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EFI need not apply.
What role does the venturi size play in performance oriented carburetors?
Is there a rule of thumb when selecting carburetors for maximizing performance?
I know it's not simply a matter of jet sizes and whatnot.
Ideally i'd run a single barrel per cylinder. Is that the most efficient aspiration for carburetors?
pls respond.
pic related, the gaping maws of 6 twin barrel carburetors.
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venturi size generally correlates with how much air the carb can flow. Too small and you lose power, too big and you can have drivability problems at part throttle, but there's ways to tune around that.
If you want an individual runner setup you will most likely need expensive ass webers because with IR the cylinders don't get to share and you need really big carbs.
Tunnel ram style intakes can make good power too and will let you run cheaper carbs.
>Tunnel ram style intakes can make good power too and will let you run cheaper carbs.
So effectively using a 4 barrel carb for 2 or 4 cylinders?
It seems like Weber is shifting away from carb production unfortunately.
>It seems like Weber is shifting away from carb production unfortunately.
Nevermind, I'm just retarded.
Yeah kind of. All the cylinders share the carbs through a common plenum.
>carb
>performance
Single barrel per cilinder is the most efficient aspiration system, the problem is that balancing them is a bitch if you have lot's of cilinders.
SU carbs are quite underrated from a performance standpoint, at most they might have slightly worse throttle response but power wise it's pretty much the same thing.
>Single barrel per cylinder is the most efficient aspiration system
>not two barrels per cylinder
NOOB PLZ!!
Forgot my image
There are too many variables you haven't provided information on.
How many cylinders is your application? At a broad guess, what is the peak VE of your combo?
Are you looking for a streetcar engine with a broad power and torque curve? Then a single four barrel over a long runner 180 degree manifold will suit. Top end power with a sacrifice in low rpm power delivery and throttle response? Two four barrels on short runners with a 360 degree plenum.
How long is the duration of the camshaft at fifty thousandths lift? A short duration camshaft will not need as large an accelerator pump shot where a longer duration camshaft with a fast ramp rate will require a larger pump shot. How much air is the engine moving at low to mid RPM when the throttle bodies are opened? A high VE engine will require a fast rate accelerator pump cam where a lower VE engine will require a more gradual delivery of pump shot.
General rule is the larger the venturi barrel size (a higher rating of flow), the poorer the effectiveness of the booster at low velocity. Annular boosters assist with this though the annular booster has larger surface area than a dog-leg booster and as a result, restricts the flow of charge air to a greater extent.
The smaller the venturi the better the function of the booster at low velocity but as a trade off, the more restriction is placed on the flow of charge air.
Do you have adequate vacuum at cruise, or do you know your target vacuum at cruise? You will need to fit a power valve to suit, or delete the power valve for an engine that lives at idle or WOT.
Are you searching for neck-snapping delivery? 1:1 linkage ratio between the primary and secondary throttle bodies. If you are looking for a more logarithmic delivery for comfortable street driving then you would be looking at a 30:70 or 20:80 linkage.
Would you prefer to remove the bowls and change jets to adjust high speed AF or have a degree of adjustment in carb before changing hangers and rods?
beetle??
what heads are those?
Feuling heads. It's a one off 4 valve pushrod head.
made 480hp @ 6500RPM out of 2232cc displacement.
Is this engine ever going to be exposed to forced aspiration above the carb? You will need to either purchase a carburettor with brass floats over nitrile moulded floats or fit brass floats to prevent crushing.
What sort of transmission is behind the engine? A manual transmission generally will sit 50 to 100 CFM lower in charge air flow demand than an automatic, and up to 200 CFM less than an automatic with a torque converter stall speed equal to or greater than half of the maximum RPM of the engine.
It is very easy to over-carb a manual transmission equipped engine. High load low RPM situations commonly found with a manual transmission are poorly serviced by high flowing carburettors sensitive to low signal.
