to make it short I will reply for the last time.
you can trust ONLY a very accurate expensive dyno or an engine dyno.
Both gives you rear HP on the engine without gessing for % of RWHP loss!
you can not trust the cheaper tuners dyno!

as somebody else said do the samme test in different days and you will get different results.
(unless you have a really high tech dyno.) Porsches dyno are with 2-3 hp on the same car, it doesn't matter how often you check it.
Dyno is not same dyno and you can not compare the Porsche dyno with the kind of dynos that most US shops use.
I saw at least 5 different dynos on the same car with at least 60 HP difference.(on 996TT)
In Geramny ALL teams who use the same dyno get the same HP for the same car (+ or - 2-3 hp) Only this is accurate
Last but not least there are many road tests with accelaration data on both cars the x51 and the stock 996.
It is a big difference there. The x51 is in real world much faster

The GT3 is even faster and hit easilyover 300 km/h top speed. the 996 with the X51 can NEVER do that
all in all the x51 is a very good solution for someone who want a faster 996 with factory reliability.
The GT3 is for the guys who want to be fast on the track!
The engine came from the GT1. it is not an updated 996 engine. (like the X51)

Konstantin

PS yes many German magzines has real world data for the 996 the x51 and the Gt3.
I would get the X51 for every day or the GT3 for the track.
As we say in geramny the 996 is for Mercedes drivers who want a porsche.
the X51 is for sporty Porsche drivers.(more street seldom on the track)
The GT3 is for Porsche racers (more track soldom on the street just on the way to the race track)
And if you want a fully race car buy the GT3 Cup car.

 

I always take chassis dyno numbers with a grain of salt. Generally useful for relative comparisions only. If you really want a real hp number, use an engine dyno. Any good racing engine shop should have one.
Konstantin, what do you hear in Germany about a flat 8 in the 997??TIA

 

I think my GT3 is just fine for the street.. Drove it to the Hamptons and back today and rode quite nicely.

 

If only they had the Gt3 last year.... actually if I had to say I have a regret it is not doing what I wanted, but didn;t think I could afford which would have been a cup car and a boxter. I went for a hybrid instead and a year later, the hybrid became track only and I got a boxster. Oh well.

 

One of the big benefits from the X51 was that until recently, it was the fastest Porsche cab. The turbo cab has changed that though.

 

ED -

Where in LI are you? Going to the Poconos tomorrow?

 

I'm in Islip. I'll be at the Metro PCA Pocono in October. I'm also doing the Potomic region club race at Summit netx weekend

 

When I said the GT3 wasn't that much faster,that's all I meant. My opinion/observation of GT3: better car than my X-51 in all ways,period.Better clutch,awesome shifter,FASTER,killer suspension,redline was 8000 rpm's.It was lighter,nothing in the trunk,no sunroof,no back seats,lightweight wheels -the car is awesome!BUT, driving it on the highway I was dismayed to find that it wasn't that much faster -it was noticably faster but not that much -very suprising to me but also a testament to the X-51.My response was not meant to be a comparison of the two cars. I was merely trying to communicate to the gentleman MY experience with X-51 and my test drive of GT3.Spending 13k on this is a tough decision and when I had to do it I had almost no input or info save Ed's extremely helpful observations regarding his own experience.It is still much cheaper to go with X-51, 21k cheaper if you compare my X-51 to the GT3 I drove.What the test drive did for me was to totally reinforce my decision to do X-51.