M20 Stroker Build: Take 2

[digger]

i dont think it is a stock cam but it is certainly very mild based on the 1mm numbers

A schrick 284/272 is around 236/230 at 1mm

schrick advertised durations are based on the end of the ramp which is fairly meaningless as we dont know how high the ramp is but id estimate it would be somewhere between 0 and 0.1mm (i.e a ramp of 0.25 to 0.35mm based on specified lash being 0.25mm)

[Lugnuts]

Finding ferrous surfaces to mount a magnetic base on can cause you to fill a swear jar...

Managed to slip a cardboard timing wheel inside the hole of the front cover (120mm in diameter), mounted to the gear with 3 double-sided 9mm velcro pads. 17mm hole in the middle, and a large flanged hex head bolt to replace the stock Torx. Worked well.

The lifting hook on the front is steel, which helped measure #1 In + Ex. The stock exhaust manifold also provides something to work with. No 6 intake was a balancing act. Unfortunately the intake manifold makes it impossible to measure 2-5 intake. I didn't fancy going to the effort of removing it.

It's also damn near impossible to measure the cam lobes with all the rockers/retainers/shafts installed. My attempts with a depth gauge on the tiny end of a lobe were unreliable.

Here's what I was able to measure, eyeballing the timing numbers using a handy casting "nub" on the inside of the upper cover as my reference point.

Lash was set to 0.007"/0.1778mm for all valves:

Valve    0-0                0.1-0.1            1-1              
#1 In.   315-101 (146)      319-94 (135)       330-80 (110)  
#1 Ex.                                         221-328 (107)
#2 Ex.   83-227 (144)       87-221 (134)       100-209 (109)  
#3 Ex.   328-105 (137)      326-100 (134)      339-88 (109)  
#4 Ex.                                         160-268 (108)  
#6 In.   132-278 (146)      138-271 (133)      150-260 (110)

Fairly consistent, give or take a bit.

Looking at Digger's M20 camshaft profiles, I can't arrive at a definitive conclusion. The 1-1mm durations seem a tad on the short side, but the total duration seems in the right ballpark?

Are IE/Schrick cam durations from 0-0 lift?

[Lugnuts]

Maybe just get calipers and measure the cam lobe lift vs. base circle. That quick and dirty measurement with the valve cover off would be your first clue if the cam is stock or not, without removing the cam for further inspection.

Yeah, I'm going to also do that when I measure the duration using Digger's procedure.

Useful degree wheel website:

https://www.blocklayer.com/degree-wheel.aspx

Turning over the engine with all the coolant pipes installed is going to be...a challenge.

Concocting a plan to video call my dial gauge using my phone, from my laptop while lying under the car ...

Edit: on second thought, poking a hole in the middle of the degree wheel and turning the engine over using the cam bolt (spark plugs removed), would be easier. Only concern is chewing up that bloody Torx bolt turning over the engine 50+ times. Might be fine. Think I'll temporarily swap for either a meaty hex head or a socket cap...

[Nader393]

Maybe just get calipers and measure the cam lobe lift vs. base circle. That quick and dirty measurement with the valve cover off would be your first clue if the cam is stock or not, without removing the cam for further inspection.

[digger]

printout a cam degree on paper or cardboard and photocopy with rescale function to the szie to suit the cam gear an attach with double sidetape or temporary glue. then use a dial indicator on the retainer measure the following (ensure lash is correct). will likely need to remove upper timing cover which is a pita. You can also count cam teeth and kind of interpolate with a nice steel rule. IIRC each cam tooth (8mm) is like 15 crank degrees equivalent

0 open and close
0.1mm open and close
1.0mm open and close

record the degrees for the open and close at each increment and apply the correct transfer function (likely just an offset and x2 or x0.5 mulitplier) to get the printed cam degree to give crank degrees

can also tighten up lash a bit afterwards to test how the engine behaves.

[Lugnuts]

So, I have a theory as to what's going on with my engine...the cam is an imposter. (supposed to be a 272/272 IE new grind, bought in 2013)

Why I think this is the case:

1. My car's idle seems very...stock; there's practically no lope. All (?) of the 272 M20 videos I can find sound noticeably different to mine (pronounced lope at idle),
2. Took the car for another dyno test, with 10 degrees cam retard (max permissible). The theory being to try and decrease DCR, and see if that allowed more timing.
   1. Tuner said he could "set any advance at cruise, and 4 more degrees at WOT" before knock. Engine also lost 10kw across the rev range.
3. Repeated a compression test with 0 degrees cam advance; cranked until the needle stopped. These seem on the high side for a 272 cam:

Cylinder	PSI
1	206
2	210
3	217
4	212
5	214
6	215

In short, I suspect my dynamic compression is too high.

