# Turbo myth...



## James (Apr 29, 2002)

Ok first off, people who say a CAI is not needed on a turbo engine because the intercooler will cool off the charge anyways... I could be totally off my keel here but a turbo will heat up the intake charge ABOVE AMBIENT temperatures!!! So if its drawing in 100 degree air it will heat it up to 140 degrees (hypothetical, negating compressor efficiency and all other sources of heat). Now if you draw in 70 degree air on that same setup you'll only be exitting at 110 degrees... a 30 degree difference is not 'small'. 

The ONLY excuse I'd accept for not running a CAI is that it does decrease the spool time because of the extra volume to pull through. Well also if your engine bay is too small to fit a CAI in...


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## psuLemon (Apr 23, 2003)

james, wasn't there a discussion about this same topic a while ago.. i could swear it was about a year ago... 

lemon


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## James (Apr 29, 2002)

yeah there might have been... i just think that people have a misconception about the intercooler and CAI


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## psuLemon (Apr 23, 2003)

^i think that a cai will help cool the air a bit more, but its not goin to be that big of a drop, i believe. With cai it will bring in denser air allowing th air to be slightly cooler but nothign like 30 degrees. you would need to get a koyo radiator for that..


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## James (Apr 29, 2002)

did you read any of the first post???


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## psuLemon (Apr 23, 2003)

are you tryin to find reasons why a person wouldn't need a cai on a turboed car..


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## James (Apr 29, 2002)

no there was just discussion on another forum about it and I feel otherwise. Maybe if I had the equipment I'd test it to be sure...


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## lshadoff (Nov 26, 2002)

For every 10 degrees you drop the inlet air temperature, you drop the compressed air temperature slightly more than 10 degrees. There is an intercooler calculator here.

I gave it a 75% efficient intercooler at 9psi boost.

Inlet Temp=85*F Compresed Temp=163.8*F Intercooler Outlet Temp=104.7*F
Inlet Temp=75*F Compressed Temp=152.4*F Intercooler Outlet Temp=94.4*F

Lew


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## James (Apr 29, 2002)

plugged in your #'s and 100 deg on the inlet temp came out 120 deg after the IC. Did the same with 80 deg inlet and got 99 deg after the compressor. On a hot day I would think 20 deg in drop of temperature would be an achievement!
http://www.teirney.net/civic/TemperatureReadings.htm

cool link! thanks!


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## lshadoff (Nov 26, 2002)

When I had the air intake under the hood, I measured the inlet air temperature sensor with my EASE Diagnostic PC tool during an acceleration run. The graphs are here. It is the lower panel, top blue trace.

The ambient temperature was 85*F. The under-hood temperature at idle was 108*F and was about 105*F at 65mph. The under-hood temperature rose quickly to 123*F under boost (6.5#).

A CAI would have supplied 85*F air.

The importance of all this is that hot air causes detonation at a lower boost level than cool air does. Therefore you can run higher boost without detonation using a CAI all other things being equal.

Lew


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## James (Apr 29, 2002)

Cool actual data on our cars. Excellent. 

I would think in the summer months, just to have that extra 20-30 deg cooler temps after the IC could save an engine from detonation on long runs.


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## psuLemon (Apr 23, 2003)

^sorry james i couldn't help that much.... ill see if i can find that old thread for you though


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## javierb14 (Jul 9, 2002)

here's a little more data  on my car i positioned the turbo so that i could eventually fab up a cai for it....it's not behind the rad or any other part that could heat up the intake charge.










here's how well it works...this was during the winter on about a 70deg night, 2nd, 3rd, and 4th gear pulls. the IAT is lower under boost than compared to temps when constant cruising. 










of course, an efficient compressor, a decent sized FMIC (26*11*3), having the car at high velocity, and good ducting helps too


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## James (Apr 29, 2002)

Javier, so looking from your data, if the CAI had been in place the IAT would be around 70 degrees initially and cool lower when the MAP pressure goes up correct?


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## spdracerUT (Jun 11, 2002)

basic compressor thermodynamics. the lower the intake temp, the lower shaft/compressor power is required to compress, in this case, air at a given mass flow rate and boost pressure(pressure ratio). So if you're intake temp is lower, the turbo should spool faster to whatever your boost pressure is set. If you just let the turbo boost as high as it could go, lower intake air temp would allow it to boost higher.

