpm?
 
Last edited:
Do it at whatever rpm you build boost at.

When I set my manual controller, I go out and put it in 4th gear, then get the car to about 2000rpms and floor it. My car starts to build boost at like 1700rpm though so it might be a bit different for you. But it doesnt matter. Just get on it till it stops rising then let off, pull over, and adjust.

I would set boost in 5th gear but I never push the car much past 4th so it doesnt really matter in my situation.
 
Do it at whatever rpm you build boost at.

When I set my manual controller, I go out and put it in 4th gear, then get the car to about 2000rpms and floor it. My car starts to build boost at like 1700rpm though so it might be a bit different for you. But it doesnt matter. Just get on it till it stops rising then let off, pull over, and adjust.

I would set boost in 5th gear but I never push the car much past 4th so it doesnt really matter in my situation.

I'll give it a whirl. This makes sense because I anticipate a shift into 4th by the end of the quarter.

Thanks!
 
If you google this issue it seems like this applies to almost any vehicle. I have been on the EVO forums and it seems that they encourage you to setup your boost in 3rd gear because you will build more boost in higher gears due to engine load. I have read this OVER and OVER and OVER.

Are you saying that I could just set my boost in 1st or 2nd gear and boost will NEVER EVER go any higher than I set it in 1st or 2nd gear and if it EVER goes higher than I set it in 1st or 2nd then something is DEFINITELY wrong?

Please let me know. You have always helped me out and I trust what you are saying, but I want to make sure that you are absolutely sure what I am saying.

Thanks

As long as you can reach the target boost in 1st or 2nd then you shouldn't be going above it in any of the other gears unless the wastegate isn't controlling the boost or the MBC is leaking so much air that the wastegate isn't really opening until later.

If you have the boost cranked up to where you can't make that boost in the lower gears then the wastegate isn't really doing anything in them, it never come into play.

This is a simple matter of does the wastegate control boost or not. It's job it to bypass enough exhaust pressure that the turbo doesn't make any more boost once it opens. If the turbo does then the wastegate isn't doing it's job.

I can hit 20psi on my B16G in second, where I have issues is with it tapering off as the RPMs climb.
 
Like stated above ^^again and again, this is a BIG turbo issue and with a properly set up BC and a good one at that( not a pos manual like T'netics) you should see the same pressure in any gear on a small turbo like the 16g. Tricks you might try to smooth things out are
1- use intercooled air for WG, it's more consistant.
2- make absolute sure there are no exhaust leaks and WG is sealed super tight
3- use a very small hose from source to BC, big line from BC to WG
(this decreases spikes and allows higher psi control)
4- lots of mbc like the air compressor regulator type ones SUCK and are not consistant. Duty % is the way for me and I'll never go back. This is from a guy that spiked 27, held 26, bled off 25@7+k on an internal WG 16g. Same in every gear.
 
Something I haven't seen mentioned yet is the time that it takes to build boost (JayRolla and Steve touched on it). Given equal loads, boost will build faster the higher the gear; it actually takes longer to build boost in lower gears, even though that seems counter-intuitive.

If your MBC is set high enough that you don't allow enough time in the lower gears to hit the final boost target, you will have lower boost in 1st, then a bit higher in 2nd, etc. That is one good reason to set your boost in 3rd...you're much more likely to have time to hit the target boost, and the lower gears should be a bit lower if not the same.

Just thought I'd toss that out there. :)
 
As long as you can reach the target boost in 1st or 2nd then you shouldn't be going above it in any of the other gears unless the wastegate isn't controlling the boost or the MBC is leaking so much air that the wastegate isn't really opening until later.

If you have the boost cranked up to where you can't make that boost in the lower gears then the wastegate isn't really doing anything in them, it never come into play.

This is a simple matter of does the wastegate control boost or not. It's job it to bypass enough exhaust pressure that the turbo doesn't make any more boost once it opens. If the turbo does then the wastegate isn't doing it's job.

I can hit 20psi on my B16G in second, where I have issues is with it tapering off as the RPMs climb.

