Need Airflow Suggestions for Overheating

[scannon]

At the track this weekend, I experienced overheating in 85 - 90F ambient temps. I removed the nosecone and bonnet and ran a few laps and the coolant temps dropped dramatically. I ran the rest of the day with the nosecone on and the bonnet off with no problems.

 

From this I conclude that the problem is getting the heated air out of the engine compartment. I don't want to run without a bonnet so I am looking for ways to improve the flow of hot air out of the engine compartment. The car is a Caterham SV with the normal louvers on the top of the bonnet and does not have a cutout for an air intake.

 

There is a turbo on the drivers side that contributes greatly to the heat load under the hood. It got hot enough under there to delaminate the foil covering on the footwell insulation as well as the foil tape sealing the edges of it. The foam remains glued to the footwell. I have insulated the brake line as it passes the turbo and the throttle cable with thermal sleeving and had no problems with fading brakes or sticking throttle.

 

The radiator and intercooler are completely shrouded inside the nose cone. I plan on removing the heater soon as I just don't see a need for it.

 

Anyone have any good suggestions for extracting the hot air?

[Boxologist]

on some of the european sites i see small scoops that are normally used to allow air into the rear of the bonnet near intake on fuel injected cars. if u reverse the direction, it should work as a vent.

 

were the turbo, UP, DP and otehr parts ceramic coated? if not, wrap them. I'd love to have a nose cone that has the top vent that the CSR does to flow hot air out from the radiator. the CSR cone does NOT fit the SV.

[Kitcat]

Run the heater (auxiliary radiator) full blast!

[scannon]

were the turbo, UP, DP and otehr parts ceramic coated? if not, wrap them. I'd love to have a nose cone that has the top vent that the CSR does to flow hot air out from the radiator. the CSR cone does NOT fit the SV.

They haven't been coated other than high temp paint on the manifold and downpipe. I plan to do some type of thermal coating this winter and that should reduce the underhood and footwell temps but won't help with getting the hot air out of there.

 

Do you really thing a backwards scoop would extract air? The dynamics of underhood airflow are such that without extensive testing, you are only guessing when it comes to placing exit vents. Maybe I should just cut some large holes in the side panels and mount some fans on them.

 

Running the heater helps a little but not enough to get the problem in control.

[slngsht]

Anyone have any good suggestions for extracting the hot air?

 

I like the side vents on the Deman

[drew...]

Two suggestions:

 

1. As Kitcat stated run your auxilary radiator full blast - an old trick we used to use with tow vehicles

 

2. Can you fabricate a "cold air box" to encapsulate the turbo then, similar to race car brakes' duct air thru the box and exit thru either a side vent or under the car?

We used to use the cold air box, more of a forced induction, on an e-production MGB. I would think you could use the same concept todissipate the turbo heat.

 

Another related option would be to seal against a set of hood louvers, similar to how the heater air intake seals against the hood, from the cold air box.

[scannon]

I think the problem is not the radient heat added by the turbo since it is downstream of the radiator and intercooler but rather the volume of air flow through the radiator and intercooler. Finding a way to extract a higher volume of hot air from the engine compartment will allow more flow through the radiator and help with both the coolant temps and the under bonnet temps.

 

The big question is how to get more flow through the radiator and intercooler as running without the bonnet produced lower coolant temps.

 

Running with the heater on did not significantly reduce coolant temps. It does help with my turbocharged Miata but didn't solve that problem either.

[Boxologist]

a hood with large louvers would be ideal. Skip, u are pretty much on the right track that the air is still stuck in engine bay. unfortunately, the easy way to vent is to duct the air to flow underneath the car. and that cause more lift in a car that has too much.

 

definetly get as much piping and the turbo ceramic coated ASAP. Deadbolt enterprises can do the turbo, and JetHot is biggy on pipes if u need leads.

 

if u vent on the sides like i suggested, u should create some sort of ducting or funneling to get the air from right behind the turbo/upipe.

[bsimon]

Skip,

 

I have a Magnehelic differential pressure gauge, ranged either 50" or 100" H2O (can't remember off hand) that might give some insight to pressures around the engine bay. You might be able to find some innocuous location on or about the body panels or bonnet that produces a large pressure differential. I'll loan you the gauge the next time I see you.

 

There was a discussion on BC a few years ago about extracting air from the engine bay. One individual propped open the back of the bonnet with good results as I recall. Although probably not practical, or at least not very aesthetic, it proved there was an abundance of heated air waiting to escape the engine bay.

 

Also there was a thread on high pressure in the prop tunnel. Go for a drive without the tunnel cover and you'll see what they're talking about.

 

Here's one idea;

The propshaft tunnel seems to have high pressure from all sides. The engine bay, open bottom, and rear suspension area. If one could get it to flow somewhere, it might extract the engine compartment. The air flow under the car effectively boxes in the bottom as though a panel was riveted in place. Somehow the rear suspension bay and wings create a high pressure zone that locks air in the prop tunnel. I believe the back of the tunnel needs to be sealed and ducted into a low pressure zone, or better yet, create a low pressure zone in the rear suspension bay. I wonder if a combination of rear diffuser and blanking in the chassis bottom might work to create a low pressure zone under the suspension. There would be some small amount of aerodynamic benefit as well, not big mind you, more like putting wheel pants on a dumpster...

