4 valve versus 2 valve engines

[leafman60]

Is the 4 valve motor better than the 2 valve?? I know, at first glance, eveyone would say heck yeaaaaah. However, I remember the days when the Daytona was current. The 2 valve version, 1100 Sport, produced nearly as much power and turned in similar test times.

 

More importantly, I was concerned at the opinions voiced by both Manfred Hecht and Mike Rich. I was considering a 4 valve project a few years ago and talked to Manfred before he "retired" from his Raceco shop. At the time, I was interested in what Manfred could do with the 4 valver. I was suprised to learn that he basically did not like that engine. He advised me to stay away from it. There were several issues regarding the valve mechanisms.

 

Within the last couple of weeks, I was talking to Mike Rich about breathing on my 2 valver. Somehow we got off on the 4 valver. He echoed Manfred's assessment. Mike cited valve/cam mechanism problems as well. He thinks the 2 valver is much more reliable and dependable. Plus, a significant amount of extra juice is available from the 2 valve engine with tweaking. Supposedly, the "reworked" Ghezzi 4 valve slated for the MGS01 has solved the issues of the old layout. Time will tell. Thoughts anyone?

[Janusz]

Let me also add that in my opinion our engine is such a fantastic machine at the pinnacle of a pushrod two valve twin development just because it retains these characteristics.

And no hydraulic valves for me please.

 

If you redo it into four valves you will gain some power at the top revs at the expense of low and mid torque hence driveability. Why do it? It will never be able to compete with water cooled modern four anyways and you end up with a bastard good at nothing.

 

Not fish nor fowl. Why do it?

[Steve G.]

I have to agree with John. If people are looking for an all out hot rod superbike, it won't be a Moto Guzzi. Moto Guzzi is always going to attract a puchaser that is looking for an old fashioned simple engine design, easy maintanence, bomb proof mechanicals, and that thing "character".

I've been very lucky to ride most every hot rod out there commonly found. GSXR 1000, Zx12, Hyabusa, FJR13, Duc 916. Most of these have truly nuclear power available at any revs or speeds. Very rarely do I wish I had one of these things in the garage. The speed is too easy. They also make half-ass riders look good because while they can't make it go into corners, they have the power to shoot up with the rest of the group. I call them point and shoot riders. I know I'm having more fun on the Guzzi because you are working harder, you are more involved, more into the feel of the bike.

You can keep the 4 valve head and the hydraulic valves. I'll just uncork the exhaust, k& n filter, and, I know you guys will think I'm nuts, put on a slightly heavier flywheel.

Ciao, Steve G

Surrey, B.C.

[Paul Minnaert]

The 4v engine is not the thing most tuners are used too. In the first 5 years from the daytona, most owners were still paying interest on the initial buy, and were not prepared to spend serious amounts of money on tuning. A diffent exhaust was enough, and it does make a lot of difference. For me it was the same. As the market is very small, tuners are still not interested in doing things. The only ones who have done things are Jens Hofmann and Amedeo Castellani. Amedeo has stopped development.

The 4v engine has a higher reach in tuning, >150hp is possible. That might be not easy power, but 135hp is a good ridable and reliable.

And no it's not the next r1, but I see all 2v owners fiddeling around with pistons, dual plugging valves and so on. So the 2v power is not good enough. So why not take a engine with a higher starting point.

The mgs01 has nothing changed in the valve train, changes are on bearings, and oil circuit. What goes wrong with the 4v, is the heads brake, because the valve guides are pressed in to tight, from factory. Once this is solved, the engine is relaiable.

[Lex]

If you redo it into four valves you will gain some power at the top revs at the expense of low and mid torque hence driveability. Why do it? It will never be able to compete with water cooled modern four anyways and you end up with a bastard good at nothing.

 

I couldn't agree more with the sentiment about not ruining the V11's wonderful drivability but I have to say I have grown tired of people repeating the demonstrably incorrect statement that a 4-valve engine will be weak in the bottom end. Four small valves simply flow better then two big ones, not just at high RPM but at any RPM. If designer sizes the valves and ports for low end and selects appropriate cam timing the engine will be strong at the low end.

 

As an example, I pulled out a road test in Motorcycle Consumer News comparing the Bavarian Murder Weapon R1150R with the V11 Sport TT. I should note that Guzzi cheated in this test, the Sport has accessory mufflers. That should even out the German bike's 66 CC displacement advantage. The peak power in pretty close, with the droopy jugs bike winning by only 1.5 HP. OTOH, torque isn't even close. The German bike is 10.1 F/Lb stronger than the Guzzi at peak. The Goose peaks, in a spike, with 60.8 at 5500 RPM, the Beemer makes more than 60 Ft/Lb from 2750 to 6500 RPM. As a result, the Beemer is 5 HP stronger at 3K RPM, 8 HP stronger at 4K, more than 10 at 5K before thing return to be nearly equal from 6K up. Which bike has stronger low and mid-range power?

