Turbos & intercooling

[buddy]

I talked with a supercharger company (ATI) and told them about my idea about the belt driven superchager and the gentleman I talked with said that the losses from both turbos and superchargers was about the same until about the 350-400 hp range he said after that there was no ? that turbos started to become more efficient with the trade off being lag time.

Thats probably close to true when the turbo introduces lots of heat into the intake temps from the exhaust temps and amount of backpressure. But not with the ATT that is much more efficient.

The turbo is making use of a waste products and the supercharger is actually using your generated power.

And of course they person was a salesman, whom you can rarely take completely serious.

 

[ak diesel driver]

It may be a waste product but it's still not a free ride (back pressure which reduces hp). The guy I talked with was there tech guy and he knew I wasn't looking at buying just asking ?s. He told me they have a guy in Australia running twin supers on his dmax. Most of the people who want supers vs turbos are 1/4 mile guys.

 

[ak diesel driver]

One more thing the tech guy was actually against the idea not from a performance standpoint but a price standpoint about $3k.

 

[Slim Shady]

One more thing the tech guy was actually against the idea not from a performance standpoint but a price standpoint about $3k.

Well then at 700.00 the ATT turbo is a steal, it was never about making big money, it is about realizing what our trucks are capable of. Nothing is worth more than blowing the doors off a stock 7.3 Ford when pulling a load or having a Stock Dmax wonder what is under the hood that sounds so good.

 

[Slim Shady]

I have always been a fan of the old roots style superchargers. I know they can at best reach 60 percent efficiency, but they sure sound nice, and if you want you can break things real easy in the drive line from the increased lower end torque. I am not sure how the 6.5 block would take the added strain at lower rpm, might break them quicker.

 

[ak diesel driver]

It would almost be worth it just to see what happened.

 

[Slim Shady]

It would almost be worth it just to see what happened.

As long as someone else is paying yep I think it would be worth it to see a crank embedded in the ground under the truck.

 

[tiredsixfive]

My parents spent my inheritance pulling a super mod 8200 lb alky truck for many years.We ran Mert Littlefields hi helix 3 lobe chargers on a 440 cid tall deck BB Chevy,alky of course.I learned that superchargers are like turbos,not one size fits all.Our hi helix made better avg numbers(boost across rpm band) but not really larger peak #s.So the hi helix was more efficient at delivering air as rpm went up.I realize that alky motor has a throttle plate where our diesels dont.Could it be that some turbos are more efficient at keeping boost constant during rpm increases than others?That would explain the better perf from the other turbo vs GM IHI series.One other note,we had to run a crank that would sustain substancial twist,as the blower put that much of a strain on the crank nose,with no harmonic balancer(no room for it with 3" wide drive belt) and cranking it 7800 rpm for pulls that could last up to 22 seconds each.I think the data tag said the crank could sustain 18 degrees of torsional twist before shortening the duty cycle of the crank below 100 hours.(think breakage before 100 hrs)

 

[ak diesel driver]

Don't know much about the super you were running but it sounds alot like a roots style. The kind I'd look at are simply a belt driven turbo.

 

[tiredsixfive]

yes.it was a root style.I kinda miss that sound.On a alky motor,ours was overdriven at 28% I believe.On gas they had to run their blowers underdriven.That sound is addictive.Its just not a sport that a working man can afford.It took yrs and $$ to get it all figured out.Mech fuel inj is finicky at best.There is a pill in the barrel valve on the throttle called a pill.It determines how much fuel is bypassed and returned to the tank(smaller pill forces more to injectors,less bypassed to tank).The saying was "pill it till you kill it.Rebuild and install one size larger and run it."

 

[tiredsixfive]

Anyone ever been to ANY truck pulls in Ohio knows of Studley Studebaker.It was like a 51 model with a 427 BB chevy.He had less $$ in his whole truck than most had in their paint jobs.It was always funny to watch him show up and win with a rig costing maybe 10% of what most others had invested.I believe they owned Bodens Machine Shop.Ive seen his low $$ motors tear JP 1 all aluminum hemis apart that cost $60K each without blower and injection

 

[schiker]

Yes, temperature is part of the gain. Since the ATT turbo moves more air easier its cooler. Turbine doc has noted this and mentioned an optimal intake air temp is 150F ish iirc ( so while an intercooler and cool dense air is good too cool might be dimishing returns vs more air and easier plumbing)

Picture this....

You ever use air hose at a Hess gas station. They use to have an adjustable air pressure regulated hose. You dialed it to a certain psi and filled your tire until it quit dinging the bell. When the tire was low it would ding fast then near the psi setting it would slow down and quit. If tire was near full it might ding once or twice real slow.

