Weber jets??All who live for their triples please read this

[Leon]

You better do a full report of your feelings with MJL I plan on doing it in the future.

 

I'm running a Mallory Mnilite dizzy with Mallory 6AL CDI box. It allows me to get good idle and total advance but it is a pain to tune right and very time consuming...

 

And I have no vacuum advance, I think it is bad, there's probably tons of torque to get back at part throttle & better economy during cruising.

 

But of course!

[zredbaron]

...so you can have a fully programmable system for maybe $250 or so. That's damn good for what you get if you ask me!

 

Off the charts good, if you ask me!

[bradyzq]

I am running Elecromotive's XDI2 direct ignition. I ran direct ignition with no MAP sensor for years.

 

I later dyno tuned my race motor (oxygenated fuel) utilizing a MAP sensor that altered the programmed advance proportional to the MAP sensor's output.

 

After tuning the motor, I didn't particularly notice a difference in mid-throttle positions, particularly in the trouble areas below 4k rpm. WOT loved the tune, but mid-throttle didn't make a difference.

 

I even unplugged the MAP sensor to see what a difference it would make. It didn't make much of one. I could tell, sure, but it wasn't enough of a difference to affect my standings in an autocross race.

 

Did I not get much of a difference because of my cam's overlap? Is it because of my oxygenated fuel? Perhaps, but in my case I didn't notice much difference. I still run with a MAP sensor just for the hell of it...

 

[EDIT - I believe having a programmable advance curve (i.e. Electromotive ignition) is the most significant factor as to why the MAP sensor doesn't do much for me. With a mechanical distributor, you don't have the varied timing to begin with, so any input that varies the timing will have a much more dramatic effect.]

 

Not a typical setup, but that's my experience. For what it's worth.

 

I imagine that with an aggressive cam overlap, you don't make much vacuum under the best of circumstances, so there would be a very limited MAP range to tune in. Have you tried using TPS (Throttle Position Sensor) as your load source instead? It will certainly give you more resolution to tune on the load axis. There may still not be much gain to be had, but at least you'll have optimized the setup. It's what I plan on doing when I get a Megajolt on my Z.

Edited October 7, 2011 by bradyzq

[bradyzq]

I imagine that with an aggressive cam overlap, you don't make much vacuum under the best of circumstances, so there would be a very limited MAP range to tune in. Have you tried using TPS as your load source instead? It will certainly give you more resolution to tune on the load axis. There may still not be much gain to be had, but at least you'll have optimized the setup. It's what I plan on doing when I get a Megajolt on my Z.

 

I see that Electromotive does not explicitly offer a TPS load option. You can either wire in a TPS instead of the MAP sensor. It will still give a 0-5Volt signal to the ECU. That will work fine. Or, you can wire in a TPS via the External Timing Control pin (pin 13 orange) and use that.

 

I am very interested in this side of Weber optimization. They should be able to be tuned to be VERY drivable, maybe not always with a lot of power, but at least pretty smooth everywhere.

[zredbaron]

I imagine that with an aggressive cam overlap, you don't make much vacuum under the best of circumstances, so there would be a very limited MAP range to tune in. Have you tried using TPS (Throttle Position Sensor) as your load source instead? It will certainly give you more resolution to tune on the load axis. There may still not be much gain to be had, but at least you'll have optimized the setup. It's what I plan on doing when I get a Megajolt on my Z.

 

You're right, I doesn't produce much vacuum, therefore MAP utilization is minimal. Cam isn't happy until about 4750, so the carbs obviously hate to be in "normal driving" rpm ranges. I completely agree that a TPS is worth more with aggressive cams.

 

 

I see that Electromotive does not explicitly offer a TPS load option. You can either wire in a TPS instead of the MAP sensor. It will still give a 0-5Volt signal to the ECU. That will work fine. Or, you can wire in a TPS via the External Timing Control pin (pin 13 orange) and use that.

