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IUST_Persian
07-19-2009, 06:41 AM
Hi everybody,
our engin uses a carburetor, and we are searching for some useful info about the optimal volume of the required plenum. Any help to gain access to these info is acknowledged.
PS: Or any article about intake system and restrictor.

IUST_Persian
07-19-2009, 06:41 AM
Hi everybody,
our engin uses a carburetor, and we are searching for some useful info about the optimal volume of the required plenum. Any help to gain access to these info is acknowledged.
PS: Or any article about intake system and restrictor.

Adambomb
07-20-2009, 06:52 PM
The restrictor is just a converging-diverging nozzle, any fluids book ought to cover that pretty well. Not much more voodoo beyond that, just remember that your flow isn't steady state...

As for making the restrictor work with a carb, I personally have never heard of this working successfully, at least the way our rules are written. The carb needs a clean vacuum signal to work right, and the restrictor fouls that up pretty badly. Not to mention the fact that with a carb, you're giving up quite a bit of airflow considering all your fuel has to flow through the restrictor too. And your manifold needs to accomodate wet flow.

If you're just starting out, and have more time than you do money, a Megasquirt would be a pretty solid start, although you may have to make some sensors. Performance Elelctronics sells a computer that is a bit pricier, but more user friendly, plus they do a lot of work with FSAE teams and have a decent selection of the sensors you'll need to make it work.

Ani_V
07-23-2009, 01:52 AM
We are using a Kawasaki Dual carburettor engine. How do we use a restrictor in this case? Are there any double pass air filters ( which allow two passages of air) or do we have to diverge the air volume through two plenums into the carburettor? And how exactly does a single pass restrictor fits into all this?

TorqueWrench
07-23-2009, 08:37 AM
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Ani_V:
We are using a Kawasaki Dual carburettor engine. How do we use a restrictor in this case? Are there any double pass air filters ( which allow two passages of air) or do we have to diverge the air volume through two plenums into the carburettor? And how exactly does a single pass restrictor fits into all this? </div></BLOCKQUOTE>

All the air entering your engine must enter through a single 20mm (19mm if E85) restrictor. If you are using two carbs, you would still have to design your intake so they both flow through the same restrictor. If you then wanted to split the air into two separate plenums afterwards, there is no rule against this.

Remember that your carbs have to be upstream of the restrictor as there are no throttling devices allowed downstream. So the only allowable order is: Carb, restrictor, plenum, runners, engine.

Ani_V
07-23-2009, 10:28 AM
Since ours is a dual carburetted engine, the air flow will have to be split after passing through air filter. Are there air filters that have multiple outlets suited for this purpose or do we need to convert a single outlet air filter to a dual one to deliver air into both air horns??

TorqueWrench
07-23-2009, 02:52 PM
Quick search on K&N's website yielded that they have a bunch of them that are dual outlets. You will have to check if any of them will work for you as you will need one specifically with your center to center distance and size.

Ani_V
07-24-2009, 03:02 AM
What all are the important factors that should be taken into consideration while determining the arrangement and orientation of the cooling system ? Like the angle at which Radiators will give max cooling and less drag? Importance of fan and shroud and the clearance between them? And most importantly what all mathematical calculations go into making cooling system more efficient?

P.S. : This is my first time with the Project

IUST_Persian
07-24-2009, 03:48 AM
Our engin had four carbs, out of which we placed one over the restrictor with the restrictor angle of 14 degrees and runner length of 10 centimeter, the volume of our plenum is 1.2 lit . and the model of engine: zx_6r. After all we failed to start the engine easily and after we started it we couldn't reach the rpm to more than 6000 with this restrictor system. Now, what do you think our problem is? Do you think if we use two carbs we won't have any problems anymore? And about the optimal volume of the plenum, what's gonna be your idea?

TorqueWrench
07-24-2009, 03:31 PM
I think both of you guys need to do a good amount of reading. No one on these forums is going to tell you how to design a cooling system from the ground up or tell you how design your induction/fuel system.

IUST_Persian, I know very little about carbs as we rip them off and throw an EFI system on the engine. I would say though that if the engine required 4 carbs to run correctly when you started, you probably need to deliver as much fuel as those 4 could for your engine to run.

Mikey Antonakakis
07-25-2009, 02:42 PM
Bigger main jet, to start.

But here's teh easiest way to fix your carb issues:
go with EFI. You'll be glad you did. Or find a carb that works for an 80hp engine and use that. That will probably be better than trying to adapt your two carbs.

L B0MB
07-27-2009, 01:44 AM
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Mikey Antonakakis:
Bigger main jet, to start.

