Re: *Cheap* Horse power Gains? Not Really
darned, anal retentive, overanalytical engineering types!!!
(for whom I actually have a great deal of respect and admiration)
So in my niave but overeducated synopsis on torque and horsepower:
if we make things like hull, gear ratio, prop, etc... constant for now,
peak horsepower is the best indication of how fast we can go (referring to wot and if propped so peak is right at wot).
peak torque is how quickly - at what rate - we can accellerate to a given speed.
as we increase horsepower, we increase top speed, as we increase torque, we increase "seat of the pants" performance (assuming throttle response, etc...).
as we increase torque, we increase the force available to accellerate, to get on plane, pull a skier out of the hole, etc...
Horsepower is the rate at which we can do work, torque represents the rate we can increase the rate at which work is done.
x ft pounds (bizzare british units...) of torque at 0 rpms, is potential energy...
Does anything think it is an accident that maring engines target peak horsepower at a relatively mild rpm range (ie. 4800 rpms), a broad, flat torque curve with a max somewhere around 3500 in many cases? This engine design gives the best all arround performance for pulling, running fast, mid range accelleration, getting on plane under wide range of conditions, etc...
Since almost everyone here when talking aobut adding horsepower is really interested in increasing accelleration and / or top end, shouldn't we think about the primary factors involved in each? Maybe it would be better to make a list of all the things that can be done that have a measurable impact on the imporant factors. While I got the comment above indicating that the sum of all the small steps doesn't necessarily equal the individual steps... it is not always worse - sometimes more. for example, say you get 10 hp gain from a little bigger carb and intake, then add a cam. the cam you choose by itself might add 10 horsepower, but the combination of the carb, intake and cam adds 40 horsepower. We're not even considering what engine speed that's at - it all makes a difference and is interrelated...
Wouldn't it be more useful rather than bantering about on symantics and definitions if we simply listed some of the things that can be done to good effect?
engine mods obviously have huge potential, but let's talk about some of the other things... and don't scoff at things that will make a 1 mph difference - remember for many average sized, average hulled recreational boats, that's on the order of 10 horsepower!
Prop selection: being propped correctly for the kind of performance you're interested in. This is a complex topic with a lot of subtleties. There are some great articles and information out there if you're interested. Many of the words of "common wisdom" are not necessarily correct if you're not the average boater or don't have the average goal in mind (that's most of us!). A lot of what people told me about propping was not correct once I really dug into things and then got even further off when I actually started trying a bunch of different props. Don't accept convention without question! Prop change can make a HUGE difference. (as can having one fixed if it's got dings on it or is out of balance...) Like many of the things here, prop selection and the related interdependance on other factors involves so many degrees of freedom that it winds up being more of an art than a science in the long run, but there are factors we can get a handle on to guide our thinking and trial and error efforts to make improvements.
GEAR RATIO: There are a couple of great older power boat articles on this topic that really opened my eyes on the relationship between gear ratio and prop selection. The point I want to make is that when we're talking aobut spending hundreds of dollars on performance mods or a new prop, don't assume that the factory handed down gear ratio will yiald the best performance for your application. Especially when you can buy a different upper for your alpha drive (sorry, most common here) and change the gear ratio. Contrary to the doctrine preached by some of the well-experienced, well-educated folks on here (no offense intended, your correct in most circumstances and I greatly appreciate the experience you share), the factory chosen gear ratio is not always the best for a given purpose or performance focus. gear ratio directly changes both torque and horsepower at the prop... It is especially important because it plays into prop selection and determines the range of prop characteristics we can take advantage of in a given situation.
weight and weight distribution: we see huge differences, especially in lighter planing boats when we take extra passengers... think about what you're hauling and why... 100 pounds puts a lot more wetted surface in the water and costs more horsepower (torque per unit speed???). Lose the extra crap you don't want or need, find an anorexic girlfriend and leave the overly healthy one at home, check your voids and foam for water!!!! This can be HUGE (hundreds of pounds)! and don't scoff at things that might be 20 pounds or so, find 10 of them and that's usually a mph or so. it all adds up and it costs the same torque and horsepower we're talking about trying to gain above... it's all about choices! weight distribution can also be a big deal - especially if it's off kilt. here the weight is, affects the aspect ratio of the hull in the water and changes the hull efficiency. and yes it is difference in different performance goals, running conditions and especially boat types.
