LexVan

Read before buying Fabspeed:

https://rennlist.com/forums/991-gt3-...r-service.html

Hothonda

FWIW...here's a copy of a GIAC advertisement for gains with the 2015 TT/TTS.

2001f4s

Thanks Lex. When I was looking at an X-Pipe for my 991.1 I decided on Sharkwerks mainly based on reviews and what I thought was pushy salesmanship at FS. I was not disappointed with the Sharkwerks product or customer service.

Your post helped me to recall the treatment from FS. Back to the GIAC option.

.2PDK

Did you feel any loss of low end torque with the Sharkwerks?

Earlierapex

Porsche is clearly radically "de-tuning" these engines somehow to provide an intentional spectrum of performance both within the carrera range and vs. the big T turbo. It's just math. Turbo'd cars run lower compression ratios and would make a little less power than an NA engine in NA form. Let's estimate 85hp/L instead of 100. So the same 3.0L engine without a turbo would have 255hp. With 13psi of boost base, it makes 370, which is an increment of 115hp or 8.8hp/psi of boost. The S makes 10.3hp per psi and the GTS makes 10.8 per psi. Usually, the hp/psi increment goes DOWN not up because of heat, so there's some major intentional choke point in the system somewhere. I bet that the ecu is probably reducing boost at higher rpms.

By the way, a Big T turbo makes 13.5hp/psi, so there's a ton of room in the 3.0L for tuners. A GTS with the same 18.1psi but with the same efficiency as a T-Turbo with the right ecu, turbos, intercoolers and fueling to make the same 13.5hp/psi would make 500hp without any more boost. Assuming the tuners can get 12hp/psi by simple "recovery" of the detuning limitation from porsche, an S tune with the GTS boost of 18.1 that stays at 18.1psi at higher RPMs would deliver about 470hp.

arter

Well the Big Turbos also have a 3.8L motor instead of a 3.0L motor so much (all?) of that 13.5hp/psi vs 10.8 hp/psi delta over the GTS is motor size.

You could spin the base 991.2 small turbo up to 18psi ( or more) to match the boost pressure of the GTS with its larger turbos , but the small
turbos lower thermal efficiency ( more heat generated) would produce less power than the GTS at the same boost pressure. Of course you could spin them even harder
to match or exceed even the GTS output. The germany tuner ads project 470hp for the base with just a tune. 525hp for the GTS with just a tune.

Earlierapex

That's a totally fair point, though countered a bit by the fact that efficiency usually falls some with engine size. A corvette makes 73hp/L whereas a 3.4L 991.1 makes 102 (GT3 makes 125!). If they are the same NA hp/L (85), the GTS has the same 3.6hp/psi/L as the big T.

Yes, I agree, but we don't really know how much of the difference is "detuning" and how much is turbo system/thermal efficiency. I'm guessing they are just turning down the boost with the ecu after about 5,000rpms to keep the power down because the base only makes 81% of the hp/psi/L of the GTS. Recapturing that likely would not result in a lot of thermal inefficiency (heat beyond ideal of boost).

It's probably some of both - easy/efficient gains from "un-de-tuning" and heat-adding (less efficient) gains from over-boosting small turbos.

A base turbo makes ~8.8hp/psi, so 5 more lbs would only add 44hp (414 total). If the tuner can remove some "detune" trick like artificially reducing boost and timing to keep power down, they could get the hp/psi back to a more normal 10 or so with these small turbos. That would put the base at 435 at 18psi and 455 at 20psi (those small turbos probably couldn't support that, but who knows for sure). Unless there is a lot of "detune," I doubt the small turbos could really get to 470. That implies 24psi. But their 525hp claim for the GTS implies 25psi at 10.77 hp/psi, so that may be what they are doing.

///M3THOD

The smaller turbos are to complement the lower target boost. The perceptible lag would be exaggerated if the same size GTS turbos were equipped. The larger turbos also allow for increased reliability amd lower boost pressures to hit certain hp numbers. The 18psi on the GTS turbos, might require 19psi on the Base car.

Its also a marketing thing to justify the cost of the S and GTS, at the power levels these cars are being sold at, the same size turbo would be sufficient. The larger turbos on the S & GTS will only see their increased flow benefits at higher tuned levels.


Intercoolers are going to play a huge role for big numbers in these cars while maintaining lower boost pressures. The stock system without the side vents on the turbos has very limited cooling.


​​​​​​​Exactly

randr

Well you quoted some numbers and you were out by a fair margin - 4PSI - my cars are extensively logged. The chart shows actual boost under real driving conditions at 600ft - which is not elevation.

The point being, if you make the effort to measure losses you can determine the actual HP the car is making both at the crank and at the wheels relatively accurately. That particular graph shows the GTS/X51 makes 454HP (out by a measly 4HP from factory spec) - Porsche don't under rate their engines - owners simply don't understand power under the curve and dont know how to integrate and thus cant calculate it.

A well managed torque curve can yield linear power delivery, moreover because of the low - mid range torque the total power under the curve on a run is very similar to that produced by a GT3. There is more to producing a good car than a brute force tune.

Anyhow, I'm out, starting to look like bimmer post - just meaningless numbers games.

Get some quality dyno work done, with measured losses and capture full data logs, accurately time the cars over a set distance - then there can be a meaningful discussion.

Unless you data log you don't know period.

randr

I've posted loads of data logs (everything from friction circles, yaw rates, PDK gear change points under race conditions relative to RPM, boost relative to throttle relative to rpm, brake pressure etc etc). In both S and SX51 form.

My data is 1Hz logging from an actual real car thats owned and tracked - It useful, accurate and meaningful Thats what people do if they really track their car.

The dyno charts I post are accurate and precise unlike your highly inaccurate and imprecise dyno charts.

Bottom line if you can't measure it accurately and precisely you can't manage it (or even understand its meaning in detail)

Over and out.

AnandN

I have no idea why people do this. **** around with perfectly optimized Porsche cars? For both performance and hopefully longevity.
If crave hp, why not buy the 911 Turbo or if strapped for cash, a Dodge Hellcat?
This sounds like a Subaru Wrx thing to me.

///M3THOD

This is just silly.. There are many arguments that could be made in response to this question. Optimized for what?

Why does the entire SEMA show exist? Why is the aftermarket business a multi billion dollar industry? Why have people been "hot rodding" since the automobile was invented?

Subaru WRX's are amazing cars, I don't really even think thats an bash if thats what the comparison was supposed to do?

AnandN

Optimized by Porsche engineers unless you think you know more. The **** industry is also a multi billion dollar industry but means **** to me.
Hot rod ding is fine. I won’t be ‘tuning” my car. It delivers enough performance to me.
Subaru WRXs are OK if you are in your twenties. Crude and unrefined.

arter

and we thank you for your opinion

Dewinator

Am I the only one that’s confused why Sticky wouldn’t pick a less obvious username to come back as?