Chassis dyno tuning...no engine load??
Thread Starter
Melting Slicks
Joined: May 2001
Posts: 3,270
Likes: 26
From: Winchester VA
Cruise-In V Veteran
Chassis dyno tuning...no engine load??
So I was talking with the guy building the new engine and he asked if I wanted to put it on their water brake engine dyno. I said no because they are really just assembling the short block and I don't want to haul the completed engine back to them. So I mentioned using a chassis dyno, to which he responded...
"..they are inertia dyno's and you need to tune it rich about 11.5:1 since they do not load the engine."
This is news to me, and in all the threads duscussing chassis dyno tuning I have never heard this before. (or I missed it??)
Discuss...
"..they are inertia dyno's and you need to tune it rich about 11.5:1 since they do not load the engine."
This is news to me, and in all the threads duscussing chassis dyno tuning I have never heard this before. (or I missed it??)
Discuss...
Burning Brakes
Joined: Nov 2001
Posts: 1,241
Likes: 9
From: Houston TX
if you mean a dynojet, the drums have an inertia which corresponds to a roughly equivalent translational mass. for the common dynojet models i believe this is about 2500lbs. this means your engine is accelerating the equivalent of a 2500lbs car on a dynojet.
there's a multiplication effect from gearing, so running in 4th gear on a dynojet will correspond to somewhere in between 2nd and 3rd gear on the street if you compare drum load to vehicle mass. so there is definitely a load on the engine, it just might not be perfectly equivalent to what the engine sees on the road.
believe it or not, this does often mean the tuning is different. first off, a dynojet usually likes to see more ignition advance than is safe for a track car. if you tune the car just short of detonation on a dynojet, it will eventually detonate itself to death if it's an open track car that spends a lot of time in 4th and 5th gears. this is simply from the difference in rate of rpm increase, so it's a known phenomenon. in fact, many of the more sophisticated racing engine management systems have the capability of changing ignition advance maps based on the selected gear.
secondly, the measured afr seems to vary as well. i believe the ecm programming does a fairly complex load calculation, so it sees things differently on a dynojet. i used to tune cars for a living, and i saw this all the time. it's not a terribly big difference, but it is a real difference in some cases.
this doesn't mean a dynojet tune is completely worthless. it also doesn't mean you can pick some magic afr number that will then properly translate to the real world.
-michael
there's a multiplication effect from gearing, so running in 4th gear on a dynojet will correspond to somewhere in between 2nd and 3rd gear on the street if you compare drum load to vehicle mass. so there is definitely a load on the engine, it just might not be perfectly equivalent to what the engine sees on the road.
believe it or not, this does often mean the tuning is different. first off, a dynojet usually likes to see more ignition advance than is safe for a track car. if you tune the car just short of detonation on a dynojet, it will eventually detonate itself to death if it's an open track car that spends a lot of time in 4th and 5th gears. this is simply from the difference in rate of rpm increase, so it's a known phenomenon. in fact, many of the more sophisticated racing engine management systems have the capability of changing ignition advance maps based on the selected gear.
secondly, the measured afr seems to vary as well. i believe the ecm programming does a fairly complex load calculation, so it sees things differently on a dynojet. i used to tune cars for a living, and i saw this all the time. it's not a terribly big difference, but it is a real difference in some cases.
this doesn't mean a dynojet tune is completely worthless. it also doesn't mean you can pick some magic afr number that will then properly translate to the real world.
-michael
Drifting
Joined: May 2003
Posts: 1,730
Likes: 1
From: Charlotte NC
St. Jude Donor '05
If a inertia dyno doesn't load the vehicle why is it that it takes about 4-5 seconds to pull thru a dyno pull? If it didn't load woudln't it just fly thru the RPM?
A dyno (regardless of inertia or load bearing) is a very useful and practical tool in the hands of someone capable of using it.
I'll leave it that I agree with him on one point and that is theres a difference between a dyno tune and a track tune. The problem is 99% of the cars out there aren't consistant enought to do accurate track tuning.
