Carburetor Doubt

[raptor93]

Does FSAE have any restrictions for the use of a four cylinder engine which has four corresponding carburetors attached to them.
If it is not allowed,is it okay to convert the system to a single carburetor engine with a manifold leading from the carburetor to the four cylinders.

[Chevalier]

The question you need to ask yourself would be why?

Why would you want to fit 1970s technology to a "racing" car? There is a reason why nothing runs carbs these days.

You will have to mount the carb upstream of the restrictor. The restrictor is of a size that limits the airflow to the engine. Using a carb you are adding the fuel before the restrictor, meaning even less air can get through!

You would have to be incredibly desperate to run carbs!

Malcolm.

[Jon Burford]

Malcolm,
Yes I agree that it is not the perfect solution, but if you had a real problem getting to a dyno, the Carb is potentially a good option.
The university of Dundee have been running a half blocked Webber for a good few years now. The first time I saw that car in 2011 it did pretty well out on track and was running really nicely.
I agree that you can get even less air through the restrictor with the carb but you don't really need all that much power to do well, so I would call your bluff on that argument.
As you say, I would have to be desperate, but I'm just saying that it can be done and you could still do very well.

[Chevalier]

Yeah I would agree that out and out power isn't too important hence the "if you are desperate" proviso. But is not a good solution other than "easy to sort". Even then (I know, I have a '76 MG Midget) they can still be a PITA to get running sweetly.

An intangible "easy to fit" excuse isn't really a justifiable option in an engineering competition so expect to take some flack from judges if you fit a carb.

http://www.formulastudent.de/a...esign-judging-stuff/ (http://www.formulastudent.de/academy/pats-corner/advice-details/article/design-judging-stuff/)

Cheers,
Malc.

[Jon Burford]

yeah the key wording from Pat there is "the exact number being relative to how well the team have incorporated the carburetor into their design"
With regards to the points loss.
If you were planning on running EFI, failed, and just said "S##t, we have 2 weeks left, lets stick an SU on there" then yeah, you should take the points hit.
If you intended on using the Carb (preferably not an SU) from the beginning and designed accordingly, then I don't see there should be a "massive" points loss as long as you have gone about it in the correct way.
As you say, there is no less work involved, it's just cheaper, simpler to design and package potentially, there are a lot fewer bits and pieces on the back (or front http://fsae.com/groupee_common/emoticons/icon_wink.gif ) of the car and dare I say it, less to go wrong.
I am not advocating it at all and I definitely don't want to drag anything back from the dead; I hate the things.
All I am saying is that we should think things through and try and see things from the other side sometimes.

[Goody]

Originally posted by raptor93:
Does FSAE have any restrictions for the use of a four cylinder engine which has four corresponding carburetors attached to them.
If it is not allowed,is it okay to convert the system to a single carburetor engine with a manifold leading from the carburetor to the four cylinders.

I believe as long as you ran all four carbs to a single 20mm restrictor/19mm-E85, you're good to go. As mentioned, it's not ideal, but if you can get it to run happy and it's what your resources allow for, go for it.

I don't believe the rules dictate anything about fuel distribution to the engine, as long as the fuel system plumbing passes tech, there are no restrictor-bypassing ports/ the intake air is restricted per rules, you could run a tunnel ram with dual quads on that thing if you wanted! http://fsae.com/groupee_common/emoticons/icon_cool.gif

[Jon Burford]

I would ask for Clarification before bodging 4 carbs into one restrictor.
The Rules use the word "carburetor" implying singular.
Which in itself I don't really recommend, let alone some kind of multi carb restrictor duct jumble.

[X Charger X]

I understand use of carburetor isn't a good idea but due to lack of resources we had to buy CBR 600 F2. Now to replace carbs with fuel injection system what should be taken care of and is it a good idea to meddle around with such an old engine?

[Charles Kaneb]

The main disadvantage is that you'll have to go with a 19mm or smaller carburetor in order to not have to have two venturis in the system. You'll be seriously hurting for peak power - I doubt you'll get much more than 30 hp with a 450 breathing through it. Maybe an XR600 would do a little better?

What you will get in exchange for mounting the tiny Tillotson pumper carb and a lawnmower magneto ignition is a significant simplification of the wiring system. No fuel pump, no need for armored fuel lines, no worries about sensors (a manual "start/run" switch between two advance settings wouldn't be bad), etc. If you combine this with an aircooled engine and eliminate the fan, your entire wiring harness could be under ten wires. The battery would only be used for starting and you would not have to run a charging system.

Think about all of the trouble everyone runs into with wiring and electronics. Put your wiring harness on a scale. Watch some old FSAE cars, particularly the singles, that have gone back to carburetors.

