turbo TOO big?

[nicstang]

Hey all. I have a shop and do chassis dyno tuning, and have an opportunity to work on my first Turbo Grand National. The 87 car has a stock engine with a Hooker exhaust system, Houston Performance downpipe, and a TA62 turbo. The customer has installed 50# injectors on this thing, which I believe are WAY too big for this street car. It runs horrible, and won't idle most times. I don't have any experience with these cars, so I would like some input on what the correct parts should be. I suggested a 42mm turbo and 36# injectors, but he disagrees, saying it won't make any more power than stock. What size injectors did this thing come with, and do the MAF sensors need to be "calibrated" to the injector size, similar to the Ford Mustang? Thanks in advance for any advice.

 

[kjizzle]

Does he have an aftermarket chip, or is it still the stock one? if its the stock one(which it kind of sounds like if it won't idle right and runs like crap) its not going to work well. the stock injectors are, i believe, 28 lbs... turbotweak has affordable chips available between $85 and $130.

the MAF sensor does not need to be calibrated with an aftermarket chip. However, it would be a good idea for him to use what is called a MAF translator (which changes the voltage output on a newer model MAF sensor to a frequency output for use with the GN computer) and a newer model MAF sensor (say from an LS1 or LT1) because the stock replacement MAFs you get from autozone aren't exactly the most amazing units.

you could try resetting the computer by unplugging the orange wire located on the passenger side of the engine compartment for about 30 seconds.

 

[2QUICK2B6]

The chip has alo to do with how well the car will idle. 50lb injectors are fine.

Ask him if it has a turbo tweak chip for his setup. TurboTweak Home

 

[turbodave231]

Your customer is right, listen to them, you are pushing them back light years.

In the rest of the world, 50 lbs injectors are huge. In the forced induction world of turbo V6's this is really mild. The TA 62 turbo may require a slightly higher stall converter to spool up nicely off idle, but not more than 2900-3000stall.

With the new generation of GT double ball bearing turbos even much larger turbos can be used on a street car without sacrificing any driveability.

There are many turbo V6 street cars running around with 65# and even 72# injectors. The modern chip guys have figured out how to control them at small pulse widths. These same cars can also get 20 MPG!!!

My current combo is 160# injectors and a GT42-76 turbo. Not a street car.......but it could be!!

Dave

 

[bison]

You really cant have too big of an injector. Ive seen v6's idle fine on 160's. Ive got a lot of experience with 83's and 96's with an XFI. They idle very well when the tuner knows how to handle the program. For you concern you are basically dealing with a stock MAF'd car with high impedance 50lb/hr injectors. This should be a a very easy chore. First make sure the sensors are set properly and that the MAF is reading correctly. It should idle at 6gpm and max out at 255gpm. After the max the chip fueling map is all that is controlling injector DC if the block learn is locked out to 128. So id start start off with a Turbo Tweak chip which is highly adjustable and some good high octane fuel. You should be able to knock off 380-400hp at the wheels after some tuning and boost/timing increases. Id guess at 25-26psi and the converter force locked you should be in the low 400's at the wheels. Having the wrong chip and or a bad MAF will not get you very far. Id shoot for 10.8:1 with 93 and limit boost to about 17psi with about 18-19 degrees advance. With 110 25 psi and 23-24 degrees will not be a problem and will make a world of difference in power. Shoot for 11.3:1 on the 110. Close the gap down to about .032 on the plugs. The MAF only sends a signal to the ecm about the air density and has impact from injector changes. All fueling and spark is read off the E-prom chip.

 

[bison]

Another thing is that the stock turbo is about 47mm so a 42mm would not work out too well trying to crank it up to make more power.

 

[GNeric]

Like a lot have said, it is all in the tuning. I have the equivelant of a 70 turbo and 83# injectors and it idles great, gets 25mpg on the highway and spool-up is so fast.

 

[nicstang]

Thanks for all the good advice. I have a piece of literature that states the 87s had a 37mm turbo stock, so that's why I suggested the 42. In order to make the 50# injectors work well at low(or no) boost, what kind of fuel press do these things like? Right now, its running 43psi at an idle.
I'm just used to having injector duty cycles around 65-75% to at least maintain a good spray pattern.
So, I assume that the stock MAF probably won't have enough voltage range to sustain the huge airflow increase, correct? I have a stock MAF from an 04 LS1 Corvette I can use if it will work.
Again, I really appreciate the help on this. The first car to genuinely kick my 5.0 liters ass was one of these monsters, and I have total respect for them.

 

[yullose]

I run a 70GTQ turbo and 83lb injectors in my street car and it idles like a stocker.

If the customer doesn't have a chip matched to his combination, it WILL run like crap, if at all.

Obviously unfamiliar with GN's... are you checking the fuel pressure correctly ?

To check fuel pressure, pull the vac line off the regulator first. If it's at 43psi with the vac line on and motor running, that would explain a lot. It will run pig rich as soon as you crack the throttle open.

I always set mine at 43psi with the motor at idle and vacuum line off. When you plug the vacuum line back on, it will drop a few psi.

My Turbo Tweak chips have always recommended 43psi (line off) as a starting point.

Also, whenever making changes, unplug and re-plug the orange ECM wire at the battery so the computer can "re-learn" the new combination.