hey p-jet I have one for you. call  or pm me 702-449-2684 Deryl

i have a street doninatoe manifold $85.00

thanks Jim, looking for a dual plane.

Frank

pjet, I would say go with the Street Dominator and use a 1" four hole spacer, works pretty well.

Just out of curiosity though, why dual a plane dealio?

GT

In my opinion, a single plane manifold is completely inefficient for a stock engine running at or below 5k.

Maybe, but just my feeling, once the engine passes about 3500 RPM it will want more even manifold pressure at each port, a dual plane will not allow that. We normally cut the web down between the two sides on a dual plane anyways, not all the way, only about 1-1 1/2".

The WOT tuneability becomes less "twitchy". (read; slop will count the same as skill LOL) On a marine/jet deal, I am a fan of open plenum, then again, I am an oval port guy as well....

Carry on sir, I was curious on the train of thought.

Sounds like you have things under control.

GT

I am an oval port guy as well, and cut the divider out of my dual planes as well and smooth out the sharp turns below the plenum.  My train of thought is that single plane = A/F mixture robbing from adjacent cylinders, uneven runner lengths.  Bad at low RPM, not an issue above 5k.  Dual plane means no cylinders sitting side by side are connected to the same manifold.

Anybody ever test this out on a dyno? sorry for the jack pjet, this has been something I have debated several times over the years.

The reason I bring it up...The Olds 455 we had in our Spectra 20 would run right to 4800 rpm and stop like it was on a rev limiter...No major mods, Crane Marine specific grind cam, built right and fresh...A impeller.

Removed the intake (Factory spread bore dual plane of iron) and traded the four hole adaptive spacer (1" spread to square) and put on a square to square four hole 1" spacer and an open plenum Torker, picked up almost 100 RPM and had better throttle response, not very scientific, but we were blown away, until then I thought like you... (< 5K=dual plane).

I may still have a Performer in the shed, will check in the AM, probably painted blue though... I'll make you a deal you can't refuse if it's still there.

GT

I have read alot of about the pros/cons of the two manifolds when I built my street engines.  My stock 455 (just like yours) will run to 5200 easy.  The DP 650 does not even get into the secondaries until about 4.5k...I am afraid to go more. 

Thanks Glenn, Blue is the color of choice!!

Frank

Sounds like you got a good one, my uncle (an automotive machinist and GM guru) said it more than likely had to do with the fact that the Jet boat motor is not running a "free" 5000 RPM, it is running a fully loaded 5000 RPM, a lot like running a car straight up a hill at WOT...whereas the car engine frees up as it accelerates..major vacuum differential in the two applications, the boat engine (specifically a jet) has very little vacuum at WOT and it never increases because the load never goes away...

On an automotive application, the load eventually fades away increasing the manifold vacuum substantially, even though still at WOT. I always put it in my mind that because of the lower vacuum levels, make it easier for the air/fuel to get into the heads. Open plenum seemed to be the easiest way. Could be totally full of crap though, wouldn't be the first time

FWIW, you simply cannot compare an automotive engine to a jet boat motor, very little of the tuning processes apply. Now a vee drive on the other hand, they are very efficient users of horsepower and therfore have some similarities with a car...Not many, but some.

GT

I wish I had acces to a dyno for like a week...