What are your IAT temps under boost?
 

I have a non-intercooled 7-psi kit on my car right now. I'm seeing 176F under full boost and then is settles down to 133F during cruising. I live in South Florida so ambient temps are generally in the low 90's this time of year.

So what are you guys' IATs under boost? I especially would like to know what the intercooled and water injected guys are seeing.

Non intercooled, on track I see 150degC

That's not a typo

Wow... 302F intake temps is intense. How do you guard against detonation? I take it you run high octane race gas, right?

He's supercharged lol

yeah I was seeing 200-220F temps with the FFS before I yanked it off. I was on e85 and it was just an experiment though. Needed charge cooling ASAP.

176 isn't really too bad considering no intercooling. With how cheap they are though, I'd throw one one asap.

With temps past 200 there's no way to really guard against detonation. You intercool or your cool the charge with fluid injection of your choice. I know that even on magical e85 pimp juice it was severely dropping power when it went past 200

Temperature rise in the turbo is pretty close to an adiabatic process. This is because the air is moving through the system so quickly that the temperature rise is almost all due to compression with little other heat transfer able to take place. Adiabatic temperature increase based upon a 90°F/Sea Level starting point is shown in the following graph (note that your starting point would be ~130°F which gives ~185°F at 7psi):

https://www.miataturbo.net/attachmen...1&d=1379370537

The above came from the attached spreadsheet where I was doing some back of the envelope calculations for power gain from an intercooler (density-based only, not taking into consideration ability to increase timing).

Effective ways to cool the charge:
1. Make sure you've got a good cold air intake. Your steady-state cruising temp of 133°F tells me you need to work on this.
2. Intercooling. 'Nuff said. (And, yes guys, I have an intercooler sitting on the shelf waiting for installation -- I'll get there).

WI/MI doesn't really cool the charge very much (maybe 10°F) but does add good det resistance. For more intake cooling, run a greater percentage of alcohol -- although water absorbs a lot more combustion chamber heat per volume than alcohol (by about 2X). I've read that injecting 100% alcohol pre-turbo gives the most cooling you can achieve with WI/MI. I don't have data on that. All of my direct experience is your basic pre-throttle 50/50 or 100% H2O injection.

I feel my IAT's don't ever see much over 100F. But i'm a big wimp and don't ever run any boost.

I get to 85F running 12 Psi on the IAT reading on Megalog viewer. Now I'm thinking that's wrong looking at all these. I've a Flyin Miata intercooler and a cold air feed through a NASC cowl on the headlight cover straight into a boxed off air filter.

Nope, just careful tuning, I don't even use the highest available octane fuel in available in the UK (99 RON, equivalent to your 93 IIRC) I'm on 95 (equivalien to your 89).

Water injection is on the cards as an octane booster

if your IAT is not plumbed into the ic piping after the intercooler somwhere then yes, its completely wrong

It's after the IC just before the TB so all good.

hmm, so 85F after a boosted pull, and what was the ambient? because that still seems very very low

55F it's cold here in England :)
Here a log of a WOT pull in 3rd taking the IAT to 95F

label your axis before you plot graphs so that they make sense.

I see, at most, a 30-50f increase over ambient. I would imagine it would be a lot higher on track. On the dyno, with 80f ambient, it got to 111f during a 29psi pull. My intercooler is directly pressed against the radiator.

But my IAT sensor may not be accurate so take that with a grain of salt.

Bottom line is, get a huge ass intercooler and run E85 for the cooling effect.

Seriously?

So, you think you'll only see 20F when boosting 250psi? Geez. :loser:

^ how does a fuel affect IAT at the sensor?

sure it helps in the combustion chamber and such... but i dont understand how iat in the charge pipe is reduced from a fuel.

Come on now.
Noone wants to read your hypothesis to figure out what a graph axis means.


The graph makes sense once you can figure out what it means.

Great info, thanks! I agree that I need to work on the turbo inlet air temps, regardless of intercooling.

Interesting... I always thought that WI provided det resistance because it lowered the intake temps.

Turbo heat shield + air box + somewhat fresh air for box + good ducting for intercooler = cruising temps just above ambient.

https://www.miataturbo.net/attachmen...ine=1379432059

Before that stuff, i would cruise at above 100f and in boost temps were silly high.

Nope. You are introducing a liquid that goes through a phase change during combustion. In doing so, it absorbs a tremendous amount of heat but still generates useful work because of the expansion associated with the phase change. It's pretty cool (pun intended).

If you think about it, you would recognize that air can only hold so much water vapor. That's why it rains. And when you pressurize air (all other parameters held constant), it holds even less water -- which is why we're always draining water from air compressor tanks. Bottom line, water generally stays in liquid state (small droplets) until the combustion event. It doesn't cool the intake charge. Alcohol, OTOH, will partially vaporize in the intake yielding some drop in temperature.

Some interesting NACA papers attached. They contain lots of hypotheses though, so shlammed may want to stay away.