Landracing Forum
Tech Information => Technical Discussion => Topic started by: 836dstr on November 15, 2006, 02:28:08 PM
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Help !
I am planning on changing from a hood mounted scoop on a Street Roadster to a air duct thru the upper front of a '32 grille shell into a air box.
I will have some options closing out the current hood opening from a flat (or stock hood surface) to some type of "bubble" to get the optimum distance above the carburator neck.
Here are some specifics:
1. '32 grille shell to a '27 body with some taper front to back.
2. 301 C.I. Chevy using a Victor Jr. manifold with 750 Demon 4 bbl.
Anticipated performance 7,500 RPM @ around 185 MPH.
3. Air duct openning 6.6 Cu. In. I plan to make it an elongated "D" shape with the flat side down. It would be 5" wide and 1 & 1/2' tall @ the center with a .60" radius @ each end.
4. The air duct would extend 5 or 6 inches in front of the grille shell and would have a constant cross section for another 6 inches to the front hood line. I currently have oblong plate 17" long by 11 inches wide attached to a air horn that has a radius necking down from 7" dia. to 5".
5. The air horn is 1 & 3/4" tall. The distance of the plate to hood tapers from 2" in front to 2 & 1/2" rear for an average total height of 4".
6. I plan on building the air box to taper back from the end of the air duct from 5" to 11" wide @ the front of the current carb plate. This transition for the air box would be 11" long and maintain the width for 17" to the back of the plate. The air box would be sealed to the underside of the hood.
After all that, my question is, "Is the average height of 4" of the plenum above the carb to the hood adequate?
Most of this will be fiberglass construction so it will be easy to add a radius at the bottom or top of the air box to eliminate 90 degree corners if that would help. Well, I guess that's another question.
Any questions or comments would be greatly appreciated !
Tom
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I dunknow!
But make sure you don't eliminate any of the Radiator Area with the duct.
Stan
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"Air duct openning 6.6 Cu. In." -- I assume that's really 6.6 Sq in ? I think you'd want a radiused opening at the open end rather than just the sharp edge of the sheet metal/fiberglass.
I'm having trouble visualizing the air box where it's under the hood. especially the "The distance of the plate to hood tapers from 2" in front to 2 & 1/2" rear for an average total height of 4" I guess you're adding the 1 & 3/4" tall air horn to the 2"/2 & 1/2" to get to 4" average ? Maybe a sketch ?
roy
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Stan,
The air duct would be above the grille insert, and the current radiator fills the whole grill shell openning and would not violate the area or contour of the grill shell for the purpose of streamlining. I checked with the SCTA Roadster Committee Chairman.
Roy,
You're correct, I meant 6.6 Sq. Inches. At the vertical centerline of the carb the height from gasket surface of the carb plus the air horn (bell) to the underside of the hood is a total of 4". A rounded or "bull nose" entry to the air duct would be easy enough to fabricate. Would this be better than a knife edge?
I made a feeble attempt on the photo of the car to erase the scoop and add the air duct using the limited photo editing feature on my PC. This was my first attempt. A sketch might be possible. Maybe I'll have to ask the kids how to do it. I hate doing that !
Thanks for the comments !
Tom
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Tom --
Ye're good for all I can see. I was just trying to see if you knew about the Radiator thing before you got in trouble.
Your sketch is better than I could produce, but it looked like it would be in part of the radiator.
Good luck on that soft record!
Stan[/i]
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Stan,
Soft? Yeah right ! Like trying to push a 4 wheeled brick to 185.
Actually the main focus is to get clean air to the carb. Being 6'2" and running a '27 body really leaves me and the cage hanging out in the air. Unfortunately can't change either body.
Tom
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A rounded or "bull nose" entry to the air duct would be easy enough to fabricate. Would this be better than a knife edge?
Yes, a sharp edged duct will only be efficient if the local air flow is exactly in line with the axis of the duct. As soon as you get any sort of off axis air entry you will develop a vena contracta (flow separates from the edges of the entry and the effective area is smaller than the physical area).
Think of the old hot rodder velocity stacks --- they all had a bit of a trumpet mouth for this reason. Usually they recommend an inlet radius of about 1/4 the radius of the duct, but any radius helps.
http://www.profblairandassociates.com/pdfs/RET_Bellmouth_Sept.pdf
Larry
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WOW Larry,
A simple question just became more complex. Thanks for the link. I am going to have to digest this info for the air duct lip design. I'm glad I have 6 months until the next El Mirage meet to get it figured out and fabricated.
Thanks again !
