slap929

"Can a 2.5 8v motor put 350ft/lbs on the ground @ 13psi? I wouldn't be so quick to say it cannot.

Here is a 2.5 8v motor with stock cam and head, IC running on a Motec M4 w/CDI @ 1.3 bar pushing the Greddy bypass open on Autothority's SuperFlow 10 years ago or so."

um... 1.3 bar is 19psi, again it is not 13 psi.

Chris Prack

Yeah you said that already and no one is disputing it.

slap929

Sorry I misunderstood what was being said (that's what I get for doing three things at a time). I just saw claim and assumed evidence was following.

As far as the 2.5 8v making 350ft/lbs @ 13psi... Pics or it didn't happen (dyno sheet) . I dont see that happening with a stock engine at 13psi (but would love to be proven wrong).

rlm328

The factory prepared Boss racing car made 410 bhp @ 15.5 psi boost. It was the 924 2.5 L motor.

333pg333

The more I see different numbers on different cars on different days on different dynos, different countries etc...the less I think we can compare apples with apples.

rlm328

I agree 100%. The same dyno will give you different numbers dependent on a number of factors.

333pg333

Even on the same dyno, same car and minutes apart. Different ramp loadings present major differences on the chart. https://rennlist.com/forums/944-turb...t-runs-59.html See post #882 for perfect example of this.

TonyG

Depends on the dyno. If you compare on like dynos, using SAE correction, then you can very much compare apples-to-apples.

The Porsche Owners Club uses the dynojet, and no matter the track or the weather conditions, elevations, etc.... as long as it's SAE corrected, my car has always been within 5RWHP.

TonyG

333pg333

I don't know how SAE correction works but assuming it's a barometric thing? As you can see on the link I posted above, (post #882) we have 2 very different results on minutes apart. Just different ramp rates. https://rennlist.com/forums/944-turb...t-runs-59.html

TonyG

They are correcting for temperature, barometric pressure, and mechanical efficiency.

The dyno you posted above doesn't look like it uses the same scaling. Take a look at the boost curves on each dyno. They are slightly different (which can have a big impact on HP/TQ) and they don't align with the same numerical values on the right side of the chart. Not sure why because the scale appears to be the same but the boost plot doesn't line up the same.

Also, what type of dyno is it?

Read this from DynoJet:
http://imageftp.dynojet.com/CMD/Trut...Runs_Final.pdf

TonyG

333pg333

The boost was slightly more on the Red line than the blue, yes, but not by a lot. Even then, the Red line shows less HP. As the tuner mentions:

“I have attached 2 files. The 1st is boost. 2nd is torque. These overlays are at different ramp rates. This shows the problem we are faced with turbo cars & ramp rates.

The higher horsepower reading is in shootout mode which is the correct ramp rate to show the correct horsepower/ torque readings. Unfortunately this does not allow the turbo to spool so therefore shows the boost coming in later. The slower ramp rate also overheats the tyres causing wheel slip. “

We were running slicks which are not the best choice for a dyno.
Dyno Dynamics brand. Tend to read lower than Dynojet and some others.

pole position

A Dynojet is easily the most "happy" dyno on the market, consistently reads anything higher than other wheel dynos ........their wheel readings sometimes match the manufacturers crank claims and is then justified that the manufacturer " underrates" their engines .....pure comedy, they charge you 500 bucks for some mundane cosmetic ad on the sticker but give you free extra horses, the irony ...

Chris White

Geez, you guys are quoting rear wheel HP, crank HP and internet HP as if they are all the same!
DTS4000 = engine dyno.
Quote about the Boss engine – crank HP and please check your history. A 924 2.5 motor? Nope, that was a 2.5 liter 944 block with a 16v head and a full race dry sump system.
Note on the DTS4000 graph – the peak pressure is listed on the bottom of the print out – 2.29 kpa = 18.5psi and 243kpa = 20.7 psi.
18.5 psi made 424lf lbs and 506hp – take off 18% for drive train and you get 360 ftlbs and 428hp. Good results and the main reason for the high HP is the ability to run high rpm. Use a stock rpm cut off and it made the equivalent of 415 rwhp.….but not 393@13psi!

Funny that somebody dug up an old post and tried to start an argument with somebody from 2011…..reviving a 2011 thread with ‘disagree’ is pretty funny.

Troll power!

KSira

What drive train loss do you use on HP measured at the wheels compared to HP measured at the hubs?

refresh951

Drive train loss will depend on power level. In other words, drive train loss may be 15% for a 250 hp vs 11% for 400 hp. I would also be interested in what Chis has to say about this as he has so much experience on the engine dyno.