SB

iTrader: (1)

Glad to see others onto this also.


Yup, no good. 4bbl carb's are rated at 1.5"Hg, and at that # they are too big of restriction. +/- a few tenths from 1.0"HG is good and usually not worth chasing for less restriction.

And that 1.7"HG on the dyno.

In an enclosed engine compartment this # can get even worse.

SB

iTrader: (1)

FF - just to make this part clear.

Again, 4bbl carb's are rated at 1.5"HG restriction.

Your carb registered 1.7"HG. The dyno measured 850cfm.

So, I hate to break it too you, if that dyno's airflow meter is correct,your carb is smaller than 850cfm.

MILD THUNDER

iTrader: (3)

Theres also more to it, than just a vacuum reading. Even IF you were to get it down to 0 vacuum, which is nearly impossible, it doesn't do any good, if the carb's not atomizing the fuel properly. You may actually see a LOSS in power.

This is why, slapping a 1050 dominator on a 330 merc engine, would produce unsatisfactory performance. Just because the manifold vacuum is very low, doesn't necessarily mean, more power.

SB

iTrader: (1)

.75"HG to 1.1/1.2 "HG will typically be fine with carburetor metering.

Metering well under .75"HG usually requires a carb guy on his game.

getrdunn

iTrader: (7)

Is that why you can throw a match in a can of gas and it goes out instead of boom?

Look at bck's thread from a while back when he posted results for us on his 548?

getrdunn

iTrader: (7)

There is clearly a restriction in this combo and until it gets figured out then larger cam is useless. I'd bet less cam at this point would make more power. But sounds like he's off to a car project and wait til refresh.

getrdunn

iTrader: (7)

I would be willing to bet that cam with 305 or 315 cnc heads and 454 R intake and dominator would bring it to life.

Although yes I get it. Cam was spec'd for his parts. That obviously went wrong.

MILD THUNDER

iTrader: (3)

Before we get too excited, anyone see my post earlier, about the throttle cable issue on the same dyno? That would certainly have an effect on tims dyno number if in fact, thats what was happening, but not in the boat. Throttle controls when using a servo, can fuk up. I like when some shops mount a camera above the throttle plates during a dyno pull, where you can see creep back.

A more common cause for both the low measured air flow and vacuum would be that the carburetor was not mechanically at WOT during the pull. Sometimes it is hard to get good carburetor travel with the available leverage and linkage. Older dyno's with the water piston used to creep all the time and loose the WOT during a test session, even the newer ones with servo or cable linkages can creep or loose the WOT capability.

MILD THUNDER

iTrader: (3)

I was pro 4500 dominator on this build from the get go, so don't get me wrong. I'd still like to see a dominator on it.

Tim, mount a vacuum gauge on it in the boat. See what you have. Then try the flame arrestors off. See what you have. Then crack the hatch open, and see what you have.

This would be alot easier if you had daytona sensors boxes using a map sensor, and data logging this stuff.

endeavour32

iTrader: (4)

Tim- what are you using for arrestors? I was loosing 3-4 mph with HP 500 arrestors compared to no arrestors on my 650 hp 509's. Like mild said above, if you haven't tried running it without them on do it. If you gain- you know that's at least part of your issue and a easy fix. I ended up going to 10X5 gaffrigs and that problem is now solved.