Newb ? About Boost @ Freeway Speeds - Miata Turbo Forum - Boost cars, acquire cats.

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Old 03-26-2008, 03:27 PM   #1
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Default Newb ? About Boost @ Freeway Speeds

I have a Nissan T25 and was wondering how much approximate boost would it be running if I were cruising in 5th gear, around 75mph? (standard turbo parts: 2.5dp, 2.5 exhuast, etc)

Is there anyway to run zero boost w/ an EBC w/ MS @ freeway cruising speeds?
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Old 03-26-2008, 03:29 PM   #2
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under atmo pressure, ie 0 boost
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Old 03-26-2008, 03:32 PM   #3
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lol hahahahahahahahahahahahahahahahahah


keep ur foot off the throttle lol


sorry i literately laughed out loud at this one

u can keep the car out of boost easily, well, sort off. (its addicting)

just drive around like a granny, if i feather the throttle, i can make it to work and back with out the motor seeing boost, (work is about 20 min drive)
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Old 03-26-2008, 03:32 PM   #4
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[QUOTE=kenzo42;233872]I have a Nissan T25 and was wondering how much approximate boost would it be running if I were cruising in 5th gear, around 75mph? (standard turbo parts: 2.5dp, 2.5 exhuast, etc)

Is there anyway to run zero boost w/ an EBC w/ MS @ freeway cruising speeds?[/QUOTE]

Yeah, dont push the pedal all the way.
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Old 03-26-2008, 03:42 PM   #5
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I didn't realize that. First time turbo setup. Thanks.
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Old 03-26-2008, 04:03 PM   #6
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75% of my driving is not in boost.

Vash-
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Old 03-26-2008, 04:42 PM   #7
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light throttle

its load based...
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Old 03-26-2008, 04:47 PM   #8
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When on the interstate the only time I get into boost is to pass people or to have fun on on/off ramps.
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Old 03-26-2008, 04:56 PM   #9
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I run in boost 100% of the time on the freeway.

What I do is pull the e-brake up about halfway but keep the accelerator to the floor. I run 14psi at a steady 75mph all day! Gas mileage suffers a little, but it's worth it for the acceleration... just release the e-brake and I don't ever have to wait for spool.
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Old 03-26-2008, 05:27 PM   #10
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Brakeboosting, it's fun.
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Old 03-26-2008, 05:56 PM   #11
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Im normaly at 15 ish in hg on highway.

brakeboosting is fun, espically when you do it in 2ed gear and spin tires ike mad =)
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Old 03-26-2008, 07:04 PM   #12
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Heh, avoid VNTs? My buddy's VW-TDI powered volvo has a variable turbo on it, and it runs ~15 psi at idle.

And there IS no closing the throttle plates.
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Old 03-26-2008, 08:21 PM   #13
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Quote:
Originally Posted by AbeFM View Post
Heh, avoid VNTs? My buddy's VW-TDI powered volvo has a variable turbo on it, and it runs ~15 psi at idle.

And there IS no closing the throttle plates.
intriguing...
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Old 03-27-2008, 06:50 PM   #14
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kenzo42, here's how it works.

Manifold pressure, be it on a turbocharged car or a naturally-aspirated one, is relative to load. If the engine is lightly loaded, then the manifold pressure is low, generally at vacuum relative to atmospheric. When you mash the throttle all the way, then manifold pressure rises. In a naturally aspirated car it will simply go to zero (equal to atmospheric) and on a turbo car, it will cross over zero and begin building boost.

When you're just cruising down the freeway, the throttle is not open very far and you are not loading the engine very heavily. In a naturally aspirated car, you'll probably be seeing maybe 15" or so of vacuum. Simply hanging a turbo on the engine does not change this.
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Old 03-27-2008, 07:35 PM   #15
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Quote:
Originally Posted by AbeFM View Post
Heh, avoid VNTs? My buddy's VW-TDI powered volvo has a variable turbo on it, and it runs ~15 psi at idle.

And there IS no closing the throttle plates.
that because it's a diesel, not because of the vnt configuration
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Old 03-27-2008, 08:49 PM   #16
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So someone has to put it out there since he's new to turbos - you should also be thinking about max time in max boost (Bell's recommendation is no longer than 30seconds of full boost - I'm sure you'd be running like a scalded dog by the time you hit 30 full seconds - I do)... Real number prob depends on alot of factors - intercooling, WI, whether turbo is oil only or also water cooled etc.. But I'm sure we can come up with a rough concensus.
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Old 03-28-2008, 06:47 AM   #17
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Just hook up a boost gauge when you go turbo. From what I have read(mostly here) cheap ones are ok, as long as its close to accurate. The most important thing they show are boost spikes, and you don't need an perfect gauge to tell you that you have a problem in that department. The gauge will tell you that you are not in boost when cruising on the freeway. With most turbos(and gear ratios), you will be boosting almost instantly when you give it a bit of gas on the freeway, but when you take away the gas, you will not be boosting anymore.
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Old 03-28-2008, 05:21 PM   #18
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Quote:
Originally Posted by mtncrvr View Post
So someone has to put it out there since he's new to turbos - you should also be thinking about max time in max boost (Bell's recommendation is no longer than 30seconds of full boost - I'm sure you'd be running like a scalded dog by the time you hit 30 full seconds - I do)... Real number prob depends on alot of factors - intercooling, WI, whether turbo is oil only or also water cooled etc.. But I'm sure we can come up with a rough concensus.
Er, basically you're getting the motor hot making that much power - more than you can dump with a sane cooling system. The 30 seconds has to be just an estimate. Many stock cars 'overboost' for a few seconds then cut back in order to keep things from melting.

If you really care, go buy some CHT guages, thread them into your cyl head, and pull out when you get to where you'll melt parts. EGT, CHT, oil and water temps are what is going to limit how long you can boost.


Quote:
Originally Posted by Mach929 View Post
that because it's a diesel, not because of the vnt configuration
Er, we had several different turbos, several different maps, etc. It definately isn't always in boost at idle, stock TDI's certainly aren't.

Think for a second about a non-VNT turbo which is spooled to 15 psi at idle - meaning it's flowing ~20 hp of burnt fuel and whatever air. Just when do you think a turbo that size will get out of its efficiency range. My guess: just off idle.
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