Juelz5420

i have a 2005 sti with a 3 1/2 in turboback, aps cold air intake, ecutek reflash,walbro fuelpump. here is the problem when i downshift like from 3rd to 2nd and stomp on it the car bogs out sometimes, and sometimes inbetween shifts if i'm driving hard. it is not alot inbetwwen shifts but it is noticable and sometimes when i downshift its bogs bad. i talked to one guy at a local shop here and he said the 3 1/2 inch downpipe is to big but if i'm planning to turbo it than it is ok. he said that might be my problem. what do you guys think?

depdivr

Juelz,
I don't think you have a mechanical problem... I think that the problem is with your driving. Don't take offence to this as 99% of the world has the same problem. When driving a manual tranny and you downshift but maintain the same speed, your car will naturally bog. Here is why. When you depress the clutch, your drive train keeps going as fast as your car is moving on the road but because you took your foot off the gas your engine slows. Your downshift, release the clutch and now your engine has to "catch up" with the car. The engines mechanical inertia slows down the car (bogs) until the engine and the drive train are going the same speed again.

Here is how you prevent it... Its called heal-toe shifting. I will try to give you a step by step.

1) You are slowing (lets say for a curve). If you don't downshift, your gearing will be too high, your rpms will be too low and you won't have any power coming out of the curve... So what do you do?
2) You use your left foot to depress the clutch.
3) Your right foot starts to slow the car by depressing the break. I personally prefer to position the break peddle pad just below the ball of my right foot with my 3rd, 4th and 5th toe just to the right of the break peddle.
4) You start your down shift by moving from 4th to 3rd gear (just for the example).
5) You rotate your right foot heal counter clockwise around the ball of your foot, keeping constant and controlled pressure on the break peddle pad, so that your right heal is over the throttle peddle.
6) Use your right heal to "feather" the throttle (remember your left foot is still depressing the clutch and the ball of your right foot is keeping pressure on the break). This will bring engine RPMs up to the 4000 to 5000 rpm range.
7) Just after the apex of the curve, release the clutch *don't let the rpms drop!*, shift the pressure from the break to the throttle and your car won't have any bog and you can have plenty of power to accelerate out of the curve.

Its kinda hard to get used to but practice and you will be much faster around the track. Things get allot more complicated when you start into left foot breaking.

Here is a great video... almost 10 minutes long with JGTC drivers driving the fastest cars in the world. Has a "peddle" view which is great to learn both heal-toe and left foot breaking. *ALL WILL LOVE THIS VIDEO*

4080wrx

iTrader: (38)

i have a 4 in dp with no problems so i would have to call bs on what your mechanic said

depdivr

Sorry, I forgot the vid which accompanied my last post... here it is, great visual to watch on footwork from the best in the world!

http://www.jexoticar.com/www_docs/Je...erCar_Race.mpg

And because I feel bad about forgetting the video... here is another great one!

http://www.superhonda.com/video/amus...es_skyline.wmv

depdivr

So I am also thinking it may have to do with your stock injectors, especially if its happening while in gear and the engine is under load. You may want to get your fuel pressure checked and make sure its in line with the load on the stock injectors... it should not be more than 30 psi but your Walbro could very easily get the pressure above that. A fix would include a fuel pressure regulator and remove your fuel pressure dampening system which comes stock in the STI. Allot of people would recommend checking your fuel filter but the STI has an in tank fuel filter (its not on the firewall like the WRX) and shouldn't need maintenance.

Do you have a shop near you that works with STIs or Evos? I ask this because there are alot of shops that can tune a civic but can't figure out the high performance ECUs of an STI.

I could be dead wrong on this but its worth a shot.

Juelz5420

ya i've seen heel to toe and it looks hard. this is what i do. ok when i downshift i just dont go from 4 to 3 and just stomp on it. i give the gas a push to get the rpms up while the clucth is depressed and once they are around 5 i let the clutch go while trying not to let the rpms get low. it is not heel -toe but it is not just dropping the clutch. when i do that it bogs it like goes then stumbles a little then goes (bogg)? is it still my driving? it does this some times in between 5000 and 6000 rpms when i am just going straight and stomping on it to? could it be injectors? i have a couple shops but not very trust worthy? dyno-comp and the guy there says it is the gas in az. and the others i hear only are serious if you have alot of mods? sort of out of options

depdivr

It sounds like your not getting fuel for a split second. I can't help but think that the Walbro 255lph fuel pump is not overkill for an otherwise stock fuel system, maybe that's the issue? I would love to hear others opinions...

Juelz5420

that is what one of my friends said that i was not getting fuel for a second. so the walbro is to much should i get injectors and finish my fuel delivery?

depdivr

Did you say you have the EcuTek re-flash? Plug it into the computer and see where your injector duty cycle is at WOT (wide open throttle) in 3rd and 4th gears. Based on your set up, and depending on your tune, your duty cycle could be up above 80% or 90%. You really want to be around 60% to 70% - this way you get good atomization of fuel in the cylinder but also have room to grow a bit. If you are above 80 to 90 percent, I would recommend getting bigger injectors and fuel rail. Your stock injectors are in the 330 cc range (I think), STI injectors are in the 550 cc range and work great on WRXs with a big turbo. I personally think you should go up to the 800 cc range for a STI, it will allow you well into the 400 whp range.

Finishing your fuel delivery will put you into a stage II tune. You have to make sure a pro is doing the tuning at this stage - you can destroy the car if your not doing thing right.

depdivr

I don't know if the Walbro is too much... as I am not a professional, its just a guess.

Juelz5420

thanks dep i am going to just finish my fuel delivery and i will tell my tuner to check my injector duty cycle. is there a order i should do my fuel management, should i do my fuel rail first or my injectors or does it even matter? thanks for all your info and yes i have a ecutek reflash. i have a sti to.

depdivr

Do it at once... my favorite package comes from Perrin. They include the stainless fuel lines, injectors and fuel rails.

Juelz5420

do you know a link that i can go to to get the package?

depdivr

I purchased it through a shop....

These are two shops that I admire alot and they know their stuff - I know they both have a great relationship with Perrin.

http://www.pdxtuning.com/

http://www.matrixintegrated.cc/

and finally,

http://www.perrinperformance.com/

Juelz5420

cool thanks for all those sites. its ok to get the bigger injectors with a stock turbo or should i wait till i get a bigger one? you live in oregan or do you drive up there. i would love pdx to tune my car.should i wait on injectors till i get a bigger turbo which will be not that long or is it ok to get the bigger injectors with a stock turbo. on pdx all the packages have the flash and i already have that are there any with just the injectors and fuel rail ...