Ok now picture this: 2 production conveyors to move air. On the conveyor are a series of cylinders shaped like the engine cylinder but one cubic foot sized. With a tire stem in top and relief valve. The conveyor moves at 1 cylinder a minute ie one cubic foot a minute or 1 "cfm". At the beginning of the line a guy has just a few seconds to use a hess style air hose to pump air in the cylinder. The conveyour moves the cylinder to the end station where a guy relieves the pressure into a weather balloon. Then returns the cylinder to the front of the conveyor.

One line the guy at the end lets out more air into a bigger weather balloon. So the cylinder is more empty when the first guy adds the air. So this line he is going to get more bell dings out of the bell and more air into the cylinder because less pressure in the cylinder to start allows the air to move faster.

So even though the lines move at the same speed ie 1 cfm (the same positive displacement pump rate) the line that lets out more air at the end will move more air even though the air hose at the beginning is at the same psi.

 

[buddy]

Im not seeing this picture

Is your point that the cylinder is not evacuating all the exhaust on the exhaust stroke in the stock 6.5TD? Its hardly much of a gain if thats the case. Its not like this is a open flow, it is absolutely choked flow so theres barely a difference in actual volume flow.

 

[schiker]

Is your point that the cylinder is not evacuating all the exhaust on the exhaust stroke in the stock 6.5TD?

I am suggesting that is a big part of it.

Yes that's my point. On the exhaust stroke there is back pressure on the exhaust valve due to the turbine driving force. With lower back pressure of the ATT turbo more air exits the cylinder and thus more air can enter on the intake stroke.

From what I understand the GM-X does start to choke or increase backpressure between the exhaust valve and turbine after 2600 rpm stock appreciably. And that would get worst with more boost and increased fuel rate of a modified engine.

So even though the constant positive displacement pump rate is fixed the throughput of air is improved due to improved effeciency.

Same reason a better down pipe and bigger exhaust helps spooling and flowrate lower backpressure after the turbine allow the front side to move more air easier because the exit flow is easier. That's why its been said it can move more "CFM" with the same boost pressure. More SCFM enters the intake and exits the tailpipe with the engine pumping the same "CFM".

You see this improvement most significantly in EGT. More air through the engine cools the EGT. Given a set fuel rate air volume and temperature are the most significant factors influencing EGT.

The with more air in the cylinder the more power you can generate.

 

[schiker]

You see this improvement most significantly in EGT. More air through the engine cools the EGT. Given a set fuel rate air volume and temperature are the most significant factors influencing EGT.

The with more air in the cylinder the more power you can generate.

Better wording the more air mass the better even though the volume is the same.

 

[buddy]

I would not think that there is a lot of exhaust left in the cylinder as the exhaust stroke is pushing it out. That is kind of conjecture, and I conjectured it a few pages back. It would be minimal factor. We have high compression ratios, so the void space at the top of the stroke is 22 times smaller than the expanding intake stroke.

And I agree, more air mass is the better explanation.

 

[Slim Shady]

I would not think that there is a lot of exhaust left in the cylinder as the exhaust stroke is pushing it out. That is kind of conjecture, and I conjectured it a few pages back. It would be minimal factor. We have high compression ratios, so the void space at the top of the stroke is 22 times smaller than the expanding intake stroke.

And I agree, more air mass is the better explanation.

So if we have an exhaust manifold back pressure of 20 psi that void must be equal to the pressure on the exhaust manifold side. So when the exhaust vale closes we in essence have a small void left with 20 psi in that void (all pressure being equal). That small void at 20 psi wants to expand and equalize itself to the next area available to expand in which is the intake stroke that started while that exhaust valve was closing.

Lower back pressure or a value less than atmospheric pressure would increase the fresh air entering the cylinder and since that void is at a lower pressure and expanding we have a rush of air which may slightly increase our initial flow rate until it fills the cylinder and starts compressing the air. So a larger displacement of air at a lower pressure would enhance this event, then if the pump had enough volume it would continue this effect where as a smaller pump would have to recover the volume before it could start to compress the air. ):h

 

[gmctd]

That is correct - currently, engines are "enhanced" to use the residual exhaust gas that remains in the cylinders to reduce oxides of noxious, where previously e\i valve overlap was used to allow the 'charged intake flow to blow the cylinder clean of those residuals to make more power (same as with naturally-aspirated hi-perf gassers (patooie!) to take advantage of hi-velocity ram-air effect at hi-rpm) - e\i overlap doesn't help much with indirect injection because part of the combustion chamber is in the pre-cup, but works wonders for direct injection engines - until federally-mandated state DOT vehicle inspection time

Naturally-aspirated wedge-type (non-hemi) engine efficiency is usually ~77% - meaning that it pumps 77% of its designed swept-displacement volume - ram-air input and tailpipe location in the low-pressure area behind vehicle can improve that efficiency as vehicle speed increases (to a point, where engine rpm cfm approaches ram-air cfm available at some vehicle velocity thru the air), and can reach 100%

The turbocharger, however, is also known as an efficiency improver - 100% efficiency is easily achieved by increasing intake pressure such that forced airflow overcomes any inlet path restriction(s) and impediments to airflow

