2 Stroke HP vs. 4 Stroke HP

[BMANN06]

Do you essentially have to double the HP in a 4 Stroke engine to get the same performance as a 2 Stroke? I understand the mechanical and combustion process differences between the 2 engine types. So essentially doubling the powerstroke/ignition is what doubles the hp? A friend of mine has a new speedster that has 2 4tec engines and a combined HP of like 430! Now this is definately a nicer boat than my 98' but his top speed and hole shot are very similar to my twin 2 strokes. He's got me beat ... no doubt about it but not by much and has twice the horsepower! Same sized hull, and weight has to be close. Is it a general rule of thumb to double the output hp in the 4 strokes?

 

[RFoster130]

If he has 430 HP, then he has a 20 or 23 foot boat, which is considerably heavier than a 16 ft. But you are correct that they are much less efficient.

 

[dsw222]

I don't know his exact boat because you didn't list the year or length, but just for an example....

a 2006 speedster with 430hp weighs 2780pounds

your 98 speedster weighs 1650 pounds

so his probably weighs almost double what yours does... thats a HUGE part of it



EDIT: CORRECTION - I listed the weight on trailer for the 06, not the weight of the boat. oops.

 

[biffdotorg]

I could be way off base here, since I am no mechanic. But I think there are many more variables to consider when making the comparison.

Boats, and especially JetBoats are very inefficient to begin with. Comparing a two-stroke and four-stroke outboard is a fair race as both put down similar power to the water.

The four-stroke will have a huge weight dis-advantage, but will have torque galore. The two-stroke will accelerate and top out higher on average. Those are very general statements, but somewhat true.

In my sleds, I have a 700cc 135hp triple 2-stroke, 500cc 85hp twin 4-stroke and a 500cc 65hp? twin 2-stroke. They are all totally different.

The two 500's are a close comparison and portray their qualities very clearly.

The 500 4-stroke accelerates like the 700 and will rock just about anything from 0-60 because of it's torque. It tops out about 85-90 on gps.

The 500 2-stroke is a wimp on the low end and tops out a bit higher, but has no pull in between. The 4-stroke wins every time.

The main reason it was developed though was for it's efficiency and reliablity. It uses half the gas, no oil, and should outlast any of my 2-smoke engines easily. I do believe that is what SeaDoo had in mind with the 4-tec boats as well. Since the introduction of 4-tec though, the BRP E-tec engines in the sleds are getting a lot of attention. We will see if they need a top-end rebuild after some years on them. Time will tell.

Someone with some mechanical background, please chime in as I am really stupid on this topic. I just wanted to talk about snowmobiling! HA!

 

[unclejay]

Welll....

The main reason for 4 strokes is emissions, within 10 years 2 stroke emissions will be banned (even used boats). Yes it will happen in lakes.

Sea Doo 4-strokes are not any more reliable than their 2 strokes, especially the supercharged ones.

Sea Doo over-states horsepower by about 20 per cent. After 60 years of running hundreds of small engines, I can tell.

Acceleration is not a function of horsepower, it is a function of torque. Advantage, 4 strokes... but more due to cubic inch displacement than anything else.

 

[BMANN06]

Wow that blows!

The main reason for 4 strokes is emissions, within 10 years 2 stroke emissions will be banned (even used boats). Yes it will happen in lakes.

Sea Doo 4-strokes are not any more reliable than their 2 strokes, especially the supercharged ones.

Sea Doo over-states horsepower by about 20 per cent. After 60 years of running hundreds of small engines, I can tell.

Acceleration is not a function of horsepower, it is a function of torque. Advantage, 4 strokes... but more due to cubic inch displacement than anything else.

I can see that coming too with all the "green peace" movement that seems to be turning into a religion. I rented an earth auger couple weeks back to punch in some holes for my fence I was very surprised to see it had a 4stroke on the unit. Oh well, if i can can another ten years outta my 2x2strokes on my boat I'll be happy. I'll migrate when forced to, or just pay up a big dirty fine when i get pinched.

 

[dsw222]

Yamaha STILL makes a carbed 2 stroke ski (their superjet has a 700cc 2 stroke even in 2011 models)

I can't see them being banned from rivers anytime soon.... maybe some lakes yeah, but i dont think it will affect most of us

 

[biffdotorg]

Banning of 2-stroke has already been done. Lake Tahoe was probably the first quite some time back. I should say, the first high profile lake to do it.

The concentration of "greenies" in Northern California is very high. So they not only "kept Tahoe blue" but made a major media event about it.

Yellowstone has taken a different tact about the subject. They first banned 2-stroke snowmobiles and limited the numbers. With the evolution of 2-strokes and E-tec, they have changed it to BAT and limited numbers.

BAT is Best Available Technology. They understand that the emissions of some two strokes were actually lower than the big tracked vehicles they were still using in the park. They do still limit the numbers to help keep the impact on wildlife down.

The laws will change with the technology, it has to. States like Minnesota live for the lake traffic and tourism in the summer. There is no way you can just flip the switch one spring and say, no more 2-strokes. It will come in phases.

 

[BMANN06]

Your right ... just talked to him about it

If he has 430 HP, then he has a 20 or 23 foot boat, which is considerably heavier than a 16 ft. But you are correct that they are much less efficient.

His is 19.5 or so he thinks (really didn't look that longer than mine while we were drag racing down the lake) and his weight is doubled compared to mine ... so good point.

 

[BMANN06]

Polocing Lake Tahoe

How do they go about policing the two strokes on lake tahoe. Is there an park official at the launch?

 

[biffdotorg]

My sister lives there and I don't, but she says it is watched very closely and the fines are quite large.

The landings on the lake are mostly fee based with officials taking payment at the gate. I do believe they are supposed to be monitoring what goes in and out at each launch. The marinas are not allowed to launch any non-compliant boats as well.

Personal watercraft are all 4-stroke and I believe that any watercraft are required to have regular emissions tests like road vehicles.

TRPA, Tahoe Regional Planning Agency actuall runs a patrol boat 7 days/week from May to September!

The regulations were set as of July 2008. They have lessened them to some direct injection 2-strokes knowing that their emmissions have met the standards set forth by other agencies.

http://www.boattahoe.com/trparegs.htm

Check out that link for a list. It's interesting. It has set a standard that some other waterways may put into place. Notice that this is a local group patrolling this.

hmmm...

 

[biffdotorg]

I did notice that Yamaha GP1300r Waverunners were allowed on the lake. This is a two-stroke fuel injected engine. It does comply with the emmission standards though.

So much for me taking my X20 out there with my 240 merc. I guess I should have bought he Optimax.

 

[RFoster130]

There might be places around the country than ban them, but i seriously doubt they will be banned all together everywhere.