Hull: when is the last time you looked at the bottom of your boat? is the running surface smooth? free of major defects? If you're running a padded v-hull, is the pad clean, smooth (or lightly sanded - lets leave that one alone for now, ok?), very flat and free from defects? this is not so hard to fix... for a padded v-hull for example, get a good straight edge and a sanding block, jack the boat up off the trailer a bit and "clean up" the running surface and make sure the pad is very flat (unless it has hook or rocker built in on purpose that you want to keep...), symmetrical and free from defects.
How about the outdrive and skeg? for faster boats, a huge portion of the drag the boat experiences at wot comes from the surface of the outdrive, is it covered in crap? scratched and gouged? or smooth, well cared for and free from defects? (take a look at a picture of a boat planing out, think about how much of the hull is actualy touching the water and then compare that with the amount of surface area of the drive is in the water....). if it's a mess, or especially if the skeg is battered and bent, this is not difficult to clean up, etc...
set up... is the boat planing at an angle where it was designed to be the most efficient? obviously this is connected with various things above and others, but for example, trim angle, prop-shaft height (most of us have little control over withour spending a lot of time and or money, usually both). would trim tabs help you optimize other things and allow you to further your performance goals?
engine issues. we've talked about these a lot and there is a lot of good stuff here. Probably the most important and most neglected is just optimizing what you have! new plugs? gapped properly? plug wires in good shape? separated adequately? ignition connections clean and tight? grounds clean and tight? carb clean and jetted properly for your set-up the way it is today - not necessarily the same as it was when you bought it or before you added that new spark arrestor or made exhaust changes... fuel filters clean? valve lash adjusted properly?? fresh, high quality engine oil (an aside here, we tend to run higher viscosity oils by habit, but don't forget that viscosity at temp adds drag inside the engine, use the right oil and better yet good quality synthetic... will that alone make a diffrerence, probably not one you can feel clearly... but it adds to the equation and taken together with many other "little" things can make a difference)? When't the last time you did a thorough tune-up on your engine? checked your compression?
Major and bolt on modifications are a huge topic and havre been beat to death, but here the key is optimizing the combination of mods to work together.
drive related... is your outdrive in good shape internally? good quality synthetic drive oil with the correct viscosity? (too thick can be as bas as to thin - no excuse for old, burnt or wet... drives are designed for a specific combination of lube characteristics, viscosity, flow, shear thinning, etc... and heat removal characteristics. Here again, adequate lubrication combined with good flow is key as are other aspects). is the drive properly aligned?etc...
OK, I'll get off my soap box. The major point i wanted to make is that there are a lot of things that can be done to achieve incremental increases in performance - most of which can be done by many of us, and for less than the cost of a tank of fuel. Lets say you do 10 "little" things... and get a .5 mph or 5 hp from each... that's the equivelent of 50 horsepower overall and on the order that adding vortec heads, mild cam, aluminum intake, 4 bbl carb and a days work would net on a 350. (oh and if you go there... the stock spark arrestor becomes limiting about there and can make a noticiable difference.. and the other mods don't make nearly as much difference if you don't take the time to tune again... carb jetting, optimizing ignition timing, etc...)
What other things like this have people had experience with that made even a small difference in preformance...
ie. adding a bow cover on a bow rider? I've heard 2-3 mph difference on this one (top end).
lightly sanding the pad and drive surface area (I'm thinking that this is somewhat of a crap shoot... enough texture and you induce minor bubble formation at the surface, lowering density and hence viscosity in the boundary layer which decreases drag in the laminar flow regime if we assume the same reynolds number and boundary layer thickness. a little too much and we add turbulent flow to the equation, thicken the boundary layer and increasing drag slowing us down... now listen to others, coat the surface with rainex or some other silicone wax / coating, dramatically increasing surface tension and what happens... my head hurts at hurts at this point, so it's time to quit before I hurt myself...)
All comments come with the disclaimer that I'm not expert, current honest opinion (always subject to change with new information or schooling by others, etc..) of a backyard hack with a mild obsession...
sorry bout the book... got carried away...
