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MG MGB Technical - Cold Air Intake

My '74 B is a commuter car and occasionally has to sit in traffic. I'd like to get some cool air to the intakes (dual SU's). Of course, running the hose itself is easy, but has anyone got a good solution for a box or something to surround the air cleaners?

I'd rather not just connect a hose to the existing snorkel, as I understand it's too constricted as it is. I also don't want to cut up my existing cans, in case I or the next owner get a hankering for originality.

So what can be adapted or fabricated to provide cool air and free breathing?


As always, many thanks.


Matt K.

Matt Kulka

Matt,
What I did on my 74B was install a set of Bob-Cleaners, and then enlarged the hole that is on the driver's side of the radiator housing. I ran a 4 inch metal dryer vent hose from the opening to a snorkel that I fitted just behind the grill. I used some mesh on the snorkel to stop any bugs from directly crashing into my filters. All parts were purchased at Home Depot. Total cost was less than $10, not including the price of the K&N filters. I was worried that it would look tacky, but it isn't even really noticeable. I had to relocate the horn on the one side to fit the snorkel. I hooked up a remote thermostat to see if this ram air/cold air intake had any bearing on the temperature where the air enters the front carb. In all tests the temperature was at least 10 degrees colder at the carbs using this set-up. I figure that the cooler air should help performance as well as cool the temperature of the fuel bowls. It seemed to have slightly more snap, but then that could just be my imagination. This allows you to put the black Cooper cans away until you need them later, and definitely provides you with better breathability. However you might find that you need to go to a slightly richer needle because you are breathing so much better. Roger Hotelling has a good write-up based on his experience with the Bob-Cleaners. His site is http://www.hotelling.com/mgb7.htm

I guess the next step would be to build a box around the air filters to ensure that the coldest air actually did get into the carbs, but I really like the look of my Bob-Cleaners.
SteveO

I should have mentioned that it probably wouldn't do any good if you were stuck idling in traffic, since you need to be moving to get the cooler air in. That's where the box would help. Let's us know where you go with this.
SteveO

Matt

Cold air (and fuel) is a good idea as density increases as temperature drops - roughly speaking 3.3 deg C will see a change of around 1% in density. An increase of air density in excess of 10%, would give a around 2psi of supercharging pressure.

At 100mph under ideal conditions ran effect generates approx 0.177psi of ram effect pressure. F1 cars do not bother to use this.

Induction hoods used on F1 have much smaller intake mouths than the plenum area, these are precisely calculated, designed, manufactured and tested, and stabilise air and increases pressure.

Therefore having trunking pick up cold air and used with a high flowing air cleaner should work, as long as there is not too much turbalance at the carb mouth. However, this may cause problems with winter summer road cars and would require some thought with regard to cold winter running and traffic jams when the carbs will have to operate with warmer air.

A friend if mine is trying this with an additional fan in the trunking to maintain the flow of cool air.

Paul
Paul

TWM Induction http://www.twminduction.com/Filter/Filter-FR.html makes a very nice cold air box, though it is rather pricey at US$275. It allows you to run a 3" duct to the hole in the radiator surround (which has to be enlarged). For under $10, I accomplished the same thing with an air box from an older, carburetted Volvo (240???)which used SUs. I had to flip it over, since Volvo put the carbs on the wrong ;<) side. Because the holes for the carbs didn't match up, I cut out the back of the box and covered the opening with a sheet of aluminum with holes matching my carb spacing. For a couple of dollars more, you can buy plaxtic bass-reflex speaker ports with a flared end and in the right size to act as an air straightener at the other end of the duct. It also makes a nice finisher for the enlarged hole in the surround. The most expensive part was 3" flexible dryer duct, because it only comes in 8' lengths (a life-time supply). I just remove the ducting in winter to let the engine breath warmer air.