Now, here's where some engineers begin gnashing their teeth, and their plastic slide-rules begin to soften and melt from agitated usage, and they begin to resemble Dr Livingstone (they're in de Nile!) - not only can the turbocharger improve swept volume efficiency to 100%, efficiencies of 200%, 300%, and greater can be reached simply by placing that exhaust gas driven turbine motor in the exhaust path, and connecting the compressor into the intake path

Let's say we have a cylinder with swept volume (B x S) is equal to 1 cubic foot (1ft3) - if we rotate the crankshaft 1 turn, air displaces the piston as it drops in the cylinder - at 180* BDC, the cylinder is filled with 1ft3 of atmosphere - the rising piston begins to displace the air till, at 0* TDC, the cylinder is empty and the pump has displaced 1ft3 air - repeat this once per second and the pump displaces 60ft3\minute at atmospheric pressure - swept cylinder volume is always = 1ft2, no matter how fast the crankshaft turns - it is the displaced volume per unit of time that increases as crankshaft rpm increases - if the pump is 100% efficient output will = swept volume

The gas-turbine driven supercharger, or turbo, is also an air pump - it must be capable of much greater airflow volume than the engine it is attached to, with capabilities to 2000cfm and greater, depending on turbine and compressor size, in order to create Boost pressures of 1x (15psig), 2x (30psig), 3x (45psig), etc, atmospheric pressure (Baro = ~15psia) into an air pump that is capable of 150-400cfm at normal Baro at normal operating rpm

Therefore, if we could measure Baro:in flowrate into the 1ft3 cylinder and output flowrate we would see 60ft3 @ 60rpm - so, let's pressurize the inlet (remember the function of a turbocharger) such that the cylinder now fills with twice it's designed swept volume, or 2ft3 - the cylinder will now pump 2 cubic feet per rotation, or 120ft3 @ 60rpm - the turbocharger has effectively doubled the pumped volume, with an effective efficiency of 200% - this is how a turbocharger can make a 150hp engine produce 300hp without altering the designed swept volume displacement

And which is why some street people refer to engine efficiencies of greater than 100% when a 150 designed-hp engine can produce 300 Boosted hp - engineers don't like terms like 'effective' and percentages greater than 100%, altho that is exactly what is occuring....effectively

The turbo, by compressing each cubic foot of air to 1/2 original volume has doubled the volume in the cylinder by increasing air density and thus weight by volume, which is measured in Mass in lbs\ft3 - air has a specific weight per volume, which varies by temperature and pressure - volume in actual cubic feet is based on flowing conditions - volume in standard cubic feet is corrected back to world-standard mean conditions, by comparing flowing conditions to 60*F and 14.696psia, arriving at a flowing temperature factor and flowing pressure factor that will be used in the calculations

Mass flow measurements can be used by doing the calcs to correct air temp\press back to 60* and 14.696psia then doing the density calcs, then the mass\volume conversion calcs, but it is (effectively) easier to refer to airflow in cfm on the street until such time as mass flow measuring instruments, which should have live Press and Temp inputs or a live densitometer input for accuracy, come down into the $19.95 price range - for comparison, one model costs 3350bucks plus another 600bucks for the gas turbine software - plus another 600bucks for the head-meter software - then you still need the turbine meter and the head and orifice plate and the temperature probe and the pressure sensor\amplifier or\and the densitometer

A simple airflow test set is available for Fluke DVM's, and one can be made with a small dc fan motor, measuring armature voltage output as airflow spins the fan

CAUTION: these are for measuring low CFM flowrates - the fans\motors can disintegrate with considerable force at high flowrates, injuring personnel and damaging engines

 

[buddy]

Can anyone confirm that the 6.5 uses scavenging/overlap at all? Ive been trying to find a reference for it but havent been able to.

You can say that the turbo in terms of CFM, makes sense, but it doesnt make sense to have more CFM at lower PSI, since the way a turbo makes more CFM is by compressing the air more in the intake to higher pressure.

A pumps rating does not mean thats its output at that rating, it just means its capable of it if it had to do it. Like a variable output pump that will fill a space to 15psi whether its a 10ft3 intake that consumes 1ft3 in a stroke or a 100ft3 intake that consumes 10ft3 in a stroke. The flow demand is higher on the higher displacement engine so it will flow the air necessary to create 15psi using greater backpressure, but it will also generate 15psi at a lower flow in the lower displacement engine but use less backpressure.

Either the GM-x or ATT will flow the same amount at 15psi in this engine, but at a lower temperature the ATT flows more dense air, so more mass per volume. And with lower backpressure the engine doesnt have to work as hard to keep the crank turning.

 

[gmctd]

The 6.5 uses the identical camshaft as used in the naturally-aspirated 6.2, with 0* e\i overlap - doesn't work with idi engines

Considerable portion of exhaust energy is in therms - BTU generates considerable cfm

V = T/P