130 TC Carb Mounts / Baseplate / Carbs/ Airbox

[Guy Croft]

I can't publish any back-to-back because I never did any, mainly because I never had 2 carbs to hand choked-up the same to try!

I have heard of 'this' or 'that' carb giving a better fuel signal but frankly I have always considered that just 'bolting on' the carbs and accepting the power they gave per-se (save for variations in choke size) was a small luxury in a difficult world!

G

[WhizzMan]

I know that David Vizard used to test different carbs on otherwise similar setups. It wasn't anything close to this setup, but if I recall correctly, the difference in droplet size mattered a lot. Some setups required bigger droplets than others to achieve maximum power and good torque along the rpm range. It may very well be that in the end, the carb that you think is inferior will give better results on a specific application, no matter how hard you try to tune the one you think is best. If you have the option to try different carbs, there could be gains made there, even if the venturi size is the same between your options.

[TomLouwrier]

True.
That is why in the States people make a difference between dry and wet flow testing. The wet flow is a lot more involved (getting water into your flow bench setup, sometimes with dye in it!) but gives more knowledge about fuel droplets, manifold / port wall wetting etc. I think a man with the great nick name 'Smokey' Yunnick came up with this concept, he was also behind the 28" water as testing depression standard.

You don't hear much talk about wet flow over here in Europe, at least I haven't. Yet more things to learn.

regards
Tom

[Guy Croft]

Crikey from carbs to wet flow testing all in one thread! One more thing for me to 'beaten over the head' with, I ain't gone none!

Don't let this fancy stuff kid you any. 28" flow testing won't - in my expert opinion - make your engine any better than the one with head developed at 10". And I am not saying that because I 'only' had a realtively small rig. And so often with new techniques of examination like wet testing and valve head flow distribution devices to name but two - all they tell you is the flow thru your head is not optimal and never will be however much metal you 'hog' out and short of redesigning it you're 'stuck' with it!

Merely in jest - I say those in favor of the most 'advanced' dev techniques - buy the gear and count how many days you last before you go 'bust' trying to make it pay..!

G

[TomLouwrier]

hi Guy,

With my limited knowledge I certainly agree with you, considering the situation this side of the pond. Many engines and designs around, most under 500cc per cylinder. You must indeed work with what you've got on the bench today.

In the USA it's a bit of a different story. Limited number of engine models, up to 900cc per cylinder or more and a market large enough to allow all sorts of aftermarket components to be developed and sold with a profit. Engineering your own line of heads (supplier), or have custom ports developed in a 'blank' (customer) would offer opportunities for this sort of equipment and testing strategy.

Over here? Nope, too much cost involved and too little market for it.

regards
Tom

[Guy Croft]

Yes the US market is gigantic,

G

[Abarthnorway - Remi L]

I know that David Vizard used to test different carbs on otherwise similar setups. It wasn't anything close to this setup, but if I recall correctly, the difference in droplet size mattered a lot. Some setups required bigger droplets than others to achieve maximum power and good torque along the rpm range. It may very well be that in the end, the carb that you think is inferior will give better results on a specific application, no matter how hard you try to tune the one you think is best. If you have the option to try different carbs, there could be gains made there, even if the venturi size is the same between your options.

Very interesting idea, and there might be something to it:-)

I have read some rumours regarding "that carb" being better on fuel atomization than "this carb", but both seems to work fine on their setups, and correctly setup deliver exactly the power You want, and where You want it. One might be marginally better than the other for a certain setup - no doubt - but all carbs (one choke per cylinder) I have tried have worked just fine once set up correctly. That can be hard work. Thing is that I do not have any chance to measure droplet size and its effects, so I am pretty "stuck" with what I have at hand.....and focus my energy on shat I CAN change.

Regarding which carb that have the highest power potential between the Weber and Solex is yet to be seen. Deeming from their barrel size, adjustability, shape of aux venturies etc my bet is on the Solexes as it will accept bigger venturies without loosing the fuelsignal - especially with slimmed throttle shafts. For a normal street engine that doesn`t matter at all, as both Weber and Solex work just perfect with 32 venturies - only differences is owners preference I suppose.

Maybe I will get a chance to dynotest the engine comparing the two carbs on the same engine in the future - but that will be earliest season 2013 if we choose to use performance cams ...... Its a big job and costs quite some money to source different Rampipes, maybe 50-60 jets, 2-3 sets of Venturies, and completely overhaul an extra set of carbs for the comparison, not to speak of the extra time spent on the dyno. I might do it for the ***l of it, just to try to prove my point...


Best regards

Remi Lovhoiden

[Abarthnorway - Remi L]

Solex jets:


C40 Tipo 37:

Blanderør.jpg (152.25 KiB) Viewed 8969 times

C40 Normal

40ADDHEnormal.gif (15.18 KiB) Viewed 8969 times

emulsion tubes with mains/airs - Idle jets - air correctors idle circuit - pump jets

Dyser oversikt.jpg (171.75 KiB) Viewed 8969 times

I am on the lookout for GENUINE jets to tipo 37 Solex ADDHE - please inform if You have a source


Remi

[WhizzMan]

The real question is, what is "better" atomization? If the engine wants larger droplets, a carb that atomizes to a very fine mist will probably work less good than one that is "less good" at atomizing. It totally depends on what the engine likes best. If you put a certain type of carb on a different type engine, you may see other carbs function better than the one you win races with on the first car.

