[sperry]

Originally Posted by Crucial Racing

sperry -- you're a little bit mistaken on some of those points. Most importantly, just the huge and extremely dramatic drop in underhood and intercooler temperatures a WRX sees with a thermal coated or heat wrapped downpipe vs. a bare one. There is a heck of a lot of exposed downpipe metal that is still inside of the engine bay and there is a lot of surface area for it to radiate heat from. It does, of course, get very hot.

If they're so huge and dramatic, it would be a cinch for you to quantify them, no? So how much is this temperature drop?

Originally Posted by Crucial Racing

Your turbo heat shield does cover an inch of the downpipe, but that doesn't prevent the other ~ 18 inches under the hood from radiating heat like crazy and, as we know, heat tends to go upwards and upwards is where you keep your intercooler. You'll notice that when you come to a stop, you can literally see hot air shooting out of your hood scoop. That hot air is going up through your intercooler and out your scoop, and a whole lot of that is thanks to your downpipe. While a heat shield does an okay at blocking direct radiant heat, it doesn't block conducted heat or hot air flow very well at all and once that heat shield gets hot, which it does!, it starts radiating its own heat into the air as well. However, if you coat the downpipe or wrap the downpipe, you're actually preventing heat from leaving it in the first place... radiant or conductive. In fact, because we coat outside AND inside, we're preventing the exhaust heat from soaking into the metal to begin with.

Now there are a lot of assumptions... first, my head shield does in fact cover the turbo and DP all the way to the firewall... that is, when I'm running it... since I never really noticed a difference, what with my FMIC and all. So, personally, I'm not having any sort issues with "hot air shooting out my hoodscoop". And I'm not sure that a ceramic coating is going to make this massive difference you're implying... by the time the exhaust is past the turbo, it's what around 600F? So the pipe is maybe 300F instead of 325F due to the coating? We're not talking about dealing with 1600F exhaust right off the headers... so we're talking about a delta of maybe 50F, which means very little in terms of how fast a TMIC is going to heatsoak due to radiant heat from the pipe... again, some real data on the effectiveness of this coating would be useful. But I'm just making these numbers up... I don't have a coated DP to point my IR gun at... hell, I don't even have a running car right now if I wanted to test it.

Originally Posted by Crucial Racing

I think you'd be shocked at the difference. Without even measuring, it is just painfully obvious when you open the hood after a drive. You wont feel a rush of hot air on your face. You'll be able to press your hand on the intercooler to find it at ambient temperature. It takes a lot longer to see hot air coming out of your hood scoop and the intercooler stays cool to the touch much, much longer after you come to a stop. In fact, we see a DROP in underhood temperatures and intercooler temps with our uppipe and downpipe vs the OEM parts with all of their heat shields. That drop isn't huge, but it's big enough that many many customers have mentioned it in their reviews and some even took the time to verify with measurements. The difference between coated and a bare aftermarket pipe.... MASSIVE.

Once again, if I were selling something and touting the underhood temp reduction as a selling point, I'd be very interested in providing actual temperature data, what with the whole "truth in advertising" ethical responsibility thing.

Originally Posted by Crucial Racing

If you're running a short ram intake, you get direct HP benefits from sucking in colder air thanks to your cooler engine bay. If you're running a TMIC, you get benefits of a higher knock threshold thanks to the lower intercooler temps and you're much less likely to knock if you drive hard immediately after coming to a stop for a little while (like after sitting at a traffic light or staging at the track before you get to race), as the rate at which the intercooler heat soaks is slowed way, way, way down.

I'm not running either a short ram or a top mount. I went to a CAI when I measured 170F intake temperatures on the dyno w/ a short ram.

Originally Posted by Crucial Racing

While it's very easy to assume that if you're moving, the air flow is going to outweigh the heat coming off of the downpipe, it's typically not true. First of all, there aren't many situations where you never stop ... BUT... there simply is not enough airflow and pressure through the intercooler and the grill (and, btw, after the air goes through the radiator it's not cool when it comes out the other side) to push all of that heat out the back of the engine bay and under the car. There is a difference in underhood temps while driving. Less than the difference after you come to a stop, yes, because of that air flow, but it is NOT sufficient to make up for all of that scorching hot, bare metal under the hood.

So you're saying that the air around the DP is heating so fast that the air rises faster than the flow of air through the hoodscoop? Unless you're running a full undertray on the car, the negative pressure of the airflow under the body of the car is going to suck the air that entered the engine bay through the radiator and hoodscoop down and out along the firewall. It may not be a ton of airflow, but it's certainly more air than the DP heats up and rises into the TMIC when you're stopped. And if these underhood reductions are only when you're stopped... well who cares, unless you're a drag racer who needs the IC to be as cold as possible the instant you leave the line... the rest of us will have reasonable cooling again withing seconds of moving.

Originally Posted by Crucial Racing

....we do a lot of custom coatings for people, btw. It's typically $85 for a shorty downpipe and $105 for a full-length downpipe... It's worth the price, unquestionably. If you don't want to spend that sort of $$$, spend the $50 and heat wrap it (which, although it also works very well in the end result of dropping underhood temps and we do have a good account with DEI, is not our preference because it tends to cause metal fatigue and the wrap is very tough on whatever is underneath it... eating into the metal and causing pretty nasty surface rust).

For what it's worth, the WRC Subaru ceramic coats its ENTIRE exhaust, in-and-out, from cylinder heads to muffler tip.

If I were running a car that regularly sees water crossings, perpetual gravel spray, snow, etc, and if I had a WRC team budget, I'd coat my entire exhaust too regardless of any possible temperature gains.

Either way, what I'm not seeing here is any claim that this coating makes horsepower. For the sake of argument, I'll concede there may be an underhood temperature decrease, but even that doesn't make additional power on a car that's got a proper intake and intercooler setup... things that do make real measurable differences in intake charge temps. And the biggest point here that I was disputing is this idea that coating the DP makes the exhaust somehow flow better, something that you didn't even mention.

I'm not trying to say that coating the DP is bad... I just don't see that there's any massive benefit to it, at least not when compared to the cost. Now if you want to do it 'cause it looks sweet, by all means. My radiator and FMIC are both anodized black... which according to the industry is only good for like a 4% cooling effectiveness gain... not worth the cost for performance reasons, but I did it because my radiator and IC were getting pretty old-n-busted looking, and they look a crap-load better blacked out. Same goes with the IC piping that I had powdercoated... looks nice, does basically nothing for performance.