I had to run my car at WOT for about 2 minutes last night, long story, but I blew a headgasket(I imagine the EGT's hit the roof with that much time in boost) and the car started to dump water out, got some coolent under the tires and the car let go into a guardrail, amazingly I came out with only a broken wheel and some missing paint on my rear bumper, anyways whats the trick to making a turbo car hold together for long durations at high boost/rpm?

 

Buy a Supra?

Seriously though, I've wondered about this myself, having read so many times on this site about 'avoiding 5th gear under boost' or 'avoiding extended periods of time'. Wonder what the secret is since you can run even the most modest of factory turbo cars under boost all day long without an issue, but our high dollar set-ups can only take it for 12 seconds at a time?

 

haha, just not a MKIII, a friend of mine melted every piston on the 7m-gte motor in his mkiii supra being under boost for right around 5 mins.

 

Try sending a PM to Paul Bird. He's building his open road twin turbo car right now. I'm sure he knows what it takes.

 

hopefully paul will chime in on this thread so it can be public

 

I imagine a cooling system with more capacity along with a big oil cooler will do the trick. All road racers have huge radiators and big ass oil coolers and they do ok.

 

yeah i thought about that, the temp increase wasnt a steady increase like a lack of cooling ability, it just shot up so its almost like the egts kept going higher and higher, chamber temps got higher, started pinging and took out a head gasket, then the motor temps shot up, i would guess some kind of water injection would help but you would need alot of water, any other ideas?

 

The temp probably did climb gradually, but you couldn't see it. Eventually something gave and that caused the spike/detonation/headgasket failure. A good oil cooler would be a good first step, and make sure you've got as much radiator as you can. Duct the area in front of the radiator to keep air flowing through it instead of around it...things like that.

 

re keeping your cool

another thing to check is any datalog you have of intake air temp, depending on your intercooler size and placement its very possible that you slowly heat-soaked the cooler, once intake temps start to go up its a huge chain reaction that heats the chambers,turbo, engine bay, all pipework and so on, especialy at speed where alot of cars front body work actualy works against decent air flow into the cooler and radiator

 

While I do not have a lot of direct experience with this I have researched cooling a ton (I love this kind of stuff) and will soon get my feet very wet with this very topic. Let me first say that running 2 minutes at WOT is a serious challenge on a number of levels. Even on the longest road racing circuits the most you will see is 70% WOT per lap. The closest thing you will find to this length of sustained WOT will be in NASCAR, the salt flats and in Silver State type open road racing. With that said, the fundamentals of cooling apply to all forms of racing so let's jump in.

Obviously radiator and oil cooling capacity are essential (as are diff. and trany cooling but we will leave that out of this discussion) and can be quantified with a somewhat linear relationship to power output. What is more difficult quantify and is of even greater importance to the cooling equation is airflow across the coolers.

The essential consideration in airflow (that is 99.99% of time ignored) is sealing of radiator, oil cooler and intercooler to the airflow. Simply put, air would rather go around a radiator than through it. Lack of ducting and sealing from the leading edge openings to the radiator is the single biggest mistake made in cooling systems.

The next biggest mistake is the underutilization of the low pressure area over the hood. More specifically the front half of the hood. The airflow capacity available out the hood is way more that from out the bottom of the car! Automakers are obviously aware of this but seem reluctant (except on the 03-04 Cobras) to tap it.

I love to reference this air pressure schematic. Yes, I know it isn't a Mustang but a Mustang's pressure zones will be very similar.
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The yellow sections with outward pointing arrows represent low pressure and the white areas high pressure. A couple points,
1) You can see why NASCAR teams pull air from the HIGH pressure area at the back of the hood into their carbs.
2) You can also see why you don't want this to be vented to anything but an air intake. If this pressure enters the engine compartment it will reduce the pressure behind the radiator and thus reduce flow.
3) You want as low a pressure area as possible BEHIND the radiator and as High a pressure as possible in front. To accomplish this you MUST duct and seal the front openings of the car to the front of the radiator/oil cooler/intercooler. You must also seal of the high pressure at the rear of the hood. And last, to maximize efficiency you must vent to hood behind the radiator.

Just like my three year old daughter, I like pictures. I have learned more from looking at elite race cars than I ever would in school. I have literally THOUSANDS (>10 GB) of pictures of professionally engineered race cars. While the drag racer guys do some things very well you must look to the highest levels of road racing for the solutions to these problems.

So lets take a look:
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Ahhhhh. This car is pure sex to me. The Prodrive group in England built and races this car for Aston-Martin in ALMS GT1. This, in my opinion, is the pinnacle of 'Production Based' race cars. The reason I have shown it here is that can and does make 650 horsepower for 24 hours in 100 deg. heat. The other reason is that it's hood represents exactly what I am talking about with venting. Notice that the leading edge of the vents have a raised lip to venturi the laminar airflow which creates even greater negative pressure behind the radiator. Nice! The last thing I want you to see is that the main upper opening in the nose isn't. That is right, the center of that opening is covered with a carbon fiber panel. Why? Two reasons, 1) Downforce 2) Reduced cooling efficiency - See RX7 above.

