L28 3.1 advance curve ?

[gacksen]

Hello,

 

just had a quick look at the curve the guys at the carb rebuilt shop put into my tune 123 dizzy.

as for the all the other cars i know the total advance should come in around 2500-3000rpm or am i wrong ?

 

3x 45 webers with vac disconnected.

 

have attached dyno sheet and dizzy print

[NewZed]

The factory sets their distributors up to have full advance by 2500 - 2800 RPM.  Curves are shown in the FSM's, Engine Electrical, if you want to browse them and see.  

 

BRAAP had some recommendations and discussion in the post linked below, Post #30.  Engine size would not be a big factor.  Maybe bore-stroke ratio but still nothing to suggest continued advance up to 4000 RPM.  Your curve seems unusual.

 

http://forums.hybridz.org/topic/95316-braaps-l6-efi-induction-advice-and-tips/page-2

[gacksen]

thanks Zed

 

will need to take the car on a dyno to get an AFR plot and try a revised curve.

 

in general would have thought about something like this ? after having read the postings.....

 

 

[madkaw]

So many factors to consider, but the curve does seem late.

[Chickenman]

Need to know C/R, cam timing ( degrees ) and fuel quality.

 

Assuming 93 - 94 Octane fuel, A C/R of around 10 to 1 and a Camshaft of 270 to 280 degrees.

 

I find this has worked well for me over the years.

 

1: Static ( idle ) timing of 12 -14 degrees. Start curve 200 rpm above idle.

 

2: Total mechanical advance of 34 to 35 degrees ( depends on fuel ). Ramp up curve quickly to 30 - 32 degrees by 3,000 RPM

 

3: Taper final few degrees so that total mechanical advance is all in by 3,500 to 3,700.

 

4: For 91 Octane fuel knock a couple of degrees off all the settings.

[Chickenman]

Vacuum advance should always be used on a street driven car. It dramatically increases fuel economy. You can pick up an easy 4 - 5 MPG by using a Vacuum advancesytem properly dialed in. David Vizard has an excellent book called " Performance with Economy " where he explains the advantages of running Vacuum advance or " Load sensing " on a street driven car. Vacuum advance is the most mis-understood part of the Ignition system... mainly due to " Racers " saying you don't need it to make Power. And you don't... IF you drive at WOT all of the time...which race cars do and street cars do not.

 

The vacuum advance pot works as a load sensing device and it really helps fuel economy. The reason being is that at part throttle and Cruise speeds, the mixture density ( Not to be confused with AFR ) is greatly reduced as is the " Dynamic " compression ratio. All this due to the reduced throttle angle. The low density mixture is much slower burning and needs to be ignited MUCH sooner in the OTTO cycle.

 

With IR carbs running a Vacuum advance gets tricky because the vacuum source off of a runner fluctuates wildly and is very strong. You usually have to cobble together some sort of " accumulator " log manifold and pipe all cylinders together to smooth out the source vacuum pulses. And you often have to alter ( soften ) the spring tension if you have a big camshaft and may have to alter the travel length,

 

However the 123 distributor makes things easier. Since you have a true MAP sensor and do not have to fiddlle with springs and stops in a Vacuum pot, you can set up a " Load " mapping very easily and take advantage of gaining some extra full mileage.

 

Put a vacuum gauge on your car with a looooong hose and run the gauge inside the car so you can read it as you drive. It's better to have a passenger do this and record the numbers while you concentrate on driving. Try various cruise speeds that you would typically drive the car at. City and Hwy. You should find the the pulsing of the IR smooths out around 2,000 to 2,500 Max. Record your maximum vacuum readings. This is the start of your " Load Mapping " process.

 

Now find a long hill and try some part throttle runs in various gears and throttle opening between 25% and 50% . Record the vacuum values.

 

Anything above a certain level of throttle is going to show 0" vacuum. You don't really have to record this as it's the High Load section and will always be zero or close to it.

 

Convert vacuum to Kilopascals or whatever your Programmer uses. Now plug in your numbers to the 2D or 3D cahrt.

 

High vacuum vacuum = Low Load = more ignition timing required. Low vacuum = High Load = less or no extra timing required. All cars should safely handle an extra 10 degrees of Vacuum or Low Load advance. This is safe. Depending on parameters , " most "  High Performance cars will safely handle 15 degrees of additional vacuum/load advance on top of the Mechanical curve.

 

Some electronic Load Maps have a VERY nice feature called " No MAP idle " or similar. This switches off the MAP sensing corrections at idle, where vacuum readings can fluctuate with big camshafts or Independent runners until you get above a set RPM. usually around 2,000 RPM. Above 2,000 RPM, vacuum readings are normally stable enough for a MAP sensor to read reliably. Check to see if your 123 Ignition system has this feature. If so, enable it with an Independent Runner manifold ( or Big Camshaft ).

 

Edit: It looks like the 123 Ignition does have a " No MAP Idle " feature. Check out the " MAP Start " box. That should be a minimum RPM setting to turn on MAP sensing.

