Difference between a 3rd gear pull and 4th gear pull on a Dyno? - Page 3 - SRT Forums - SRT4, SRT6, SRT8, SRT10 & Dodge Forum
 
 


Go Back   SRT Forums - SRT4, SRT6, SRT8, SRT10 & Dodge Forum > SRT-4 Technical Discussion > SRT-4 Discussion

SrtForums.com is the premier Dodge SRT Forum on the internet. Registered Users do not see the above ads.
Reply
 
LinkBack Thread Tools Display Modes
Old 05-07-2006, 01:54 PM   #31 (permalink)
SRTforums Member
 
Join Date: Nov 2005
Member Number: 35869
Location: Illinois
Posts: 193
Default

Quote: Originally Posted by wonderboy
I am confused


isnt power (hp)= torque x (rpm/5252)

so if torque is increased (multiplied. amplified or whatever other word you want to use).. isn't power increased as well since the relationship between power and torque is bound by the constant above?

I am not a physics major (actually i sucked at physics in high school) BUt

if the rate of acceleration is a measure of torque, and a cars rate of acceleration decreases as you from 1st to 2nd, 2nd to 3rd.. etc.. that must mean that there is more torque getting to the ground.. if more torque is getting to the ground and torque and hp are an expression of one another.. then the transmission does multiply power and torque.

sounds like you guys are arguing semantics....

Torque is multiplied using gear ratios. Those gear ratios also decrease the speed (the "rpm" in your equation). Power stays constant. It's conservation of energy.
__________________
life's too short to own boring automobiles.
pitviper33 is offline   Reply With Quote
Sponsored Links
Advertisement
 
Old 05-07-2006, 02:12 PM   #32 (permalink)
SRTforums Member
 
Join Date: Mar 2005
Member Number: 25195
Location: Deltona Fl
Posts: 2,456
Default

the answer is "because"....


/ thread
boostking is offline   Reply With Quote
Old 05-07-2006, 03:54 PM   #33 (permalink)
SRTforums Member
 
MoparbeastSRT4's Avatar
 
Join Date: Aug 2005
Member Number: 32388
Location: KlamathFallsOR
Posts: 947
Default

Quote: Originally Posted by MunkysSRT4
What happens when you do a 4th gear pull on the dyno in an SRT.

This is from the N2MB Dyno Day on 4-29-06 at Crazy Horse in NJ. It's Andy(Nosuchluck) car from GMR.
http://videos.streetfire.net/video/F...E54C019E12.htm


Man, that was close.
__________________

http://www.cardomain.com/ride/2098862/1

Power Mods
Mopar Stage 1|Mopar CatBack|NWs V5 DP|AGP WG+PTP's spring|Greddy TT|Profec B Spec II|MPx FMIC|AEM SRI|AEM UEGO|Scan Gauge|ED Pipes+HKS BOV|MSD SPW+NGK@.32|MM Inserts|WeaponR CC|PTP's 75 FPR Mod, MAPTIP Clamp, Cooling Kit, Check Valve|

Quote: Originally Posted by yeah
My srt is possessed with deamons.

MoparbeastSRT4 is offline   Reply With Quote
Old 05-07-2006, 05:31 PM   #34 (permalink)
SRTforums Member
 
Join Date: Mar 2005
Member Number: 25892
Location: New England
Posts: 3,716
Default

Quote: Originally Posted by MoparbeastSRT4
Quote: Originally Posted by MunkysSRT4
What happens when you do a 4th gear pull on the dyno in an SRT.

This is from the N2MB Dyno Day on 4-29-06 at Crazy Horse in NJ. It's Andy(Nosuchluck) car from GMR.
http://videos.streetfire.net/video/F...E54C019E12.htm


Man, that was close.

They only used 2 straps, and i have seen many posts by Nivo and many other dyno operators saying to only use 2 instead of 4 is asking for trouble, it allows the car to sway which is bad to begin with. If the car is not strapped down properly even a second gear pull can go bad, or even if the straps are a little worn.
__________________
Mods: AGP GT3076R DBB Turbo, vehicle sold and missed!!
"The Cobalt firmly grabs you and whisks you along your way instantly. It does so with authority and poise, but while slipping relatively unnoticed through traffic, never being violent, or dare I say it, frightening. When you ask the SRT-4 to take you somewhere fast, it punches you in the face, throws you over its shoulder, and runs, screaming, so quickly that its tires can barely keep up."
madwax is offline   Reply With Quote
Old 05-07-2006, 05:34 PM   #35 (permalink)
SRTforums Member
 
Join Date: Mar 2005
Member Number: 25195
Location: Deltona Fl
Posts: 2,456
Default

on a fwd car always use 4...you get the least little bit off center and things can go very wrong....