But here's teh easiest way to fix your carb issues:
go with EFI. You'll be glad you did. Or find a carb that works for an 80hp engine and use that. That will probably be better than trying to adapt your two carbs. </div></BLOCKQUOTE>

A single 80hp carb... No motorbike engines come to mind but there are plenty of car engines that would have 80hp carbs like 80's model Corollas and the like

From what I have seen carb engines have virtually no plenum. Any 'plenum' that exists is the same diameter as the runners. Any big volume will have slow gas flow hence fuel will drop out of suspension and pool in the intake manifold. Not good. So the exit diameter of the restrictor may be limited to the same diameter as the intake runners so there are no step in the flow

A carbed setup may be possible to get running but will never be as powerful / reliable / tuneable as an EFI setup.

An EFI setp would be much cheaper than flying a car to comp and not passing tech inspection... http://fsae.com/groupee_common/emoticons/icon_smile.gif

Ani_V
08-01-2009, 12:48 PM
Iam new to the FSAE project. Got very little idea about the detailing of the engine subsystems. I have to start on the intake restrictor and the manifold. Please suggest me some useful technical literature for this purpose

Mikey Antonakakis
08-02-2009, 07:05 AM
For the new guys,
Having a good intake and exhaust system counts for NOTHING if you cannot tune your engine (with respects to timing and fueling). If you have never written a fuel map from scratch before, get your intake/exhaust set up as fast as you can and start learning to tune. If you spend too much time designing, you will not have time to write a decent fuel map which will make your car difficult or impossible to drive, even if you have the best intake ever made (as if there were such a thing). Just make a solid design that isn't BAD, and get a good fuel map written.

TorqueWrench
08-02-2009, 08:28 AM
+1 to what Mikey said. Another thing to check when it comes to tuning is to see if there are any local tuning shops that would be willing to come in and TEACH you guys how to do it. At the same time, they will normally make sure you don't do something dumb and damage the engine in the process.

Another thing to keep in mind when designing your intake system is that it is, as with everything on these cars, a compromise. You are going to have to come up with your own goals at the start and design to meet them. Not only will it make your system a lot easier to design from the start, but it is going to be the first thing the design judges want to hear most of the time.

There are several good SAE papers published on intake and restrictor design of FSAE cars. The nice thing about these is that they take the restrictor into account and can therefore be directly applied to your application. Only downside is that they are almost exclusively for 4 cylinder engines, so they will have limited applications if you are running something else.

After that, I would recommend looking through the book list on the main page as there are several good books in there. "Internal Combustion Engine Fundamentals" and "Design and Simulation of 4 Stroke Engines" are also good and I don't know if they are on that list.

Ani_V
08-03-2009, 12:00 AM
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Another thing to keep in mind when designing your intake system is that it is, as with everything on these cars, a compromise. You are going to have to come up with your own goals at the start and design to meet them. Not only will it make your system a lot easier to design from the start, but it is going to be the first thing the design judges want to hear most of the time. </div></BLOCKQUOTE>

At the outset thanks for your patient reply. But Iam not sure what factors are affected by the changes in the intake manifolds and restrictors. As in how changes made to these would improve or decline my performance. So can you please suggest what we should target at?

TorqueWrench
08-03-2009, 09:15 AM
That is really going to decide on what your car's goal is and your driver's style/ability. Nothing on these cars is disconnected and the entire car must function together to work.

Here is an example. If you have a real close ratio gearbox, you can normally have a much narrower powerband than if you have a wider ratio. On the other hand, you are going to lose acceleration time to shifting if you run too close of ratios. Also, your driver has to be skilled enough to keep the car in its powerband to make it work.

Your intake manifold is going to have a great impact on volumetric efficiency, which in turn affects torque, which in turn affects HP. As a general guideline, longer runners tune for low RPMs and short runners tune for high RPMs. Same thing goes for exhaust, but on a larger scale due to the higher temperatures.

Above a certain RPM, your restrictor is going to limit the amount of air your engine receives which lowers your VE. Most restrictors I have seen are a modified venturi, which you can find the base template online.

Ani_V
01-26-2010, 05:52 PM
Mine is a dual carbed engine, virtually has no plenum at all ! I read stuff about ram and tunelling effect to find the lengths of the intake pipes and effective volume.

Wanted to know which RPM is most desirable for tuning the engine. I mean whether to tune engine for low rpms or high. And what is the difference in performance of both?

PatClarke
01-27-2010, 09:33 PM
Ani-V,
If you wish to stay with the carburettor, then you need to throw one carb away and make a simple 'Y' type manifold to adapt your carburetor to the engine.
Put the 20mm restrictor between the carburettor and the manifold.

This should permit the engine to run, but how well it will run is just a guess.
You will need to adjust the fuel mixture and ignition timing to suit your new setup.
The engine needs to be run on a test bed, preferably under load to do this. Access to an exhaust gas analyser would help analyse whether you need more or less fuel.

I can not envisage any way you can adapt your two carburettors that will work effectively.
You would need to make a manifold adaptor that fed both carbs through the restrictor. Then another manifold to adapt the restrictor to the original manifold. Crazy!

If you have to make a manifold, do it once and incorporate the restrictor.

