LS1 V8 Miata Cooling and Hood Venting 101

TECH OVERLOAD ALERT!  This post is long and techy so if you have no interest in solving cooling issues (or seeing what I mess I made of it) then skip down to the bottom couple of photos. 

 

With the dangerous 250 degree temp reading at the autox I went back to work on the cooling system to see where I went wrong.  And the answer is pretty much everywhere!  (Note to self if the temp gauge ever goes over 225 again at a track event take the hood off ya bone head!!) 

NEWS FLASH +++ This just in from the well duh department +++  

There has to be less air pressure under the hood than outside for air to flow into the engine compartment. 

No kidding...

So with a bit of tape and plastic streamers I quickly found out that at speeds over 20 mph I had more pressure under the hood than outside it.

Why?  Because my hood scoop was open to the rear which is a very high pressure area.

At 20 mph streamers at the back of the scoop sucked into the vent and by 60 the airflow is so strong one of the streamers broke off and went inside the engine compartment.

Hey I know, I'll leave the parking lights out to get more air flow :-)

Sure what a great way to funnel a ton of air pressure into the engine compartment BEHIND the radiator.  Over 20 mph there was so much pressure under the hood it was impossible for air to flow through the radiator.   

OK lesson learned time to get out the saws all…

Check out these pressure measurements on the hood at 60 mph.

As you can see having the scoop open at the back was a disaster for air flow out but what is more interesting is how negitive it is in the front.  The scoop he has here actually had air flowing out of it! 

So with that info I plugged the hole in the back of the scoop with Great Stuff foam

 
and added new vents in the low pressure area just behind the radiator to draw air out.

 I went the low budget cut and bend route.
The photos don't do them justice they really do look cool on the hood.

For more info on airflow see this great 3 part article CLICK HERE 

 

OK so now that I have the pressure lower under the hood than above it will air flow through the radiator? 

NEWS FLASH +++ This just in from the dope slap department +++

A 4 core radiator with a 2 core A/C condenser in front of it has considerably more resistance to air going through it than the unobstructed gaps all around it. 

Roger that... 

OK so not only does the pressure have to be lower under the hood than outside, there also has to be no other way for air to get in except through the radiator. Lesson learned and here we go.

This is how I had the radiator set up before I put the bumper cover on.  There are 2 problems with this.  First it is wide open on 3 sides for the air to go around and second I had the pusher fan wired backwards so it was pulling.  (Insert dope slap here...) Hey I turned the fan blade around when I put it in so it should have been right!


So I stopped by the scrap aluminum scrap yard and picked up 3 bucks worth of old signs and flashing to make duct work. 

First up more foam to seal up gaps in the frame.

Then with a roll of high temp aluminum tape and a pile of rivets I went to work making ducts around the radiator.  I built a wall with roof flashing on both sides of the radiator sealing it to the frame,
  then made a box around the bottom, 

and sealed the sides to the radiator with more flashing.
(Notice the new larger power steering cooler. The one 5 photos up was not big enough and I cooked the pump at the autox. I got this one off a jeep in the bone yard for 6 bucks.)

I recycled a railroad sign!

I sealed up the top,

put the bumper back on and sealed the sides of the bumper cover with an old license plate.  Yep it needs paint...

Since this is grass hopper season I put a screen on it but still ended up with dozens of them in there.

Results?  AMAZING!!  It still heats up to about 210 in an autox run but cools back down to 195 right away when you stop flogging it. I am a little concerned about track days but am hoping with the higher air flow at speed it will be alright.  

Problem with it is it hanges down too far and is too ugly so it's back in the shop to take most of the part below the bumper off it.

In other news I corked up the exhaust cut out and took my sweetie down the Loess Hills Scenic Byway on Sunday afternoon.  That’s 210 miles of hilly, twisting 2 lane with epic views and wonderful corners.  We spotted a 427 Cobra on the way and as tempting as it was I respected the legend and did not pass him.  (Truth to be told had I been alone I would have challenged him to a duel.  On guard you Cobra!)

Anyway after a lovely dinner in downtown Omaha it was 80 mph on the freeway back home.  425 miles of all kinds of driving and I got 24.8 mpg. 
Now that is a hybrid worth driving!  

 

9/20/13 Update.  Check out the newer posts for added vents to the hood and changes to the cooling system. She still overheats at the track so the radiator and ducts will be replaced with larger ones.