Carb spacer

[haymish]

carb gives a certain flow! yes it does but no car engine gets even close to the max flow possible.just changing your filter to an easier breathing[k&n type]improves your flow rates


i've/you have simplified it somewhat other factors to be concidered.the velocity is increased as the gas/air mixture leaves the carb-but what you not taking into account is the flow rate through the carb.if flow rate through carb at max then it would not improve matters but flow rate through any carb is way down on max!average flow rates through a modern carburettor is in the region of a pressure equal to 1.5 inches of mercury.-a nascar [very well sorted breathing] manages approx 4.5 inches of mercury and that's still not max flow!flow is section x speed.creating a venturi whops up the speed-you can call the section constant-therefore the flow increases.putting it basically-with using a venturi you increase the vacuum-therefore ,as a modern carb[never mind a vintage style carb] is operating at way below max flow, then the flow increases-as does the speed.it is slowing down going through the manifold but still hitting the back of the valves at a conciderably higher velocity that it would without the spacer.
if you call the drag in the manifold dmetres/second.if initial velocity without spacer is say 6m/s then final velocity is 6m/s-dmetres/second.now if new velocity is 8m/s,manifold drag is still dmetres/second and 6m/s-dm/s is going to be smaller than 8m/s-dm/s.not only that but due to the higher vacuum present that helps overcome the manifold drag and encourages swifter movement of fuel/air mix.

[haymish]

forgot to add-if a carb at max flow then superchargers/turbo's would not work .the actual max speed that a venturi can work at before it starts choking itself is mach1-the speed of sound -so room for a bit of improvement on the flow rate of a gaz carb .if you put a spacer on your gaz you will hear a different sound out of the carb-induction roar increases as the vacuum increases as the flow increases as the speed of the air intake increases!

[haymish]

question for gaz 69 owners-do your engines spit back through the carb in certain circumstances[like gaz 66 engines ]-when you take carb off is it dirty and black?,cos if is is a sign that its doing it.

[iannima]

question for gaz 69 owners-do your engines spit back through the carb in certain circumstances[like gaz 66 engines ]-when you take carb off is it dirty and black?,cos if is is a sign that its doing it.

Well mine is certainly not as shiny as it once was, but that could be for any number of reasons. By "spitting back" and "doing it" you mean?

[haymish]

splutters a bit trying to pickup revs in certain situations.the odd cough out of the carb.when running without the filter do you see a fine mist above the carb[hard to see but sunlight or a bright torch helps]

[iannima]

splutters a bit trying to pickup revs in certain situations.the odd cough out of the carb.when running without the filter do you see a fine mist above the carb[hard to see but sunlight or a bright torch helps]

Spluttering VERY occasionally yes... I have not run it without the filter for a couple of years so cannot say much on that. What I do notice a certain flatness in certain situations: uphill drags where changing into third (top gear ) is a struggle...

[haymish]

just wondered cos if carb does pop and splutter at certain revs/load conditions then often spacer helps that.
bit complicated but will simplify for clarity.imagine air/fuel mix rushing down runner in manifold and flowing out past the open valve.all fine but then the valve shuts!the air/fuel is still moving down the runner.it crashes into the back of the closed valve and bounces back along the runner the wrong way towards the carb.then it bounces back towards the still closed valve and repeats-normally at least five times until the valve is opening again.when the air is moving backwards and forwards it is creating areas of high and low compression and acts rather like a sound wave-and is travelling at the speed of sound![330m/s at sea level].now this is normal in an engine but in older /cruder designed engines it can cause problems.ideally the bouncing back air/fuel column is halted at the bottom of the carb by the incoming pressure created by the carb.assorted equations and it is possible to work out the ideal runner length to make this happen[but never tried it on a sidevalve].problems occur on engines with low vacuums cos the bouncing air column actually hits the bottom of the carb itself and keeps going up the carb -in effect momentarily stalling the carb.that is often the cause of the carb spitting back,popping and not picking up the revs as it should.obviously one cannot just set too and redesign the inlet manifold[with the possible exception of zoltan with all his available workshop toys ]but if you add a spacer it lengthens the runner and increases the flow/vacuum which does tend to alleviate the problem.as said before the gaz 66 does a fine job of coughing and spluttering through the carb whenever it sees fit and i did the maths for that and found that the runners needed to be 2 inches longer to eradicate it.
now this is a simplified version of events-you can actually boost a cars power by careful manifold tuning-getting the valve timing to coincide with a forward pulse increases engine power and modern cars have all sorts of tricks to benefit from it[extra valves in the manifold that shut to stop rearward pulse hitting carb etc].lots of clever gizzmology involved too but not relevant for old russian engines in my youth i spent multiple hours trying to tune the splutter coughing out of a triumph motorcycle-totally convinced that it was a carb/timing problem.i changed carbs -redid timing etc and i just could not remove the problem until i met an old boy who used to tune race ducati's.he puffed on his pipe/hummed a bit and suggested spacers between carb and inlet.he made me a couple,turned them up on a lathe and problem solved-plus all the other benefits like more torque etc.took me about 10 years before i actually understood vaguelywhy it worked but it does.
p.s. but beware that running idle jets a bit weak has the same effect-creating popping coughing on pickup etc.

