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porting precups

buddy said:
.. and you have to believe GM was conservative with just about everything....
Click to expand...

That is for sure.

I can't help but think about the battles between the engineers and the bean counters, internally, at a corporation (GM).

On the pre cups, these are essentially our 'combustion chambers' - think gassers here- so they do create the turbulence for a more complete burn. 'Cause we ain't got no combustion chambers or flame pockets in our pistons. :smile5:

With us raising boost levels and using WAY better turbos (read- more overall AIRFLOW) this is adding the turbulence that would allow us to open up the pre cup opening some. The key is keeping them exactly the same cylinder to cylinder. Kinda like CC'ing heads on a hot rod gasser.

The valve reliefs in the 6.5 pistons are just that, I think, reliefs. Valve/piston clearance had to be addressed in some way. Although, these 6.5's valves are perpendicular to the flat of the piston, so this frees up some interference issues and eliminated the need for combustion chambers.

I'm still getting to know the humble 6.5. :thumbsup:
 
Precups

The reliefs are for the compressed air in the cylinder to be directed into the precup not the other way around . Just think about what you are saying , 400 psi of hot air to ignite the fuel being injected or 2000 psi of ignited gas pushing on the piston . The reliefs have more of an effect on the compressed air than the ignited mixture has on the reliefs . This is the Ricardo (sp) combustion chamber and the 6.9L IHI/Ford has similiar reliefs on their pistons .
 
Interesting stuff

Ah yes. makes sense. Kinda like the theory behind a gasser using a flat top combined with a smallish combustion chamber that is less than half of the diameter of the cylinder bore, going to 'zero deck' height using only the gasket thickness between the piston face and head (though not exactly the case in our IDI diesels). It's often called a 'zero deck' engine. The thinking is the same, with the 'close collision' it creates a WHOOSH of turbulence within the cylinder towards the spark plug and valve area.

That's a round about way for me to wrap my head around it. Have done WAY more gas engine performance than diesel for sure.
 
The "Diamond" Chambers were the final word in the development of the 6.5 TD

Slightly bigger wont really hurt anything. The benefits are going to stop when the port size reaches the width of the inside of the cup.

After this point the flow rates will likely fall off.

The Ricardo bowl in the heads (reliefs) are designed to direct the initial hot gasses that eject from the port around in counter swirling directions. This effectively causes very good mixing of the fuel and all oxygen in the combustion chamber.

The small ports of the 6.2 days had a very high velocity from the air stream and thus better mixing.
The amount of fuel was very conservative too and the two combined to render some very impressive MPG numbers even in Burbs and pickups.

As the demand for Power went up and the Turbo was added the fuel was also increased.

With more fuel to burn the port size increased slowly over time from the original 6.5's of 1992 and then on into the days of the DS4.

The 92 and 93 engines used The "T" cups which have a port that is only slightly smaller than the Diamond cups but also has a slightly different shape on the inside too.

Also the larger port cups have a slightly higher volume inside, which reduces the compression ratio a little bit.

Either the "T" cups or the "Diamond" cups will make real good power and also keep the mileage numbers liveable too.

Running without the cups would be almost impossible due to the head gaskets lack of support in that area.

I suppose that the cup could be hogged out to eliminate the port altogether but the results would likely be POOR.

The amount of design work that has gone into these things was HUGE.
Granted the designs anymore are "crippled" by the ever present pukes at the EPA and of course the "Bean Counters"

If the engineers were left to their own devices and allowed a free hand to work out issues and build things the best that they could, we would see far different engines on the street than we do..

Emissions laws have a severe crippling effect on good design parameters.

Now add to an already crippled engineering department, the bean counters wanting it all out the door on the cheap.

Lets look at another facet of this thing.

GM as well as the others were interested in basically one thing here, the "CAFE" numbers.
By having a few models that could do fairly well on mileage, the bread and butter rigs that only got 12 -14 MPG but that were popular and made them big profits.

The diesel crowd was and is a small segment of the market place, even today after a long run with diesel pickups/SUV's

The largest demand (as long as fuel prices were low) was for the big power SUV's

The 2500 Burbs with 454 BBC's were king for years.

