Petevb

Actually it's significantly better than that. I need to run but I wanted to leave this here- this is an early data slice from an autocross, mostly 2nd gear (brake bias was off so those Gs as limited). Second gear is relatively short but it's very effective...

randr

Turbo lag is indeed real and is measurable

I'm also an engineer - its one of my faults too well played. I'm pretty sure we understand one another and our different perspectives Cheers.

TB993tt

Whilst I do of course agree that turbo on off throttle response can never be like a N/A one I would like to state that if you sat in my 2017 turbo S and I floored the throttle at 1000rpm in say third gear and I shielded the boost gauge you would not be able to discern from your buttometer when the engine went from atmo to positive boost pressure on the gauge - this is what I describe as zero lag.
Moreover when the settings are in nutter mode with the anti lag system active (keeps the throttle open during on off throttle) the boost is pretty much instant, not linear enough for the sub 2 foot adjustability but that will always be the domain of a N/A motor IMO.

fxz

it s actually the opposite
There s no turbo lag with dual clutch trasmission that can be a loss of control feeling in some circumstancies

Jean

Pete it could well be, and it looks from this graph that it definitely is, I don't doubt it, quite a jewel you have I don't know the specifications so I used a 964RS with 997 Cup engine and a 4 gear gearbox on 16" tires. Close to 1.5G lateral on narrow tires, you must be on full slicks!

- A 997 Cup reaches peak 0.72G @ 5,000RPMs at the tire but has slicks. (0.52Gs @ 3,000RPMs)
- A 991 Turbo S 1st generation peak 0.8Gs. @3,000RPMs upwards

All above are approximate.

GrantG

A 1969 911 (912) with carbon body panels and PCCB's is a FAR lighter car than a 964. And Pete has a 6speed gearbox.

Build thread in his signature here: https://rennlist.com/forums/porsche-...9-gt3-cup.html

Jean

That explains it.

Wow.. And those are not narrow tires

Roughly estimated at peak 0.77G acceleration in 2nd gear based on 993TT box with the listed weight.

ipse dixit

Yes, indeed.

Infinitely better than talking about flippers or the value of the R versus the GT3 with a MT.

Loess

I have to say I enjoy the technical discussions with logical (not butt-hurt) people with different views.

Why would you need to make on-off throttle adjustments mid corner? Neutral throttle through the corner and gradual acceleration on the way out? Why would there be lag in this situation? Adjusting the throttle to play with the traction limit would upset the balance with a turbo or NA car especially with a 911, although it can be fun. I would think that turbo lag would only be an issue if you close the throttle and then open it again expecting instant linear response. If you need to do this in a corner didn't you over brake?

My 3RS has turbo lag in low rpm range. I press the gas and not much happens for a bit. But maybe it's just the relatively low torque between 1500-2500 rpm. NA cars don't have linear response curves either.

The problem is that if you want a lot of horsepower and torque it's hard to get that from an NA engine. Even the 812SF has less torque than the 2RS. Some people like miata's some people like the feeling of torque.

hf1

The only way to find and stay close to the grip limit/peak mid-turn is by straddling it. The only way to straddle the grip peak is by making small steering and throttle adjustments that make the car oscillate between a little bit under and a little bit over the grip peak. With turbos, these 'little bit' adjustments are all but impossible, making the oscillations around the grip peak much wider, hence riskier and less efficient.

This great article explains this in much more detail, especially the graphs on Pages 2 and 3:

http://www.motoiq.com/MagazineArticl...r-Control.aspx

Petevb

Close. Here's the 2nd gear thrust curve based on the wheels dyno and race weight. The gearbox ratios are custom and it has a short ring and pinion, aero losses are not taken into account:

bccars

I drove the 991 and 991.2 turbo cars. I can feel AND hear the lag. No need for a boost gauge in the dash !

Jean

Very impressive thrust curve, 0.9+ Gs in acceleration. A bit speculative without more details, but vs. my calculated 0.77G, and assuming a shorter 3.89 R&P, it would put you right at 0.92G at around 6700RPMs and 0.55G @~3000RPM.

I will go listen to my turbo lag with bccars now

T10Chris

Throttle response is not linear in a turbo car- turbos respond different based on throttle, rpm, load on the engine going up or down a hill, engine temp, your facial expression, etc etc. Whether or not you define this lack of linear response as lag is semantics, but it is a fact. It is also something that you learn to drive around and deal with. I love tracking turbo cars.

NA car is linear and mostly predictable on throttle. NA car is pretty much same response at the same time, every time. You can focus more on driving the car, steering inputs, what chassis is doing mid corner, what tires tell you, etc etc. I learn more and improve skills much more driving my NA car, and it translates over and makes me faster in my turbo car. It is so much easier to learn a technique in something that is linear.

Even with a high compression ratio mostly NA design engine with turbos added, yes response is great but you still get the non-linear wave of power when the turbos light up. Complicates that whole balance the throttle thing, but you learn with seat time/experience what to expect and how power comes on and chassis handles it and correct way to react in the specific car.

One is juggling, other is juggling on a unicycle. Easier to learn what to feel for and what is going on and what to look for without the added variable of the unicycle... or in this case, the turbochargers

Petevb

It's actually a 4:1 R&P from a 993 cup car, should get you to right around .95 Gs and then I think our math is aligned. No question you've still got me for low end torque... until I can find coin to spring for the 4.0L upgrade, anyway