Low end torque - 4 stroke vs. 2 stroke
 

Wanted to get some opinions on this subject. Assuming the HP is the same, say 225hp for this discussion. From my practical experiences there seems to be a NOTICABLE difference between the 2 stroke and the 4 stroke when if comes down to low end torque. Given the same boat, with comparable weight and prop sellection, the 2 str. seems to jump on a plane a lot faster than the comp. 4 stroke. The 2 stroke winds up faster also. The 4 strokes seem to respond slower out of the hole but preform equal after about 10 seconds when steady on a plane. I know the 4 strokes weigh more when compared to the 2 stroke, but the powerband/torque curve must be different too, to make such a difference when comparing engines of the same power rating.

is everyone elses experinces similar??

Re: Low end torque - 4 stroke vs. 2 stroke
 

The Suzuki 250 has a TON of bottom end torque and a HUGE diameter prop.

Re: Low end torque - 4 stroke vs. 2 stroke
 

yep

Re: Low end torque - 4 stroke vs. 2 stroke
 

2 stroke all the way!!

Re: Low end torque - 4 stroke vs. 2 stroke
 

Don't get me wrong . . . I love two stroke motors (especially old lightweight stinky ones with a LOT of power), but the Suzuki 250 is very impressive.

Re: Low end torque - 4 stroke vs. 2 stroke
 

Big, I wouldn't have thought otherwise :cool:

Re: Low end torque - 4 stroke vs. 2 stroke
 

I heard some bass fisherman have those new 4 stroke V-Maxs' strapped to the back of their sleds and love em. Those guys are all about hole shot as much as top end.

Re: Low end torque - 4 stroke vs. 2 stroke
 

as a rule of thumb 2 stroke has a great holeshot but poor low end torque and a 4 stroke has good lowend torque and a poor holeshot, relatively speaking... A lot of time people confuse holeshot with lowend torque... But running the right prop and having a lighter boat tends to mask a lot of it

Re: Low end torque - 4 stroke vs. 2 stroke
 

I'd have to disagree when it comes to outboards. A 4 stroke won't spin the same prop as easily as a 2 stroke on acceleration. The 2 stroke will rev quicker.

Re: Low end torque - 4 stroke vs. 2 stroke
 

You would be surprised how much the variable valve timing on the new 4 strokes helps. That and Suzis 16" props is very impressive.

Re: Low end torque - 4 stroke vs. 2 stroke
 

thats holeshot....we don't disagree...lol

Re: Low end torque - 4 stroke vs. 2 stroke
 

The Zukes use a lower gear ratio in the lower unit to swing the bigger prop and compensate on the low end power, it apparently works. The 2's will usually give better performance, the yami guys say they needed 25HP more to equal the sanme feel if at all.

Re: Low end torque - 4 stroke vs. 2 stroke
 

I ran a 250 2 stroke yamaha on my 23 with a bracket then switched to a 250 suzuki 4 stroke. I'd have to say that the suzuki with that bigger prop had more noticeable low end torque. I loved that zuke.

strick

Re: Low end torque - 4 stroke vs. 2 stroke
 

Seems like there are two different torque issues that matter to boaters, (1) hole shot and (2) ability to stay on plane at low speeds. I can see where the fast rev ability of 2 stokes would get you out of the hole faster(maybe that's not torque?), but does that have much effect on torque delivery relatively low in the torque/rpm curve, needed for low speed planing. My experience is only with 2 stroke outboards vs 4 stroke 1/0s, but the i/0s seemed to have far more torque delivery low in the rpm curve and much better low speed planing ability. I never put much attention on hole shot, maybe because divers load so much weight into the boat.

Re: Low end torque - 4 stroke vs. 2 stroke
 

I would think planing speed would be determined by a combination of hull design, propeller design and weight distribution. You would only need enough torque to move the hull forward to a speed that hydrodynamic forces take over, whether it be a 50 horse or 250 horse motor. It would be interesting to see what that torque number would be on a properly set up SeaCraft hull vs. others. Do any of these new motors have a torque display? Bushwacker showed me some interesting print outs from his E-tech; no torque readings though.

Re: Low end torque - 4 stroke vs. 2 stroke
 

I don't think it is quite that simple in practice. All those things affect planning speed, but when its sloppy, the forces on the boat keep changing rapidly. If you don't have the low end torque to maintain prop rpm, what happens is: its sloppy and you want to plane slowly, so you increase throttle until the boat gets up and planes, then its going to fast for comfort, so you reduce throttle a little to slow down a little, but then the boat falls off a plane and you're going 6 knots again, repeat. If you have sufficient torque, you can hold the boat on a plane at a slow and more comfortable speed.

Re: Low end torque - 4 stroke vs. 2 stroke
 

If there is enough torque and Bite of the prop.

Re: Low end torque - 4 stroke vs. 2 stroke
 

Yamaha F225 four stroke has a reputation of being woos-bag motor.

