Duckstu

So that's how they're getting such unrealistic results.

Of course the higher a gear you choose,.. the more it loads the engine,.. and the earlier the spool threshold will be. That's pretty shady of them to do their tests in 6th to skew the results.

BUT WHAT"S IMPORTANT is when usable power comes in in the gears you use boost the most,.. like 2dn, 3rd, and 4th. And if the turbo's don;t come on until 3,500 rpm in those gears,.. then that's your effective power-band.

I can't say I've EVER gotten into positive boost in 6th. That gear is for quiet highway cruising only (or making 190 mph runs at an airstrip)

Essentially what they're doing by testing in a way that eliminates the "shift recovery" aspect of turbo spool,... and trying to come up with a theoretical, "spool threshold only" rpm for the turbos. But that isn't representative of how cars are driven in the real world.

The industry standard uis usually 4th gear on a 6-speed. Probably has to do with dyno tuning. You would never do a full dyno pull in 6th. The speed would be too high for the rollers. And also,.. the hp numbers are the best when the trans is in a 1:1 ratio,.. or as close to a one to one ratio as the trans has in it.

Anyway,.. THANKS for clearing that up for me.

I do have a way to data log. I have an Accesport int he car,.. and besides allowing me to switch maps, use Valet modes etc,.. it can also display multiple data streams in real time,.. and datalog anything.

aa909

OP if you've never gotten boost in 6th then you 've confirmed my suspicions that you're not getting on the pedal or you have a mechanical issue. If you floor it in 6th you will get boost pretty much at all Rpms.

And you will get boost in the 2K range in 2nd as I stated earlier.

First thing is to Go out on the freeway and floor it in 5th and confirm you get 17+ psi at 3K-4k RPM. If you're not getting this you've got a problem

Good luck

TB993tt

This is actually completely incorrect

Your view is from the ricer style tuning "community" which has flourished in the USA (and has now moved onto Porsches) and has little to do with how manufacturers test the power on their engines.

If you are interested you can educate yourself using the link below which uses a car manufacturer industry standard method for measuring power and torque and bears little comparison to the 8 second 4th gear dyno roller runs popular with ricer tuners !

Have a look at the torque curve in the link below and you will see it pretty closely resembles what the manufacturer says, read around the site and all wll become clear

http://rototest-research.eu/popup/pe...p?ChartsID=785

A418t81

The VTGs are a bit lazy on the low end compared to my old GTR. That said, a good free-flowing exhaust and a reflash go a long way to improving things. Cobb pushes the redline out to 7k. Nearly 4k of full boost isn't bad at all.

This is a 3rd gear pull that I logged with the AP. 20 psi by 3100 rpm.

Screen Shot 2015-07-27 at 1.43.53 PM by glmmd81, on Flickr

Duckstu

That's about what I saw tonight. Your boost is coming in a bit after that 3,198 line. like 3,250 ish,.. which is where mine comes in in 3rd and 4th gears.

Duckstu

When boost comes on in 6th is about as meaningless a stat as I've ever heard. It is NOT indicative of when a turbo actually spools up,.. but it merely a measure of the turbine's aero profile and turbine housing size. It ignores the other half of spool entirely,.. which is shift-recovery (which has to do with the weight of the two wheels (turbine and compressor),.. and how much energy / time it takes to spin them up to such a speed as they not only move air,.. but also pressurize it).

In my last car I had a one-off compressor wheel cut from billet. The goal was to cause the compressor map to shift to the left,.. so it would be more pump-gas friendly,.. and would "pressurize" air at lower shaft speeds. This caused it to make positive boost some 400 rpm sooner that other similar turbos on similar engines.


Perhaps I should re-phrase my original question so that it's clearer what I'm really wanting to find out?

Considering BOTH spool-threshold AND shift-recovery,.. where do your tubos come on in 2nd through 4th gear on the street?

TB993tt

The 6th gear test is easy (for showing spool threshold) and one can compare car to car quite easily, I have a few of these videos in different turbo configurations and it is easy to spot if eh a new exhaust is causing a later spool, if it does it on the 6th gear test it will be less responsive everywhere.

The only proper way to do the shift recovery or boost response to throttle opening is to data log. If you log (at least) throttle %, boost and speed you can measure the time after you slot in the next gear from when you hit 100% throttle to when your boost peaks..... I can tell you that VTG is waayyy faster than K24 to recover full boost but the ferocity of the recovery can unsettle a GT2 RWD chassis somewhat (with a high torque engine) compared to a K24 delivery which is more gentle relatively....

Duckstu

Good to know.

Any experience with the "hybrid" turbos? I was chatting with Neil Switzer and they offer them (perhaps the same ones as other do?).

Anyway,.. basically a different compressor wheel and some porting of the compressor housing.

