patman

iTrader: (3)

Ok so i just got done building my high compression TII.
s4 TII with NA rotors. stock turbo and IC right now.

since i am running the high comp, i want a better IC right away, even at stock boost. the question is, should i enclose the stock one in a jacket and make it into a heat exchanger for A2W, with a electric water pump, and the a/c radiator for the rest of the system? or should i just go get a big intercooler from the junkyard?
i am operating on a budget, but have the skill to fabricate most anything. i als have a local junkyard where i can get parts at very low prices, provided they are from an older model car.

one more question. i have a friend who is a subaru guru. i know that he legacy rs turbo had an a2w system stock and im sure he could get one for me. anybody ever seen one of these, and if so, think it would work well in my 7?

thanks,
Pat

andrew lohaus

i say it depends on what you are gona do with the car.
if its gona be mostly street driving i say go air-air for simplicicty and reliability.

however if you are building a drag car or a dyno diva go water-air because it will have a greater ability to absorb large amounts of heat in a short period of time.. i duno about converting the stock unit into a water-air. but most water-air ICs ive seen are fairly small becasue water is a much more efficeint cundoctor thatn air.

are these the 9.7 or 9.4 n/a rotors?

wankel drwankel

there is only one problem i can see with enclosing the stock intercooler. the problem is that you will have to make a volume box on both sides.there needs to be some fluid volume in there. if you dont there will be one cool spot in the intercooler and the rest will be kind of worthless. try to find a 300.00 ebay special and go front mount or if you can weld alu. go air to water and let us know how it goes. good luck

RETed

A2W IC's have no place in a street driven vehicle.


-Ted

NZConvertible

Water-air intercoolers work great on the street as long as they're properly designed. The most common mistakes made are an undersized radiator (A/C condensors are good) and not enough water (the system should include a reservoir). Water is able to absorb far more heat than air for the same change in temp (four times more), and because boost is only used for short periods and not very often (i.e. a small percentage of total running time), the large heat spikes are easily absorbed and rejected.

patman

iTrader: (3)

ok heres what im thinking...weld plates on the sides of the stock ic..with inlet on one end/side and outlet on the other end/ side...so if you looked at it longways it be like a parallellogram shape..thinkin the plates will be welded directly at the non-tube side and about an inch raised at the tube side. will do baffles if i think its necessary. this way the water will go in at one end on one side and have to pass thru and go to the other end/side to come out. this should have enough volume to eliminate the need for a reservior as a2w only req's a few liters.

this is a street car, but i like to build stuff as if it were for race just for redundancy (and i drive as hard on the street as more than a fw ppl drive on the track). also with the high comp i want the very best intercooling system i can get. (rotors are 9.4:1, s4 TII>s4 NA)

pat

NZConvertible

No, you should always use a reservoir. The more water you have, the more heat the system can "store" and the less likely it is you'll have problems. Even a couple of litres in a reservoir will double or triple the total system volume.

philiminilli

http://www.johnnyracecar.com/

this guy builds fmic for really cheap. i think it is 190 for a 5 inch and 240 for a 6 inch. you dont have to deal with ebay either.

HAILERS

Try this site: http://www.gnttype.org/techarea/turbo/intercooler.html

and about half way down he talks about air/water heat exchangers. Para 6 I think.

That link came from this link: http://www.xmission.com/~dempsey/shelby/turbo101.htm

RETed

For the benefit of those people who are too lazy...


"Air-to-water. If we use water as the cooling medium instead of outside air, we can see a big improvement for several reasons: Water can absorb more energy with a lower temperature rise. This improves our DTlm, makes it bigger, which makes Q go up and outlet temps go down. A well designed water cooled exchanger also has a much bigger U, which also helps Q go up. And since both DTlm and U went up, you can make the area A smaller which makes it easier to fit the intercooler in the engine compartment. Of course, there are some practical drawbacks. The need for a water circulation system is one. A big one is cooling the water down after it is heated (which means another radiator). This leads to another problem: You heat the water, and cool it down with outside air like the Syclone/Typhoon. You can't get it as cool as the outside air, but maybe you can get it within 20 degrees of it. Now you are cooling the turbo air with water that is 20 hotter than the outside air, and you can only get within 15 degrees of that temperature so coming out of the intercooler you have turbo air that is 35 degrees hotter than outside! (turbo air is 15 deg over water temp which is 20 deg over outside temp). You could have easily done that with an air to air intercooler! But... if you put ice water in your holding tank and circulate that... Then maybe the air temp coming out of the intercooler is 15 deg above that or 45 to 50 deg. Hang on! But after the water warms up, you're back to the hot air again. So, great for racing, not as good for the street."

READ IT.  People just don't believe my sorry ***...