 

I love the engine in my V11, I've owned three R259 Beemers and don't care for them. Whatever its strengths the R1100/ 1150 flat twins sound like a lawn tractor, are as charismatic as a refrigerator, are not fun to work on and have some serious design problems. OTOH, if I could have a version of my much loved Guzzi engine with more power everywhere, as a well designed four valve version should, I'd be willing to put up with adjusting a few more valves. Add the fact that the four-valve can be bored to more than 1200 CC (there is no replacement for displacement) and I'm very interested. I'm willing to trust Paul's experience and believe his post above is the truth about the four-valve Guzzi engine. In short, bring it on!

 

Your curmudgeon,

 

Lex

[dlaing]

I had a friend with a Yamaha that would go on and on and on to my Norton riding buddy and myself with a V65SP, that 4 valves are better than 2.

We nicknamed him "four balls"

Granted they do flow better and give especially more high end power, it is at the price of added complexity.

Here are some dynos of a Centauro. http://www.centauro-owners.com/articles/palma/

I found it interesting to compare to our bikes. http://www.sportrider.com/bikes/dynos/

With just a few modification the bike is making more power than that of few of the high performance two valves on the list, but the bike does appear to have to be revved a little more.

If one compares the Centauro power curve to the Daytona RS the RS has a much peakier curve and it does loose low end power. So there is some truth to the myth, but it all depends on tuning. You could also get 100 HP out of a well modified 2 valve V11 if you put in a cam that would destroy the low end power and driveabilty.

 

Another interesting comparison might be a four valve VW golf or Jetta engine compared to a two valve. Again a big increase in peak HP. I think they tune it that way because either engine has sufficient driveable low end, but for exhileration they can easily get more peak power out of the four valve. Giving the four valve more low end power than the two valve was possible but would not be as marketable.

[Lex]

So there is some truth to the myth, but it all depends on tuning

 

I'm sorry but there is no truth to the myth. ALL engines of a given type and size allow you to move the power around the RPM range. The difference is that with a four-valve engine you just have more to move. The designer can choose to give you a little more everywhere, more on the bottom, in the middle or on top. More complexity, yes that is certainly a trade off. Not just the valves but two cam drives, two cams, etc. Another point is the all that "stuff" is up high and can raise the center of gravity.

 

I would recommend you be VERY careful in comparing dyno runs from different dynos. I picked the example I used in my post because the engines are similar and they were run on the same dyno by the same operator and at the same time. Also, I know MCN uses a Super Flow dyno. Super Flows are know to be both more accurate and more consistent than the much more common Dynojet. Based on the much higher numbers from Sport Rider I'd guess they use a Dynojet

 

I apologize for not including the peak numbers for both bikes in my post. The Beemer made 76.9 HP and 70.9 Lb/ Ft of Torque Vs. 75.4 HP and 60.8 Ft/ Lb for the V11. As an example of why you should never compare separate dynos look at the number from Sport Rider: 79.3 HP and 63.5 Lb/Ft. Now remember the Guzzi in MCN had nearly open pipes and wich we all know that is worth a couple of HP on top.

 

Your curmudgeon,

 

Lex

[dlaing]

The truth of the myth is not that more valves will rob low end power, but that more valves open up the bottle necks to power, especially to higher rpm power, so that there is more temptation for a tuner to design for more peak power at the expense of low end power.

Guzzi with hanging tits :-) chose to maximize mid-range, the Daytona RS designers took it to the extreme to get lots of peak HP at the expense of low-end.

If you compare the RS to the Centauro to the Guzzi with hanging tits :-) to the V11S or to a V11 California, you get very different curves. It is the engine design engineers choice that led to the myth.

I am sure you can find many examples of engine designs going to multi valves and peak power increasing much more than low end. Can you find example of the low end decreasing? Probably not too many,

In the case of comparing a Daytona RS to a V11S the V11S has more low end. This is an example of the myth having some truth.

True the V11 displaces more CCs and is tuned differently, but it is an example and when someone asks which is better comparing the MGS01 to the V11S, there may be less low end on the multivalve, so there is truth to the myth, but it depends on how they will chose to design and tune it.

 

Could you mount a Guzzi with hanging tits :-) mulivalve head to a Guzzii? I guess it will not work, but a Centauro or Daytona Engine could learn from the Guzzi with hanging tits :-) design.

 

Sorry, I think I made a mistake on the VW example. The multi valve is also turbocharged, so the comparison is not valid.

[Paul Minnaert]

The centauro and daytona RS have only one difference: the cam. Originally they have the exhaust with the nasty thing under the gearbox, that takes all midrange.

What a centauro with a decent exhaust can do, can be seen at http://www.centauro-owners.com/articles/palma/

The centauro has the first daytona cam. Which isn't tuned to real midrange either.

Today, there are only 4 different cams for the 4V I know off.

 

1 daytona/centauro( and US daytonaRS)

2 C kit and daytona RS

3 dynotec cam

4 raceco cam( is somewhere in between cam 1 and 2)

 

But a real mdrange cam could be made, but nowone cared for that.

