Att dyno results

[Slim Shady]

It doesnt matter what the horsepower is. Torque is a function of force and distance. A long crank arm (stroke) and a high force (burning lots of fuel) will make big torque. Torque is not RPM dependent, but horsepower is, and at higher RPM you can burn more fuel in a given time to make more total power. Having torque early just means your injection pump is capable of outputting fuel early on and you have the oxygen to burn it. I think the DB2 is more RPM dependent than the DS4. As RPMs increase transfer pressure and advance increases allowing more fuel to be injected. Thats partly because of higher pressure and partly due to earlier injection likely rides on a steeper part of the cam ring lobe, allowing more travel of the plunger in the given injection event. So cam ring profiles are a big factor of where you get the most fuel. That happens to be how GM made the "high output" DS4-5068 spit more fuel at low-mid RPMs, with a different cam ring.

My point exactly, the 6.5 is a short stroke big bore engine. "Over square" if you will. I just think the number 438 at 1800 rpm may have been an error. I don't see any of the dyno results posted coming anywhere close to that in any combination. Unless I missed one?

Are we moving this post to a more appropriate discussion topic? MODERATORS???

 

[6.2 turbo]

My governor is solid. Its more of a timing issue.

 

[WarWagon]

I think that's a big contributing factor, but I have to agree maybe not all of it. Has anybody ever done a side-by-side comparison of a 6.9L /7.3L IDI precup against a set of Diamond 6.5L precups? I'd love to see measurements / specs of the two side by side. Perhaps that "oh-so-important" hole exiting to the cylinder bore is larger on the IH than compared to the 6.5L

1986 6.2 military head on the left, 6.5 NA head on the right, and 1995 6.5 turbo precups sitting on the heads. The OP has something similar to the 6.5 NA precups.

It makes a big difference where the 6.2 precups smoke like crazy with higher fuel. Yet as designed the MPG could be around 25 MPG 6.2 NA. I have run all 3 precups and the 6.2 cups smoke slightly more with a GM3 and the same fuel settings. The MPG at full power is the same ~7MPG. Light power is where the difference is. Bigger turbo's and more fuel you run out of time to get the air in and out of the 6.2 NA precups.

My 1993 with the 6.5 NA precups runs like a raped ape. The 1995 with the double wammy of 3.73's and the 6.2 precups runs in the upper end but smokes. Even with a different HX40II turbo. It also has a 4" soot trap that did not make a difference. It is bad enough for me to seriously consider pulling the engine to change precups. (Head studs make it easier to pull the engine.)

I am sure the injector angle 6.2 vs 6.5 is also a factor on the 1995. How and how much of a factor I do not know.

 

[Slim Shady]

http://www.google.com/url?sa=t&rct=...jr3VCQ&usg=AFQjCNHm8A5y4XSkLdvUnUfHqHatZbGr8A


Look at the torque and horsepower ratings on page 24 through 27.

Also some more numbers from a actual dyno run. http://www.youtube.com/watch?v=43CDDHC5Jr0



My point is I don't see those numbers in real life data!

 

[buddy]

Although dont miss the point that torque is not RPM or horspower dependent. If you can get the fuel in and burn it, there will be high torque.

I would consider it a large bore but not a short stroke, compared to some other diesel engines, perhaps and some other big blocks, but in general its not a short stroke. The 6.5 does not mirror other gas big blocks. It uses diesel, which contains more BTU than gas. It has the turbo, and does not have valve overlap to assist getting more air in so that you can burn more fuel. So air to burn fuel is solely dependent on displacement and boost.

Ian's 6.5TD truck made almost 600ft-lbs of torque at 2300rpm at the rear wheels, so he likely had over 430ftlbs at 1800rpm at the rear wheels, and his extra fuel of propane probably kicked in gradually until 2300rpm. He had a GM4 turbo and a NOS of course. When you get the fuel in, and have the air to support it is when you get the torque. GM's stock fueling with DS4s peaked at 1800rpm and the GM8 could build 10psi boost by 1800rpm, so it makes sense that their torque curve peaked at 1800rpm. When we turn up fuel, and that can be RPM dependent, then more fuel later could yield more torque later. And if more boost happens later then more fuel can be burnt later.