Are you searching for fuel economy at all? Perhaps a spread-bore (difference in size between primary and secondary throttle bodies) carburettor is more suitable than a square bore. Looking to flow ungodly amounts of charge air and perhaps nitrous? Fit the largest square bore carburettor you can.
Single carburettors per cylinder looks attractive and delivers high RPM flow in spades. As another poster pointed out, multiple carbs must be balanced in fuel delivery, throttle body rate and vac signal. Bit of a pain.
Are you thinking of running Methanol, E85 or Alcohol? You will require a carb with larger passageways and metering blocks to deliver a higher rate of fuel for the same vac signal, due to the decrease in density of these fuels. If you go down this route, you cannot slap one of these carbs on a pump fuel motor without resigning yourself to frustrating low speed AF issues.
Tl;DR go to your local speedshop with every detail you can find on your combo and work with them to select a carb that suits the flow rate and signal of the combo, not a carb that suits what you want the combo to achieve.
Necro with sum Pro Systems.
Damn. Link where I can read about it?
>carb
might as well just use a coal fired steam engine
>Carb
May as well just use an old format of universal analogue density based fuel delivery that achieves target AF with simple mechanical circuits!
Wait up....
That's a carb.
Shit.
>bong vs tiny water pistol that shoots fuel
hmm
can't you search what he said and the pic?
don't you have google installed on your interwebs?
>Fuel delivery method that achieves target AF versus fuel delivery method that achieves target AF.
Hmmm.
>being a boomer vs not being a boomer
hmm
found the kid going to UTI
some bad news for you kiddo: working in the real world is not the same as having a comfy half-a-car on a lift, you dont get 8 hours of no-pressure time to remove and inspect a single spark plug.
i bet you felt smart as fuck posting that definition lol. quick! give us the textbook definition for an egr valve!
>uti fags be mad that the GS thats been working at the shop for 2 years gets paird $3.00 more an hour than him with a degree because real world experience trumps all
seen it many times, never ends.
I wish I was a boomer. I'd probably have a lot more Papua New Guinean kinas than I have now.
What is UTI? I assure you I've never had a urinary tract infection. I studied with MAN Diesel and Turbo Werkstudent.
An EGR valve is usually a poppet valve actuated by vacuum signal or an electronic solenoid. It regulates the flow of exhaust gasses through the EGR passageways for re-introduction to the charge air. Recent advancements in actuator design have allowed for the implementation of Pulse Width Modulation control of the solenoid for a variable flow of exhaust gasses.
I've put together combos with carburettors, I've put together combos with electronic fuel injection. Beaten cars with EFI using carbs, beaten cars using carbs with EFI. Horses for courses.
Yeah, but sometimes I can get a good link without having to slog through shit.
no it didn't
Fuck you fags just let me carb in peace.
I wish I knew more about carbs to be honest. They are clever devices and they got the job done.
Jim Feuling was a fucking wizard when he was alive and did some crazy shit before the internet was a thing.
Then now is the time to start finding out more information on them. Is there something in particular you would like to know?
Yeah actually. Can you point me in the right direction of a good resource that covers the basics? When I learn something new I always come up with legitimate questions.
Inb4 Wikipedia
I'll have a look for you when I have a spare moment. Cross section diagrams will help you understand the flow of fuel through the metering and emulsion system. User and service manuals are also a great way to understand the functions of each carburettor system as they differ amongst their designs, but the basic foundation remains the same.
If you can spare a few dollars, try and get a hold of a mechanical secondary Holley 4150 of any size, in any condition. This model is easy to reduce to bare components and is extremely well supported online. The metering system is straightforward apart from the power valve, which in itself is not a difficult component to understand though understanding what rating power valve to use is a little harder. If you can understand the 4150, everything from a Thermoquad to a Stromberg will make sense.
If the thread necros before I can point you towards a good resource, good luck on your knowledge adventure.
The sound a 4 barrel carb makes when the secondarys open is god tier
(You)
Thank-you Mr longpost American
You seem to have alot of what seems to be v8/dragstrip knowledge.
