MarkRobinson

Yeah, that's not fair, not planning on running a built supra engine...btw that's an SC300 or NA supra valve cover...rarely used on non-turbo supra engines...probably one with a spacer headgasket...still good for 800hp or so.

Not fair, but hey, it's not a Porsche either.

If my 951 powerplant fails to keep my interest I can always plot a 928TT engine in there.

62-65mph was fast for 1980 and the boat has a "hook" designed into the hull, same as a car having a large racing spoiler in the back: it sticks good but creates a LOT of drag. It usually takes 450hp to surpass 75mph in my boat. :/

DR

Sometimes even 75mph is really fast and getting up to 90 can get you in a little trouble....especially in 6-8' seas :-)

Tass 928

Can I get some opinions on exhaust system performance results ? The back story:
Initially I wanted headers that were more in keeping with the drag boat style so I bought some BBF headers ( remarkably close port spacing to a 928 head). These headers have fittings for direct water injection which is supposed to provide header cooling and some sound suppression. Unfortunately the low engine mounting, the high "floor" of the boat and the exhaust port angle all added up to no clearance, or at least not with a margin of safety.

Plan B is the water jacketed "log" type manifolds you see in the picture below. These manifolds will run a lot cooler and probably a little quieter . I have them mocked up with a set of rusty old 3" pipes with supertrapp mufflers and I think this may be close to the final set up. I will make the new pipes out of stainless and likely keep the supertrapp baffles.
This is an 83' Euro engine.

Would you leave the exhaust diameter at 3" all the way back?

Or reduce to 2.5 "?

I'm thinking of working an "x" pipe into the vertical portion of the pipes, thoughts on this idea ?

Overall look...Awesome? Goofy, WTF are you thinking Tass?

jej3

I don't know much about boats unless they have a Center Console and fishing rods hanging off of them

But I think where you're going is sexy if you move everything to a subtle Porsche style (i.e. Silver boat) with kick in the pants visible 928 motor

123quattro

Keep an eye on those copper elbows on the front pan return. I've heard they can have a tendency to crack in automotive type applications.

The engine is looking really nice. I don't think the logs look bad. Obviously they will lose some power to the BBC headers, but who cares. The logs sit far enough away from the engine that they show off the cam carriers more.

MarkRobinson

I'd keep it dual 2.25 or dual 2.5 so it'll sing & hit the high notes.

Water-injected manifolds are mostly for enclosed engines: you could ditch that altogether since it's exposed if that's any easier.

Mark

Leon Speed

Footage of Tass practicing some high speed runs.

AirtekHVAC

Omg! WTF?

tilac999

I like it Tass!

Ducman82

did you see the sunglasses hit the window edge and stay in the boat??? bet they were expensive....

Tass 928

Hi Mark, thanks for the reply.

I'm using a tunnel hull and the engine is dropped into a shallow center sponson (see pic). The adjacent full length stringers come up right under the exhaust ports of the 928 heads and I am concerned with exhaust heat on the fiberglass. (see 2nd pic).

I agree with the your thoughts on keeping the proper 928 sound by using smaller dia. tubes. What do you think of the x-pipe idea? Is it worth the effort on this stubby little exhaust system?

Tass 928

Thanks, I'm anxious to get through the last of this mock-up stage so I can get the hull stripped down and into paint.

Thanks for the tip on the copper..I'll keep an eye on them. I figured they were not pressurized so no big risk. That was part of my effort to clean up the front of the engine. I'm trying to get away with no belt driven accessories up front.

Thanks ! The sooner we get rid of the 70's graphic and red carpet, the better!

OBehave

One more post Tass and you become a member of the Grand People Club!
Make it a good one!

docmirror

I don't see any value in using an x pipe near the header. The work involved wouldn't pay much dividends in power, and although it might change the sound some, it could also make it worse. Exhaust design is kind of a black art. Without pressure test ports, and a dyno, and all that stuff I'm of the opinion you should just keep it neat and clean, with some exit water injection down near the lower elbows to keep it a bit cooler.

<edit: I should mention that the water injection has to be done so that water when sitting can't back up into the combustion chamber. The old water logs use those funny humps to provide a backwash block, and if you inject down at the lower end right into the exhaust, it could provide a path for water into the cylinder, which would not be good. >

123quattro

dubstepified...
http://www.youtube.com/embed/77E8H6QkDvg