Regards,
Jerry
Jerry Causey

SteveO,
Actually, I have a pair of brand new quart-size paint can lids to do the Bob-cleaners. The ambient-pressure hose is a good start, but I'm really looking for a 'sealed' system. When the car is idling in traffic, and the under hood temps get hotter and hotter is when I'm most interested in drawing cool air into the intakes.

Paul,
Your details of air density and pressurization were very interesting. However, my interest in this regard is to the cooling effect. As you say, trying to get ram effect from the oncoming air stream is impractical if not impossible.

Terry,
The TWM is a good solution, until you get to the price list. They must be hand made and platinum coated. Your solution of the Volvo box is what I was looking for. Coincidentally, I was a Volvo mechanic about the time they switched over to EFI. I don't recall a box over the carburetor air cleaners, but it's been a long time. I'll be checking into this solution.

Thanks to all. You've all been very helpful.


Matt K.
Matt Kulka

Matt,

You may be interested in my friends fan system which in theory will draw cool air in when stationary. It's a home made system using standard cans. Hopefully an article will appear in EMG. I can't say how succesful it is but the car is running on the roads with this system.

Paul
Paul

To move air when idling, a 12 V cooling fan (as used in cooling electronics such as PCs) could be inserted into the ducted air path or "Y-ed" into it via another short length of air hose. Just a thought, I will let those with more time work on that one.

I liked Jerry's idea to use the bass reflex ports. A good exercise in seeing an alternative use for existing hardware from other field of endeavor. It is making those connections as you all have done that makes for some effective homebuilt modifications. :-)
Bob Muenchausen

(Jerry, sorry for screwing up your name last post.)

Bob,

The thought of forcing the air via a small PC fan crossed my mind too. But it would still only throw cooler air in the vicinity of the intakes, and then hope they'd pick it up. I think as long as I'm making the effort, I'd like to seal things up so all of the air is drawn from outside.

I think I'll take a trip to the Volvo parts counter to get an idea of their air box. I like that idea.

Thanks again.

Matt


Matt Kulka

Austin Healey 100's with the "M" conversion about 1955 had this very settup. It was an aluminum box that bolted to the carbs, with trunking going forward ahead of the radiator. To this day, I don't know if they had an inline filter somewhere.

Pete Haburt
Pete Haburt

The fan idea is a good one but it will actualy decrease perfromance. I race and modiy mustangs too. There was great discussion and dyo test on people putting fans into the airstream to make sorta of a supercharger affect. It atually makes the air very turbulent and this cuases lost in power whenit goes thru the carbs.
matt kaser

Matt,

I would agree that to make a fan system work properly you would need to slow air down and reduce any turbulance before reaching carbs. It is a lot simpler and less trouble just to dump cool air near the filters avoiding turbulance problems.

Paul
Paul

About how much of an increase in HP would a cold intake box create for a B engine?
Steve

All:

The MGC with dual carbs had a stock system that is very close to what you are describing. It had a fan in the system but did not draw air from outside but near the radiator. Some C guys have added an cold air "pipe" to the front of the standard C system that picks up air below the grill. The inside engine compartment temp on the C gets between 20 and 30 degrees higher then outside air. Don't know if the setup would work on a B but the plates and stuff are designed to bolt on a standard SU 1 3/4 inch configuration.

Steve
Steve

See what we learn via dialogue?! Thanks Matt and matt, for the informed opinion on using a small fan. After I posted that comment it occurred to me that the fan is meant to force air through a duct or to simply move tubulated air around heat sinks, etc. It would definitely be an obstruction to free air flow once the car was moving.

The cold air box is an established idea in racing and probably holds more promise for real gain than simply lowering under hood air temp as a simple hose does. Sure, the lower under hood temps would be of some help but I doubt they would be as effective as much colder air directly from outside.
Bob Muenchausen

Paul, Thanks for the info out of David Vizard's book. I completely forgot about chapter 6 on ram charging. It is a great reference.
Jeff.

