Jump to content
Kuni0

ANSWERED V11 Engine Hot Rodding advice

Recommended Posts

Am thinking cooled intake charge more than any velocity increase. Cool air, like me, is dense. While I might make less cognitive HP, the bike will should make more. Reciprocal aircraft engines use cooled air to great advantage. Except for carbureted aircraft. Then, heat is your friend, as ice-makers should be confined to refrigerators, not intakes. Anyway, I am glad for theories. 

  • Haha 1

Share this post


Link to post
Share on other sites

This just in. Found a NIB V11 air box lid on eBay. $32.95 shipped! I helped the seller out on shipping, as he was essentially giving me the lid. Now, to study it and ponder..

 

IMG_2937.JPG

IMG_2938.JPG

 

IMG_2939.JPG

 

  • Like 1

Share this post


Link to post
Share on other sites

Yeah, these stock airbox sellers always deserve a bit of "helping out" . . .  ;)

V11airbox.jpg

The "pinches' and constrictions in the intake runners are really obvious in the bottom view of the lid you got. Ripe for "porting and polishing!

Share this post


Link to post
Share on other sites

(Ahem!) Well, the runners are larger in the first 75mm/3 in. or so  as they leave the box. So, might lop them off there and use 75mm silicone automotive turbo hose to just above the oil cooler (was going to say abreast of the cooler, but...) Fortunately, I have time to ponder this. Have an email into Uni-Filter, but no reply as of yet. I think their MG1 is for the 850-T and such machines. It is said that they flow as good and filter better than (brand redacted to prevent ...ummm...venting) the competing brand.  

  • Haha 1

Share this post


Link to post
Share on other sites
On 2/5/2019 at 3:44 AM, ScuRoo said:

 

Thanks guys! See, now that was worth it - I’m sure from the number of readers there’ll be many cogs spinning & awhirrin’ around with these thotfull gems.

 

I cannot quite remember where I read this, I think maybe on a Thumper forum but I’ll try & paraphrase what some old hand opined his recommendation to “economically” do to ports - which I retained in my head because it was a ‘best bang for buck porting tip’ I’d heard put forward succinctly.

 

It went something along lines of - if you find someone experienced with porting heads - but hasn’t previously worked on heads like yours before now, just ask him to do his favourite angled valve job, clean up & pocket port only - I seem to recall it was suggested to even excessively hog out on the pocket AND then lay down epoxy for raised flat floors & D shaping the SSR.

 

It wasn’t the nth degree in porting advice but always produced improvement across all & sundry heads .

 

...care to add your thots?

The major concern is velocity, because that's what rams in the most air before the intake valve closes. Velocity and port shape have a correlated relationship; air will turn a given corner smoothly only up to a certain velocity. Then things get turbulent and the velocity is lost. So you smooth the path, and do it over again. There is a point of velocity at which mixture goes supersonic, and no larger volume can be drawn in; this is the point at which the port volume must be enlarged, to control velocity. Reduced high-rpm velocity also causes reduced low-rpm velocity, which hurts drivability. 'Guzzi heads as cast cannot be brought near the theoretical maximum velocity for intake valve size, because they simply have too sharp a bend, particularly in the port floor which leads to separation at relatively lower velocity (inertia of the mixture 'leaps' from the floor, like separating from an old carnival carpet slide). So no matter how you shape the port, ultimate charge density is lower than a better port with the same intake valve size. 
So, if you raise the port floor and D-shape the intake port, you increase the potential velocity before separation but without raising the port roof, you reduce volume and increase velocity past the point where the charge goes supersonic at high rpm and you lose top end power. Not to say that there isn't some room for improvement this way, but no path to theoretical maximum without raising the roof. To the statement above, "hogging the bowl" only leads to a worsening of port floor shape. 


This is not specific flow bench and dynomometer data from Moto Guzzi testing, this is general port design theory coupled with conversations with my engine guy about my '85 LM1000 heads (and 25 years of engine development discussion). 
 
So it's my somewhat informed opinion that having a competent and experienced flow bench man port your heads is very valuable, and easy for any garage mechanic to install, and the best bang for buck simply because a different cam is still sucking through the same holes. We're not talking about turning a Honda CB into a superbike, a V11 is already closer to max potential than some pedestrian under-performing engine- the stock cam is pretty stout by most OEM measures. That is to say, a 'hot' cam isn't as much different in your Goose as it would be in your '85 Chevrolet. So the more air you can suck in through the ports, the better the cam can work as is. 
Is any of this clear? While Guzzi ports are not "good" compared to a lot of other engines, it's still the least expensive place to find significant gains IMO and benefits any other mods you may make besides. 

