EFI versus Carby

Be forewarned, I am no EFI expert.  I had a similar build done a couple years ago (636 bhp).  Dennis Quella had recommended we go with the Sniper 2 Terminator X.  But by that point, those were backlogged, and my builder got a FAST EZ instead.  Ultimately, we couldn't get it to work well for any length of time once we installed it in the car, it kept fouling O2 sensor and plugs, and the EZ is not laptop adjustable.  I know at least one P-car owner using a better FAST model that has worked well, but with more adjustability.  I know the Sniper 2 has a generally good reputation now.  I also know a member on here who had one installed/tuned by a performance shop, who has had many of the same troubles my system had.

I decided to swap out to a Holley DP chokeless (I'm in NC so that can work) carb custom set up and tuned by Chuck Nuytten out of Rockwall, TX.  He is well known for this, he will have you furnish all relevant engine specs and your performance/driving style needs and build accordingly.  I have nothing but positive things to say about this carb so far.  In my (generously long) phone conversation with Chuck on the front end, as I recall he said my issues were common and that the extremely limited O2 sensor placement option in Panteras can inherently create challenges.  My point is, if you were going to spend the money to "upgrade" to a Sniper 2, Chuck is another option, for less cost, easier installation, easier parts availability in a pinch, etc.  The only possible drawbacks I see would be some sacrifice of fuel economy, a little attention to the throttle on cold start, and a good mechanic friend of mine says Holley carbs can get sticky with periods of sitting unused.

Buttondoor,

I may of misunderstood your post but did you have issues tuning Chuck's carb? I also have one of his carbs and have plug fouling issues.

The main issue with spark fouling is due to high cams producing not enough vacuum at idle speed. To overcome if everything else is fine (carburetor settings) is to rise idle rpm to anything between 1250 and 1550 rpm.
I know it’s ridiculously high but the only solution. I am hoping with dynamic timing setting in combination with an EFI the issue could be partially cured which allows a bit lower idle rpm as for the carby

All of these systems are going to have limitations for varying reasons.

The aftermarket EFI systems are using existing sensor components already in use from other vehicles.

One advantage is easy walk in parts availability and also cost. Using production GM parts is a great advantage.

The MAP sensor used in any of the systems is going to be key for the ECU in determining the "load" on the engine. That is used in combination to the engine rpm and the oxygen sensor.

With a camshaft timing of over 250° @ .050" lift, the MAP may not have the ability to sense the engine load correctly and add too much fuel to the injectors at only a partial load? That is probably the biggest factor in causing "fouling" of the plugs BUT that may not be a 100% accurate assesment?

You may need to run a one step hotter spark plug and you may need to alter the advance curve of the distributor?

A big port iron 4v head Cleveland is going to be the toughest to get the fuel curve right on with. I wouldn't go assuming though that you can re-write the curve in the computer. You likely will make it worse.

The cam you are using is a bit over the limit for a primarily street driven car. The cam that I am using is at 244° and I am thinking of dialing that down one step already. That is more of a "track day cam" for a car driven to and from the high speed track event.

It sounds really cool but is more of a "boy racer" thing and I'm getting way to old for such an adolescence based showboating?

I think that most likely dialing down the cam timing on a flat tappet lifter cam to the perverbial 237° @.050, or going to a roller lifter like the Ford Racing 304X cam will coexist better with any of the EFI systems?

You are asking for information that only custom tuners have experience on and have arrived at on other vehicles and likely unique to those vehicles as well.

When I ran Holleys on my 351c's, there was always this issue of getting the a/f ratio just right. It was never really a battle with the carb jetting, it was more an issue of matching the ignition power, advance timing, fuel quality variations and plug heat range to get the plug color just right at dark rust brown v. black and sooty.

One custom tuner thought that it was just an issue of the ignition spark not being strong enough. i.e., a "weak spark".

All I can say with that, is good luck because I don't think a perfect tune exists. For one thing, it will literally change with the weather. You may be a better man then I though, so go for it.

