Trash

You really need a wide band to see what's going on. Reading plugs isn't going to cut it. Put a wide band spacer plate between the manifold and riser/elbow prior to where the water gets dumped in the exhaust.

Get rid of the 23" prop. You need to spin closer to 5500 rpm to be near peak HP which is where you will see peak speed. Don't get hung up on slip numbers just yet. Get a prop that allows the engine to achieve peak hp, then play with blade dimensions if need be. There are trade offs with different props. 3 blades will likely net your fastest speed, but perhaps not best overall performance.

I agree a lot with what 94sylvan says, any detonation is going to make the motor lay down, especially when over propped.

Baja Rooster

iTrader: (1)

ezstriper

couple of things..as said wideband needed to see where you are...may be way to rich now due to carb signal. need to talk to cam people about your combo and find out where the H/P and torque are RPM wise, you may need to spin 5500 or so to reach the needed power gain..if running stock merc dist they have pre-set rev limiter in them and may not let you get to where you need to be. if you are looking for performance I would go with Holley hands down over a edelbrock, used the eldebrocks for years, very user friendly but down on HP vs Holley to me. and last some hulls just wont go beyond a certain speed no matter how much H/P you throw at it.

guimond47

NHGuy

I have a 21 and a 19, both are Mirage plus. But the 19 is recent and I haven't got it to wide open throttle.
I just tried to run your stats in the UEM pistons compression ratio calculator, The deck height was a little unclear. But if its .002 in the hole you have 11.4:1 static CR, and if it's .030 (?) it would be 10.62:1.
I have flat tops too. I had to get some big 76cc chamber heads to drop my cr down to 10:1. Unless I am missing something you probably ought to bag quench and get your CR down with head gasket thickness.

If I'm wrong great, but if I'm right you will either want more gasket or less total timing or some combination of the two.

And If the motor isn't assembled I'd just put in some pistons that get perfect quench at 9.4:1. Otherwise you'll be chasing troubles for the few hundred it would take to build it better right now.

guimond47

So your saying at 10.62CR is too much for this engine?

I myself inputted my specs in the dynamic calculator. i got 13.83 static and 11.1 dynamic CR. Right now i have 93 Octane in there. i will want to be running 91 octane or 89 at times..... i think i miscalculated when i was building it causing it way too high CR.

I also Bought a sniper EFI system and installed that last weekend. i run around 12.5-12.6 Air fuel ratio at WOT. 13.8 around cruise. and 14 at idle. engine seems to run strong and smooth like this.

For my prop. i THOUGHT i had a mirage. its a vengeance 19P.
Turns out my buddy had a mirage plus 21P and i tried that tonight and got a max of 58mph at 4650-4700 rpm.

Let me know what you guys think about this compression ratio.. maybe this is causing all my problems

guimond47

i can lower it to 10.64 CR from 11.1CR with some .041 Thick head gaskets i have here in the shop.

SB

iTrader: (1)

What is your actual compression ratio ? I don't care about dynamic...it's useless.
If you are ever going to use 89 octane gas you want to limit your physical compression to under 9.5:1 . Closer to 9:1 will provide more safety.

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guimond47

well static compression ratio is 13.8 and dynamic is 11.1:1 . not sure what you mean by actual. i had my engine WOT and i tweaked the timing where it ran best at within 1-2 degrees to dial it in..

SB

iTrader: (1)

actual = as measured physically. When you use : Piston dome / combustion chamber/headgasket thickness/piston in the hole/etc/etc

No dynamic compression stuff please. This messes more people up than it helps and it's not needed anyway.