Adding an Intercooler

[Steve in VC]

It is my understanding that part of the boost pressure comes from heating the air. If so, adding an intercooler, without changing the pulleys, will reduce the boost pressure. Is this correct?

Lower boost pressure requires less drive power. Cooler air allows more timing advance before pre-detonation, providing more output power.

I understand there is a noticeable difference in throttle response between coldside and hotside. How much does an intercooler effect throttle response on a hotside?

[Tom @ Fast Forward]

Hmm. This is probably one of those discussions that will generate a LOT of interest. Especially if Bill and I disagree. :)

Anyhow, this is strictly my opinion and you have to remember that I tend to think outside the box. Kind of like E-Cool vs. A/A. Now there's a can of worms. LOL

Boyle says that PV=nrT. So, we can say that:

P1V1 = nr T1 or nr = P1V1/T1

Likewise with a different set of values, we could say that :

nr = P2V2/T2.

That develops into:

P1V1/T1 = P2V2/T2

Assuming that the available volume can't change, then:

V1 = V2 and we get:

P1/T1 = P2/T2 or P1/P2 = T1/T2 (QED)

What we need to know next is that these are absolute values. Pick any base you want to work in like *C, *F, *K and PSI, Newton-Meters or furlongs/fortnight. As long as they are in absolute values, it works. Lets take *F and PSI (actually, PSIA. The A is for absolute). Let's say that we are working non-intercooled at 10 PSI (P1) or 25 PSIA (I rounded atmospheric pressure to 15 PSIA to make the numbers pretty :)). Also, let's say that non intercooled, we have an intake temperature of 150F (T1) and intercooled, we have 80F (T2). Those will become 459+150 = 609F and 459+80 = 539F, respectively in absolute temperatures. So, if blower speed stays the same then:

25/P2 = 609/539 = 1.13

25/1.13 = P2 = 22 PSIA or 7 PSI Boost

What that means is that everything being equal, you will have the same amount of O2 and 'should' make the same HP at 3PSI less boost. Another way to look at it is that, at the same boost, you should have ~13% more O2 and make ~13% more HP.

It is all about how much air you can burn. Gasoline is only along so that you can burn the air. If you can get more air into the cylinder (more boost or denser air because of lower air temperature), you can add fuel and burn it and make more power.

Of course, this is just MHO. :)

[Steve in VC]

Ya - what you said... (I avoided posting the math - but that is what it said)

I suspect you get a bit more power with no change in pulley:

I believe drive power is linear, if a supercharger needs 20HP to drive 10PSI, then it only needs 14HP to drive 7PSI (6 more HP to the tires).

Cooler air requires less timing retard, which builds pressure in the cylinders earlier, increasing torque / HP.

Of course if you want to increase boost, that works too.

[Tom @ Fast Forward]

What you said is true but remember that once you cool the charge enough to run maximum timing, cooling it further doesn't help. I have found that if the temperature in the IM is less than 150F, you can run about the same timing as you can at 90F on 91 or better octane. You could cool the charge air to 50F and still not run 10PSI on 87 octane at maximum timing, for example. With E-Cool, I cool the IM charge air to below 150F and can run 17PSI with only about 2* pulled timing. I believe I could ditch the 2* if I had 93/94 octane out here. My point is that once you have cooled the air to allow maximum timing the further benefit is probably 1 HP per 10F. Picking up 5 WHP can get expensive that way when all you need to do is up 5mm on the pulley and pick up 7WHP.

[Steve in VC]

I can't do any of this because of one 4 letter word - CARB.

What you are saying is cooling the air a little further adds safety margin, cooling it a lot further adds unnecessary cost.

I fully agree.

[Serpico]

Just remember that an A/A intercooler is a restriction (some more than others). With no other changes other than the intercooler, your boost will go down.

The good news is that the intercooler will allow you to spin the blower faster to raise the boost level back up. It's all a matter of finding the right balance to reach a safe power level.

Bigger intercooler core = more throttled air volume= idle droop .

[Tom @ Fast Forward]

Everything in life is give and take. There are no perfect answers.

[FormerDatsun510Man]

I managed 240rwhp I think because I have an air/air IC. However, I am open minded about this and look forward to visiting FFS this summer :). Partly because Tom and I are both running 130 pulleys and I think it will be an excellent opportunity to compare apples to apples Coldside to Intercooled Hotside. I found that I need timing control on the track afterall. It isn't a problem on the street, but on the track I started to get some ping after about 10 laps. Keep in mind that I was hitting 130mph (6800rpm in 5th) on the main straight :biggrin:. This was using 93 octane. I took care of the problem by fattening up the a/f to 11:1 and giving the car some cool down time. But my permanent solution is going to be adding the Timing Controller. Also, keep in mind that I am currently running the factory midpipe. When I dynoed 240rwhp I was running the Goodwin 2.5" midpipe without a cat. I wouldn't be surprised if I am closer to 230rwhp now and then will be in the mid 220rwhp range once I put in some timing retard to keep things safe under all conditions.

Based on what Tom is saying about his setup, it sounds like the relative ping threshold on his Coldside vs. my Intercooled Hotside is pretty close, but we will see for sure soon. Who knows, if I really like the Coldside a lot, I might sell my R4 setup to someone looking for mega hp. :biggrin:

Bill

[Tom @ Fast Forward]

Bill,

How long was the main straight? I was getting 128 at Firebird on the 5/8 mile straight. That included using some of that 5/8 mile for breaking. :) That was back when it was 202WHP. It was, however, about 96 octane as I would mix 101 and 91 about 50/50.

[FormerDatsun510Man]

Not sure on the main straight length... I would guess somewhere around a 1/2 mile. Part of the problem was that it was raining lightly when I was doing the runs at those speeds LOL, so I was having to be very careful both coming on the main straight and also had to brake early. I was entering it at only 60mph and gradually going to WOT near the top of 4th whereas before it was raining I was entering at around 80 and going WOT immediately. However, before the rain we had a kink in the main straight that consisted of 4 x 40mph turns LOL.

Bill

[Tom @ Fast Forward]

I am well known for thread drift. ;)

Anyhow, I am lucky to come out of the harpin on to the straight much above 30. That is the start of the 1/4 mile dragstrip and there is a scary surface change. People who take it fast have left a lot of marks on the far wall.

[BlownMX5]

...That included using some of that 5/8 mile for breaking. :)

Might want to leave the "breaking" part out? :rofl:

[Tom @ Fast Forward]

Only thing I ever broke on my Miata was right there.