Inliners International Forums General Discussion Engines Cold air intake

Hi all,

I have a question.

Would there be an advantage to installing cold air intake to a mildly massaged 235, 4 barrel, cam, headers?

This is a big must do for tuners. New cars all have some form of circumventing the radiator heat. I have always wonder what a cold air/ram air would do.

I do have heat to the bottom of my Clifford, would introducing cold air defeat the purpose of heat?

I am very interested in where this will go.

Luis

You probably will not feel any difference.(maybe)
Unless your engine tends to detonate at all?
It might take away some detonation.

Introducing cold, more dense of an air charge is always helpful.

You can run a cold air set-up & have no ill effects on driveability (sp)even when using a heated intake.

So ,,,go for it, only positive improvement will be your outcome.

MBHD

Cold air is always good but I agree you won't see any giant leaps in overall driving performance.

As far as the ram air effect, about a dozen or so years ago one of the more credible engine builders did some tests and found out it did nothing until the vehicle had passed 90 mph and then it only added about a 1 to 1.5% gain in hp. He also reported that depending on the twists and turns in the cold air duct most factory ram air packages showed no difference from ram effect and only from the cooler air and even this was minimal because the ducting ran so close to hot parts on the way to the carb.

The most effective results came from a plenum box at the base of the windshield like is done on NASCAR stock cars, or from a big old scoop on top of the carb sticking out through the hood.

I am surprised that some of the long time members didn't reply to this query. I was hoping to toss around some ideas about the cold air and the hot manifold. I would like to change the way my engine bay looks, but I do not want to effect the reason for the hot manifold. For years I didn't heat the bottom of my manifold. Then with all the chatter going on here, I added it. Not much of a difference to me except maybe during winter. Maybe the CA weather.

Thanks for the help.

Luis

Dear Luis;

The "cold air effect" or Ram Induction only aids the higher horsepower engines and only then at high speeds as Mike explained.

I remember when that 'fad' started in the mid 60s & it was just that. The 'muscle car' kids just had a new gadget to show off.

I used to rib them about having a "rock catcher" on their hood. Otherwise they (hood scoops) did look kinda cool @ the time.

Happy trails.

Luis,

A true ram air intake can increase the pressure entering the carburetor by no more than the the dynamic pressure, q, of the external air flow, which can be calculated by the equation q = 0.5*(rho/gc)*V^2, where rho = the density of the air (0.0765 lbmass/cubic feet at sea level), gc = 32.2 (lbforce/lbmass)ft/sec^2, and V = velocity in ft/sec. Thus, at 100 mph, V = 147 ft/sec, and at sea level the dynamic pressure will be about 25 lbforce/ft^2, or about 0.18 psi, or about 5 inches of water. This could increase the power by 1.2%, which is line with what Mike G reported in his post. At 50 mph, the theoretical gain would only be 0.3%, but at 200 mph it would be about 5%.

The "first-order' correction for the effects of changing the intake temperature is to assume that the power varies inversely (added by HWW after reading the post) with the square root of the intake temperature. Thus, if the intake temperature drops from 100F to 60F with a good cold air box, the power could increase by about 3.7%. As Mike G pointed out, the ducting would need to properly routed or insulated to keep from picking up heat on its way to the carburetor

Hoyt- You must be one smart cookie! You sound like my girlfriend who is majoring in Bio Chem. Good info though, I had never seen the math break down.

I did use a ram air set-up on my YSR 50.
I tested it @ 50-55 MPH I did get positive boost pressure of 1/10th of one psi!!!

People asked me if it helped, I'd reply it can't hurt & BTW I did win the championship in that class.
All the little things help, & adding all the little things up equaled a definate power gain over others.

Superbikes use have been using ram air/pressurized air box for quite some time now.

Testing bikes like a ZX-12 against a Hyabusa (sp)
Static the ZX-12 was way down on power.
Then they pressureized the air box as if the bike was going 150-170 MPH & bamm 10-15 more HP IIRC?
I think it got a positive boost pressure of .4-.6 PSI IIRC?

