Effectiveness of Vented / Extractor Hoods?

[Massive Lee]

Lee likes this thread. ;-)

[cledbetter]

It is a pretty awesome thread.

I have a question, is it better to block of the kidney grills and leave the bottom open or block the bottom and leave the kidney grills open if the radiator is being ducked though the hood?

Christopher

[raamaudio]

I am going to block the kidney's and tilt the radiator as far forward and low as I can mount it, part of why going dry sump on the LS swap, to move the engine back and down as far as possible so I can duct all the air possible out the hood.

I am searching for the right radiator, shortest one I can find, as well.

Rick

[albrazzi]

I may be the King of dumb ideas but has anyone developed a wheel that moves air across its center, I think F1 did, or does something like that, it would seem to at least go in the right direction for air flow and reduced under car pressures. Or will simply ducting do all that can be done without creating more than is solved.
I move a lot of air across the brakes or at least I think I do, without hoses, with openings and diverters in the front and even though I don't need cooling in the rear I am considering moving some air there also.

[nondescript]

I may be the King of dumb ideas but has anyone developed a wheel that moves air across its center

Isn't that what the flat disk oz racing wheels did on dtm and e30's for a while?

[bimerok]

Very interesting thread.



I know it's been a while, but wouldn't the duct for the radiator be better slanting the other way around (from buttom up and intake from the bumper instead of kidneys) since the venting is on top of the hood? Or is it doesn't really matter and air passing through the radiator fins will straighten out anyway?

[TOOLEAN]

The goal is to force the air to go through the radiator and not escape around it.

[flink]

I don't think it will matter - the flow rate through the radiator is low - 15mph at 100mph according to these guys:

http://forums.hybridz.org/topic/5594...nel-test-data/
http://forums.hybridz.org/index.php/...datsun-s-30-z/

(those are two very interesting threads btw)

When thinking about flow through a radiator, don't think about air speed or air direction or such. Think about air pressure. It's the pressure difference between the front and the rear which forces air through the cooler. The aims should be to get the pressure at the front high, the pressure at the rear low, to prevent any air from escaping around the cooler and to avoid letting air into the car without that air doing something useful (ie: cooling something that needs it).

I was at Miller Motorsports Park last weekend. It has an utterly ginormous front straight - 131mph, despite it being 4400 ft above sea level. It's a great place to test aero drag changes. First session I went out with the lower grille blocked off and did a couple of laps. Jumped out, removed the cover then did a couple more laps. According to the GPS data it made exactly zero difference

[sstecker]

I don't think it will matter - the flow rate through the radiator is low - 15mph at 100mph according to these guys:

http://forums.hybridz.org/topic/5594...nel-test-data/
http://forums.hybridz.org/index.php/...datsun-s-30-z/

(those are two very interesting threads btw)

When thinking about flow through a radiator, don't think about air speed or air direction or such. Think about air pressure. It's the pressure difference between the front and the rear which forces air through the cooler. The aims should be to get the pressure at the front high, the pressure at the rear low, to prevent any air from escaping around the cooler and to avoid letting air into the car without that air doing something useful (ie: cooling something that needs it).

I was at Miller Motorsports Park last weekend. It has an utterly ginormous front straight - 131mph, despite it being 4400 ft above sea level. It's a great place to test aero drag changes. First session I went out with the lower grille blocked off and did a couple of laps. Jumped out, removed the cover then did a couple more laps. According to the GPS data it made exactly zero difference

and your exiting through the hood? nevermind see it in picts on page 1.

[raamaudio]

If we could duct the air of the radiator like the C5R and C6R Vettes it would be the best way to do this obviously and not just for cooling, free downforce, less drag, better cooling.........smaller inlet........

If not for keeping the chassis legal for certain classes if I go W2W in the future I would move the engine way back and then could do the hood that way. I am moving it as far back and down as possible while still having a stock firewall location(I will have to get a waiver on that as we replace nearly all of it with new sheetmetal to clean things up a bit)

Looking at different CAI units, had a Y shapped one before on one of my Vettes but had to have the MAF after it so no real space savings. The other method used commonly is a big elbow to the driver side but it would still block a huge amount of air as limits the ducting to much.

