Ok - it's Sattiddy nite, nuttin' on the toob, an' I feel chatty, so how's about some discourse on Diesel vs Gasoline tech........

Diesel engines and Gasoline engines have only one thing in common, aside from some of the general configuration hardware - blocks, heads, pistons, cranks, etc and etc.

One thing, only - fuel, air (O2), and fire.

Infernal combustion is the name of the game, folks - takes fuel and air to make fire, no two ways about that.

Fuel and water - nope. Dirt and air - nope. Dirty fuel and humid air - well, maybe..............and that is not a definite maybe.

So -
Gassers function very well with vacuum in the intake manifold.

Diesels do not.

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REFERENCE -

Vacuum is not a force - vacuum does not 'suck' air and or fuel into the cylinder(s).

Vacuum is a measurement for a lessening of force, that force being Actual Atmospheric pressure at 15psiA, or 30"hg on the mercury column.

Atmospheric pressure is measured at 0psia in space to 15psia down here at the bottom of this sea of air we have become so fond of breathing, and is normally measured on a column of mercury, called a Barometer.

When Bambi the Weathergirl says the Barometer is falling, atmospheric pressure is lessening in her area, rising in some other area.

(Watch it, guys - those comments are more suitable for the other forums you spend lots of time watching!);)

2"hg in the mercury column is 1psia, and is 27"H2o in the water column, a similar device for measuring pressure\vacuum in smaller increments

15psiActual is 30"hg is 0psiGage is 0"hg vacuum

0psiActual is 0"hg is -30"hg vacuum, usually represented without the minus sign

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Configuration - 400cuin Diesel, 400cuin gasser, 3.82" stroke, 4.08" bore, samo samo, no sweat, GI.

Diesel intake tract is wide open to atmosphere - piston drops in the cylinder, 15psi rushes in, completely filling that 50cuin volume between piston crown and the cylinder head.

Gasser intake tract has closed throttle plate(s) and carb venturi(i) between it and atmosphere - piston drops, throttle plate blocks intake air flow, now we got 50cuin cylinder swept volume (bore x stroke), 20"hg intake vacuum, which is -10psia (no such measurement, of course), or 5psia in cylinder\intake manifold, 15psia otherside of the throttle plate.

This difference of pressure in a gasser intake is the major difference in ability to produce power.

Diesel always takes in full volume of air on each intake stroke, low rpm or high rpm.

Inject a little fuel, we get idle, and we got a lot of air left over.

That's right, folks - a good running Diesel ALWAYS runs 'lean'.

Add more fuel, as required, we get power, add lots more fuel, we get lots more power.

Ain't a matter of air, folks - we got all the air we need. Just add fuel.

Gasser air intake is restricted by angle of throttle plate(s), and venturi(i) diameter, even at full throttle.

As air flows thru venturi area, velocity increases due to smaller area, then decreases as diameter increases, but with slightly reduced pressure.

15psia pressure on fuel bowl forces fuel thru the jet(s), spraying into low pressure area just below venturi, which mixes with air flow, then heads for the huge 50cuin low pressure area in cylinder.

Or, fuel is injected into the intake port, mixing with the air flow as it enters the open intake valve.

Add spark, and we got combustion - open the throttle, allow a little more air, force in a little more fuel, we get a little more power.

We can add more fuel to the air charge by installing larger jets in the carb, or larger injectors, but why?

Problem is, if we add more fuel than available air, engine chokes up on rich mixture, and don't run so hot, or not at all.

Because the fuel is trucked in as part of the intake air charge, the fuel\air mixture must be maintained at a specific ratio of 14 air to 1 fuel, for the 14:1 stoichiometric ratio that allows enough air for complete combustion of the fuel charge.

Exceeding that ratio does not increase power - the engine runs 'rich', blowing black, unburned fuel smoke, and loses power, similar to, but not the same as, a Diesel on too much fuel.

Gasser rpm and power is governed by amount of air\fuel mixture flow past carburetor throttle plates, or by amount of air flowrate past throttle plate, and amount of fuel injected stoichiometrically into that flow at some point before the intake valve(s)

Got Boost? Even under pressure, fuel must be stoked at that correct ratio to achieve expected power.