 

[Slim Shady]

Although dont miss the point that torque is not RPM or horspower dependent. If you can get the fuel in and burn it, there will be high torque.

I would consider it a large bore but not a short stroke, compared to some other diesel engines, perhaps and some other big blocks, but in general its not a short stroke. The 6.5 does not mirror other gas big blocks. It uses diesel, which contains more BTU than gas. It has the turbo, and does not have valve overlap to assist getting more air in so that you can burn more fuel. So air to burn fuel is solely dependent on displacement and boost.

Ian's 6.5TD truck made almost 600ft-lbs of torque at 2300rpm at the rear wheels, so he likely had over 430ftlbs at 1800rpm at the rear wheels, and his extra fuel of propane probably kicked in gradually until 2300rpm. He had a GM4 turbo and a NOS of course. When you get the fuel in, and have the air to support it is when you get the torque. GM's stock fueling with DS4s peaked at 1800rpm and the GM8 could build 10psi boost by 1800rpm, so it makes sense that their torque curve peaked at 1800rpm. When we turn up fuel, and that can be RPM dependent, then more fuel later could yield more torque later. And if more boost happens later then more fuel can be burnt later.

I agree torque is not rpm or horse power dependent, but the 6.5 does not have the mechanical attributes as a design to get those torque numbers in real life.

I would have to see the dyno sheet to believe that. I am not taking someone's word on that one. LOL Call me a doubting Thomas but that I have to see in print to believe. Nothing stock I have ever seen or looked at in the gm 6.5 L made 438 foot pounds of torque at 1800 rpm. I am not saying it isn't possible and Ian probably came close with the propane and NOX but that is no where near close to stock fueling. That is what we are talking about, isn't it or are we talking about possible scenarios based in theory, not actual dyno run data. I would think the military would want the most torque down low. The charts certainly didn't show the 438 flb we are talking about and they were using JP-8 and diesel. Please show me a dyno sheet that shows the 438 torque at 1800 rpm for our 6.5. I just have never ever saw a 6.5 gm make that on a real dyno.


Also Oversquare or short-stroke engine

An engine is described as oversquare or short-stroke if its cylinders have a greater bore diameter than its stroke length - giving a ratio value of greater than 1:1.
For example an engine which has 100 millimetres (3.94 in) bore and 80 millimetres (3.15 in) stroke has a bore/stroke value of:
100 mm / 80 mm = 1.25:1An oversquare engine allows for more and larger valves in the head of the cylinder, lower friction losses (due to the reduced distance travelled during each engine rotation) and lower crank stress (due to the lower peak piston speed relative to engine speed). Due to the increased piston- and head surface area, the heat loss increases as the bore/stroke-ratio is increased excessively. Because these characteristics favor higher engine speeds, oversquare engines are often tuned to develop peak torque at a relatively high speed.
The reduced stroke length allows for a shorter cylinder and sometimes a shorter connecting rod, generally making oversquare engines less tall than undersquare engines of similar engine displacement but wider and longer (for engines with vertical cylinder axes).
By changing the crankshaft and modifying the connecting rod(s), piston(s) and/or engine block an engine can be "de-stroked". This reduces the displacement and consequently the torque of the engine, but can allow it to run at higher speeds and in fact develop greater peak power.


[edit]


For the informed reader. the difference between gas an diesel engines.

http://auto.howstuffworks.com/question381.htm


I am still not convinced. I would still like to see that torque curve plotted out on the 6.5 L 438 foot pounds of torque at 1800 rpm, with 150 horse power. We just don't have the lever arm to generate that kind of torque in the stock parameters.


