Ultra Street Malibu testing MIR 9-23-12

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DOTracer
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Ultra Street Malibu testing MIR 9-23-12

#1 Post by DOTracer » Tue Sep 25, 2012 7:13 am

Hey guys,

Been racing all season and I may have forgotten to stop by and update how the Malibu has been running this season since the rebuild was completed.

The car has been running consistently in the 5.3x range at 129-130 mph in the summer heat. Tried to make some tweaks, but it was stuck at that ET level. I decided to switch to Q16 fuel with another carb built specifically for the fuel and while changing the carb I saw the intake gaskets slide down and blocking the top 1/4" of the port roof in every cylinder. Replaced the gaskets and Q16 and the car was back running consistent 5.2x passes like it did back in May. Here I thought the weather caused the car to slow like it did.

Anyhow, we went testing at MIR this past Sunday Sept 23rd. I had made a lexan grill blockoff as well as working on a carb air pan (not 100% complete).

The air was better than we've run in all season, 518' D/a on our first hit, 960' on the last.

pass #1, 518' D/A
1.163 60'
3.355 330'
5.204 660'
132.56 mph

Pass #2, 718' D/A (front end climbed, had to pedal and hit the rev limiter)
1.182 60'
3.400 330'
5.280 660'
131.48 mph

pass #3, 812' D/A
1.160 60'
3.343 330'
5.183 660'
133.26 mph

pass #4, 960' D/A
1.138 60'
3.319 330'
5.162 660'
133.22 mph

Spent all season working on a bad air/track setup, yesterday I had to work on a good air setup really tightening the front end up a good amount.

Image

Here's the new air pan I threw together. Still need finishing by closing off some areas by the rear of the hood.

Image

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supernova
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Re: Ultra Street Malibu testing MIR 9-23-12

#2 Post by supernova » Tue Sep 25, 2012 7:48 am

Nice pass'es!
I wonder about your air pan though. The car moving that fast is going to create a vacuum in your air pan. The cawl hood will want to draw air from the back and with no air allowed in from the front could cause air depletion in the air pan plenum. We run our pans all the way to the front of hood and leave it open in the front and close off the back of it. Doing it his will cause positive pressure in the air pan plenum. Doing it the way yours is acts as a siphon at speed, no air can reverse direction and enter in the back.
Your mph is low for that et. Could be not enough air.

Just my opinion though.
Blackhoodmafia!!!! :mrgreen: :mrgreen:

1972 Nova SS
572 C.I. BBC

Best to date: 1/8
et: 5.28
mph: 134
new wt. 3340 lbs

DOTracer
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Re: Ultra Street Malibu testing MIR 9-23-12

#3 Post by DOTracer » Tue Sep 25, 2012 9:42 am

supernova wrote:Nice pass'es!
I wonder about your air pan though. The car moving that fast is going to create a vacuum in your air pan. The cawl hood will want to draw air from the back and with no air allowed in from the front could cause air depletion in the air pan plenum. We run our pans all the way to the front of hood and leave it open in the front and close off the back of it. Doing it his will cause positive pressure in the air pan plenum. Doing it the way yours is acts as a siphon at speed, no air can reverse direction and enter in the back.
Your mph is low for that et. Could be not enough air.

Just my opinion though.
You can draw air from the front or back depending on the setup.

I hate air pans period, they are a PITA. This was a simple test. Didn't slow the car down, actually set it's best MPH ever Sunday. Car has never broke 132 mph before.

Pulling air from the front is a HUGE and I mean HUGE fabrication project I'm not looking to get into during the season. This would require me to build a new tubular core support with the top tube moved down, lower the radiator mount down, but then the hinge hood bracing at the latch area (latch not used) would be in the way trying to seal the air pan to the hood. Just about the most labor intensive way to get forward air. Heck, going to a flat hood and a forward facing scoop would take less time and even that is a 40 hour labor job.

Remember, I do chassis work for a living and have have done these jobs for customers and know how long it takes.

I saw signs of fuel on the top of the carb, but after cleaning and making more runs found it was from turning the fuel pump on and the pressure spike shooting some fuel out of the vent & air bleeds if the bowl isn't full. That reminds me I need to call my carb guy and ask about that.

I felt closing the grill off forced to to try the air pan again as the engine would not get any fresh air from the front and could hurt power without the pan.

I take it your a power adder car? Better look around at other N/A cars as my MPH is NOT low for the combination. The engine only makes 1056hp at the crank. If anything the car is more efficient on the front half than most which may make one think the MPH is soft when it isn't. Buddy's car has a 12 degree 632 that makes 1280 hp and ran 137 mph at 3100 lbs compared to my 133 mph at 2950 lbs. His car is by far the highest MPH N/A car in our class and has won most every event this season.