Diesel power is governed by the amount of fuel injected into a cylinder filled with maximum volume of air.

Wanna make more power - inject more fuel.

Wanna make even more power - Boost in more air, inject even more fuel.

Wanna make even more power - Boost in even more air, inject even more fuel.

Now - how do we make Boost, and what is Boost?

Read my previous 'paper' on Boost for that concept.

Now - why would we want a camshaft with altered specs?

Increased valve lift allows less restriction to intake air flow.

Restricted flow is a problem at high rpm - ~7000rpm, or so - in a naturally-aspirated engine, because the window for fuel\air intake is very narrow, and any restriction reduces the O2 volume needed for power.

Increased duration, where the valve is held open longer, allows more time to fill or exhaust the cylinder, and is related to overlap.

Not much of a problem for a Boosted engine at only 3750max rpm - required charge is already at the valve, ready and waiting.

Overlap, where the intake valve opens before the exhaust valve closes, takes advantage of another effect associated with high flow rates, at high rpm - ram air.

The high-speed exit of the exhaust charge rushing out of the cylinder, and the high-speed column of air rushing into the cylinder create an effect similar to turbocharging.

Holding the valves open together - overlap - allows a super-quick exchange of fresh charge, as 15psia atmospheric pressure rushes in, pushing what's left of the old charge out, as the old charge rushes out and down the ehaust pipe, driven at high velocity by the piston and cylinder pressure.

The higher the desired rpm, the more degrees of overlap can be designed in, within limits.

There are limits.

This is state-of-the-art, and works very well - except at low-to-medium rpm, where window across TDC is wide, and over-lap reduces intake vacuum, reducing intake air flow, reducing fuel intake, with rough running, poor idle as result.

That's the loping, choked-up idle we all associate with a hi-performance racing-tuned V8 gasoline engine.

The greater the rpm-required overlap, the higher the required idle rpm.

Absolutely kills low-end torque.

In a Turbocharged Diesel engine, where the combustion chamber is in the piston, a small degree of overlap can be designed-in, which allows Boost pressure to blow the previous charge out the open exhaust valve, ensuring the cylinder is completely filled with fresh charge for the next combustion cycle.

Does not effect low-rpm use, because a Diesel does not require vacuum for the fuel charge.

Each intake cycle gets a full supply of air, and rpm is regulated by the amount of fuel injected.

A little less air from overlap, inject a little less fuel to get stable idle.

NO rough, hi-performance idle, here, folks.

NO loss of low-rpm torque, here - we got a compressor puffing that cylinder full of fresh O2.

More fuel we give it, the greater the heat of combustion, the greater the exhaust energy, the higher the exhaust velocity thru the turbine nozzle, the faster the turbine spins, the faster the compressor puffs, the more Boost we get, the more fuel we can add, the m..........well, you get the drift, right?

That's the difference, folks - we get a full charge of air on each intake stroke, to which we can add as much fuel as needed to make low-rpm power.

We can inject as much fuel as needed, because of that full air charge, to increase Boost, which increases the mass of the intake charge.

A gasser is dependent on the volume of air flow,which is required to DELIVER the fuel, which makes power.

They ain't the same, folks - you cannot power them up, the same, or think to the same references that gassers are accustomed to.

Tuned pipes? What for - we only got 3500rpm to work with.

Tuned intake runners? Why - we got a magic puffer on the intake, puts the O2 at the intake valve long before it's even ready to open.

Polished intakes, heads? We got no fuel-air mixture that separates easily in rough surroundings.

Etc.

Etc.

KnowwhutImean, jelly bean?;)

Thanks for your insightfulness (is there such a word?) Another great job explaining the operational info about the wonderful world of diesels.

Now, here's where I like to throw the monkey wrench in the whole tinkin' here. I've raised this point before, yet, it doesn't seem to get any answers. The idea of a valve overlap, where both the intake and the exhaust ports are open at the same point in time to help to "cleanse" the clyinder of all products of combustion is a great idea. This is not really a new idea, two stroke diesels are out there and "blow" fresh air through the cylinder to allow a fresh batch of air for combustion.