Reading on long and short stroke motors with definition. [/FONT]http://en.wikipedia.org/wiki/Stroke_ratio



Undersquare or long-stroke engine

An engine is described as undersquare or long-stroke if its cylinders have a smaller bore (width, diameter) than its stroke (length of piston travel) - giving a ratio value of less than 1:1.
For example an engine which has 90 millimetres (3.54 in) bore and 120 millimetres (4.72 in) stroke has a bore/stroke value of:
90 mm / 120 mm = 0.75:1At a given engine speed, a longer stroke increases engine friction (since the piston travels a greater distance per stroke) and increases stress on the crankshaft (due to the higher peak piston speed). The smaller bore also reduces the area available for valves in the cylinder head, requiring them to be smaller or fewer in number. Because these factors favor lower engine speeds, undersquare engines are most often tuned to develop peak torque at relatively low speeds.
An undersquare engine will typically be more compact in the directions perpendicular to piston travel but larger in the direction parallel to piston travel.
An engine can be "stroked" by replacing the crankshaft with a so-called "stroker" crankshaft and modifying the connecting rod(s), piston(s) or engine block to accommodate the increased piston travel. This increases the displacement and therefore the torque of the engine, but may reduce the peak speed at which it is safe to run.



Just my humble opinion, I can't change what I have known about cars, trucks and heavy equipment. Now if everything I thought I knew is wrong then I apologize in advance for being an ass.

 

[Edzzed]

I assume you could change rear wheel torque by putting smaller diameter wheels on it. I once took an 81 tbird with stock 14 inch wheels and put mustang 13 inch wheels on it for giggles. I could spin the tires much easier. I would have tried 12 inch (if they made them) to see what happens but me thinks clearance for the brakes would have been an issue.

 

[Slim Shady]

I assume you could change rear wheel torque by putting smaller diameter wheels on it. I once took an 81 tbird with stock 14 inch wheels and put mustang 13 inch wheels on it for giggles. I could spin the tires much easier. I would have tried 12 inch (if they made them) to see what happens but me thinks clearance for the brakes would have been an issue.

Excellent example of final gearing or gearing in general. Gearing an engine to maintain the peak torque and efficiency designed into the motor is the key, Other wise if the 6.5 made 438 foot pounds of torque at 1800 rpm anything over that would in "theory" become inefficient and we would need more gears to go faster or gain speed. Big over the road trucks are a prime example of that low rpm torque motor. I see now how just torque or horse power numbers are just part of the whole equation.

 

[Edzzed]

Excellent example of final gearing or gearing in general. Gearing an engine to maintain the peak torque and efficiency designed into the motor is the key, Other wise if the 6.5 made 438 foot pounds of torque at 1800 rpm anything over that would in "theory" become inefficient and we would need more gears to go faster or gain speed. Big over the road trucks are a prime example of that low rpm torque motor. I see now how just torque or horse power numbers are just part of the whole equation.

that is one of the reasons ships and trains use electric motors to turn the props and wheels. having to add that many gears to get the proper power to whatever needs to be turned would add huge amounts of weight not to mention that many more parts that can break.

 

[buddy]

430ft-lbs is simply the stock rating on a curve out there, and yes it shows 150hp at 1800rpm. Maybe its wrong, maybe not. Could show how much fuel has changed since then, or how much drivetrain loss there is. The point about Ians truck is that fuel and oxygen dictates when peak torque is. With 430ftlbs at the flywheel, you would expect to see around 360-370ft-lbs at the rear wheels. What RPM did Green Machine hit his 359ft-lbs using the GM4 and a primitive BD chip that could have been little more than stock.

The same wiki page the info is copied from says this "oversquare engines have a reputation for being high-strung, low-torque machines" and opens with
"While the stroke ratio can provide insight into the goals of an engine's designer, it has no direct effect on the speed at which an engine reaches maximum torque"

The military document posted shows peak torque on NA mechanical injection engine at 1600rpm. And the NA version produced 300ft-lbs at 1600rpm with ULSD. Throw in 30% more fuel, more advance and boost from a turbo and I could see how GM got 430ft-lbs at the flywheel at 1800rpm, using LSD that probably used to have higher cetane to boot.

