[Mk2] [Turbo] Do uprated cams help reduce turbo lag?

[Chris]

Because I never removed it...

Ok then, So Jim is running 850's, it idles crap. So it must really have 1600cc injectors in it for your theory to be correct? Nothing to do with the cams, just the monster hidden injectors.

As long as large injectors are controlled correctly at idle there should be no issues. A good mapper is able to do this I'm sure. The kitchen sink with a fire hose example is crap. The mapper is not going to run injectors on full duty on idle is he???

If cams do not cause idle issues, why do old Mk1/2 Escorts with Kent cams idle so poorly.....Must be fitted with a monster carb eh??

[RyanRs]

edited.

[Chris]

Obviously you have found my above post offending from the PM you have sent me. There is nothing in the above post to that nature at all? I was clearly stating that injectors do not cause idle issues. You then posted I was wrong, so I posted the above post to show my theory.

I am not saying I am 100% correct, mearly stating my opinion.

I am going to report the PM as being called a looser and various other insults is just not on. Banter is on ALL internet forums. Maybe you should not take it all so seriously.

Chris.

[cantfindausername]

Now now girls, stick to the subject.

I think Ryans comments about large injectors generally giving poor idle is true... in some cases. It depends on the injector and how quick it can fire.

Please note these figures are fictional, and just used to give an example
Say you've got a 1600cc injector that can open and close in say 1ms, and it gives good idle. If you have the same cc injector but one that can only respond down to 5ms, then it is going to be chugging the fuel in there on idle, hence raising the tick over to get the injector to respond in a usable way. The same goes for any size injector. If it can't fire quick enough to be usable on tickover, then a trade off will have to take place. I.E higher idle speed.

[Marf]

The resolution of the ECU also plays a part here. if it has load/rpm cells with big gaps it will interpolate the values between them. This is less of an issue with things like a Link ECU as you can add in extra load/rpm cells to give a better resolution where you need it and stop the ECU guessing values when it interpolates between two cells.

[JJ]

I have loads of experience in elminating problems that arise / problems I've created

Mines currently nailed at 900-1000 rpm ... 272 duration 10.4mm lift ( the highest HKS lift ) 850cc injectors and driven by a PFC.

When messing with the exhaust cam for more performance.. the increased overlap caused the idle to become unstable and thus stabilising was only possible at 1300-1400 rpm. Any lower and hunting / stalling would occur / a/f ratio would go irratic. Didn't matter how much adjustment I did with the ignition timing or fuelling.. it was mechanically not feasible for a smooth low idle.

[steve b]

Now now girls, stick to the subject.

I think Ryans comments about large injectors generally giving poor idle is true... in some cases. It depends on the injector and how quick it can fire.

Please note these figures are fictional, and just used to give an example
Say you've got a 1600cc injector that can open and close in say 1ms, and it gives good idle. If you have the same cc injector but one that can only respond down to 5ms, then it is going to be chugging the fuel in there on idle, hence raising the tick over to get the injector to respond in a usable way. The same goes for any size injector. If it can't fire quick enough to be usable on tickover, then a trade off will have to take place. I.E higher idle speed.

Aren't low impedance injectors supposed to give a better idle than higher impenance ones as well. Injector size does certainly make a difference to idle. If you read abot how to spec injectors for builds it always tells you to spec as small as you can safely so idles not too badly effected.

[jimGTS]

I have loads of experience in elminating problems that arise / problems I've created

Mines currently nailed at 900-1000 rpm ... 272 duration 10.4mm lift ( the highest HKS lift ) 850cc injectors and driven by a PFC.

When messing with the exhaust cam for more performance.. the increased overlap caused the idle to become unstable and thus stabilising was only possible at 1300-1400 rpm. Any lower and hunting / stalling would occur / a/f ratio would go irratic. Didn't matter how much adjustment I did with the ignition timing or fuelling.. it was mechanically not feasible for a smooth low idle.

so given this, it must surely be a case my cams/cam have been moved from a default position, ie advanced/retarded for top end performance gains. but cons are it wont hold idle at lower rpm.

my car doesnt idle crap (say at 1k rpm) cause its been setup wrong, or the map is no good, its cause the orginal owner wanted gains somewhere in the revs, so adjusted the cam/cams which ment the downside was a high idle.

i dont mind my idle at 1400 at all, i love the way the car sounds, just maybe concerned come mot time when they say its to loud. as it is dam loud at idle compared to my rev2 with nur spec. different kind of loud tho. more engine noise, than exhaust.

[steve b]

Jim 1400 idle won't get through MOT as it must idle below 1000 i think.

[jimGTS]

Jim 1400 idle won't get through MOT as it must idle below 1000 i think.

ive seen a recent mot doc that said idle can be 500-1500


it passed last year before i got the car, so hoping its alright.
probably a friendly mot person tho.


http://img513.imageshack.us/img513/285/motcatdn3.gif

[Century Motorsport]

You can get away with bigger injectors (1600cc) if they are ball pintle design - they have better control at low cycles than normal injectors.

Regards,

Nathan

[Chris]

Jim 1400 idle won't get through MOT as it must idle below 1000 i think.

ive seen a recent mot doc that said idle can be 500-1500


it passed last year before i got the car, so hoping its alright.
probably a friendly mot person tho.


http://url513.imageshack.us/url513/285/motcatdn3.gif

Idle is at the descretion of the tester. When I had 272's in mine, idle was 1200rpm. Explained the cams were fitted to the tester and he was OK with it.

[Century Motorsport]

Just take your passenger seat out ... you then get an allowance for higher emmissions!

[jimGTS]

Just take your passenger seat out ... you then get an allowance for higher emmissions!

hows that work?? do you need to declare the car is a track car or something?


edit, just looked on the mot thing i posted, do you just follow "no" on the "is it a passenger car" so then higher emissions test
?

[JJ]

Jim... you do some worrying dont you ??!! You grey yet ??! Stop worrying about it... deal with it when the occasion arises ( if theres an issue !)

[Dale_V]

My car passed its MOT WITHOUT an idle! it needed MOT'ing before it went for mapping

[jimGTS]

just wona be prepared and see what options i have.

i was going to pop buy an mot place within the next few months anyway and get em to check emissions. just so i got the heads up.

[greeny]

I think IIRC mine idles at 900-1000 steady when warm, 272's & 1150's AEM controlled.

IIRC moving the pin over on the stock cam wheels changes it 6 degrees i think

[cantfindausername]

Yeah its 5 or 6 degrees. Mine had this done when I first got it. Had strange timing marks when peeling back the timing belt cover. Made quite a difference to mid range, but did lack a bit top end. Worth doing on a basic/mild set up I reckon.

[salamanzer]

and mine idles @ 1500rpm on 288's high lift cams and 2200cc injectors (low impedence) so anything is possible!!!