Ignition Timing 2.7 with Carbs and Crank Fire

[wndsnd]

Would ignition timing settings max advance change if you were running FI or Carbs?

I noticed that the 2.7 spec manual basically says ignition advance not to exceed 38 degrees.

I have been running 30, but the spec manual is for OEM cars running CIS (75).

I am doing some fine tuning and have read others run 33-35 with some as talking about sweet spots of 33.

So my question is, now that I am running Webers, do I have something to worry about if I want to try pushing upwards, towards 35, and if not at what RPM should I start the push. I don't think I would want to exceed 35 but maybe someone is and has an argument for that. I am running Electromotive TEC2

Not on a Dyno yet, and don't want to set any records, just seeing if there is a little more to be safely had. This is all feel of the pants stuff so far.

Thanks Guys.

[Walt Fricke]

Well, on my 2.7 race motor (ported, big cams, nominal 10.5/1 CR, twin plug, 220 RWHP with Electromotive HPV1 and Weber 46s, I set the timing at 0 static, 12 at 1,000 rpm, 26 at 3,000 rpm, and 28 at 8,000 rpm (which is as high as that system went for rpms). This was based more on advice than dyno pulls - I was told such an engine didn't need a lot of advance, and of course you want the least advance you can get if more advance won't gain you more HP. My dyno time was spent on validating my main jet choices.

On my 2.8 race motor with Tec3 (EFI and crank fire) I run 34 total advance, but draw it back to 33 at 8,000. Again, this was mostly based on advice, with race style fuel mapping (set for WOT, don't worry about off throttle)the main variable.

Isn't the standard advice here to keep nudging the advance up until the HP stops increasing, and then back off a degree? Something like that? Cams, compression, head work, valve and port sizes, maybe even your air/fuel ratios, don't they all have some effect on how much is useful, and how much is too much?

[Steve@Rennsport]

Originally Posted by Walt Fricke

Isn't the standard advice here to keep nudging the advance up until the HP stops increasing, and then back off a degree? Something like that? Cams, compression, head work, valve and port sizes, maybe even your air/fuel ratios, don't they all have some effect on how much is useful, and how much is too much?

Not really.

Failing to account for outside air temps and variations in (pump) gasoline in air-cooled engines leads to broken rings and holed pistons. You simply cannot use "Kentucky Windage" if you want the engine to live very long.

True enough, cams, compression, fuel mixtures, fuel octane, piston design, and even exhaust all play a role in optimizing ignition timing.

For street engines, I would NOT go over 32 deg total using pump gas (single-ignition). Less, if your CR is over 9.7:1.

[Jack Stands]

My carbed 2.7 with an HPV-1 ignition, RS pistons, and S cams is using the same specs as Walt's and puts out 200 rwhp. Don't know if further advance would help, but since it runs well on pump gas, I'm not pushing it.

[Schwarzeritter]

I'll add my two cents, it depends on what kind of ignition system you are using. I pretty much only ever now these days use programmable ignition. It depends on how complex or which parameters you are using to factor in when or why ignition is added or pulled. It also depends on what the intended use is. Obviously, displacement, cams, compression etc. A lot of times what is acceptable in a race car or track or club car is not pragmatic for a road car.

I don't run a whole lot more than 6-7 degrees with a maximum 17 degrees before top dead center. I generally only ever use 91. Once I set the baseline on the Dyno, I'll record data and get into a bit of road tuning. I am more interested in looking at temp and altitude, humidity changes. I really do not care about power but the response and thus far had no issues with summers being 115+ here in Southern California. This particular car hasn't seen below zero, (chuckles.) The only two things are a custom exhaust system and air box. The average AFR is 13.4-13.7. I usually just use Mobile or Shell. Once in a blue moon, I'll use something else. This particular factory doesn't see much over 5,500rpm, once and a while I'll do 6,200.

On complete vehicles a complete Stand-Alone, there isn't much to discuss because nothing I have or use would directly correlate to your as far as modified cars. A lot of owners like using this or that factory derived (camshaft or piston) or a combination. There would be enough things different that giving information would not be beneficial. In general, unless I am being crotchety, it's all about StandAlone. I haven't really looked back unless I was just staying period correct to be retro BECAUSE and nothing more.

Happy Holidays, and hopefully I have given some tidbits. (shrugs) Too much ignition advance will lead to hammering bearings, usually a spun bearing is an oiling issue. Depends on the car. They'll look all jacked up, I always see Subaru owners doing this and often followed by tears shortly after a few months.

[wndsnd]

Thanks guys.

All helpful comments. I am taking the conservative approach and will keep it to 31.

[prschmn]

The change to carbs shouldn't change things much if any but without knowing more about engine particulars it's hard to give an accurate answer but
I agree conservative is best to start. When you dyno tune it becomes obvious-advance until torque-not hp- drops then back off a bit.

[wndsnd]

Mark,

How do I get you on a dyno for a day? You have someone in the area you work with? Pm me if it is some thing you would like to do.

Maybe we spend a 1/2day at your shop dialing in, and 1/2 day at dyno. Or full day each.

[wndsnd]

Back to my original question.

Some say with twin plug, you would start with advance retarted about 10 degrees under single plug. This would fall I line with Walter's suggestions that he was advised to go t
o 28 degrees, and my little spec book is calling for a max of 38 degrees on stock single plug OEM.

Can you tell my why I should maybe retard with my twin plug set up vs. advance from the 30 up a bit.

[Plays with cars]

Proper timing is about generating maximum cylinder pressure at the right crank angle to generate
maximum torque without creating spontaneous combustion of the unburned mixture. Engine geometry (bore, stroke, rod length) is a factor, but fixed for a given displacement so factory advance specs are a good reference as a starting point. Then it's about adapting based on factors that would change the speed of the flame front in the combustion chamber from what it was in the factory configuration. Lower octane fuel, faster flame speed, less advance. Higher compression results in a denser mixture which will burn faster, so less timing needed. Lower intake air temp also results in denser mixture so less timing needed. Higher volumetric efficiency from a matched cam, port geometry, valve size, induction and exhaust system comb results in higher density (in a specific RPM range). All of these are moderate influencers in total timing.

Twin plug however is a significant influencer on timing. Because there are two flame initiation sites on opposite ends of the combustion chamber, each flame front only has to travel 'half' as far to ignite all of the mixture in the combustion chamber. Because of this much less advance is needed to generate peak pressure at the right crank angle to maximize torque output.

[wndsnd]

Thanks Mark,

First I have to correct my first post, the Controller is an XDI2 not a TEC2.

It is very easy to make timing changes and upload, so I will try retarding to the 28 and see how I like it.

Also Mark at Exotech PM'd me and volunteered to help out with some dyno tuning, so it looks like I will get this dialed in for Hershey which is what I am after at this point

[Plays with cars]

Sounds like you're on your way. Anxious to hear what you end up with.

I'm currently developing an ignition curve for a 2.4E⁺ that I installed in my 914-6. I'm also running a crank fired ignition system made by MegaJolt that supports 3D mapping based on engine speed and load.