jclark10

iTrader: (1)

So I put a "imitation" (unfortunately don't think a compressor map or much data on it exists and I don't think its near any of the Garrett GT45 models) GT45 on my 2011 Sierra Denali L9H and running about 10-11 psi at steady state with a 38mm wastegate, 4in downpipe, 2.5 in crossover, 3in intercooler tube with 24x12x3in bar and plate intercooler.

What really surprised me is the effect I see when IAT's change from heat soak and standing still with no airflow. I have my intercooler actually mounted in between and right below the frame rails right behind the hole in the front bumper. I didn't put it in the usual spot in the radiator stack area because I didn't want to have to cut up or damage my stock supports and I figured this would maybe be the next best place to put it. However I understand I am probably not getting much heat transfer do to it not being in the radiator stack and the e-fans having little effect on it.

Anyway, I notice when ambient temps are in the 70s usually my IATs when driving around not stopped don't get much about 85F and as long as they are in that range I can brake stall it and boost it up to 6-7psi (with the stock converter) in 10-15 seconds or so. But after a run and then sitting still and IATs getting around 95-100F(I have a cone air filter attached to the turbo inlet so no "cold air" intake) it gets extremely sluggish and trying to brake stall it will sit there for 30 seconds or more and only be at 3-4 psi and not go really any higher.

So only thing I can think of going on here is the chicken and egg thing and because the IATs climbed 20F or so it decreased cylinder airmass and therefore resulting exhaust energy and therefore turbine speed and it hits a critical point where it just won't spool.

I guess it may be possible my LS7/LS9 MAF temp sensor calibration is off (I am running 100% stock closed loop MAF but early (around 2000rpms) dynamic airflow enable since I had lean spike issues I couldn't figure out). However, fueling is right on during all these runs and while brake stalling it is in PE mode and richened to about 0.81 lambda (I run E85 100% of the time). I have double checked the temp sensor calibration and running 2011 Corvette LS9 values since I have the LS9/LS7 MAF sensor. MAF sensor is located just before throttle body so its under boost. Maybe I am just hitting a lot higher IATs than I think. Also I can consistently turn up the boost controller and hit a certain boost and it will start perfectly and consistently knocking once you turn it up to that level and bump the **** down just a little and zero knock.

So anyone have any of the same experiences? Eventually I am upgrading to a real turbo, I mainly bought the cheap GT45 to get my setup and tune and everything else dialed in and experiment with. I just find it hard to believe once I hit a certain IAT within a few degrees it has such a profound effect and I start instantly getting knock right at a certain boost level.

On that same note I am thinking about wiring up a auxiliary fan behind the intercooler, but don't see any info about this since I assume its not something much people do because their intercoolers are always in the stack. Not sure how advantageous it would be to get maybe one of those auxiliary trans cooler fans to put behind my intercooler or maybe a junkyard fan and just power it off the same fan relay.

MikeGyver

iTrader: (5)

My experience with IATs is that 100° is not enough to cause the problems that you describe. I agree that you should be suspicious of the actual temperature. Check that before you start adding fans or in my opinion, ductwork would be more reliable than fans.

jclark10

iTrader: (1)

By ductwork you mean like the plastic mat thing that gets held on by those plastic push tab things that divert air through the radiator? I was thinking about that trying to figure out a way to do that I just can't figure out any options I would have with my setup the way it is. I'll have to take some pictures of it and post it since its hard to describe.

I also have a spare GM IAT sensor, but I would need to weld a bung in my intercooler tube to put it in to test, so I am kind of scared to do that and take a chance screwing it up then having to order a whole new intercooler pipe kit, but I guess in theory I shouldn't mess it up. I will say every time I have braised MAF bungs or circular threaded IAT bungs in this cheap Chinesium aluminum intercooler pipe it has been really difficult given that I have to basically melt the Chinesium aluminum intercooler tube material to get the low temp "alumiweld" brazing rod to melt. If you don't and try to pass it over the torch flame as a shortcut to get it to start melting you will get basically zero penetration and your bung will end up blowing off and flying through the hood under boost.

I guess I need to also start playing with the IAT sensor calibration in the tune file and just see what it starts reporting. Although I kind of have done that before and everything seemed fine which seems weird. I don't know of any quick way I can think of to measure the temps inside of the intercooler tube going into the TB, especially while the engine is running and the truck driving, without just tapping a new bung and putting the older 90s GM standalone IAT in there.

MikeGyver

iTrader: (5)

I meant to fabricate custom ductwork from sheet metal. Study circle track race cars for ideas. If you are nearby (you could put your general location in your signature), I could weld a bung in for you

smokeshow

iTrader: (16)

Most of that delay in spool time is going to be due to the reduction in torque and therefore ability to rev the engine as quickly under load. If you do the math on it, 20°F isn't much change in mass at all. But getting into IAT spark reduction can have a large impact on ability to rev and feed the turbine to get the turbo moving.

jclark10

iTrader: (1)

So I feel like my LS7 MAF is not reporting the correct IAT for whatever reason, yes the increased air density from the IAT is very small and that much more torque will stall the stock torque converter that much of a higher rpm to increase the rate of spool that fast. I still don't know how I could test it without having to weld (braze, since I can't weld aluminum) in another bung.

smokeshow

iTrader: (16)

If you have access to a thermocouple-style handheld thermometer, you could just sneak the probe in between the coupler and the MAF housing. Probably best bet. I've had to change IAT cal when swapping MAFs before, but I don't think your stock one and the LS7 IAT cals are different.

jclark10

iTrader: (1)

I have a muiltimeter that I think came with one, however I would have no idea how its calibrated but I wouldn't think it would be calibrated for that to get an accurate enough measurement to know what's going on.

It does seem accurate logging the IAT as I will get about 5-10 degrees or so above ambient and then 20+ degrees after sitting there and letting it soak, although the 5-10 degrees above ambient does seem kind of optimistic given the air filter intake is hooked up right at the compressor inlet under the hot hood next to the hot turbo.

What are some people with turbo kits with intakes at the turbo inlet seeing for IATs, like how much above ambient when sitting still and moving?