Chase, another question. Aside from the water inlets, what are the differences between that drive and my XZ drive?

I'm almost positive there is no difference in the lower units between a Performance Bravo 1 and a lower unit of the XZ Bravo 1. I believe all the differences are in the uppers. That is where the weakness in the Bravo drives are and where they improved with the XZ. I will try to contact a Mercury rep that I know to verify, check what references you have as well.
The lower I have has 128hrs on it, fresh water, 1.5 ratio. It is a swap you can easily do in your driveway. There is a total of 7 bolts. 3 nuts on each side and a bolt in the trim tab. Drain oil, remove 6 nuts and 1 bolt, drop lower unit, replace lower unit, install bolt and 6 nuts, fill with oil, done.
Give me your zip and I can get shipping charges.
I'd also be willing to buy the lower unit back, minus shipping charges, if it doesn't solve your cooling problem for some piece of mind on your end.

Well doing a little search here tells me that the XZ lower has a larger prop shaft, so your prop would need a new hub. Now, need to check out if the drive shaft is different too which I would think would make it not possible to install without swapping, which then would probably not be cost effective.

HotLavey,
have they checked for a restriction anywhere. We have the same lowers and with a high X dimension I'm pounding well over 60 lbs if I don't regulate it. If you open your 4 nose holes to 5/16, this will be in effect identical to the single 5/8 hole found in all of the IMCOs and such.
Your pressure will be derived from the ram effect on the nose so I don't know that the big ole dual stage will help you at all. It still has to pull the water from the nose. You may also (per Dustin) want to install a 5/8 restrictor plate where your thermostat would normally go. This will also help keep the pressure up where Whipple likes it.
Don't get frustrated and start throwing more money at it YET. I think your issue can be resolved without much additional cost.
Good Luck,
Dave

Dave,

Good to hear from you again. I hope you're having a great summer. I opened up the nose inlets as you suggested a while back. Didn't seem to make much difference. The restrictor plate sounds interesting. How does that affect the flow? We noticed that the intercooler dump has a pretty strong flow at idle and the dump from the heads is pretty weak. When the boat accelerates the head flow seems to stop. It's really hard to see clearly tho as there is a lot of exhaust water and turbulence back at the transom. At idle the pressure shows zero, although I am getting a strong flow from the intercooler dump and less from the heads. The only mod that really made a difference was plugging all the side inlets. Max pressure went from 10 to 15 at WOT. As for the dual stage, another pick up is also installed along with a sea-strainer.
Is that restrictor plate available through Whipple? Tell me a little more about it if you have time.
Thanks again for your help-

Tom

Tom,
Great summer to date Thanks.
The restrictor plate is a simple stainless or aluminum plate that is the same size as a thermostat. It would just go where your thermostat went originally. Just a flat piece with a 5/8 hole drilled in it. I’m sure Dustin or Gary Teague stocks them or can whip one up for you easily enough; Probably only about $5. This just keeps the pressure up in the block by restricting the outlet of the water a bit. This is the size that they feel works the best all around for their setups and creates good pressure. This also helps to eliminate steam pockets along with your rear dumps. I assume your rear dumps are only ¼” right?
I was getting a zero reading on my gauge at idle also. I purchased a 5 lb check valve with ¾ fittings and installed it on the out let hose of my intercooler. This keeps the water running through the block at idle and not through the intercooler. As soon as I start to plane I have intercooler flow and at idle I have good water flowing though the block to cool it after those hard runs.
Hope this helps…
Dave

Dave , I just spoke with the installer and he did install the restrictor plate in my engine.
The rear dumps are 1/4".
After talking with the rebuilder we decided to intall a seperate pick-up for the intercooler along with a check valve to limit the pressure, as well as a sea-strainer. No dual-stage water pump at this time. I hope this will solve the problem.
We just returned from a week at Lake Mojave out of Cottonwood Cove(on a houseboat). I have never seen so much flat water in my life. The ski hissed, it was like skiing on a mirror. The problem was self-control with the throttle. At 15# pressure we had to stay out of the boost and it was tough. I buzzed it to 76 mph when I was testing max pressure and had 4 lbs of boost and backed out real quick. I could run 60-65 with no boost so that's where we kept it. Heading for Mead in Sept for the Regatta and we should be good to go then.
I'll let you know.

Tom

Hey Tom,
Sounds good. You won’t need a check valve though. Beings you can’t run both of the pickups with one pump, one of the pickups will be feeding the intercooler by ram/forced pressure only and it won’t flow until your on plane anyway. No desperate need for a sea strainer on this water source because it never draws.
The sea strainer will be inline with the pickup to pump/motor line.

Been dying to try Mojave. Looks fun and doesn’t have the water issues we’re dealing with in these parts. Email me and let me know what you thought of it.

Also, I do have a transom mount pick-up. Polished from Stainless Marine if you haven’t ordered one yet.
Dave
[email protected]

Dave,

If you are able to rent a houseboat out of Cottonwood, do it. I have never seen such a huge amount of glassy water in my life. We did have some wind chop at times but most of the time it was glass. Catherine's Landing area can get very busy and rough, that's why we opted for the houseboat and Cottonwood cove. There are no other facilities on Mojave except for Catherine's, Cottonwood, and Willow Beach. Cottonwood and Willow are well above Catherine's(i think approx 20 miles for Cottonwood, and another 14-15 miles to Willow)We have already reserved the 70 footer for next year. We did it early as they only have one of those. This year we had the 59'. It was great but we have a few more people going next year so that's why the bigger one. Big problem there- gas was $3.20/gal. Yikes! Not going into boost probably saved me a lot of money. Oh, another thing, very few boats in that area during the week. We may have seen 5-10 all week but weekends are busy there.
Thanks for the pick-up info, I'll take a look.

Tom

Tom,i just did a leakdown test on 540 to see if short block can stay together in boat or has to come out and be freshened for the new afr heads this winter. # 7 cyl is SHOT (80% leakdown with LOTS of hissing coming out valve cover breather,120 psi cranking compresion after 10 turns compared to 150-160 after 4 turns for rest of motor),i'm wondering even with stock size injectors if never having bored out fuel rail (like you did on this build up) caused # 7 to run lean under the conditions i run my motor,i'm now thinking that ANYONE running a supercharger with merc mpi system should do this mod as insurance,once i have motor out and torn down i'll see whats really happened to # 7 and i'll post pics. Believe it or not boat still ran 84.5 and 84.2 last two times this season,Smitty