Roy was "on spot" as the Brits would say.
Tom
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"The air duct would be above the grille insert, and the current radiator fills the whole grill shell openning and would not violate the area or contour of the grill shell for the purpose of streamlining."
If the radiator fills the whole grill shell and the '32 insert fills the grill shell how can the proposed air duct be within the grill shell and not effect the area specifided by the rules?
DW
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If a new performance only rule prohibits a former common practice then I trust
that all previous records set without the performance restriction will be retired.
Let us look and see.
"TRUST BUT VERIFY." :roll:
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I have the same concern as Dan. To me the only way I feel a air intake could be used as described would be if I could look through the intake opening and see the radiator tubes which by the rules must fill the shell.
As I look at a car in impounds for a record to "cert" the body I look underneath and for obvious infractions of the class. I do not feel at this point the impound technicians do not need the protest arena to accomplish this. If we see something, we stop that process on the car and get clarification. That's why some records are not immediate after we measure an engine.
This is a tough spot. Most who work in this area have more that just a passing knowledge of rules for every class of vehicle. Dan is instrumental in writing the book every year and over years has excellent knowledge.
I have 2 cars and they have been able to run in 5 body classes over 30 years so I feel fairly competent in those areas. Others in the Special Construction work also in impounds and have that knowledge. For the most part we are very lucky.
It appears 836dstr is not trying to circumvent the rules and by talking with the rules chairman of his class is apparently wanting to make sure what he is doing will be legal. I believe the entire committee should be contacted and perhaps they have.
As far as I can remember, we have never seen an air intake protruding thru a grille shell in Street Roadster before so this may be new territory. To me it's thinking outside the box which is ingenuity at it's best. But the ideas still need to meet the rules for the class...J.D.
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J.D.
On page 50 of the Rule Book regarding Street Roadsters it states:
"The radiator must fill the shell opening". Then it goes on to talk about using only a stock grille shell insert. It doesn't state front or rear opening, but I would think the intent is to fill the front opening.
By chance I took a picture of the Stuhaan/Kranz 848 car at El Mirage last Sunday which has an air duct almost the same as what I'm considering (photo attached).
Tom
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JD,
Well I tried to attach the picture of the front of the 848 showing the duct coming out of the top of the '27 grille shell but got a message that the attachment size was too big. I don't understand that, but maybe since I've already attached a picture I've exceeded some file size limitation.
Oh well, back to the point, the 848 STR has a metal air duct welded to a stock '26-'27 grill shell with a radius at the base. It could be 'glass. I didn't tap it to check.
I guess I could E-mail you the picture if you would like.
Back to my main question, is the 4" air gap from the carb gasket face to the underside of the hood OK?
Tom
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JD,
On page 59 of the 2006 Bonneville Program you can see the air duct on the 848.
Tom
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Tom --
I take it all back.
I'm certainly not an official, nor an inspector, but . . .
Just because someone else is doing it doesn't make it legal.
What I read into it is there's no room at the top of the front radiator/insert/grille shell to put an air intake. You're either recontouring (or eliminating part of) the shell from stock with the intake (which I think would be illegal) or taking up radiator area.
I'd be very careful going down that road.
Stan
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I'm not familiar with 848 but will look. For me it has not come to impounds and I don't remember inspecting it. I did see it at El Mirage but did not look at it.
I do not believe it is required to run a grille insert but if you do it must be stock or fill the entire opening if the shell has been sectioned down to the 530" limit. T's and 28-31's did not have an insert for Fords.
Like I said before. I'm not saying you can not have an air intake but it must meet the rules of 1. radiator must fill the opening, 2 insert if used must fill the the shell.
I'll use a 32 Ford shell for this example. Your air intake could attach to the grille bars and the air goes thru the area alongside the radiator tubes and then into the engine. We don't tell you how many rows your radiator needs to have, only that it fill the area of the shell.. This may not pass tech but, in my opinion only, it meets the definition. It could not be tapered in any way because that would cover part of the opening which is illegal. This would be highly questionable and definately not the best way to go with an air intake. Probably would hinder air flow. but like I said this would possibly be a way to do it....You could also duct the air under the hood to the back of the radiator and just take the air rushing thru the radiator from the speed your going. Nothing to stop you from doing that.
I believe the air intake on the Barbee #357 car was one of the best and it was above the 27 shell.
Gook Luck
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Tom --
The #1091 Weber/Vanderley Model A D/STR ran at Bonneville with the air ducted thru the whole back side of the radiator and intercooled with ice! It made it to impounds, as I remember, but couldn't back up their 1st run.