In a two-stroke application, it uses a blower to "push" air into the clyinder. Now the difference comes in with using a turbo to boost air coming into the clyinder. Basic operation of a turbo is using the exhaust air to increase the intake air. To create that boost pressure, it has to create that much and more back pressure for the turbo to operate. So, at 10psig of boost, you've got 10psig+ of backpressure between the engine and the turbo. The (+) comes in with just basic friction that will reduce the overall effectiveness. Now, add in there an a turbo that GM uses that helps to bottleneck that into an even higher backpressure, then you've really got more soil than your shorts can hold.:)

So, all that to say, unless you've got a way to overcome the (+) psi of backpressure, the exhaust gases may actually move backwards into the intake, moreso than through to the exhaust.

I'm no auto mechanic, but I work on compressors in refrigeration all day long. If you could get refrigerant to move better, go for it. But air or refrigerant, I think the same thing applies.

This is only my take on this setup, so, if I have befuddled myself here, let me know. I'm willin to learn more.:)

>That's the difference, folks - we get a full charge of air on each intake stroke, to which we can add as much fuel as needed to make low-rpm power.< "Quote"

You can't get a full charge of air in a turbocharged engine. At any given boost pressure there is going to be a corresponding amount of exhaust back pressure in the exhaust manifolds before the turbine wheel. Only in highly tuned race engines do you see like for like pressure. In most cases the ex. back pressure will be almost twice or more than the boost pressure.
Suggest people who are really interested in making power measure the exhaust back pressure before the turbo. Think you will be quite shocked.
The high exhaust pressure will prevent the cylinder from filling completely.

That's where reducing overlap would be beneficial... Another problem with our engines is the indirect injection. It's not too easy to blow that prechamber clean.

GMCTD's explanation is pretty good. Some of you folks would do well to read and absorb.

His statement on a full charge is pretty close to right... a lot closer than the critic wants to admit.

All correct, guys - what you're referring to is differential.

And I'm not talking that east-west thing between the rear wheels that makes your truck go north-south. ;)

And you may well be surprised to measure 45psi exhaust back pressure in the GM-8 turbine at 15psi Boost, with 3.5"exhaust system, and still feel the power, as acceleration is pressing you back into the seat.

Wonder why?

Saturday nite? What did i miss, its thursday here?

That's when I started it, CR - takes lots of proof-reading.:cool:

Now - first you must distinguish between direct injected engines with combustion chamber in a dish in the piston crown, and indirect injected engines, with the combustion chamber in a pre-cup in the heads.
Both have close crown-to-head dimension, with the flat I-I piston being closest.
D-I run typically 30-50psig Boost at 18:1cr, I-I run 10-20psig Boost at 21.1:1cr.

D-I runs overlap, so Boost can completely clear cylinder.
I-I does not overlap, as valves would hit flat piston at TDC, and pre-cup chamber cannot be efficiently evacuated.

So - 6.5 exhaust valve closes just b4 TDC, with piston having displaced the preceding combusted charge out the valve.
All but the teeny bit between the crown and the cylinder head, where GM flatly states that the heads should not be shaved, which would cause piston\valve clearance problems at TDC.
'Nother words, the piston almost totally force-evacuates the cylinder - may be some back-pressure left in there, but at what VOLUME?

Intake valve pops open to 15psig Boost pressure, and cylinder almost totally fills with fresh charge, 'cept for the small small small volume in the cylinder and the pre-cup. This reduces available power, somewhat, but the large volume of 15psig new charge and new fuel still makes for some good indirect-injected power.

Exhaust valve opens, exhaust at high cylinder pressure zips out thru the turbine, piston right behind it, and exhaust back pressure is 'regulated' to only 45psig, with compressor kicking out 15psig easy.

Close valve, repeat as necessary.

D-I, with similar turbine setup, larger wheel, has more input pressure to overcome high exhaust back pressure at blow-thru.

Volumetric efficiency is the kicker.

Yep - had to cut it short on the D-I side, due to heavy eyelids.

You are entirely correct, kn, and that 'differential' is the delicate balance between 'driveability' and flat out power production.

Any time a turbo off one of the several D-I TurboDiesels is installed on a 6.5L, immediate complaint is turbo-lag - no spool-up off-idle and lower rpm- but with improved power across mid-to-upper rpm ranges.

This would indicate greater turbine exhaust flow capability, required for the greater power output of the D-I engines, and which really frees up the lower 6.5 output.