@husker posted:

Buttondoor,

I may of misunderstood your post but did you have issues tuning Chuck's carb? I also have one of his carbs and have plug fouling issues.

No issues yet with Chuck's carb, it has literally been plug-and-play.  But I had concluded that, worst case scenario, changing out fouled plugs will be a lot simpler and cheaper than trying to get my former (FAST EZ) EFI system to function properly given that it was repeatedly going to get inaccurate O2 sensor readings from a fouled O2 sensor (and those 4-plus wire O2 sensors aren't cheap, of course).  We did follow Chuck's advice in his notes that come with his carb regarding things like type of plug, filters, etc.--I assume you would have done so, too.

My situation with that EFI was further complicated by my EZ model's not going into self-learning mode until 140 degrees of coolant temp as I recall, at least that.  And my engine is slow to warm up to that.  So in the meantime, even with new plugs and new O2 sensor, the first new cold start would be obviously just dumping fuel as I was having to baby the throttle to hopefully keep it alive.  The whole tuning process for that model seemed to me to be doomed, at least with my particular unit, with my engine build, in a Pantera.  But I will also say that once I began searching online for other users' experiences with that model to try to find some magic solutions, it became evident to me my issues were common.  And our local auto electric guru who was knowledgeable about tuning various throttle body EFI systems had spent considerable time trying unsuccessfully to resolve the same sort of issues on a more standard American classic car and ultimately concluded it was an issue with that model.

Thanks for the feedback and thoughts so far. Appreciate.
Just to add that on my new engine I have foreseen countermeasures for the sharp camshaft by applying hydraulic rollers. That makes the whole setup a bit smoother while still providing enough torque over a broad range. Additionally an ICE distributor helps additionally for better (and stronger) ignition and hence idle improvements. In any event if will try to test the Sniper-2 with the dynamic timing setup and will see how much that improves over the Holley carby. It’s a bit trail and error.
@panteradoug I am in agreement with the fact that A/F ratio is the most important point in question and hopefully the EFI is capable of doing this mostly right. I have gained a lot of experience recently with my restomod Kawa Z900A4. The bike comes with Yoshimura Mikunis and open dual stack funnels. It’s a bit of a challenge to get that setup properly through the entire rpm range and it’s a lot of testing required, especially when you are going WOT on the Autobahn. Burned twice holes in my nice Wössner pistons until I found the right setup…

I do know that the location of the oxygen sensor is important. It typically needs to be installed in the header collector at 3 o'clock, 9 o'clock or higher. Below that it will foul.

I have always been advised that "there is no such thing as a bolt on". I think that I can extrapolate that in the case of a conversion to EFI, there is no such thing as a plug in? There is always going to be a bit of finagling involved.

I once saw eight oxygen sensors installed in the primary header tubes and the complete flexibility just complicated tuning the engine and the effort didn't help.

Ironically my older son sees me as the "carburetor guy" and criticizes them as barbaric. He reburns cpu's for production high performance Fords.

The Pertronix high energy multi-spark system improves idle.

With a Holley 750 cfm carburetor with mechanical secondary and double pumps I had a stable idle with an AFR of 15.5, so "lean" that does not foul the spark plugs. The vacuum at 900 rpm was however only 11 in Hg with my hydraulic roller camshaft of 231° at 0.05''.
With the new camshaft of 235° at 0.05'' and the new distributor I have not yet refined the settings and I cannot say what it will be.

Buttondoor,

I didn't see any plug recommendation only initial gap. I'm using Autolite AR25s.

@FWJ posted:

The main issue with spark fouling is due to high cams producing not enough vacuum at idle speed. To overcome if everything else is fine (carburetor settings) is to rise idle rpm to anything between 1250 and 1550 rpm.
I know it’s ridiculously high but the only solution. I am hoping with dynamic timing setting in combination with an EFI the issue could be partially cured which allows a bit lower idle rpm as for the carby

With your Holley carb and the engine idling at 1250 to 1550, it would seem that you are no longer running on the idle circuit of the carb.  Once off the idle circuit, the idle air bleeds are meaningless.  I use the air bleeds to tune for maximum vacuum at idle and also tune for a lean idle to avoid fouling spark plugs.  Running above the idle circuit can also result in the engine dieseling upon shutdown because the butterflies are essentially open.

