Ignition Timing Advance Curve Map, Delco Remy HEI, EST. LH 350

Can anyone provide a timing advance map or other data for a LH 350 ( 1985 454 cu in). The distributor on the engine is a Delco Remy HEI / EST. I suspect it is an after market or upgrade system, since the bell housing tag on the engine has point gap and dwell specs.

I have the base timing set at 8 degrees BTDC in the time mode at 700 rpm. I end up with about 22 degrees in run mode at 700 - 1000 rpm. Seems high.

While researching this distributor I find it appears it is used in both small block and big block 4,6,8 cylinder engines. In cars, boats, trucks and farm equipment. Often the module for the distributor is the same in many of these applications (using part number info). This doesn"t seem possible. What am I missing. This application has no ECM data input (knock or oxygen sensers ect). How can one module fit so many applications. I assume the timing advance is derived from within the module using tachometer info.


clipper

That's a retrofit and you id'ed the smoking gun in you first paragraph. That distributor will fit the small and big block v-8. physically should fit the six cylinders, too, but won't work without a cap change. The module is were the advance curve is set and is 'hard programmed' into a given module. the 'hei' tag is usually applied to the auto type were voyaguer or est gets slapped on the marine units. I'd make sure it is a marine unit before going any further.

as far as the curve goes, the factory manual is the best source. Most all OEMs used the recommended GM curve in that timeframe. That translates in the advance starting around 1000 rpm and progressing up to provide a total advance of 30-32 degrees by 3400 rpm. the upper end of the curve is much more critical than the lower end. The 'performance modules' we use have only 20 degrees of advance. We set the timing to yield 34 degrees at 3200 rpm and then live with the idle timing around 14 deg. As long as the engine will restart when hot, the initial value won't matter much. yes, all the figures are BTDC.

.." have the base timing set at 8 degrees BTDC in the time mode at 700 rpm. I end up with about 22 degrees in run mode at 700 - 1000 rpm. Seems high."

I agree. You'll need to retard the initial advance significantly to get a total of about 26 to 28 degrees full in. Any more than that and ou might turn your pistions into Catholics (holy!)

Jeff

I totally agree with the two prior posts, your timing should still be near base at 700 and 1000 is too soon for the advance to begin....Lee

IMO, 1k rpm wouldn't necessarily be a deal breaker, but there is no need for any progressive this early. If the progressive were to begin this early, the "Full In" may follow suit..... not sure with EST.

Question: which Delco HEI is this?
There is an EST version (electronic spark timing), and a conventional mechanical advance version.

I'd rather risk being called the Ignition Timing NAZI, than to not mention this:

Note that BASE is BASE and is BASE all day long........ We fire up and idle on BASE, and that's about it.
BASE should remain up to approximately 900/1,000 rpm.
No need for anything other than BASE at this RPM.
Progressive will begin at about .9k or 1k RPM.... (and hopefully no sooner)... and will limit out at/near 3.2k to 3.5k rpm rpm or so.

A Full In advance too early will cause piston damage as Jeff refered to as turning into Catholics (holy!)
I'll refer to them as that piece of chicken that didn't get taken off the BBQ screwer.


If this HEI is EST, and if it interfaces with any sensors, don't be surprised if in run mode (at lower RPM) the advance increases some.
You must be in BASE mode to set this.
The important numbers will be the progressive advance while under load.
See your OEM Engine Iginition Timing specs for this, and compare to the actual progressive numbers on your engine.
(you'll want to strobe this to see what's taking place)

Mark makes a good point, although some SBC and BBC Marine Engines share similar advance curves.
Again, see your OEM timing specs, and not just BASE.
You must have the Progressive or TA or TAT in order to gain the most performance, yet steer clear of Marine load Ignition induced Detonation.
"Detonation" should be a very bad word for us ...... and is one reason why we CAN NOT use automotive or farm equipment ignition curve information for Marine.

Baring any EST... ECU/ECM Knock Sensor data, here's an example of what you'll be looking for re; your OEM timing specs.
(example only.... and note that BASE is seldom shown in the vertical scale, and must be added when doing the math)

Correction to my earlier comment:
IMO, 1k rpm wouldn't necessarily be a deal breaker, but there is no need for any progressive advance prior to 1k or .9k rpm.
If the progressive were to begin much earlier than 1k or .9k rpm, the "Full In" may follow suit..... not sure with EST.

(sorry, I was unable to edit the previous post)

.."I'll refer to them as that piece of chicken that didn't get taken off the BBQ screwer."

Ah hah! Good one.

Jeff

The marine EST modules provide 20-22 degrees of advance @ 2800 RPM when used with the V-8s. I've never seen a GM document that shows it but many posts scatterred over many www sites show these data consistently for many years. The only 'paper' I've seen covers their use in the 4 cylinders and they start the advance function @ 700 rpm....So, the "best" way to dial them in is to set the total advance @ 3000 RPM and verify the 'base' timing will let the engine restart easily when hot.

Jeff, I couldn't think of anything but the chicken anology! Glad you liked it!

Putting it into proper prospective, try this:


Or this:


Doesn't even ressemble chicken, does it?

