Dyno Results In 3rd Or 4th Gear

[ebola]

Theory is no problem. Theory is easy... its practice that I am interested in...

care of wikipaedia:

kW = (Nm * rpm) / 9549 (k constant)

I just hadn't thought that ramp rate / engine load would make such a large difference. Then again, I geuss the stock rb20 turbo runs out of huff pretty quickly (like around 3.5k rpm) when compared to a large aftermarket turbo.

So power would be the same, but torque up by ~1.3 x (3rd gear ratio). cool

keeping with the idea is the original question (3rd or 4th gear), would there be any difference in transmission loss b/n the gears? or is 20% squishy enough not to care?

[Cubes]

lol at the stock rb20t turbo running out of puff at 3.5k, they are small but they aren't that bad.

Mine used to get going at 3.5k @1bar and would hold 1bar until a shade over 7000rpm where I would shift up.

Poor boost controllers would have boost dropping off at high rpm, fitting up a decent controller picked up 10rwkw and gave it the feeling that it keeps pulling and pulling until a shade over 7000rpm.

[jazza08]

When i was happy to blow my rb20 turbo, i ran an old elc boost controller which made 1bar by 3000rpm and 18psi soon after, it would drop off to 1bar by 6500-7000rpm (didnt used to watch boost controller that much at those rpms lol) and hold 1bar well into the 7000rpm's!

The stock rb20 turbo isn't too bad if you have a good boost controller at holding decent boost, but it wont hold too much obviously due to the wastegate spring and of course its size!

In regards to the dyno i thought it was well known 4th gear gives the best readings, 3rd (if you ave speed limits etc) shouldn't be TOO far off, closer obviously if ur car is closer to stock also hehehe

[Busky2k]

Well one would think that in lower gears the less load on the motor will mean potentially less power with a turbocharged car.

But how come when I gun it in 1st gear to redline I'll still get the same peak AFM voltage as I would if I had kept going through the gears? Ie ~4800mV on a Z32... its interesting cos first gear only last a split second where as 3rd might last about 5 seconds which gives plenty of time for the turbo to spin hard.

Its been the same case in both cars I've had.

[Cubes]

  Busky2k said:

Well one would think that in lower gears the less load on the motor will mean potentially less power with a turbocharged car.

But how come when I gun it in 1st gear to redline I'll still get the same peak AFM voltage as I would if I had kept going through the gears? Ie ~4800mV on a Z32... its interesting cos first gear only last a split second where as 3rd might last about 5 seconds which gives plenty of time for the turbo to spin hard.

Its been the same case in both cars I've had.

Thats quite interesting... I don't hit my peak voltage until third gear, granted first and second are wheelspin.

[Sydneykid]

  Cubes said:

Thats quite interesting... I don't hit my peak voltage until third gear, granted first and second are wheelspin.

You shouldn’t confuse what happens on the road (in the 2nd or 3rd compared to 4th) with what happens on the dyno. On the road the car accelerates so fast (or wheelspins so much) that it doesn’t have time to build up the load to produce the exhaust to spin up the turbine. This is not the case on the dyno, where the operator can vary the load (on the rollers) to slow up the rpm increase and give the engine time to build up the load to produce the exhaust to spin up the turbine.

So when talking gear comparisons on dynos you can ignore load as a factor of difference.

cheers

[hrd-hr30]

4th gear should produce a handfull more bhp at the wheels. 3rd gear is a helical gear set meshed between gears on the mainshaft and layshaft. the helical gears will create side loads and extra friction and drievtrain losses.

4th "gear" on the other hand simply connectes straight through the mainshafts in the gearbox - no gears involved, no side loading, no meshing frictions. all of this equals less drivetrain losses.

but it will only be a few kw.

[Busky2k]

  Sydneykid said:

You shouldn’t confuse what happens on the road (in the 2nd or 3rd compared to 4th) with what happens on the dyno. On the road the car accelerates so fast (or wheelspins so much) that it doesn’t have time to build up the load to produce the exhaust to spin up the turbine.

Ah but what I mean in my experience that despite the lack of 'load' in 1st or 2nd gear (wheelspin in both gears), I still get pretty much the same AFM readings, both on my old car with a stock turbo and my current car with a bigger one.

Hmmmm...