A remedy for the above is to increase ignition timing at idle via vacuum advance or the Progression Ignition distributor (or something similar).  The Progression Ignition distributor lets you simulate vacuum advance at idle within its software table.

Increasing ignition advance at idle lets you close the butterflies and thus run off the idle circuit and tune the idle air screws to lean out the idle.

I learned most of this while trying to resolve a dieseling problem on engine shutdown.  It consumed much of my brain's available processing bandwidth for a week or two in order to stop the dieseling and fouled plugs.

The Progression Ignition distributor is essentially half of an EFI system.  In the timing curve table, give it 25 (or more) degrees advance below 1000 RPM.  Above 1000, give it a normal value starting at 16.  Thus at idle, the advance is 25 and when you blip the throttle it instantly drops to 16 and then climbs as RPM's increase.

That sounds like a very nice capability (the ability to advance timing to 25* below 1000 RPM)….

Does the Progression distributor allow you to retard the timing when cranking?  

I’m pretty sure that is one of the capabilities of the “red strain relief” (California configuration) DuraSpark module.

Rocky

@rene4406 posted:

The Pertronix high energy multi-spark system improves idle.

With a Holley 750 cfm carburetor with mechanical secondary and double pumps I had a stable idle with an AFR of 15.5, so "lean" that does not foul the spark plugs. The vacuum at 900 rpm was however only 11 in Hg with my hydraulic roller camshaft of 231° at 0.05''.
With the new camshaft of 235° at 0.05'' and the new distributor I have not yet refined the settings and I cannot say what it will be.

I think René you are on the save side with your setup. This will run well.

@stevebuchanan posted:

With your Holley carb and the engine idling at 1250 to 1550, it would seem that you are no longer running on the idle circuit of the carb.  Once off the idle circuit, the idle air bleeds are meaningless.  I use the air bleeds to tune for maximum vacuum at idle and also tune for a lean idle to avoid fouling spark plugs.  Running above the idle circuit can also result in the engine dieseling upon shutdown because the butterflies are essentially open.

A remedy for the above is to increase ignition timing at idle via vacuum advance or the Progression Ignition distributor (or something similar).  The Progression Ignition distributor lets you simulate vacuum advance at idle within its software table.

Increasing ignition advance at idle lets you close the butterflies and thus run off the idle circuit and tune the idle air screws to lean out the idle.

I learned most of this while trying to resolve a dieseling problem on engine shutdown.  It consumed much of my brain's available processing bandwidth for a week or two in order to stop the dieseling and fouled plugs.

The Progression Ignition distributor is essentially half of an EFI system.  In the timing curve table, give it 25 (or more) degrees advance below 1000 RPM.  Above 1000, give it a normal value starting at 16.  Thus at idle, the advance is 25 and when you blip the throttle it instantly drops to 16 and then climbs as RPM's increase.

Thanks Steve for the advise. This is the route I am following as well.

I found that using a Holley carb from a 85 Mustang GT, that the idle circuit is revised to give you a 14.7 a/f at idle.

It was idling so lean, in pulling plugs to check them,  that they were so clean that I could not find evidence they had even been run.

The issue with that became that the primary tubes on the headers were glowing red. I would think that condition would mean regular steel tubing headers would at least need to be ceramic coated to help them survive that kind of heat at idle?

That series of Holley carbs is called 4180's.

No matter what you do to those carbs, you cannot change the a/f ratio of 14.7 at idle. You can only increase the amount of fuel at idle which by design won't change th a/f idle ratio.

I had revised the fuel bowls and other emissions plumbing on those carbs to a 4150 configuration so that they looked like a 1850.