2 straight, 2 crossed...its the best way
chalk the non drive wheels and strap them too
boostking is offline   Reply With Quote
Old 05-07-2006, 06:21 PM   #36 (permalink)
Premium Member (Lifetime)
 
Dimarini's Avatar
 
Join Date: Apr 2005
Member Number: 26399
Location: Pflugerville,TX
Posts: 1,334
Lifetime Premium Member
Default

PitViper is correct. The Dyno is actually measuring torque and calculating horsepower. As long as the proper gear ratio is input then the correct horsepower numbers should come out on your graph.
Dimarini is offline   Reply With Quote
Old 05-07-2006, 07:03 PM   #37 (permalink)
SRTforums Member
 
Corners's Avatar
 
Join Date: Jan 2006
Member Number: 37239
Location: KC Metro, JOCO
Posts: 1,184
Default

Quote: Originally Posted by pitviper33


Torque is multiplied using gear ratios. Those gear ratios also decrease the speed (the "rpm" in your equation). Power stays constant. It's conservation of energy.

Pitviper is absolutly correct. Power CANNOT be changed through gearing. I've always wondered the same thing why it matters at all to be at a 1:1 gear ratio for a chassis dyno pull. The only thing I can think of is the 1:1 is irrelevant, but a taller gear would equal a longer (time) dyno pull, thus the computer's sampling of the dyno's drum's change in speed would be more accurate. More data = more accurate. For instance, if you did a 1st gear pull, the dyno pull would take like 0.5 seconds, so you'd only have 0.5 seconds of data to sample.

Another thing to think about why the 1:1 doesnít matter is because of tire diameter. Sure, the engine, transmission output shaft and wheels are spinning about the same speed, but different diameter tires will spin the dyno drum at different speeds. The tire to dyno drum ratio is not 1:1, and the dyno is measuring the drumís speed, not the tires.
__________________
"Go that way, really fast. If something gets in your way, turn." - Charles De Mar.
Corners is offline   Reply With Quote
Old 05-07-2006, 10:37 PM   #38 (permalink)
SRTforums Member
 
Join Date: Apr 2005
Member Number: 27011
Location: Texas
Posts: 46
Default

Well some of you got the idea....but most of you dont. I dont have all the answers, but i DO KNOW OFR A FACT THAT 3rd gear gives lower #s than 4th gear. Same with rearend gear ratios....most people who switch from 3.27 gears to 4.10 gears in mustangs drop close to 10RWHP on the dyno.
We have a guy on stangnet that knows ALL about the dynos and how they work and explains how everything is working and how its effected.

And for your turbo SRT-4 guys, TURBOS LIKE LOAD! 4th gear puts a high load on the engine. Try dynoing your car in 1st, you would get much boost...+ the dyno measuring lower anyways.
If you guys try a 5th gear run you would probably pick up 15RWHP on the dyno...but it would be accurate. 4Th gear all the way as it also loads the cars A/F/ EGTs CLOSER to what they would be on the street....thus more accurate A/F readings. NEVER LET ANYONE DYNOTUNE A CAR WITH A 3RD GEAR PULL! It will actually read richer than it really is....then when you get on the street it could go dangerously lean....especially in a 5th gear highend run

Thus the reason for mustang dynos...they load your car to what its actually seeing on the street. Best for tuning...not good for # comparing lol. It can vary depending on what weight they enter for your car, as well as other factors.
__________________



1966 stang HEAVILY modded 331 stroker.All 4340 forged W/ 8.5-1 CR soon to be supercharged W/ ICd novi 2000 .
quick04GT is offline   Reply With Quote
Old 05-07-2006, 11:12 PM   #39 (permalink)
SRTforums Member
 
Join Date: Nov 2005
Member Number: 35869
Location: Illinois
Posts: 193
Default

So here's another thing I don't get... a few people have mentioned higher load in a higher gear and longer pulls in a higher gear. Why would the gear affect the length of time spent on the pull? Why would a higher gear load the engine more? On the dynos I've worked with, I set the rate I want the speed to climb. The engine is at full load the whole time. There will be more torque in a lower gear, but the dyno will match that torque to hold the speed it wants. If I want it to hold a certain speed, I just tell it that speed and it figures out what load is necessary to hold the engine at that speed. (It's always at full load, because the engines I usually work with don't have throttles.)
What am I missing here? Do the dynos you guys are using work differently?
__________________
life's too short to own boring automobiles.
pitviper33 is offline   Reply With Quote
Old 05-07-2006, 11:25 PM   #40 (permalink)
Tex
SRTforums Member
 
Tex's Avatar
 
Join Date: Sep 2003
Member Number: 3622
Location: san jose califo
Posts: 13,261
Default

you use a 1:1 so you dont have to calibrate your computer. we calibrate it EVERY time we make a run, so we can run it in 2nd if we so choose and get the same numbers. people are just lazy
__________________
How absurd men are! They never use the liberties they have, they demand those they do not have. They have freedom of thought, they demand freedom of speech.