Jeff Schlemmer

Maybe I've missed the point. Cold air equals more power, but this isn't an issue in traffic.

If you want to keep the fuel cool then that's a different story. I've tried lagging the exhaust manifold, but that seems to be giving me problems with burnt gaskets at present. I once had a MG Montego Turbo which had a fan and trunking to cool the carb when the engine was switched off - it seemed to work okay (at least, I never had any problems with vapourisation), but the fan wasn't very powerful and surely wouldn't counter the effect of the heat coming from the exhaust manifold. I made up a massive aluminium heatshield - not very original but easy to remove!

On my 1970 UK car there is a hole in the radiator shroud to let the air through. I connected a hose to this and ran it to a bellmouth (an old carb ram pipe) glued to the radiator grille. I didn't bother with anything the engine side of the shroud. Seems to work okay - at least plenty of cold air is getting to the general vicinity of the carbs. Whether this amounts to a measurable gain in BHP is debatable, but it cannot be making it any worse!

An 1800cc engine is consuming about 900cc of air every revolution. At 5000rpm that's about 75 litres per second. If you make some assumptions about losses (like there aren't any) you can work out the size of trunking/pipe needed to get that much air in at any speed. Its not a straight line relationship, but as an example we worked out that a 100mm pipe (to make the sums easier) would flow 75 litres per second of air at about 21mph. The effect is clearly better the faster you go. So it seems like a cold air inlet could be worth while.


Neil
Neil

Neil,

You're quite right, my original post contradicts itself. Weak an argument as it is, here was my thinking:

When I sit in traffic on a hot day for a long time, my temperature guage rises a little over "N" - not enough to be alarmed - and stays pretty stable. As I sit longer yet, the temperature guage stays still, but my idle slowly drops. Very slowly. Eventually, it may get low enough where I rest my foot on the gas pedal to keep the motor from dying.

I could only assume that the stagnant hot air over the exhaust manifold was heating the carburetors (intake air and float bowls) and changing the mixture for the worse. (Before you ask, yes I do have my heat shield in place.)

And that, flawed reasoning though it may be, sparked my original question. I'm quite happy to be corrected. I care more about knowledge and a well running car than I do about my pride.


Matt K.

(BTW, I haven't checked into the Volvo airbox. I've just finished dropping the rebuilt motor back in, and that's taken my attention.)
Matt Kulka

Matt,

Sorry: I didn't mean to be, or sound, patronising!

I took a big sheet cardboard and pushed it over the studs on the manifold where the carbs go. Then I cut bit by bit until the cardboard just fitted in the space. It took ages. You need a bend about half way down so as it doesn't touch the exhaust manifold. I then transfered this to a sheet of 16 gauge aluminium. The only tricky bit is cutting out the 1.5" holes where the carbs fit!

The under bonnet temperature seemed to drop - subjective of course.

Neil
Neil

I wrapped my header with heat tape - and that drastically reduced the underhood temp. The same could be done with the early factory exhaust manifold. I'd be afraid to limit air intake by building a fresh air box, unless of course you could guarantee that it flows at least 400cfm. That would either need quite a large opening or have some form of "scoop" to to create a ram charging effect. Even then performance is based on the design - to create smooth airflow.
Jeff.

Jeff Schlemmer

Neil -

I didn't take offense. I hope my reply didn't sound like I did. Haughty spirit comes before a fall and all that. But I missed your meaning of "I've tried lagging the exhaust manifold." I'm not familiar with the term. Could you explain further?

Jeff -

Actually, that's not a bad idea to wrap the manifold. (I have the stock iron in place.) I had heard that the tape can hold in moisture and increase rusting, but on further thought, how can moisture rest on something that hot?

The one difference you and I have is climate. In North Carolina in the summer, 90 degree days are common. If I wrap the headers, the heat which would have radiated off into the engine compartment is trapped until it gets past the wrap - under the driver's side floorboard. I don't know how much difference it would make, but as hot as it is to drive this car in the summer, I'd hate to make it worse. (Insulating the foot area is another project coming up.)