When those guys are diggin' for power over factory equipment, they have optional turbo configurations to work with - we do not.

The post was a generic comparo Diesel vs Gasoline engines, so the arguments were posed as generic.

As knkreb and Dieselpro pointed out, it's the specifics that stack the cards.

The turbo-engine combination can be tuned for power within a certain rpm range(s), but would be impractical on the street, as the 'driveability' rpm range is 1500 to 3500rpm, in our case, and 1500 to ~6000rpm in the D-I cases.

'Nother words, it is a compromise - if you want a big show on the dyno, put your large turbo on for the run, and rage.
Put your street turbo back on to pull the trailer back home.

So...

combining the logic of GMCTD and Diesel-pro, A belt driven supercharger would be the absolute cats-ass on a diesel engine. Has anyone tried it on a 6.5? Would it be worth losing that turbo sound?

Tim

marine Diesels use turbo & supercharger probably too much grunt for a 6.5 tho, you are still up against limitation of the weak parts of the engine.

The main drawback would be the weak crank, which breaks at the second main journal with defective harmonic balancer or accessory drive pulley.

Check the Hummer sites for a whipple-type s\c.

The turbo-engine combination can be tuned for power within a certain rpm range(s), but would be impractical on the street, as the 'driveability' rpm range is 1500 to 3500rpm, in our case, and 1500 to ~6000rpm in the D-I cases.
Most of the D-I engines I've been around are max governed at about 2500 rpm and advised for 2200 rpm for max continuous usage.

Yep - I was overlooking the old-style mech injection, referring to the new breed, with full PCM management, Pilot Injection, 22kpsi inj pressure, 4-valves per cylinder, 600hp, 900ftlbs torque - they ain't yer grampaw's Diesel, fer sure!;)

But, those are an even better example of making power at low rpm, with big torque across those long crank-arms.

New cam balances valve actuation around BDC.(lobe sepeation 111.3* centered on BDC) Reduce the back pressure with a larger turbo, lazy to spool but lowers EBP.

I know there will not be a dramatic increase in power with this cam but the other changes(increased boost, lower CR) will work with it. I see the new cam as the balance of power. the stock cam actuates the exhaust valves for over lap 39* bbdc and seems lopsided and I'm wondering if it helps ruin the cranks on these engines to have the power cycle fade to the exhaust cycle as it does. a spirical(sp?) (out of balance) inertia instead of a cyclic rotation of inertia.

Warning all thoughts are virtual.

The cranks break, QM, due to one all-encompassing fact - the engine was designed around a low specific power level, which a cast-iron crank could handle.
The rod and main journals required rolled fillets to handle the additional stresses of Diesel service - high compression accel\decel inertia, greater low rpm torque band, accel\decel twisting forces with manual transmission, etc.

Even required a harmonic balancer\shock absorber on the drive end - the dual mass flywheel.

The firing order was altered from GM normal 1-8-4-3-6-5-7-2 to 1-8-7-2-6-5-4-3 to redistribute stress patterns thruout the crank.

The crank is externally balanced in the front hub and on the flywheel.

It was determined that the block could be cast with lower nickel-content - nickel strengthens cast-iron by allowing more 'flex' - because of the low power level, which could not cause much stress.

Chevy engines were called "stove-bolts" for many generations, because the oil pump coverplate was attached with screws resembling common wrought-iron stove bolts.

The 6.2\6.5 should also be called 'stove-bolt' because the block is closer to cast-iron stove alloy, than engine alloy.
Work it, and it breaks.

6.5 is low rpm, low-power designed, and the power-upgrade patches were done in an attempt to keep up with Cummins-in-a-Dodge and Navstar-in-a-Ford, real Diesel engines designed for real Diesel work, with turbos applied to really enhance that work.

Marine service requires a Diesel engine be kicked up to 80% power output for long periods of time - where the Cap'n is trying to get his yacht, with a bevy of beauties aboard, from Galveston to Miami in short order - and 18:1 pistons with altered cam timing could allow better efficiency\economy in that specific power band.

Also, the turbo would be sized for higher rpm, with no wastegate, because the prop offers little torque requirement at low rpm.