If not for the cost to run one, I would have one of those 500 inch monsters in a Burb.

The old 95 "454" Burb we had was wonderful. It got 9 MPG around town and 14 Hwy
Never at a loss for power though and they were just about as dependable as the sun coming up in the morning.

The diesels have always been a curriosity to many and more of a novelty to most.

To us real diesel buffs that understand and love them, they rule supreme.

Many folks just absolutely hate the added noise and SMELL. Oh yeah, fire the beast up in the garage downstairs and skunk up the whole house.


Just some thoughts


Missy
 
X2. Insightful and somewhat insane. :D:thumbsup: Just the way we roll around here.

Edit: I should speak only for myself... not calling anybody insane here. Just some humor.
 
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Other intersting aspects?

We cannot forget all aspects and the possible interactions. For example, fuel economy and fuel efficiency are not exactly the same thing. The smaller cups are perhaps more fuel efficient at a lower load factor (perhaps less than 150 Hp). Thus this would equal better fuel economy for a rig that is not towing. Perhaps my '93 6.2L pickup at 80 mph with 3.42 gear netting a consistent 28 mpg would be considered light load factor. In general, the larger cups might be more fuel efficient at the higher load factors, like towing your 20k lb trailer? Perhaps another trade off? I suspect there is an interaction with the precup volume, port shape, port size and compression ratio?

Any of you that have owned a small port 6.2L vs. a T-Cup 6.5L will certainly prefer the small port for idling creature comforts at sub-zero temps. My 6.2L would melt the snow off the box from the glow of the cab when idling at 40 below (C or F). My 6.5 can't keep the stats open at 25 below (F). This is clearly a demonstration of fuel efficiency at low load factor. The creature feature is not measured in mpg, it is comfort for sure. I don't have fuel rate info, but I know I didn't put as much fuel in that 6.2 as I do in the 6.5 when either of them spent more time idling than driving.

Our family Suburban is not running yet, but it is a fuel economy experiment without sacrificing creature comfort. We have a couple small creatures in our family. Thus, this project is going together with "fuel mizer" pre-cups.

Hope you find this interesting and enlightening.
 
NODAK

You hit the nail on the head. There are different designs for pre cups that work more efficiently at different load factors and other important engine parameters.

My uncle worked at Detroit Diesel as a design engineer for power, fuel economy, and worked for a little while on the 6.5 when they were turbo charging it.

We have had many interesting discussions about the 6.5 and why things were done the way they were. in theory the 18:1modiifcation is a fuel efficiency killer for our engine, however it does have it's place if one realizes the trade off for a slightly less efficient combustion ratio.

Sadly my uncle passed away last year and my ace in the hole is gone, I did learn quite a bit from him though. :D
 
So in short, we're always compromising to get around the fact that IDI diesels have inherent limitations. Kind of?

Much the same as camshaft, compression, port volume, RPM range is to a gas hot rod. You change one thing, gotta change all the rest to optimize. It's gotta jive...
 
Oh yeah, more thoughts

Well, one could say that another way... DI engines have inherent limitations. Our '02 Jetta TDI and my brothers D'Max are both DI and they act the same as my '95 T-Cup IDI, in that they all don't like to make heat out of a tiny bit of fuel when it is sub-zero (i.e. -30F).

Back 15 or 20 years ago, in the Diesel engine application business, one used to alway's recommend an IDI for light load factors and less than say 100 or 125 Hp. But, if you loaded things heavy or needed more than 150 Hp, you'd go with DI. I guess one could say the larger pre-cup ports are a way of bridging the gap in between there, eh?

IDI can get by with lower injection pressure, that would also equate to lower parasitic injection pump requirement and thus a better fuel mizer.

I think Missy is on track with the emissions requirements as to why the IDI is out of current engineering/production. Coupled with the technology of pilot injection, rate shaped injection, etc. on current DI's, it is clear why the modern push is in the DI direction.

Oh boy, I hear that giant sucking sound about to pull this train of topic.....