  • Like 1

Share this post


Link to post
Share on other sites

For most of us non-competitive, street guys, "hot-rodding" may be an exaggeration. "De-restricting" or "opening up" what is stuffed up probably nets the greatest practical increase for the money. A freer intake and exhaust will net a noticeable difference when one enters the second half of the rev counter. And re-flashing that which may not have been all that well flashed in the first place. 

  • Like 1

Share this post


Link to post
Share on other sites

In reply to Pressureangle: In your post I'm missing the terms 'laminar flow' and 'turbulent flow', and I'm missing an explanation for the difference between them and also an explanation of how they affect the possible charge or 'grade of delivery' in a given port geometry with sharp bends underway and then a straight connection between in and out.

According to my humble understanding of fluid/aero dynamics the Guzzi heads, 2-valve especially, with their sharply bent inlet ports and relatively huge valves are designed pretty close to what is possible. The overall shape still might look the same as in 1966, but actually the V11 and even more the later and last 2Vs were absolutely top notch. These engines are nearly on the same level as Ducati's Desmo 2Vs which can benefit from much easier geometrical constraints and, on top of that, a much quicker valve train. 

So, personally I wouldn't expect too much for my Guzzi money if put into porting work. I'd rather experiment with cams and airbox mods, the more as here the mods always can be undone.

 

Share this post


Link to post
Share on other sites

I can say that porting SEEMS to have made a decent improvement in how the wife's bike runs. But I have no empirical data (dyno runs) to back it up. I have seen the ports in a Guzzi, and there is easy room for improvement. Just doing a basic 5 angle and cleaning up the ports, matching the ports to the manifolds and seat, can make a good improvement. I try to avoid using my experience as solid proof of the effectiveness of porting a Guzzi, mainly because while seat of the pants experience is 100% positive, I just don't have any good back to back dyno runs to support the claim. I did do dyno runs, but they weren't back to back and they weren't even on the same dyno and / or the same dyno operator. The results were substantial, but they are not scientifically verified. And I long ago lost the dyno chart results. So I tend to avoid quoting the results as fact. But seat of the pants the improvement was clearly noticeable.

I seem to recall seeing where someone had cast the inside of a port in silicone, and it showed a fat spot right before the valve, where the port turned down into the valve opening. I could be wrong, but that isn't good port design. Changes in port size like that affect velocity, and that would likely reduce velocity right before the valve. I think in this case a good port job might actually fill the port and not enlarge it. Spending some time improving that area could yield substantial improvement. But even without that, just cleaning up the port as first mentioned should give a good increase in power.

  • Like 1

Share this post


Link to post
Share on other sites

5 angle cut, with a different seat angle, indeed is good practice. A friend once called his tool for this his "tuning steel" :) That was 40 years ago. Maybe today I just lack a bit the fire of those days. On the positive side: today I always find a ready assembled and ready to run motorcycle when I open the garage door. 

When I talked about different cams as doable and interesting experiments then there should be enough time for such easy head modding as you described it. Let's see, I have a spare engine left from my previous V11, maybe I'll put part of my interest in this direction next year.  Tuning then is something different as Hot-Rodding.

Share this post


Link to post
Share on other sites

I would enjoy luhbo's observations of the condition of that engine, especially the valves and guides.  This is from your V11 with some 200.000 km, yes?

Share this post


Link to post
Share on other sites

It is, yes. But I swapped the heads at around 150.000. The guides were worn out, also the camshaft and, most of all, the tappets. I don't think it made much difference performance wise, I'm maybe not that sensitive, but it developed substantial noise above 7500. The first time it's rather frightening when you suddenly rev into a massive valve clatter. Surprisingly it didn't do any damage to the valves or the pistons, although it very much sounded so.

  • Like 1

Share this post


Link to post
Share on other sites
On 10/22/2019 at 11:26 AM, luhbo said:

In reply to Pressureangle: In your post I'm missing the terms 'laminar flow' and 'turbulent flow', and I'm missing an explanation for the difference between them and also an explanation of how they affect the possible charge or 'grade of delivery' in a given port geometry with sharp bends underway and then a straight connection between in and out.

According to my humble understanding of fluid/aero dynamics the Guzzi heads, 2-valve especially, with their sharply bent inlet ports and relatively huge valves are designed pretty close to what is possible. The overall shape still might look the same as in 1966, but actually the V11 and even more the later and last 2Vs were absolutely top notch. These engines are nearly on the same level as Ducati's Desmo 2Vs which can benefit from much easier geometrical constraints and, on top of that, a much quicker valve train. 

So, personally I wouldn't expect too much for my Guzzi money if put into porting work. I'd rather experiment with cams and airbox mods, the more as here the mods always can be undone.