-Ted

patman

iTrader: (3)

ok..so going by his own data..his a2w example has an approach of 35*, whereas his a2a has an approach of 55-60*. dont get me wrong..i still havent decided yet..just trying to get all the facts straight.

water has a specific heat 4 times that of air. since air is being cooled by the water, and being used to cool the water at te other end, this means that if you can get 4 times the volume of air thru the radiator as goes thru the exchanger, the water temp will stay at the outside air temp. make it 5 for inefficiency losses. i think that that is a very reasonable expectation.

right now the plan is looking like if i can find a good a2a at my junkyard im going for it just for simplicity's sake...then i will work on the a2w thing and compare results.

pat

projekt

something i was always curious about with a/w I/Cs is in Bell's book. he says that if you convert a a/a i/c to an a/w version that the boost air should go through the face of the intercooler and the water should go through the core.
can anyone explain this to me?

Wankel7

Another idea could be water injection and keep the tmic.

James

patman

iTrader: (3)

yeah but water injection is expensive. and not very diy-able..unless im mistaken...

pat

andrew lohaus

PREACH TED, PREACH!!

to reiterate, over an extended period of use (as in more than 30 seconds use with less than 5 mins inbetween) a W2A IC is LESS effective than an A2A because the water will not be at ambient temp. a A2W is only advantageous when the water used is at or lower than ambient temp.

a steady state heat flow from intake air-to water-to ambeint air is not as good as going directly from intake air-to ambeint air.

A2W ICs only belong on drag cars, and possibly autox, but im not sure how the scca specs them.

HAILERS

If you do something like this it SEEMS to me that what you should do is put a K type thermocouple before the intercooler and one after the intercooler. Then drive the stock outfit and gather temps/data.

Then when the other/whatever is installed, do the same and compare the results. But then, that takes a small amount of what you don't have right now. I don't see how your going to be able to gauge how good/not good it works.

patman

iTrader: (3)

i'll just put a temp sensor in the intake after the ic and get a guage, i suppose. not sure how this is all gonna fall out yet...hell i don t even have the motor in the car yet.

pat

BigTone

People are just not used to " direct, one word answers, that dont follow what they want to hear."

NZConvertible

Seriously, when was the last time you used 30sec of constant boost on the street? Even 20sec. Ever?
And yet they regularly appear on mass-produced forced induction engines...

That info on water-air intercoolers makes the assumption that you've driving around the street on boost all the time, which far from what happens in reality. On average, street cars are on full boost less than 5% of the total driving time, so heat is not constantly being added to the water as the article implies. In reality some of it is slowly being released back into the intake air (no prob at low load, all intercoolers do this), and the rest is being rejected by the radiator.

Read this article on how intercoolers work, and what it says about water-air set-ups.

projekt

like "god is dead" right?

andrew lohaus

hey this isnt the neitzche forum

patman

iTrader: (3)

the problem with direct, one word answers is that they are just that..one word with no fact to back them up. i realize that RETed knows way more about this than i do, but that doesnt make him God...and on a debatable topic...proof is always good.

anyway..ive been reading some articles...and from here also...i realize that a2a is for me, but for the opposite reason than everybody thinks...because my driving style is fast all the time rather than slow with spikes. in other words..i drive more like a race car, not less...and i need the continuity of the a2a rather than the ability of the a2w to control spikes. were i a more normal driver, however, i would definately pick a2w.

pat

patman

iTrader: (3)

by the way thanks everybody

NZConvertible

Don't they have intersections where you live?

RETed

If you think about it enough, pure logic will hit you.
If you're driving around, the cooling water mixture will heat up, period.
THINK ABOUT IT.
No matter what you do, the intake charge will be way above ambient.  The only way it'll stay cool, is if the ambient is significantly lower than intake charge temps.  If you live in Alaska, I can think this being valid, as ambients are consistently low.  But what if your summers are hovering in the 100F range?

Keep in mind, intake charge temps will easily surpass 100F just idling.  Under boost, it'll easily surpass 200F.  The cooling water mixture will start to heat up when you first start the engine.

Now, for the best part...  The cooling water mixture will never go lower than ambient temps, except for maybe the first few minutes the engine is running!  This means, after those first few minutes, you A2W IC will basically turn into an A2A IC.  Consider the "added complexity" of the hoses and water pump to make everything run correctly, there's more chance of leaking and failure due to these added devices.

Yes, there are some stock OEM A2W IC's in production cars (i.e. Maserati), and these systems were designed that way due to the engine configuration and very tight space for another heat exchanger.  These are the typical reasons for going with an A2W system - tight engine bay space or impracticality of an A2A IC.

I'm not totally against the idea, but my opinion is that an A2A IC is a lot more reliable and easier to install in an FC3S.



-Ted