You can look it up in any basic thermodynamics or compressor book.


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## lshadoff (Nov 26, 2002)

Javier,

That is just what I would expect if the intake point is pulling cool air. The piping under the hood is heated by the engine operation, and when the air flow into the engine is low, the piping heats the air. When the flow is high, the air doesn't spend as much time in contact with the piping, so the IAT drops under boost.

Did you have the sensor in the piping near the MAF?

Lew


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## James (Apr 29, 2002)

spdracerUT said:


> basic compressor thermodynamics. the lower the intake temp, the lower shaft/compressor power is required to compress, in this case, air at a given mass flow rate and boost pressure(pressure ratio). So if you're intake temp is lower, the turbo should spool faster to whatever your boost pressure is set. If you just let the turbo boost as high as it could go, lower intake air temp would allow it to boost higher.
> 
> You can look it up in any basic thermodynamics or compressor book.



you would think that wouldn't you? but i run into people on this forum and other forums that believe the CAI on a turbo only reduces like 1-4 deg anyways...


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## javierb14 (Jul 9, 2002)

James said:


> Javier, so looking from your data, if the CAI had been in place the IAT would be around 70 degrees initially and cool lower when the MAP pressure goes up correct?


with a CAI i might be able to reach near ambient temps on a good day....ambient right now is ~108 :crazy:


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## javierb14 (Jul 9, 2002)

lshadoff said:


> Javier,
> 
> That is just what I would expect if the intake point is pulling cool air. The piping under the hood is heated by the engine operation, and when the air flow into the engine is low, the piping heats the air. When the flow is high, the air doesn't spend as much time in contact with the piping, so the IAT drops under boost.
> 
> ...


right on. thats one of the reasons i used steel piping for the hot pipe, compressor discharge, since it's near the exhaust manifold. reason being, is that steel is much less conductive than AL...i didnt want the charge air to heat up anymore. the IAT sensor is on the intake manifold plenum right next to the map sensor.

i have also seen dyno comparisons of CAI setups vs non CAI setups on turbo cars. the CAI didnt add more power or benefit in anyway compared to the non CAI. one of the reasons i think it didnt make a difference is the fact that the car wasnt "loaded" on the dyno like it was on the track....100+mph vs spinning the rollers with a couple of fans. when i get the car running again, i will test the CAI vs no CAI on the dyno and on the track and see what happens.


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## James (Apr 29, 2002)

108, that's suicide, get me some AC temperature...  

Yeah I don't think CAI's will ALWAYS make the intake charge cooler, just that when the car is moving the CAI will always draw air from a cooler source.


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## lshadoff (Nov 26, 2002)

I have some header wrap. I think I'll wrap the turbo piping under the hood to insulate it.

Lew


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## James (Apr 29, 2002)

I want to get some of that turbine wrap as well to wrap the turbine section. I think that's good for a point or two of efficiency too no?

I need to reroute my intercooler piping because my pipe comes right out of the compressor straight over my manifold...


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## lshadoff (Nov 26, 2002)

James said:


> I want to get some of that turbine wrap as well to wrap the turbine section. I think that's good for a point or two of efficiency too no?
> 
> I need to reroute my intercooler piping because my pipe comes right out of the compressor straight over my manifold...


I've done that:

http://www.brazosport.edu/~lshadoff/turbo/twrap.html

Mike Kojima warned me that, based on his experience, if I want to track race my car (e.g. SCCA), the thermal wrap (or Swain white lightening thermal coating) will cause the housing and the manifold to crack eventually.

Lew


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## James (Apr 29, 2002)

yeah but my turbo is old anyways. it blows it blows, time to sell the car for smog next year anyways!


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## webninja (Oct 15, 2002)

I've been wondering about this too and this post has some great info. I did do a few things to reduce the intake temps in engine. I built a cold air box out of sheet metal and used foam strips to seal it off from the rest of the engine bay. I also wrapped my downpipe and intake pipes. I haven't done any measurements, but the car seems to pull hard even when it's above 90 out, but before all the wraps and the box the car felt a little sluggish when it got realy hot out.


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## James (Apr 29, 2002)

actually that is a better idea than a cai because you can keep the length of the pipe down and still draw in cool air. I would have done that but... no motivation... its hard to find a will to work on your car when you know in 2 yrs you have to remove it all and smog it....


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