This makes sense. It was hard for me to understand but after reading this a few times I get it. I guess I can just set my boost in 2nd....save me speeding tickets and crap.

Thanks

Like stated above ^^again and again, this is a BIG turbo issue and with a properly set up BC and a good one at that( not a pos manual like T'netics) you should see the same pressure in any gear on a small turbo like the 16g. Tricks you might try to smooth things out are
1- use intercooled air for WG, it's more consistant.
2- make absolute sure there are no exhaust leaks and WG is sealed super tight
3- use a very small hose from source to BC, big line from BC to WG
(this decreases spikes and allows higher psi control)
4- lots of mbc like the air compressor regulator type ones SUCK and are not consistant. Duty % is the way for me and I'll never go back. This is from a guy that spiked 27, held 26, bled off 25@7+k on an internal WG 16g. Same in every gear.

Hey for some people it does take again, again, and again...but thanks for your patience. I see exactly where you are coming from. With a cheap MBC I can expect some deviation as you explained. Thanks for showing me some neat tricks to negate that. I bet this helps someone someday.

Something I haven't seen mentioned yet is the time that it takes to build boost (JayRolla touched on it). Given equal loads, boost will build faster the higher the gear; it actually takes longer to build boost in lower gears, even though that seems counter-intuitive.

If your MBC is set high enough that you don't allow enough time in the lower gears to hit the final boost target, you will have lower boost in 1st, then a bit higher in 2nd, etc. That is one good reason to set your boost in 3rd...you're much more likely to have time to hit the target boost, and the lower gears should be a bit lower if not the same.

Just thought I'd toss that out there. :)

Hey Calan, it's the FIC 650's faults! :D j/k

Do you mean short shifting in the lower gears and not allowing it to build enough boost?

Man you guys are awesome!
 
Did I sell you those 650's? I thought the name looked familiar. LOL (nice little injectors there ;)).

Yes, and as you can probably tell I just now got around to putting them in!

i usually set boost on 3rd gear pull. but thats jus me =] im sure alot of ppl set theres at 4th too.

Thanks for the thought!

Look at my mod list.

I'm running a External gate as well, turbo ported to hell. I have a 1 Bar spring aka 14.7psi. Because of the porting my lowest possible boost is 16-17psi.

Lower your boost controller to "zero" or "no addition", you should be at wastegate spring pressure now.
Now do a WOT pull, don't worry about re-tuning as you should be rich anyway. See what your boost is at.
Do you know what wastegate spring is in your external gate? Say it's a 1Bar like mine.

Hypothetically if you have a 1Bar(14.7psi) and under WOT your loosing/dropping boost lower then 14.7 you have a leak in the charge piping/ injector seals,TB seals,etc.,etc.

Now if that's your case do a BLT!



Look at his mod list, internals shouldn't be a problem at the power his setup is capable of making.

Well I set the mbc to no addition and although my gauge is hard to see it appeared to be at 14 psi.
 
Well I set the mbc to no addition and although my gauge is hard to see it appeared to be at 14 psi.

Any RPM. That's good and normal - if it was below 14 - you'd have a leak.
Best place to get your target boost set is the freeway - in 3rd or 4th at any MPH/RPM.
That way the engine with act as a brake as well - keeping you from blowing past the speed limit.


I cant hit full boost in 1st or 2nd on my 16g. Either can my brother and some others I know. Just not enough load or time to get the full boost.

Time to do some port & polishing :D OMG
<img src="http://www.dsmtuners.com/gallery/files/7/2/2/1/8/pict0002.jpg" alt="Ported & Polished E316g" />
 
Thanks for all of the advice here. I was finally able to set target boost (I did so in 3rd and 4th). Boost is only about 1 psi less in 2nd so that seems to be pretty good.

This is what is happening. If I gun it in 4th at a low rpm, I get my 21 psi but at around 4800 rpm it falls to about 20 psi. At around 5500 rpm it falls to about 18 psi and appears to fall to about 17 psi by redline. I know that the B16g falls off at a certain rpm but this seems to be too low.

Is this a boost leak situation?

Any ideas?

Thanks!
 
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