 

The XDI series doesn't offer an input for a TPS, but the TEC series do. The TEC series is laptop programmable in as much detail (ie very fine data point intervals, interpolating between tabled settings) as anyone would be willing to program/tune. The XDI series is literally 4 knobs: a rev limit, initial advance, 3k advance, and 8k advance (varying linearly between the data points). XDI works wonderfully compared to a mechanical distributor (in terms of optimization, spark accuracy and of course spark energy), but the TEC series is just as much of a step up if not more. Add the EFI portion, and well, it's as good as an NA tune can get as far as I know. In addition to air intake temp, MAP and TPS inputs, you can individualize fuel delivery and timing for each cylinder! Crazy potential. I know there are other products out there that do all of this, but like I said, I'm partial to Electromotive.

 

That said, it's expensive as heck. It's the Apple product of ignition(/fuel delivery) in my book. You get what you pay for...

 

 

I am very interested in this side of Weber optimization. They should be able to be tuned to be VERY drivable, maybe not always with a lot of power, but at least pretty smooth everywhere.

 

They should be, and they are. Ask any ASE Master, and they'll agree. We experience tune-ability problems because we're asking more of it than the engine system *as a whole* is capable of adjusting to. (i.e. tuning carbs cannot make up for exhaust or intake runners that don't support the head flow, etc.) As mentioned throughout this thread, the more streetable the head is, the easier it is to tune our Webers. Upgrading one component just causes a choke point somewhere else, and a choke point always manifests a poor driveability range in addition to capping max power output. When we start getting upgrading the head porting and cam (ie anything other than stock), then we need fancy ignitions, fancy intakes and fancy exhausts to help make up for the motor's tendency to have an rpm range that it runs poorly in. We eventually need fancy fuel, too.

 

I still haven't forgotten how well tuned a stock 2.4L with a solid mechanical dizzy, SUs and street headers was. Crazy bang for the buck over OEM. Ever since that stage, I've been chasing around varying degrees of less than stellar driveability. (Well worth it, of course.)

Edited October 9, 2011 by zredbaron

[zredbaron]

Also, one thing I always thought would help a lot (I'm personally putting it off for my ITB project) would be a throttle cable conversion. As we all know, the bellcranks and pushrods make it really hard to open the throttle plates "just a little bit" / smoothly, especially in conditions like autocross where the car (+ driver!) is being thrown about and you're trying to be smooth with the pedal. A throttle cable setup would reduce much of the friction, and ideally it would be non-linear so you can gradually open the first 25% of throttle with say 50% of pedal, since that's where most of the driveability challenges occur.

 

Just my two cents... if you're going to install a TPS, you might as well go with a throttle cable while you're at it!

[bradyzq]

Oops, I thought you had the laptop programmable XDI2:

 

http://www.distributorless.com/products/xdi2.php

 

Sounds like you have the XDI.

 

You can still swap out the MAP sensor for a TPS on the XDI and dial in some advance under cruise conditions. You just won't have the flexibility of the XDI2. You'd likely have to tweak your base advance curve upwards by a couple of degrees since the TPS will probably never read 5Volts at WOT (maybe 4.4 or so, depending) like the MAP sensor would at sea level.

Edited October 9, 2011 by bradyzq

[zredbaron]

Hmmm... I bet you're right. I thought I had the XDI2, but clearly my memory is wrong. Oops? Mine is definitely not laptop programmable, but I didn't know you can swap the MAP sensor with a TPS, thanks! I'll definitely look into that before I visit the dyno! Luckily their manuals are quite thorough. Concur that the manual indicates that the MAP sensor may be replaced with anything that outputs 0-5V...

 

Edited October 9, 2011 by zredbaron

[duragg]

So it seems like from day to day I am seeing slightly different idle RPM and mixture on the Wideband.

 

Drove the car home last night and it was maybe 90f outside.

Set to about 900rpm and low 12s on my wideband (which seems to read a little low numberically).

 

This morning it is colder and I am at 700rpm and mid-10s AFR.

 

Is this all just Air Pressure and Temperature fluctuations?

Just when I start to dial it in - it goes the other way... Or is this just the way life with Triples is?

 

Thx.

[zredbaron]

Is this all just Air Pressure and Temperature fluctuations?