I know a guy that mounted a centauro engine in a T3 sidecar combination. He never complained about missing midrange. It made wheely's:-)

 

What can be learned from Guzzi with hanging tits :-)'s ?? The cam in the head design is similar to guzzi as far as I know.

 

 

What I learnd from a lecture from Hartmut taborsky ( HTM), is that gas flows in the head with a maximum of 105 m/s, no matter how hard you try( only a turbo helps). Power comes from as much mixture with high compression. To get much mixture, you need big intake valves, to have place for big valves you need a big bore. In the same bore you get more intake diameter with 2 intake valves instead of one. With a big piston and 2V configuration, dual plugging helps to illuminate the mixture at the same time.

The speed in the intake chanel reaches 300km/h. so that's why a small obstacle there is allready a problem. And also why he doesn't like k&n on the throtle body, air has to much resistance through that. Better a big airbox where the body can get nice air.

[Murray]

After riding them both the standard Daytona motor VS the two valve there is not much in it the fourvalve spins up a lot more easily and is smoother. However when directly compared to a C kit daytona or a RS (not the munted version they got int he US) where the two valve starts to loose intrest the four valve takes off. Was there a significant difference in low down torque it was noticable but probally is only around 5 NM if that. It depends on what you want if the two valve does the job for you then stick with it. However if you are after more power thats more acessable with minor mods the fourvalve is the way to go.

[Guest Fonzarelli]

The way I view the 4 valve situation is that the only downside is added expense.

 

Other than extra parts and expense, and the additional headaches that come with those two items, 4 valve heads are actually better in almost all areas.

 

For instance:

 

-more valve curtain area

-lighter valve springs can be used

-smaller lighter valves are used

-less radical cam profiles can be used (better reliability)

-intake ports can be designed smaller for more efficient cylinder filling (at any speed)

 

The areas two major areas that will affect your power band personality are:

 

-camshaft design

-cylinder head intake port design

 

Paul is correct in saying that you can only flow so much air/fuel mixture through a port. We call this the choke point. It is usually around velocities of 550 fps. This is the point of diminishing returns as it will consume more power beyond this point than is capable of being produced by extra air speed.

 

As far as a Moto Guzzi is concerned; if someone wants to maximize power I would suggest retaining the standard head and have is professionally ported and flowed. I would also optimize the piston to cyllinder head dimensions. These two modifications would bring a great increase in performance.

 

I also believe that much of this four valve conversion is a 'more is better' attitude. Of course, if we were trying to build the maximum amount of power possible, a platform other than an air-cooled v-twin would be chosen.

[Guest Nickos]

Having owned a Centauro for more than two years and my riding pal (and cousin) a 2001 Lemans (stock exept for a pair of Mistral carbon pipes) I was able to ride them back to back and here are my conclusions.

 

The refinement of the V11 was my first impression.

 

First the hydraulic clutch and the 6speed gearbox are excellent. Gears are very well spaced (no extra long second gear like the C threatening to stall the engine in low speeds) and smooth Japanese like engagement.

 

In fact although it makes about 10 less HP I wouldn't be surprised if the gearbox makes for most of the difference on the road. Second, the mechanical noice from the engine is much lower and you can actually hear the beautiful roar of the pipes.

 

Most important, no hesitation or coughs were evident right off the box (literally since we took delivery in the crate) OK perhaps a very very tiny when going down to idle from high RPM but really nothing to complain about.

 

The rear drive has a breather so there shouldn't be more blown seals there. The rear wheel is a 180 section which I believe is mostly for fashion as the 160 should be enough for the power and also make it more flickable. You don't need to stretch like Tiramola to lower the side stand when sitting on the bike and it stays there. (The spring loaded side stand must be the nastiest invention in biking)

 

The black finish is also classy but it is expected to peel off sooner or later. The fairing looks big but provides less protection than you'd expect for its size. The handlebars much lower than the C make for some sore wrists and the saddle is just a tad higher (we shorties tend to notice such things

 

And get this from the owner's manual about greasing the drive shaft: Every 20.000 kilometers! I suppose the new shafts are made in planet Crypton while the old ones were made from recycled tin cans in a Chinese sweatshop.

 

Here's another discussion from the C owners forum:

http://centauro-owners.com/phpBB2/viewtopic.php?t=80

 

You can look in my site at the section about my Centauro for the dyno results but the seat of the pants dyno says that the Centauro is definitely faster but the V11 more refined.

 

Also there may be several issues about the 4valve engine especially with the electrics, oil leaking and ECU tuning but they are reliable as far as mechanical parts go. I hadn't heard about cracked heads before.

 

Now, if you ask me, a new refined 4valve engine with a 6speed gearbox would be great for the engine of the future.

 

O ====== = = = = =

// > ===== ==== === = = = =

[+] < [+] ====== ==== == = = = = =

Nickos Costopoulos - Athens, Greece

1986 K100RS

http://flyingbrick.freeyellow.com