My poor attempt at understanding & calculating DCRs for different cams (substitute the calculated stroke value (DST) in a static compression calculator). The biggest unknown in my calculations was the volume (CCs) of the Mahle stroker pistons.

https://www.enginebasics.com/Advance...20Dynamic.html
https://diamondracing.net/p-10-compr...alculator.html



























If my cam is eg, a stock grind 256, then the DCR is going to be in the region of 8.4 (maybe even 8.6?) :1, which as I understand it, is on the high side for a 10:1 stroker running pump gas. This would explain the knock at seemingly low timing, and why more timing (and less knock) is possible with the retarded cam.

I naively installed the cam, (which has been the one consistent factor in both of my stroker builds), and didn't confirm any duration/lift values. I understand the cam has a duration stamp on the rear end of it., which isn't particularly helpful...

Now I just need to get clear in my head how to confirm this with the engine in the car...

[digger]

It’s the right direction but 8 degrees at crank (4 at cam )

[Lugnuts]

Set the timing 4 degrees retarded and went out for a drive.

Gotta say, factoring in butt dyno, I feel like I've lost some top end...bottom to mid feels like it has a bit more pep. Which doesn't make a whole lot of sense...

Maybe now 15 degrees isn't enough timing to make top end power???

99.995% sure I turned it the right way lol:

[digger]

others found it runs better, but the reduction in dynamic compression ( later inlet valve close )would help in your situation though I’m not sure it will be a drastic change as it would help more so with knock in the lower rpm area

You want to run the coldest plug that doesn’t foul, it might not help but it won’t hurt. The next step would be BPR7ES

[Lugnuts]

What I’d try is setting the cam retarded by about 4 degrees as that’s what others found to work with mild cams 284/272 on a 2.8/3.1 where it made more torque and power. That might help a little but there’s something odd going on. I presume you’re using something like a BPR6ES plug ?

Ok, I'll try adjusting the cam gear 4 degrees retarded. Wasted spark and no dizzy rotor makes changing it pretty straight forward.

Retarding should reduce dynamic compression on account of the later valve opening, correct?

Should probably coincide with another dyno session - see how (if) it gives us any extra headroom on the timing.

Yes, fresh set of NGK BPR6ES - all looked fine yesterday when I pulled them. Only done ~400Km since install.

I think previously you had suggested running a cooler plug, which I tried (unfortunately without any noticeable reduction in knock - purely butt/ear dyno though). They'll be in a box somewhere...might dig them out and see what condition they're in.

[digger]

I have now ;)

Pulled the fuel pump relay, all 6 spark plugs and zip-tied the TB open. Cranked the engine 10 times for each cylinder:

Cyl	PSI
1	200
2	200
3	200
4	205
5	205
6	200

The old timing map was very similar to the one above - max 18-19 degrees at WOT across the rev range. Similar issues with knock. Talking to the tuner after the dyno, I got the impression this engine knocks more than the previous. I suspect on account of the increase compression ratio.

Fuel was fresh in the tank a few days before the dyno run.

I should probably mention, I installed a Nuke adjustable cam gear since I figured I'd taken about 15-18 thou off between the head and block...wanted to account for the small amount of retard introduced.

Currently 1 degree advanced. I checked all the gear teeth line up with a stock one and the P2V clearance...she's good.

What I’d try is setting the cam retarded by about 4 degrees as that’s what others found to work with mild cams 284/272 on a 2.8/3.1 where it made more torque and power. That might help a little but there’s something odd going on. I presume you’re using something like a BPR6ES plug ?

[Lugnuts]

Have you done a cranking compression test ?

I have now ;)

Pulled the fuel pump relay, all 6 spark plugs and zip-tied the TB open. Cranked the engine 10 times for each cylinder:

Cyl	PSI
1	200
2	200
3	200
4	205
5	205
6	200

The old timing map was very similar to the one above - max 18-19 degrees at WOT across the rev range. Similar issues with knock. Talking to the tuner after the dyno, I got the impression this engine knocks more than the previous. I suspect on account of the increase compression ratio.

Fuel was fresh in the tank a few days before the dyno run.

I should probably mention, I installed a Nuke adjustable cam gear since I figured I'd taken about 15-18 thou off between the head and block...wanted to account for the small amount of retard introduced.

Currently 1 degree advanced. I checked all the gear teeth line up with a stock one and the P2V clearance...she's good.

[digger]

the other questions i had were with old setup what was the timing map like? you sure the fuel is any good and not old and stale?

[ForcedFirebird]

^^^agreed. Check your cranking compression. Something could be off, you don't want to see over 225psi.

The timing looks to be very low as we run more advance than stock in the 9.4:1 b27 race cars.Cranking compression is 190psi with the 272 and a touch under 200 with the stocker.

Here is a stock table from a 173.The vertical WOT map is basically your horizontal 100kpa in MS.

[digger]

Power is in the head, cam and intake manifold. Have you done a cranking compression test ? Might tell something about cam timing