27 ZR Power Upgrade Questions

[tomahdonzi]

I currently have a 2008 27 ZR with the 496HO power. I did add Dana Headers this year as well, but otherwise stock. I am running a 1.65 ration Bravo X now with Bravo 4 blade 28 pitch prop. Also have the Bennett Trim Tabs, which are pretty worthless. Anyway, I'm considering upgrading the power to around 525 (or about 560 with the headers). Probably will go with the Raylar kit as opposed to buying a used Merc 525. I would also upgrade the drive to the Bravo XR (1.50 ratio with 28 pitch Bravo prop), and add Merc K-Planes (280's).

My main question concerns take-off performance. I don't know that there were too many 525 27's from the factory, and I'm not sure if anyone on this site has upgraded their power from the 496HO. I'm wondering, though, if anyone has any thoughts on what I could expect on take-off performance. Right now, with 5 adults and full tank of fuel, getting on plane is pretty tough. Usually have to move people forward, rock the steering wheel back and forth, to get on plane. Putting the Bennett Trim Tabs down does not help with take-off. So, I'm wondering if I added the extra power, as well as the K-Planes, whether I would see better take-off performance. I spoke with Chuch at Donzi, and he doesn't really think I will see much difference, until I get on plane. Then of course, I will see a difference in performance. I guess one question is whether the K-Planes themselves would help with take-off performance, and maybe I start there and see before I spend a chunk of money on more power. I'm pretty sure I'm going to do the K-Planes regardless, because I'd like a little more control at top end, which the Bennett's just don't provide.

I'm able to run 70-72 at top end right now, and I don't really care about running faster (it would be nice, but it's not critical). I'm mainly looking for better take-off performance. But maybe the hull design of this boat, with the single engine, just means that take-off will always be a challenge.

Any comments would be appreciated.

[smokediver]

You should see a significant difference with the k-planes .. I would do that first and go from there . My 27 fever needed the planes buried in order to get up and running ..

[mrfixxall]

usually alot of tab and stepped hulls is not needed,,it will hold the azz of the boat to the water..what you need is a maximus 5 blade prop,try one and you will notice a big differance in plaining,,you may loose a few mph in the top end but you will save $$$ in fuel with a lower rpm cruise speed..

[smokediver]

I have to disagree . The planes actually lift the back of the boat and thats what brings the bow down . As you bring the planes up the drive can also be trimmed out a bit . trim on a stepped hull isnt as dramatic as on a conventional hull as the drive height is usually higher . My fever was a single step with about the same performance as the 27 zr . The maximus would be a great prop and with the k-planes that would get you out of the hole much quicker and cheaper than adding more power ... unless you want more speed then add more hp.

[450rrrr]

i have been considering k planes as well.i have the o8 zr27 496 ho.the first of the year i installed a set of bennett st16 plates on her.with four people in her i have to say it has made a big difference.jumps right onto plane.so i could only think the k planes would be better.also they have helped out with that top end chine walk.just the wife and i in the boat and almost a full fuel load and a very flat sarasota bay we got 74.8 on the gps.all stock.
if you put them on please post up your thoughts

[The Hedgehog]

Not all steps act the same. I hear that the 27 likes them though. I would do the merc 525 over the Raylar. Ray has a nice setup but I am seeing friends get better dyne numbers with a 502 block.

[rsg69cpa]

I too have the 2008 27ZR and use the (small) tabs to help reduce the planing time. Even with the 496HO, the 28" 4-blade prop adds a bit to the planing time. I would be very interested to hear how the larger tabs work for you. Top end for me has been 70 mph with 5 passengers and 3/4 tank of fuel without pushing her too hard (4600rpms)

[tomahdonzi]

Thanks for the comments. All very insightful and helpful. I think for sure we'll do the K-Planes and go from there. I haven't noticed much benefit from the Small Bennetts on take-off, but they do help settle the boat down at top speed (not completely, though, as it still has a tendancy to get squirrely if I encounter some cross waves at top end). I think the K-Planes should help on take-off, and do a much better job controlling the boat at WOT. Even if it doesn't completely solve my take-off issues, it will do a much better job controlling the boat at WOT, and that's important to me.

I've looked into different props. I've spoken with Mercury Racing and BBlades. Merc thinks that I'm propped just about perfectly right now. Based on 72 top end at close to 5,050 rpms, I'm getting something like 11% slip, which is pretty great, I'm told. Obviously, I could go down in pitch, and get more hole shot, but then I'd have to be careful at WOT to not hit rev-limiter. I think as far as props, my best option would be to consider a Merc labbed prop. Merc indicated that a 29 pitch labbed Bravo 4 blade would give me another 150 rpm at WOT, and maybe a little more rpm's on hole shot as slip would be a little greater. But I haven't done that yet. I was going to wait and see what difference the Dana Headers made, which I installed this summer. So far, I'm not noticing a huge difference, although I have not tried 5 people in the boat with full tank since putting them on.

rsg69cpa - 70mph at 4,600 seems strange with 28 pitch prop. Do you have the 1.50 drive ratio? I have the 1.65 and I'm turning 5,000 rpm's.

The Hedgehog - I share your feelings on the 525 versus Raylar. I think the trick is to find a decent used 525, though. I don't want any headaches. Want the boat to run when I want it to run. But I will keep my eyes open for used 525. That would be my preference by far!

[tomahdonzi]

You should see a significant difference with the k-planes .. I would do that first and go from there . My 27 fever needed the planes buried in order to get up and running ..

Thanks smokediver. Pretty similar boats, and it's good to know your experience. What motor are you running?

[smokediver]

Thanks smokediver. Pretty similar boats, and it's good to know your experience. What motor are you running?
Sure ... I no longer have the boat . came back around and now have a 22 blackhawk . The fever had a bbone stock 496 mag ho .. 2004 . The ZR has the extra step and the drive height is real high which is good for speed but not so good for getting on plane with a bunch of people on board . There is a set of 280's for sale on offshore only in the swap forum . I think 1500 for the whole set-up ... Indicators arre a good thing to have as well and they really helped me out alot when I was learning the boat .

[rsg69cpa]

[ QUOTE=$originalposter]{$pagetext}[/QUOTE]No, I am merely a bit uneasy about that "squirelly" feeling you describe. Hitting 70 was my goal, and it only took 4600 to get there. I spent the summer in the UP on Lake Superior and noticed a lot of impact based on the wind, current, rollers, etc.

[rsg69cpa]

[ QUOTE=$originalposter]{$pagetext}[/QUOTE]P.s. 1.65 drive as well.