All,

I have read every archived post on this topic and I really hate to beat a dead horse here but tell me if my conclusions are correct. The bottom line to me (presently I might add)...don't do this mod on L98s (vice LT1s)...which boils down to time and li'l money. My conclusions based on reading all posts:

1) On an L98, MAT controls EGR (vice A/F mixture) so don't do the mod.
2) On an LT1, the IAT should be relocated as it impacts Air/Fuel mixture and possibly performance as a result (makes sense to me).
3) Yes, this IAT (vice MAT) mod is done at the factory on newer Vettes but only because it makes sense since the Air/Fuel mixture is affected.
4) I've only noticed performance (smoother hot start-up/Idle) impact on LT1s.
5) GM does not produce "performance perfect" engines...no one does.

Agree?

Thanks all!
Bill

 

MAT controls egr only on maf l98s. On speed density it does more.
By relocating it on stock map cars it can have a positive effect-however you should retune it for the relocation. (in the prom).
It would take pages to go over pro/con for map cars and the "right" way to do it.....If you want to go into details check out thirdgen.org-diy prom and do a search on it; lots of info....and some controversy! :)
As for GM and performance engines.....look at how many cars they crank out-and what are production tolerances? So how could they get a "perfect" assembly/tune? Only way for a "perfect" engine is diy or pay a reputable tuner.....but then it still won't be perfect for all conditions....look at how race teams change their tuning according to temp/humidity etc.

 

My take on the the whole thing is to leave it in the stock position. Its there to measure intake air temperature. If its in the intake, that what it is doing. If its in the air filter housing, it is not doing what it is supposed to. I have mine relocated in the filter housing becasue for the Miniram you have to run it there. Now that I have the Super Ram I'm going to put it back. I have noticed that my tune can gets a little off when it gets real cold outside.

 

when I moved mine I only noticed a difference on warm re starts...

 

Don't forget two important issues with the stock MAT position under the plenum:
-the MAT picks up heat from the plenum by conduction and the intake base by radiation.
-the intake air is moving pretty fast; doesn't get heated much by the plenum walls.

The MAT located in the air filter housing provides a truer intake air temp value.

So, that's where I relocated the MAT on my L98.

Also, EGR is only open during light throttle after coolant temp has reached about 150 deg F or so.

 

65Z01 - I did some boning up and as a result conclude I may do the mod (knowing also it is easy enough to revert back if the original sensor is left in place). I would really like your input on the below if possible.

I think the real question is...what is the impact on a 88 L98 and to me, this would boil down to the real impact on EGR and the EGRs impact on engine performance. This lead me to read once again about EGR and after boning up to refresh I offer the following condensed version:

Since the EGRs primary purpose is to reduce combustion temperature (when open) would also mean when the EGR is open too much, you get weak combustion (combustion temps too cool) which gives a rough idle, rough running engine and possibly engine surge - open too little you get overly strong combustion (combustion temps too high) which provides for detonation and engine overheating. A macro level temperature impact summary being: As engine temps increase, EGR opens to cool/maintain proper combustion temps (considering also vacuum and exhaust backpressure of course). The EGR is open at warm engine temps and above idle speeds.

Now, knowing that...the MAT's job is to delay EGR opening until manifold air temp. reaches +40 deg (IAW uncle Haynes). And of course, we know where/why this delay is happening...at the ECM via the MAT. Ater +40deg, the MAT still has a role in maintaining proper EGR along with coolant temps as you state and throttle position.

Some have said they get a smoother idle and better warm start conditions with the MAT relocated. Now, assuming cooler temps with the MAT relocated, cooler temps at the MAT means less EGR to permit the combustion temps to warm up. This somewhat makes sense for those who say they get a better idle as they may have experienced too much EGR (too cool of combustion temps) due to the hotter reading from the MAT. Recall that too much EGR, as stated above, makes for a rough idle meaning...the MAT is sending a higher temp and thus EGR is opening too much providing too cool of a combustion temp. If relocated, the MAT would be a little more in line with coolant temps (also sensed for EGR operation) I would think.

What do you think? Does this sound accurate to you?

Thanks!
Bill