The reason that I mention this here, is that if anyone is having issues with something like a 4779 750cfm dp Holley and they need to lean the idle but can't, any of the 4180 series carbs are a useful tool to experiment with. They are all going to be 600cfm carbs and the ones with truck applications are just as good to work with as the Mustang GT carb and less expensive to find.

As far as spark plug heat range goes, if we are talking about original Ford iron 4v heads, either closed chamber or even open chamber, the 4v plug should be an AF32 (or equivalent) but it is not uncommon to run one step hotter to an AF42 to help on keeping the plugs cleaner.

In the Ford heat range system, a 25 is a racing plug, too cold for street traffic driving and will foul up within 60 seconds or so of idling on a cold engine. It is way too cold for street driving.

I even found them too cold for Autocross, which I did regularly 30 years ago. Even the 35 needs a WOT burst occasionally. For Autocross I actually found that the 45 was better.

These numbers are how I cross reference spark plug heat ranges.

When you switch to other brands you will find that the other brands do not index heat wise exactly the same and can be 1/2 step higher or lower then the Motorcrafts.

The ONLY heat ranges that accurately cross over to the Motorcrafts are the Champions. NGK's are close but do not have as wide of a range so are not exactly the same.

I hope any or some of these details helps. I'm not here to criticize, just share what I have learned over the years.

Incidentally, the P-E engine controller, which replaces the Motorcraft ignition brain, does retard the ignition at starting.

@husker posted:

Buttondoor,

I didn't see any plug recommendation only initial gap. I'm using Autolite AR25s.

@husker, I don't have Chuck's instructions handy at the moment, I think mainly he was recommending gap and non-resistor, we chose AR 3911s (mine is a Dart Windsor FWIW).

@panteradoug I don’t get this point?

You can only increase the amount of fuel at idle which by design won't change th a/f idle ratio.

Why should it not change the A/F ratio when fuel amount is increased?

@FWJ posted:

@panteradoug I don’t get this point?

You can only increase the amount of fuel at idle which by design won't change th a/f idle ratio.

Why should it not change the A/F ratio when fuel amount is increased?

I don't know precisely but to increase idle speed you are opening the throttle plates and not changing the idle circuit.

The idle circuit in the 4180's is a revised design from the 4150/60's.

In a 4150/60, you can set the idle set screws in the metering block and richen the a/f but in the 4180 that is locked out.

The 4180 idle circuit is much like the Weber 48ida's in that you have in essence an air jet and a fuel jet that you cannot change. The idle screws only react within a 1/4 turn or so and it doesn't change the a/f ration of the "jets" it just increases or decreases the amount of fuel being fed to the intake manifold.

It is different thinking from Holley and you need to work with the 4180's to get the picture. It is a bit brain twisting initially.

The explanation to me was that there is a fine to the auto manufacturer of $25,000 per vehicle that when tested if the emissions results do not comply with the US Federal mandates the fine will be levied.

So Holley designed an idle system that can not be changed to modify idle a/f ratio. This is probably the biggest reason that the Holley carbs on the Mustang GT's were only used for one year before going to EFI.

Those would be the largest risk for Ford v. the 351w trucks that were using essentially the same carbs but with different production list numbers.

That was a project that I did with the 347 that I built 10 years ago and built it with a 2x4 induction system.

The 4180's were not on for long as I found the regular Holleys much easier to understand and tune.

I just point this out as a possible tool to use in identifying the "culprit" in why plugs may be fouling. I have never seen spark plugs that clean again...ever.

@rocky posted:

That sounds like a very nice capability (the ability to advance timing to 25* below 1000 RPM)….

Does the Progression distributor allow you to retard the timing when cranking?  

I’m pretty sure that is one of the capabilities of the “red strain relief” (California configuration) DuraSpark module.

Rocky

Yes, the advance is always 10° BTDC during cranking up to about 300 RPM.

When manifold vacuum is low and RPM's are 900 or less then advance is 10 degrees.  Those are the conditions at engine startup.  Here is the table that I am currently using.  You can increase idle advance to more than 25 degrees if needed.