[iannima]

i just could not remove the problem until i met an old boy who used to tune race ducati's.he puffed on his pipe/hummed a bit and suggested spacers between carb and inlet.he made me a couple,turned them up on a lathe and problem solved.

It's a scene straight out of a movie! or a novel...
Seriously though. Thank you for this advice. I have contacted the usual suspects for a 33mm. bore manifold. I think this is the first thing I should try. Also found a 10x20 cm. bit of phenolic sheet off Ebay. It is 9.5 mm thick and I cannot imagine running into any trouble with the air filter hitting the bonnet. With this one I might try and experiment a bit. So the idea would be to have the bore at 33mm. at the carburettor end and 32mm. at the manifold end. Now my problem will be to find somebody who will be able to cut it precisely this way, as I don't think I can do that.

[haymish]

precision not as important as you would think.just get the hole at 32mm and mark round top edge half mm-then file it out.more importantly dont leave the bottom edge sharp.radius it slightly with a file because sharp edges encourage fuel to drop out of the air/fuel mix-and once out and in the manifold you can't get it to remix properly.definitely would be better with the correct manifold.however my brain works the other way-i'd say goody goody got the 38mm manifold-where can i find a 38mm carb

[iannima]

precision not as important as you would think.just get the hole at 32mm and mark round top edge half mm-then file it out.more importantly dont leave the bottom edge sharp.radius it slightly with a file because sharp edges encourage fuel to drop out of the air/fuel mix-and once out and in the manifold you can't get it to remix properly.definitely would be better with the correct manifold.however my brain works the other way-i'd say goody goody got the 38mm manifold-where can i find a 38mm carb

Cool because a 32 mm. saw is easier to find ... 38 mm. carbs are actually difficult to come by. Lahti up here has got two ... the K124 he has mounted and the exceptionally rare K22 KSE... which he does not like. To give you an idea of the price difference:
A new manifold is €40:
http://russianspares.com/shop/product_i ... ucts_id=92
A K124 carb is €265
http://russianspares.com/shop/product_i ... cts_id=604

[haymish]

fair enough-new manifold definitely wins.yes 32mm easy size to find tooling to cut out/drill

[Geronimo]

