06 Vette, LS2, 440 CI, Auto, 500 RWHP, Fast 102, big cam, ported heads - Cold Idle

[swingtan]

In recent days I've heard a number of reports of poor idle when using a FAST manifold. I was suggesting replacing the FAST with a stock manifold to see the impact.

As for the tune, I think you are simply not getting sufficient airflow when cranking and for cold idle. As a quick test, try setting {B1650} to 3600 and {B1651} and {B1652} to about 4%. You may need to lower your settings in {B1829} though, as 41gm/Sec should be nearly 10 times too much.

See what those changes do.

Simon.

[RD in SD]

In recent days I've heard a number of reports of poor idle when using a FAST manifold. I was suggesting replacing the FAST with a stock manifold to see the impact.

As for the tune, I think you are simply not getting sufficient airflow when cranking and for cold idle. As a quick test, try setting {B1650} to 3600 and {B1651} and {B1652} to about 4%. You may need to lower your settings in {B1829} though, as 41gm/Sec should be nearly 10 times too much.

See what those changes do.

Simon.

OK thank you, I will try it as soon as I get back to the car tonight. However I have a question so I can better understand what I am doing. It looks like from what you are saying that the idle airflow table has been limited by the max idle area which has allowed us to increase it by 10 times more air than the car needs. When I open up the max idle area I am now going to have to much air because the idle airflow table is 10 times too high. Is this assumption correct? You said that idle airflow table is 10 times too high do you want me to reduce the entire table by 90% for the test or where should I start?

On another totally unrelated subject, I noticed you are from Australia, I also have an 09 Z06 with a Harrop Hurricane manifold on it. As you may know that Harrop is made in Australia. The engine is modified in a similar way to this one we have been discussing in this thread except that it has bigger heads a little less duration and more lift. It is putting out 600 RWHP. I have spent a lot of time and money getting this manifold working on the car and it now has better drive ability than the 06 in this thread. It idles nice, starts perfect and the horsepower and throttle response is nothing short of incredible. However I just finished testing it last weekend and do not have extensive seat time. The reason I mention it is that I can't find anyone near me that knows anything about the Harrop. I have found a local tuner to assist and we have been able to dial it in through a lot of trial and error and it's finally perfect except that maybe it would be nice if I could get the idle a bit lower (800 now). My point is that it would be nice to find someone with experience to assist in case we run into more issues. Do you know anyone down under?

[swingtan]

1. Yes, the max idle throttle % will hard limit how far open the throttle will ever go. The problem is that I think there's another setting that we don't have access to. The trick is to reduce the ECM's expected maximum throttle area, so it thinks it needs to open the throttle more for a given calculated airflow. Then you can actually command more air and get the throttle to open further. I'd start at 10gm/S for the idles cells and work from there. You may get down to 8 or need to go up to 13, depending on the rest of the setup. Generally though, you start a little high, get the idle settled and work down.
   
2. The Harrop Hurricane! I'd love to have one of those, best looking intake I've seen and I'd probably prefer one over a blower.... maybe.... I think it'll come down to the response of the engine to throttle changes, as you've said, it's very responsive. If you want to send me some idle logs and a matching tune, I'll have a look. You can PM me for details.