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Re: Ultra Street Malibu testing MIR 9-23-12

#4 Post by John_Heard » Tue Sep 25, 2012 9:50 am

Really great numbers Todd! It's certainly impressive for sure.

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Re: Ultra Street Malibu testing MIR 9-23-12

#5 Post by supernova » Tue Sep 25, 2012 11:00 am

Oh that's right your car is a N/A car sorry I forgot about that. Your right we use power adder's. and yes that make bigger mph runs.
The air pan I built for mine is real simple. But I still have the stock support it goes over in the front. It's open to nothing but fresh air at that point.
I work in R/D engineering in the aircraft industry. I just wonder if there is any pressure (change) difference. The cowl hood act as a reverse NACA duct, and if it caused any, ANY pressure drop in the air pan plenum it hurt carb performance.
Just sayin.
You could test real easy and know for sure. Put a vacuum port in the pan area and see what it draws running down the track than take the pan off of it and see if here is a difference. At least we all would know if there is a difference.
Blackhoodmafia!!!! :mrgreen: :mrgreen:

1972 Nova SS
572 C.I. BBC

Best to date: 1/8
et: 5.28
mph: 134
new wt. 3340 lbs

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Re: Ultra Street Malibu testing MIR 9-23-12

#6 Post by John_Heard » Tue Sep 25, 2012 11:47 am

It likely makes a big difference depending on if the grill is blocked, vs un-blocked, if the car has fenderwells, no fenderwells, or a belly pan, etc. From what testing I have done with a manometer on a open grill, no fenderwell car and no ductwork, a measurement probe at the cowl opening does not pressurize down track at all. There's an old post on here about that somewhere. There was a LOT of positive pressure when we placed the probe in the grill on the same car.

Some day I would like to test something like Todd's setup to see what that would measure with the manometer setup. My gut feel is the primary gain would be lower temps, but little to no positive pressure.

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Re: Ultra Street Malibu testing MIR 9-23-12

#7 Post by DOTracer » Tue Sep 25, 2012 12:05 pm

John_Heard wrote:It likely makes a big difference depending on if the grill is blocked, vs un-blocked, if the car has fenderwells, no fenderwells, or a belly pan, etc. From what testing I have done with a manometer on a open grill, no fenderwell car and no ductwork, a measurement probe at the cowl opening does not pressurize down track at all. There's an old post on here about that somewhere. There was a LOT of positive pressure when we placed the probe in the grill on the same car.

Some day I would like to test something like Todd's setup to see what that would measure with the manometer setup. My gut feel is the primary gain would be lower temps, but little to no positive pressure.
I agree about the pressure. I was mostly looking to keep the engine from breathing under hood air.

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Re: Ultra Street Malibu testing MIR 9-23-12

#8 Post by supernova » Tue Sep 25, 2012 12:37 pm

Wouldn't you want positive pressure? Like a scoop, air pan set up. The scoop allows pressurization. That's how our top sportsman car is set up. My air pan does the same thing it's just under the hood and allows for cooler air.
The way his is set up I would think it would have negative pressure do to the air rushing over the back of the hood and up the windshield, creating a negative pocket inside the pan plenum. Knowing aerodynamics of how a negative NACA duct works a cowl hood air pan set like that would try to draw air out of it not put air in it. I would think it would have a negative effect on the carb intake.
But it might be so minuscule it doesn't mater. Test his set up and find out. His motor might not make much vacuum so any negative pressure will act opposite of what it needs
Blackhoodmafia!!!! :mrgreen: :mrgreen:

1972 Nova SS
572 C.I. BBC

Best to date: 1/8
et: 5.28
mph: 134
new wt. 3340 lbs

DOTracer
Posts: 466
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Re: Ultra Street Malibu testing MIR 9-23-12

#9 Post by DOTracer » Tue Sep 25, 2012 2:39 pm

From what I read here, the pressure inside a properly built forward facing scoop isn't as much as you might think it would be. I'd have to dig through this thread to find the exact figure most experts agree was possible.

http://www.yellowbullet.com/forum/showt ... hood+scoop

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Re: Ultra Street Malibu testing MIR 9-23-12