Ok, after lobbying for cold weather creature comforts of the fuel mizer pre-cups, one can't forget about the warm weather aspect of same engine... that would be idling with the truck or 'burb' with the air conditioner screaming when it is hot or hot-and-humid. Here is another fuel saving reason for IDI mizer. I've also found that the warm weather creature comfort is significantly enhanced with Kennedy's fan clutch. Granted, we can never keep the radiator package clean enuf. But if you start out clean and put a screen over the grill and the nostrils, you are down on air flow all the time, but at least you can wipe the screen off daily, without a major ordeal. Once you get moving again, assuming you are not towing heavy, the fan clutch backs off without a noticable fuel economy penalty.

Ok... we'll get back on track with pre-cups, but just had to get a few pennies in for the logic of the smaller port pre-cups.
 
Good stuff

I can see virtues of two types of diesel injection now. Very well put. The larger 'ported' cups would in fact bridge the gap for an effective compromise, DI, IDI. As far as fuel atomization (of lack thereof) at lower speeds with the larger 'ported' cups, I wonder if one could gain more efficiency by playing with port shapes more radically than GM did.

Perhaps that's where Hank was going (where it this fella at anyway?) when he CNC milled a set for his engine. Maybe he's like a mad scientist running back and forth between his mill and his truck.:willynilly:

I can envision wet flow testing atomization patterns of various cuts. Reverse taper, hourglass cross section, the reverse of that etc.

Maybe a larger cup opening can benefit from slightly more pressure of a hotrodded DB2 or even a retro fitted 8 cyl. IP... At least my '93 is still mechanical. Hmmm.
 
You know I have truly enjoyed reading this thread. You guys raise questions and post points that keep us all thinking. As some of you might know I right a little freelance here and there for some of the different diesel magazines. This idea about pre-cups and head work on the 6.5 has me very interested as I am sure many of our future 6.5 readers would be interested in. If any of you have done anything outside the standard GM box so to speak and have documented the built with pictures, graphs, dyno runs, ext. I would love to hear about it. I feel it has become my job in the 6.5 community to take what happens here on this forum and convert it into something that will be read by thousands in the magazines. So if you would like to talk with me about any future plans you have or projects you have done, please email me so we can continue to raise awareness that the 6.5 is alive and well.

Thanks,

Ian Carver
[email protected]
 
Slim Shady said:
NODAK

You hit the nail on the head. There are different designs for pre cups that work more efficiently at different load factors and other important engine parameters.

My uncle worked at Detroit Diesel as a design engineer for power, fuel economy, and worked for a little while on the 6.5 when they were turbo charging it.

We have had many interesting discussions about the 6.5 and why things were done the way they were. in theory the 18:1modiifcation is a fuel efficiency killer for our engine, however it does have it's place if one realizes the trade off for a slightly less efficient combustion ratio.

Sadly my uncle passed away last year and my ace in the hole is gone, I did learn quite a bit from him though. :D
Click to expand...

Makes sense there is a trade-off as a given IDI chamber port size is going to have range of flow rates/velocity/turbulence varying w/ mass airflow & rpm. If there is an "ideal" velocity, changing port size is gonna change where that ideal velocity occurs.

I wonder if there is any significant difference in the idling fuel rate of our 18:1 (mine's actually ~19:1) engines? Aren't idling conditions are where you'd expect the biggest difference in IDI chamber turbulence (from lowering comp ratio) to keep the air combusting/peeling away at the diesel droplets sprayed from our relatively low pressure injection system. So there might be enough difference in fuel/air interaction to require slightly more fuel to maintain a given idle rpm?

Beyond cold weather starting differences, I expected lowering compression to hurt fuel economy more than I've seen. Wish the glow plugs (supposedly on the diesel technology horizon) that also have cyl pressure sensing capability were a reality now. I'd be curious to see how different the actual dynamic cyl pressures running down the road are 21:1 - vs - 18:1?