 

Mostly, yes. When you tune your carbs it is for those conditions only. Temperature, humidity, and barometric pressure are the biggest factors in actual O2 delivered per unit volume of atmospheric "air." Pollution, particulate (dust, etc) and fuel inconsistency are also factors, though less significant. Even with the same temperature, weather fronts (or lack thereof) will noticeably affect your carb tune.

 

Also, mph matters. You will also find that 5k in 2nd performs differently than 5k in 4th. You should tune the gear you drive the most (or the one you want to pull the hardest). I tune for 2nd gear, but that's because I autocross.

 

The inundation with changing variables is why most people are content with getting the main jets right and calling it a season. The more aggressive your engine is, the more sensitive it is to changes in O2 density.

 

Me personally, I tune my carbs the day before race day. This gets me "close enough" since I can't realistically tune my carbs the day of. The day before my race I tune them for the time of day I expect to race. I usually only change the mains by 5 and the airs by 5-10 (if the car wants any changes at all, sometimes it doesn't depending on time of year). It's always experimentally determined. I never did make some master spreadsheet for my car, mainly because I upgraded parameters too often. As stated throughout this thread, *never* change more than one variable at a time, and *never* bump your changes up by much. If you overshoot the peak, you may never know.

 

This is why cars are all fuel injected now. Tune it once (fuel delivery / timing) on the dyno, and the computer automatically adjusts for changes in O2 from then on.

 

And that's also why triple carburetors inspire the nostalgic "awe" factor when they have a full song. Some people are aware of that when they run right, someone spent a lot of time enabling them to do so.

 

Carbs are more of a hobby than a performance part in my book. A fun hobby, at that...

Edited October 14, 2011 by zredbaron

[duragg]

Can you who race them like this please explain your pre-race tune procedure?

 

Check timing?

Pull Plugs?

Check valves?

Re-sync?

 

It has to be a lot easier if you really don't care about part-throttle manners and mostly concerned with WOT.

 

TJ

[RebekahsZ]

Run it a little rich so it will start fairly easy and not backfire too much-then just run it like a dog and enjoy how they look and sound (including the occasional part-throttle backfire). Lift your hood a lot and enjoy the pleasure of the view, but not the pain in the butt that comes with it. My 240z has had SUs (10 years) and Dellortos (basically Weber-style) for 10 years. If you have triples, you will either get used to them being unpredictable, or you will LIVE for them. After 20 years with this car, I have other things to live for. I'm going to computer controlled EFI, because here in Alabama, the weather changes daily. Try not to be too picky with side drafts or you will go nuts. If you have to be on time to work in the winter, buy a second car or you will be late to work from time to time.

[duragg]

A guy named Bob Ream here in Phoenix makes a pretty neat ITB EFI called: Imagine Injection.

www.imagineinjection.com.

 

His system still has a vintage look, but is all electronic.

 

I do find myself rearranging my life to tweak the triples (like all day today planned!)

[zredbaron]

Can you who race them like this please explain your pre-race tune procedure?

 

Check timing?

Pull Plugs?

Check valves?

Re-sync?

 

It has to be a lot easier if you really don't care about part-throttle manners and mostly concerned with WOT.

 

TJ

 

 

I don't put many miles on my car, so I only do maintenance before the first race of the season. This includes new plugs, valve adjustment, and synch.

 

I only touch timing when the motor or fuel changes. I go to the dyno for this. My ignition utilizes solid-state electronics, so I pretty much assume it remains at the settings it's been adjusted to.

 

WOT is what I tune for, but driveability matters a lot for autocross. When dialed in (always wiggle room with mechanical devices such as carbs), you'll find that two mains will perform pretty much the same way AFR-wise (assuming increment of 5 with the mains). I use my butt-dyno to distinguish the two (the butt dyno is worth more than a number to me; what I need is the car to be forgiving of throttle changes). One of the two main jets that perform similarly will be more forgiving of partial throttle before the cam kicks in, and that's the one I go with. The idle jet only affects driveability at low rpm, and the main takes over around 1500 with my motor. The more your engine flows (displacement, porting, cam, etc), the earlier the main circuit takes over from the idle circuit. Most cars probably still are affected by the idle jet closer to at least 2000 or so, so you'll have to experiment with where your motor transitions.

