EMI thunder headers?

So here's the deal. My Nautique SV211 with Excalibur 330hp has had 4 different props and I am still not quite satisfied with the performance. One's not quick enough, one's not fast enough, etc. There is just not enough power across the range to make me happy. I only need another 2mph to hold enough speed to do what I want to do barefooting, but I cannot seem to squeak it out of the stock motor without bogging down the holeshot to unacceptable levels.

I am considering adding the EMI thunder headers for two reasons. More power and less weight. I can always add weight but I would like to reduce the unloaded weight to improve the slalom wake (or get it back to where it was before adding the stereo batteries). The headers are $1100 and they claim at least 10% hp/torque increase and save 70lbs. Any thoughts?

Hey mike,


What props have you tried? Are they all Acme? Or another brand?

Kinda compare the pro's and cons of each, try talking to Acme and see if they think there is a prop that may do what you want.

As for headers, you may loose a little bottom end. At least thats what I remember from fixing up cars, the free-er flowing the exhaust the less bottom end you retained, but the more top end you picked up.

Mikeski, also validate that 10% gain. My personal experience when in the 330hp area already is that you will only get around 10 to 15hp. Which as you can see in the math doesn't come to 10% over 330.

See if you can get dyno sheets that validate where that supposed 10% comes into play, I'd be curious to see them.

Headers alone might not net a noticable power difference, unless your stock manifolds are highly restrictive. Headers work best if all components on the intake side and the exhaust side match ie. bigger TB or carb-higher flowing heads-then headers and free-flowing exhaust.

If I were looking for seat of the pants gains I wouldn't even consider this approach.

The Acme 13.5x17.5 is just too tall for decent holeshots, the 13.5x16 is better but it's slow out of the hole and does not have the top end either, the 13.25x16 has adequate holeshot but top end is just a bit shy of the mark. I also have a custom Acme that has been handworked by a prop shop to have a progressive pitch from 16-17.5 and it doesn't have the holeshot. I have already split the hairs with props and the stock Team prop is as good as it gets (what I currently run).

I don't even care if I cannot feel the difference. I would just like to run the 13.5x17.5 prop with decent holeshot.

It would be great if somebody could chime in with some real knowledge on these headers. I have speculated this thing to death and I don't think it's a problem I can solve without talking to somebody that has done the swap.

Luke, they are short tube headers, I had the same experience with long tube headers. I think our exhaust manifolds have a low rpm - high load reversion issue that I hope to alleviate.

maybe try asking on the wiener boat forums. i think this is one of the more popular ones:
http://www.hotboat.net/forums/index.php

I know a guy on lake hartwell that barefoots with a 22ssv and had the same problem with speed. He wet sanded the hull with 1000 grit and gained the speed he was looking for. I did not hear the mph he wanted but love the results.