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New Cams: dialling in the idle

OK I'm getting it, but slowly. Please de noob me on cams :hustler:

Background: installed Maruha cams, 252in/256ex 8.5mm lift. Also installed cam gears, zero adjustment for now. Idle has intermittent stumbling. MAP value has increased from ~30 to ~40, idling with no load.

Need help on this translation from Maruha:

http://www.maruhamotors.co.jp/parts/valvetiming.htm

Quote:

Central angle:
If the exhaust top dead center IN (0 degrees) at the times from which the criteria is a method of representing the angle at the center of the cam action.
In the 252 degree cam, cam starts to open at 10 degrees just before top dead center closes at 62 degrees after bottom dead center. Half of 252 degrees at 126.
But the second time it becomes a second time 126 and 116 counting clockwise from top dead center.
In other words, this case represents a central angle 116 degrees.

https://www.miataturbo.net/attachmen...ine=1316263495

If you use the 252 degree cam EX, combustion (explosion) is set to begin in the exhaust valve opens 62 degrees during the descent procedure in tea ceremony under the dead, and close 10 degrees after top dead center exhaust.
As in the IN, counting from 0 degrees top dead center (clockwise only) and therefore, represents the central angle 116 degrees.

https://www.miataturbo.net/attachmen...ine=1316263495

When this overlap is 10 degrees and 20 degrees +10 degrees.
Overlap refers to the state and are open both intake valves and exhaust valves.

My exhaust cam is 256 duration, do I just adjust the numbers accordingly?

Like so: "If you use the 256 degree cam EX, combustion (explosion) is set to begin in the exhaust valve opens 66 degrees during the descent procedure in tea ceremony under the dead, and close 10 degrees after top dead center exhaust.
As in the IN, counting from 0 degrees top dead center (clockwise only) and therefore, represents the central angle 118 degrees. "

I assume tea ceremony under the dead = bottom dead center? :facepalm:

And the drawings all assume that the cam gears are set to zero adjustment? Or are they adjusted 10 degrees?

So...in English: How do I get 110 center lobe separation, in terms of adjusting the cam gears?

If I zero the cam gear adjustments, do I get this?

[(252/2) + (256/2)]/2 = 127 degrees center lobe separation? If so, how do I get to 110?

How much overlap do I have at 127 CLS vs 110 CLS? And is the 127 CLS the reason why I have this crappy stumbling idle right now?

Thanks for reading :makeout:

:vash:

argh was in the middle of replying and windows crapped out on me.

anyway!

when I run more than 15-20 crank degrees of advance with the VVT on my 01, the idle suffers considerably. that works out to somewhere around 10-15 degrees of overlap.

For your cams, i'm interpreting that they designed them to run as described without cam gears (ie 0 adj). that is intake opening 10 degrees BTDC and exhaust closing 10 degrees ATDC (well not for the 256... but for the 252).

Stock 01 at full retard runs zero overlap (actually -5 overlap). At max advance, it runs about 30-35 degrees overlap. It wont even idle at max advance.

I made a cheapy timing graph to help me at one point. it's not super accurate, but it's useful for visualizing. Corrections to it would be awesome.

https://www.miataturbo.net/attachmen...1&d=1316273444

Reality check:

Place the crank at #4 TDC firing.
Look at the cam lobes on #1.
Intake should juuuust be starting to open, and exhaust should be almost finished closing.

As y8s was alluding to, if both intake and exhaust are well open at this point, (meaning lots of overlap), your idle will be crappy.

Quote:

Originally Posted by y8s (Post 772306)

For your cams, i'm interpreting that they designed them to run as described without cam gears (ie 0 adj). that is intake opening 10 degrees BTDC and exhaust closing 10 degrees ATDC (well not for the 256... but for the 252).

Thanks for the reply y8s! I translated the preceding part and it goes:

Quote:

Become the first criterion, the piston position. For example, the IN (intake side) for the cam.
(Example: 252 degree cam)
Exhaust top dead center piston (TDC) position (0 degrees), once you start down the cam, the intake stroke bottom dead center into the piston (at BDC/180) still passes through a valve is open. Valve closes at 72 degrees after bottom dead center turned further. Meanwhile, the piston is rotated 252 degrees crank angle.
https://www.miataturbo.net/attachmen...ine=1316298654

It changes with the slide cam cam pulley. Let's say 10 degrees advanced.
Valve opens and begins to turn 10 degrees toward the exhaust top dead center. The valve closes after bottom dead center point of 62 degrees.
https://www.miataturbo.net/attachmen...ine=1316298654

A point of the piston top dead time (eg 10 degrees crank angle) from the valve starts to open state.
The former, the latter both from the cam's 252 degrees the same working angle (time by pressing the valve) is the same.
However, the valve timing is changed.

I guess it means the first pictures I posted had adjustments made- the intake was advanced 10 degrees, the exhaust (not sure if it was retarded 10 degrees). Would that be more logical for a mild street cam that at TDC, there would be zero overlap?

And on another page:

Quote:

IN side At 252: 8.5mm: Compatible HLA
The EX At 256: 8.5mm: Compatible HLA

Recommended Valve Timing:
Valve timing 110 degrees recommended maximum angle at the center (both IN • EX).
You can reuse the OEM pulley, valve timing will be recommended despite the large, to set the valve timing more precisely targeted, effective pulley slides.
In addition, research head surface, we recommend a combination of slides, etc. If you can pulley gasket replacement.

Found a cam calculator here:
http://www.webcamshafts.com/

If I plug in what (I think) I have now, with the cam gears adjusted to zero
Cam Calculations - Lobe Center / Duration
Overlap: .0 degrees
Intake Duration: 252.00 degrees
Exhaust Duration: 256.00 degrees
Intake Installed Centerline of 126.00 degrees ATDC.
Exhaust Installed Centerline of 128.00 degrees BTDC.