Stan.
(I still don't think cutting a hole in the upper grille shell is going to pass muster, even if you miss the radiator area.)
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Here is the grill on the 848 car.
(http://pages.sbcglobal.net/dean4/_images/Roadster%20Grill.JPG)
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OK, That is an A shell with an area above the radiator opening that a air scoop can be built. You mentioned a 32 shell. I looked at my street rod with a 32 shell an found that a max. there is maybe 1.5" to build an air scoop.
DW
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I don't know what shell it is, Could be a T....However if what is shown is legal, a 30-31 has a nice large area above the radiator opening. I think 836 want the "point" of a 32 but with the bars there I don't think it could add any areo advantage....The Vanderly street roadster idea is what I was trying to say only not using the entire area...Good Luck
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JD, Dan --
The Rule Book says "The body shall not be altered in height, width or contour . . ."
The Radiator Shell is a body part, right? (It's not a mechanical part.) And putting a hole in it certainly recontours it.
And its not very "Street Roadstery" in having a hole through your top tank.
Maybe all this will be addressed in the Rules Meeting.
In the mean time, I'd probably make a $100 bet that this is not legal in Street Roadster.
Stan
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Stan,
I don't know about the $100. He claims he spoke with Russ Eyres and got his OK. I'm confused.
DW
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Hi Dan,
I had talked to Russ 3 or 4 months ago about the optimum air intake and he did the calculation on the opening size of 6.6 sq. in. At the time I was considering using a "scoop" that was flush to the hood very much like on the Barbee's 357 car.
After considering the grille shell air intake I made a paper template of the opening and had it with me when I saw the 848 car with the Model T grill shell and air intake. As it happened, Russ came throught the pre-staging lanes at the same time and I showed him the car and my template. My proposed intake is actually a little smaller, but about the same shape with rounded corners.
I am not assumimg that because the 848 is running this type of intake that it is class legal. I had a long talk with them (nice guys !) and the topic never came up other than me saying I was following a similar approach. I guess the benchmake of "legality" is established when a class record is broken and is checked in impound and then possibly protested later. I'm not sure where the 848 guys are in pursuit of a record.
In my case I'm just getting comfortable running the 836 and sorting out the handling and performance. I am currently running 35 MPH off the record (@ El Mirage) and realistically could pick up 15 - 20 MPH with the current engine/trans configuration. My short term goal is to get the most out of the existing combination through tunning and driver technique.
Shortly after Bonneville this year I was talking to a guy that's very much into aerodynamics. I mentioned that I was thinking about removing the hood scoop and making a NACA duct. I had done some research, but not enough. He shot me down in flames stating that to be effecting you need a long flat approach for the air, not exactually what you have with the air bouncing off the nose of a Street Roadster.
Picking up the air in back of the radiator as JD and Stan mentioned is a possibility I had not considered. Obviously the straighter the air flow path the better. I'm guessing the intake would have to be sized larger because of the restriction of the radiator tubes and fins, grille shell insert vains, etc. Also picking up the air in the middle of the radiatior would be best to minimize the turbulance cause by the air stacking up in front of the radiator and rolling around and over the grille sheel. Running a Moon tank on the front would probably also give the air flow a double wave effect so maybe higher is better?
I haven't decided which way to go yet. Is it better to ask forgiveness rather that permission as Jack Dolan would advocate, or formally submit the question to the rules committee. If so, how do I do that?
Either way I go, I still have the same basic question, is the air gap of 4" from carb to underside of the hood sufficient?
I do appreciate all the comments.
Tom
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I don't advocate "Forgiveness is easier to get than permission."
but that is often how the system seems to work.
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Hi Jack,
Just yanking on your chain a little ! Maybe "advocate" was the wrong word, but you know what I meant. Do you think Rick Y.'s trailing engine in is Streamliner would have passed muster if the "Tech" guys had been advised in advance.
In the long run I want to be running "Legal". In the short term I just want to go faster.
Tom
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Larry ("Hotrod")
On the 7th post you gave this link:
http://www.profblairandassociates.com/pdfs/RET_Bellmouth_Sept.pdf
I finally read the article and while not fully understanding all of the technical discussions I did get the major points that you did well in summarizing in your post.
I was kind of amazed at the varitions of air inlets/scoops I saw at Bonneville this year. It's clear that a round bellmouth with a half radius would be the optimum design.
Thanks for the info ! Now all I need to do is to figure out how to interject "vena contracta" into a casual conversation.