He said they are more responsive than stock turbos. I failed to ask him if he meant shift-recovery,.. spool-threshold,... or both. I suspect a bit of both,... which would be great. Even if they didn't make any more power.

I came out of a Subaru that was violent,... so the 997, even with a tune and catless exhaust is a tame little kitten by comparison.

aa909

His boost isn't coming in at 3200 rpm, it's peaking at 3200. He doesn't have the x axis marked but by eyeballing it, it looks like the boost starts to come in below 2500 rpm then peak at 3200

Duckstu

Yeah,.. it does start to ramp up much lower than that,.. but the car starts to haul a_ _ at about 3,200. So that's what I consider the spool point to be. When it's there,... not when it;s starting.

At least on my car,.. the turbo portion of the power comes on rather abruptly. I would have thought Poreche would have used turbos that spooled 1,000 rpm sooner,.. and then used the boost controler to smooth things out. The hardest thing on pistons is allowing a turbo to produce high boost at the engine's peak torque point. In Subarus this was 3.500. If you let the turbo make too much boost there,... you'd break some ring-lands on the pistons.

I'm not familiar with what the VE looks like of these engines,... but I'd guess it is near there. So the keys are to not over-rev them,... or let them make too much torque near 3,500.

If I could get the turbos to come on sooner,.. and then reign in that boost peak,... it would be faster AND easier to drive. Perhaps a bit less exciting though.

Anyone have experience with the Do88 turbo inlet tubes? I have a new set here in the box. Bit of hassle to install them,.. so I need to know more before I go through all the effort. In my last car the turbo came on a touch sooner,.. and the car boosted 2 more psi (at least until the ECU learned and corrected for the change). That showed that at last on that platform, they there were a good investment.

A418t81

I run more than 20 psi, about 22.5 through the midrange actually. Most people do not, so the topic of "full boost" is dependent on what you consider full boost. The more aggressive canned Cobb tunes don't hit 20 psi from what I saw.

I have the Do88.se pipes on mine. I ran a 6.7 60-130 on pump gas, which I believe is the pump gas record on the OEM VTGs also. The turbos do spool up relatively quickly down low, but the actual onset of full torque is somewhat abrupt compared to Japanese hardware. Once you are set up to make a lot of torque there, it's a lot of fun.

Duckstu

NICE !

I'm guessing you did the Do88 tubes and some other stuff together,.... so you can't say exactly what they're worth on their own?

I'd love for them to be worth 300 rpm of spool,.. and then have that boost peak at 3,200 rounded off a bit in the tune.

I knew all along that I would likely get a custom tune done one day (I probably had 15 done on my last car,.. by 5 different tuners),.. but the Cobb is a great platform to do it on,... and it allows quick map switching (such as down to 91 or up to 100 octane gas),.. and has immobilizer and valet modes. What's more,.. I can set it back to stock,... un-marry the device,.. and sell it and get a good bit of the money back.

It also functions as a set of gauges in the car,.. and can data log any parameter without having to have a laptop rigged up in the car. So while OTS maps always leave something to be desired,.. the hardware itself is world-class.

I know one of the tuners at Cobb a bit. He tuned a previous car of mine,.. and he does remote tuning as well as travel tuning. Perhaps next year I'll meet up with him somewhere and have that done. In the meantime I can find some time to install the Do88 tubes,.. and perhaps a used pair of GT2 RS IC's. (two pair sold here recently). Then I'll be ready for such a tune.

A418t81

Yep, the turbo inlet pipes, GT2 ICs, and exhaust are all you need to make a lot of power with Cobb on pump gas....enough to make your stock clutch slip, so get ready unless you dial it back some

The turbo inlet pipes were the only hardware change at that time other than the injectors as far as performance goes. At the boost pressures I'm running, there was less taper at high rpm. They are worth it, the factory inlets are junk when it comes to flow.

There are a lot of custom tuners for the Cobb platform. I used ProTuning Freaks and was very happy with their service.

MadScience

This sounds like a variation of something I've not been able to work out with this car. Unless you're on it, you're off boost. You can be completely off boost at 6000rpm if you're just running at some constant speed.

IMHO the folks that claim that there's no noticeable lag are simply not particularly perceptive, or at least insufficiently impatient.

I really don't understand how I would go about getting a really top lap time in a car like this. I suspect I'd just need to anticipate corner exits and get into the throttle a bit early. This is very different from non variable vane turbos where you'd just make sure to be above some engine speed at all times when you want to be ready to go.

Dstutler

This thread sorta intrigued me to go see what mine does (I was thinking my TTs didn't spool correctly). My car is a PDK so I'm not sure I did this right but they start to build at 2100 rpms and with the pedal to the floor is does build to full power +. I tried it several ways and the best (auto/PDK) I could achieve was to put it in Sport+ and slam the pedal. I didn't try to do manual mode but may fiddle with that at another time. I guess the net results I discovered is/was that my turbos seem to spool up normally.