 

My tune procedure is pretty simple. I accept that I can only tune my carbs for about a 4k range of rpm at most. Beyond that, something is compromised. I make a run and check the AFR in the desired rpm band (coincided with my cam), and target 12.5-13.0. Keep in mind that the air corrector also plays a role in conjunction with the mains. My motor is affected above 4500 more by the air corrector than the mains. You will have different results as to where this happens, but to test, do a run and watch the AFR and note how it progresses relative to RPM. Then swap out an air corrector with one that's waaay too small (rich, to be safe). When the AFR *starts* to drop below your previous run's profile, that's where the air corrector kicks in.

 

I personally will make no more than two main jet adjustments in a row, since they are too closely tied with the airs. Then I will adjust the airs up to two increments and go back to the mains, assuming of course that the car is still going in the right direction. Do not skip jets, do not change more than one variable at a time. If you adjust too much of an increment, you may pass the peak and not know it.

 

Typically, from weekend to weekend I won't see more of an increment of 5 mains or 5-10 airs (if at all, sometimes I'll do one run and realize no change is necessary). Usually the idles only change once or twice a year (seasonally, depending on severity of your seasons).

 

There's probably a better system out there, but this is what works for me. Hope that helps.

Edited October 17, 2011 by zredbaron

[240zip]

zredbaron question - all things being equal, if you go up in altitude, should you go down in choke size (e.g. 32mm to 30mm)? I checked my stash and I have 28mm, 30mm, and 32mm chokes for my 42DCOEs. I may have a set of 34mm ones but I could be wrong about that. I also have these sleves that go inside the chokes. I've only come across them once, but they will turn a 32mm choke into a 30mm one. Supposedly cheaper than getting a new set of chokes.

[zredbaron]

all things being equal, if you go up in altitude, should you go down in choke size (e.g. 32mm to 30mm)?

 

The best answer is always to determine it experimentally, to try both (and tune!) and see which better suits your intended driving conditions. I'll assume your choke selection is already "ideal."

 

All things being equal, if you go up in altitude, air density goes down, necessitating larger chokes for the same O2 intake. Unfortunately, the "air" volume will be moving at a slower speed due to the larger diameter, which means you will sacrifice driveability for the same power output that you had at a lower altitude.

 

Bottom line, altitude is bad and you will lose performance. The question you need to determine is, which performance do you want: driveability or peak power? You can't have both, not even at sea level.

 

I personally would not recommend going down in chokes with higher altitude. You need higher volume air, not lower. The choice at hand is to stay the same or go larger, not to go smaller. Then again, I haven't ever tried to tune for high altitude, and therefore this is theoretical. Keep in mind you must adjust and tune all jets to compensate for the choke changes. Only then can you compare the change.

Edited October 23, 2011 by zredbaron

[240zip]

I was checking my choke stash and I have 28mm, 30mm, and 32mm chokes. These are for 42DCOEs. The 28mm chokes look tiny. The 28mm ones came from a 40DCOE. It seems most of the 40DCOE and 42DCOE parts are interchangeable. I don't know if I have a 34mm choke. I think those might be on the car right now. I'm going to get with Jeff Winters of Ralley/Sport and have him put the car and dyno and dial in the settings. We're adding the distributor with the mechanical advance (thanks again) and after that's dialed-in we'll do a few hours of tuning on the dyno. Like you, I have boxes of air corrector jets, idle jets, emulsion tubes, and other bits. The combination is daunting - hence the reason I value someone like Jeff who an expert on these carbs.

 

My biggest issue right now is a bit of bog off the line and then mid RPM bog. If I'm lugging alone at 2500 RPM and I hit the gas, I get a bit of hesitation. On the track, where I'm constantly keeping the RPMs up ... there's no problem. It screams. Oh ... speaking of altitude. I'm at 5,400'. It's a pain to tune Webers at this altitude.

[duragg]

I might have guessed at higher altitude a smaller choke would keep the lower mass of air moving at an equivilant speed.

Driving a DCOE car to higher altitude would frighten me.

 

This is where a Wideband and Butt-dyno are pretty critical.

[zredbaron]

I might have guessed at higher altitude a smaller choke would keep the lower mass of air moving at an equivilant speed.