MBHD

Attached is an article from sport rider on some ram air tests on several high-performance bikes. The peak boost from the ram was about 25 mbar, or about 0.4 psi, at 180 mph. The theoretical equation would give about 0.6 psi at 180 mph. We have tested hundreds of ram air intakes in wind tunnels and the boost is seldom, if ever, greater than what the theory predicts. However, if the wave dynamics in the ram air duct reinforce the wave dynamics in the engine's air induction system, there could be a significant increase in boost at some engine speeds. This is seen in the European Comprex supercharger, the pulse jet engine ( the V-1 buzz bomb of WW 2), or the pulse detonation engine that has seen a lot of press in recent years.

Sport Rider article

If someone has some data that shows different results I would love to see it. I've been doing this work with jet engines for over forty years in the aerospace industry, but I never cease to be amazed and surprised by the inventiveness, ingenuity, and the ability to just "know what works" that most hot rodders have. I wish that a lot of the engineers that I work with were as good with engines.

Hoyt, good find !!!!!

Heating an intake doesn't generally heat the air pulled into the cylinders much. All it does is heat any fuel droplets that hit it and re-vaporize them, keeping them from condensing out of the intake air stream.

However, drawing intake air from under the hood instead of outside does make the intake charge hotter and you will notice a small power differance.

It is just fine to heat the intake while pulling in outside air, it isn't counterproductive.

Thanks for the post and info. My next project is an air cleaner for my 3x1 setup. The 3 paper air cleaners tend to get dirty quickly. So I can assume that a cold air intake with one easy to access filter into a heated intake will work.

Is there a difference in fuel economy? I have read that heating the air before it reaches the Carb will help vaporization.

Almost all late model vehicles duct outside air into the intake or the manufactures wouldn't bother doing it.But probably cause the new vehicles have very hot engine bays.And yes it will reduce engine detonation if your engine is tuned to the point of detonation.
Anyways,if you duct in outsdie air,make sure the system has a sharp bend and a drain of some sort at that bend so any water or rain will not reach the carb or throttle body.I've read of a few newer vehicles suffering engine damage when driving through water and it was picked up by the air induction system.
The catch 22 here is many inline guys heat the intake for fuel vaporization ,better low speed performance,especially on a highly tuned engine.The heated intake can promote detonation when the engine is under load,so cooler out side air may help.A vacuum operated flap valve may be nice like on some newer engines to draw engine bay air when cruising and then open to outside air when you're on the gas pedal.But then the engine gets complicated like a 70's smog motor

The original question seems to be about cold air instead of ram air. A general rule of thumb : For every 10 degree drop in intake charge, you will gain apx. 1% in power. This doesn't seem like much but consider this. If the underhood temp is 180 degrees, that's after the radiator and over the exhaust, with the outside temp being 80 degrees. That's a 100 degree difference, on a 300 horse engine you are gaining 30 horsepower. That my friends, you can feel.

Dear Armond;

I'm sure your arithmetic is correct.

However; a 235 engine is a 120+/- horsepower engine and most spent their money elsewhere to get the performance.

Those aluminum hood scoops were outlawed here a long time back. Before that; the "big block" (400 CID+) were the only ones to use them etc.

Happy trails.

I'm just answering a question, not telling anyone how to spend their money. I didn't spend a dime on my truck, just pulled the side panels off to let the world see all those beautiful inline cylinders, made adjusting all those carbs easier too ......

All the 'tuner' cars with ram air that I have seen having problems with water is because they are putting the ram air scoop in the front air dam below the bumper. I have seen 3 such cases (one brought to you by the local PD after they had impounded the car, gee Barney why did you think it was a good idea to hydroplane a car with 3" of ground clearance??).

There is a check valve of sorts that is available that goes in the tube and if water hits it it plugs off the inlet and draws air from under hood. If you draw the air from the top of the core support (before the radiator) this should not be a problem. IIRC Smokey did this on his NASCAR Camaro (the one they wouldn't let him run)it picked the air up at a reverse angle so inertia would carry any debris (or rain) into the radiator instead of the intake.

Of course a high mounted cold air intake could still have a problem with water, if you like fording rivers.

Don't they use those things up there to suck the snow off the streets?

The new "Mini",the little car with the BMW 4 cylinder engine has had a reall for water getting into the engine from the outside air inlet.Seems that when driving in heavy rain,a few inches of water on the road,that sort of thing,the water get into the intake,hydro locks the piston(s),destroyed engine,not covered under warranty.
Fresh air is good,a minute amount of moisture can help cool the intake charge,but a gallon of water is fatal.