EvocentriK

I have Tomei Type-R's and I really like the way the engine feels now vs stock cams. ~20kw gain in the top end, and a nice full midrange with excellent throttle reponse. Problem is they lope like S2's and I want a smoother idle. I installed them without cam gears, but I want to add some and dial out some overlap by advancing the exhaust cam to start with as I dont want to change the low-mid range focus of these cams (changes to the intake cam would be done as a last resort and could probably move about 2 degrees before the midrange would be compromised too much).

They have 50 degrees overlap installed straight up. I noticed S1's with similar idle timing/rpm to mine idle much smoother, and they have 48 degrees overlap. The stock 8MR cams have 36 degrees overlap.

Will taking out say 2-4 degrees overlap really smooth the idle out or not?

Original valve timing

Intake opens: 30
Intake closes: 60
Exhaust opens: 70
Exhaust closes: 20
Inlet lobe centre: 105
Exhaust lobe centre: 115
LSA: 110
overlap: 50


Advanced exhaust cam 2 degrees:

Intake opens: 30
Intake closes: 60
Exhaust opens: 72
Exhaust closes: 18
Inlet lobe centre: 105
Exhaust lobe centre: 117
LSA: 111
overlap: 48


And for comparison the S1 specs:

Intake opens: 27
Intake closes: 61
Exhaust opens: 67
Exhaust closes: 21
Inlet lobe centre: 107
Exhaust lobe centre: 113
LSA: 110
overlap: 48

EvocentriK

No one knows from experience how much difference a couple of degrees overlap makes to idle lope? Surprising.

sslevo

iTrader: (6)

To me this sounds silly as the whole reason you put cams in is to pick up power on the top end. But no i do not have any value to add, lol. I have the S2's and love the lope!

EvocentriK

Power in the top end isnt all about the overlap only. In fact, since the closing of the intake valves are the single most critical event in terms of defining the power band position, retarding the intake cam can often shift more power to the higher revs. Go look at all the guys running -4/-1 setups on their HKS cams to see what I mean.

I got cams for mid range enhancement, I dont care about top end since I spend 90% of my 'fun' driving in the midrange. The lope at idle just screams EPA me please so I'd rather it sound a little more normal that's all.

Maybe Im asking this the wrong way since most people like the sound I want to get rid of. Does changing the cam position a couple degrees make the cams lope when they didn't before?

ace33joe

iTrader: (2)

I will be installing Tomei Poncam type-R cams soon, and I am interested in making the idle more like stock in expense of little bit loss in peak power.

Did you try cam gears yet?

I will also install cam gears with it, and I am thinking about trying advancing intake cam +2 to make less overlap, and hopefully that will help a little bit more on the lower rpm torque/turbo response also.

If you have done some experiment already, please share. I will also perform some when I get mine and share here.

Thanks!

10isace

iTrader: (12)

I'm on GSC S2's. Sometimes want the smoother idle and sometimes I want a rougher idle (I get bored easily). All I do is change my ignition timing map. I think I'm at 11* at idle and it's fairly smooth. I bet with cam gears it could get smoother. If I go down to 5-7* at idle then it's pretty rough. Have you tried changing your ignition map?

ace33joe

iTrader: (2)

According to EvocentriK's post at UK forum (happened to find it during searching for similar answer), he is even running 14* of timing and open loop AFR 13:1, but he still experiencing rough idling.

Not sure whether he went to other milder cam options though.