Considering the compression ratio variable by itself, raising comp ratio increases thermal efficiency but the law of diminishing returns is starting to show as comp ratio's go above 17:1. On our IDI 6.5's, lowering compression should give up both some thermal efficiency & a degree of IDI induced turbulence.

I'd been averaging 19 mpg for ~5k miles. Going from 180 to 195 degree stats appears to have gained ~ 1 mpg over the past 2 tankfuls although it's gonna take a couple thousand more miles to have what I consider a meaningful average. Regardless, I didn't expect this truck to get ~20 mpg.
 
Smithville Yeah, its hard to say if fuel rates would need to be changed and how adjustable are they before issues. You could compare commanded fuelrates if you had a scanner with others and probably see just a bit difference. The PCM controls idling fuel metering and adjusts accordingly. Not sure of its range before code and think its moreso a problem if it can't maintain balance. Timing would also affect idle. I think these issues come more into play just off idle initial acceleration or idling down and drivability depending on program parameters and an engines setup (compression ratio, injectors, IP time and program). I have read of mixing and matching and rough idle too that might be more common when an IP can't quickly make adjustments. I sometimes get launching shutter as I launch from idle and my IP is getting long in the tooth. It is mostly affected by fuel quality. I guess cetane, lubricity, and viscosity.

I like the mixing and matching and understanding of interactions. I like 18:1 with 195 stats. The speed of combustion (flame propogation) is also fairly dependant on combustion temperatures - this would also affect precup exit velocity I would think. Earlier timing builds more heat right... so early timing might make up for velocity issues bigger of precup mixing.
 
schiker said:
Smithville Yeah, its hard to say if fuel rates would need to be changed and how adjustable are they before issues. You could compare commanded fuelrates if you had a scanner with others and probably see just a bit difference. The PCM controls idling fuel metering and adjusts accordingly. Not sure of its range before code and think its moreso a problem if it can't maintain balance. Timing would also affect idle. I think these issues come more into play just off idle initial acceleration or idling down and drivability depending on program parameters and an engines setup (compression ratio, injectors, IP time and program). I have read of mixing and matching and rough idle too that might be more common when an IP can't quickly make adjustments. I sometimes get launching shutter as I launch from idle and my IP is getting long in the tooth. It is mostly affected by fuel quality. I guess cetane, lubricity, and viscosity.

I like the mixing and matching and understanding of interactions. I like 18:1 with 195 stats. The speed of combustion (flame propogation) is also fairly dependant on combustion temperatures - this would also affect precup exit velocity I would think. Earlier timing builds more heat right... so early timing might make up for velocity issues bigger of precup mixing.
Click to expand...

I also went up approximately 1 mpg by going from the 180 to 195 thermostat. Thermal efficiency is what we have to start looking at not just the standards we have taken into account in the past. More cylinder temperature and better efficiency? Well that opens a can of worms doesn't it. Hope the EPA guys don't read this thread NOX will be through the window:D
 
Wouldn't you think the higher coolant temp basically results in better fuel economy due to less heat robbed out of the cylinder into the cooling system?

Besides the cylinder walls being surrounded by coolant, there's the additional comb chamber surface area the IDI chambers add - pulling out heat into the coolant.

I started out w/ the 180 stats because they came with my HO water pump & dual stat crossover kit. In 100 degree summer temps, my coolant temps while towing were always under control, so I'd been meaning to get 195's swapped in. If the +1 mpg continues long term (& Slim's results suggest it will), I should have swapped the 195's in earlier.

With almost 11 qts oil capacity & the bigger 48 stacked plate oil cooler, I also like the idea of a warmer coolant temp to help hold oil temps somewhat warmer. Went to the bigger cooler for additional peak cooling capacity, but oil that's too cool can be just as much a problem & that 11 qts is somewhat of a temp buffer - both gaining & loosing temp more slowly than the engine coolant/antifreeze/water. I suspect my setup will prolly benefit from something blocking airflow across the oil cooler when outdoor temps head below zero.

No doubt higher cylinder pressures result in higher NOx. Believe the IDI design inherently results in some residual exhaust gas left in the prechamber, so there's a little EGR effect in that.
 
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