Would you have any thoughts on lower displacement non v8s aswell?
Say a 2.3l inline 6 currently making peak power at 145hp @ 5500rpm, hoping to make far more peak at 6500rpm, disregarding any performance below 4000rpm? A Camshaft will of course be needed?
Ayye, I'm not from the states.
What kind of engine is this? Specifically what is the head? Crossflow two-valve? If I was to arbitrarily pull a number from my rectum I think you would move between 400 and 500 cubic feet to make that power. With a straight six you can utilise a two barrel with no issues though you will still get the low and part throttle benefits of a four barrel with progressive linkages. I like Holley carburettors for cars, I find them pretty intuitive to tune and easy to strip. If you were to put a 500cfm 4150 with a 1" either spacer or shear plate over an adapter for your manifold I'd say you will be in the ballpark. That's too large for a small camshaft though. If your duration at fifty thousandths lift is more than 210 or so you'll be fine.
I'm very curious man, what's your engine and what are your plans?
So, other than restoring an old car, why would you want a carbureted engine? Are they just interesting to work on, or what?
I'm not trolling, I'm honestly curious.
Ease of use. I have a tweecer rt (aftermarket piggyback computer) on a '90 mustang. Heavily modified engine won't run on factory computer. But I refuse to have someone else work on my car, so I had to learn ALOT about ford's efi system to program it correctly.
Also have a '66 F100 with a 406 and holly 650 cfm double pumper.
I can rebuild and tune the 650 in a half hour, blind folded while drinking a 12 pack.
With the mustang I have to plug in my laptop and go through 50 scalars and 100 algorithms - being careful to cross check maps that are affected by the one I need to change.
There's just something about a loud, smog puking, hot engine that gets me moist.
Thanks user
Any good sound examples?
What car?
Some info on weber carbs (Has info on chokes sizing, air and main jet sizing guide lines.):
s262612653.websitehome.co.uk
A no nonsense explenation of weber emulsion tubes:
youtube.com
>2016
>using carbs
the fuel eats that shit up so fast too now..
Muh ethanol
It's only purpose is to put money into farmer pockets for votes.
It wastes food and money.
Thanks
For naturally aspirated engines running gasoline, ~14 bar BMEP is typically the upper limit you'll ever see.
2.4L V8 F1 was ~14.3 bar
DTM, NASCAR Cup, 1L MotoGP are 14.0 bar.
Something like a Honda K20 is 11.0 bar stock.
A 2013+ Mustang 5.0 is 11.7 bar.
480hp @ 6500rpm @ 2232cc @ 4-stroke is 29.6 bar.
So no, it's thermodynamically impossible. It'd be the talk of every SAE journal (Fuck that, every Mechanical Engineering journal on earth) to this day if it actually existed.
A 2.2L @ 6500, NA, will produce somewhere in the ballpark of 180-220 hp.
Sorry guys. Miracles don't exist.
Thanks
it's not about thermodynamics, it's about getting enough oxygen in in time
Thermodynamics very much involves gas compression, and the energy involved in combustion reactions. How dumb do you have to be to think otherwise?
I don't see an actual argument here, or are you just shitposting? Everything above is factually correct and indisputable, as there are no opinions offered.
dumbest post of the day award goes to this user
>Thermodynamics very much involves gas compression, and the energy involved in combustion reactions. How dumb do you have to be to think otherwise?
where did i say it wasn't?
>it's not about thermodynamics
Right there, friend.
ITB's rest is M00T
okay i was referring to the amount of specific torque they made.
if they can get enough oxygen in quickly enough, via forced induction, nitrous or exotic fuels they make the numbers. simple as that.
You retard
It's a naturally aspirated engine
We are solely discussing NA engines
Reading comprehension, do you have it?
yes user i can see that, but i'll keep putting in red herrings as long as you keep going for them okay?
all you need is the right choke size. the rest is tuning.
a performance car has two settings: zero throttle and full throttle.
power valves, secondary chokes, etc is all economy and street stuff. race cars dont run power valves and shit.
cfm is all that matters for performance.