I want to apologize in advance for putting a Chevy on this forum. Take comfort in knowing that it is as much a Chevy as Jeff Gordon's NASCAR.
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Ahhhhhh again. This, BTW, is the Pratt & Miller C6R Corvette. Let this be Exhibit A in how to vent AND DUCT a hood to a radiator. (Yes, I know, it has no fan. More on that later.) Of note here is that 100% of the air entering the radiator comes out of the hood. Smart? Indeed. Also take a look at how much air enters at the back of the hood - None! Again 650 horsepower, 100 deg., 24 hours. Just as an FYI, the hood I am building for my car is a 100% direct copy of this, just on a Mustang and just 5 lbs. at that.

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This is a shot of a Japanese Touring Car Supra to show that this can work with turbo cars as well.

BTW, If you want more pictures of this kind of stuff let me know. I have hundreds on just this topic.

Now a word on radiators. I hit this second to airflow because in my opinion airflow is more important and much more often screwed up. Conventional wisdom would say thicker is better but this isn't necessarily the case. The thicker the radiator the greater the air pressure drop and therefore the lower the airflow across the core. The increased capacity and surface area can often make up for this however. My philosophy is that just like an intercooler, you are better off with a tall and wide radiator than a thick one, especially at low speed. Obviously there are constraints with height and width so thickness often must be increased. Where a thick radiator becomes a problem is in stop and go traffic. With a fan supplying all of the airflow, a four inch thick radiator will often not cool as well as a two inch thick one.

With respect to fans, you will notice that the cars pictures above don't have them. Why Not? Because they hinder airflow at speed and these cars spend very little time sitting still. I have read that on a Mustang anything over 45 mph you are better off with the fan OFF than on as the spinning blades restrict flow. This is with a largely unsealed (to airflow) radiator. I would guess that this speed is much lower with a completely sealed and ducted radiator. I won't go into fan size, style and shroud here as that would be a whole other thread but keep in mind that sealing the fan shroud to the radiator is essential to creating flow across the core.

I am out of time right now but my suggestion to you in summary would be to:
1) Seal (100% air tight) the front of the car to the radiator
2) Make sure you are running the stock vertical air dam under the radiator
3) Use as high a percentage of water as possible (100% would be best) with a bottle of Water Wetter
4) If at all possible look into a reverse vented hood
5) Make sure the back of the hood is sealed
6) Data logging is essential - coolant temp, ambient air temp, intake air temp, and oil temp. To really break things down you would want to also watch air temp pre and post intercooler, coolant temp pre and post radiator and oil temps pre and post oil cooler.

Do this then adjust the radiator, fan, oil cooler, and intercooler size and configuration as necessary. And be careful. 2 Minutes of WOT means close to 200 mph with 600 rwhp. 200 mph in anything resembling a street car is pretty insane. Especially on a public road.

 

Great info!! Thanks a lot Paul.:tu:

 

So, if you're posting this the next morning, I take it you got away???

 

Re: Re: How to keep a turbo car running cool with high boost and extended time at WOT

haha, good job, and yes barely. Great post paul thanks a million!

 

Very good info Paul. Even though it's not my thread, thanks a lot, it will help me out a lot when it comes time to start buying things for my car.

 

7m is a powerful motor if build correctly, mine put down 562 on a tuned 62-1 set up, kept egt's low, had a big pull fan and push fan, big oil cooler, intercooler sprayer and big front mount and blah blahb ut i never climbed above 192 degrees under 25lbs of boost. i have a buddy that has a 2g dsm running an air to water cool set up also and never climbs above 180 degreses and when using ice water gets 60 degree air intake charges... thats the way to go

 

Funny you say that actually. A year or more ago I read a thread on Supraforums about someone asking a similar question(they were gonna be highway racing someone a distance for high speed race or something). Pretty much the same thing you said was mentioned in that thread.

 

Paul, great information there, but it got me thinking. Do you have one of those airflow profiles from a front perspective? My question right now is what keeps the hot air in the low pressure zone from recirculating right back into the high pressure air at the rear of the hood? If I were to duct from the radiator out of the front of the hood, and use ducting from the rear of the hood to the turbo inlet, what keeps the hot air from being sucked right back in? I'd love to see a wind tunnel test of one of these cars running on rollers and a smoke trailer running over the car. It seems to me that when the boundry layer comes back down to the hood at the rear the air would be warmer that ambient air drawn from the sides of the vehicle?

 

BTW, Paul, I'd love to see some more pics on different types of vehicles. I'm wondering if the effect of the low pressure is somewhat dimished since I have a flatter, less sloped hood (1978 Trans Am).

 

Ok, this has really got me thinking now. To combat the restriction induced by the spinning fan blades at higher speeds, what about this:

Duct the radiator, much like the C6R, but put a fan on it, with a full shroud covering the entire radiator, so all air is drawn through the fan. However, the shroud itself could be made of slats of metal that were hinged with an electrical control to open the slats at say, 45 mph and allow the air to be drawn through by the low pressure above the hood.

Even cooler than that, to me at least, would be to have the slats each spring loaded so that when a pressure differential is created between the fan shroud and the air inside the ducting the slats open. The thinknig behind this is that at idle when the fan is drawing air through the fan shroud, the obstruction created by the radiator would create a slight vacuum created in the area inside the fan shrouding. When you're at higher speeds and the fan shroud and fan become the restriction, there would be a positive pressure inside the shrouding and the slats would open up, letting the air flow freely around the fan.


Ideas?

 

That's actually pretty common allready, they just put holes in the shroud and rubber flaps over them. When the pressure behind the flaps is lower than the pressure in front they blow open and vent air to outside.