Quietness of 4 vs 2 cycles.

[Texasmark]

Was reading on the "Optimax vs 4 stroke" thread where the 4 strokes are much quieter than the 2's.

Having had a 4 cycle I/O I can attest to that fact, but it may have been due to the engine cover's insulation.

I know on my engines, even though they have a cowling with foam and a plastic "tuned" air intake over the front of the carbs, when you are over about 4500 rpms, engine and air ingestion noises come right thru all that insulation and right into the cockpit.

So I was thinking about mechanisms as to why one would be quieter than the other and I only have 2 things that may be the answer. On the 4's The carb may not be staring at you and the bangs are half as many for a given rpm.

Where is the carb located on a 4; in particular, where is the carb inlet located?

Got any other ideas why 4's may be/are quieter?

Just curious as others may be.

Thanks,

Mark

 

[rickdb1boat]

Re: Quietness of 4 vs 2 cycles.

I think you hit it on the head Mark. Half as many bangs per rev. make half the noise. But with the right technology (E-tec), 2 strokes can be made quiet...

 

[Scaaty]

Re: Quietness of 4 vs 2 cycles.

Yep, half as many bangs.........

 

[DJ]

Re: Quietness of 4 vs 2 cycles.

Self edit

 

[Scaaty]

Re: Quietness of 4 vs 2 cycles.

Actually, know that I have thought of it, a 2 stroke has only a thin head, so a lot of that noise resonates out. A 4 stroke has a heck of a lot more mass in front of the "bang" (thicker head, valves/rockers, cam if overhead), and muffles it much better than a 2 banger. And water cooling jackets muffle out most mechanical noise on for 4 strokers

 

[Texasmark]

Re: Quietness of 4 vs 2 cycles.

Hear you Scaaty, but most of the noise I'm observing is coming right at me, out the front of the engine, not the back......but you have a valid point about the thicker head......maybe that's part of the I/O 4 cycle quietness.

I'd still like to know where and which direction they mount the carb(s).

Thanks,

Mark

 

[Silvertip]

Re: Quietness of 4 vs 2 cycles.

You hear more noise out the front of the a two stroke is because that's where the fuel/air intake is. It is also a very short intake path so at wide open throttle there is little obstruction to air noise and internal noises making their way out. With a four stroke, intake runners are very long tuned passages to create torque. That coupled with less commotion going on with each power stroke, there is inherently less noise. An oil pan with a couple quarts of oil in it is also cancels noise. A roller and needle bearing engine is also noisier than an insert style bearing engine. But I too am and will remain a two-stroke fan for its inherent simplicity and power to weight ratio.

 

[rodbolt]

Re: Quietness of 4 vs 2 cycles.

ill put up my 175 E-tec against most 4 strokes I have ridden for quietness, it shakes slightly more at idle than most 4 strokes though.
however the F250 yamaha is very very close.
the DBA is about the same but the tone is different.

 

[Texasmark]

Re: Quietness of 4 vs 2 cycles.

I heard a big bore V6 2 cycle (Yammie) groan out of the no wake zone the other day. I think it said 300 hp on the side. Regardless it sounded awesome.....It sounded awesome. That's it. No kind words. Know nothing about them. My engine is black and they will stay that way; as is boy-son's.........smart lad.....takes after his dad... 8)

Mark

 

[roscoe]

Re: Quietness of 4 vs 2 cycles.

2 cycle 4 cycle
Completely different engines.
no valves vs valves

open exhaust and intake ports vs closed valves on a 4 cycle

 

[Texasmark]

Re: Quietness of 4 vs 2 cycles.

Don't know where you come up with that. On the 2 cycle, intake reed closes when the piston passes/closes off the intake port (bout half the rev) and the exhaust is on the side and deflects down; absolutely no connection to the front of the engine.

When the bang occurs on both types of engines, all external ports are closed.

Mark

 

[roscoe]

Re: Quietness of 4 vs 2 cycles.

