Engine/Transmission (1994 - 1998) right gear ratio?

[HBarlow]

I think cerberusiam is a politician. He changes the subject and the focus of the argument in every post.

He reminds me of the old advice I learned as a young sailor; "if you can't baffle them with briliance dazzle them with bullship. "

 

[cerberusiam]

Are you guys engineers or lawyers?

Your still reading so there must be some attraction, however visceral it may be.

I think cerberusiam is a politician. He changes the subject and the focus of the argument in every post.

This from the self appointed post police who can't address the issue at hand thru lack of experience, and doesn't understand the term "jerk pump". The IRONY is sooooo rich!!!! :-laf:-laf

 

[hsmith]

Fun, huh. Oh, I forgot, I ain't sain nuttin!!!!!

 

[hsmith]

Or is it, I told you so.

 

[cerberusiam]

Or is it, I told you so.

Just another day at the office.

 

[HBarlow]

My Initial Statement and the Proof

Here is what I wrote:

You should recheck your facts. Torque curves for the various engines used to be published on the Cummins website and in Dodge truck brochures every model year.

All 24 valve engines used in Dodge Rams produce maximum torque from 1600 to 2700 rpm in a wide flat band.

All HPCR engines used in Dodge Rams produce peak torque from 1600 to 2700 rpm.

All ISB6. 7 Dodge Ram pickup engines rated at 350 hp /650 tq produce peak torque from 1500 rpm to 2700 rpm.

ISB6. 7 engines of the 305 hp version used Dodge Ram cab and chassis trucks produce peak torque from 1600 to 2700 rpm.

You are mistaken. They absolutely DO pull hard at 1600 rpm, that is where peak torque first occurs.

I've never owned a 12 valve engine and am not certain about where their torque band begins and ends but I do know it is much narrower than 24 valve engines. I think it begins at 1500 or 1600 rpm but tapers off by around 2400 rpm.

Electronic engines which are all 24 valve and HPCR engines do not have a torque PEAK as you stated. Their maximum torque is produced in a wide flat band from 1600 (or 1500) rpm up to 2700 rpm because 24 valve engines breathe better at higher rpm and because the magic of computers allows the control of fuel and air to maintain a flat torque platform.

and here is the proof:

Cummins Every Time - Ram - 6. 7L Turbo Diesel

 

[AClayton]

Harvey,



I think the point that cerberusiam is trying to get you to understand is that flywheel rated hp and tq will not match true dyno results as measured to the wheels of your truck. There are way too many variables along the length of the drivetrain that can skew the readings on a chassis dynometer. A truck with 3. 42's and the same truck with 4. 10's will show different readings on a chassis dynometer even though they both have the same Cummins engine under the hood. An auto and a manual will give dfferent readings with the same ratio and same engine under the hood.



Both of you are right!!



Not a sermon... ... just a thought!!



Alan

 

[HBarlow]

Of course there will be different readings at the wheel but the differences will primarily be the result of torque multiplication due to the gear the truck is on or due to slippage at the tires or through an automatic transmission or manual clutch.

A rear wheel dynamometer is not going to alter the fundamental torque curve of a low rpm long stroke Cummins engine that produces peak torque in a wide band from around 1500 rpm to 2700 rpm to something like a V8 that has a torque peak at much higher rpm.

In addition, we have no idea what engine was tested on a chassis dyno, what condition it was in, or what modifications or limitations it may have had.

Personally I would put far more trust and confidence in engine dyno testing in the factory by Cummins engineers under controlled conditions than a portable chassis dyno hauled around the country and set up for events.

All this long discussion results from another poster stating here that I was incorrect, that a Cummins engine does not produce low rpm torque but has a torque peak at something like 2000 rpm. That is not true and is not going to become true.

Even the graph he posted demonstrated exactly what I have been saying except for a tiny little bump at 2000 rpm, hardly peak torque for practical understanding.

 

[fest3er]

MDTDC's dyno events have shown time and again that gearing and tire size* only move HP earlier or later on the graphs with respect to engine RPM.

Everything else equal, the torque (work) the engine produces will be the same regardless of driveline gearing. The main exception is how much time the turbo has to spool up; a higher final drive ratio doesn't always give 'slower' turbos enough time to spool up, so those engines may well produce less torque and power on a dyno.

Most diesels don't turn fast enough to produce lots of torque multiplication through a torque converter. That's why the quicker drag racers lock up the TC clutch 20-40 feet after launch while they're still in 1st gear.

* - If you think about it, the effect of a taller or shorter tire effectively changes the final drive ratio; thus tire diameter and driveline gearing can be considered the same thing for this purpose.

 

[cerberusiam]

In addition, we have no idea what engine was tested on a chassis dyno, what condition it was in, or what modifications or limitations it may have had.

In the same vane we have no idea of the conditions at the time of the engine test, condition of the dyno, sobriety of the operator, atmospheric conditions, etc. One engine dyno result versus HUNDREDS or chassis dynos, validation is in the numbers.



Engine dyno results differ in the same way an accelerometer dyno will differ from a load dyno. When one understands what they are trying to portray and how they relate to what we are doing with the trucks THEN one knows what to believe, its self evident.

 

[LVJUNIOR]

If I could come close to the torque curves you guys are posting I would be ecstatic. Mine looks like a triangle

View attachment 75723

 

[JohnBoy5]

His Auto trans will take it and take it all day long. Dave G. built it. I pull MUCH MUCH heavier then that all day with mine and quite a few HP mods and more to come... Ticking like a Swiss watch still!

 

[JohnBoy5]

You can't pull that weight at those rpm's and not trash the transmission, it won't take it. For towing you need to be over peak TQ and out of the harmonics range of about 1700-1900 rpm's. This is why its geared the way it is, to save the hardware. Adjust to run at about 2000-2100 rpm's in OD\lockup at your targeted hiway speed, thats the sweet spot for efficiency.



Use the lockup to adjust between 3rd and OD, locked drive and unlocked OD make the splits a lot better but you have to have the TC to get the TQ multiplication right or it flares too much.



No, the 6 speed just had a smaller jump from 1:1 to OD, still a crappy split.

His Auto trans will take it and take it all day long. Dave G. built it. I pull MUCH MUCH heavier then that all day with mine and quite a few HP mods and more to come... Ticking like a Swiss watch still!

 

[cerberusiam]

If I could come close to the torque curves you guys are posting I would be ecstatic. Mine looks like a triangle

OH LOOKY!!! A 12V with a TQ peak at 2000 rpms ad a large hump instead of a flat curve.



Hmmmm... . wonder where that was suggested?

 

[glhs]

Everytime you modify a Cummins with turbos, housings, intake horns, fuel plate, injectors, cams, etc. , the factory torque and hp curves no longer apply.



As you get higher in elevation the same thing happens.



For instance, with my 62/71/14 turbo I can run the rpms down to 1200 in Vegas but, driving through the Rockies I very seldom can run it below 1900 and hope to pull a grade.



Back to the topic;



A better cam could make the sweet spot bigger.

Gear Vendors overdrive?

Different size tires?

Smaller/better turbo?

4:10's?

New truck?:-laf:-laf:-laf