[Cubes]

So you really get exactly the same load, must be an sr thing?

I had a fiddle today, dropped boost right back to 7psi, first and second gear saw less load, third and fourth saw the same, I am unable to really wind fourth out as thats past the speed limit but comparing similiar rpm saw almost the same load... My third is little due to the lack of rpm 5500rpm max until valve springs are sorted. which fingers crossed is next week.

[Busky2k]

Yeah must be an SR thing. Power in any gear. Or.. I again need a bigger turbo

I guess by dropping the boost back and getting the same load, that means that your boost is tapering up top? So just a phatter midrage with larger boost... Still cool I say.

Edited June 28, 2006 by Busky2k

[Cubes]

  Busky2k said:

Yeah must be an SR thing. Power in any gear. Or.. I again need a bigger turbo

I guess by dropping the boost back and getting the same load, that means that your boost is tapering up top? So just a phatter midrage with larger boost... Still cool I say.

Sorry I didn't mean the same load as when the boost was up, I dropped boost as with the higher boost level I can't get the power down in first, second even third tends to spin up a little when the diff decides its going to open wheel a tad causing less traction on the other so they both eventually go.

But yes the peak lower boost voltage 3rd and 4th appeared to be the same, first was a tad less than second but still spun slightly, second hooked up completely and was still tad less than third. Which was smack on 4v on the Z32. When I say a tad i mean 3.95v vs 4v.

[The Alchemist]

3rd gear usually produces slightly less than 4th gear, say 2 to 3 kw. This is due to the more load on the engine in 4th and the slightly longer time to complete the run allowing the turbo to work a bit more.

We do a lot of NA holdens as well and with similar differences of 2 to 3 kw between gears.

Cheers,

Mike

[dezz]

so who wants to explain how my bog stock R33 made this graph?

[Busky2k]

The Shootout parameter, IT (intake temp) is 55C. That would overinflate your readings by a good amount.

Cheers

PS on a side note, since when did R33s reach 180kmh in 3rd gear lol.

[dezz]

  Busky2k said:

The Shootout parameter, IT (intake temp) is 55C. That would overinflate your readings by a good amount.

Cheers

PS on a side note, since when did R33s reach 180kmh in 3rd gear lol.

so you're saying the dyno operator made an error?

he had the inlet temp sensor where i've indicated in the photo...he was telling me how not many dyno operators do that, but how it gives the most accurate readout!

[Cubes]

If what you are saying is true then the fan would have been hammering the snorkle with clean air that is not 55degree's.

The only other explaination is that the room really was 55degree's but he had the AT sensor located in the fridge or outside.

I've never had a dyno run where the IT and AT readings are much different, the interesting thing is the dyno I run on is situated at the back of a workshop that gets no fresh air. Its actually pretty badly setup with regards to the lack of fresh air as after a tune my eyes sting for ages.

[dezz]

  Cubes said:

If what you are saying is true then the fan would have been hammering the snorkle with clean air that is not 55degree's.

The only other explaination is that the room really was 55degree's but he had the AT sensor located in the fridge or outside.

I've never had a dyno run where the IT and AT readings are much different, the interesting thing is the dyno I run on is situated at the back of a workshop that gets no fresh air. Its actually pretty badly setup with regards to the lack of fresh air as after a tune my eyes sting for ages.

hmmm it was definitely not 55 degrees in the workshop

I think it can be put down to incompetence, just as i initially thought

[Cubes]

Maybe the plastic was hot? Transfered a little temp to the sensor or something.

A temp difference doesn't mean he's incompentant.. but do quiz him next time the car is in there as to why the inlet temp is so high.

[dezz]

  Cubes said:

Maybe the plastic was hot? Transfered a little temp to the sensor or something.

A temp difference doesn't mean he's incompentant.. but do quiz him next time the car is in there as to why the inlet temp is so high.

i quizzed him as to how a car with a 187kw engine could make 182rwkw at the wheels

he told me

"you never know whats under the heatshield of one of these things"

I said, yeah I do...its stock....

he just kept trying to tell me that I have some mystery mod, which I dont have.

[Turbine]

Maybe it's correct temp after all. 55*C for the temp into the throttle body seems pretty normal for around 13Lb boost with say a R32GTR intercooler.

??