Re: Low end torque - 4 stroke vs. 2 stroke
 

I have a 300 Suzuke on my 23 CC turning a 16 by 20 three blade wheel. Most noticeable difference for me is the boats ability to stay on plane at just about any speed in any water/wind/wave combination condition.

Re: Low end torque - 4 stroke vs. 2 stroke
 

Crudely illustrated, the difference is not whether it's 2-stroke or 4-stroke. The difference is the torque curve and horsepower "powerband".

For example, if a 225 hp motor only develops the torque to reach 75% of the full 225 hp between 3500 and 4000 rpms, then below 4K it will perform like it's only developing 170 hp or less.

On the other hand, a motor which has the torque to spin up to say 90% of it's rated horsepower at only 3000 rpms, then at 3K it's developing over 200 hp already. Both motors may develop a true 225 hp at the top of their respective powerbands.

Take Mercury Verados. A 225 hp rated Verado develops its max hp (238 hp) at 5800 rpms. (It actually makes more at even higher rpms, but the torque curve falls off) It has a very flat torque curve, thanks to the supercharger. Mercury doen't reveal the maximum torque developed, just the shape ot the curve. So that same 225 motor is already developing over 200 hp at only 2650 rpms, giving it tremendous acceleration potential. It's greatest drawback is its weight.

Contrast that with the old OMC 90* V6 225. While it also developed 230 hp at the top of it's powerband, it didn't break the 200 hp mark until the motor was turning 4100 rpms.
I don't know how much the max torque developed was, but the torque curve is much steeper, not achieving 75% of torque until above 3000 rpms.

Not just horsepower, ladies and gentlemen, but the torque to develop and apply it when you need it.

And just for the record, the Etec is supposed to develop about as much torque as the Verado, although with a bit steeper torque curve.

Re: Low end torque - 4 stroke vs. 2 stroke
 

The 2006 BRP brochure has plots of WOT torque and HP vs RPM for the 225 E-Tec and the 225 4S Yamaha. The Yammi just barely makes 225 hp at max rpm, while the E-Tec makes about 240 HP in the 4500-5500 rpm range, so yes the Yammi is weak compared to the "225" E-Tec. The E-Tec puts out almost 2X more torque down around 2000 rpm.

The 2007 brochure compared the 150 E-Tec and 150 Yamaha 4S with similar results. The E-Tec put out about 165 HP from about 4500-5500, while the Yamaha made about 155 HP over a much smaller rpm range. The 150 E-Tec also had a huge torque advantage down in the 2000-3000 rpm range, so it's no surprise that it easily won the "tug-of-war" against the Yamaha. I've pulled points off those curves and plugged them into a spreadsheet that I can send to anyone that want's it if you'll PM me your e-mail address.

When you're looking at acceleration, it's the AREA under the torque vs. rpm curve that counts! When comparing an engine with lots of low speed torque and a flat torque curve to a "peaky" engine with higher peak torque but less area under the torque curve, the flat torque curve engine will win every time, all other factors being equal. With the Zukes, they've changed the "other factors" and gone to more gear reduction to increase torque at the prop, allowing them to use a much larger slower turning more efficient prop, which helps to compensate for less torque at the powerhead. Putting a lower pitch prop with more blade area on ANY engine will tend to improve low speed acceleration, although at the expense of maximum boat speed.

The low speed planing ability and torque vs throttle sensitivity Connor mentioned is a little bit different. I think what he's experienced is the difference between a small displacement/high output/high rpm engine vs a MUCH LARGER displacement/low specific output/lower rpm engine. The larger engine will tend to have more torque at ANY throttle setting just because of it's displacement, and will therefore be more stable under conditions of varying load, such as going up and down hill in a big following sea. Denny

Re: Low end torque - 4 stroke vs. 2 stroke
 

If anyone on Cape Cod wants a run on a 23 with bracket and a Gen 1 250HP Verado let me know (post April 15 when Cod season opens). The motor is dialed in now after working some items out in 09 (batt ground cable had a crack out of sight causing some weirdness, and new impeller, other minor stuff).


Plenty of torque :). With a Rev4 17P blade prop it jumps out of the hole! With a Mirage Plus 3 blade 17P it does not jump out of the hole as fast, but has a better top end speed. It is an amazing motor. Heavy though prob ~50lbs more than other 4S. Hydraulic pumps/reservoir is under the console so that helps.

Came with boat, do like the engine, and since all rigged with Digital throttle, new N2K gauge that networks into MFD, analog digital gauges clip into each other, and hydraulic steering pump/reservoir under the helm sort of committed to Merc moving forward :). However I'd be tempted to go Suzuki new for the price. Local Merc dealer while pricey is very good. Thats the other factor besides torque/hp/MPG...whose your dealer and how close and good?

Since with a 4S, forget wrenching more than a few things yourself(oils changed,plugs,etc). Its a modern car engine and needs a laptop to diagnose.