> Has never taken a sweeper turn in his life
>>thanks man
Just your usage of inches made me think USA
Its an m20b23 in an e30 BMW
Sohc 2v per cylinder
With a primitive but effective old ECU
Thing is I pretty much need to replace the entire loom and ECU if I want to as much flash tune the thing
Have been thinking a 272 camshaft
Would love to go hotter but the factory permissable continuous engine speed is only 6000 and with a higher lift camshaft I swear the wear on the components will be even worse. I am unsure If I need better rockers and new valve springs
I was thinking if possible repurposing sidedraft bike carburetors? I have absolutely no clue how an adapter plate could be made for my manifold...
Dreaming of pic related
Doesn't matter, you barely ever feather. You still tune for WOT.
>You still tune for WOT.
only if you're a clueless hack
You're right man, I'm just playing with you.
Why do you want carbs? You can get megasquirt 2 and ITBs for the same cost as 3 webers. Then you can run crank fire and probably make 20hp more than someone on carbs and mechanical ignition.
cam will just wear your shit more. if you want to go higher than 6000 you need better or double springs and probably will start breaking rockers. m20 rockers are known weak, but hd rockers are cheap.
anyway, you can do bike carbs or any carbs, but you'll have to make a manifold. either cutting up one or casting/cnc your own.
im sure hundreds of people have done it so theres info out there. but youre talking a lot of work for minimal as fuck gains.
he said he want baiku carbs, making an inlet is easy but bogg bros would charge about £400 for a 6 cyl
85 e30 323i manual
Bogg Bros?
I am really after making my car as mechanical as possible, removing electronics within the drivetrain if I can. I just love mechanical/very simple electrical things.
The dutsun 432s and box skylines are dream cars to me and I'd love a euro version of that as much as I can.
I'm in Australia at the moment man and an itb setup is 2.5k then add on the 325i loom for atleast 500 then add megasquirt on top of that.
I have seen for around 1500$ a set of 40mm sidedraft carburetors
Just need to make an adapter and linkages and I don't see much else missing?
Also, For 15k you can get an entire e36 m3 with s52 and itbs and everything. I'd just love one car pre airbags, pre abs, pre fuel injection.
Also, if anyone here knows the 2.7l bottom end swap well, I'm considering it but to do it well looks to cost about 2k
All to end up with a car that will hardly break 200rwhp........
>I was only pretending to be retarded
>australian prices
wtf im so glad i live in the us where everything is cheap.
So idle bleed, number of idle passages, transition slot geometry, linkage ratio, booster design, power valve signal reference type (protip: the power valve is not just for fuel economy), throttle body size and some more equally as important variables mean nothing to you when you are deciding on the most suitable carburettors?
And you only tune for WOT? I think you may be used to garden equipment tuning. Even then I wouldn't trust you with a Mikuni slide.
If you are focused on performance, which your post indicates you are, the choke horn will either be milled off or the casting will not have a choke horn so I am not sure why you have highlighted choke size as an important variable. As a heads up, Holley and Edelbrock carburettors have one choke size across the product range apart from 4500 frame carbs.
In short, please stop typing. You do not know nearly as much as you need others to believe you do.
G'day buddy, this is fellow ausfailian from below
That's a really cool project. What about a long 180 manifold with the 1-3 pots sharing a volume and the 4-6 sharing a volume with a divider between them. Mill the top of each volume for a Holley 250 or 300 two barrel. I would think a fabricator should be able to knock this up fairly cheaply using the factory cast aluminium runners as a base and building the plenum from that.
A 272 advertised duration cam should end up between 220 and 230 at fifty thousandths. You won't overcarb this until you push 500 cfm or more. Your low end vacuum may be a bit weaker with an LSA of 110 or less so the more I think about it, the more I think a pair of two barrels will match pretty well.
What a cool project, I hope you enjoy doing it.