Guys, think!
A 2,12l engine is designed for a 33mm opening in the manifold and in the carb. A 2,43l engine has a 38mm opening in the manifold and in the carb. This is because the bigger cilinder needs a bigger amount of mixture.
It is the downgoing piston with an open intake valve that creates a vacuum and thus the airflow through the airfilter, carb and manifold. This airflow varies of course with the rpm of the engine and also a little bit because of losses due to friction (for example dirt in the airfilter) and turbulence (for example sudden change in section). The speeds in different sections of the filter-carb-manifold is given by the flow and the section. The factor speed is most important at the jets of the carb. At that point (there you have a venturi) the mixture is formed and a too high speed will give a too lean mixture, a too low speed will give no mixture at all. The possibility exists to regulate the mixture within the limits of the specific carb. Than we come at the carb and manifold opening. The mixture prepared in the carb leaves at an opening and speed according the need of the engine. A 2,12l engine at (for instance) 2000rpm will create by vacuum a flow of 8,83l/s. The 2,43l engine, however, creates at the same rpm a flow of 10,17l/s. The speed in the 33mm hole of the 2,12l is than 10,33m/s and the speed in the 38mm hole of the 2,43l is 8,97m/s. Anyhow, both flows at both speeds arrive in a vast chamber of 90x70x50mm where speeds drop to 2,52m/s (resp. 2,9m/s), taking the turbulence in this chamber into account even less. Than the mixture is sucked through one of the four intake channels measuring 22x34mm. Speeds are increased there to 11,81m/s (resp. 13,59m/s) considering still the 2000rpm. My conclusion is that the opening of the carb-manifold is designed for the carb which belongs to the given engine and any local alterations without changing the whole traject will do more worse that good. So, in my opinion, a spacer of appropriate material will help prevent the heat problem but should not obstruct in one way or another the flow from carb to manifold.
Also the "bouncing" theory is of little importance here because of the low speeds in the manifold chamber and also, from the moment one valve closes, it's another one that starts sucking. Comparing a Nascar with a Gaz 69 is like comparing a cherry with a banana, although both are fruits.
By the way, Matteo, the manifold you see on the picture of Russian spare has an opening of 38mm because of the two little bulbs indicating a manifold for a 2,43l engine.

[iannima]

By the way, Matteo, the manifold you see on the picture of Russian spare has an opening of 38mm because of the two little bulbs indicating a manifold for a 2,43l engine.

Now that is a useful piece of information! By little bulbs I presume you mean those both on the inlet and on the outlet manifold as in this engine here:

Which incidentally is a 2.12 because of the absence of the little bulbs on the cylinderblock next to the fuel pump but might be all right given our discussion here because it has a K124 Carb mounted with a 38 mm. bore like the manifold.
Whereas this engine here has a 33 mm. bore because there are no bulbs on the manifold and that's right because the engine is again a 2.12 one

That's what fora are all about: sharing precious information!

[haymish]

the 'bouncing theory' is relevant to each and every petrol engine that has ever existed-not just nascar! if you want some homework look up helmholtz resonance in manifolds.the car industry spends unpteen millions on manifold design to make the most of the phenomenom-from incredibly efficient little fiat engines to out and out performance cars-and even more millions designing out the problems of it-and you dismiss it out of hand in one sentence as not relevant to a gaz 69-i love it .
not wishing to sound rude -but your level of understanding of the internal combustion engine is schoolboy science class level.do some reading!

[haymish]

p.s. look up inertial supercharging as well-the other name for it.[at least its one of the effects of it]

[Geronimo]

Haymish,
Let us continue this discussion based on arguments, with other words let's play the ball, not the man.
I did some homework and found immediatly a "Fluid dynamic study of intake manifolds of internal combustion engines in presence of acoustic resonators" of a certain Daniele Bortoluzzi and I quote:

"The intake process strongly influences the performance of an alternative engine, because the power generated depends on the capability of elaborating a large mass flow. For this reason, especially in the field of high output engines, several devices and solutions are introduced in order to improve the fluid mass aspirated during the suction stroke. The ratio between the effective and the ideal aspirated gas masses is defined volumetric efficiency: the engine output, in terms of delivered torque, is proportional to such quantity.

The volumetric efficiency of an engine depends both on quasi-static phenomena, like viscous losses and charge heating, and on typical dynamic phenomena, connected to the pulsating nature of the compressible fluid flow and overall defined "acoustic phenomena". The acoustic phenomena become more and more important as the engine speeds grows, so they are exploited in high speed engines (for example, F1)."

Which proves my point.

The main issue here are our different goals. You try to introduce modern technology science (tuning) into an engine designed in the 50'ties, while I try to understand the original design and make the most of it.

