zt260

So your running 1500HP race engines and thought you could use mufflers to tame them? At this level its dry pipes and strait exhaust. I doubt anyone can really help you without sizable power loss. You weren't planning to just idle 1500HP around were you? Put a helmet on and head offshore. Should be one hell of a ride!

Mudball

GPM, I see a big ole step in your mufflers...
I also see less than 4" with your tape measure...
At least with my 4" ones, they are 4" inside all the way through. These are 6" OD at the muffler area, with a 5" OD exit. No step at all inside.
That doesn't look right, somehow...

GPM

Actually it's fairly tame, the efi helps a lot, the wife unloads and loads the boat. I tow the kids around on the tube, and on a good day it will run in the upper 140s. But not with any of the GGBS mufflers installed. I don't expect any mufflers to make the boat legal and not kill the top end power, but I do expect to get what I payed for. Especially after the Third time.

zt260

From what I've seen Graham will refund your money if it doesn't work for you. I would just buy turn downs from Gibson and be done with it. It will kill 10+dbs at idle easy. GGB may come out with a bigger diameter mufflers in the future, but for now it doesn't look like he can help you, unless you want to try the insert type mufflers. I really like my extremes, but I'm making a couple hundred less HP.

Mudball

This is what I'm talking about...
Check this out compared to yours, GPM. Maybe it's just the camera angle with yours, but I don't see a smooth muffler in your pictures...
With mine, you can run a straight edge down the entire muffler...

GPM

I've spent some time on the phone with Graham, I even drove to his shop in Burkes Falls, Canada. I tried a couple of sets of his mufflers last summer, he never sends what I order. The set in the picture above is a replacement for one set he sent last year that didn't work. I would like to be able to run 5000 rpms without melting the pistons out of my motor. We talked about the design in person when I was at his shop. They were going to be a custom set, 6 1/2 OD. with a 4 1/2 ID straight through, you can see what he sent. If he can't build it, he should say so before he takes your money, and wastes your time.

GPM

No, it's not the camera angle, that's what I expected to see, only 4.5 id. Maybe that's why I'm a little upset. And the fact Graham uses pictures of my motors on his web site and in his ads. He's never built a set of mufflers that I can use, other than the ones I run on my stock Chevy Suburban.

Mudball

That doesn't sound at all like Graham...
I am shocked.
If I were you, I would call him post haste.

Something is very wrong in this picture...

GPM

I talked to him yesterday morning right after I opened the muffler box. After waiting 6 months now he tells me he can't build what I need. He wants me to try the ones you see in the picture above and let him know how they work. We just modified a set of CMI Big tubes to fit my boat to get more flow, how do you think those mufflers will work.

Lofty

GGB is trying to get out of the custom building business because it's a loosing proposition. Graham has always been very responsive when I've asked him for anything though. I hope this is worked out for you.