Again, thanks to both for some interesting ideas.


Matt Kulka

Matt: You mentioned that your idle was dropping as the temps rise. This is probably due to the bimetallic temperature compensator used in the HIF carbs. I wonder if anyone ever developed something to hold the jet in place without this piece.
Another problem that occurs in traffic is vapor lock. If you really need to keep the fuel temperature down then you could do what Rover did on several models: run a fuel return line back to the fuel tank. The return line must be a smaller diameter, and the fitting at the tank should have a restrictor so that enough fuel pressure exists at the float bowls to keep them full. With this setup there would be a continous flow of fuel into and out of the fuel tank. The volume of fuel in the tank will absorb a lot of heat.
Andrew Blackley

Hot air is less dense and holds less oxygen for a given volume. Same volume of air is going into carbs, but mixture is now richer due to less oxygen content in the air. So, when we are sitting, at idle, in the summer, the idle speed tends to drop. The Bi-metallic compensator in the HIF4 carb was designed specifically to move the jet to conterract this condition. This is a good idea, in principle, but I don't have experience with this carb to speak to how well it actually works!

Bill
Bill Schooler

Jeff & Matt-
Actually, although wrapping the exhaust manifold in insulating tape seems to be a good idea in principle, it is a very bad idea in practice. Why? because the heat gets trapped inside the metal of the manifold and will cause the manifold to warp! Instead of wrapping the exhaust manifold, get it Jet-Hot coated. Jet-Hot coating is a ceramic coating that will coat the interior of the exhaust manifold as well as the exterior. The heat has nowhere to go except out of the exhaust system. How much does it effect underhood temperatures? Well, I can rest a bare hand on it after a hard run! If you're interested, Jet-Hot has a website at http://www.jet-hot.com/
Steve S.

Steve,
I'm wondering how the manifold can warp. The metal cools down more slowly than an unwrapped manifold, so it should be less likely to warp. Actually I have an aftermarket header, as I've had on many cars in the past with the same wrap, and never a problem. Headers even seem to last longer - rust less - with the higher temperatures. And there seems to be no real increase in floorboard temperatures, although they are insulated so I may not notice anyway.
Jeff.

Jeff Schlemmer

Jeff-
The heat can't escape from a wrapped cast iron exhaust manifold. It just builds up and up, far beyond what the factory engineers designed it to handle, so it warps. Peter Burgess mentions this problem in his book "How to Power Tune MGB 4-Cylinder Engines". He's not the only person that I've known to experience this problem. The only way to keep the exhaust manifold from radiating heat is to keep the heat from getting into it, hence Jet-Hot ceramic coating. Try it, you'll like it.
Steve S.

Another coating, which I have on some different sets of headers and with which have been pleased is by "High Performance Coaings" (HPC); they have a facility near (east of)Hartford, Connecticut. I've had some sets coated inside and out; they run cool, as exhaust headers go, and the finish holds up for as much as 12 years so far - no signs of chipping or rusting. I suspect it will hold up as well on cast iron as it does on tubular steel. You might want to check them out too.
Marvin Deupree

Matt,

Sorry, I forgot that we don't speak the same language!

By 'laggging' I mean that I have used exhaust wrap (the asbestos-esque stuff that looks like a bandage). I concur with the guys who reckon it warps the manifold. A bigger problem for me seems to be manifold gaskets - I assume that the additional heat is too much for them. I did a bit of gentle motorsport last weekend and the gasket burnt away on the exhaust port for number 4 cylinder. It has happened before, but on the front inlet port. The engine also heats up qucilky in traffic - even with a huge (special) radiator core, a new water pump and an electric fan!

I am going to take it off to see what the effect is.

Neil
Neil

This thread was discussed between 12/03/2002 and 31/03/2002

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