Mark, what say yee?
If we add a BASE of 8* to the 20-22 degrees of advance @ 2800 RPM ......, you'll have a TA of 28* to 30* @ 2.8k rpm.
If we add a BASE of 10* to the 20-22 degrees of advance @ 2800 RPM ......, you'll have a TA of 30* to 32* @ 2.8k rpm.

Me thinks that's a tad bit too much and/or a tad bit too early. Yes/No?

.

Our BBC's have been running at 14 deg of 'base' timing for over a decade with NO issues. They were rebuilt with a CR lower than stock (~8.2:1) so that they would run without issue on whatever grade of fuel would be available thru the rest of their lives. Yes, a unique situation but a 'real' one. and the advance is full in by 3000 RPM (uses the TB-IV setup with the V8-HP modules - they only have 20 degrees of advance).

I would think if GM had a concern for full advance @ 2800 RPM, either they or the aftermarkey would have modified the modules by now...they've been around for a while and, as far as I know, haven't changed their advance curve (for the V8's).

Mark,

Just to understand this more, are you saying that all replacement modules are "programmed" this way with 20 degrees of advance or might there be others that are different. Only wondering as I have not checked total advance and did replace 1 module 2 years ago. I am wondering that it matches the other side. Starting, ONCE WARM, is like a new fuel injected automobile.

I see in the future many more pistons looking like those above with so much timing.

Swarmy Jeff

An engine operating and idling with a BASE of 14* is not necessarily an issue, but occasionally a warm engine @ 14* may "Buck" on us while cranking.......Yes/No?
Mark, your BASE of 14* added to your progressive TA of 20* gives you 34* @ 3k rpm. It sounds like you are OK with that.

knuckle47 said:

Mark,Just to understand this more, are you saying that all replacement modules are "programmed" this way with 20 degrees of advance or might there be others that are different. Only wondering as I have not checked total advance and did replace 1 module 2 years ago. I am wondering that it matches the other side. Starting, ONCE WARM, is like a new fuel injected automobile.

Click to expand...

Merc apparently offers several modules that each provide a different advance.
Keep in mind that BASE affects TA (minus any knock sensor ECU/ECM influence).
IOW...... a 20* module w/ a BASE of 8* totals 28* at the crankshaft when Full In.
That same module w/ a BASE of 12* totals 32* at the crankshaft when Full In.

fastjeff said:

I see in the future many more pistons looking like those above with so much timing.
Swarmy Jeff

Click to expand...

Dear Swarmy Jeff, I see no emoticon idicating sarcasm, so I'll take it that you're serious. If so, I'd agree.
BTW, those images are pretty extreme examples, and they're not necessarily from marine engines.... I just grabbed them from the Internet.
Thank GOD that I don't have a bunch of them here for photo sharing!

Good news is....., that type of damage does not occur all that often if we follow OEM specs.

What can get us into trouble, is when an automotive guy (no offense re; their auto knowledge) gets to messing around with a buddy's Marine engine ignition timing.
The two engines share a completely different type of load...... and the more extreme Marine loads accellerate the potential for detonation.

your TAT NAZI, Ricardo

Al: All the marine ESt modules I've seen offered had a total advance range of 20-22 degrees. I haven't looked for any auto modules so I can't say more there. FWIW, this is the 'default (dumb)' advance that is only a concern when no ECU is available to adjust the timing. The newer setups (ECU driving EFI with knock sensors) will bypass this 'feature' and use the advance curve programmed into the ECU.

makomark said:

Al: All the marine ESt modules I've seen offered had a total advance range of 20-22 degrees. I haven't looked for any auto modules so I can't say more there. FWIW, this is the 'default (dumb)' advance that is only a concern when no ECU is available to adjust the timing. The newer setups (ECU driving EFI with knock sensors) will bypass this 'feature' and use the advance curve programmed into the ECU.

Click to expand...

Were does this info come from? - I haven't been able to find any actual manufacturers ignition curve data for the various Marine Ignition Control Modules available, which is leading to confusion and engine damage. Some people say you mustn't use your original engine base timing (ie 8 deg BTDC in my case - 4.3 V6 Mecruiser 175 HP, pre-Vortex) but use 2Deg ATDC when using the Deco/GM Marine Ignition module to achieve 22Deg BTDC Total Timing.

I have just received a new CDI IGM as a replacement under warranty for a newly purchased Sierra Marine (Deco EST kit) that was failing to advance. It came with no instructions/data regarding what to set the base timing at. The Sierra Delco EST instructions says to base time to the "Engine Manufacturers" spec (ie 8 BTDC based on the original label on air cleaner) but still left with the dilemma and potential engine damage....should it be 8 BTDC or 2ATDC? (The latter setting is very hard to to start from cold and runs poorly on idle and revs lazy but is the one some others say to use to avoid over timing and damaging the engine....confused!

most of it is empirical, some of it comes from researching the service data available....I'd suggest starting with the OEM service manual.

If you listen to "some people" you will get "some answers" - you need to figure out what applies in your case and then reach your own conclusions.

Personally, I prefer to set up the Voyager ignitions by setting the full advance timing and then making sure the engine starts easily when it is up to operating temp.