Hi. I am planning to buy a C6 LS3 convertible with Automatic Shift from the US and have it shipped to Switzerland for my private use, including traffic jam's in the morning and evening and week-end fun.
My question to you guys is, how could I add extra power without it being visible when one looks at the engine? I ask this because here in Switzerland the authorities are extremely strict and modifying engines is seriousely forbidden or has to be registered with very laborious effort. I would like the power to be above 500 HP so I can keep up with Porsche 911 Turbos from which we have soo many here in Switzerland. I had one too but sold it because of my love to US V8's in the form of Corvettes. So I need an upgrade which the guys at the governement test center wouldn't identify (we have to show the car every 2 years to them)...Of course the car has to be reliable and if possible the fuel consumption should not bee much different from the factory consumption - if possible...thanks to all and greetings from a Corvette fanatic from Switzerland

 

Right off the bat, the idea of 'appearing' unmodified or stealthy along with unchanged/stock type fuel consumption will be difficult to achieve.
It would be hard enough to maintain the car's great fuel economy even if one could show the mods (long tube headers for instance can actually help fuel economy but they are visible) but trying to do it secretly can make it even more so.
But all hope is not lost.

I'm thinking of a sort of 'California' (with their more strict emissions etc.) type set up in this case.
A set of C6 Z06 exhaust manifolds (maybe have them well ported/extrude honed for added flow?) and connection pipes.
A (ported?) FAST 102mm intake manifold painted flat black with the writing shaved off along with a 102mm throttle body (optional). This can also be substituted with a ported stock LS3 intake manifold and ported stock throttle body for even more 'stealthiness' (and cost savings).
A mild cam and valve springs.
Some mild head porting/polishing/milling.
A 3200-3600 high stall torque converter (along with an auxiliary transmission fluid cooler).
Higher flow air filter with the 'propped shroud' mod.
160 degree thermostat.
And of course one of the KEY ingredients, professional dyno tuning to bring it all together.
Possibly gears (depends if it comes with 2.56s or 2.73s).
Drag radial tires in the back.

That combo, while not ideal, is almost entirely invisible, makes roughly 500hp (at the crank), should beat any stock Porsche Turbo (non 'S' and non GT2 models at least) in a straight line from a standing start and will even still return 25+mpg on the highway at under 75mph.

 

Wow...that is a professional reply! Thank you. What about a head/cam performance package? I have found many such packages on-line. They say those packages are complete and bolt-on. What would you think of such a solution?

 

You're welcome.
Yes, there are many good heads & cam packages/combos out there and for making great power that is a far better path to take than the 'barely cammed/mild cylinder head work' approach that I'd outlined above.
But if you go too aggressive in that area you will likely need long tube headers and lots more air introduced into the motor via a good cold air intake system to make it all work properly. And those two additions simply won't meet your other criteria (they're blatantly visible during an inspection).
Plus the 'lopeyness' or sound of a larger, more aggressive cam is quite difficult to conceal.

Another possible option, an STS Turbo (rear mounted twin turbos) kit.

 

Depending on your budget, the other option would be to put an LS7 in the car. I did this on my car a few years back and it ran 10.644 in the quarter mile while still idling at around 600RPM. Even with the hood opened the setup looked bone stock but would still outrun pretty much anything else on the road.

 

That's also a great (though more costly) suggestion.

 

You can basically do everything...

You can do a full heads/cam setup with a painted/shaved FAST intake and have it look and sound pretty much stock. You could run Z06 manifolds, or even port them and throw them on and run punched out catalytic converters.

 

why not just buy a ZR1, stock is 638 hp. everyone i know that has one, really enjoys the power and the fact it's under warrantee, gives peace of mind if something breaks. good luck and enjoy whatever be your choice

 

....or even a C6 Z06, amazing cars as well.
And we know he can afford it (insert international stereotyping here LOL ) as ALL of those Swiss people are very wealthy LOL.

 

I live in California and have stealth mods like a Z06 exhaust, a shaved-painted-ported Fast 102, ported heads and a mild cam.

I also think the LS7 is the best option recommended, aside from more displacement it has:

• Z06 manifolds already
• The best flowing stock intake manifold (which can be ported)
• Heads that are already superior to ported LS3 heads
• More cam stock

Another less costly option is to stroke the LS3 to a 6.9 Liter with a 4" crank and rotating asembly.

There is nothing to be gained by extrude honing the hydroformed Z06 manifolds.

 

Have people tried it?

 

Just buy a Callaway Vert........problem solved. It's a bit more expensive,but since you had a 911TT,it shouldn't be hard to swing.

 

Honed out Cast Iron manifolds barely pick up $hit, they're mainly used by racers in classes that must stay stock. Some of the gain is smoothing out the casting, hydroformed steel doesn't have any casting grain.

I don't know of anyone who has bothered to try it for a potential 1 hp gain at the high end.

 

I hear ya. I had merely put it out there (with a '?' of course ) because I'd thought that if there were any ridges or smaller orifices that could be opened up with some porting/grinding or smoothed out that it might help. I figured that even if it was only a few horsepower here/there that it might just help bring the C6 Z06 manifolds that little bit closer to some of the gains obtained from actual long tubes while still maintaining a stock 'look'.
But as you've said, there are gains from it but certainly NOT enough to warrant the effort/expense.