Dyno tuning close to Tallahassee

[roc111672]

I know this question has been asked but my search results seem to be a little outdated . I live in Iron City Ga which is about 60 miles north of Tallahassee . I am looking for someone to do some work on my 01 c5 . The previous work was done at Vengeance Racing but i am looking for some one a little closer. What i want done is have a super charger installed . Then dyno tuned . So if any of you have any experience with a shop close to me please let me know where they are located .

Thank you Rusty

[Rich Z]

Good luck with that. I know of only two shops who work on Corvettes with dynos locally around here and I would not personally recommend either one of them. South Georgia Corvette and SS Performance Group.

In your shoes I would continue having Vengeance Racing do the work for me. If they have been doing acceptable work for you, then you may want to consider sticking with someone who has treated you right and you can trust.

[roc111672]

I recently purchased this car. From someone who lived in Cumming Ga which is where Vengeance is located. I have been to SS performance group . I had and still have an idle issue. They checked and adjusted the air fuel mixture. But it didnt help . My problem comes and goes. Sometime when i come to a stop it idles up to 2000rpm and hangs there for a couple seconds some times it doesnt .

May i ask why you wouldnt recommend SS ? Are there any shops within a 2hr drive you would recommend ?

Thanks , Rusty

[Rich Z]

That sounds like a tuning issue. There are tables in the PCM that control that function. Throttle cracker and throttle follower tables are normally the ones that would control that function. Any competent tuner should be able to fix it for you. It's also possible that your throttle body blade could just be physically hanging, but normally something like that would trigger an error code.

Sorry, I don't know of anyone to recommend to you. You are new to this site so you likely don't know of the nightmare I went through with my 2002 C5Z. Make a big bowl of popcorn and read this novel sometime -> http://www.corvetteflorida.com/forum...ad.php?t=44697

[roc111672]

Here is what has been do to my car .

It has a Fast 90 intake , LS2 90mm Throttle body, Nasty Performance LSXR 102mm billet fuel rail kit , A Vengeance Custom Camshaft, Revised Comp 918 valve springs (.650 lift), Comp 7.400 hardened pushrods, Katech C5R timing chain and a Melling hi volume oil pump for LS engines . It also has full length headers with competition cats and Billy Boat exhaust. Thats all i know about it

[Rich Z]

Just the change in throttle body size will alter the parameters necessary to get the throttle working correctly. The amount of air that each step of the throttle plate movement allows has changed, so unless the relevant PCM table(s) was changed to reflect the new values for air, then it will tend to overshoot or undershoot where it needs to be to idle properly. It could require nothing more than just changing the constant for the area of the throttle body plate that the air calculations are based upon.

The throttle body plate isn't controlled directly by your gas pedal in these cars. This is what is known as "drive by wire". What happens is that when you press down on the gas pedal, a sensor sends a signal to the PCM telling it that the gas pedal has moved X amount, so that gets calculated into the number of steps that the PCM tells the throttle body plate to move. There is a table the relates the amount of air volume change to stepper motor steps applied to the throttle plate. The tables for idle values are expecting that a certain amount of air is coming in through the throttle body when the gas pedal has no pressure on it. There are separate tables for when the car is moving (vehicle speed > 0) and then the car has stopped (vehicle speed = 0). BTW, "idle" is defined differently for manual transmissions and automatic transmissions. An improper tune will have a substantial difference in idle speed between those two states. What happens at idle is that the PCM is trying to stabilize engine idle speed by controlling the amount of air coming in through the throttle body. It ASSUMES that each change to the stepper motor allows a set amount of air in. If that value is wrong, then it could overshoot trying to allow more air in to increase engine speed, then undershoot trying to reduce the engine speed. So you get an idle that yo-yos up and down trying to get an idle speed that it just cannot match.

I had a similar problem with my car, except it would idle too low at zero car speed that I corrected by altering the IAC (Idle Air Control) Effective Area table. I basically just shifted all the cells down 6 steps in the table and that worked. I have a 90mm throttle body on my car as well, so I had a similar problem to deal with.

Anyway, I would assume that someone took a stab at tuning the car after all that stuff was installed. Of course, everyone can SAY they know how to tune, but that doesn't necessarily make it true.

You could always get EFILive or HPTuners and learn this stuff yourself. It's a pretty steep learning curve, but not impossible to do. If you have any basic knowledge of EFI engines, the insight you gain by learning some of the tuning stuff will likely be well worth the effort. Just don't be in a hurry with it.

Of course, take all this with a grain of salt. I'm certainly no expert.

[roc111672]

Thank you so much for helping me understand better what is going on . This is my first modded car and i am trying to learn what makes it tick . So i can learn how to tinker with it . Although i will be getting someone to do the big jobs for me . Like a super or turbo charger.

[Rich Z]

Yeah, it's pretty intimidating looking under the hood of these beasts. But it's nothing that anyone cannot do if they just make up their mind to do it. As the vette tech at the local Chevy dealership told me, most of it is just nuts and bolts. These cars were made with the understanding that things will break and have to be fixed or replaced. So nothing will be impossible to do. Pain in the ass sometimes, yes, but it CAN be done.

Let's face it, this isn't rocket science or brain surgery requiring years of schooling and training to do. Quite likely nearly everyone working on these cars started out just as you an me with no prior knowledge but just jumped in and started doing it. Yeah, it used to scare me to death to read about a mod where it would say "minor fitment may be required". But heck, once you just put you mind to it thinking it WILL work, then you WILL succeed.

Heck, YouTube is a Godsend to do-it-yourselfers. I don't know how many times I have needed to do something and found a video explicitly showing me exactly what I needed to do. Once you've watched someone do it a few times, heck, you'll be feeling that it will be a piece of cake, and raring to go.

Heck, check with the manufacturers of the supercharger or turbocharger system you think you may want. They normally come with extensive install manuals that will clearly spell out all that needs to be done. Get the manual and look it over to see what is expected from YOU. You may find that it's something that isn't nearly as hard to do as you had thought it would be.

Good luck with your mods.

[roc111672]

I was wondering, my car runs super cool. I figure the thermostat has been removed . I was out for a driv a minute ago and the coolant temp never got over 165. Could the car running so cool make it idle up like it does?

[Rich Z]

Possibly. A lot of tables the PCM references have values and state switching points that are dependent upon the engine coolant temperature. 165 degrees does seem rather low. But it just might be because of the cooler temps this time of year. Do you have an aftermarket radiator in there? Seems kind of odd that a stock radiator would work that efficiently.

How long have you had your car? You might want to wait till you drive it in the heat of the summer before thinking about doing anything about the thermostat. It COULD just have a a 160 degree thermostat with one hell of an efficient radiator in it, and the cooler temperatures outside are influencing what you are seeing. And it has been rather chilly in these parts this Winter.

In any event, if the tuning is presuming a stock thermostat and not the one (or lack of one) currently in your car, it could even cause your PCM to constantly run in open loop, as closed loop mode is normally set to kick in based on the engine coolant temps. So you would be constantly be running in "engine warm-up" mode as far as the PCM is concerned.

I guess buying an already modified car does present some challenges trying to figure out exactly what has already been done to it.