Idle with Sheet Metal Intake and 70mm TB

[Reggie West]

Guys I am trying to get the GN to idle with this intake and a 70 mm TB.

I can get the idle speed down to around 850 but it is rough and it surges.

I have played with the AF ratio table. It was set at 12.5 and ran great with the stock ( hogged out Duttweiler intake) intake but I cant seem to get enough air in the intake to make it happy. I have tried AF ratios from 14.0 to 12.5 and no change.

Using a FAST system and this is a Mease Intake.

Any thoughts?

 

[Reggie West]

MAP shows KPA of 58 to 60.

I went so far as to disconnect the IAC motor and it is still rough.

 

[TurboDave]

Just a guess, but vacuum leak somewhere you can't detect maybe? Like into the valley or on the ends??

 

[The Radius Kid]

Maybe a little more idle timing would help?

 

[Reggie West]

Dave I hope it is not a leak.

We pressure checked that manifold with 35 psi into it and no leaks.

I guess I can always get a can of carb cleaner and check it out.

 

[turbolou]

Reggie have you checked your timing with a light to see if it corresponds with whats calibrated in the map. sounds like something isnt configured right & the engine is fighting it self.also are you sure you don't have any tight valves, compression problems etc.

 

[Reggie West]

Hey Lou how is it going?

Yeah I know the timing is right on the motor. We used the light when we figured out the crank sensor was wiped out a couple of months ago.

We are taking it to a dyno on Friday up here in the hot as hell desert.

I'll keep you posted.

 

[bruce]

Originally posted by Reggie West
Guys I am trying to get the GN to idle with this intake and a 70 mm TB.
I can get the idle speed down to around 850 but it is rough and it surges.
I have played with the AF ratio table. It was set at 12.5 and ran great with the stock ( hogged out Duttweiler intake) intake but I cant seem to get enough air in the intake to make it happy. I have tried AF ratios from 14.0 to 12.5 and no change.
Using a FAST system and this is a Mease Intake.
Any thoughts?

Other then the obvious, checking for leaks, you might consider a few other things.

The more an intake uses Hemholtz or Acoustic tuning, the more peaky it gets, so everything outside of this sweet spot suffers. There is no perfect manifold, so they are always a series of compromises.

Once you get to a minimum PW any injector will get erratic. there is just so fast that one can open and close.

If you increase the idle speed a little and it gets back to the way it was, I'd say your just at that point where hitting the min PW that makes your injectors happy. And that PW is very voltage sensitive. If your running a small crank pulley, and marginal alternator that might be something else to look at. Also, look at your PW to voltage correction table, if you have one, and you might try min the difference from one step to another.

Dems my thoughts.

 

[JoyOf6]

I idle my 160#s in open loop, and adjust the idle cells to what works best. Just me...

Art

 

[Reginald West]

Thanks for the input guys we will be going to the dyno tomorrow morning and we will use the info to get this thing running right.

REG

 

[turbolou]

Originally posted by Reggie West
Guys I am trying to get the GN to idle with this intake and a 70 mm TB.

I can get the idle speed down to around 850 but it is rough and it surges.

I have played with the AF ratio table. It was set at 12.5 and ran great with the stock ( hogged out Duttweiler intake) intake but I cant seem to get enough air in the intake to make it happy. I have tried AF ratios from 14.0 to 12.5 and no change.

Using a FAST system and this is a Mease Intake.

Any thoughts?

Hey Reggie! Did you ever get your problem solved? I worked on a buick last week with similar complaint. Wouldnt idle, surged & stalled.Turns out that the idle speed motor circuit in the E.C.U.
was damaged because of the battery cable ground to the block wasn't connected & when the engine was cranked it grounded
through that curcuit & took out the computer. There were no check engine lights or any codes to assist the diagnosis. So I wonder if anything like that may have occurred with your complaint. Just a thought,

 

[Reggie West]

Hey Lou.

No our problem was much more simple. The bottom of the manifold was off by .015 all the way across it.

We were blowing air into the valley of the block.

Got that fixed and it idles much better. It is still a little rough but I can work with that.

Now all I have to do is get it to idle in gear and fix the rest of the map!!


Its getting there.

 

[turbolou]

Originally posted by Reggie West
Hey Lou.

No our problem was much more simple. The bottom of the manifold was off by .015 all the way across it.

We were blowing air into the valley of the block.

Got that fixed and it idles much better. It is still a little rough but I can work with that.

Now all I have to do is get it to idle in gear and fix the rest of the map!!

Great glad to hear it! Who found that your crew chief Paul! LOL

 

[Reggie West]

I have no clue where Paul is anymore.

I have not seen him in a while.

You know the first place he goes is your shop. He is always wanting a Stage block for bucks from you.

 

[TurboDave]

Always seems to come back to a nasty leak somewhere.