[haymish]

its not modern tuning-without the resonance effect your gaz engine would be basically dead in the water.the power curve on an engine [if resonance did not exist]is basically a flat line.the peak point of your gaz engines power is the point that the resonance matches the valve openings.this isn't about tuning an engine -its about making one run well.you basically state that the max air/fuel mix that can happen in the engine is the displacement-but that is untrue.when the resonance coincides with the valve opening-then inertial supercharging takes place-in ANY petrol engine.the air /fuel mix is compressed and moving forward at way higher velocities than normal induction[the pulse is estimated at 0.6 of mach1 in an 'old' tech engine!]and way more fuel/air mix enters the chamber than the actual physical dimensions of the chamber because it is compressed and moving fast-that is why you have a peak point in your power curve.flat spots in an engines rev range can be caused by the resonance being out of harmony with the valve opening and less fuel charge entering the chamber cos it bouncing the wrong way when the valve opens.
this was well understood way back even in the 1930's and developement of your gaz engine would have been done with the knowledge of this phenomenon.its pretty basic stuff-if you want an engine with low down torque and not too high revving you design long thinner manifold runners with some taper on them to encourage the venturi effect.if building an fast car you use v.short runners with basically no taper and make them big and fat.this matters cos the resonace effect is greater with shorter manifolds-but puts power up the rev range.longer manifolds and resonance effect smaller and more torque produced at lower revs.the clever bit is in the maths to get the right lengths/taper for the desired effect and trying-round the constraints of mass production and costs-to get the desired effect without a plumbers nightmare of a manifold.the early gaz 66 manifold has equal length runners- which the russians were so proud it gets a mention in the manuals-and that is a major contributary factor to the fact that the engine has lots of lazy low down torque.
your belief that the driving force behind induction is the piston dropping and creating suck-is simplistic to say the least-wasn't trying to be rude when suggested that that was schoolboy science class stuff but it is.there are multitudes of tweaks-even in a gaz engine to improve the flow.done by the manufacturers not by engine tuners.never looked at a gaz 69 engine but the gaz66 has two venturi in the carbs.each manifold runner is a venturi.and beneath the carb is a phlenum chamber to absorb the resonance pulses to try to stop them reaching the carb.these engines struggle a bit on modern petrol which upsets all the carefully made russian plans as to how they run.doing a little tweak,helping out the engine by slightly altering the runner length and adding another venturi, is not f1 technology but just using available run of the mill old school technology to try and smooth out the power delivery.
could put up acres of highly technical blurb about it all-some dating back to the early cars-even got a photo of a 1930's car with two extra external resonance chambers on the exhaust manifold-used to help keep the exhaust gases moving away from the exhaust valves-scavenging in modern parlance- to increase the piston movement speed so more efficient engine.but trying to get across the point that this is not f1 technology but everyday normal engine technology-just most of general public have no idea of the true complexity of the actions/reactions etc going on in a engine just to get it to run well.
there are a thousand and one other things that interact-lets just take one.fuel temperature.the fuel and air need to be as cold as possible-air obvious cos denser air holds more oxygen.but fuel -one would think nice and warm so burns better-but doesn't work that way.the ideal fuel temp is well below vapourization point-because if it vapourizes then it expands enormously and displaces the air being sucked into the carb.the best is coolish petrol broken up into the tinyest droplets available.now the venturi in the carb,venturi in the manifolds all have the effect of cooling the fuel charge down-if you place an extra one [venturi]underneath the carb it cools it more so less chance of vapour lock,loss of power when trying hard etc-again the taper on the spacer helping,cooling the charge and getting the fuel in a fit state to burn-not f1 technology but decades old technology that is allready being used on the machine and just helping the engine cope with modern fuel that,because it burns slower, tends to create more heat than old 70ish octane fuel.[especially as modern still burning as the exhaust valve opening .
all the 'stuff' i have mentioned is old school technology-not f1 stuff but the basics that make a petrol engine act the way it does.without resonance your gaz would crawl along very slowly indeed-instead of just slowly

[Eastblock]

I've never played around with 4-strokes in terms of trying to improve performance but I have on 2-strokes back in my moped and model aircraft days. Even small changes on either intake or exhaust side can have a huge impact on performance.

