Hood Clearance Effect on Engine Power - 460 Ford Forum
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post #1 of 25 (permalink) Old 12-30-2010, 09:35 PM Thread Starter
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Hood Clearance Effect on Engine Power

I have a 4" cowl hood on my bbf powered fox body with a holley 750 dp and weiand stealth intake. Clearance between the carb and hood is minimal and I use no air cleaner as the car is track only.

A machine shop tech told a buddy of mine that the clearance issue is costing significant power loss and that I could pick up 2 tenths or more with additional clearance. The concept makes sense, but I'm surprised the benefit would be that great. Anyone have any thoughts on the matter before I spring for another hood (or cut this one up)?
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post #2 of 25 (permalink) Old 12-30-2010, 10:20 PM
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if u want more u could do k member spacers.
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post #3 of 25 (permalink) Old 12-30-2010, 10:32 PM
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WOuld make a difference with a hood scoop but not with a cowl. I have had both on my car and now I have the smallest cowl on my car I could put. Times are still the same.
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post #4 of 25 (permalink) Old 12-31-2010, 04:35 PM Thread Starter
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WOuld make a difference with a hood scoop but not with a cowl. I have had both on my car and now I have the smallest cowl on my car I could put. Times are still the same.
So I guess a 5-6 in cowl makes no sense then. I'm gonna start looking around for scoops even tho I prefer the cowl look more.
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post #5 of 25 (permalink) Old 12-31-2010, 04:48 PM
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I know a guy who raced without an air clearner once (ME!!). I had a valve cover stud come out and fly down the carbuerator when I was 4/5's of the way down the track. It made a tremendously hiddeous noise. I thought I just broke the motor. When I disassembled the motor I found the valve cover stud pounded into my nice soft aluminium head by the #4 piston. It also scared the cylinder so bad that it had to be sleeved. That was VERY EXPENSIVE!! ....take my advice. Don't race without an air cleaner. It just isn't worth it. I hope you learn from my own (dumb) experience. Did I mention that was EXPENSIVE??


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post #6 of 25 (permalink) Old 12-31-2010, 05:27 PM
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^ What he said, or at least put a screen over the carb.
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post #7 of 25 (permalink) Old 12-31-2010, 06:45 PM Thread Starter
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Maybe it's not such a bad thing to have so little hood clearance!

In all seriousness, I may have already gotten my warning from the Air Cleaner Gods. In one of the rare occasions last season where I was actually going rounds in a bracket race I developed a bad miss and had to bail in the qtr finals. Started pulling plugs and turns out the plug in the #1 cyl was closed shut. Could very well been a foreign object sucked in and spit out.
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post #8 of 25 (permalink) Old 12-31-2010, 07:19 PM
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Could have been something soft like an acorn or other such debris.... Dude. You got lucky. I killed a whole motor.

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post #9 of 25 (permalink) Old 12-31-2010, 10:19 PM
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I`ve seen this cause problems on two cars, both bbf fox body. The engine would lay down at about 5000.You could space the back of the hood up or make a pass w/out the hood to see,I think it`s worth checking out.

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post #10 of 25 (permalink) Old 01-01-2011, 01:56 AM
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We fault this for a few years. WE run a 65 Mustang with a 3 1/2 cowl hood (tube frame car). There is about 4 inches from the carb to the bottom of the hood. It would lay down about 2/3rd down track and just do nothing. We tried all kinds of trays sealing to the hood, completely open under the hood, even tried to ram air it from the front of the hood. Finaly we seen a picture of the car at speed and it looked like the hood was pushed down, so we put a stand from the carb to the hood and that fixed the problem! Oh and we run no air cleaner. 4 inches is enough for us, but anything less and it just lays down.
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post #11 of 25 (permalink) Old 01-01-2011, 01:03 PM Thread Starter
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Appreciate the info guys. Sounds like there may be something to this. My best so far is an 11.20, so an 11.0 would be nice with nothing but a hood swap.
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post #12 of 25 (permalink) Old 01-01-2011, 01:06 PM
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We fault this for a few years. WE run a 65 Mustang with a 3 1/2 cowl hood (tube frame car). There is about 4 inches from the carb to the bottom of the hood. It would lay down about 2/3rd down track and just do nothing. We tried all kinds of trays sealing to the hood, completely open under the hood, even tried to ram air it from the front of the hood. Finaly we seen a picture of the car at speed and it looked like the hood was pushed down, so we put a stand from the carb to the hood and that fixed the problem! Oh and we run no air cleaner. 4 inches is enough for us, but anything less and it just lays down.
Gotta love them track photographers! lol
Rob

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post #13 of 25 (permalink) Old 01-16-2011, 12:58 PM
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Gotta love them track photographers! lol
Rob
They can be a big help when trying to isolate a problem.

If you're not living on the edge you're taking up too much space!
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post #14 of 25 (permalink) Old 01-16-2011, 01:48 PM
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1st... don't space the K-Member to get more hood clearance. Keep in mind you need proper driveline geometry and that don't help! You need a taller hood!

2nd... If this is a track use only car then you need to have a pan built that seels around the carb and only allows air from the cowl to be used. Otherwise you get turbulent air and hot air up through the engine bay... and if the carb is close to the hood then it doesn't get "clean" air.

Hope that helps!

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post #15 of 25 (permalink) Old 01-16-2011, 03:01 PM
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Don't forget to get some kind of screen over that thing to keep from sucking crap in. Did I mention that was EXPENSIVE??

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