I believe the story of Vizard is actually from the time he was still in Europe and was racing some "less than 2.0 liter four cylinder" car, I think English, quite possibly a Type-A engine in a BMC Mini.

Doing high pressure tests and wet flowing have their merits. You may see turbulences and other effects occur at extreme flows of air, that you would miss at 10" water. You may spot that air will flow your inlet tract just fine, but fuel mist will all splash on the end of the inlet bowl, making it more beneficial to slow down the mixture so it can make the turn in some cases. For the big two valve engines, those things may be more significant, but they could be beneficial in some cases for smaller engines too.

[TomLouwrier]

Given a 'perfect' engine then optimal droplet size should be no droplets at all; fuel and air as dry mix of ideal gases. Combustion is a process with chemical and thermodynamical aspects that strongly influence each other, but in principle independent of what the container looks like.

In the imperfect world we live in droplets do have a size and therefore their mass (and maybe even shape) play a part in how they travel from carb to combustion chamber. Same imperfection goes for the inlet tract and the chamber, with unequal flow, turbulence, condensation etc, etc...
So what a particular engine 'likes' has more to do with many imperfections that more or less cancel each other out than with optimal droplet size as such.

As Guy says: you work with what you have in front of you and make the best of it.

regards
Tom

[WhizzMan]

Given full stoichiometric burn, you'll want droplets small enough to burn fast at ignition time, distributed evenly across the chamber. No droplets at all makes for a gas mixture that is harder to ignite and keep burning in the initial stage after spark. Remember, we want burn, not detonation. If only very few fuel atoms are burning, the flame might extinguish if our spark wasn't long en powerful enough. Even if it doesn't go out, it will take time before the chain reaction of burning gets momentum. Once you have a proper flame front going, you may want other conditions to apply than at ignition time.

If you have minute droplets, each burning droplet will have it's own fuel supply and there will be plenty of chances for it to set fire to it's neighbors. If you have too large droplets, they will take a lot of time burning, possibly even run out of oxygen and not burn completely.

Before you ignite, it doesn't really matter how big the droplets are, as long as they are evenly distributed and in suspension. You might benefit from the cooling effect of the vaporizing of the fuel on the air you ingest.

What is the exact "best" droplet size for that time, engine and application changes every millionth of a second. It's a very dynamic process in the combustion chamber and even the most advanced computer simulations (think formula 1 multi-million dollar setups with software that costs just as much) can only model it up to a certain extent. Once you set fire to the fuel, pressure, temperature, shock waves, reflections, resonance, chemical composition all influence the burn process. Even if you divide the chamber into small 3D cells, you can only calculate a very small time frame of what is happening per cell. All these cells influence each other. All cells are only valid for that time frame, since the piston moves. The next time frame, you have to re-define your cell layout, put in all data you got from the previous time frame (try extrapolating values for a few million cells) and start all your calculations again.

The dynamics and complexity of the model is easily larger than that of the Met offices computers. Those use a 3D cell model as well and use external input variables like pressure, solar power, cloud cover, resulting wind speeds, ground temperature and such. In a way, they can be compared to a model of a combustion cycle. Try calculating the weather for over a week, in 15 minute interval time slots and see how accurate you are after a week. I've worked for the Dutch Met office and believe me, it takes hours to do a weeks run for just the country and you only get to maybe 50 percent accuracy for the 7th day. That's 700 time slots for one week. If you try to do an entire combustion event in just 700 time slots, you'll never get the accuracy you need to calculate things like ideal droplet size. Even if you'd do 10 times as much, you'll only get droplet size for one very specific load point at one RPM number, engine temperature, barometric pressure, air temperature and so on. Coming up with a full range data calculation for just one design of engine is not practically possible, let alone for all possible variations on that engine. Currently, F1 is picking specific situations for partial calculations using models like this. Also they are doing a different modeling called Fluid Dynamics, where they treat gasses like a liquid and compute the flow of the "liquid".

It's a long post, but I hope it's clear now that "you want the fuel to be atomized completely" does not hold up. Gasoline is a complex mixture of hundreds of different substances that all have their role in the burning process. You don't want a violent explosion, where you'll convert fuel and air into a hot gas at a rate of hundreds of meters per second. If you do that, you'll shatter your piston and be left with nothing but heat and no energy to move your crank around. Getting the correct pressure build up requires careful burning of the mixture and thus a careful preparation of that mixture.

[TomLouwrier]

Holy ships, Homme! That's a lot of very valid points you've got there.
I'd like to bring in some stuff about lean burn and gas (LPG, methane) engines that relates strongly to this. But since I'm in a hurry today, it'll have to wait.

Will be back here.
Thanks for putting my feet back on the ground.

respectfully,
Tom

[Abarthnorway - Remi L]

Hi!


Very interesting input here - and its appreciated - though fuel droplet size and F1 predictions of burn rates might be more suited in a new thread.

This thread is about the original intake system from rampipe to manifold of the 130 TC - Carb mounts / Baseplate / Carbs / Airbox.

No offence intended:-)


Best regards

Remi Lovhoiden

[TomLouwrier]

Hi Remi,

yes, you are right. One thing leads to another and by now we have hijacked your thread :-)

Guy, could you split the discussion from about top of this page into a new subject please?

regards
Tom