Anyone try an IAT Resistor mod? [Archive] - Cherokee SRT8 Forum

: Anyone try an IAT Resistor mod?


GotStroke?
02-28-2007, 09:25 PM
With the recent interest in phenolic spacers I thought I'd bring this discussion to light. GSM keeps assuming that the power loss associated with "heat soak" comes directly from the intake manifold, however, it only takes the incoming air a fraction of a second to flow all the way through the casting. In short, it won't heat up much if at all.
IMO we would see much better results with an IAT resistor mod (shoving a resistor, bent into a U shape, in the female end of the IAT) to trick the computer into thinking the ambient air was cooler (thus adding timing/fuel) than it really is.
We've done it for years with other cars, with repeatable success. Check out www.ghostcobraracing.stangnet.com for some basic info and some documented results with a stock longblock 98 Cobra.
The resistor values will be different for our Jeeps but the idea and the ability to control this variable remain. At around a dollar and change per pack of resistors at radio shack, it might be worth a shot.

edit: I see the site is no longer up, I'll try to find and post the results from another source. Long story short with a stock longblock N/A 4v we were seeing a .15-.20 reduction in quarter mile ET with a trap gain of 1.5mph+. GTs/2Vs showed similar gains. This was all done in same day back to back testing fashion. The trap gains equate to around 10-12rwhp in a ~3450lb Mustang.

HoustonSRT-8
02-28-2007, 09:43 PM
I chalk this up with the throttle body spacer.

Black_SRT8
02-28-2007, 09:46 PM
Great idea - I would be interested. Keep us posted...

GotStroke?
02-28-2007, 10:25 PM
I chalk this up with the throttle body spacer.


:confused:

Do you mean the phenolic spacer or the IAT? The IAT has been proven to work, independantly by dozens even hundreds of users for other types of cars (imports, domestics, etc.). The only issue we have is nailing down the correct ohm/temp. scale for our Jeeps.
To put it simply, a phenolic spacer is a band aid, since timing is pulled in the PCM when ambient air temp rises. Whereas, sending a false signal to the PCM via the IAT (it's just a thermocouple afterall) is taking things to the heart of the matter so to speak.

GotStroke?
02-28-2007, 10:27 PM
Great idea - I would be interested. Keep us posted...


My Jeep is at Stainless Works having a full exhaust fitted as I type this. When I get it back in ~3 weeks I'll have some resistors waiting.

BuilderBill
03-01-2007, 05:42 AM
My Jeep is at Stainless Works having a full exhaust fitted as I type this. When I get it back in ~3 weeks I'll have some resistors waiting.
I looked into this a few weeks ago. There are variable resistors available for this purpose.
http://www.hurricane-horsepower.com/#F5

I may try to order one quickly and test next week at Rockingham.
Bill

AlexT
03-01-2007, 07:10 AM
I looked into this a few weeks ago. There are variable resistors available for this purpose.
http://www.hurricane-horsepower.com/#F5

I may try to order one quickly and test next week at Rockingham.
Bill

We need a sticky cataloging each of your mods and the respective change in strip results.

Alex

BuilderBill
03-01-2007, 07:55 AM
We need a sticky cataloging each of your mods and the respective change in strip results.

Alex
I am working on an easy to read matrix that will document the past and future changes. Should be helpful to see what gives the best for the buck. I will also do the "Bill ram air brake snorkel" connected and detached from the Volant. Any other suggestions to try for my rental day at the track next week?

Various launch techniques with the new 2600 converter
3 different drivers (sounds more like golf)
with / without the GSM intake spacer
Variable resister on the IAT sensor
Ram air connected / disconnectedBill

gculver
03-01-2007, 08:16 AM
I am working on an easy to read matrix that will document the past and future changes. Should be helpful to see what gives the best for the buck. I will also do the "Bill ram air brake snorkel" connected and detached from the Volant. Any other suggestions to try for my rental day at the track next week?

Various launch techniques with the new 2600 converter
3 different drivers (sounds more like golf)
with / without the GSM intake spacer
Variable resister on the IAT sensor
Ram air connected / disconnectedBill
Yea, a pit crew!

HoustonSRT-8
03-01-2007, 09:08 AM
:confused:

Do you mean the phenolic spacer or the IAT? The IAT has been proven to work, independantly by dozens even hundreds of users for other types of cars (imports, domestics, etc.). The only issue we have is nailing down the correct ohm/temp. scale for our Jeeps.
To put it simply, a phenolic spacer is a band aid, since timing is pulled in the PCM when ambient air temp rises. Whereas, sending a false signal to the PCM via the IAT (it's just a thermocouple afterall) is taking things to the heart of the matter so to speak.
No, I meant a throttle body spacer. You claim .15-.2 tenths and 1.5mph. Did you accomplish those changes on the same day at the track?

gerry_miranda
03-01-2007, 10:13 AM
IAT manpulation is suppose to trick the computer into thinking its cooler out and therefore increase timing. Doing this can cause detonation if the actual IAT is high.
My SC M3 has IATs in the 180F. Fooling the IAT caused detonation. Placing an intercooler knocked IAT down to 110F and a gain of 20 whp. But that is a huge IAT difference that is real.

