Couple of thoughts:

- Twin cams don't like straight pipes. M8's like them even less (not enough back pressure for good bottom end)

- If you want to keep your Harley powertrain warranty intact you're stuck with using their tuner. That's the reality, no matter how un- American it sounds

 

Does the Twin Cam or M8 hate Vance & Hines short-shots? Can pipes be tuned to put out the correct back pressure?

 

And if you want to stay compliant, pipes without catalytic converters are a no go.

 

You have no idea the number of times I've had that conversation with spanking new owners and bitching their bike won't run right after installing straight pipes, had a couple guys I thought were going to trade hands with me over it they got so pissed not being told what they wanted to hear.

 

Okay.
You've got it all figured out.

Not sure why you asked about aftermarket.

 

Here is my sneaky idea: I would keep the original exhaust at home. I would ride with no-cat pipes. If I should ever have to bring the bike into the shop under a warranty claim, the original exhaust would be swapped out again.
Can Harley be easily fooled?

 

And soon as they hook up the laptop to read the CPU which they do with every bike that comes in it will snitch you out because your readings history will be so far out of spec. You cannot get around the snitch ware in these things anymore. Worse part is it isn't the dealer, the program automatically sends everything to the moco through the internet and your **** get flagged there.

 

So the new Harley customer is paying a crapload a money to get spied on by Moco.

 

OMG not another "how can I scam harley" thread......Either you need to keep your warranty and that's ok...., or you dont and are fine dealing with the consequences. Its very simple.

 

As I always say: if you can't afford to push it off a cliff, don't modify it. Warranty is no longer a guarantee if you do.

Now, that said...straight pipes on an M8 are untunable. All your bottom-end torque goes straight out the tailpipe.

You have to determine your goal: all-out performance, or compromise performance for personal preference? Do you care about warranty? If so, true performance is only marginally achievable. It would seem you are conflicted on those points. Good luck.