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Discussion Starter #1 (Edited)
Hi,

Can a informed person tell me if there is any overlap on the FD2 exhaust cam? I am potentially going to be creating a bit more back pressure in the exhaust manifold in order to comply with new MOT rules.

Unless I am completely misunderstanding it? Which is quite possible.

Thanks
 

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Overlap is literally where the inlet and exhaust are both open at the same time.
The inlet timing is adjustable so you can effectively increase/descrease the overlap too.
Might just need a retune with the cam angle/timing ;)
 

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Discussion Starter #3
Overlap is literally where the inlet and exhaust are both open at the same time.
Indeed, my concern being that back pressure will get to a point where the gases do not leave the cylinders.

The inlet timing is adjustable so you can effectively increase/descrease the overlap too.
Might just need a retune with the cam timing ;)
Never knew that :)
 

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I`ve got a Skunk 2 adjustable exhaust cam gear lying around that I still need to fit If I can find the time for it.
With this cam gear it`s possible to give the exhaust cam advance or retard relative to crankshaft position. Because the pulse plate at the rear of the exhaust cam has an extra bung for the cam sensor the exhaust cam position also dictates the position of the intake cam relative to the crankshaft.
If you retard the exhaust cam 1 degree, the intake cam is also retarded 1 degree, so overlap stays the same. But because you can vary the low and high cam advance any way you like on the intake cam with flashpro you can vary overlap in such a way that you can choose to let overlap on the low cam stay stock, but increase the overlap on the high cam by remapping it.
I want to try this out on my car to increase the efficiency of my nitrous sytem. In this case a nitroused engine likes the exhaust cam to be advanced because the mixture inside the combustion chamber burns much more rapidly thus the exhaust valve needs to open slightly sooner to get rid of the exhaust gases. This setup produces more low and midrange torque.
back in the old days I experimented with this on my old Peugeot GTI`s and had some good results with it. Hopefully this will also work on the FN2.
 

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Discussion Starter #5
I`ve got a Skunk 2 adjustable exhaust cam gear lying around that I still need to fit If I can find the time for it.
With this cam gear it`s possible to give the exhaust cam advance or retard relative to crankshaft position. Because the pulse plate at the rear of the exhaust cam has an extra bung for the cam sensor the exhaust cam position also dictates the position of the intake cam relative to the crankshaft.
If you retard the exhaust cam 1 degree, the intake cam is also retarded 1 degree, so overlap stays the same. But because you can vary the low and high cam advance any way you like on the intake cam with flashpro you can vary overlap in such a way that you can choose to let overlap on the low cam stay stock, but increase the overlap on the high cam by remapping it.
I want to try this out on my car to increase the efficiency of my nitrous sytem. In this case a nitroused engine likes the exhaust cam to be advanced because the mixture inside the combustion chamber burns much more rapidly thus the exhaust valve needs to open slightly sooner to get rid of the exhaust gases. This setup produces more low and midrange torque.
back in the old days I experimented with this on my old Peugeot GTI`s and had some good results with it. Hopefully this will also work on the FN2.
culasse, so there is a slight overlap on FD2 cams?

Also are you saying I cannot change the overlap without the Skunk 2 adjustable exhaust cam gear?
 

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Yes. Most cams on cars have overlap to get a more efficient running engine.
If you have flashpro you can vary the overlap by changing the intake cam advance.
 

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Discussion Starter #7
Yes. Most cams on cars have overlap to get a more efficient running engine.
If you have flashpro you can vary the overlap by changing the intake cam advance.
Thanks! :D
 

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If you're swapping to the Piper manifold, it's likely that the gas flow characteristics will be signficantly different to the Toda, which will mean a remap to get the best out of the system, especially with the addition of a cat
 

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Discussion Starter #9
If you're swapping to the Piper manifold, it's likely that the gas flow characteristics will be signficantly different to the Toda, which will mean a remap to get the best out of the system, especially with the addition of a cat
Yeah definetly getting a remap as a imagine the VE will change quite a bit.