Driving a DCOE car to higher altitude would frighten me.

 

This is where a Wideband and Butt-dyno are pretty critical.

 

Agreed, AFR and dyno are critical!

There are several variables here, fluid density (air being less dense at higher altitudes) and speed (grossly metered by venturi size). The combination of the two dictate both the volume of air mass ingested by the motor and also how laminar or turbulent the air/fuel mixture is as it enters the intake ports. Even worse, if we increase a volume of air that is less dense... are we getting more or less O2? Depends! Enter the AFR. Testing is worth 5x as much as theorizing.

 

Laminar flow is more dense. With a slight amount of turbulence (particularly on the edges of the runners) flow increases slightly but then quickly drops off and diminishes flow. This is a critical step of engine buidling; ensuring the head work / cam selection is also paired with intake runner shapes, lengths, diameters, etc. That's beyond our Weber thread, but it is a significant factor to how they perform. The engine is a complete system. Changing one variable requires other variables to be changed, too.

 

Unfortunately for simplicity's sake, air is compressible, so changing areas and shapes have more complicated effects than our generalizations that "area goes up, speed goes down." Our generalizations should also account for the fact that as compressible fluids are metered into smaller diameters, they encounter more friction, and both mass flow rate and volumetric flow rate are both decreased (the latter more significantly, the former being what we care about) *relative* to that of an incompressible fluid (they still speed up, just not as much as incompressible fluids). Sipping out of a smaller straw is harder to do, therefore sipping a compressible fluid out of smaller straw results in decreased amounts of fluid that makes it through the straw per unit time. And now we also decrease the density of the fluid by going to higher altitudes (making it even more compressible), which helps the fluid go through the straw more readily than the denser fluid, but since compressible fluid incurs losses with smaller diameters, this [small part of the equation] is even more exaggerated since the fluid is more compressible. Overall, more dense fluid encounters more friction of course, but we're talking about combining two variables at the same time -- density and diameter. You will always sip more mass through a straw if it's more dense (up to a point, of course molasses would not be a good example). It doesn't matter how much easier it is, just compare mass sipped from a glass of water to mass sipped from air. It doesn't matter if if the air is flowing faster, you got less mass.

 

To maintain less dense air at an equivalent speed, you need *slightly* larger chokes (increasing to the next increment would likely be too much). The air is less dense, therefore it encounters less friction, and travels *slightly* faster through the venturi. Air speed is not total O2 delivery, which is what we truly care about. The speed *does* however help our carbs mix fuel. Decreased air density does not. Which one wins for combustion engines? Density. We always want dense air, without exception. Since we don't have it at altitude, we need to open up the choke size to deliver the same amount of actual O2 that might have been delivered via a smaller choke size at sea level.

 

Confusing enough? Sound like we're talking in circles? We are! That's half the point. We can theorize all day, but in the end all that matters is what does the car like? Does the AFR indicate it's getting enough air? If your dyno graph shows your AFR go uncontrollably rich at higher rpms, that's because your chokes produce too much resistance to flow to support the O2 delivery required at that RPM.

 

Dynos have an SAE correction factor. It takes into account humidity, temperature and pressure altitude and makes a theoretical "standard day" (25 deg Celsius, sea level, no humidity) hp rating. A car making 200hp at altitude might have made 225 on a standard day, so the SAE shows the latter. You're at altitude, so essentially you're trying to minimize your handicap. Sorry, bud.

 

And all of this is part of why "how do you intend to use the car?" is always the first question asked in engine building and tuning threads. This case isn't different from any other; if you want driveability you want smaller chokes, if you want power, you want bigger chokes. I personally always preferred power over driveability. I can feather the throttle to keep the carbs happy(ish) at awkward RPMS, but if my chokes are too small (which they are) then I can't do anything about it short of an upgrade.

Edited October 23, 2011 by zredbaron

[240zip]

The nice thing about Webers DCOEs are that they're are very easy to change. My usage profile would be 3 or 4 track / autocross events a year and then a weekend barnstormer / ride in the hills. So I'd likely set it up for the weekend drives and then have another set-up for race day. Again ... the beauty of these things are that you can do a quick change with a flat head screw driver.