Sounds good Mark, but the exhaust ports will be open about 1/2 through the powerstroke, blowing part of the explosion out the exhaust. And the exhaust and transfer port will be open at the same time. Thats what creates some of the inefficiencies of a 2 stroke, and a reed isn't gonna stop much sound. And the reed closes when the internal crankcase pressure builds, on the power stroke. If the reed closed when the piston closes off the intake port, it would not allow fuel to enter the crankcase to be charged for the next cycle.

 

[Texasmark]

Re: Quietness of 4 vs 2 cycles.

Stay with me, this is educational for all readers.

Well, if suction from the piston doesn't pull the reed open, what does? And if the piston shuts off the connecting port how do you get suction to hold the reed open?

Haven't looked at the porting lately but the last time I was in one there wasn't any exhaust crud in the intake side indicating to me that there isn't any exhaust crossover to the intake; but I may have missed something.
---------------------

Still no one has told me where the carbs are located on a 4 banger.

Thanks,

Mark

 

[rodbolt]

Re: Quietness of 4 vs 2 cycles.

its all in the design of the exhaust and the airbox.
2 stroke DFI does not rely on exhaust scavenging nor intake air charge to move fuel.
both engine designs open the exhaust long before the fire goes out.
both make a lot of intake air noise, remember the old carbed 350 in your dads car? the fasted way to make it sound cool was flip the air cleaner lid to allow the intake air noise to be heard.
however by injecting the fuel on a DFI after the ports are closed we tend to lose less unburned fuel out of the exhaust port.
out of all the things we can control the one thing that cannot be directly control is when the fire goes out.
we can control the amount of air to fuel,we can control when compression pressure spikes and when fuel is injected and when the candle is lit, we cannot directly control it once its lit.
thats also the reason for variable cam timing in modern small displacement high HP 4 strokes. the same valve overlap that works well at low RPM's so we can make power there wont work at 6000 RPM as the inertia of the air willl lose its ramming effect.
at 6000 RPM time to open the valves,introduce the air,close the valves, compress the air, burn the air and open the valves to allow the spent air out is very limited.
and with good combustion chamber designs and valve layout 4 strokes get a scavenging effect as well.
some of the biggest decreases in noise levels have little to do with engine design and a lot to do with intake,airbox and exhaust laybrinth designs as well as better water shielding of the exhaust.
over the years quite a bit of money has been spent trying to make engines idiot proof at starting and quieter in almost all industries.
its funny to watch some of my young coworkers trying to cold start older yammies and C models without using the warmup lever, usually just before they kill the battery I will go show them how to start a carbed motor that does not have a prime start or quick start feature.

 

[Texasmark]

Re: Quietness of 4 vs 2 cycles.

Very nice. Yes I do remember the carb noise and was annoyed after flipping the lid. Could never understand why GM put that stupid little hole in the air cleaner when you (joe hotrod) were trying to get that critter to suck all the air it could. d

Now you opened a new question..............but I still don't know where the carbs are. d

How do you vary valve timing as a function of rpm's? Makes sense (after your explanation) why one would want to do it. I know with conventional valving racing folks talk about valve floating where things start to happen that you described.

One more for this round. So, to help get this air to move fast at the high rpm's do marine OB's have 4 valves per cylinder and a single overhead cam or dual cams or what?

All this is not wasted air. I am thinking ahead to my next engine purchase and like to think things through. I am predujiced to 2 cycles right now, but I am learning about 4's and my choices could change when the time comes.

Thanks for your support in this and the next time I see rodbolt talking, I'll pay more attention to what's said. You're earning my respect........not that I disrespected you in the first place, but on here you never know to whom you are talking/listening to, and whether or not they are factual, blowing smoke, or just don't know. 8)

Mark

 

[Big Al1]

Re: Quietness of 4 vs 2 cycles.

