StingrayBR

Kornegle,

That makes total sense. When I first got my Bblades OB/FX Four blade it was a 15.25" diameter. With that amount of blade area it was VERY stern lifting and it would start chining in as low as 60. Another reason we labbed it down to 14" diameter. It is also driven by conditions. More waves and particularly angled set it off. Feels amazing to drive it when it is so light on the water though.

I am thinking I am going to lab my 25" Mirage Plus this winter. Would love to try it at 14" diameter and with sharpened blades. That should give me a little more speed than the 4 blade. At this point though I think I am about done with speed upgrades both because the amount of time you can be in conditions to drive above 80mph is low and pushing my current block any harder will be diminishing returns with the reliability cost.

ACrooks69

One of my favorite props was the 23p Offshore or Vensura 4 blade. Smaller diameter and that extra blade held the load real nice. The P5X-25 was still the best in overall holding and keeping it from rocking side to side. I'm getting less interested in ringing out every last MPH (getting old). I redid my procharger with a better impeller and am getting more boost than I have my motor mapped for. I really need to put my 66lb injectors back in and rescale the fuel table for the added boost if I want to go faster, but I think I just going to put the bigger injectors back in and put a bigger pulley on the blower to slow it down. I'm OK with 76-78. Now if I can get may hands on a -2 imco, whooweee, crank that boost and see what's in her! I think 85 with the p5x and 11-12 lbs of boost is totally doable. But is my ass if I pop the motor again. (Though it last popped when cruising and coming off plane). Be sure to keep an eye on your plugs when running hard on boost.

Don't you have an intercooler on that Whipple? Temp really doesn't matter to my setup, I make my own nice weather.

CDShack

"Stock 300hp - 57mph
385PT stock + headers - 350hp (said 370 w/headers) 62mph
Whipple added 5lbs boost and XR drive - HP unknown but speculate 470 - 70-71mph
Now - 561hp (@5300) - 75mph with my boat loaded - I think 588hp @5,600 rpm and 80mph possible in very ideal conditions"

You know there is no cure for this, right?

kornegle

I ran 67 mph with a 25P Mirage Plus that was labbed. It had more bow lift after labbing but it did not gain any speed. It held the bow higher and porpoised a bit less and drove a bit better but no faster.

StingrayBR

I do have an intercooler. Did you custom tune your EFI? My setup has some conservatism in it. With the exhaust open it runs right around 8.5psi at full throttle and 5600rpm. Whipple said 10psi is the absolute limit with my compression and running pump gas. I have been running 93 in it. They also put a different manifold on it than what came with Whipple so that my fuel/air mix is more consistent across all cylinders.

What grenaded your engine? Was it a bad plug or were you too lean with the high boost? 11-12psi is a lot. Your compression must be in the low 7s?

ACrooks69

I have an Acell DFI7 setup and tuned it myself. I wouldn't say I lean burnt it. I think I was running too hot of a plug and it melted and caused some pre-ignition which caused the top ring on my tightest piston to butt and pop the top off after crusing at about 45 and coming off plane. Motor locked up with hard parts obstruction. Fortunately the only damage was the piston and a bunch of valves. I had about 7-8 lbs of boost at thay time and now is over 10, but I haven't datalogged to see what it goes to because my injectors are too small. I have 8.4:1 compression

StingrayBR

Ugh. Losing an engine over a plug. Are you running 11-12PSI on 8.4:1? I have 8.0:1 and Whipple says no more than 10psi on pump gas. Are you retarding timing or making the mixture rich at high boost?

Kudos to you for self tuning. I got a lesson from Jason's team on how to do it but still have not dug in. So far his tune is very good.

Out of curiosity, how much does your boost drop when you open your exhaust? I have seen my boost gauge move noticeably downward even at levels like 3psi around 50mph when I open the exhaust.

ACrooks69

I have my timing map set to pull a few degrees when boost gets to the higher levels. Fueling is around 12:1 at Wot, maybe high 11's if I pay attention to the Wide Band under way. I cruise in the low 13's. I don't run switchable exhaust, not legal in MN and has no buisness on engines set up like ours. I feel pretty safe running 10-11psi with premium. When I switch over to my Holley Dominator EFI setup, I'll have knock sensors as well.

StingrayBR

ACrooks69 - how much speed do you lose with the P5x - 25 compared to a four blade?

ACrooks69

I didn't, it's my fastest prop. I just like the Bravo XS better all around. Great hole shot, good holding, just doesn't hold it as solid at WOT.