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View Full Version : Lowering boost, how low is too low?



AmF_15
08-21-2006, 06:39 PM
Given you have the tool(s) to lower the boost
Question 1: How low is too low?
Question 2: Would your MPG skyrocket?
Question 3: With a way lower boost can you run lower then 91 pump fuel?

Thanks

AreSTG
08-22-2006, 12:34 AM
not giving it too much gas will increase your mpg

AmF_15
08-22-2006, 12:47 AM
:D thanks for answering "none" of my questions.....next

Matz
08-22-2006, 04:33 AM
Given you have the tool(s) to lower the boost
Question 1: How low is too low?
Question 2: Would your MPG skyrocket?
Question 3: With a way lower boost can you run lower then 91 pump fuel?

Thanks


FWIW, I have an MBC. On my previously-stock maps, I had it set to min, which is about 14psi. I never had any problems.

My MPG was around 25-26mpg, mainly because I didn't have the urge to floor it. The same might apply to you if you also lower the boost. So Tim's answer actually does answer one of your questions. In any case, if you don't boost as high (either from not "giving it too much gas" or from capping the boost at 14psi), your car won't need as much gas, so your mileage will increase. But will it skyrocket? I don't know. If you drive WOT all day long like you're at the racetrack, then you're currently getting like 6mpg, and the answer is yes. If you drive like a granny like I did before, then the answer is "probably not".

Can you run 87 octane? that's a question that I would also like answered. I would think that you can do it if you're tuned properly, but at the same time, the minimal savings on gas (for me, at least -- it depends on how often you drive your car each year) makes it not worth even owning the Evo. You need to enjoy the power every now and then! ;)

KareBearPowa
08-22-2006, 08:48 AM
Given you have the tool(s) to lower the boost
Question 1: How low is too low?


You can only go as low as wastegate pressure, 14psi.



Question 2: Would your MPG skyrocket?


No, since what makes you get good gas mileage is staying in vacumn / closed loop and not boost, your boost pressure has no standing on MPG.



Question 3: With a way lower boost can you run lower then 91 pump fuel?


In theory, yes, but you would also have to tune for it, not just lower the boost

AmF_15
08-22-2006, 08:54 AM
Perfect! Thanks for the info guys.

turbotiger
08-22-2006, 08:55 AM
Given you have the tool(s) to lower the boost
Question 1: How low is too low?
Question 2: Would your MPG skyrocket?
Question 3: With a way lower boost can you run lower then 91 pump fuel?

1. No such thing as too low. The minimum would be the wastegate spring. But then there is no reason to do that.
2. No
3. You don't need to lower boost to run a lower octane. The knock sensor and low octane map will take care of that. If your ecu is stock that is.

If you want to save gas, don't do it by running 87 octane. Just learn how to drive smoothly without mashing the gas pedal all the time. If you're really strapped for money, I'd advise you to sell the car and get a civic or some other higher mileage car that runs on 87 octane.
The price difference per month between 87 and 91 is negligible when compared to your monthly car payment.

GokuSSJ4
08-22-2006, 09:21 AM
Scot G. and other members have been able to tune for 87 octane. If saving gas is what you want or would like. My advice is to get tune for it. Maybe even having 2 maps, one for 87 and the other for 91 octane. I believe they were able to accomplish better milage as well. You should pm scot (Blak94GSX ) for details and to pros and cons of such tune.
here is a link with his user name in socalevo.net
http://www.socalevo.net/index.php?option=com_smf&Itemid=37&action=profile;u=437

AmF_15
08-22-2006, 10:21 AM
I was more or less asking a few simple questions never intending to do so myself. I am here to learn every ins and outs about my evo, mostly without using my ride as an experiment.

GokuSSJ4
08-22-2006, 10:52 AM
the reason why i have mention (tuning) is because air/fuel ratio and egts are affective on whether you run too much boost or if you lower your boost.

turbotiger
08-22-2006, 11:14 AM
I don't know why you'd tune for 87, unless that's the only grade available to you, which isn't the case in pretty much anywhere in the US.

gOt BoOsT
08-22-2006, 11:20 AM
I heard that if you remove the turbo completely...you'll get GREAT gas mileage

GokuSSJ4
08-22-2006, 11:40 AM
I don't know why you'd tune for 87, unless that's the only grade available to you, which isn't the case in pretty much anywhere in the US.

i dont know either but people have done it. Some for great milage and less amount of $$$ on gas.. Also keep in mind that its very easy to accomplish this changes on an SAFC. also the unit carries 2 different maps, so you can switch maps very easy.

KareBearPowa
08-22-2006, 11:44 AM
i dont know either but people have done it. Some for great milage and less amount of $$$ on gas.. Also keep in mind that its very easy to accomplish this changes on an SAFC. also the unit carries 2 different maps, so you can switch maps very easy.


Tuning for 87 using a SAFC? I dunno if I would even want to attempt that since you have no timing control.

GokuSSJ4
08-22-2006, 12:05 PM
i dont know either but people have done it. Some for great milage and less amount of $$$ on gas.. Also keep in mind that its very easy to accomplish this changes on an SAFC. also the unit carries 2 different maps, so you can switch maps very easy.


Tuning for 87 using a SAFC? I dunno if I would even want to attempt that since you have no timing control.
its been done.. remember that ECu+ not many have tried it or at least not a few years ago. Open ECU just came out not to long ago and most of the DSMers guys trust and know the SAFC.. It has been done, running less amount of boost and making sure you monitor your afr and egts.

KareBearPowa
08-22-2006, 12:14 PM
I didn't say it hasn't but done, just that I wouldn't want to attempt it.

Since one would be running such low boost, you would actually be in lower load columns then even negative fueling gives you on the SAFC, which means even more timing.

24+ degrees of timing up top on 87 octane makes me cringe.

AmF_15
08-22-2006, 12:23 PM
ohh btw we should be basing this off the new 06 evo IX.