Thought I might jump in the discussion. Here's some real numbers from a real test:
Mercury Verado 4 stroke:
1000rpm - 4mph - 64dB
4000rpm - 27.8mph - 87dB
5500rpm - 39.1mph - 94.5dB

Mercury Optimax 2 stroke DFI:
1000rpm - 5.1mph - 72dB
4000rpm - 33.3mph - 92dB
5400rpm - 45mph - 101.8dB

Yamaha 4 stroke:
1000rpm - 4.3mph - 65.5dB
4000rpm - 27.9mph - 84dB
5500rpm - 40mph - 92.5dB

E-TEC:
1000rpm - 5mph - 69dB
4000rpm - 34.4mph - 89dB
5500rpm - 48.8mph - 97.5dB

 

[lowe160]

Re: Quietness of 4 vs 2 cycles.

I don't know where the carbs are on a 4 stroke but my injectors are in the rear along side the plugs. Never really got to look at a carbed four, come on guys, somebody got the answer. I am learning alot here.

Thanks, Wayne

 

[Texasmark]

Re: Quietness of 4 vs 2 cycles.

Geez, I totally forgot (tunnel vision) :% . Let me retitle the question: Where's the air intake (Intake manifold entrance) for the 4's?

------------

Hey big Al, thanks man. Great info. Beins db's are power/voltage ratios depending on what you are measuring, you are really talking about some sound level differences with those numbers.

Let's see VI = power : 3 db = change in level of 2x (double intensity of previous level)

---------------------------10 db = ----------------------10x
-----------------------------20 db = -------------------100x

I had heard (on here from a guy with a new CC and Optimax) that they are quite noisy for a newly designed engine. Looks like your numbers prove that.

But curiousity got me again. The e-tec was faster, hands down. Were these tests conducted on the same boat, with the same hp engines, under the same conditions with the same type/pitch prop? Or were they based upon sound comparisons and performance just fell where it fell?

I realize that would have little effect on the sound level, but for those contemplating an engine purchase and performance won out over noise, looks like the e-tec steals the show.

Thanks,

Mark

 

[lowe160]

Re: Quietness of 4 vs 2 cycles.

The air intake box is right in front where they normally are on a carbed engine. Hope this is what you need.

Regards; Wayne

 

[rodbolt]

Re: Quietness of 4 vs 2 cycles.

depends on the motor and model as to where the throttle shutters are.the F200 and F225 use six,three on each side. the F250 uses a single shutter mounted fwd of the crankcase and very long intake runners,tuned, it uses the ECU and various sensors from the cam lobe to detect cam position and uses oil pressure contoled by an ECU activated solinoid to alter the actual position of the cams.
the F250 uses 4valve per cyl as do the f200 and f225.
the F250 runs all 4 cams from a single belt while the f225 and f200 drive two ofthe cams with a belt and two with a small chain cam to cam.
valve float is completly different than valve timing.
with conventional push rod type motors with hydraulic lifeters you can foat the valves due to excessive valve speed(engine RPM's) due to the inertia of the opening valve overcomes the ability of the valve spring to keep the slack out of the system and it can allow the lifter plunger to rise to the top of the plunger travel and as oil pressure is behind the plunger and it cannot bleed off fast enough the valves can be held off their seats creating a loss of compression.
the V6 F motors from yamaha do not use pushrods nor rocker arms and with 4 smaller lighter valves the valves can react rapidly with much lighter springs.
the v6 f motors cam lobes operate dirctly on the valve and clearence is adjusted by changing the thickness of the wear pad on top of the valve"bucket".
this arrangement has worked well and has been in use at least 50 years that I know of.
maybe even longer.
but at 6000 RPM the cam is turning 3000 RPM so the valve does not have much time to open, allow gas in and out then close for a compression cycle.
thats where valve overlap comesinto play. in a perfect 4 stroke there wont be any however RPM will be incredibly limited. to much overlap and low speed engine operation suffers terribly.
so by having the ability to vary two cams out of 4 we can actually alter valve overlap while the engine is running for the best of both worlds.