LT1 intake air temperature question

[Pranav]

Guys, those that can read this from their computers at hot idle with the hood up, what kind of IAT temperatures are you getting?

Long story short, we all know I've been through all kinds of hell with misfires when I put in a new motor last year, and chasing my tail on all kinds of components and even lost that motor over running with those misfires too long. I've done an opti job a couple of times, swapped out ICMs/Coils, re-done all of the plug wires, new plugs, etc. I thought I had this nipped in the bud at TWS, but then again I only made 5-6 laps at 50% pace before I popped the motor.

Yesterday on the dyno the car with a fresh new motor, new plugs/wires, freshly cleaned injectors, it again started breaking up above 5k RPMs after a couple of pulls. Instinctively I remember some comments that were made about my aluminum intake elbow, which was put in with the new motor last year; it was piping hot to the touch. It would break up above 120-125*F IAT. We put a small fan right on it, and then were able to get the IATs much lower and make 6-7 back to back pulls with no problem with the oil/water temps going up as expected.

Went home, couldn't find my old plastic/rubber piece, so I insulated and wrapped the hell out of it with 15ft of gold tape. I saw an improvement in IAT and the elbow is now just warm to the touch, but it will still 110-115*F at idle. (90*F outside, probably 100*F in my garage, coolant at 195-200).

Later on I found and put on a stock plastic elbow, and was getting 115*F-120*F at idle compared to my super insulated metal elbow; so it actually was a little worse.

I then punched a small hole in the plastic assembly right after the filter and put in a second IAT sensor there and moved the wire over to it, IATs readings are now down to 100-105*F, the starting temps under which I was able to get solid pulls. Yes I know this actually is just fooling the computer, just wanted to see if it would sound less rich at idle and decel, and it does so for longer now.

I think I may be good now, but to be safe I'm getting some more gold wrap and insulation, and a heat shield for the air filter. I will likely re-dyno later this week to make sure this all works before I go to Hallett.

The only other issue I can think of is I'm picking up a lot of heat from the oil cooler/lines that are near/below the filter. Attached are pictures of everything I just talked about. Those of you not familiar with the LT1s note that the elbow/TB is right above the waterpump/neck, and the stock IAT sensor location is right in it.

Can you guys with running LT1s and scanners see what your IATs are at hot idle with the hood up?

Wondering if I have just been cooking my air filter the entire time or if something else is wrong with the system that is causing it to react so poorly to higher IATs.

[Pranav]

I can't get images to work, just click here and scroll down:

http://imgur.com/a/tMuVE

[GlennCMC70]

I see your problem..... Your feeding hot air off the oil cooler right to the air filter and the air filter is also pulling hot engine bay air into it as well.
You need to run a 100% stock set-up. The stock set-up pulls air from in front of the core support. You also now know why my oil cooler is on the passenger side. It was just the best place for it.

[Pranav]

Yeah, you're right. I've got an IAT issue, I could try to bandaid it with more wrap and heatshielding, but in reality I've got a big source of heat too close to the filter.

Already started pulling the cooler lines off, waiting for some more hose to come in so I can run it to the other side.

Found all my stock intake parts. Just going to wrap it all up to be safe.

[Pranav]

One more thing I can't believe I forgot to mention.

Morning after the dyno I got to work on the intake swapping and testing, and got the motor nice and warm in my corner of the garage. It was 90* outside but with little ventilation I'm sure ambient temp near the front of the car against the wall was close to 100*F. Needless to say things were toasting, but the car should be able to handle it at idle as it always has.

Anyways suddenly the car started stalling and dying, in some cases attempting to restart would cause backfiring thru the intake, and it refused to start. No codes as usual. Went out for lunch and let the car cool off for a couple hours, started right back up, once it got warm it started acting up again. With it hot I swapped out the ICM and it fixed it right up, has been starting up and staying running while hot since.

Took a close look at it and there's a big crack in the plastic case near the connector.

So I'll be going back to the dyno with an all stock intake wrapped with gold tape, relocated oil cooler, and a replaced ICM. This better work or I'm throwing in the towel for Hallett.

[y5e06]

wow, what an incredibly frustrating collection of problems. Good look man.

[Pranav]

Thanks, it's the right combination of bad luck, bad decisions, and everything that goes with building a race car for the first time.

I've got a spare MAP sensor too, may throw that on just in case those back fires cooked it...

[Pranav]

Moved the oil cooler to the other side of the car. Wish I did this sooner as I can set it further back with the way the inner fender is (favorably) shaped on that side.

Got a new intake elbow and stock airbox/pipe/snorkel in place along with a brand new delco ICM; turns out the replacement and the one that broke were both for a '93, not a '96. Instead of 10-11 degrees of advance at idle with the wrong ICMs I now get 15-16 degrees at idle, could make a difference.

At idle now I'm getting like 105*F at idle in the stock sensor location, about 100*F in the airbox; airbox actually cools off more than the elbow when I blip the throttle. I will dyno with the stock location sensor and switch over to the airbox location if I still have issues. Compare this to starting temps of 115*F with the wrapped aluminum...

Went to the dyno today without calling in advance (they said Friday was OK earleir in the week). They had issues with a customer's car stuck on the dyno and sent me home; going back on Monday for almost no charge for the inconvenience. Kind of a blessing in disguise because I still need to finish the rest of the car (nuts/bolts/clamps etc).

I was hoping to dyno with an unwrapped plastic intake to see what happens first; will go ahead and just wrap this one to get the IATs down further.

As long as I can make pulls withou misfires again I'll be clear for Hallett!

[Pranav]

Between the last dyno and today's dyno:

1. Diagnosed/replaced busted ICM model, that turned also out to be from the wrong year range
2. Found no-so-great upper/lower/IAC throttle body sealing, fixed that too
3. Plugs were partially fouled and indicative of retarded timing.
4. Moved oil cooler to other side, swapped back to 100% stock intake plastic and gold wrapped elbow to be safe.
5. Swapped my NGK TR55s gapped at 0.055 to TR6s gapped at .045 (LT1 spec is 0.050). Never had an issue with TR55s with the first motor, but figured a tighter gap could only help when I've had constant issues with retarding/losing spark.

Swapping the ICM netted me an improvement from 10-11* of timing advance to 15-16* at idle. Swapping the plugs, fixing the TB gaskets, and re-setting the rockers netted me another 4-5* of advance to 20-21*, where it should be, and a slight bump in vacuum idle up to the 20mm/hg I remember having for the longest time.

Seeing the numbers and hearing the car start/idle had me feeling pretty confident. Dyno operator commented that the car started and idled way better than last time so it wasn't in my head.

Re-ran the dyno, saw that IATs were in the 105*F range at WOT, used to be 125*F. No misfires, pulled nice and strong for 7 pulls without the help of a fan this time. A/F ratio was right on the money via wideband.

I'm happy. Now to finish buttoning up the rest of the car...

[Casey_SS]

Need to add a Like button for your last update. Congrats man! Good job getting it all sorted it out. I was rooting for you