Butterflies , lots of them.

[Dr Goggles]

Hi all .
I've been toying with the idea of making an injector stack style manifold for our V6 for a while now.....oh , oh .I know that getting the injectors themselves close to the valves will help, that there will be "some" tuning involved in getting the length of the stacks right but what I want to know is .....does anyone know of a good way of working out what size butterflies will get me into the "ballpark".......I'm currently battling a too large throttle body on my road car that runs LPG...goes great on limited openings but that's it , but that's a side line and not important right now .Are there some "sums" I can do that will say "six of these will flow X and get you near where you want to be".......


Why ..........just because

[JackD]

You can try this at home :
Depending on the angle of the dangle, you can do a lot to slow the opening and with it the airflow at mid throttle or anyplace else with the geometry of the flap in relation to the actuator.
So to with a racer, if you wish to maintain slow speed driveability and flow the max at WOT, the plates might not want to open directly as the as the pedal is pinned to the floor.
You can make a model to prove the concept with your degree wheel as the central point and an indicator pinned at the middle to record the result in degrees.
Now off to the side, establish various hinge points in a vertical line next to it.
Those will represent the various test hinge points of the actuator.
Now make an actuator arm to hinge on those points that has multiple points for the link to the Flutterbye shaft.
At WOT the Flutterbyes need to consider the flow rate (mostly the size) of the port + whatever losses occur around the hinge shaft and possible nozzle projection that might disturb the flow.
There is a formula floating around that speaks to stack diameter and length that is every bit as important as exhaust science.

[wolcottjl]

Dahlgren will probably pipe in soon.  In the meantime there is a website that you can find more information than you care to read.  www.speedtalk.com    Quite a few engine guys post on the site including Darrin Morgan from Rehr Morrison and other top engine builders/designers.  Use the search function to narrow down the multitude of posts.

[Sumner]

................I know that getting the injectors themselves close to the valves will help, ................

...............does anyone know of a good way of working out what size butterflies will get me into the "ballpark".......I'm currently battling a too large throttle body on my road car that runs LPG................


Why ..........just because

Some of the F1 engines and others are moving the injectors away from the valves and further up the intake tracks, so I wouldn't be afraid of that.  I think a recent Hot Rod magazine explained why they were doing that and if you are interested I'll try and find it.

Usually the cfm of the throttle body for an EFI engine is not as critical as getting the size of a carb right and can be a lot larger than a carb as it is not handling the fuel.  What is the engine size on the road car??? and what size body are you using?? and how is the LPG injected??

c ya,

Sum

[ddahlgren]

OK to either clear this up or muddy it worse.. you can pick.. The flow response from a butterfly type system is 1-cosine of the opening last I looked but taking it from memory. What you need to remember is it is an s shaped curve with a large change initially fairly linear in the center and slow at the end per degree of change. So your linkage and tps sensor needs to have a similar response in order to maintain some drive-ability and tune-ability as well. A good modern ECU can do this or you can do it with a linkage to the TPS if the ECU is a bit more modest and won't let you define the sensor response curve.. As far as butterfly size typically the same area as the valve area will work OK 99% of the time. Size matter size always matters if you want to make some torque and if you have no torque you have no hp period underline exclamation point. The typical engine drops 15% torque between max torque and max hp over what is usually around 1500 to 2000 rpm.. so torque is your pal. Too large a runner and butterfly equals lost torque, not your pal at any time..
Injector placement is a matter of desired driving style. Smooth off idle good mileage and emissions is close to the valve big power is see if you can shoot it across the room and still get it in the top of the stack.. real life a compromise but further up the stack will make power as long as it stays there and does not have tons of reversion because you either made the stacks too short too large in diameter or the cam timing is very off the wall..

See clear as mud read it twice and the light will blink on..
Dave

[JackD]

SEE LONG FORM ABOVE ^   

[Bow]

The further you get the injectors from the Valves, the better the Air/Fuel mix you will have.

As for your Question of Diameter and length figuring,

Here is a spreadsheet I made after reading a few books on the subject, and planning mine out: http://www.riley-music.com/BowsStuff/TunedIntakeandExhaustdesigns.xls

Some of the information is for my setup, like Velocity Stack length... but the basic idea is that you are tuning for the air pulses.

EDIT:

Link Fixed

[tortoise]

Linky no worky.

[wolcottjl]

http://riley-music.com/BowsStuff/Tuned%20Intake%20and%20Exhaust%20designs.xls

[Evil Tweety]

Linky no worky.

You gotta love Microsoft and the ability to easily put spaces in a file name.
(signed, a Unix weeny)

[tortoise]

http://riley-music.com/BowsStuff/Tuned%20Intake%20and%20Exhaust%20designs.xls

Thanks. Above about 13,850 rpm we need a negative length intake port and stack, according to your sheet. I can't figure out how to fabricate such.

[Bow]

http://www.riley-music.com/BowsStuff/TunedIntakeandExhaustdesigns.xls

Thanks. Above about 13,850 rpm we need a negative length intake port and stack, according to your sheet. I can't figure out how to fabricate such.

No, I did say that the Velocity stack section may not apply to your application, didn't I?

Also, you need to know the distance front the face of the Head to the center of the valve stem....
mine is 3.25"

If yours is 3.25", then your total intake length front the lip of the Velocity Stack to the head side of the flange should be around, depending on what pulse you tune for:

Second Pulse Length:   4.58   In.   116.2   mm
Third Pulse Length:   3.78   In.   96.0   mm
Forth Pulse Length:   2.11   In.   53.7   mm
Fifth Pulse Length:   0.66   In.   16.8   mm

Look at the Motorcycle setups that run at 13800 rpm, the entire intake is about 4" long

[tortoise]

I did say that the Velocity stack section may not apply to your application, didn't I?

Sorry, missed that! Your TB is 7.8" long, I take it.

[Bow]

From the Head side of the intake flange to the intake side of the Throttle body, without out the Velocity Stack, mine is 7.75"... yup

This is not exact, but it does get you in the ballpark, according to my Engine Analyzer Pro Software.

It should give you a good, close starting point. If you take the Total length needed, then subtract the length of the Intake Valve port (in the head), Intake Manifold runner, and Throttle body, you will get the required length of your velocity stack.

[ddahlgren]

runner length does not work like a musical instrument..
way more going on than that.
think in terms of injector placement air velocity and inertia..
Dave