Boost set point is the boost pressure requested by the ecu control program, whereas the boost pressure is what the engine actually produced. IAT tells you something about how well the intercoolers are working. The engine load value is expressed in percent, and it is pretty close to the "volumetric efficiency" which is defined as the volume of air passing through the engine divided by the theoretical displacement for air at standard temp and pressure. VE is computed as follows:

VE = 2.63*MAF*(IAT+273)/RPM

The 2.63 comes from unit conversions, 273 gives absolute temperature. The temperature is needed in the formula to include the effect of the density of the incoming air. This number can be larger than 100% for a turbocharged engine because the turbos compress the air to a density higher than standard pressure (1 bar). In my car, VE computed above is about 5% higher than the reported engine load. Other guys seem to get closer readings. There was a thread about this a while back:
https://www.6speedonline.com/forums/...y-comparo.html
Search this forum for "volumetric efficiency" and you'll find some other threads that should help you understand better how a turbocharged engine works.

Your boost gauge reads so-called gauge pressure, which is absolute pressure - ambient pressure, which is normally about 1 bar. Durametric boost output reads in mm Hg, where 1 bar = 980 mm Hg. Your baseline value of 1000 or so indicates the barometric pressure that day was slightly above 1 bar, typical for warm sunny days.

Hope that helps.

Your logs should be very useful. Lots of us have posted logs, but mostly after the engine has been modified. You could help give us a baseline.

Jon

 

Subscribed....
Good thread.
Frank

 

Hi Guys,I have never data logged and no nothing about the fine details of how to read the info.....But I do have this question because I should get one for my own piece of mind to check everthing out......Wouldnt it be better, if you had the room,to do a run in 4th gear because the engine is loaded more then in 3rd?? ....Thanks....

 

I do my runs in 4th gear. The only difference that I can see in the logs is that I get more data in 4th gear because it takes a longer time to sweep through the rpm range. Plotting any of the data versus rpm seems to give the same answer. The load is the same at WOT.

The speeds are a lot higher, so you need to find a safe place to do it.

Jon

 

Hi,Thanks,,,But.....In 3rd gear at 3,000rpms ,on a 70 degree day,,,I hit 1.2 bars then it goes to 1.3 bars in the upper RPM range,,,,If I am in 4th at 3000rpms it will go right to 1.3,thus because of the load,,,,So then how would it be the same info in 3rd when it is 1.2 at the same RPMs in 4th at 1.3???Thanks for input

 

It's not. The higher the gear the more load you will place on the motor at a lower speed as you just indicated, even at WOT. I think the point is that you can get excellent data and an indication of your car's performance by data logging in 3rd gear without having to go crazy fast.

 

Yeah 3rd usually tells you a lot of what you want to. Intercooler performance measurements need more load though.

 

OK then??...I have been on the Dyno many ,many times with my car over the yrs,,,from Porsche dealers as the Porsche Exchange,to shops as AMS and others and to tuners shops as EPL.....They put the car in 4th gear to simalate road and load...Then why do you think 4th and not 3rd like with a data logger?? Just asking and learnig and sharing info

 

many cars have 1:1 gearing in 4th which can give more comparable dyno #s across brands of cars. Non load bearing chassis dynos will never be able to accurately capture road conditions but can get in the ballpark for rough tuning and comparison purposes. The 3rd gear street pulls can give you some decent info without sending you to jail.

 

HI,Thanks,Yes I know all that....But whether or not we are talking about speeding or going to jail,forget that point.....My question still remains that will a 3rd gear pull be as good as a 4th gear pull that puts a load on it down low right away to get it to the max boost verses a 3rd gear that has a slightly lower boost at first and then goes to max boost higher up the RPM band.......

 

No...and a 4th gear pull isn't as good as a 5th gear pull which isn't as good as a 6th gear pull. 5/6 pulls can uncover IAT, EGT and other issues that are difficult to see in 3rd or 4th gear.

 

HI EARL,,I think you may be wrong with that thought,,IMO...I have had many Dyno sessions under my belt all these yrs....First,Ask any tuner and they will tell you,,that None of them,as I know of , have a fan system to simulate the air flow needed in a 5th gear pull ...AND....The time it takes to do a 5th gear pull is to long that will cause Heat soak,,which pulls timing and richens up the mixture....Believe me I know this BUT we all have our opinions and share them on here...Its all good....

 

I think it depends on the type of dyno too, whether it is brake or inertia. For many transmissions, 1:1 gearing is simply the input and output shafts locked together, not really a gear set. This eliminates loses via gear teeth and give higher power numbers in that gear. Running too low of a gear could result in the engine outrunning the turbo. Higher gears slow engine acceleration which allow turbos to spool earlier and more consistently which would result in a better quality dyno assuming acceptable IATs can be maintained.

 

Hi,Yes agreed,,,But as I stated above about cooling flow and pull time is not conducive info in 5th gear pulls......Point,,,When I went to AMS[Rear wheel Dynojet then] to have my car dynoed after EPL sent me my flash,,,,They did some 5th gear pulls,which I told them they did not have the cooling to go with that,But they still did it...they said they had to pull timing and lean it out,,,,,Well when I left there the car did not run stronger and they even bumped the boost up a little.....I called my friends in the gearhead world and they all told me and agreed with the cooling fan and time it took to do a 5th gear pull to heat soak it..I drove my car to EPL then,Yes I am annal about this stuff..lol..',tony put the timing back in and fuel curve back and I went up on HP and TQ,,,And I felt it when I left the shop..He did not use 5th gear,,,,,,,Just my info to help......

 

Manthey would disagree...

Honestly I'm a little confused as to what you're asking.

Are you asking why most tuners tune in 4th gear on chassis dynos? Its quick, relatively cheap, safe and provides a 90% solution to most of the enthusiast crowd as well as pretty sheets to brag to one's buddys about. Does it adequately simulate real world conditions? Maybe, really depends on how the car is used.

Would a 5th gear dyno pull be better? As you said, not really unless you can adequately represent airflow in these conditions. Is a 5th gear pull on the road better? IMO, heck yes! (safety & law considerations aside)

As an example of when this type of dyno tuning (non load bearing) may miss the mark... there have been many that have dyno'd well & been tuned in 4th gear with no apparent issues and then have had the cars fall flat on their face doing actual (non dyno) runs to 200mph (because of the issues I mentioned). If you never run the car this hard, this its probably no big deal as these issues won't surface. Some examples in the link in this post ("technical data on flashes"):

https://www.6speedonline.com/forums/...ml#post2932471

Note: I'm am NOT saying EPL does this, I have beat the p*ss out of their tune (well beyond 4th gear) and the logs look beautiful.

Does that help?