If your car concept doesn't rely on your having much power, there is an advantage there to exploit. You'll save weight and you'll probably spend more time driving and less time fixing.

How much power do you need?

[Will M]

Originally posted by X Charger X:
I understand use of carburetor isn't a good idea but due to lack of resources we had to buy CBR 600 F2. Now to replace carbs with fuel injection system what should be taken care of and is it a good idea to meddle around with such an old engine?

-X Charger X


The PE engine controllers seems to have some features the would really help when converting from carbs to EFI.
Specifically the 'Pulse to Sync' feature.

http://fsae.com/eve/forums/a/t...607348/m/97020897151 (http://fsae.com/eve/forums/a/tpc/f/125607348/m/97020897151)


Originally posted by Charles Kaneb:
If you combine this with an aircooled engine and eliminate the fan...


Yeah ditch the F2 and grab the engine from a TRX400EX.
Air/oil cooled, dry sump, lots of after market parts.
Whats not to love? (besides having no EFI)

-William

[Adambomb]

First thing to consider is how a carburetor works. What does it use as a signal for how much fuel to add to the mixture? How is this affected by a restrictor? And finally, what happens to the quality of the fuel/air mixture as it passes through the rest of the intake system? All of these things have been discussed quite a bit in the past.

Carb tuning isn't quite as simple as people talk about "in the good ol' days." A Holley 600 will usually work pretty well out of the box on a stock or slightly modified small block Chevy, but carbs on bikes can be particularly finicky. If you want to discover how finicky, try pulling off the airbox on any carb'd bike and riding it...you'll be lucky if it even starts without jacking up the idle mixture, at which point it will promptly fall on its face again as soon as you get off idle. Now add a restrictor to that mix...


Originally posted by Goody:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by raptor93:
Does FSAE have any restrictions for the use of a four cylinder engine which has four corresponding carburetors attached to them.
If it is not allowed,is it okay to convert the system to a single carburetor engine with a manifold leading from the carburetor to the four cylinders.

I believe as long as you ran all four carbs to a single 20mm restrictor/19mm-E85, you're good to go. As mentioned, it's not ideal, but if you can get it to run happy and it's what your resources allow for, go for it.
</div></BLOCKQUOTE>

Going back to those first principles again, what kind of vacuum signal you figure you could get from a 19 or 20 mm restrictor branching out immediately to four 32+ mm carbs? What kind of tunability? I'd imagine it would be similar to putting a pair of Holley Dominators on a Geo Metro with a blown head gasket.

[jlangholzj]

Originally posted by Adambomb:
I'd imagine it would be similar to putting a pair of Holley Dominators on a Geo Metro with a blown head gasket.

I want to see this done...minus the blown head gasket of course

[X Charger X]

Thanks a lot for all the help. Matters a lot to a freshmen team like ours.

Now....
I find more troubles changing the carbs to EFI and looking at the resources and lack of enough time and experience. I think going with carbs should be a good choice for now.

Now if i just place 4 restrictors one connecting each stock carb to corresponding intake. This allows me to keep the stock manifold design intact and reduce the troubles of making manifolds (lack of funds).

Worry here is - "Any major design issue or possible problem which I didn't make a not of before thinking of this design?"

[Kirk Feldkamp]

The throttling device(s) has to be before the restrictor. You really need to read through the rules some more and think about what they're saying in practical terms. If you can't make a simple intake manifold because of a "lack of funds", then perhaps this isn't the right project for you or your team. This sort of item is truly the tip of the iceberg when it comes to the cost of one of these vehicles!

[AxelRipper]

Quick tips from someone who was on a carbed single team for a few years. You have a 20mm restriction pulling a venturi. You also have a carburetor trying to pull a venturi. Keep these sizes in mind as you're sizing your carb.

If you try to run in cold weather, especially if you try doing something like e85, you're going to see some interesting things around your restrictor. Ice will form. Liquid through a pressure change. Much fun.

And finally, as with all restricted singles, volume is key. However, you've also got a potentially long distance between your fuel injecting system and your intake valve, so keep that in mind that you might see some delay if it gets too long. For a first year team if you absolutely positively can't get EFI working (and early development stuff can be an issue, especially starting, or if you're starting with a non-injected single) it can be a good way to get yourself to competition. It may not be very powerful or fast, but being able to start and run is far better than the alternative.

And for a mind-freak, I give you our 2010 car intake.
https://fbcdn-sphotos-c-a.akamaihd.net/hphotos-ak-prn1/30976_423576401759_4823116_n.jpg

[Z]

Some further comments.

IMO a carb'd FSAE engine is entirely feasible, has the less-electrics advantage mentioned above, could produce the same maximum power as an EFI'd engine, would probably have slightly worse fuel consumption (but not too much worse), and would have a lot of old-fashioned problems that you younger generation have never even heard of, but are also quite easy to fix.