I personally tune a vehicle very specifically in order to run the best at the track, not put down the best number.
A dyno (regardless of inertia or load bearing) is a very useful and practical tool in the hands of someone capable of using it.
I'll leave it that I agree with him on one point and that is theres a difference between a dyno tune and a track tune. The problem is 99% of the cars out there aren't consistant enought to do accurate track tuning.
I personally tune a vehicle very specifically in order to run the best at the track, not put down the best number.
Team Owner
Joined: Sep 2003
Posts: 88,393
Likes: 2
From: eville in
Originally Posted by MSR
if you mean a dynojet, the drums have an inertia which corresponds to a roughly equivalent translational mass. for the common dynojet models i believe this is about 2500lbs. this means your engine is accelerating the equivalent of a 2500lbs car on a dynojet.
there's a multiplication effect from gearing, so running in 4th gear on a dynojet will correspond to somewhere in between 2nd and 3rd gear on the street if you compare drum load to vehicle mass. so there is definitely a load on the engine, it just might not be perfectly equivalent to what the engine sees on the road.
believe it or not, this does often mean the tuning is different. first off, a dynojet usually likes to see more ignition advance than is safe for a track car. if you tune the car just short of detonation on a dynojet, it will eventually detonate itself to death if it's an open track car that spends a lot of time in 4th and 5th gears. this is simply from the difference in rate of rpm increase, so it's a known phenomenon. in fact, many of the more sophisticated racing engine management systems have the capability of changing ignition advance maps based on the selected gear.
secondly, the measured afr seems to vary as well. i believe the ecm programming does a fairly complex load calculation, so it sees things differently on a dynojet. i used to tune cars for a living, and i saw this all the time. it's not a terribly big difference, but it is a real difference in some cases.
this doesn't mean a dynojet tune is completely worthless. it also doesn't mean you can pick some magic afr number that will then properly translate to the real world.
-michael
there's a multiplication effect from gearing, so running in 4th gear on a dynojet will correspond to somewhere in between 2nd and 3rd gear on the street if you compare drum load to vehicle mass. so there is definitely a load on the engine, it just might not be perfectly equivalent to what the engine sees on the road.
believe it or not, this does often mean the tuning is different. first off, a dynojet usually likes to see more ignition advance than is safe for a track car. if you tune the car just short of detonation on a dynojet, it will eventually detonate itself to death if it's an open track car that spends a lot of time in 4th and 5th gears. this is simply from the difference in rate of rpm increase, so it's a known phenomenon. in fact, many of the more sophisticated racing engine management systems have the capability of changing ignition advance maps based on the selected gear.
secondly, the measured afr seems to vary as well. i believe the ecm programming does a fairly complex load calculation, so it sees things differently on a dynojet. i used to tune cars for a living, and i saw this all the time. it's not a terribly big difference, but it is a real difference in some cases.
this doesn't mean a dynojet tune is completely worthless. it also doesn't mean you can pick some magic afr number that will then properly translate to the real world.
-michael
Burning Brakes
Joined: Jun 2006
Posts: 1,096
Likes: 28
From: Baltimore MD
Not to mention that DynoJet isn't the only game in town....
Dynojets gives the highest numbers, yes.
but...
A Mustang Dyno ( www.mustangdyne.com/locator.htm ) or Dyno Dynamics ( http://www.dyno.com.au/near_usa.htm ) brand (maybe others as well) can put a load on the car, as well as simulate a 1/4 mile pass...better (IMHO) real world tune, but it gives you a lower dyno sheet to show your friends.
Dynojets gives the highest numbers, yes.
but...
A Mustang Dyno ( www.mustangdyne.com/locator.htm ) or Dyno Dynamics ( http://www.dyno.com.au/near_usa.htm ) brand (maybe others as well) can put a load on the car, as well as simulate a 1/4 mile pass...better (IMHO) real world tune, but it gives you a lower dyno sheet to show your friends.
