I've searched around this forum but couldnt' find an answer.

I've modified the location of the IAT sensor on my FD to my Greddy elbow. My question is where should I position my meth injector, before or after the IAT?

 

i think the IAT relo is a good mod and suggest you position the meth after it.

good luck,

hc

 

If the meth injector is after the IAT then there is no possibility of tuning for the charge cooling effect of meth or meth/water, which is significant.

I would say you want the meth injector before the IAT, but you want to get far enough upwind of it to ensure that most or all of the liquid has evaporated before passing the IAT, in my opinion, this is as far back from the elbow, without being in or before the intercooler as you can get, this will also ensure that the meth gets an even distribution to the rotors.

 

i respectfully disagree w placing the IAT after the meth.

when the meth hits the charge temp will go from (just an est) 150F to zero degrees. if the IAT can change that fast it will trigger all the enrichening for cold start as well as timing changes etc. this really confuses things.

you don't tune by looking at IAT. you tune by reading AFRs and EGTs. i have run my setup w the IAT ahead of the meth and have been happy as to tuning.

caveat: i may be wrong and am not necessarily the last word on the matter but i am not changing my setup.

hc

 

Your right on one point, you want as little liquid as possible hitting the IAT sensor. Which is why you should have the injectors well upstream of the sensor and throttle body.

I respectfully disagree with the rest.

To do this correctly you need a fast reacting sensor, such as the GM sensor. The stock sensor tells you what the temp was 30 seconds ago (maybe a slight exaggeration).

That said I have the IAT sensor in the base of the elbow (within 1in of the TB) with a single injector (will expand too 2 soon) roughly 12 inches upstream of the sensor. The heat soaked max temp (I have no intercooler) is right about 150-155 degrees. Going strait into boost causes the sensed temp too fall too 130f (within 2-3 seconds), the temp continues to fall (more slowly) as the car stays in boost, I suspect that its mostly due the elbow un heat soaking, in never falls below 100 degrees F on a 75 degree ambient day (I am hoping to improve this with a better intake).

There is no instant temperature change

Next point, enriching for cold starts is triggered not by the Air temp but by the coolant temp.

Further I believe you are using a PFC which is nowhere near as flexible as the haltech E8, I am using, but the basics you need for a good secondary tuned in failsafe should still be there.

Which is this, fuel enrichment (lots) and reduced timing (lots) if the system fails to activate in boost. (based on the higher than expected IAT's)

And Fuel enrichment and increased timing with decreased IAT's.

The haltech offers 3d maps for IAT based IGN correction, and multiple 2D maps for IAT based fuel correction, (there is a low load and I high load map).

I do agree that tuning is should primarily be based on Knock, EGT and AFR (in that order), but if you don't know what IAT the engine is seeing (the IAT that would be sensed after the meth has mixed with the incoming air. Then your not seeing the full picture.

 

slo,

what are you injecting? using methanol, my upper intake manifold is probably at freezing to the touch after a dyno run. my charge temp is probably cooler.

that's probably why my knock is around ten at 8000 rpm at one bar.

as to the Power FC... it has fuel and ignition corrections based on air as well as water T. for instance at +10C the fuel correction is just over 11%.

as to reaction speed for the OEM sensor... on a 4th gear dyno run from 2000 rpm to 8000 my temp dropped from 36 C to 34 C. and yes i know their are faster sensors. maybe i will get around to that this winter but i still like my positioning.

i do agree there is something to be said for either position.

BTW, i should have mentioned knock as the other key tuning element...

hc

 

I am currently injecting 50/50 meth water, but will be going to 100% meth when I get a better way to store it (fuel cell). The Elbow on my car is just starting to get cool after a run into boost.

In order for what I am talking about to work you would have to be tuning those correction maps. The biggest benefit is that it adds a significant failsafe.

If you where to switch to an E11, you could control aside from controlling your AI from the E11 or E8:

Do closed loop boost control,

Close loop 02 control with a 32 x 32 map of AFR's to load points off a wideband, (IE closed loop 02 at idle 12.5:1, at 2000 RPM 13.5:1 at 4000RPM 14.9 to one, with variance based on MAP also.)

Use the about 10 extra input channels (E11) to datalog all onto one box.

Many possible extra fail safes for stuff like AI such as really safe tunes, if something isn't right. Extra maps for ign and fuel that can be change with the flick of a switch.

One of my AI failsafe's consists of an extra pressure bypass in the high pressure line activating an ign cut rev limiter to 3000 RPM (if line pressure drops below 115 PSI, vs the normal 125-130 range), we all know that the most likely failure points are the pump, the pressure lines or the alcohol level. This takes care of all those, the only remaining possible failure is the HSV or a clog.

Many other possibilities from the plethora of features.

 

I should also mention in testing the OEM sensor compared to the GM sensor back to back, there was a huge difference.

The OEM sensor is coated with plastic which is an insulator before it can sense a temp change, the plastic must first cool or warm. The GM part has an open element.

 

all good stuff...

i may upgrade my ecu and have a couple of options each of which would deliver a great deal more options than my Power FC which has served me well to this point.

hc

 

Thanks for all the great info!

 

^^ I was wondering about this the other day. I am using the stock tables for airtemp/injection correction and have witnessed leaner running AFRs when starting to drive just after a little heat soak (say, if I stop the car for a few minutes), since the correction is leaner for warmer temps and the air going into the motor is actually colder/denser than what the stock sensor tells me.

Is there a way to adapt an aftermarket open-element sensor to the stock wiring harness? That would be a nice solution

 

With a PFC?

If so yes, search the PFC and FD forums I'm sure this is covered.

 

hey does anyone know if having water/methanol mix hitting the gm open element sensor would end up corroding it or causing it to malfunction? i want to put a few sensors in the air stream to datalog temperature changes before and after the injection point. should i go with the slower reacting closed element sensor?

 

I'm running straight water and have easily sprayed over 5 gallons of water on that sensor so far and its still workign fine. As for meth, I'm not sure.

 

For the GM sensor can you just wire it up and go??? Is there anything else to worry about or is it that simple?

 

I have no choice but to install the injection before the IAT.

 

looks like i may have to install alky noozle before IAT noozle as well

 

I don't see the problem with installing it before. You have AIT correction maps that you can change the effects of the temperature change vs fuel injection or timing. It could as mentioned before, be used as a failsafe to see if your aux injection if failing.

 

So does anyone have any further information on a better IAT sensor?