[Geronimo]

Haymish,
Please answer me one thing:

So, the mixture reaches the valve and enters the cilinder until the valve closes. Due to inertion, an amount of mixture hits the closed valve and bounces back to the chamber. When it arrives there:

In one post you wrote: "ideally the bouncing back air/fuel column is halted at the bottom of the carb by the incoming pressure created by the carb."

In another post you wrote:"it crashes into the back of the closed valve and bounces back along the runner the wrong way towards the carb.then it bounces back towards the still closed valve and repeats-normally at least five times until the valve is opening again."

Then you wrote: "and beneath the carb is a phlenum chamber to absorb the resonance pulses to try to stop them reaching the carb"

And finally you wrote:"when the resonance coincides with the valve opening-then inertial supercharging takes place-in ANY petrol engine".

Now my question is; If this resonance is so important, and I am talking about a Gaz 69 engine, because "without it your gaz engine would be basically dead in the water", why did anyone design this phlenum chamber to absorb it?

[haymish]

if nothing to act as a buffer when the resonance pulse gets to the bottom of the carb it just would keep going up through the carb[causing chaos and probably stalling the engine].the pulses are in set wavelengths which would just keep repeating until fade away if in a long enough tube.but the phlenum chamber acts like a spring and bounces them back along the runner back to the valve.if it didn't then inertial super charging would not happen.all to do with fluid mechanics.in an enclosed space the air/fuel mix acts like a fluid because it has mass.if you imagine ripples in a bath.drop the soap in one end and ripples hurtle off to the other end-then bounce off the end wall of the bath and head back to where you dropped the soap.slowly losing speed and power but keep going for an amazingly long time.just the same effect in the runner but hitting the air/fuel mass in the phlenum chamber instead of the end of the bath.as that can't get out of the way it acts like a spring and bounces the moving column back again.by halted i mean that it doesn't continue back up into the bottom of the carb -which causes momentarily stalling of the carb-spitting back/coughing /poor pick up the end result.it is easier to halt/reverse if it is near the end of one of the wavecycles or moving slower which is why just by using a spacer can greatly improve the pick up of the engine.when working out the runner length its from the top of the carb right to the valve back.this is the total column moving towards the valve seat.when the cycle reversed the column is shortened by the phlenum chamber-sort of works like a one way valve.but because you have altered the original length of the runner by putting in a spacer[increased the size of the phlenum chamber] then the wavelength changes and slows down a touch-[longer runners slower waves]which creates more torque/low down power and normally eases the problem of spitting back througfh the carb.
on the average 'normal' engine this cycle repeats about 5 times before the valve is again open[the waves move very very fast!].if you wanted a track engine you would shorten the inlet manifolds to get the minimum number of bounces because the wave is decaying rapidly.if you catch it sooner to create inertial supercharging you get more effect-but the power is way higher up the rev range-which is why on the gaz66 the full inlet tract is about 25"" long. .the big square lumpy bit on your inlet manifold is the phlenum chamber.
the basic definition of a phlenum chamber is a positive pressured container designed for the distribution of the fuel/air mix to the assorted runners.because the fuel air mix is fast moving as it leaves the carb-when it hits the phlenum it slows and pressures up the containment area-for distribution to whichever valve is open.when a valve opens it hurtles down the runner, speeded up by the venturi effect in the runner,until the valve closes and the resonance occurs.it shouldn't bounce back right into the carb cos the phlenum chamber -being pressured up- should act like a spring and bounce it back.this as said normally occurs five times before the valve is open again.the amount of power you then gets depends on how much the resonance is syncro'd to the valve opening.your point of max power in the engine is the point of max syncro with the resonance cos then max inertial supercharging.
the phlenum chamber sort of acts like a gas shocker on a car /motorcycle except it is a column of fuel/air mix -not a plunger-hitting it.
p.s. forgot another bit because you have put a venturi on the spacer-then the fuel/air mix is travelling faster -so when gets to the phlenum chamber it slightly increases the pressure in the chamber.so triple whammy effect.alters the resonance wavelength to slower speed and increases the pressure in the phlenum chamber as a whole and increases the size of phlenum chamber which helps too so less chance of the resonance hitting/penetrating the bottom of the carb.