Jim Rockford

Surprised this hasn't been put up yet... came across this video yesterday. Should be good for some controversy I would think. Additionally, it has JCR exhaust fitted, not saying at all that this is at all the cause of the result, but what is going on here?

And unless I missed it, they never talk about drivetrain loss. The guy who works the dyno doesn't look like it's his first day on the job, so I am guessing they are indeed factoring that in and not comparing wheel HP to catalog numbers.

kart125

If they are showing whp, 395 whp is actually pretty impressive! With 10% drivetrain loss it would mean arround 440 crank hp, with 15% loss close to 460... they didn’t mention if they did a coasting pull in neutral to estimate drivetrain loss. If they did then yeah! Pretty lame numbers!

Jim Rockford

I am hoping the same... that this is all whp, and it makes directional sense that way, as you hope the GT Dept. understates the catalog output a bit. If it is indeed the other way though that's more than a little concerning.

Archimedes

Stupid video. They don’t give any specs on the dyno, whether it’s wheel or crank, and if crank what drive line loss assumption, etc.

Again, Porsche has said that the test every motor and they don’t let anything out of the factory that is more than 5% off spec.

Jim Rockford

Porsche also said their diesel engines were a-ok. I tend not to believe everything I am told.

Archimedes

Because Porsches routinely underperform in performance tests indicating bogus hp numbers...

Jim Rockford

How does that go again?

Fool me once...

JCR-Porsche

I’m getting the overlay, the stock 718 GT4 made 380hp and Luke’s car made just a touch shy of 395hp. Around 15hp up on a stock car on the same dyno.

The car has one of our Silenced Valved Race Pipes installed, numbers tie in with our results in other tests but the overall number is low for whatever reason, be it no dyno mode, sub optimal air flow, bad fuel, altitude, weather. So many variables. Not that it should matter.

Dyno’s are a tool for testing differences and not boasting about peak numbers.

This is why I much prefer to quote real world results, peak speed at the end of a straight around a lap of Silverstone is so much more relevant than a dyno graph ever would be.

JC

GTChamp

I read modern transmissions now only have 5-8% drivetrain loss. Which would put the HP at crank where you’d expect 420 or so. I’m not sure why Luke thinks it’s ‘low’ unless the measures are at the crank but the dyno is clearly measuring at the wheels

Pokerhobo

The video seems to show a clear misunderstanding of how dynos work. Pretty disappointing video. Looks like just a clickbait title and video to me.

blackholescion

There’s more to loss than just the transmission. Tires, wheel size, driveshaft (if applicable) etc. You can get closer with a hub dyno but even then you’re at the mercy of the rest of the components. A dyno measuring crank horsepower is a dyno that’s simply wrong. It’s calculating just like we are and that’s not a good measurement. To truly get crank power, you have to take the motor and stick it on an engine dyno. There’s lots of variables as mentioned. Sea level, weather, etc. even the best dynos, which standardize to weather conditions, are still approximating.

BGB dyno’d one on a dynojet (IMO the gold standard) and it made 375 at the wheels which implies right at 414 with 10% loss. But again, it’s all calculation (and dynojet is approximating by standardizing to specific weather conditions. Hell you can make a dynojet read 5% higher just by changing the method (sae vs std) which uses different weather parameters)

JCR is definitely spot on. Dynos are useful for measuring differences in cars or mods if you do a before/after the mod on the same day or the vehicles the same day. Otherwise, the same dyno, 6 months apart, will read differently for the same car.

Gorro47

maybe some of the hp loss have to do with the wing risers he installed
JK

But still the numbers seem low

Jim Rockford

Agree with all this, there are so many variables... but dynos are also good for strapping two cars down back to back (Ie. 981 GT4 vs 982 GT4) or 982 with exhaust and without exhaust and seeing the results. It is hard to tie dyno results back to catalog numbers because of the variables and unknowns, but back to back comparisons on the same dyno should be a good method to orient the results.

Rennolazine

Its hard to compare 2 cars dynoed on 2 different days unless they have the same DA and you are comparing the same pull from a given sequence. 15 hp is alot for just a muffler. Soul boroscoped the stock pse muffler and its basically wide open with the valves disconnected. It still sounds like crap compared to the jcr but the 2 x 400 cell cats and 2 opf seem way more restrictive than the muffler at least if valves are wide open. After watching countless sound vids as all these companies roll out exhaust system i would say the gt4 design is one of the only cars i would consider an exhaust just for sound. Its night and day. Stock doesnt sound like a flat 6 to me at all. My 2c

JCR-Porsche

I prefer to say that we’re 4mph up at the end of the Hangar straight vs stock 718 GT4 with our exhaust installed than quote numbers. 148mph peak vs Weissach GT3RS at 152mph, no arguing with those numbers or the fact that our 718 GT4 drives past a stock car in a straight line

As for the sound, no doubt. Any system which doesn’t properly merge gasses from bank 1 to bank 2 will sound pretty flat and uninteresting.

JC