Southocg

Anyone know (having set-up and run personally) the right X dimension on the Heat?

Steve Zuckerman

Yes,
What are you running into? If it's excess slippage (high teens to 20%), and/or lack of bow lift, you are probably too high.
For years, the step hull boats went out at 19.25"s, which is just too high for most Heats.
I have a 1" spacer in mine, making it an effective 18.25"s. Props also have similar effect. 5 blades will perform better than 4 blades at 19.25"s because of their additional blade area. I never had much luck with Bravo 1 4 blades at the stock XD. They will work at 18.25"s. The 5 blades don't seem to mind the extra 1" of depth either.
I am also running an Imco case which seems to help by loading the prop better at speeds above 85. And it handles very well at speed. Keep an eye on your water pressure if you add the Imco. They ram a lot of water at higher speeds with their LWP, and it will send your water pressure through the roof.
Regards,
Steve

Southocg

My problem has been RPM's. I need to spin above 6 and for the life of me I can't seem to get there. Slip always around 9ish. Bow lift not a problem. Getting on plane, no worries what-so-ever. Every prop I run whether it's a 4 or 5 blade I always top out around 5800. I've run stock 26 and 24 B1's as well as labbed 26 and 24's with very little in the way of movement on my tach with almost identical results. My thought was that I may have to much drive in the water and might need to shorten the lower (Imco standard height with lwp) but I'm not sure what it's currently set in terms of XD.

Don't get me wrong... the but runs great but I know theres a little left and it bothers the $$$hit out of me. In havasu last week at 113 with 15 gallons and 2 people (25 PX5) I ran 88 at 5800. Put on a labbed 26 B1, little more fuel but just under a 100 when I ran, 87 at 5750........

Linster

You may be running out of torque. Most engines make peak torque at 4200-4400 and about a 1000 rpm after that the curve drops fast. A super charger flatens the curve but it still falls off in that range due to the cam size. Boats respond to torque more than HP. The faster you go, the more drag, the more torque is needed. AT those speeds in a heat. the hull vs HP could be at the max. Just a thought. Steve & Dave have the most experience with these boats
Good Luck

Steve Zuckerman

I also remember some conversation from someone regarding your boat. That conversation was concerrning correcting the drive height. They told me that yours had been lowered to 18.25"s. Measure from the bottom of the gimble to the top of the notch (not the XD, which is a little more complex) along the transom. I'll measure mine and we can compare.
Linster's comments regarding HP and torque are valid too. I have never run an Ilmore/Viper, and don't know much about the 700. A friend in Knoxville, TN has one in a 26' Lavey Craft and it runs really well....low 90s/high 80s. Sounds a lot stronger than the other 2 versions.
With those small props turning the same RPM, your rev limiter may be set lower than than you think. I would get a knowledgeable tech/rep to run a scan and check the limiter.
What is it supposed to be set at?
It may just be the heat. With the exception of the new Merc 600/700/850/1075 with variable boost, all of our motors are going to fall off in high heat and humid conditions.
Regards,
Steve

Southocg

As far as the rev limiter goes, I have spun one prop at 62. I dropped to a labbed 24 B1 (done by a certain havasu shop). My slip went through the roof and my speed fell way off (7-8 mph).

I'll play with it a little more this week and see what I come up with. The latest props, a stock 25 PX5 and a Bronson 26 B1, both ran well in the heat last week so we'll see what they do at altitude. The only problem, we're supposed to be in the mid to uppper 90's here all week too.

Steve Zuckerman

From the top of the transom notch, to the bottom of my transom bracket (not the trim line housing), measured along the transom, is 6 3/4"s.
That equals 19.25"s XD on my boat.
You might want to measure yours.
Regards,
Steve

Southocg

I talked to IMCO and they had me measure in a different direction.

From the bottom of the keel to the center line on the prop shaft = 4 1/2". The drive needs to be level with the keel of the boat.

Steve Zuckerman

The "X dimension" is the vertical (not measured along the transom angle) distance between the driveshaft, and the bottom of the boat.
I use a flat or square yardstick taped to or held against the pad. Then, you can measure off the top of the yardstick with a framing square, to the tilt pins on the side of the gimble bracket. The tilt pins are located at the same height as the drive shaft.
It does help to level the yardstick, and check the framing square for vertical alignment.
Since I know mine is 19.25" measured this way, I thought you might want to measure yours "the easy way" along the transom from the bracket to the top of the notch. If your's measures 6 3/4"s, you're at the same height. Above (unlikely)or below that, would give you something else. Either way, you would have a known height to work from.
For instance, 19.25" is generally too high, and a 1" spacer usually results in much better slip %s with a 4 blade. If your "bracket to notch" measurement is more like 6"s to 5 3/4"s, you are lower by 3/4" to 1" and closer to what we have generally found to be a better performing XD on a Heat.
What Imco is asking you for is propshaft depth. Another practical way to determine gearcase and propeller depth. That is partly how they determine whether or not a nosecone, standard length Imco case, shorty, or spacer would help a specific boat.
What did they say?
Good luck and keep us posted with your progress.
Steve

Rage

What was the slip with the "labbed 24 B1 (done by a certain havasu shop)." at what speed/rpm?