SpeedRacer333
03-01-2007, 11:29 AM
IAT manpulation is suppose to trick the computer into thinking its cooler out and therefore increase timing. Doing this can cause detonation if the actual IAT is high.
My SC M3 has IATs in the 180F. Fooling the IAT caused detonation. Placing an intercooler knocked IAT down to 110F and a gain of 20 whp. But that is a huge IAT difference that is real.

Nice M3 project! Which kit are you using?

I would hope that if knocking does occur, it would be minor and also detected by the knock sensors causing the pcm to make the necessary changes.

SpeedRacer333
03-01-2007, 11:32 AM
I am working on an easy to read matrix that will document the past and future changes. Should be helpful to see what gives the best for the buck. I will also do the "Bill ram air brake snorkel" connected and detached from the Volant. Any other suggestions to try for my rental day at the track next week?

Various launch techniques with the new 2600 converter
3 different drivers (sounds more like golf)
with / without the GSM intake spacer
Variable resister on the IAT sensor
Ram air connected / disconnectedBill

What effect would a resulting mix 96-97 octane have on our NA motors??? My understanding is that a system with knock sensors is constantly keeping the advance at the limit (but within a programmed window). The question is does our stock pcm have a wide enough window to take advantage of it?

GotStroke?
03-01-2007, 11:33 AM
No, I meant a throttle body spacer. You claim .15-.2 tenths and 1.5mph. Did you accomplish those changes on the same day at the track?

I realize you were speaking about the TB spacer, but comparison of that to the IAT mod is ridiculous. From my post above:

edit: I see the site is no longer up, I'll try to find and post the results from another source. Long story short with a stock longblock N/A 4v we were seeing a .15-.20 reduction in quarter mile ET with a trap gain of 1.5mph+. GTs/2Vs showed similar gains. This was all done in same day back to back testing fashion. The trap gains equate to around 10-12rwhp in a ~3450lb Mustang.

I was the tester, and yes it was all done at the same track (Nat'l Trail, Columbus OH) day with literally minutes between runs--there were less than 10 cars at test and tune that day.

GotStroke?
03-01-2007, 11:35 AM
IAT manpulation is suppose to trick the computer into thinking its cooler out and therefore increase timing. Doing this can cause detonation if the actual IAT is high.
My SC M3 has IATs in the 180F. Fooling the IAT caused detonation. Placing an intercooler knocked IAT down to 110F and a gain of 20 whp. But that is a huge IAT difference that is real.


I would never use the IAT mod with forced induction period. We never experienced detonation with N/A motors, granted we always ran 93 octane anyway. If you ever did experience detonation you could simply swap in a different resistor, not a big deal.

HoustonSRT-8
03-01-2007, 11:40 AM
Whoops, my bad. I read right over that part of the edit.

I have heard of this mod doing maybe .1 at the track, but anymore than that is hard to swallow. You claim that the test car was running a stock longblock. Did the car have any mods at all?

GotStroke?
03-01-2007, 01:02 PM
Whoops, my bad. I read right over that part of the edit.

I have heard of this mod doing maybe .1 at the track, but anymore than that is hard to swallow. You claim that the test car was running a stock longblock. Did the car have any mods at all?


Yes, at the time the car had 4.10s, CAI/filter, O/R h pipe and Nitto 17" Drag Radials--these mods remained constant throughout testing. I made over 15 passes that day with quite a few different resistors. The largest gains in both ET/mph came with a 120K ohm resistor which equated to ambient temps of around 19F.

pjvreede
03-01-2007, 07:02 PM
IAT manpulation is suppose to trick the computer into thinking its cooler out and therefore increase timing. Doing this can cause detonation if the actual IAT is high.
My SC M3 has IATs in the 180F. Fooling the IAT caused detonation. Placing an intercooler knocked IAT down to 110F and a gain of 20 whp. But that is a huge IAT difference that is real.

Since the 6.1 Hemi has knock sensors, wouldn't you be protected from too much timing advance from the IAT mod?

GotStroke?
03-01-2007, 07:19 PM
Since the 6.1 Hemi has knock sensors, wouldn't you be protected from too much timing advance from the IAT mod?


Worst case scenario, yes.