27ZR Capabilities
 

Good evening,
Hoping to catch the eye of a 27ZR expert or perhaps someone with experience/knowledge of the boat.

I have a 27ZR with the 525 and K Plane Tabs. Has a Hardin stage 3 kit which is supposedly bringing the 525 to around 600hp still naturally aspirated and with normal compression.

The boat will porpoise above 70 with the incorrect tab/drive trim. With tabs at a 4 (which appears to be straight level with the hull) she will stay stable in flat water (even better in a light chop) up to max throttle where she is 80/81/82 mph (in fresh water) depending on load and conditions. Have not been able to hold max throttle with tabs up due to instability/porpoise.

I would like to procharge the boat and try to get close to tripple digits. Will the 27ZR hull be capable of this with the kplanes to help hold her stable? If not what is the maximum achievable speed without certain disaster? Would getting bigger tabs and a drive extension help if I do find she wont stay stable with my current settup?

Any constructive input is appreciated,
Thanks,
-Pat

I owned one for a little while but it was only a 496 ho powered boat so I never even saw 70!

I know they don’t like a lot of trim, better to run with just a touch of trim up but no more. You said she’ll run flat out low 80’s with the tabs level, I think that’s a pretty good speed. Bring the tabs up and she porpoises. Maybe that’s part of your answer, you need level tabs to keep her stable at those speeds. If you ad hp, you might still need the tabs. Porpoise at mid 80’s isn’t something you can drive through on a 27ZR, I doubt it’s got much left in it safely.

Chasing the “maximum achievable speed without certain disaster” sounds scary to me. Tne only way you could be 100% certain where that lies is to achieve “certain disaster” then back off a little….🙂

Good luck with your project, they’re a fun boat. I hope you get some more helpful replies.

RR

A buddy of mine had a 27ZR with a built 496HO & Whipple. It would run 90+mph but the conditions had to be perfect. It would chine walk pretty bad above 80mph. It's definitely a drivers boat above 80mph

Thanks,
I would like to avoid disaster and an investment that would result in no real usability past where I’m at.

Do you know if he had KPlanes or the smaller tabs? I think the 496 boats came stock with the smaller tabs. Also do you know if he had tabs in or running them all the way up at 90?
Thanks.

I think it's time for you to upgrade to a 35 or 38 if speed is what you're after.

He installed 280 K-Planes on it but it didn't have indicators. Difficult to use them properly at speed. They were used mostly for plaining and left up after that.