Tom
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Hey, everyone- what about the SPIRIT of the rules, maybe a Nebulous term (sorry Jack) but , we all know that MOST Land Speed street roadsters are purpose built for speed trials, but the idea is, they're supposed to LOOK like a street driven hot rod.
How ' bout making competitors DRIVE them to the events?
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Hey, everyone- what about the SPIRIT of the rules, maybe a Nebulous term (sorry Jack) but , we all know that MOST Land Speed street roadsters are purpose built for speed trials, but the idea is, they're supposed to LOOK like a street driven hot rod.
How ' bout making competitors DRIVE them to the events?
The rules for Street Roadster evolved from the LA Roadster Club wanting
a suitable class for their Street Rods that were driven around So Cal. long ago.
They are mostly gone but not forgotten and the class remains.
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We have seen that the spirit of the rules does not mean much. Should we have 185 MPH vehicles running single hoop roll bars, no fire systems, no fire suits, chutes, no AIR INTAKES, and leather helmets. So much for the good old days where a Street Roadster looks like it could be street driven.
Kudos to Jim Kitchen, and the So Cal Speed Shop group that have taken a true street roadster and made them competitive in class with bolt it roll cages.
The Class rules are in place so let's work with them.
I started this thread with a very simple question about an air box question. This Forum is for technical questions. Not conjecture. I have probably brought some of this on myself. I had asked a very simple question about hood clearance and have asked 3 or 4 times for this question to be addressed to no avail.
Jack, I'm sorry I brought you into this in jest. You've "been there and done that" and I respect you for that !
Stan, Dan, JD, Larry, let me thank you for the "technical" discussion that's taken place here.
If I sound a little frustrated, maybe I am, or it could be 2 glasses of wine. I'm glad it's 6 months until the next meet, I may have a definative answer by then.
Tom
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The rules are whatever comes on the wind.
As for the original question, the best result we ever had with a carb on a
V motor was with a Moroso/ aftermarket air cleaner top and bottom.
The shape of the base directed the air into the carb better than any of the
inserts we tested on a Dyno.
The top was about 4 inches up and helped a bunch to gather air from all
sides and down the hatch.
Important to the scheme was to get the heat generated by the motor away from the intake air.
We did it with flat panels the went to the sides of the engine bay at the height of the carb base.
That put all the heat down and out and used the whole hood space above as a plenum.
We did not use an air cleaner element but spaced the top from the bottom
the same distance. :wink:
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JD, Dan --
The Rule Book says "The body shall not be altered in height, width or contour . . ."
The Radiator Shell is a body part, right? (It's not a mechanical part.) And putting a hole in it certainly recontours it.
Stan
Using this logic a hole in the hood top is no different..huh :?: . Nick
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Thanks Jack !
I like your idea about the heat shields.
There is a new product out that fits under an air cleaner top that is scalloped (or radiused) from a larger diameter at the top to smaller at the bottom and fits on the air cleaner stud. It purportedly aids in directing air into the carb.
This might work well with a closed plenum where intake air passes over the carb primaries and around the sides of plenum and stacks up at the back of the plenum and reverses direction back toward the carb.
It would be interesting to have a small wind tunnel where you could test various configurations.
Tom
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The S+S side draft teardrop style has the type of peak feature you
describe and has worked well for a long time in the center of a 1 barrel.
The drop center shape of the Moroso top complemented the shape of the base
and worked in a 4 B application.
NASCAR stuff has the same internal shape but a surround that takes air
from the base of the windshield.
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"Using this logic a hole in the hood top is no different..huh . Nick"
If you cannot see a hole in a plane view is that changing the contour?
DW
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Having read and re-read the rulebook there is, imho, NO WAY you can have a hole in the grille shell and be legal for Street Roadster.
Taking the discusion in a slightly different direction, Jack D's hints on a properly countoured air cleaner base and top like NASCAR is obviously a power booster, disregarding how the air arrives there (scoop or under hood). The K&N people among others have worked with some NASCAR teams on items like that.
One should isolate it from engine heat, though.
For port injected motors things become a little more difficult . but a properly designed plenum and an AIR FILTER in the right location will help with power.
It isn't by accident that people like K&N supply both Formula One and IRL with filters-both series port injected.
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Hey, go easy with the speed secrets and let them discover it themselves. LOL
The cheap deal rather than an expensive K+N was to get 2 pedestrian type from Pep Boys and glue them together.
Put them both in the system on top of each other.
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Jack D- I'm flattered that you PERSONALLY responded to one of my posts.
