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ea82 dizy advance curve turbo vs NA


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20 replies to this topic

#1 fredsub

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Posted 17 December 2005 - 06:03 PM

Does anyone have the dizy advance curves for both the turbo dizy (the older one with vac advance) and a normal dizy? maybe its in the FSM ? (i don't have it)
Anyway I am running a NA dizy in the ea82t, but now also have a ea82t dizy, it will probably need to be re-curved etc (as I had disassembled it for look-see)...I'd like to understand it a bit more first...
For instance wondering why there is such a big difference for the static timing for the engines ea82 - 8deg vs ea82t - 20deg - thats alot of advance at what is 0"...so going into boost >+0" surely the advance must be falling, otherwise pinging results, no ? (ignoring the knock sensor part of it)
I had run it at 8deg for years (out of ignorance), but now at 20deg, performanc is not really that flash - or it really needs the turbo dizy for this ??

#2 calebz

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Posted 17 December 2005 - 06:19 PM

What year is it. That will make a difference 85-86 is completely different than 87+

#3 ausubaru92

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Posted 17 December 2005 - 10:17 PM

The ea82 na disty is set at 8deg cos the advance unit advances the timing beyond 8deg when the weights and the vaccum come into action.
The turbo disty, on the other hand, is set at 20deg cos that is its max timing advance, then the ecu than retards the timing as it needs to.

Im pretty sure that that is how it works;)


Gannon

#4 fredsub

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Posted 17 December 2005 - 11:00 PM

I think,I doubt Electrically the ECU could retard the advance the whole range ,say 45deg typical, due to mechanical limitations of where the contacts are, I think I had info b4 that -15deg is the max retard, and its only from knock...not as part of the normal advance curve ?

the dizy would be the earlier one i'd say?, 85-86, no optical cam angle sensor etc...

Would it be correct then, if using the NA dizy, then the advance should be set at 8-10deg?

#5 fredsub

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Posted 28 January 2006 - 06:12 PM

I have established by experiment that if you run the N/A dizzy in the ea82turbo, you still set the static timing advance at ~8deg. You do need the turbo dizzy to use the ~20deg static advance setting, as this dizzy works completely differently in how its vacuum advance mechanism seems to work.

#6 Ross

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Posted 29 January 2006 - 01:14 AM

The ea82 na disty is set at 8deg cos the advance unit advances the timing beyond 8deg when the weights and the vaccum come into action.
The turbo disty, on the other hand, is set at 20deg cos that is its max timing advance, then the ecu than retards the timing as it needs to.

Im pretty sure that that is how it works;)


Gannon



Na, the turbo engines have a larger base advance mainly because of their lower compression ratio. Pre '87 turbos still have both centrifugal and vacuum advance like N/A engines. after '87, the ecu advances the ignition as it sees fit.

#7 ausubaru92

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Posted 29 January 2006 - 01:37 AM

On the NA Mpfi engines, 87>, the disty is set to 20deg also.

This is because the ecu has the ability to delay the electrical signal to the coil as it needs to, (in much the same way as a guitar effects pedal applies a delay/echo to the sound)

The timing is set to 20deg on cars with an optical sensor disty cos this is the max timing and the ecu electronically retards it depending on load, rpm, tps & temp signals ect.

On cars with a mech disty, it is set to 8deg cos it then allows the vac and mech advance unit to 'advance' the timing as needed, based on manifold vac and engine speed (though crudely compared to elect disty)

Hope this makes sence


Gannon.

#8 Ross

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Posted 29 January 2006 - 06:06 PM


The timing is set to 20deg on cars with an optical sensor disty cos this is the max timing and the ecu electronically retards it depending on load, rpm, tps & temp signals ect.


The ecu advances the timing much further than 20 deg at higher engine speed - more like 40 or 50 deg btdc.

#9 Dylan86GL10

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Posted 09 February 2006 - 08:38 PM

Hmm the chiltons manual says 25 degrees for an 86 turbo. Does that sound right? I believe my distributor has weights in it.

#10 calebz

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Posted 09 February 2006 - 10:08 PM

Hmm the chiltons manual says 25 degrees for an 86 turbo. Does that sound right?



yes, That is correct 85-86 - 25DBTDC
87+ 20DBTDC

#11 Matty B

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Posted 09 February 2006 - 10:29 PM

Everyone know what is going on now....
Then please excuse the hijack but,

I am in the process of squeezing 6psi (max) of boost into the Wonder Brumby via a toyota 1gg blower.
Now- I have a disty in the EJ22 and its obviously set up for natrual aspiration. It runs at 12 degrees advanced at idle and about 20 at full advance (full noise).