 

[Slim Shady]

430ft-lbs is simply the stock rating on a curve out there, and yes it shows 150hp at 1800rpm. Maybe its wrong, maybe not. Could show how much fuel has changed since then, or how much drivetrain loss there is. The point about Ians truck is that fuel and oxygen dictates when peak torque is. With 430ftlbs at the flywheel, you would expect to see around 360-370ft-lbs at the rear wheels. What RPM did Green Machine hit his 359ft-lbs using the GM4 and a primitive BD chip that could have been little more than stock.

The same wiki page the info is copied from says this "oversquare engines have a reputation for being high-strung, low-torque machines" and opens with
"While the stroke ratio can provide insight into the goals of an engine's designer, it has no direct effect on the speed at which an engine reaches maximum torque"

The military document posted shows peak torque on NA mechanical injection engine at 1600rpm. And the NA version produced 300ft-lbs at 1600rpm with ULSD. Throw in 30% more fuel, more advance and boost from a turbo and I could see how GM got 430ft-lbs at the flywheel at 1800rpm, using LSD that probably used to have higher cetane to boot.

Now I agree with all of that. However everything we see is peak torque and without that graph we don't know where that peak torque falls. The point I was trying to make.

 

[Twisted Steel Performance]

Nice thread,...... I haven't started a build thread yet, but I have started the build, has anyone used other than stock precups??? My GEP had military square cups and I had them machined out to .850" .. about .100" wider than diamond cups...

I am thinking that with my DB2833 pump being "re-worked" by Unique Diesel, being set up at 375 hp, and my Pro HX40W turbo, I should be able to supply plenty of fuel & air in the lower RPM range... thus giving me a little more torque down low for towing... I will be using Kennedy's 18:1 pistons also...

Any thoughts toward the idea of a larger mouth on the precups helping with allowing for a quicker burn rate ???

 

[nmb2]

This is just an observation, obviously I don't have a DD.... but you guys seem to be focused on the pre-cups way too much. International made the cups bigger to reduce emissions....

All the pre-cup is responsible for is the first 20-30% of your burn, and helping to atomize the fuel. The larger you make the cup, the more fuel can burn in the cup, reducing smoke and emissions, but also reducing power potential.

 

[buddy]

This is just an observation, obviously I don't have a DD.... but you guys seem to be focused on the pre-cups way too much. International made the cups bigger to reduce emissions....

All the pre-cup is responsible for is the first 20-30% of your burn, and helping to atomize the fuel. The larger you make the cup, the more fuel can burn in the cup, reducing smoke and emissions, but also reducing power potential.

I do not believe this is true. GM used larger precups on NON-Emissioned trucks that had more fuel output and higher power ratings. We have members that have already experimented with porting the cups larger with some feedback of better results. there is a thread on that somwhere. Conversely, I have worked with a member that has a 6.2 engine with smaller precups than ever came on a 6.5 and we cannot get it to burn as much fuel as 6.5 engines. It accepts more than stock fuel alright and makes good power up to a point where it just stops burning more fuel and produces tons of smoke at any RPM or injection timing with 17+psi of boost from 3 different turbo sizes. We could pull serious grades with a heavy trailer behind us no problem, but put in a little more fuel and on came the smoke and EGTs through the roof.

The size of the opening also dictates how fast the fuel and air crammed in it can expand into the cylinder. The faster it can expand the more combustion you can get at higher torque angles and the faster your fuel can mix with the air in that crunch space. There are also exhaust gases left in the precup when the exhaust valve closes before TDC, and so its not going to be all fresh air to aid in combustion. Better to get it out of the precup as fast as possible.

