? about Ram air and turbochargers

[JUSAV6]

what's up everyone? I have a ? I was hoping some of you could help me with. I know this guy that says that adding ram air to a turbocharger will help it. Any info on this subject would really help to clear up an ongoing debate. Thanks

 

[strikeeagle]

I have read many times on this board and elsewhere that "ram air doesn't work on a turbocharger". But, if you raise the suction pressure (Ps) of a compressor stage, for a fixed discharge pressure (Pd, or boost), it operates over a lower pressure ratio (Rc), and thus makes less heat (Td). And that's a good thing.

Even see where the big boys mount their turbos? Right in the grill area, with no filter, just that big old compressor wheel hanging out there on the nose of the car, all by itself.

 

[azgn]

turbos sitting outside the hood and behind the grill may serve to provide cooler air, but I sorta doubt any "ram effect" is achieved.......that turbo is suckkin' its brains out....

no engineer, but just can't see any advantage

 

[zam70]

A turbo spins ALOT faster than any ram air system could help.

It's all about the cold/cooler air.

 

[bruce]

Ram-Air, has become a marketing term.

At one time it infered that the opening for the intake tract was large enough, and was unobstructive enough, that at speed, it would serve to force air into the engine.

But, it's fallen to include hoses, and ducting that has so much wall surface area, the it's more a restricton then an aid.

Lots of cold air kits do the same thing, ie add restriction to they system, and their net effect is actually just making the engine a little richer, or making the AE artificially rich. With all the tubing running close to the radiator it winds up soaking up heat.

 

[scottyb]

Originally posted by zam70
A turbo spins ALOT faster than any ram air system could help.

It's all about the cold/cooler air.

I agree.
I also agree that ram air does help, but I also feel that the amount of "ram" you could acheive is insignificant. I don't have the details, but I recall reading about a test with a ram-air TA, and the conclusion was also that the important factor was the cool air and not the ram effect.

 

[strikeeagle]

Well, there you go. The "it's all about cold air" and "it spins too fast to matter" theories.

I am an engineer and we increase the capacity of our plants by adding single stage compressors in front of our existing air compressors. This practice, interestingly enough, is known as supercharging. Supercharging raises the suction pressure of the existing air compressor, much like ram air, if you will.

Even huge compressors have high speed stages. Granted, these stages are much larger and thus not as fast as automotive turbochargers but gearboxes get these stages spinning quite fast.

When we execute a project like this we plot a revised compressor curve over the existing curve to establish the proper functional specifications for the supercharger. That elevated suction pressure improves performance is obvious from the curves.

 

[strikeeagle]

Oh, and if the effects of pressure loss on the suction side of a turbocharger compressor don't matter, explain:

Larger, open air filters
Larger, smoother. straighter, shorter ducts
Mass air pipes in lieu of ducts
Larger, gutted MAFs
Discarding MAF screens and MAF venturis
Adding cones and venturis to improve flow potential
4" compressor inlets
billet, ported compressor bells
and so on...

It all matters. Even a few inches of water column loss on the suction side of a compressor operating at or near atmospheric pressure has a profound effect on its performance. Which explains why we pay so much attention to it.

 

[JESTER]

Do the math

Based on an 850 cfm turbo and the equivalent free area of a 5" round ram air opening, you would need to be travelling at 70.8 miles per hour before you get a true ram air effect and overcome the resistance of the intake tract.

You only benefit when you are travelling fast enough to overcome the resistance of the piping added by the ram air system itself. Of course the cold air is a nice benefit.

Eric

 

[azgn]

yah, but we are not talking about putting a compressor ahead of the turbo!

I seriously doubt just putting a turbo into free air will help anything until one hits, say 200 mph? (once again, I don't know squat, but logically, it would seem so)

the cooler air helps if it gets there efficiently

 

[strikeeagle]

Well, it sounds that we agree ram air is a benefit.

Your point that providing it is somewhat problematic on a street car is a good one.

 

[strikeeagle]

Woddy,

I love ya, but you're wrong.

True, the supercharger we provide makes several pounds of head, but the theory is the same - raise Ps, improve performance.

 

[JESTER]

Not trying to take sides, just state the facts.

Reducing the inlet or outlet pressure of any air moving device will allow the device to operate more efficiently and therefore move more air.

Is it worth it to add ram air? That depends on how much piping is added by the ram air system, the size of the ram air opening, and the speed at which the car travels.

A car that will rarely travel at or above highway speed is probably not going to benefit from the ram air as much as from the cold air. A car that will travel mostly at highway speeds will benefit from the ram air as well as cold air.

Eric

 

[azgn]

uuummm, a TR cruising the freeway is running at 0 boost

so I would have to ASSume at WOT and at some speed, a turbo sitting in clear air would benefit?

I still doubt much could be realized (other than cooler air)

how in the hell is a stock configured TR gonna get ANY "ram air" (short of a hole in the hood)

 

[Ormand]

Like Eric said, up there somewhere, EVENTUALLY you will get a ram effect, and it will help. BUT.. up until you reach that speed, about 70 mph in his example, the losses in the extra piping can outweigh the benefits. The cool air will help at any speed, however, since it is mass air to the engine (density) we are after, not just psi. If you want some numbers, the Stealth316 site (Turbo Performance Calculator ) will let you vary the inlet pressure to your turbo, as well at the turbo efficiency, etc. So you could see how much boost you will gain from a half-psi increase in inlet pressure. If you want a "real world" example, ask those guys in the Rockies, who have to deal with "weak" air on a day-to-day basis.

 

[turbojimmy]

Originally posted by azgn
how in the hell is a stock configured TR gonna get ANY "ram air" (short of a hole in the hood)

Those kits that various vendors were selling claimed a ram-air affect, didn't they? The ones with the scoop in the RH air dam and the "box" by the charcoal canister? I had one on my car for a while until I read somewhere that they actually impose more of a restriction than anything else. I think I buy that theory because my K&N filter would consistently have a 4" diameter dirty spot on it where the "ram air" tubing hooked up. The rest was clean. I ditched it in favor of a homemade kit that just has a K&N filter in open air by the air dam. Now the WHOLE filter is dirty. Unscientific I know, but I think it's getting more air.

In a semi-stock arrangement I think it would be tough to come up with a plumbing arrangement that wouldn't negate any "ram-air" effect you get at any speed. I like Chris Chow's "ram air" setup for his twins.

Jim

 

[JESTER]

Thanks Ormand, I forgot to about the latent heat of compression scenario to throw at the mix. Thanks for that link.

Eric

 

[JUSAV6]

thanks all for all the info. I was just helping close a debate between two friends on this subject. I appreciate it all. Thanks