So, I might use or make and intake over the top of the radiator, that will be laid forward as far as possible and shorter than stock height, lowered in the chassis, etc....This would take a bit more fabrication and sealing but allow the largest and most effective duct out of the radiator and over the hood.

I have a GTP style hood and another hood with a nice center exit duct from another project I am considering molding it into the GTP hood.

I am doing many other aero things to the car as well, E46 CSL style bumper, ducted undertray/splitter, biggest Brooks wing custom made to bring the uprights out of the fenders by the trunk lid, dual plan, huge, tunable diffuser, flushed in Lexan, vented fenders, lexan 1/4 mirrors, small CF mirrors barely poking out into the wind........

I might also go ahead and do a ducted, directed, etc....flat bottom

[sstecker]

I don't think it will matter - the flow rate through the radiator is low - 15mph at 100mph according to these guys:

http://forums.hybridz.org/topic/5594...nel-test-data/
http://forums.hybridz.org/index.php/...datsun-s-30-z/

(those are two very interesting threads btw)

When thinking about flow through a radiator, don't think about air speed or air direction or such. Think about air pressure. It's the pressure difference between the front and the rear which forces air through the cooler. The aims should be to get the pressure at the front high, the pressure at the rear low, to prevent any air from escaping around the cooler and to avoid letting air into the car without that air doing something useful (ie: cooling something that needs it).

I was at Miller Motorsports Park last weekend. It has an utterly ginormous front straight - 131mph, despite it being 4400 ft above sea level. It's a great place to test aero drag changes. First session I went out with the lower grille blocked off and did a couple of laps. Jumped out, removed the cover then did a couple more laps. According to the GPS data it made exactly zero difference

you need to invest in some 5v absolute pressure gauges, around $10 each. hook them up to your gps datalogger. ive got a couple along with a 5v differential gauge.

[flink]

you need to invest in some 5v absolute pressure gauges, around $10 each. hook them up to your gps datalogger. ive got a couple along with a 5v differential gauge.

I'm old school



Yes, it would be nice. Also some way of measuring downforce (strain gauges, shock pots?). CFD, wind tunnel... I'm rather tired of making changes and not being able to measure or notice any effects!

What have you been using those sensors for? Are they useful?

[raamaudio]

You know you have the wrong car when you can hit 122 on the shorter straights then only 128 halfway down the main straight then like hitting a brick wall, just will not go faster. Then pull into the pits and the head instructor comes down from the tower to look over your "little SUV" because he could not believe the lap times then notices on street tires and says something like holy sheat! Also when you get sideways at 90 and made the save even though you are supposed to let it go if that far gone but your decades of dirt and snow kicked into autopilot. When you have $30k into mods, still get 28 MPG on road trips, full interior, Recarro Speeds and 3 point Schroths, no real safety gear besides long sleeve cotton shirt and long pants, helmet......and just ordered your 4th brake upgrade and 18x10.5 wheels and slicks....enough time on the long straight at MMP to figure out going faster was going to cost another $30k so you would have a $90k Forester which is pretty retarded at best, it is time to build something else.

So I did, twice, and actually had another track car and went through a couple of others short term ones....now building a pretty nuts E36M3. I should of finished the Vette or the other car but wanted a BMW because my son loves them so much, having fun with it but it will be the most expensive car I ever finished building and the fastest.

Rick

[Damon in STL]

What's the big deal.....just make some room for the air to flow up and out!



I'm seriously considering running a NASCAR style rear spoiler. The whale tail numbers in the link piqued my interest!

What the hell....I may just stick the bubble hatch from an old Capri and a whale tail on it and call it a day! I need some weight back there anyway.




All kidding aside, if there were no rules (other than safety) how would you modify the aero side?


Damon in STL

[flink]

All kidding aside, if there were no rules (other than safety)

That's NASA GTS.

how would you modify the aero side?

I want to bolt a couple of cessna wings to the doors. I see nothing in the rules to prevent it, but it might be a social faux pas.

