In my search I came across the terms max/sustained boost. What's meant by "sustained" boost? am I supposed to see some constant level of boost during normal high speed (highway) driving? On my car, I only get boost going up to 0.6-0.7 (and once 0.8 for a split second) during hard acceleration only then it quickly goes back down to 0.0. With moderate acceleration (passing another vehicle) I get 0.2-0.3 for a second or two then goes back down to 0.0 again. I have a stock Turbo S. Is this normal?

 

Seems pretty normal. Turbos will only spool up under engine load. So if you are just cruising and don't floor it, they may only spool up a little.

If you are giving it a little gas, then they may spool up to max, then back off once engine load falls off as you gain speed and the engine doesn't have to work as much and starts to cruise.

If you floor it and go up through the gears, you should see your max boost a good amount of the time as the turbos spool up till you start to shift. If not, you may have a boost leak or something awry.

.6-.7 is normal boost for a stock K16 car. .8 if you have a cool day and/or get on it hard!

 

You will get lower sustained boost in hot environments..

You have a turbo S which is K24 turbos... you will see 0.8, 0.9 only on cool days.

 

But what do you mean by "sustained boost"? I only get boost for short bursts of time, during moderate to hard acceleration, and immediately goes back down to 0.0 as soon as I stop accelerating. I guess the term "sustained" is throwing me off.

I live in Dubai and today's temp was 45.5C (114 F), I got 0.5.

 

Once you let off the gas, the wastegates will open and let the boost off. I would think you would get more than .5 on a hot day. We have been around 100 here lately and I get full boost no problem.

I would do a boost leak test from the turbos and verify no leaks - you can search and find an easy way to do that.

 

I got 0.8 on the way home, is that full boost?

 

Sustained = while your foot is buried in the carpet.

X50/S should Max at .8/9 then settle to .7/.8 (as long as throttle us max and no shift)

 

i'm no expert but i have been on a recent learning curve re: this issue. my stock x50 ( k24's ) would hit .8 bar regularly but was indeed sensitive to ambient temps. i haven't yet found a freeway that would allow "sustained boost" so we hit it when/where we can, yeah?

but i think that's what's going on with you, as raineycd says. the heat really affects how these things run at full boost. my more recent acquisition which is another tt with k16 hybrids and flashed is able to hit 1.0 bar and they spool MUCH faster than the stock 24's did. but are also definitely affected by the outside temp conditions. first foggy AM in la the other morning was the first time i hit 1.0 bar in either car, and it's a gas, lemme tell ya. ymmv!

 

All good advise, Sam you are in soem serious dry heat so the numbers yo are giving seam fine.

'02996ttx50, Love it!

 

Sam,

Welcome! I think that you need to get a basic understanding of how a turbo-charged engine works. Try this site:
http://www.turbobygarrett.com/turbob...o_tech101.html

Your engine only makes boost when you need it, as in under hard acceleration. It stops making boost when you let off the throttle because it doesn't need the additional air.

The boost level is determined by the ecu program and the equipment on the car. If you were to start in 4th gear and go WOT from, say 2000 rpm, and hold it to redline, in your car you would probably see a max boost of 0.9 to 1.0 bar on your car, depending on the weather as others have noted, and a sustained boost (boost level through most of the range) more like 0.8 to 0.9.

If you did a similar run in a lower gear, you might see lower boost levels because the engine spools up so fast it doesn't have enough time to build up manifold pressure.

Hope that helps a little.

Jon

 

yeah, thankin' ya daily!

 

Woohoo! I reached 0.9 boost last night (was around 40C). Tried to push it to 1.0 but no luck ;-)

Agree, 02996ttx50, LOVE your car.

 

thx man! SamboTT had very tastefullly modded it. i'm just the caretaker
ps.. its been over 100f daily out here lately, so i have to apply boost at dawn!

 

Thanks for asking this.. I was also somewhat scared that it might not be normal to see no boost when just maintaining a constant speed. Good to know that is normal.

 

Glad you found this thread useful! It sure helped me.