some techy questions

[vxer]

Hi Guys,

I have some semi-techy questions i\'m curious about :

a) Primary and secondary injectors - why are there two sets of different sizes?

b) leading and trailing ignition - again why have two and why do they have different advance curves?

Cheers, Paul.

[munkay]

at a guess i would say the secondaries are bigger because when they are used its because more fuel is required..

leading and trailing.... it keeps that rotor spining right...

[Martiny]

The trailing plug fires after the leading plug. Our combustion chamber is moving, remember. So the flame doesnt burn to the trailing part of the Rotor efficiently. Its mainly there to complete the combustion to reduce emmisions.

The car will run fine on just the leading plugs.

[vxer]

at a guess i would say the secondaries are bigger because when they are used its because more fuel is required..

I kind of thought it might be something like that - for when the second turbo kicks in, perhaps. I couldn\'t figure out why you couldn\'t just change the pulse-width to increase the fuel amount, though and have a set of identical injectors.

The trailing plug fires after the leading plug. Our combustion chamber is moving, remember. So the flame doesnt burn to the trailing part of the Rotor efficiently. Its mainly there to complete the combustion to reduce emmisions.

Ok, that makes sense. I remember reading that the le mans car had three plugs to increase efficiency and power. Does the rx8 engine have three plugs?

Anyone know why there are separate advance curves for each plug, though?

Cheers, Paul.

[Martiny]

The RX-8 has 2 plugs per chamber.

I think the trailing is retarded a lot on overrun, to prevent the engine "bucking". A lot of racing guys setup the trailing and leading to fire at the same time.

[Martiny]

I couldn\'t figure out why you couldn\'t just change the pulse-width to increase the fuel amount, though and have a set of identical injectors.

 

QUOTE]

I am not sure about this, - but probably because a big injector on a short pulse may not spray the fuel evenly, and therefore it would hamper efficiency, mileage, and cause more emissions.

[dandan]

I think the primary and secondary sets of injectors might also be there because the rotary engine sucks so much damn fuel! as stock it has 550 and 850\'s (ish) which is larger than you would find on almost any other car, you can upgrade the secondaries to 1650\'s and primaries to 850\'s, it just needs all the fuel it can get from 4 injectors!

im probably technically wrong but the fuel guzzling capabilities of rx\'s is certainly true.

[sdminus]

as a rule the closer you can get to zero split the more power you can make. But this will come at a price if the trailing fires before the leading. creating a negative split.

[vxer]

as a rule the closer you can get to zero split the more power you can make. But this will come at a price if the trailing fires before the leading. creating a negative split.

Can you clarify those terms for me?

Cheers, Paul.

[Martiny]

Paul, the leading sparkplug fires slightly before the trailing sparkplug. What is meant by split is the timing difference between them, usually around 5 degrees. In racing a lot of guys  have no split - plugs fire at the same time. SDMinus is saying that "negative split" means the trailing is firing before the leading.

[vxer]

Paul, the leading sparkplug fires slightly before the trailing sparkplug. What is meant by split is the timing difference between them, usually around 5 degrees. In racing a lot of guys  have no split - plugs fire at the same time. SDMinus is saying that "negative split" means the trailing is firing before the leading.

Thanks Martiny!

Anyone know the effect of reducing/increasing the timing split between those plugs?

Cheers, Paul.

edit: ah, i see SDMinus already answered that, the closer together the more power. So, in an ideal world, you want as much advance as possible on both plugs with little gap between?

[M@r]{]

This is an interesting thread.  So when you are advised to upgrade your injectors (in my case my standard injector set up goes in the 90% and above every now and then)  are you advised to upgrade both primary and secondary injectors?

[Red and Single]

{\']This is an interesting thread.  So when you are advised to upgrade your injectors (in my case my standard injector set up goes in the 90% and above every now and then)  are you advised to upgrade both primary and secondary injectors?

As I understand it, for most people, 1600cc secondaries are plenty. This is fine for at least 400 rwhp iirc.

If you want massive power, you may need 850cc primaries and 1600cc secondaries.

Then put your foot down and wave bye bye to your fuel :rollin

[Martiny]

Thanks Martiny!

. So, in an ideal world, you want as much advance as possible on both plugs with little gap between?

errr NO!

There is an optimum point in the timing where it is best to fire the spark. If you fire it too soon ( too advanced ) , you will lose power, and , in a Rotary, you can destroy the apex seal.

The trailing plug timing makes very little difference to performance. Its just a little helper for emissions, and  smooth running.

Mazda chose the advance curves carefully for both plugs, for a variety of conditions. Racing setup is not the best setup, except for racing.

For a standard engine on a standard ECU, thats what you should set the timing to - standard!

I have a book at home by Kenichi Yamamoto - I think its got graphs in from timing testing, I will have a look for us.

[vxer]

errr NO!

There is an optimum point in the timing where it is best to fire the spark. If you fire it too soon ( too advanced ) , you will lose power, and , in a Rotary, you can destroy the apex seal.

Perhaps i should have qualified \'as far as possible\'!

I meant as far forward under the following two conditions:

1) no detonation
2) still making power

For a standard engine on a standard ECU, thats what you should set the timing to - standard!

Well yes, but i will be getting an apexi soon enough and would like to at least know for certain how all the parameters actually affect engine performance. Not that i will be messing with them...

Although it might be nice to be able to reduce the knock figure by retarding the ignition slightly, should the need arrise (providing i have a working knock sensor, that is).

Cheers, Paul.