 

 

[locostv8]

I am sure I will have to address this problem. A couple of thoughts are to space the rear of the side pannel out as Jeff did, a gap between the hood and frame fail of about an inch, though you would have to insilate the tunnel I don't see where it would hurt to put some kind of a sucke fan on the tunnel to pull air thru it.

[scannon]

There would be some small amount of aerodynamic benefit as well, not big mind you, more like putting wheel pants on a dumpster...

 

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Bob,

 

I will take you up on the loan of the gage. I don't want to start cutting holes in the bodywork without at least a good idea that they will be effective.

 

I will look into lifting the rear of the bonnet for track use. I don't have a problem on the street so it can sit normally when not on the track.

 

I have driven with the tunnel cover off and there is a vertible blast furnace effect. Way too much to drive on the track with it open but maybe I can make a new temporary track only tunnel cover with a chimney on it like the F1 cars use.

[BobDrye]

You’re going to find it difficult to measure pressure difference. The figure that you’re looking for is a delta/p of 25 Pascal’s

[bsimon]

Hmmm,

 

Must be a 5-10" gauge, not 50-100". Will look tonight.

 

 

[bsimon]

Skip,

 

The differential pressure gauge I have is scaled at +-15" of water. Bob is correct. We need something that measures in the 0-1" range. Let's fabricate a u-tube manometer by gluing some clear PVC tube to a board. We're not concerned with actual numbers, just relative changes in pressure from place to place on the car.

 

I had to miss work yesterday with some medical issues. I believe the speedo sensors should have been delivered in my absence. Tom M. is stopping by today to pick up his six speed and bell housing. I'll make sure he gets the sensors.

 

Maybe I'll see you this weekend at Jeff's.

 

 

[scannon]

Bob,

 

A Miata club friend has offered the use of his magnehelic gage that he has used for checking underhood pressures on his Miata. I'll check with him to see what range his gage has.

 

When are you going to be in Greeley, I'll try to get there around the same time. It's going to be great to finally have a functioning speedometer! I finished and mounted the bracket for the sensor for my car but want to take some more measurements on Tom's car before I make one for him.

 

Skip

[bsimon]

Skip,

 

I'm not sure what the schedule is this weekend. Connie had relatives in from the Midwest for most of the week. I figure I'm owed an extended kitchen pass for the weekend. I'm just not sure when the diplomatic time to execute that leave might be yet. :blueangel: I was hoping to shoot a round or two of sporting clays sometime this weekend too.

 

I'll be up by 8 bells tomorrow. After I log the morning watch, I'll let you know when I can get to Jeff's. It may be on the way back from shooting.

 

I gave Tom the wheel speed sensors today. I understand he'll be plugging along on the new car all of the weekend, regardless of who shows up.

 

 

[SR27.Seth]

As some of you know, the Orange SR27 of Paul and Dino's had a very similar problem at VIR during the UTCC. Unfortunatly they pulled off the hood and the nose, which caused it to over heat even more (the nose on our car is the radiator shroud.

At the autocross during the 7/7/7 event, even with the car doing double time with 2 drivers it ran quite an acceptable temp. (for that engine 100-110 deg C) with the bonnet off.

 

The thing about a turbo under the hood of the car is that, uncoated and under boost conditions, it releases a tremendous amount of heat- think of a chunk of large chunk of metal at 800-900 deg. sitting in your engine compartment. As we all learned in elementary school- that heat rises and sits at the top of the engine compartment- slowly coming out of the vents, unless it is pushed out of the vents. That hot, stagnant area then blocks the other hot air that should be coming off of the radiator and up and out of the hood vents. If you look at production turbo cars (WRX, Silvia, Skyline) the hot radiator air gets pushed (or pulled with massive CFM fans) out of the BOTTOM of the engine compartment. That does not seem to work on a Seven body.

 

SO:

Get the air moving more under the hood with a second fan or a stronger fan on the Rad (Dino switched out the stock 800cfm fan for a 2300 cfm fan and put a fan to blow the hot air off of the turbo out of the side pod!- big difference)

 

And get the turbine housing, exhaust manifold and downpipe coated- but caveat: regular header coatings will not withstand the heat put out by a turbo. Double layer 'jet aircraft quality' type coatings are the best- just expensive.

 

[locostv8]

This might help http://mcneilracinginc.com/off-road-fiberglass/Fiberglass/Accessories/index.htm

 

http://mcneilracinginc.com/off-road-fiberglass/Fiberglass/Accessories/pic_main.jpg

[scannon]

I have already upgraded the fan from the 9" supplied with the kit to a 12" Spal rated at 1230 CFM. It was the biggest that would fit on the radiator and still clear the sway bar. I have it set to come on at 88C.

 

I plan to have the manifold, turbo and downpipe thermal coated this winter.

 

Right now I am contemplating cutting a large triangular hole in the side panel just in front of the foot well on the driver side. I will then make a heatshield for the turbo and downpipe that will divert the hot air out the side of the car. Should help with engine temps as well as foot temps.

 

Maybe I should cut a round hole in the side and mount a fan in it to draw the hot air out.