Pat

Ani_V
01-28-2010, 11:36 AM
I thought of a "X" shape structure with top two branches connected to the carb and bottom two to the intake runners. Restrictor could occupy the elongated intersection. something like this.

&gt;==&lt; .

Can you please suggest the necessary calculations that I should do regarding the pipe lengths, specs of C-D nozzle etc. In short the important inevitable calculations to get the design right for the starters.

Ani_V
01-28-2010, 11:37 AM
@Patclarke

How do we adjust the ignition timing and fuel mixture as you suggested if I use a single caarb?

TorqueWrench
01-28-2010, 03:58 PM
At the most basic level, the pipe length calculations are pretty much modifications of the pressure waves you must have learned in physics class. Your restrictor is a converging diverging nozzle, which you should have learned how to analyze in fluids.

As for the ignition timing and fuel mixture for a carb, look into how you would adjust them on any car.

Ani_V
03-09-2010, 02:36 AM
The Kawasaki engine i am using is dual carburetted with a 34 mm bore. since the restrictor comes at 20mm for gasoline, there will be large pressure reduction. Plus, its difficult to get the runners made coming from a dual carb and converging onto a single restrictor. I am thinking of using a 28mm mikuni carb that comes Enfield 350/500 cc.

My doubt is : Will this new carb be compatible to the bike? What all tuning changes would be needed to be done on the carb?

L B0MB
03-09-2010, 08:35 PM
I'm guessing you are running a twin cylinder

In this case you'd probably want to have two intake runners the same diameter as your intake ports. Join the two intake runners in a Y shape at your desired length. Taper the feed pipe down to 20mm then back up to 35mm and connect to your single carb.

That would make your restrictor have a 35mm intake, 20mm choke, 35mm outlet

The Y shape join is a guess, a T shape may work better in directing pressure waves down to the closed valves of the opposite cylinder for improved wave coupling...

A carbed setup will have low power potential as there is no plenum to damp the intake pressure waves. A plenum most likely wouldn't work with a carb as the air fuel mix would slow down and fuel may drop out of suspension causing very poor running. Unless you can inject fuel into the intake runners, remembering no throttles allowed after the restrictor...

Take a look at Megasquirt ECUs. Low cost if you have the time to make one

Ani_V
04-01-2010, 06:12 AM
Yes ours is twin cyl engine. Dual carb (34 mm bore) in it go virtually no plenum. Its like the A/F mix from one carb feeds into one cyl and similar with the other cylinder. It has individual intake runner system. Now because of the 20mm restrictor in between the carb and intake runners, pressure drop will be high. For pressure recovery, i am planning to use a log type plenum with the simplest of construction. But as you say, using a plenum wont work with carb as the A/F mix would slow down causing poor filling of cyls.

Now, I am left a bit confused to make this trade off. Please help.

Adambomb
04-09-2010, 12:58 AM
I wouldn't say you're confused, I'd say it sounds like you've figured out exactly why carbs don't work in FSAE!

But, in the interest of getting the car running, I'm imagining you're best off to compromise more on the side of making the carb work well over trying to make power. Mostly because the only thing worse than not making much power is not making much power and also having it not start, run, and get around the track well. If it were me I'd try doing the simple log, and make it small-ish, maybe with a volume roughly the same as the displacement of the engine.

Ani_V
04-12-2010, 05:02 AM
I am in a process of designing the restrictor section (I am using a venturi type with maximum pressure recovery design) of the intake. I surfed for stuff and found some calculations from other teams/authors. I fed in my data to obtain the exit diameter of the venturi. But Iam having confusion over fixing the lengths of the converging and diverging sections. I am not able to account for the pressure that has to be generated by my intake. Please suggest some ways to:

1) Calculate the lengths of each section i.e. conv and diverging.

2) Calculate optimum pressure to be generated after at the exit. Rough estimations would help as this is my first time. I dont have a data log of testing the car.

Wesley
04-12-2010, 10:52 AM
Yeah, the very nature of an engine that is restricted the way ours is makes it difficult to fuel with a carbuerator. In other restricted carbuerator setups (NASCAR comes to mind) you can actually size your venturis to the same diameter as the holes in your restrictor plate.

By Running a venturi restrictor you're making the lowest pressure part of the system downstream of the carbuerator - where for efficient fuel metering you need the lowest pressure point to BE the venturi.

In this case, it seems like the best option would be to design a carbuerator with a 20mm venturi. And in your case, that doesn't really seem like an option. So, in backwoods carbuerator talk, you need to maximize the vacuum signal that the venturis see to properly meter fuel flow and jet your carb appropriately. You'll have to jet up and likely modify air bleeds in order to get sufficient flow from a motorcycle carb.

As far as carbuerator selection goes, you might consider a downdraft carbuerator from some type of V8. If you can get ahold of a single Weber or Stromberg carb it might be better suited for your purposes than a motorcycle carb (whose floats aren't usually well suited for high-g turns anyways)