Street Diesels require power off-idle to hiway rpm, and require dynamic range of output from idle to acceleration thru the gears to cruise to acceleration, etc.
The wastegated turbo functions well in that scenario.

Marine service torque is clockwise-only, driving a propeller.
Shut it down, and water across a prop does not offer much reverse torque to the crank.
This is similar to 4L80E application, where the torque convertor clutch unlocks when driver lets off on the pedal, or the brake is tapped, etc - little reverse torque.
(Also reduces reactionary rotational (torsional) stress to the 4L80E hollow input shaft)

Back off in a manual trans truck, and the inertia from the entire vehicle is transmitted thru the drivetrain in reverse-torque to the crankshaft.
Manual transmission service required a harmonic balancer on the accessory-drive end and the output drive end of the crank.

Would tend to indicate a weak crank, 'n est ci pa?

Where can I learn some of this stuff? Can anyone recommend a good book on the principals of diesel technology/operation?

Act like a sponge and keep reading GMCTD posts...

My thoughts exactly Billman.

I didn't realize how much I didn't know until I realized how much I didn't know.

Thanks, jd.

how it works.com, banks website, and hang around other gearheads like GMCTD some of it will rub off,

Hey........I resemble that remark! ! ! ! ! !;)

But, yeah - TD and I have posted that info any number of times.

For complete practical theory of Diesel function, written by an expert for non-experts (and some "ex-spurts"), Banks Talks Tech is excellent reading.

Note that the products are slanted toward the function, and not vise-versa, as most detractors loudly proclaim.

Banks offered enhanced towing experience with the 6.2L turbo kit - no promise of suitability to compete at Daytona, Pocono, the salt flats, in Nascar, in Nastruck, and etc, was mentioned, or inferred.:ro)


(Sorry, folks - just absolutely could not resist!):cool:

bump

Quite a few new members to the 6.2 & 6.5 forums go to the top of this thread and read all the way through, there is a LOT of useful info in this post.

GMCTD,

Excellent thread.
Maybe when you finish trimming your bonzi trees, you could teach me to catch a fly with chop sticks.:agreed:

They don't seem to have trouble with superchargers on these

http://www.marinedieselusa.com/assets/images/Md-tiger2.JPG

Saturday nite? What did i miss, its thursday here?It appears we missed a lesson, oh well I'm sure it will get hashed and hashed again and again again.

A number of considerations must be taken into consideration, when making comparison.

That is a recently-released marine engine, which utilizes the new re-designed 6.5 - it is a MERCRUISER replacement.

Marine engines have the entire lake, sea, ocean for cooling.

Marine engines work at constant loading, constant rpm, for hours on end, unlike wheeled vehicle engines, which work off-idle to whatever is demanded, dozens of times per use.

Marine engines never encounter clutched manual transmission shock-loading.

Marine engines seldom have air conditioning compressors strapped on.

A Whipple-type sc is also available for the 6.2\6.5 Hummer, but, supposedly, Uncle Sam got the good engines, we got the drop-outs and floor sweepings.

Just pulled the pan on mine again, yesterday - still no sign of cracks, breaks, varicose veins, or other.

Pistons sure look like they wanna be 18:1's, but I was looking for Cummins-signs...............

I didn't realize how much I didn't know until I realized how much I didn't know. Thanks, jd.You never know what you don't know till you know what you don't know.

Everyone on this site (Earth) can learn something from someone else, if they are just willing to listen to others and not just themselves, Tons of knowledge out there if we wll just harvest it. Right Guys :exactly:

Can we look at this from the gasoline engine getting a turbo charger perspective?
With the throttle plates and 14:1 f:a mixture to consider, what does the gasser have to have to run a turbocharger and ~12 psi boost other than the obvious parts.

A blow-off, or pop-off, valve in the pressured intake tract

A fuel pressure regulator, plumbed for Boost control

A pre-ignition knock sensor, preferably connected to the electronic ignition advance circuit

Preferably, fuel injection

Among other things........

does a throttle body efi count as fuel injected?

Yes - allows easier fuel pressure control with varying Boost levels.


Can be done, but port EFI is better

Found this while looking for another pice of nifty info bumped it back to the top, with recent influx of new 6.5ers on the forum thought this might be interesting reading for some.