Samps

Maybe this is a stupid question, but I'm asking anyways. I looked through all the info I could find and nothing answers my question. How can a turbo boost differently in different gears? The airflow through the motor should be the same regardless of gear selection right? How is it that people get higher boost in fourth gear than in first?

2kwik4u

This was side wondering of mine that kinda links to my other thread about the wastegates and boost and such....The only thing that I could think of would be the time you spend in each gear. For instance say you get 5lbs in first...Well you are only in 1st for short time so boost creep has little effect, then in 2nd you will hit say 7lbs...boost creep had longer to work because you are in 2nd longer....then third and so forth....However this only seems to hold true for people who get increasing amounts of boost through the gears...For those that get say 5 in 1st 7 in 2nd and 5 again in 3rd...I ahve no idea..I would suggest something is slightly wrong there.

1FastT2

iTrader: (1)

It all depends on the load one the engine. In first gear it doesnt take as much HP to pull as say fourth gear does. When there is more load on the engine the exhaust gases are hotter making for the turbo to spin faster. Its kinda hard to explain fully. For instance, you really cant spool or build boost when you are just free reving the engine. You need a load on the engine for a turbo to really spool. But when you drive the car its a whole different story. There your creating a load, where more fuel is interduced creating hotter exhaust gas temps and spooling the turbo. I hope I explained it ok.

2kwik4u

SO...Once again it comes back to an overworked wastegate. the wastegate is simply not large enough to let the extra/hotter gasses out so the boost goes up. DAYUM YOU MAZDA for not building a better wastegate.

Erik

hehe...port it to hell

1FastT2

iTrader: (1)

Well that is true for the most part but it happens even to people with large wastegates. I have my boost set at 15psi. In first gear ill probally hit about 10psi but after that the boost stays right at 15psi through all the gears.

Boost creep and the ability to build boost in lower gears is a whole different story.

adamlewis

Did you even read what he posted?


It has nothing to do with the wastegate. Its all about the amount of load on the engine.

I could run a 20G with an external TiAL WG, and Id still have trouble getting full boost in first.

Besides, if you have a SMALL wastegate youd have problems with TOO MUCH boost. Youre trying to blame it for not getting enough

Samps

So according to the info in this thread, I guess you could possibly change the boost pattern of a car with a different ring and pinion ratio.

adamlewis

Putting more load on the engine will create more boost, yes.



What is so hard about this to understand?

Tom93R1

iTrader: (2)

That would only work in a turbo car without a wastegate or if you set your wastegate to some insanely high boost level. If you have a wastegate the boost will be limited to whatever you set it at.

2kwik4u

I understand that the more load you get the more boost you will get, BUT>>>>>The wastegate is supposed to control that. Theoretically (and usually practically) you should spool to your desired boost level and then stay there througout the rest of the pull. IF you have boost set at 5psi and then you hit 10 in first 15 in second and 18 in third.....IT is still over your set boost. NOW....IF you had your boost set at 20 and you got the previous mentioned values then it would be an issue of load and restriction.

1FastT2

iTrader: (1)

Once again,

What you said is correct BUT, we arent talking about boost creep we're talking about the ability to build boost.

Samps

Is there an exact science to calculate boost patterns?

2kwik4u

OK I see I was thinking that we were talking about boost control.

RylAssassin

Yeah i have that problem Ive yet to do it properly however like reving to an exact rpm, but ive noticed when im trying to boost i only hit like 5 psi in first, then i hit like 8-10psi in 2nd then like 10+ in third and 4rth i would imagine from the logic you guys are stating would be like maybe 15+psi because of the load.
Yeah so how again would one make it an even lets say 10 psi across the board, negating first gear. would this simply be a boost controller? With this device could i simply set my boost to lets say 12psi throught the gears?
And one last question why exactly would someone want there boost to be even in all gears?

Samps

I am not sure, but I believe an EMS (or ECU) can only be tuned for 1 gear (usually 4th). So if your boost keeps jumping around it will be much harder to tune for the entire range. You will end up making some sacrifices to compensate.

This is just a wild guess.

ZeroBanger

I didn't read all the responses but I am very sure the MAJOR reason you get more boost in higher gears is because the amount of airflow into the intake. More air=more boost.

2kwik4u

To me it just makes sense to run one constant pressure....That way once you tune the car to run at the pressure at WOT then you should be set for all gears....Run the car WOT through 2nd and you should get the same fueling and power as 4th (although the acceleration would change)

HOWEVER after thinking about this for a minute...it appears that it would be a "sliding scale" of sorts as in if you add 10% fuel at a given rpm, that would just be 10% more rather you have 5psi or 7psi...

I dunno, all turbo cars/trucks I've ever had an experience with all had a set "base boost" and that was reached around 2500~3000 in 1st and stayed at that boost for the rest of the run.

RacerXtreme7

iTrader: (2)

If your car is only boosting 7 psi in first, and your turbo's boost is set at 15, and you do reach 15 in taller gears (more load placed on engine) then NO a boost controller will NOT give you more boost in lower gears. If all your doing is 7 psi and its set for 15 then thats ALL your going to make in first gear no matter what unless you alter your turbo system (going smaller turbine trim, smaller turbine A/R,) different exhaust confiuration {like smaller runners}, or intake track so its tuned for more torque lower in rev band...... Doing this of corse is going to lower your torque band and your engine will most likely fall on its face in upper RPM's in taller gears. You can raise your lower gear ratios to gain higher boost numbers BUT, most likely your car is going to be SLOWER, BOOST does not equal SPEED in this case. I would'nt want to trade off my early excelleration or hole shot just to be able to have a consistant boost number. Better yet, you want consistant boost number. Put a tiny turbo on it so it reaches full boost by 2500 RPM in first and regulate it so it never goes higher,,, theres your steady boost, this is why factory cars make consistant boost, because the potentual boost level is reached do to smaller turbo and a low boost setting, you raise that boost setting higher and it most likely WONT reach that higher setting in first gear either.... Having lower boost in lower gears is a benifit......why shread tires when you could be going forward??? More power is needed the faster you go and the more load is placed on the engine,,, so reaching higher boost #'s in taller gears is wecomed!! All the above only makes sense if your boost is regulated and theres no creep. Hope this helps.... ummm you could tow a trailer in first so you reach your high boost number and cut it loose early in 3rd gear,, that'll be consistant boost ...I know its sarcastic, but if you think about it, it might make more sense to you.

~Mike............

RacerXtreme7

iTrader: (2)

Ita all a matter of RPM vs. load. If your engine is tuned from zero to max load at all RPM points, it doesnt matter what gears are used, you will ALWAYS have a point on a map were load and rpm match, there for your computer will know what the appropiet fuel amount should be squirted. Remeber, RPM vs load are ALWAYS varying. If your going 50 MPH with RPM's at 2300 just cruising your not loading the engine (shouldnt see boost), Now if you stomp on it and theres an imaginary giant holding you at 50 MPH and 2300 RPM your load is HEAVY and the engine is injesting lots of air compared to just cruising. Set the EMS up in a tall gear (4th) and load the hell out of it while tuning from low RPM to high and your map will be no load to the highest load for every RPM that you rev through. Like I said earlier, then you have every possibility of load vs. RPM and your engine will not care what gear your in, it only sees load and RPM. Your load vs. RPM will form a 3D map, not 2D,,,,,Hope this helps as well.....

~Mike............