In which direction should I be modifying it to give better performance with boost.

More revs + more advance????
The rev and boost curve is not like a turbo, its almost a constant increase.

Shall I just twist the bastard around a bit more and have a go?

Thanks in advance:lol: :lol:
Could't resist.

BTW I bloody hate the dancing banana!

#12 Dylan86GL10

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Posted 09 February 2006 - 10:56 PM

yes, That is correct 85-86 - 25DBTDC
87+ 20DBTDC


Calebz, as the 86 has a vacuum line, shouldn't I disconnect this when setting the timing? The chiltons manual skips over 86 thanks.

#13 calebz

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Posted 10 February 2006 - 12:55 AM

Calebz, as the 86 has a vacuum line, shouldn't I disconnect this when setting the timing? The chiltons manual skips over 86 thanks.



Sorry man, Iam going to have to let someone else answer that for you. I tend to stay away from the pre-87 stuff;)

#14 ausubaru92

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Posted 10 February 2006 - 06:21 AM

I think that you have to dissconnect the vac line and plug it so that the disty is at base timing, not influenced by manifold vac.


Gannon

#15 Ross

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Posted 10 February 2006 - 04:24 PM

Calebz, as the 86 has a vacuum line, shouldn't I disconnect this when setting the timing? The chiltons manual skips over 86 thanks.


Yes you should, although that vacuum line sees very little if any vacuum at idle - ive found it makes no difference at idle on my ea81t (same set up).

#16 Dylan86GL10

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Posted 10 February 2006 - 04:53 PM

Yes you should, although that vacuum line sees very little if any vacuum at idle - ive found it makes no difference at idle on my ea81t (same set up).

The vacuum at idle is about the highest the engine sees except for decel so it should have a fairly large impact on timing.

#17 85Sub4WD

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Posted 10 February 2006 - 05:09 PM

My 1985 FSM lists the NA MPFI having a sharper advance curve than the turbo, maxing at 20-degrees advance at 3k RPM for the NA, vs ~14 @ 3k for the turbo - keep in mind that the vacuum levels the vacuum advance sees are different for both fuel systems, and there is no data for how the NA disty would work in a boost situation - I think the NA one would give a much stronger reaction to boost though if I had to guess - the may be a stop on the NA disty vac. advance movement though that keeps it from retarding the timing

the vacuum line will/won't make a difference based on whether or not your vacuum advance assy is gummed up - I thought it did not make any difference either, until I found the advance assy had frozen - my expierence was that it DID make a big difference for the NA carb vehicle when I disconnected the vacuum line at idle with a working advance mechanism

good luck

#18 naru

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Posted 10 February 2006 - 05:19 PM

The vacuum at idle is about the highest the engine sees except for decel so it should have a fairly large impact on timing.


It would if manifold vacuum was the source.Almost all dizzys use ported vacuum(ea-82 included).Big difference.Only time removing the hose makes a difference is if the throttle stop is misadjusted.
(carb or FI)

#19 Ross

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Posted 10 February 2006 - 05:23 PM

The vacuum at idle is about the highest the engine sees except for decel so it should have a fairly large impact on timing.


That is correct, however the line to the vacuum advance does not see manifold vacuum - it gets a vacuum from the throttle body that seems to increase with d(air flow)/dt.

#20 Dylan86GL10

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Posted 11 February 2006 - 05:17 PM

It would if manifold vacuum was the source.Almost all dizzys use ported vacuum(ea-82 included).Big difference.Only time removing the hose makes a difference is if the throttle stop is misadjusted.
(carb or FI)


The vac line changes my idle timing by 8 degrees (advances).

#21 Dylan86GL10

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Posted 11 February 2006 - 05:19 PM

That is correct, however the line to the vacuum advance does not see manifold vacuum - it gets a vacuum from the throttle body that seems to increase with d(air flow)/dt.


Thanks for the clarification, I haven't dealt with a vac distributor for the past ten years. With the line connected, my 86 has 25 degrees advance. Unhooking the green connector doesn't change anything.




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