[QUOTE=class6;4500876]Mine always crank near the weld. I fill the header with argon and keep it flowing from a second bottle as I weld to try to cool and keep environment as clean as possible. works a lot better. no cracking since I have been doing that.[/QUOTE
That is the only way to weld stainless tubing.

I have not seen this from them (Ptaff ) but have not seen their 655. Will add that's great they upgraded and updated their marine builds ECM / electronics side of the coin, I have to say NOT knocking them but 4 or up to 7 years ago and back I seen and worked on few of their engine builds with MEFI 3. That is 20 years behind the times for new builds plus no montoring of wide bands using it, I am saying this as they are looked at as high end builder and was kind of shocked seeing MEFI 3. That's all I am saying no other intention.

What ECM are they currently using and for the engine builds with 8 widebands ? Thanks

Is this engine a max race effort build? I also did 8 02 sensors just for dyno on dyno headers. There is power mounting injectors high or above the bells on the injector tubes. So chasing a few hp on individual o2 corrections I don't understand? Help me!

I wanna say they were using Motec ecm's or there is a company across the street from Motec they were using. Can't remember that was probably 3 years ago I had spoken to the guy that was building there cylinder heads for there big N/a motors. Claimed 1050hp pump gas @ 5,000rpm which I found a little hard to believe.

Do yourself and everyone else involved a favor and put header drains on the headers so when the engine stops running the water drains out of the headers. When they are drained the headers don't swet as much. This will help keep moisture out of the O2's and it seems like the headers last longer in general...

wouldn't it be just easier to buy a used big cubed motor and detune it.seems much simpler.the big boys already figured it out.

A new boat with a used motor? wouldnt be right. It doesn't seem like used stuff sells for much less than new on yb or racingjunk. Wouldn't be many 665s to choose from either.

MoTec has an ecu that will do closed loop per cylinder.

You are correct that with the Hilborn the airflow per cylinder is going to be more even than say on a single plane manifold. I personally have seen swings of 30hp+ on normal engines in the 700-750 hp range with individual corrections on. It may be as low as 2-3% with the Hilborn best to worst cylinder which may only be 10-15hp.

The real reason is so that I can put a good, solid tune up in it and know that I don't have one cylinder that's a little on the lean side. We are making no bones about it, this is a high-performance effort the limits imposed being compression ratio to run pump gas and rpm for longevity.

Mark months ago brought up to me about he likes these certain drain plugs but did not realize that I have at the very least 150 in stock of those exact drains Plus 3 other styles including your blue style drains. Anyways we cover that already about putting drains in for the systems.

Also the simple way is to pull the water hoses off at the headers to drain them. I never leave water or even anti freeze sitting in marine exhaust headers or manifolds / risers / because you never know when internal leaks pop up while just sitting there especially 6 months of winterization sit times. That's the last thing I want is a liquid sitting in the exhaust system for 6 months straight.