Engine/Transmission (1994 - 1998) Dyno info

[pwerwagn]

i was goin to take my truck to the dyno the other day and the guys there told me that they can give me a hp figure but no torque figure because they have no capability to get an rpm reading on a diesel. Just wondering if any of you have ran into this problem?

also, how does a G-tech work in our trucks? Just curious because it picks up the rpm signal from the cig lighter, but ours has no signal, so does that mean it has no rpm ability?

 

[JGK]

There is an RPM sensor on our trucks (it runs the tach). It is above the vibration damper. You can see it from above. It has 2 or 3 wires coming out of it. One of those will provide a signal if you have the proper inductance clamp thingy. It can't be one like used on a spark plug wire because the voltage is so much smaller on our trucks, but same idea.



However, most dyno shops that aren't set up to deal with our trucks use a light and pickup device and a piece of reflective tape on the damper. It's common to try to mount this source/pickup device to some sort of clamp or magnetic base, afix that to the oil pan or some such and aim it at the tape. But the violence of the engine under a power run usually shakes it out of alignment. The best approach I've seen for the money is to use a cinder block or two under the front of the truck and a chunk of heavy flat steel on top. Then use a magnetic base to hold the light source/pickup and stick it to that steel plate. Then just aim it at the edge of the damper with the reflective tape.



We had a whole dyno day run that way last spring. Worked on every truck Dodge, Ford, GM).



-Jay

 

[pwerwagn]

Makes sense.

What I now wonder after thinking about it is this, and please correct me if im wrong. HP can be figured using Velocity over a period of time and using kinetic energy (much like the G-tech does) and then be converted to torque using the formula (torque=(hpxrpm)/5252)). But when using a dyno, torque is what your are reading and hp is what you are deriving based off that same formula correct? Basically, I cant see how horsepower can be figured with a dyno without knowing the torque output. So basically a G-tech gets hp and derives torque, and a dyno reads torque and derives hp. So, a g-tech wont work in our trucks, right?

 

[Nick2]

A G-tech will work in our trucks, it DOES NOT get the RPM through the cig lighter. It does not measure RPM. It is an accelerometer (spell?)... which basically means it derives HP by calculating changes in velocity (acceleration) per vehicle weight. It's like calculating HP from you 1/4 mile MPH and truck weight. Long story short, with an accurate vehicle weight, the G-tech should give you a fairly accurate HP number.

 

[pwerwagn]

yeah, accelerometer was the word i was lookin for. But the newer G-tech's (maybe the older ones too, dont know) do give torque readings on a gas engine right? But they cant on a diesel because of no rpm signal.

 

[Berrigan]

Ya they can



The alternator is generating ac and the diodes rectify it to dc for charging. This creates a pulsating dc that can be monitored by the G-tech. When you first set up the g-tech the instructions say to rev your engine to a certain rpm. Then to another rpm. The g-tech memorizes your pulses and calculates any rpm. It is accurate but only to that vehicle. As you may have guessed the pully sizes under the hood of differebt vehicles vary and you have to calibrate it to vehicle 1, vehicle 2 etc. I have a g-tech and when I do runs the graph shows my shift points at 3k and that is what the factory tach says also. They really are amazing. Bill

 

[JoshPeters]

I have a G-tech. I wondered on it's accuraccy. I went out on a back road checked for the "locals" and then gave it a few 1/4 runs. Best of 15. 3 at 88mph. A month later I went to Muncie. Best of 15. 3 at 89. 3. Pretty accurate I'd say.



Josh

 

[Berrigan]

What I like are the HP,TQ RPM graphs. You can see the corrilation between torque and acceleration rates. Great for doing bombing or tweeks then checking for performanve improvements.

 

[Nick2]

I have one of the older models, no torque reading. I see what berrigan is saying though with the newer ones. crazy stuff

 

[pwerwagn]

Maybe I'll get a new G-tech to try out then.

Anyone know why the dyno place said they can get hp and not torque from my truck?

 

[DavidTD]

It sounds like it is a Dyno Jet. A dyno Jet measures HP and calculates Torque based on HP measured at a given RPM. To read RPM on a diesel, the tape and sensor are used but this is optional equipment and not all dyno Jet owners have them.

 

[tgrfan2]

JGK, sounds like you have some experience with this. I have a debate going with a Dmax friend. My 47re is stock and original with 139K. With the engine stock I had no slippage pulling my fiver. Added the #6 plate in stock position, adjusted my transmission pressure per Bill K's web site, and still get slippage at 26# boost on hills. I was wondering if anyone could tell me the approximate torque at that boost at 2000rpm. I am assuming I am still not at the TST chart 650#. I showed him where the Allison web site still specs the 1000 at 520# and of course he thinks the Dodge autos are trash. I just need some ammo to at least make him as quiet as his Isuzu engine!

I also heard the new 605# Dmax limits torque to 520# in 1st & 5th gear. Anyone else heard this?

 

[JGK]

tgrfan2,



Can't comment on the transmission from personal experience since mine's a 5spd. (I do have a friend who's not a member with a '98 auto who's been in and out of his more times than he can count trying to get it perfect for racing at the local 1/4 mile track. He can probably offer answers to specfic questions if a member here doesn't. ) But you might go out to the Dmax site and do some searchs on transmission issues. Let his own brethren hand you ammo. I've heard the Allison is not as ideal as was originally expected.



The only way you're really going to know where your at as far as power goes is to get it dyno'd. To me, that's worth the expense, and kinda fun, too!



-Jay

 

[Joseph Donnelly]

The formula quoted above is incorrect. Torque = hp x 5252 / rpm



It's easy to remember since torque is about double the hp at around 2000-2500 rpm

 

[JGK]

Sorry to sidetrack here, but...



Hey Joe, we haven't heard a lot from you lately! What's up with Sickly? Are you putting her out to pasture? Time for new games with an '04 HO, it appears. And what's with the relocate to NM?



Regards,

-Jay