 

[nmb2]

I do not believe this is true. GM used larger precups on NON-Emissioned trucks that had more fuel output and higher power ratings. We have members that have already experimented with porting the cups larger with some feedback of better results. there is a thread on that somwhere. Conversely, I have worked with a member that has a 6.2 engine with smaller precups than ever came on a 6.5 and we cannot get it to burn as much fuel as 6.5 engines. It accepts more than stock fuel alright and makes good power up to a point where it just stops burning more fuel and produces tons of smoke at any RPM or injection timing with 17+psi of boost from 3 different turbo sizes. We could pull serious grades with a heavy trailer behind us no problem, but put in a little more fuel and on came the smoke and EGTs through the roof.

The size of the opening also dictates how fast the fuel and air crammed in it can expand into the cylinder. The faster it can expand the more combustion you can get at higher torque angles and the faster your fuel can mix with the air in that crunch space. There are also exhaust gases left in the precup when the exhaust valve closes before TDC, and so its not going to be all fresh air to aid in combustion. Better to get it out of the precup as fast as possible.

I digress.....

the cup size matters to a point. I didn't mean to say to use the smallest cup you can. However, going too large WILL have adverse effects. You have to keep the cups functional... the bigger you go, the less functional they become, so there is a fine line.

I searched around but couldn't find it, has anyone actually CC'd your cups? I seem to remember reading the biggest cups were used in the military engines. I'm in the army, I have a lot of seat time in hmmwv's... and the 6.5's both N/A and turbo in them are the lowest emission, most gutless engines I have ever driven.

On another note, I use the smaller of the cups available for the IH engines. I also put out almost 650rwtq through a CC Dually on fuel only..... so please understand where I am coming from.

EDIT:

On another note, what aftermarket cams do you guys use? I tried finding your stock specs but couldn't. I know that your stock cam has a narrow LSA. Camshaft has a huge impact on IDI performance once turbocharged.

 

[buddy]

I digress.....

the cup size matters to a point. I didn't mean to say to use the smallest cup you can. However, going too large WILL have adverse effects. You have to keep the cups functional... the bigger you go, the less functional they become, so there is a fine line.

I searched around but couldn't find it, has anyone actually CC'd your cups? I seem to remember reading the biggest cups were used in the military engines. I'm in the army, I have a lot of seat time in hmmwv's... and the 6.5's both N/A and turbo in them are the lowest emission, most gutless engines I have ever driven.

On another note, I use the smaller of the cups available for the IH engines. I also put out almost 650rwtq through a CC Dually on fuel only..... so please understand where I am coming from.

EDIT:

On another note, what aftermarket cams do you guys use? I tried finding your stock specs but couldn't. I know that your stock cam has a narrow LSA. Camshaft has a huge impact on IDI performance once turbocharged.

Well there was no difference in the cam from NA to turbo engines, and you would have been laughed away if you brought it up a year ago. Our high compression leaves little room for valve clearance which is why there is a large gap between exhaust closing and intake opening, negative overlap. That, the high compression and low pop injectors also makes boosting them to the moon rather destructive.

The military had heavy vehicles and primarily mechanical injection. The civilian trucks can be quite quick.

The military did not use the largest cups available either, the NA cup is smaller than the turbo cup in civilian trucks. I do not know what precup the military used in turbo applications, but the Turbo "diamond" cups we use already have larger mouths than the Ford cups. If larger cups reduce emissions, does it do that by getting a more complete burn?

Appropriately titled "porting precups"

Hank said his truck picked up considerable grunt with just the precup porting. I'm not saying to go direct injection, and there are some priciples to maintain on them, like making sure they converge on the flame guide rather than diverge out towards the cylinder walls. Basically, its just good to ensure you have the diamond cups when messing with the heads. Smaller could hold you back. A few people have gone bigger than diamonds, like Hank.

 

[littleboy]

Well there was no difference in the cam from NA to turbo engines, and you would have been laughed away if you brought it up a year ago. Our high compression leaves little room for valve clearance which is why there is a large gap between exhaust closing and intake opening, negative overlap. That, the high compression and low pop injectors also makes boosting them to the moon rather destructive.

