mmb

Hey Rob, It's Mark thanks again for the ride in June!! Boat is wicked fast!! I'm going to have to stick with my heavy tank though!!

I can tell you from what I just went through on mine... Your prop is harder to spin because your trans dics are starting to warp. Soon that thing will be locked in forward. Hate to say it but you’re going to be refreshing those trannys soon.....

If it does trun out to be the trans you and you need help with it let me know. Those things are cake to build yourself. (Plus I have about 15 years experience building larger versions for Caterpillar!)

tssteph

I will chime in here... I know the boat pretty well . The port prop is tighter because it recently had rebuild from Matt at TnT and is barely broke in, it was tight when it came back. Call Matt and ask him about it, I already did once.... I would not suspect drive issues at all. To prove it to yourself disconnect the drive shafts and spin both props, you will find the port drive is tighter than the starboard. Eight bolts and that test is done. This also eliminates the trans disks as being warped, also warped disks would likely only affect the drag when in neutral, not when in gear so the fuel usage would not be a issue. The trans also have very few total hours on them, but hey anything is possible in the boating world. Every twin engine boat I have had used unequal fuel amounts, however that thing was fairly close when I had it. Maybe 5 gallons difference per tank. One thing I will say is make sure both tanks are really full to begin with, that thing always belched a couple times when close to full. I threatened to plumb both tanks together so I could fill both tanks from either side and it would use equal amounts of gas.

leak downs and valve lash are good, I knew I would miss those motors...

I would suspect something in the carbs, just my guess. Swap both carbs from one motor to the other and run it for a tank full and see what you get. I think your will narrow it down some.

rob vanharten

I just noticed some more people had commented on this, ( I am no longer getting auto alerts) Anyways, the motors are tight. Leak downs, and valve adjust proves it!! Drives, and trans, seem excellent also. No reason to doubt them. I have to imagine it's in the carb's..... But they were just rebuilt and matched exactly the same. I want to try swapping them. Or different boost. The port motor uses more fuel, and has a slightly different pulley setup than the starboard motor. The port motor makes 7psi, and the starboard makes 5psi. Not sure that could make up that much difference though. I am not into boost until about 3500 rpm's. And I really don't run around in boost all that often. I have also had bungs welded into my headers, and really need to plug my fast meter into them. Just been a crazy busy summer!! A pig rich reading on the port motor would explain some things.

Kyain

why would you be running more boost on one engine compared to the other? That right there is probably the main factor of fuel useage. More boost is more air being slammed into the engine, which requires more fuel, otherwise it would be lean and hurting the engine

MILD THUNDER

iTrader: (3)

That could be your problem Rob. Even though the carbs are setup the same, one blower may be sucking harder on them (the one making more boost), therefore consuming more fuel. Many times with a pulley change to increase boost, no rejet is necessary, because it simply pulls more fuel as the blower spins faster on a roots.

Whats up with the pulley setup? Is the overall drive ratio the same on them or different?

rob vanharten

They both have a 45 tooth upper pulley, and the port has a 48 bottom, and the starboard has a 46 tooth bottom. This seems to equate to the port making roughly 7 pounds max boost, and the starboard making roughly 5 pounds max. I understand more boost will take more fuel. But... I have 52-55 gallon tanks. Each tank is dedicated to it's engine ( no sharing). And the port tank will take 48 gallons and the starboard tank with take 36-38 gallons to fill. Now keep in mind I am only in boost maybe 20 percent of the time. I just can't see using that much more fuel when I am in vacuum most of the time. Now if I was under full boost 90 percent of the time in a poker run or something, that would make sense to me.

I received the boat with the slightly mis matched pulley's. The owner stated he never realized they were different. Which is understandable. To the naked eye it's very hard to see the difference in two teeth. But I just happened to count them while I was in the bilge doing some maintenance. After that I watched the boost gauges more closely, and sure enough about a two pound difference.

MILD THUNDER

iTrader: (3)

Even though you aren't making boost, the rotors are still turning at different speeds. How much difference that would make, I couldn't tell ya that. I'd prob get them even though. Ultimately you just need to get the AFR meter going though.

rob vanharten

10-4

Kyain

Change in pullies is going to be a change linear across the board due to the different rotating speeds of the superchargers.

mmb

One blower obviously needed to be spun a little harder to make the same power. Might have a little more clearance in the teflon, little more wear in the case/rotor etc. I would leave the pulleys alone if it was mine.