Intercoolers

[JohnEd]

I talked to a DD rep years ago about air intake temp.  He had all the info at his finger tips and was decisive....as I recall.  My question to him was how much good does a DD water to air after-cooler do in terms of performance.  I don't think it is common knowledge that a inter-cooler or after-cooler will actually "lower" your power.  That's because it represents a restriction that reduces air flow into the engine.  That is unfair to say and drop the subject at that point.  Engineers like to do that sort of thing to us mortals.  Thing is that the inter/after add no power above what the max possible would be without them.  The real issue is the TEMPERATURE of the intake air.  Without some device to lower the air the air coming out of the "blower/compressor" that sits on top of the engine would get pistol hot under wide open throttle conditions.  Hot air, such as this post will be seen as by some, robs the engine of power.  The DD rep had all the numbers down pat so he knew what the HP would fall to if the stock after-cooler was getting no water flow.  Huge reduction in power and efficiency. 

Water injection into the intake has the same affect.  It cools the intake air.  It doesn't matter that much if you cool the air going into the blower or cool it after the blower has compressed the intake air charge.  A little cooling goes a long way and a lot is better.  Alcohol and water mix injection give you an added boost in power due to the increased cooling that can be attributed to the alcohol.

I knew all that at a basic level prior to talking to the rep.  He certainly pulled a lot of info together in my mind so I benefited significantly from our "chat".  Then came my primary question.....why doesn't a DD 2 stroke have a "intercooler" between the turbo and the blower?  All the info I have says that a intercooler pays for itself in a 4 stroke by reducing the charge air temp.  Given that the air entering the cylinder will have a temp reduction equal to the reduction achieved by the intercooler, even after having the temp bumped by the compressor and then lowered by the after-cooler and a reduced air temp is "good" then why?  Clear?

All I got from him was that I was correct that there would be the same gain as I would get from intercooling a straight turbo engine without the aftercooler installed or working. In other words...mine....every turbo truck engine has a aftercooler so its cost effectiveness isn't open to discussion and a 2 stroke would benefit hugely from the incorporation of a intercooler into the intake charge air system.

DD never put a intercooler in one of their engine installs that I ever saw in my short and sheltered life.  WHY?  Why have no Knuts done this?

John

[bevans6]

I don't know about DD, but intercoolers, also known as "charge air coolers", are indeed commonly used when someone takes the time to modify a  turbo engine setup from the normal.  Usually a big air - air cooler, tucked up in front of a radiator, and with long plumbing.  Obvious advantage - external to the engine, cools the air, makes power.  Disadvantage - longer throttle response.  I'll probably consider one in phase two of my turbo engine install.

The advantage of an after-cooler is you know it's parameters pretty exactly and you and predict what it's going to do.  You know the water temperature you are circulating through it, it's size, air flow, etc.  so it's very repeatable.  External charge air coolers are less exact.

Brian

[luvrbus]

JohnEd my friend DD used the inter cooler on the 2 strokes not many buses used one but a lot of trucks and off highway stuff you remove the after-cooler and install a deflector in it's place in the DD book shows the increase in hp with different air temps


good luck 

[OneLapper]

A healthy 8V71N only produces 2.5 psi positive pressure in the air box via the blower.  Because the pressure is so low, very little heat is generated from the compression of the intake air, that is of course compared to the 25 psi which is common with turbo diesels setups.  Because of that, a N really doesn't need an after cooler or intercooler.  But since every little bit does help, an air to air intercooler or water/alcohol injection would help increase HP, but plumbing it is impractical due to the location of the blower on the 8V71 (except for the water injection, that would be easier).

Not sure this helps or answers any questions.

[JohnEd]

Clifford,

I haven't a clue what DD  did with truck installs.  Certainly I will take your word and it only makes sense.  Now, I have never seen a DD 2 stroke in a bus that incorporated a intercooler. that I recall.

I didn't think that rep was lowing new ground but it is nice to know what the return is based on a degree reduction of intake air.

I have heard this bit of removing the after-cooler to save some flow restriction.  Makes no sense to me unless you were building the engine and were designing the intake to relieve the requirement to reduce the temp further.  But, the blower adds temp all by itself and the only way to dump that specific heat is with a aftercooler.  I guess it must pencil out but it isn't intuitive to me.

Brian,

Yours is the answer I was looking for as it validates my hunch.  One of our knuts that installed the Cummins in his MCI 9 made two separate intercoolers and stuffed them in front of the side rads.  What was one of the best pieces of info on that install was that while he upped the HP a bunch and he obstructed the rads to a significant degree......his temp dropped and he had no cooling problems.  His 6V92 had been overheating with those same rads.(I think)

John

[luvrbus]

Just trying to passing on info for you  DD had 3 different types of air cooling since the moon was the size of a golf ball they were the first with air to air brings a 2 stroke to life FWIW Don installed air to air on TomC's 8v71 no aftercooler

good luck

[TomC]

Detroit did experiment with air to air intercoolers on their 6V-92T engines for buses.  They also did reverse coolant flow so the aftercooler got the coolest coolant from the radiator first.

As previously stated, I went from a 8V-71N to a 8V-71TATAIC (Turbocharged Air To Air Inter Cooled) engine.  2 Stroke engines are the only engines that can have either an intercooler (cooler between the turbo and blower [done often on marine engines]) or an after cooler (cooler after the turbo and blower).  Since I had recently overhauled my engine (which I had the block bored to straighten the cylinder bores out with new oversized on the outside liners), I wanted to use the existing engine.  I had a custom air to air intercooler made for my bus and did the plumbing. Don Fairchild did the conversion with changing the injectors from brown tag 65 to 9G75 injectors, bypass blower, fuel modulator, 12.7 liter Series 60 turbocharger, and hooking it all up.  I also had to enlarge the radiator, air cleaner, muffler and added an auxiliary transmission cooler.

Detroit originally had the 8V-71T without an aftercooler that with 75 injectors put out 350hp and 930 lb/ft torque.  My engine on the dyno put out 375hp and 1125lb/ft torque.  So you can see the difference with using the air to air intercooler.  Good Luck, TomC