#10 Post by Mike Peters » Tue Sep 25, 2012 3:34 pm

John and I have had a few lengthy e-mails about there being positive pressure created by cowl induction hoods. One of the few things we never agreed on. This is my take on the situation - The cowl hood was very popular back in the early days as I believe it was GM engineers who knew there was a positive pressure area at the base of the windshield. To take advantage of this positive pressure, the cowl induction type hood was created. This was back in the 60's when discovered. The cars back then weren't nearly as aerodynamic as the modern day cars since they had steeper windshield angles. Also, if you'll remember the cowl scoops weren't nearly as tall or extended as far back to the windshield as the trend of the cowl scoops being used today. The new style 5"-6" scoops may offer clearance for taller manifolds but, they also negate the high pressure area at the base of the windshield by being too tall and also by usually extending to the match the contour of the windshield angle. The area of the windshield that is exposed to the oncoming air is what creates the eddy of air and therefore the high pressure area. If the scoop is too tall it pushes the oncoming air over the windshield. There has to be a certain amount of windshield exposed to keep the air still at the base while the rest of the oncoming air rushes over it. If it extends too far back, there's no area for the eddy of air to be created and therefore no high pressure area as once again, the air is just directed over the windshield. However, in Todd's case, the pan might be effective enough to create air that is more calm and still air is preferable to turbulent air.

BTW Todd, those are freakin' awesome #'s!!!!! That 1.13 60' is killer dude.
Last edited by Mike Peters on Wed Sep 26, 2012 7:03 am, edited 1 time in total.
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DOTracer
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Re: Ultra Street Malibu testing MIR 9-23-12

#11 Post by DOTracer » Tue Sep 25, 2012 3:49 pm

I've been debating on a way to get fresh air to the carb for a while now. My choices were.

1. forward facing scoop on a flat hood
2. air pan feeding from grill opening
3. rear racing air pan on existing hood

I chose #3 for now as it was the quickest and cheapest method to try near the end of this season. Over the winter I will think this through more, but each has their pros & cons.

Forward facing scoop might look out of place on such a square body style car. Also the scoop cannot be placed in a typical location due to the vertical/flat grill/nose. The scoop would need to be fairly far forward to catch air, otherwise the air would likely go right over the scoop and no pressure benefit.

The forward grill opening air pan idea would require another new tubular core support built and move the radiator down to give room for the duct work. Also weight of the duct work on an already 54-55% nose heavy car is a concern.

If I stay cowl hood rear pan, I should put a new hood on as the carb is a bit close at around 2" from the carb base to the hood on the front side. Vent tube barely clears. This is a 5" hinged cowl, so I'd have to have a custom 6" hinged hood made. This hood cost me $900+ back in the mid 90's to have made, new 6" would be the same deal all over again...and this one is crazy heavy at 45 lbs being alot of it is nearly 1/4" thick.

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Re: Ultra Street Malibu testing MIR 9-23-12

#12 Post by John_Heard » Tue Sep 25, 2012 4:35 pm

I'm really wanting to play with a forward scoop passing through the grille area, one of the reasons I switched to the water tank setup to get the radiator out of the way. Now the dry sump pump is in the way lol.. But, there should be enough room now I think. Might be a winter project, I would love to try and see if I can make something like that work. I think the grille is the place to be if you can get the ducting to work correctly, etc.

My car is a pain in the butt now there is not a lot of room on top of the carb, I'm going to have to take off my one inch spacer. That should leave 1" above the bowl vent, not as much as I'd like.

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Re: Ultra Street Malibu testing MIR 9-23-12

#13 Post by DOTracer » Tue Sep 25, 2012 7:58 pm

I just had to post this as I thought it was kinda funny.

After that last run I stopped the car and looked for my water bottle to get a drink. Couldn't find the bottle, but once I got out to take my jacket off, I turned around and there it was.

Image

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Re: Ultra Street Malibu testing MIR 9-23-12

#14 Post by supernova » Wed Sep 26, 2012 6:44 am

That's funny!LOL
If your like me 6' tall and 250 lbs, 49 yrs old you'll find naborhood kid to get it for you. It's hard work crawling in the back.

Your car definitely runs hard for sure. My car only runs 6.10's wih no bottle, 5.50's with.

I did some research on hood scoops and pans. What pro stocks are looking for is minimum pressure all the way down track. But they do want positive pressure not negative pressure. Too much positive pressure is as bad as negative pressure. They're looking for consistency that doesn't upset the carburetors even at 200 mph. We all know how pro stocks run.

Still I would be curious to what is going on I your pan. It may not mean anything, just something to look at when you time.

Lets us know if you test it and what the finding are.
Blackhoodmafia!!!! :mrgreen: :mrgreen:

1972 Nova SS
572 C.I. BBC

Best to date: 1/8
et: 5.28
mph: 134
new wt. 3340 lbs

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Re: Ultra Street Malibu testing MIR 9-23-12

#15 Post by Craig W. » Sun Sep 30, 2012 10:03 pm

I can't get over the 1.13 60' times. Just wicked. Care to share any tips on what's got it moving so fast early in the run?
Craig Watson
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