Timing Issue

[astglenn]

OK. I am new to the flat, air cooled earth. I do have 20 years of V-8 race tuning and building behind me. I gotsts uh question for the air cooled brethren.

Background:

1600 DP, type 3. Runs strong, I can see that the heads are fairly new. I know nothing about the history of this engine. It ran like a dog when I bought it. Ignition and carburation tweaks show a very strong engine. It tunes into a very snappy little engine.

The issue:

I have found that this engine needs about 16-18 degrees of initial timing in order to stabilize the vacuum signal above 13" and will settle to a maximum signal of about 15" maximum@ 18 degrees initial. This much initial advance results in good combustion with jetting that is mathematically sensible. I have re-worked the, springs and vac advance to provide a very steep curve for an all in of 38 degrees at 3200. 28 degrees at 2200.

The problem:

I am used to seeing pre-ignition upon starting (Push back) in my liquid cooled world, on a WARM engine. Here, I see it on a COLD engine. The running profile with supreme fuel and a warm engine is great. No knocking, pinging, start push back, nothing. Short shifted and flogged, it pulls and grunts without complaining. It pulls well to about 5K. It has dual ICT's. I have run the LM2 and AFR's range from high 11's to mid 13's. All is good.

I do however see the typical over initial advance kick back when cold. Once the engine is remotely warm, this issue goes away. This is not cold oil. This is absolutely a negative torque reaction to early ignition.

My usual list of suspects would be: (But IDKJS about these engines)

Valves that wont seat properly upon warm up (Retiring cyl pressure)
Ring tension that croaks with warm up (Retiring cyl pressure)

Can someone please offer enlightenment before I take a bath with my toaster?

The engine displays none of the typical evidence to support either of the conditions above.

I know not what is inside this engine. It does seem to behave like a retarded cam timing problem.

Thank's in advance (No pun intended)

[Clonebug]

I have EDIS ignition with a Megasquirt ECU and I have run 15-18 degrees advance at idle.

I do have a 400 rpm 9 degree advance set for starting though.

My new engine that I have been working on wouldn't run cleanly without 43 degrees advance at idle so I know what you are going through.

Typically you should be at 8-10 degrees at idle but with a distributor you are sometimes stuck with what you can get especially when using an 009 full mechanical advance distributor.

Each engine is different though. What are the numbers on the distributor you are using???

Are you using the Fuel Injection distributor with that??? I think they have a dual point setup inside for timing the injectors also.

[Slow 1200]

timing for max vacuum will destroy your engine

[Jadewombat]

Can you post a picture of how your distributor is mounted in the car? Sounds a bit silly, but whenever someone is building one of these engines it's fairly common to put the distributor drive gear 180 degrees out. I'm not saying this is your issue, but the stock distributor is supposed to retard the #3 cylinder because it gets the hottest of all four. This may at least account for some of this issue you're having if it's retarding #1 instead.

[Marc]

Depends upon the vintage of the distributor. Early engines with the oil cooler inside the fan shroud did usually have ~3° of retard built into the lobe for #3 cylinder, but with the inception of the "doghouse" fan housing that was no longer the case. Simple enough to check, switch your strobe light pickup between #1 and #3 to see if there's any difference in timing.
IMO anything over about 12° initial advance is too much for most engines...many variables to consider here, for example rodlength-to-stroke ratio and mixture stratification, but my gut feeling is that your ~17° is just too much. Your other numbers sound like they're in the ballpark to me, so try backing down the initial and keeping ~40° total at high (3800+) RPM / light-load, with ~30° @2500 RPM.

[Piledriver]

No toaster baaaaaaaaaaaaaaaths required.

Do a cold and hot leakdown, should tell most if not all.
Your hot leakdown theory has merit, the jugs may not be staying round too.


*********************
I keep forgetting how often I used to get frustrated with the limitations of distributors.

Now I have cranking timing (5 degrees, -10 works too, go figure)
idle timing (variable, maintains idle speed +/- ~20 RPM to target, varies from 5 to 45 degrees, YMMV as it's adjustable)
and the main timing map, which IIRC has 24-28 degrees in the idle area when warm.
ignoring overrun, which cuts fuel and spark to drop RPM as quickly as possible,
and cold timing, adds (or removes) timing based on CLT. (can be set to always active just bt setting the table up right)

I'm probably forgetting something...
It helps to have ADHD with so many knobs to tweak

It came with an almost FREE fuel injection system too!
The warm up table can also add fuel% at high temps... No need to have it turn off, table can go to meltown if you set it to do so.

[astglenn]

Thank you guys for the thought process. I see I have found the right place. There have been a couple of updates. I have a distributor machine. I took a 009 and set up a very quick curve. Hell I left points in it. The mechanical advance swing is worth about 17 degrees now, after a bit of tweaking. So it looks like I can live with 12-13 degrees initial and a total of 32, all in by about 2900.

My idle vacuum is about 1" hg below peak value. Some snap was lost, but not too bad.

[supaninja]

TOS has it's role (I like giving Tram a hard time ), but this is where the smart people are

[astglenn]

The tune seems acceptable now. I appreciate the help. I am leaving my favorite engine porn video as a thank you.

Crank up the speakers. This is off the hook.
http://www.youtube.com/embed/y2iBbwocYZw?