More practically: learn from the DTM cars. The 2012 rules. I doubt if anyone does more CFD and wind tunnel work on production body shapes than those guys.

[Damon in STL]

That's NASA GTS.



I want to bolt a couple of cessna wings to the doors. I see nothing in the rules to prevent it, but it might be a social faux pas.

Go for it! Wait that's Chump Car or Lemons.......

DTM is very secretive other than what you can see. Have searched and searched and uh searched.....

So, what is wrong with NASA GTS? There is absoultely nothing wrong with using your brains instead of your wallet.

Damon in STL

[beaner06]

JongBloed wheels are designed to flow air across the brakes and be more aero effiecient. that is their claim. your results may vary.....

[flink]

Go for it! Wait that's Chump Car or Lemons.......

http://blog.caranddriver.com/lemons-...r-honda-civic/

DTM is very secretive other than what you can see. Have searched and searched and uh searched.....

Easy! http://www.sportscardigest.com/car-p...-benz-clk-dtm/

So, what is wrong with NASA GTS? There is absoultely nothing wrong with using your brains instead of your wallet.

I like GTS, although I do wish they'd drop the "g" and consolidate it with STx and perhaps PTx. But I hate with a passion making changes and being unable to measure their effect!

- - - Updated - - -

JongBloed wheels are designed to flow air across the brakes and be more aero effiecient. that is their claim. your results may vary.....

Yes, there are some wheels which are also fans/turbines and I expect they'd help cool the brakes and possibly increase downforce. I've seen some on production cars, but they're the same on all four wheels, so two of them blow in the wrong direction!

I once came across a patent on exactly this concept, presumably not enforced...

[Tonester]

A proper vented/ducted hood makes a difference. My setup is fully ducted intercooler/rad/hood and you can see the "heat haze" exiting the hood. Of course I only notice the haze when I'm on my cool down lap.

Our kidney grilles are blocked off, with the kidney grilles open we saw loss in cooling efficiency due to disrupted airflow.

[sstecker]

you need to do differentials ie test on both sides of radiator at same time. with kidneys open, the air from bottom duct may be exiting the kidneys. with the headlight opening you could be pressurizing the engine bay. without fender liners you may be pressurizing the engine bay. without a gurney lip on the leading edge of your hood exits, you may have air entering the hood instead of exiting (check 2013 dtm). check how tonester tapes all the edges, leading edges of exits, etc.

exits on 2013 dtm
2012-bmw-m3-dtm-geneva.jpg

[tammer]

Yes, there are some wheels which are also fans/turbines and I expect they'd help cool the brakes and possibly increase downforce. I've seen some on production cars, but they're the same on all four wheels, so two of them blow in the wrong direction!

I once came across a patent on exactly this concept, presumably not enforced...

If only we knew of a car maker who thought of this 20+ years ago ...


-tammer

[Inflame]

Any body else experiment with this? Looking to add additional cooling under the hood, especially exhaust side.

[ZimDoc]

Any body else experiment with this? Looking to add additional cooling under the hood, especially exhaust side.

What part?

We have talked about venting at the center section of the hood right behind the radiator and seen reduced coolant temps with increased front end grip. Blocking off the front bumper inlets to reduce drag on time attack cars. Venting like the GTR hood with vents on the side but those are just general engine bay cooling if the air flow in the engine bay is playing nice.

Buying wheels because they could cool your brakes are cool if you are trying to get the most of out a limited brake system but most of the time ducting from the front bumper works best for the price.

[eye145]

Any body else experiment with this? Looking to add additional cooling under the hood, especially exhaust side.

Wrap headers with header wrap or get them ceramic coated to try to keep the heat in the exhaust and not in the engine bay. Venting the hood helps in numerous ways. Lets out heat, lowers pressure of engine bay for better cooling (radiator) and better front end grip.
I wrapped my headers and it made a huge difference.

[Spec3HOR]

I wrapped my headers and it made a huge difference.

+1, even on my stock headers I wrapped them. Underhood temperatures went from "pop the hood after a race and hot air to the face" to "pop the hood and wasn't hot till you got really close to the engine". My hood vent goes in this week.