-Soren Kierkegaard
Tex is offline   Reply With Quote
Old 05-08-2006, 06:04 AM   #41 (permalink)
SRTforums Member
 
Corners's Avatar
 
Join Date: Jan 2006
Member Number: 37239
Location: KC Metro, JOCO
Posts: 1,184
Default

Quote: Originally Posted by pitviper33
So here's another thing I don't get... a few people have mentioned higher load in a higher gear and longer pulls in a higher gear. Why would the gear affect the length of time spent on the pull? Why would a higher gear load the engine more? On the dynos I've worked with, I set the rate I want the speed to climb. The engine is at full load the whole time. There will be more torque in a lower gear, but the dyno will match that torque to hold the speed it wants. If I want it to hold a certain speed, I just tell it that speed and it figures out what load is necessary to hold the engine at that speed. (It's always at full load, because the engines I usually work with don't have throttles.)
What am I missing here? Do the dynos you guys are using work differently?

Sounds like you're were using an engine dyno (water brake maybe?). We were all talking about a chassis dyno, which is usually an inertia type dyno. How it works is your car is parked over a drum with known moment of inertia (a dynojet is like a 3,000 lb drum). The dyno's data acquisition system then measure's the speed of the rotating drum vs. time. Knowing the rate the drum was accelerated and its moment of inertia you can then calculate the torque applied to the drum. So, using a higher gear will spin your tires and inertia drum faster, but less torque will reach the drum (same power, though). With less torque spinning the drum, the longer it will take to spin up.

It's the difference in riding a mountain bike as fast as you can from a stop in 1st gear vs. 24th gear. 1st gear will take no time at all to get to max speed, and 24th will take a while, but still, the same amount of power is being applied by your feet.
__________________
"Go that way, really fast. If something gets in your way, turn." - Charles De Mar.
Corners is offline   Reply With Quote
Old 05-08-2006, 08:25 AM   #42 (permalink)
SRTforums Member
 
Join Date: Nov 2005
Member Number: 35869
Location: Illinois
Posts: 193
Default

Both the chassis dyno and the engine dynos I have experience with use water brakes. That's the only kind I've worked with, and I guess I figured that all dynos had adjustable load.

If most chassis dynos work like you described, I can see why a higher gear would be better. Wouldn't there be a lot of cars you'd almost have to go to the highest gear? And wouldn't it be really hard to tune any speed really well? It actually seems like a pretty crappy system to me without being able to adjust the load. Oh well, I guess it gets the job done.
__________________
life's too short to own boring automobiles.

Last edited by pitviper33; 05-08-2006 at 08:27 AM.
pitviper33 is offline   Reply With Quote
Old 05-08-2006, 12:31 PM   #43 (permalink)
SRTforums Member
 
Razathorn's Avatar
 
Join Date: Jun 2005
Member Number: 29751
Location: Lenexa, KS
Posts: 121
Default

A transmission multiplies torque. If your engine outputs 200 torque at x rpm, in first gear the number will be dramatically higher than that at the wheels -- this is okay because the power in the rotational system does not change, just the torque due to the difference in rotating velocity (rpm). Given that the torque at the wheels is NOT the number you get on your dyno, the dyno needs the tach signal (for rpm) to calculate back to it given the engine output shaft velocity. The idea on the dyno is you want the gear that ends up being closest to 1:1 that allows you to see enough granularity on the dyno. IF you use a gear that's too low, say 2nd, you will fly through the rpm span and not collect very granular data, not to mention there will be more loss (lower numbers) than in 3rd or 4th. 3rd or 4th is the best gear because it has the least amount of loss -- additionally, you want to load your motor somewhat so you can see if it will knock or not.
__________________

[ black '03 rsx type-s ] [ 274 whp @ 9psi jackson racing supercharged / alcohol injection ]

Last edited by Razathorn; 05-08-2006 at 12:34 PM.
Razathorn is offline   Reply With Quote
Sponsored Links
Advertisement
 
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On



All times are GMT -6. The time now is 10:35 PM.



(C) SRTforums.com

Search Engine Friendly URLs by vBSEO 3.3.2