Regarding maximum power, the argument that the fuel flowing through the restrictor reduces the amount of air that can flow, and so reduces power, is pure bulldust. The fuel mass flow rate of a rich mixture is ~1/10th the air mass flow. But the fuel will typically still be in liquid form (fine droplets), so its volume will be less than 1/500th the air volume flow rate. So the fuel reduces the air flow by less than 1/5,000th! And since maximum air flow through a 20mm restrictor is good for ~120hp (see long discussion other thread http://fsae.com/groupee_common/emoticons/icon_smile.gif), and no team yet achieves this, why worry about losing less than 0.024 of a horse!?

The main practical problem is that the carb piddles petrol into the plenum, which then forms puddles on the floor, which then occasionally pour into the intake pipes!!! http://fsae.com/groupee_common/emoticons/icon_smile.gif If this happens, then expect rough running and the occasional spectacular backfire! The solution is simple. Mount the carb up high with all pipe/plenum internal walls sloping downward towards the intake valve, and with no little pockets to collect the liquid fuel.

The other practical problem, as mentioned by Axel, is that carb-heating may be required (in fact, very likely, even without a restrictor). You can fix this with some of the hot exhaust gases (VW Beetle, and others), hot air from an air cooled engine, or hot water from a water cooled engine (as on most carb'd cars forever).

Look for a single carb with a throttle plate about 25-30 mm diameter (hint: look up).

Z

[X Charger X]

Originally posted by Kirk Feldkamp:
The throttling device(s) has to be before the restrictor. You really need to read through the rules some more and think about what they're saying in practical terms. If you can't make a simple intake manifold because of a "lack of funds", then perhaps this isn't the right project for you or your team. This sort of item is truly the tip of the iceberg when it comes to the cost of one of these vehicles!

The cost matter was for EFI conversion. My bad I wasn't clear there.

To give a better picture of what I intend to do; I have made a flow chart (sorry arrows are in wrong directions http://fsae.com/groupee_common/emoticons/icon_razz.gif)

Why i thought of it :

1. The hassle of designing the manifold will be cut down.
2. As mentioned the distance between carbs and intake will be reduced to avoid gasoline deposition and sudden drip in the cylinder.
3. The stock carbs and the manifold is light and compact.
4. Making Four restrictors will be way easier and accurate (CNC).

Please Check this Picture:
www.facebook.com/TeamGearShifters/photos_stream (http://www.facebook.com/TeamGearShifters/photos_stream)

Looking forward to any criticism http://fsae.com/groupee_common/emoticons/icon_smile.gif

[Michael Royce]

X Charger,
Before you go ANY further, STOP!

Rule IC1.6.1 says "...a SINGLE circular restrictor must be placed in the intake system between the throttle and the engine and ALL engine airflow must pass through the restrictor." My capital upper case) letters.

If you turn up at Technical Inspection/Scrutineering at any official FSAE/FS event, or at any of the unofficial events in North America or Europe, you stand zero chance of getting your car approved.

If you want to stay with a carburetor(s), while it is technically possible to have 4 carbs flowing into a single restrictor, it is a terrible design choice. I highly recommend that then you throw away the 4 carbs you have, and design and build a complete new intake system with a single carburetor and a restrictor between the carburetor and the engine.

This restrictor requirement has been in the FSAE Rules since before even I became involved, and that was in 1986! In addition to the stated objective of limiting the engine's power output, I suspect another reason is to force teams to design and build a new intake system AND to have to do some sort of engine calibration work. It is all part of the education/learning objective of Formula. You cannot just take the engine out of a bike and bolt it into your car! You have to do some powertrain work.

[Jon Burford]

X charger, after all that has been said above you clearly didn't get the point.
Don't you think that if you used 4 restrictors you might have a significant advantage?
Read the rules and clarify them if you have doubts.
Although you won't get any clearer that what Mr Royce has already given you.

[X Charger X]

I guess I need a break with this and start with this from the basics and design it from scratch. Thanx a lot for your advice http://fsae.com/groupee_common/emoticons/icon_biggrin.gif

I will go with one carbs and SINGLE Restrictor.

I have a fair amount of knowledge in transient flow analysis for the Plenum design. Any Literature you could suggest out of your experience. And Yes I shall Google for sure.

[Z]

Originally posted by Jon Burford:
X charger, after all that has been said above you clearly didn't get the point.
Don't you think that if you used 4 restrictors you might have a significant advantage?
What a golden opportunity missed by the Washington team.

Imagine their WWU V8 breathing through EIGHT x 20mm restrictors !!!!!!!!! http://fsae.com/groupee_common/emoticons/icon_biggrin.gif

Z