The military had heavy vehicles and primarily mechanical injection. The civilian trucks can be quite quick.

The military did not use the largest cups available either, the NA cup is smaller than the turbo cup in civilian trucks. I do not know what precup the military used in turbo applications, but the Turbo "diamond" cups we use already have larger mouths than the Ford cups. If larger cups reduce emissions, does it do that by getting a more complete burn?

Appropriately titled "porting precups"

Hank said his truck picked up considerable grunt with just the precup porting. I'm not saying to go direct injection, and there are some priciples to maintain on them, like making sure they converge on the flame guide rather than diverge out towards the cylinder walls. Basically, its just good to ensure you have the diamond cups when messing with the heads. Smaller could hold you back. A few people have gone bigger than diamonds, like Hank.

Buddy, if precups are so important, how did 6.2turbo make such good power and boost on the 6.2 precups????

 

[buddy]

Buddy, if precups are so important, how did 6.2turbo make such good power and boost on the 6.2 precups????

Anythings possible I suppose, including bending a bunch of rods. Not having seen his truck run I couldnt tell you how it compares in good power. He uses smaller exhaust housings than standard on the turbo to get drive pressure up. He also had considerable fuel output, as I had guessed he had about 110mm^3 of fueling, and more down low to create a lot of drive pressure. Without modifying the pumps you cannot get that kind of fueling.

 

[Cumminsfever]

Anythings possible I suppose, including bending a bunch of rods. Not having seen his truck run I couldnt tell you how it compares in good power. He uses smaller exhaust housings than standard on the turbo to get drive pressure up. He also had considerable fuel output, as I had guessed he had about 110mm^3 of fueling, and more down low to create a lot of drive pressure. Without modifying the pumps you cannot get that kind of fueling.

So what you're saying is- with higher fuel rates, and better turbo, it don't matter what precup is used?

6.2turbo noted more turbo lag, and more smoke with his larger (t ?) precups.

And just for clarification, 6.2turbo is using STANDARD 16cm turbo housing. Keep your facts strait buddy.

 

[nmb2]

Well there was no difference in the cam from NA to turbo engines, and you would have been laughed away if you brought it up a year ago. Our high compression leaves little room for valve clearance which is why there is a large gap between exhaust closing and intake opening, negative overlap.

I wouldn't call it negative overlap. The reason I ask is because I designed the first "turbo cam" for the International IDI. It is HUGE in comparison to stocker, and was laughed at, told it would never fit.

That being said, I called my cam grinder, your cams are .416"/178 int, .416"/202 exhaust, with a 110LSA. That's actually not too bad. It could definitely be improved upon.

As a comparison, the IH IDI is .380"/185, .380"/185 with a 105LSA

The military did not use the largest cups available either, the NA cup is smaller than the turbo cup in civilian trucks. I do not know what precup the military used in turbo applications, but the Turbo "diamond" cups we use already have larger mouths than the Ford cups. If larger cups reduce emissions, does it do that by getting a more complete burn?

Larger cups generally reduce emissions by burning more of your fuel in the cup itself... as much as 40-50%. In a high performance app, this is not what you want. That's why I said its fine line....you need the cup functional enough to only start the burn, and atomize the fuel to be pushed out into the main chamber where it will be used as power. You are not getting your torque from the explosion pushing out of the cup itself....

The other thing not being addressed here that I could tell is the cup volume, which is more important than the mouth.

Appropriately titled "porting precups"

Hank said his truck picked up considerable grunt with just the precup porting. I'm not saying to go direct injection, and there are some priciples to maintain on them, like making sure they converge on the flame guide rather than diverge out towards the cylinder walls. Basically, its just good to ensure you have the diamond cups when messing with the heads. Smaller could hold you back. A few people have gone bigger than diamonds, like Hank.

Thats the thing about seat of the pants. Its not consistent, and its not factual. Not to try and discount what Hank said, but without a real back to back dyno its impossible to know truthfully the differences.