You were no doubt in the Dago area far enough back to remember the late Jim Ward-we could probably share a few tales- if your kidney and my prostate hold out long enough!
REX,
Where are you with all this "Technical" discussion going on?
Or are you waiting for all of us to make fools of ourselves?
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Jack,
I think that the question of plenum height has been answered. There have been other threads talking about hood scoop design and plenum volume.
The air intake question boils down to 3 options: 1) The duct through the grille shell, 2) A duct along the hood (like on the 357 car and others), or 3) A duct picking up air in back of the radiator.
The basic plenum design around the carburator would be pretty much the same. For now I will look at only last 2 options (although I do have a spare 'glass '32 grille shell on the shelf).
Using option #2, I can envision using a round duct with a bellmouth and simple radius lip. Because of the rake of the car, and the slight taper from the front to back of the hood, the outlet of the duct would be about 1/3 of the way back on the hood; whils laying flat on the grille shell top.
The link to the article on bellmouth design is very interesting !! You see a lot of rectangular scoop openings, most likely because of ease of fabrication. This article is an eye opener on air flow efficiency.
Using option #3 (air thru the radiator) the 3 problems I see are the proper duct or pick-up sizing to offset air resistance thru the fins and tubes; a more severe turn of the air up to the plenum; and the temprature increase of the air. Primary engine cooling is a 20 gallon water tank and electric water pump but the radiator is plumbed into the system. Any ideas on cooling the air? How about spraying Nitrous into air stream? JUST KIDDING !
Another question would be about air reversion at the back of the plenum, assuming a round back surface sealed to the hood. Would some type of air bleed system or port be helpful or detrimental?
Tom
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Just a BTW: the S+S side draft teardrop style was developed by Jerry Branch for the Harley-Davidson KR with Tillotsen carburetor about 1965, manufactured by Rick Bray under the Cy-Cal Products name in Long Beach. Web-Co had it in their catalog.
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8-What fins?
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Hi JD,
In the air thru the radiator option, I was refering to the resistance and heat transfer of the radiator core, fins, vanes, what ever you want to call them.
Tom
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Tom,
Don't even think about taking the air through the radiator core, adde heat, potential inlet restrictions, not a good idea.
Here is another thought, looking at the rules it states that a street roadster may have a hood scoop per section 4.R which allows you to have a scoop up to 11 inches above the hood. It does not state that the scoop has to be on the center line of the hood, so how about centering the scoop in front of yourself and make its shape to help shroud you and your roll bar. You are already a big "blivit' on the frontal area of your roadster, use the air scoop to direct the air around you and not increase the frontal area of your car. The obvious thing that this brings is you have a scoop that doesn't contribute to additional frontal area, and it helps clean the air up going around you. The not so obvious things are that now you have an air plenmum that is sealed to your carb top that has huge volume and this will assist in reducing the air inlet speed to a minimum and recovering the maximum amount of pressure from the high velocity air that is coming into the inlet, i.e. "a little additional air pressure at the carb inlet never hurts!!!!"
Rex
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The rules do not say the radiator has to be used to cool the engine. They do not say what the fin count has to be. I could point out a truck that set two records this year at Bonneville that used the front grill opening to channel air that was cooled by a radiator (recirculating ice water) to a collection box that was then fed to the carburetor. Not the first and I'm sure it wont be the last, ask MacDonald, Eakers, McKinney, Fox, etc.
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Thanks guys !
The input is greatly appreciated ! Many things to think about.
An offset scoop (or bulge for a plenum) is an interesting idea. Good thing it's 6 months to the next El Mrage.
Circulating ice water to cool the intake air is also worth considering. The current radiator in the roadster has a 2" core and a large top tank. A single row core purpose build radiator is a definite way to go.
Thanks again,
Tom
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With a small thermostat, you can further use the ice water that has
soaked enough heat from the intake charge to no longer be useful for
that and add it to the block cooling system to work some more.
By the time you are done with those two stages the run will be over and
you will have the hot water for coffee all around. :wink:
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Several years ago when we were running a draw-through turbo system, we experimented with MANY different types of air cleaner arrangements. The very very best was the cheapest MR. Gasket set up. It was worth 50 HP on the dyno. Nice piece on a carb.
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Richard,
Was this the dropped base air cleaner bottom or one where the filter bottom is roughly on the same plane as the carb gasket flange? In either, the cross section of one side would look like a "D" lying on the flat side.
Tom
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Dropped base.
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Thanks,
I just might have one laying around, or did I take it to a Swap Meet thinking I would never need it again.