Performance?

[86Pirata454]

When upgrading a boats engine do you have to beef up the trans? also do you want low end or highend hp and torque. and whats mroe important hp or torque?

[Fman]

When upgrading a boats engine do you have to beef up the trans? also do you want low end or highend hp and torque. and whats mroe important hp or torque?

Your prop alone can give a lot more low-end torque. I would say if you are a wakeboarder you need more low end power to plain the boat with all the ballast weight. For direct drives, you can get away with a little more top end power.

My '08 uses a 14.25x14 wakeboard prop, what prop are you currently using on your boat? A prop change is simple and will give you more or less top end/torque.

[jet]

Go straight to the prop man. I bought the biggest prop i could get 14x14x.105 cup. It was like putting a supercharger on it and turning the boost up to max! Jet

[sybrmike]

Direct drive tranny's are fairly bullet proof. V-drives a little less so due to the input/output angle. However, a prop cutting through water doesn't shock load the trans like drag slicks on the track, so they can handle some extra hp/torque without problem - just keep good fluid & cooling thru the hx & should be fine (unless you're talking blown nitro race league - there are special tranny's for that...).

It's a "tow" boat - not a racing hydro. Torque over hp. Most marine engine cams are similar to RV cams - designed for pulling a load. You need lots of low end grunt to get a sac'd out hull on plane & then a flat torque curve to be able to hold speeds from 10 mph surfing, 20 boarding, to 30 skiing. Big hp motors get "peaky" and our tranny's can't shift to keep the engine in it's sweet spot.

The right prop makes all the difference - it's the equivalent to the differential gear ratio in your axle. You can "gear" it for towing or for speed - but you can't have both. These hulls weren't built for speed & only the footers need anything near 40 mph. Talk to the prop guys (Nettles, Acme, etc.) & they can recommend the right prop for your combination of engine/boat/use.

[86Pirata454]

thanks guys. im currently looking at some new boats and wasnt sure on what to do since i am used to my old 86 pirata (454) and everything ive looked at has a 351

[beast 496]

You need to remember to keep the engine in the proper RPM range, to low of RPM at WOT can burn valves, To high can spin brgs, ect. The heads and cam have alot to do with recommended RPM. Just by putting on a higher pitched prop can do more harm than good, you might go alittle faster but take off will suffer as well as engine strain. On our personal Supra, we ditched the enemic 454 and swapped in a 496 HO MPI. Still using the Standard Borg Warner tranny. 425hp @ 5,000 rpm. Al

[Salty87]

thanks guys. im currently looking at some new boats and wasnt sure on what to do since i am used to my old 86 pirata (454) and everything ive looked at has a 351

what size boat are you looking at?

don't sell the 351 short. it's got plenty of power and is alot less thirsty than 454. in a 19-20' boat the only difference you'll notice is you can pull the same load, have more top end, and spend less on gas all with the same prop than with the saltare/pirata hull and 454. these are my observations having spent around 50 hours in a sunsport with 351 and an acme prop. actually, the load may have been lighter because the smaller hull required less weight to get a better wake.

[86Pirata454]

its a 97 pirata. also its a GT40.

[jpeters]

I recommend Stock. The engine , Tran etc was all engineered for that particular prop. Anything else puts undue stress on something.
My opinion. After 50 yrs of trying to modify my stuff, I have accepted the fact that A group of qualified marine engineers are smarter than me.