What do you have in your IAT/CT blend table and where is your IAT sensor mounted (front of rad, in duct, TB, manifold etc)?

I'm having trouble getting my tune to respond to changing ambient temps. Rich when cold/lean when warmer. I know basically how to adjust but it seems to be inconsistent. My "stock" bin's slope started at ~100% at very low flow and dropped quickly to ~12% from about 1/4 throttle up. I have been changing the slope and/or raising the entire table together and can't quite get it right so I thought I would see what other tuners have done. Please help.

 

RBob does a pretty good job of explaining the IAT/CTS Blend in this post:

https://www.thirdgen.org/forums/diy-...ml#post3095524

 

Thanks for that link. It's the first time I've seen anyone with an intake duct similar to mine post a table. Waaaay different than mine. Currently I'm set up more like a tbi motor and that explains a lot. I understand the tuning principal but don't have a way to actually determine how much heat the air would pick up. That's why I'm asking for examples. How is yours set?

 

I currently run a heated high rise dual plane intake with the TBI on top and an under hood air cleaner that sucks in hot air. My CTS/IAT blend table looks like the second table (iat-cts2).

I set it up before I found that post actually. Based on my application and what the two tables look like for their respective applications I think mine should look closer to the table for a heated intake with an under hood air cleaner (first table - iat-cts1). The car runs well enough for me as it is, but I'll probably try to change it this summer and see what happens.

One could also probably calculate some starting values to put into that table based on the setup of their motor using science. I have no background in physics, so that is not an easy thing for me to do. I just play guess and check until it runs decent.

 

I agree and have the same limitations. Having a good starting point and trial and error seem to get me close.

 

My IAT is in the radiator shroud. In stock config, the MAT was mounted in the air horn. To start, I took the values in the table for typical operating temperatures and moved them down to the part of the table with the temps more likely to be measured as it enters the radiator. Then it became a matter of tweaking the table to maintain a consistent BLM as temps for intake air change.

 

My IAT is in the radiator shroud. In stock config, the MAT was mounted in the air horn. To start, I took the values in the table for typical operating temperatures and moved them down to the part of the table with the temps more likely to be measured as it enters the radiator. Then it became a matter of tweaking the table to maintain a consistent BLM as temps for intake air change.

 

Dom don't you have the 32 valve motor? Does it have a long dur cam? I ask because I haven't had good success with closed loop so I'm running open. It makes this temperature issue a bigger problem. What data do you currently have in your blend table?

 

Due to the 4 valve config, the cams do not need to be as radical to achieve top end breathing. Altho each valve is smaller, they move faster and 2 of them have a larger surface area than single large valve. So the specs on my regrinds are:

Intake 236* .425"
Exhaust 220* .415"

Pretty mild when compared to Z06 cams as an example. But these cams make 454rwhp@6850/402rwtq@5250. Runs nicely in C/L.
Played w Prop Gains and O2 windows at idle. Idles at 850-925

IAT table is a bit different than what you have but I have attached stock vs my modded one for comparison.

 

Thanks Dom, your tables are helpful even if there a different type. At least it gives me some data to evaluate what is going on.

I do understand the advantage of the extra pair of valves! It is also an advantage in regard to the duration from a tuning perspective. I believe I can get into closed loop when I have some of these other issues resolved. A 236/242 cam in a 414ci motor isn't really that wild.

I did a couple of things last night that seem to be helping. First, I had a fouled plug which was giving me fits so changing that out seemed to help. Next, I moved my IAT sensor from the air duct right above my radiator fans to in front of the radiation where my filters reside. I noticed immediately the reported temps are very close to ambient and probably won't heat soak nearly as much. I set the IAT/CT blend table to the posted values in Bob's post so we'll see how it goes.

 

The roller cam I had in my 84 Xfire was a 218/218 @. .050. LSA was 108*.
Lift using 1.6 rockers was .535. It idled fine in C/L once the calibration was adjusted. It made 284/347 to the wheels.

 

Ok, placing the IAT sensor up in front of the radiator right at the intake filter improved the readings so they are very close to ambient. It does still heat soak when parked or in traffic, but since it is reporting the temp at the filter it is true intake temp. As soon as it hits ~40MPH for a minute the readings are back to ambient. Before when the sensor was in the duct the elevated readings would continue to be high. This gives the opportunity to better tune to actual conditions using Bob's port table as a starting point.