Their dollar isn't our dollar...
It's all relative.
I've been racing probably longer than you've been alive.
Choke size isn't an important variable, interesting. I'll choke my side drafts down to 30mm and see how it goes, thanks for that sick tip.
Power valve is absolutely for economy. You're a moron, lmao.
2500 aud is 1800 usd.
i can get a whole itb manifold with fuel rail and linkage for $900
He's not gonna put a fucking holley downdraft on a m20, go away
go on, link it
>itb manifold with fuel rail and linkage for $900
Sweet. I've always wanted itb's.
> dat induction sound
maybe honda stuff, your not getting 6 itbs and a mani that cheap otherwise
What state mate? Vic here
My ideas are probably never going to come to much but I like thinking this stuff out. Id also love an m50 carbed but I don't think they even have a distributor. Its some smart coil pack shit I won't pretend to understand.
220-230 at fiftythousands? Sorry what do you mean?
I am ignorant of all the technical terms.
My experience with carburetors is limited to the lawnmower.
Yeah the things in aus are ridiculously overpriced, regardless of the exchange rate. Every one of the 20middlemen importing takes his cut...
As for your idea, it sounds very smart man, reminds me of old 70s inline motors with one carb.
But personally I feel drawn towards having independent barrels per cylinder? If done correctly they should be tuneable to each cylinder? Kind of like having independent throttle bodies but out of carburetors?
Also where are you thinking labour? I swear any machinist will want a minimum of 500$ for their time for such a thing? I see how you could do it but the stock intake manifold is rather restrictive on m20s?
My uneducated guess is that short runners with smallish carbs per cylinder would promote a rev happy motor? At not even 390ml per cylinder and the valve train not going past 6000- 6500 I shouldn't need that much flow per cylinder?
If the 1.6Ls in ae86es have about the same displacement per cylinder and they get converted to have 40mm manuki sidedrafts am I on track? But the 86es Rev far higher? To about 8k?
i like you.
Where did you learn this? i wish i did some kind of formal engine education.
How long you've understood things incorrectly is none of my concern. If you want to swing dicks around I suppose I could say at this present time the engine operated and maintained under my watch outputs the sum of every combo you've built per cylinder. It means nothing on an anonymous seedless watermelon forum.
What do you mean by 'choke down' a carburettor to 30mm? What I am not sure what nomenclature you use but it's not standard. A choke is a butterfly valve that restricts the flow of charge air above the booster to form an overly rich mixture for cold starting. You do not adjust the size of the butterfly for it's purpose is to seal against the venturi wall or the wall of the choke horn. If effect, it is sized to fit this diameter. I am not sure where the confusion comes from? Again I state with certainty that the majority of performance carburettors either mill off the choke horn or are cast without one.
In forced induction situations the power valve is referenced from below the blower housing. This changes the power valve operation from full enrichment at target vac signal at part throttle to full enrichment at part throttle where there is vacuum under the throttle bodies but positive pressure below the blower. In a blow through design the power valve operation is Changed again to prevent full enrichment from the pv when there is positive pressure above the throttle bodies and bowls but vacuum under the throttle bodies. So no, unequivocally, the power valve is not just for fuel economy. You would know this, or at least should, if you were as experienced as you would wish others believe.
If it meets the target specifications what is the issue? Does a Stromberg magically energise the charge air to form the only substance suitable for a crossflow single cam six banger?
I'm from QLD but I'm mostly at sea so I don't really have a home state. I'll have a better read of your post next swing when I've got a sec.
Duration at fifty thousandths is an accurate benchmark for the duration of the camshaft from when the lifter has been raised by the lobe to .050 until the lifter is reseated at the end of the lobe. When camshaft manufacturers label their camshafts with Advertised Duration, there is no format for when the duration begins. Do they rate the duration from .020, .010, .040, who knows? It is entirely possible for a '272' Advertised Duration degree cam to have a longer duration in reality than a '282' if the AD rating began earlier on the 272 than the 282. By working from fifty thousandths lift it levels the playing field somewhat.