Present lobe center separation: (126 + 128)/2= 127

That is way more than "extremely wide" according to that site!

If I try to get a lobe center separation of 110, with both intake and exhaust lobe centerlines at 110, this is what I get!
Cam Calculations - Lobe Center / Duration
Overlap: 34.00 degrees
Intake Duration: 252.00 degrees
Exhaust Duration: 256.00 degrees
Intake Installed Centerline of 110.00 degrees ATDC.
Exhaust Installed Centerline of 110.00 degrees BTDC.

That translates to 16 degrees advance on the intake and 18 degrees retard for the exhaust! :facepalm:

You will idle better at rich AFR with cams. idle at 12:1 afr.

Trust me.

...Continue cam timing discussion.

Only if you run lots of overlap.
These maruhas aren't particularly aggressive?

Quote:

Originally Posted by JasonC SBB (Post 772534)

Only if you run lots of overlap.
These maruhas aren't particularly aggressive?

No they're supposedly pretty mild. Supposed to plunk in and be compatible with the stock ECU, give a midrange bump.

Here are videos of what I'm seeing.

I thought it was some sort of vacuum leak, but the hiss sound is coming from the intake- is it the intake valve? Engine warming up here.

I attached a vacuum gauge- it is at ~20, but drops to ~17 intermittently. Engine warm.

Help :vash:

How is your valve lash?

I just changed the cams, didn't mess with anything else- still have the stock HLAs, so I assumed they would self-adjust..?

he makes more rich at idle it smooths out?

he fools with injection timing at idle it smooth out?

is the hissing noise when the idle drops your anti stall solenoid?

No the solenoids aren't the culprit, they're the first things I checked-removed and plugged their vac connections, the intermittent hiss was still there.

Did you do a quick visual check of the intake and exhaust lobe positions at TDC overlap?

Got a reply from Maruha:

Quote:

On 9/20/2011 10:51 AM, maruhamotors wrote:
> Hello Greg,
>
> On our Fcams, these are the same timing as the stocks, but as you might know that it is changeable depending on the situation.
> then the most accurate way is that you must measure the correct valve-timig by you first.
>
> This is the MUST job to have the accurate timing.
> ____________________
>
> Xxxx

Just to confirm: the stock NA cam specifications are:

duration 236 in 248 ex
intake timing: open 5 BTDC, close 51 ABDC
exhaust valve timing: 53 BBDC, close 15 ATDC
overlap: 20
duration: 7.8 mm
Intake Installed Centerline of 113.00 degrees ATDC.
Exhaust Installed Centerline of 109.00 degrees BTDC.

I did some calculations to figure out the exact timing of these cams...

Calculation A: intake opening and exhaust timing the same:

duration 252 in 256 ex
intake timing: open 5 BTDC, close 67 ABDC
exhaust valve timing: 61 BBDC, close 15 ATDC
overlap: 20
duration: 8.5 mm
Intake Installed Centerline of 121.00 degrees ATDC.
Exhaust Installed Centerline of 113.00 degrees BTDC.

Am I correct that the intake valve opening and exhaust valve closing are the same as stock, and the overlap is the same? This is what I will get if I install the cams with zero adjustment on the slider pulley? Then I should set both the intake and exhaust centerline tp 110, to get a center angle of 110 as well?

Or since it is a regrind, am I correct that the centerline of the cam will no change? Therefore it will be:

Calculation B: cam centerlines remain the same, half the duration added to the timing on each end:

duration 252 in 256 ex
intake timing: open 13 BTDC, close 59 ABDC
exhaust valve timing: 57 BBDC, close 19 ATDC
overlap: 32
duration: 8.5 mm
Intake Installed Centerline of 113.00 degrees ATDC.
Exhaust Installed Centerline of 109.00 degrees BTDC.

Quote:

Originally Posted by JasonC SBB (Post 773282)

Did you do a quick visual check of the intake and exhaust lobe positions at TDC overlap?

Not yet, haven't had the chance. Gathering info, and RL getting in the way :crx:

Interesting .... I just put the same 252/256 Maruha cams into a mildly modded NA8 today (ported, socketted ECU, etc) using the stock sprockets and HLAs.

On the bright side the car is obviously making more power from 3000 to 7000 and especially from 5000 up. Redline arrives in a bit of a rush now. ;) There are a few problems though.

When cold the car is missing, hissing and backfiring back into the airbox pretty badly and the idle is total shite at 900 with regular stalling. I know that backfiring back up the intake usually indicates things are too lean. It smooths out a lot above 3000.

When warm there is no idle below about 1800 - it's driveable below that but it just stalls instantly in neutral.

Are there any general rules about which way to move idle and open loop AFRs and ignition timing after moving up a step in cams?

EDIT: sorry, ignore all this. Car started up fine after sitting overnight. It now idles almost perfectly after re-setting idle air screw and ignition timing. It's very driveable at low revs and pulls hard from 3000 to redline. Absolutely no idea why it was so cantankerous last night.

-Put crank in #4 TDC firing position.
-Take several photos of #1 cam lobes in overlap position.
-Shrink photos down to 2 Mpixels or so so I don't get irritated by photos that take up my whole 1920x1280 screen.
-Post said photos.

Quote:

Originally Posted by JasonC SBB (Post 773399)

Will do. That's 180 degrees right? :hustler:

your veritcal cam marks should be pointing to 6 o clock.

TDC mark on crank will give you either TDC firing on #4 or #1. If #4 is firing then #1 will be in overlap, and it will be easy to take lots of photos of the lobe positions on the lifters. Also easy to move the crank back and for on either side of TDC to eyeball how far open the intake and exhaust valves are at TDC.