ignition timing questions for a EA82

[2nd Hand Yank]

I did a search on ignition timing and found out how mechanical ignitions nights work. mechanical advance is your normal advance for change in rpm. Vacuum advance is often used at low to medium throttle openings for better fuel economy...

My engine knocks easily under load at low rpm.
Can I avoid some of this when I go offroad by blocking the vacuum advance?

I also notice that on 91 octane I can only get to 90-95 km/h in 3rd before detonation.
Too much total timing perhaps?

I'm curious because one poster said his l series with a carby didn't detonate at any rpm on regular fuel

[Cliff R]

I am not answering your question cause I dont know the Subaru answer but taking me back to the very early 80's when I was obsessed (spelling) with Datsun's we used to take out the standard distributor timing plate and replace it with (brain hurts now) 12 degrees timing plate and block off the vacuum advance.
I still have a 12 deg plate for a Datsun 200B distributor in my box of tricks but others may be able to answer the effects of distributor timing plate changes to modify the timing of the engine while blocking off the vacuum advance.

[scoobymine]

I use PULP and set my timing about 6-8 TDC, it'll go anywhere.

[Cliff R]

Um...whats PULP (do you mean Premium Unleaded Petrol) ?

[scoobymine]

Yeh! that's it.

[steptoe]

I have brazed up the outer ends of the slots in the mechanical advance limiter in my EA81 dizzies to limit the max mechanical advance as i have wound initial timing up to about 14 ~16 DBTDC and the reduced travel within the dizzy slots keeps the total combined max advance at about 28 degrees as desired by slower burning 109 Octane LPG that loves advance down at the lower rev range, hates too much advance up the higher end. In my EA82T running up to about 12 psi boost the knock control box is still waiting for detonation to enact upon - I'm monitoring the output signal of 1.7V and still waiting to see it hit 4.5V which will then retard the timing but 12 psi and a hammering is still to see any detonation

A nice option for a carbed EA82 would be to try an early EA82T efi dizzy complete with knock sensor and its separate knock control box to cater for fuel ranges giving max timing to suit all fuels and cotrol timing by rtarding spark when need a rises

[2nd Hand Yank]

I recently tried a tank of 98 octane fuel because I wanted to take some friends out for some sand driving and this would obviously put the engine under high load. 98 octane always makes it run smooth. What I didn't expect is this time I actually had slightly better fuel economy than with 91 octane. Nearly 10% further on the odometer for a given fuel gauge level change. I can even drive at 15 km/h in 3rd and there's no detonation. (just to test high loads at low rpm )

So if I switch it to 6-8 BTDC it will give me a little more power than my current ignition timing?
LT65 set it to factory timing settings which is meant for 91 octane.

[Cliff R]

There's a thread on here somewhere discussing how to get an EA81 engine to perform better.
Wasnt there something about higher octain fuel and advancing the timing too ?
Is this the same for the EA82 engine ?

[El_Freddo]

2HY, it is possible that someone has rebuilt your engine at some stage with a higher compression - this could explain why you get detonation in various places in the rev range, or you've got excessive carbon build up from running rich and this is enough to bring on the effect of pre-detonation where the flame front comes from the piston before the spark occurs, it also makes the top of the piston run hotter which can lead to damage in the form of a hole.

The other thing you need to remember is that you need to adjust the timing on the old carb'd engines to get the most out of the fuel. If yours has been tuned on the 98 it's going to run best on 98. Drop 91RON in it and you'll have a power loss, economy loss and detonation issues.

The timing on 91RON is usually set by the manual at 6-8 deg BTDC. Running 98 you should be able to push this out further without detonation occurring (as it would with 91 if you did this).

I hope this all makes sense!

Cheers

Bennie

[TOONGA]

Bennie I did a compression check on his engine a while ago, all the cylinders were in the 120 psi range.

I think some one ran this car on PULP and had the timing set near or on 20 degrees, and the over advancing of the engine has worn it out. I did tell Matt all of this ages ago when I did the compression test but I think he is still looking for answers.

In reality the carby EA82 shouldn't be advanced past 10 degrees regardless of fuel used, unless you want to wear the engine out prematurely.

TOONGA

[El_Freddo]

Bennie I did a compression check on his engine a while ago, all the cylinders were in the 120 psi range.

That sounds a little under done to me! No wonder it likes the higher octane stuff!

Cheers

Bennie