Sorry, I should have worded it better. I'm on the phone/taptalk...hard to type lol. I didn't mean to give percentage of heat gain from the grille to be blocked. I just meant that if you block your grille, you are in essence blocking some airflow(external) away from the IC radiator. If you do that, you Decrease the efficiency of the IC. So the IAT's go up. That I don't think we can argue. Forget the bypass, if you have stock IC.
So we agree stock IC with blocked grille will be just a wee bit hotter. Not much, never gonna notice. But higher IAT's offer less power at same boost. Can we agree on that? Now how much, just higher or lower.
Now add the TSB. It isn't bypassing the outside, if I understand correctly. It is just bypassing the coil(internally...important). So the size of your IC coil is smaller and you said it bypasses 80%??? If so that's crazy if it that thing ever sticks open when it's 100degF you are at full boost and your intake has malfunctioned.
100F air pressurized to 25psi....That has to get pretty hot right. I need to get my charts one of these days. Anyway, my point is. At 25psi, it's going to be HOT! If that bypass stuck, 80% of IC is not helping get rid of it. If your intake manifold is failed (which is why the IC kit is in there to begin with...just pretend Intake flaps are stuck shut.), then you have NO airflow. No air = no air out. I hope you are on the train already, cause this heat train just went down a hill with no brakes.
No air out is important. x volume of intake=x volume of exhaust. Can we agree? That is a valid equation? We have the variable of fuel, but just to make it easier in discussion, let's say coasting down a hill in gear...so fuel is removed from equation for now.
If we agree that equation is correct, let's play with it.
100cfm in = 100cfm out. Check mark, smiley face
50cfm in = 50cfm out. Check mark, smiley face
Ok, now let's complicate it just a bit.
Let's give some value of heat to the cfm, tells us useful info for volume, we don't know if it's 100F or 1000000000F.
Let's just say 1:1 cfm to joules. Keep everything constant in the environment.
So 50 cfm has 50 joules, 100 has 100, etc. I'm just trying to show the heat flow, heat in = heat out minus losses.
So if we flow more air we can carry more heat. Bigger exhaust, it gets out faster. But we have a problem? If what I said was correct, then my exhaust should be 100 joules. Let's just call it 100F, the intake air temp. It's definitely way hotter. Oh that's right the fuel!
We took that intake air, boosted it at 100F to 25psi. We took 80% away from IC if bypass sticks. So what we can't remove stays on the heat train.
So god only knows how hot that intake air is. Now add fuel, with very little air because of a bad intake manifold. You have a rich mix, afterburn, high egts. Bad stuff yo! Unless you went to a tuner and had something taken out. Once that is gone, you can get rid of all that heat, with it, it's got nowhere to go (of course some loss but mostly inside exhaust piping) for a while...Low pressure egr stuck open, with a malfunctioning egr cooler....Rut row. That's some hot stuff going straight into an IC that we already agreed is much less efficient with bypass open. Exhaust flap stuck closed....it's like driving over the GW bridge trying to get out. If everything goes right, it's ok, but too many cars(heat), especially when you keep adding them, can't go anywhere if you keep closing lanes and exits. You get a pile up of heat. Watch a rush hour traffic jam....It builds and go backwards. Always more heat towards the end of the restriction. But if you don't clear the traffic ahead, and keep adding cars, eventually you get gridlock. No movement of HEAT.
So let's think about detonation. I only brought it up, because I swore in the IC thread I read someone say they detonated, but I, like you, said no way....But the code you diagnosed got me thinking. And you saying 80% only strengthened my suspicion.
Covering up a car with TSB can REDUCE efficiency enough to trigger a CEL. What happens when it's hot? Now this is where I would think ECU would step in at some point with IAT sensor, but I am ignorant of when ECU steps in. I would think it would be able to avoid it.
It sounds simple to undo TSB then. Just shut the bypass and have a good day!