What do you know about the plenum?

Who designed it? What volume is it? Who determined the volume - why was this chosen? Why isn't it tapered? I'm interested, but need some proper info!

 

dont know about the jamsport one but feild motorsport one was designed and then modified on his dyno



think he done the math and then modified it to suit



worked well

 

Rick, I am interested in your opinion of what you consider to be a good inlet manifold design.

Simon.

 

Simon - it depends what for. It really would require an essay to get across all my thoughts!

There are generally 2 parameters to an inlet manifold - runner length, and plenum chamber volume. The runner length takes advantage of something called "acousting supercharging" The idea is that by altering the length of the runner, you get can dramatically (it really is a lot) increase the VE of the engine at a certain RPM. You have to decide where u want the power to be boosted, and then decide the runner length. Have a look at some Honda inlets, they are a good example. Short runners, move power up.

However, this all goes out the window with forced induction. The speed of sound, and the reflection speed of the waves if u will, changes with air density. In practise, on a turbo car, its a bit like having variable length runners - its virtually impossible to tune for. Also, it can become pointless to tune for. You can get to the point that you are forcing that much air in, that it would be impossible to flow anymore through.

So, on a turbo car, the runners are made as short as possible without too much of a restriction.

Plenum chamber volume is next. On a NA car, ur looking at a volume aprrox equal to the engine capacity. On a turbo car - well, the bigger the better in terms of power. You should aim for a plenum equal to the amount of air consumed under boost. So a 2 litre car with 2 bar of boost, the plenum should be 6 litres...

Next, u have plenum shape. This should be done so that each cylinder is seeing the same airflow into it's port. The throttle body should never be directly infront of any cylinder. On a centre entry manifold, (Std RST,Fiesta) the air is designed to hit a flat wall. It then dissipates equally into the cylinders. Disadvantage is that you slow air speed. On a side entrance manifold, you can have much higher gas speeds. Probelm is gas distrubution. The cylinder closest to the entrance is going to have the highest entry speed. This is because as the air enters the plenum, to maintain the pressure, it slows down. To combat this, you can taper the plenum so it becomes smaller at the far end/last cylinder. By getting the taper right, you effectively increase the gas velocity, and equalise the airflow into the cylinders.

There are drawbacks into making the plenum too big though - namely response. The engine can feel laggy and lazy. This is because the plenum responds to any throttle changes before the engine does. So, if you boot it, the turbo has to fill up the plenum before it does the engine. Like with all tuning, it's a compromise.

I will say though, the Fiesta inlet is garbage. It is far too small for turbocharging. It will give good response though, ideal for the fiesta turbo which was never meant for motorsport. The S1 - which WAS meant for sport, haas the best manifold - ford arent stupid.

Jamsport have the right idea IMO. Use the short runners of the fiesta, and put a decent plenum on top of it....

There's loads more too manifold design, but ive simplified it to the important points i hope - if anyone spots anything wrong - let me know - im always learning

Rick.

 

I hope these essays get saved in the technical archive

 

I dont know why you boys up the power in Series 1/2's

132bhp is ANIMAL

was in mine

 

You better abandon ship on that project of yours if you consider a standard RST an animal

 

 

Rick, I couldnt have said it better myself.


I am just trying to work out why Ford desinged the cossie manifold in the way it did, when it would have been much easyer and cheeper to design one like the "Sweedish" one.

I think I am going to sell my Cossie one.

 

Whats peoples opinions on the rover turbo manifold that people are using on zetec conversions? Any good? Obviously not as good custom ones...

Dave.

 

can the s1 plenum be made to fit the fiesta efi runners..???

 

Yes, Its normally used in the Cossie Management conversion, As it splits and can be machined easier

 

is there much work involved..?? and is it expensive..??!!!

 

Im not to sure tbh, Await someone elses reply

 

Whats the diff between a s2 and s1 inlet? Never had that much of a look at a series1. Cheers

 

s2 plenum has a knock sensor under the servo pipe...

 

Thanks mate why does the lack of a knock sensor make it better though? Any other differences?

 

the injectors go into the inlet
not the injector plate
so you only need one gasket not 2
also got a support bracket which gose to the fuel pump blanking plate

 

This is an S1 Inlet, You can see where it splits




and a S2 inlet, No split - its an All-in-one item

also has a vacuum pipe for brake servo, not sure on anything else

 

whats this one from then, has a knock sensor AND a seperate plenum!!!

 

Might be an early S2 but looks Series 1

 

is the knock sensor the green connection below where the brake servo pipe bolts in? just wanna be sure as my s2 don't have that sensor in the plenum anywhere.

 

sure is...

 

i was under the impression that all s2's had a knock sensor fitted from the factory. any ideas why it would be removed?

 

early s2s didnt have them

 

how early are we talking? mine was registered in 87 on an E plate.

 

retards the timing...

 

Mixja thats a Series 1 item , probably just had the knock sensor hole tapped in

homer j, very early ones, anything after 86 should have a knock sensor i think. Only really D platers ive seen without them

 

mine was chipped before i bought it. any chance the people who chipped it removed it and does it have any sort of significance? sorry bout all the q's but bit of an engine management donkey. don't really understand a great deal about them and always trying to learn a bit more.

 

The knock sensor you mean?

Have you got a redundant Green plug by the heater box? And does your engine have a secondary CTS plugged up to the loom?

 

yeah there is a green plug that doesn't connect to anything behind the inlet manifold. i take it the cts is the sensor that bolts into the inlet manifold then yes there are two sensors there. one directly central to the manifold and one opposite where the coolant pipe connects to.

 

It would all be down to the ECU you have then, your car originally had the knock sensor. If your running the proper ecu your ignition curve will be very flat

And the sensors, the one opposite the coolant pipe is the 1st CTS, the central one is the TTS, the secondary CTS is bolted up with the auxiliary air device in the T piece

 

auxiliary air device? where is this and what's it look like?

 

Underheath the left side of the inlet manifold.

Anyway thats not overly important. What ecu has it got

 

the ecu has three coloured squares. blue, red then white.

 

Thats a later Series 1 ECU. Doesn't require a knock sensor. Problem solved

 

fair enough. seems odd though that a series2 has a series one ecu.

 

got recommended to fit one by powers when mine was tuned...

 

Series one ECU's are the better ones, the knock sensors can be affected by noisy top ends etc.

No knock sensor = no ignition retard

 

what advantages does the s1 ecu hold over a s2 item? just trying to figure out why mine has one fitted now.