My concern was just that thing I told you about that someone advised me "gasses re entering/not leaving the cylinders if exhuast manifold pressure was high due to exhaust cam having an overlap"
 

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Changing the cam timing to reduce the overlap can reduce the HC content, but I'm not sure how back pressure effects the MOT unless you mean that it keeps the cat hot?
 

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Hi,

Can a informed person tell me if there is any overlap on the FD2 exhaust cam? I am potentially going to be creating a bit more back pressure in the exhaust manifold in order to comply with new MOT rules.

Unless I am completely misunderstanding it? Which is quite possible.

Thanks
I know ash I will not put anything new, but my condolences about your MOT, while we don't have such big troubles in our country to pass those stupid tests even without cat or loud exhausts...
 

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Discussion Starter #13
Changing the cam timing to reduce the overlap can reduce the HC content, but I'm not sure how back pressure effects the MOT unless you mean that it keeps the cat hot?
Im gonna have to put a cat onto the exhaust in order to comply with the MOT changes, no cat = automatic failure regardless of emissions. which causes issues with insurance.

The back pressure obviously is going to go up :-( which will reduce performance

I know ash I will not put anything new, but my condolences about your MOT, while we don't have such big troubles in our country to pass those stupid tests even without cat or loud exhausts...
Your lucky. Sadly we are not.
 

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Ashley, I don`t know if this is clear but if you want to increase or reduce cam overlap you need an adjustable exhaust cam gear for the k20 engine.
Just altering intake cam advance will not help, the total overlap will stay the same no matter if you advance or retard VTC.
The ecu takes the position of the exhaust cam pulse plate as a basis and the intake cam will be advanced or retarded the same amount as the exhaust cam. Hence the overlap will always stay the same.
Hope this will avoid a misunderstanding about cam overlap.
 

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Ashley, I don`t know if this is clear but if you want to increase of reduce cam overlap you need an adjustable exhaust cam gear for the K20 engine.
Just altering intake cam advance will not help, the total overlap will stay the same no matter if you advance or retard VTC.
The ecu takes the position of the exhaust cam pulse plate as a basis and the intake cam will be advanced or retarded the same amount as the exhaust cam. Hence the overlap will always stay the same.
Hope this will avoid a misunderstanding about cam overlap.
How come ?

I thought the exhaust timing was locked...but the intake timing was variable from 25-50 degrees advance.
If the exhaust timing is locked and the inlet timing is shifted the overlap has to increase and decreae.

This was the whole point of the i in iVTEC.
Increasing the overlap changed you from a street profile to a race profile moving the peak power up the rpm.
Where it would normally sap low rpm power as gas speeds werent high enough to scavenge the chambers and sucks exhaust instead.
You got the best of both worlds with variable inlet timing.
 

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That`s not how it works. As long as you don`t use an adjustable exhaust cam gear to alter exhaust cam timing the overlap between the intake and exhaust cam will stay the same, no matter which way you vary VTC timing.
It`s because the exhaust cam pulse plate has an extra bung which is used by the ecu to measure the exhaust cam timing relative to the crankshaft.
It`s possible to vary intake cam advance by advancing or retarding it but with an adjustable exhaust cam gear you can also vary lobe separation between both cams.
 

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The exhaust cam stays fixed to the same position relative to the crank, but vtc allows the intake cam to vary the advance.

Would be a nice thing if we had VTC on the exhaust cam aswell as that would make the engine even more efficient.
However this would make for an expensive engine as this would require a very sophisticated engine management system.
And to remap it after you put in some aftermarket cams would be a major task.
 

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The exhaust cam stays fixed to the same position relative to the crank, but vtc allows the intake cam to vary the advance.
So the lobes have to spread and the overlap has to change then :popcorn: :D

I know the sprockets are fixed relative to each other but the actual inlet cam has to rotate....and this changes the inlet vs exhaust cam timing and the overlap.
The video even says VTC is designed to modify the overlap.
:confused:
 

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Discussion Starter #20 (Edited)
So exhaust cam timing is adjustable or not in Flashpro?

I have to admit I thought it wasn't until Relic's first post, but I'm happy to accept otherwise.

... in fact, I'll ask Vit.
 
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