We have simular troubles here with my Cig Bullet exhaust thru prop...! Twin 600hp on dyno with 5300 rpm and only 70 mph on fresh water. :-( (Bravo 1 - no notch - 3 blade props 27 labbed or 4 blade 26 - 5000 rpm) X-dimension is 7" below pad. Boat weights 4 tons - 31 feet.

Looking into dart heads and the cyclon header
Where did you buy your heads from

Buddy had a 31 bullet with 600s. Turned 26p bravos to 5500-5700rpm. Had CMI headers

[QUOTE=TELLefant;4515634]We have simular troubles here with my Cig Bullet exhaust thru prop...! Twin 600hp on dyno with 5300 rpm and only 70 mph on fresh water. :

You are trying to get 600hp worth of exhaust through the prop hole?
How many CI engines?

[QUOTE=14 apache;4515670]Yes, we have to go thru prop - that's the law. :-( We have custom lightening headers which fit with the y-pipe. They are 454 mags with Edelbrock Viktor 24 (7748) aluminum heads. We know that we loose some hp thru prop but even silent choice is not allowed here.

[QUOTE=TELLefant;4515684][QUOTE=14 apache;4515670]

Yes, we have to go thru prop

Wow that is killing you for sure.
Wonder if you could do some porting on the drive. LOL


Smaller camshaft could help make more speed.

You're right - that's killing us since years! Terrible issue, and yes, cam is changed.

The thru prop exhaust law,there is part of a conspiracy by volvo penta lol....
.....but i have heard their drives offer less backpressure through the prop ..

[QUOTE=TELLefant;4515684]just curious, does the law state "thru prop" or below waterline? if you have speed masters or arnesons there is no way to do that. if it states below water line could you not just run down pipes that exit at the bottom of the transom. would be better than trying to put it all thru a 2 1/2 inch hole in the gimble.

prob has 500 hp or less at the prop - maybe something like this - Dyno shop a higher correction factor than believed as its way in their favor, Not uncommon,

Auto headers to marine non true headers loss of 40 to 50 hp., Dynoed with no or min accessories bolted up front to engine - 10 to 20 hp loss depending, also on the dyno for peak numbers maybe timing was or could be have advanced more so than currently. Next is, Hp loss thru the drive. IMO - this engine 475 to 500 hp at the prop max.

[QUOTE=compedgemarine;4516922]Actually it's not 'thru prop' the law says. It's a matter of noice. The max. they allow is 72db (!) and that's nothing we could reach with dry exhausts.

I absolutely agree with your thoughts. I also assumed that there is not enough fresh air passing through these original old carb flame arresters we still have on the new Fast TBI (combined eith MEFI 4a). I saw 4-5 black spark plugs on each engine after 4-5 hours on the lake next to the others which looks pretty different: they are almost brown, blue and ending in violet. They look like washed down by fuel. Next to that, I think my X is too low (7" below pad direct in front of each drive). But I couldn't find any experience with a -3 extension box on a Bullet yet. Well, also with this idea next issue is how to go from Y-pipe thru -3" extension box...!?

But I couldn't find any experience with a -3 extension box on a Bullet yet. Well, also with this idea next issue is how to go from Y-pipe thru -3" extension box...!?[/QUOTE]

1 block off plate welded on each end of a tube, then drill out the block off plates
http://eddiemarine.com/exhaust-block-off-plate

i would research short drives first,
http://www.offshoreonly.com/forums/g...es-bullet.html

Has this boat been weighed? If the water is coming off the step at a 45 it seems heavy in the ass. With a stock 454 magnum the water should be smooth off the notch. Maybe the wood is saturated.

Interesting point Katanna. We put the Bullet on the scale and we weighted exactly 8850 lbs with 1/2 fuel. That's the same weight as in the old Bullet datasheets. The 454 isn't stock anymore. We installed aluminum Edelbrock heads, Fast TBI, Mefi 4a ECU but we have to go thru prop with all that (law)...

Trasome is dry had it all checked out

You are not getting close enough to your higher Tq and HP numbers.
2000 27 Fever with an HP500EFI and a 4-blade Bravo prop runs about the exact same as you are seeing when it's at the rev limiter.
You have too much prop, and typically a 5-blade prop will not be your fastest top end prop. You need to get a 4-blade Bravo 1 or similar.

Remember, you have to over trim to get your top speed to get RPMs up, and then back the trim back down to get the prop to bite; old school "Pamlico" trick.

I have. To try that on the trim
I have a 23 hydro 4 blade its 15 1/2 dia I will see how that spins up

Darr