 

There are a couple distinctions that need to be made; First, between what is theoretically possible between a valve of a certain size, and an inlet opening of a certain size. Secondly, between what Mother Goose has built, and what is theoretically possible between the existing valve and existing inlet opening. On injected Guzzis, moving the port mouth is a huge undertaking, so we are realistically left modifying what's between the inlet and the valve. So no, there is no way to make a Guzzi (or 2-valve Ducati) flow as well a modern 2-valve automotive port, simply because the ports are not as straight. Laminar flow is a function of velocity and delta of direction; if the change of direction is too severe, flow separates and becomes turbulent. So because we can't move the ends of the port, we have very limited ability to reduce the severity of change of direction. I'll have to hunt in my data and see if I have a record of the stock cfm on my LeMans heads to compare with what's there now, and if somebody can come up with a stock V11 head data that would be interesting as well. 
The thing about cams is that they're a lot of labor to change, relative to heads, they're not cheap, and ultimately still suffer the limitations of the stock heads.

  • Thanks 1

Share this post


Link to post
Share on other sites

Re; high compression pistons.

The historic battle within hemispherical combustion chambers is always between compression and detonation. Firstly, in the U.S., the DOT mandates than anything sold for highway use operate on 87 octane fuel without destroying itself. So, if you're willing to use premium always (who doesn't, anyway?) there is a little room for increases.
Here's where things get messy.
Firstly, tuning an engine to take advantage in the difference between 87 and 93 octane is something only an expert with a dynomometer, or a very experienced butt and ears, can do meaningfully. Secondly, there really isn't that much difference anyway. If you're capable of such, you're also capable of tuning your intake and exhaust, fuel and timing as is to achieve 80% of the difference with such a mild compression increase. 
Lastly, altitude and camshaft have huge effect on cylinder pressures, particularly at the medium RPM range where detonation is most prevalent. 
Hemispherical combustion chambers are the most efficient design from the perspective of (2-valve) valve/flow size and efficiency. But they are the worst for detonation. 
The most effective counter to detonation is turbulence during compression, which achieves 2 specific things; improves homogenization of the mixture which removes 'dead' or 'late' spots in the burn; and speeds completion of burn which removes unburned mixture from corners which overpressure and detonate. 
Without enormous and expensive changes, there's little we can do with stock Guzzi castings to improve squish, which creates turbulence. What I did on my LM1000 though, was to carefully measure quench-the actual distance between the piston and head- to be certain it was optimized. The term 'quench' is used, because it's known that the fuel/air mix *cannot* ignite within a narrow margin of distance. That distance is somewhere between .050" and .025". It's typically recognized that the worst contained distance for detonation with gasoline is about .080". 
You can measure your quench with a piece of soft solder through the spark plug hole, to discover to some degree where you are and if taking a little off your cylinders may have some benefit. IIRC I took about .015" off the LM, which raised the compression by about half a point. 
That said, it has a Web 86b camshaft, which although has far more lift than the stock cam, also creates much more cylinder pressure in the low RPMs. The combination requires that I retard the timing a couple degrees from stock to kill any apparent detonation. Tuning is ongoing, currently. 

I always read these back before posting, and I'm never sure they convey sufficiently the information. :/

  • Like 2

Share this post


Link to post
Share on other sites

The injection, good as it is, is not nearly as refined as that on our cars. Cars require no "cold start" lever, have more engine condition sensors, much more powerful computers, coil-on-plug and particularly detonation/knock sensors. Thus, the highest performing cars can run on 87, or even the gasoline substitute called Pemex in Mexico. Not saying they'll be happy. but they'll run. 

Hemispherical combustion chambers trace back an awful long way - to a time before flame propagation was thought of as influencing the production of power. Aircraft engine designers had to deal with pistons melting from the immense dome absorbing so much of the combustion heat. Few had yet thought of tilting the valves toward each other and flattening the chamber. As usual, racing forced the issue and Cosworth et al showed the gains to be had in multi valves and compact combustion chambers. 

Have not really examined the 4-valve Guzzi heads, but they are no doubt much more efficient than the two-valvers. The valve train being the wrench in the gears of the 4-valve Guzzis. 4 valves done right, plus liquid cooling of cylinder and head would show real gains, but at the cost of complexity and increased maintenance - but maintenance is part of Guzzi life, is it not?

Sadly, Piaggio has fallen for the "Italian Harley" niche and sport bikes and power production have taken it in the shorts. Even Harley has stealth liquid cooling as they are forced to compete. Ducati consistently shows what a 4-valve V-twin can do with the application of cubic Euros to the formula. Guzzi has not had that freedom since the V8. Oh, but these old hemis do alright for what they are.

I have ridden 500s and 650s as my largest bikes, so 1064cc seems like a revelation. Trade up from a smaller bike and the V11 seems much more satisfying.  Still the carrot dangles and 100 hp up from 91 seems so close that one can reach it.  

  • Like 1

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...

×
×
  • Create New...