The Lobe Separation Angle is the angle between the peaks of the intake and exhaust lobes. A narrow LSA means the exhaust and intake valve will be open together (overlap) for a longer period. A wide LSA is the opposite. Narrow LSA sets up effective scavenging during the overlap period but results in poor vac signal and the traditional choppy idle. A wide LSA will be effective for nitrous oxide and forced induction combos where you want to seal the exhaust valve before opening the intake to preserve precious cylinder pressure.
The ramp rate of the lobe dictates how steep the gradient from the Base Circle to the peak of the lobe. A fast ramp rate is more strenuous on the lifters and valve train where a slow ramp rate is far easier on the valve train at the expense of volumetric efficiency. A fast ramp rate solid roller cam is very violent on the valvetrain compared to a slow rate hydraulic cam.
So a camshaft with a long duration at fifty thousandths with a narrow LSA and fast ramp rate will be a top end monster with fair to poor idle characteristics and poor bottom end torque for your engine. A lower duration camshaft with a wide LSA and moderate lift around the half-inch mark would give you an increase in top end power not as severe as the previous cam, but the idle and part throttle characteristics will be vastly improved.
You can certainly have one carburettor per cylinder if you wish. I certainly do not mean to insult you as that's of no help but if your experience with carburettors is lacking, six individual carbs is not the best plan for a first project. Balancing carbs is not an easy task and can be downright unpleasant. A pair of carburettors will pose enough of a challenge for a first time user.
But if you are serious, go for it. There are a few ways to learn but the best method is hands-on tactile learning. Just be prepared to spend time diagnosing hiccups .
May want to hide it from VicPOL! Those dudes are chrome-seeking missiles with defect notice warheads. They couldn't tell you one side of your exhaust pipe from the other but they will book you for anything that looks out of place.
With the plenum, the labour will be the killer though you can decrease the labour costs by providing all details you possibly can and schematics to the fabricator. There is a big price difference between rolling up and saying 'weld this bit to that bit so it does the thing' and saying 'fabricate this in this way to these dimensions.'
The tight runners may help you build port velocity, they may end up restricting your flow. Without measuring your engine it's all just pissing into the wind. But if the runner and bowl area are more than 80cc I think you will flow enough air without restriction for your power goals.
Thanks for sharing your ideas mate, rip into that project.
>it's not about thermodynamics, it's about thermodynamics
fixd
No insult taken. Your information is much appreciated. I understand I'm clueless, and had originally planned to install the carburetors then take them to a specialist to have it finetuned.
I guess I'd rather just jump into the deep end so I can see the dream developing in front of me, even if it takes a few years.
Dont worry I'm likely only in Vic for one more year.
If I get around to putting a torsen in the back and extractors I'll be pleased with myself. Final years a bitch and I think I don't manage to even go for a drive more then once a week.
Yeah I definitely need more measurements before I go much further with this idea. There are a few mean m20s online, but as always there's never all that much fine detail.
At the moment I'm wondering if I even want to open the motor up as my price estimate for camming it sits between 600$ and 2k$
Might just enjoy that stock fuel economy for a while longer...
Love your ideas man. Hope I continue hearing from you through all the carbie threads
Forgot pic
>thermodynamics
>mattering before the combustion phase
Hey dude you aren't clueless at all. You've already made a good enough start that you are aware of camshaft duration, that you may need to strengthen your valve train, you are aware of the limitations of your engine and are already making positive modifications like your extractors and differential etc etc.
Got the jump up on a lot of people already. Like you said, dive deep. No learning like tactile learning.
I'll keep an eye out for a M20 beemer on here.
Have a good one man.
Thanks for the kind words man.
I guess I just need to get my ass into gear and start throwing money at things
On that note, how hard does anyone think it is to change differential centers? I'm not sure if it's within my ability to correctly install it, but the 900$ for the center is a scary enough figure before I get professional help...
Same to you man, enjoy yourself