 

Sorry for the Novel... but I hope this helps some.

 

Here's a link where I've used some personal Data to illustrate:

 

http://www.the510realm.com/viewtopic.php?f=30&t=28374&start=15#p247318

Edited September 28, 2015 by Chickenman

[Chickenman]

^ And of course Braaps article the NewZed linked to says essentially the same thing. Could have saved myself a lot of typing if I read it first

Edited September 28, 2015 by Chickenman

[bradyzq]

Since your advance curve is programmable, when you next visit the dyno, why not try adding or removing advance and see what happens to power or torque?

 

It is safer when dealing with an unproven curve to first remove a couple of degrees then test. If torque drops everywhere, then advance the timing on the next test pull. If it _doesn't_ drop, you were overadvanced.

 

Repeat until you have determined the optimum curve for best torque.

 

You may, depending on the type of dyno, be able to dial in the vacuum advance curve in a similar way. If the dyno is not able to, then Chickenman's suggestions for doing the vacuum advance tuning on the road should work great.

[gacksen]

thanks for all the support and detailed descriptions. bought the car used in CA last year and the engine builder passed away in the meantime.

what i do know from the mechanic of the seller is that the CR should be around 9.5 and cam should be around 270 - 280 of unconfirmed lift and duration.

he told me that he remembered total davnce should be 32 and as per their test not exceed 34.

 

as for the fuel in germany we have 98 RON octane available almost anywhere. if needed 102 octane is also available at some stations a little extra but normally i use the 98.

i remember there there had been some country differences :

 

( RON Octane Rating x 0.95 = AKI Octane Rating )
98 RON Octane x 0.95 = 93.1 AKI Octane (US measure)
102 RON Octane x 0.95 = 96 AKI Octane (US measure)

 

the most simplified curve i could do would be the the curve in the attachment.

 

do i get something wrong or has the weber dcoe 152 an advance port ?

[Chickenman]

Your RON Calculations to North American Octane ( R=M/2 ) looks about right. So you have good quality gas available.

 

The simplistic curve you attached in the last post can be improved on a bit, but it's not bad. You don't need to Taper the final few degrees all the way to 8,000 RPM. Anything over about 3,700 to 4,000 RPM can be flat lined  across the Axis.

 

Assuming an idle speed of 1,000 rpm, which is good for a 270- 280 degree cam. Try this for 98 RON fuel.

 

Note: This is a fairly sophisticated curve, taken from Tech Info from Haltech and 123. . The 200 RPM and 700 RPM set points are Optional and can be eliminated if not needed.... but it does help smooth things out.

 

              RPM        BTDC

Point 1: 200            10  ( Cranking RPM. Reduces load on starter )

Point 2: 700            15  ( Stabilizes idle and prevents stalling . Value = +2 over Idle Timing. )

Point 3: 1,000         13  ( Idle RPM )

Point 4: 1,200         14  ( Start of mechanical curve )

Point 5: 2,800         30

Point 6: 3,700         33

Point 7: 8,000         33

 

This will give you a very nice curve with good idle stability, a quick ramp up which is good for Torque and then the slow taper for the last few degrees to avoid detonation. 98 RON should handle this curve well.

 

Note the higher timing figure at 600 RPM. This is to prevent stalling upon quick stops. Especially helpful in Autocross or if Air Conditioning kicks in. On cars without an IAC valve, ( Non EFI )  this is a simple method to stabilize idle. Keep this RPM set point figure set to approx +2 timing degrees more than idle timing degrees.

 

After that you can take some Vacuum readings and let us know what they are and when they are stable.

 

I do not know if your Weber 152's have built in Vacuum ports. Some do have ports for attaching Manometers to each barrel and some don't. The manometer ports are used for balancing carbs, but they can be used as a Vacuum source for other purposes.

 

Edit: Important!! Always verify the programmed timing settings with a Timing light. How the distributor is " Physically " timed affects the total mechanical timing programmed in. ( 123's Website seems to have their Instruction links scattered all over the place ).

Edited October 1, 2015 by Chickenman

[gacksen]

Your RON Calculations to North American Octane ( R=M/2 ) looks about right. So you have good quality gas available.

 

The simplistic curve you attached in the last post can be improved on a bit, but it's not bad. You don't need to Taper the final few degrees all the way to 8,000 RPM. Anything over about 3,700 to 4,000 RPM can be flat lined  across the Axis.

 

Assuming an idle speed of 1,000 rpm, which is good for a 270- 280 degree cam. Try this for 98 RON fuel.

 

Note: This is a fairly sophisticated curve, taken from Tech Info from Haltech and 123. . The 200 RPM and 700 RPM set points are Optional and can be eliminated if not needed.... but it does help smooth things out.

 

              RPM        BTDC

Point 1: 200            10  ( Cranking RPM. Reduces load on starter )

Point 2: 700            15  ( Stabilizes idle and prevents stalling . Value = +2 over Idle Timing. )

Point 3: 1,000         13  ( Idle RPM )

Point 4: 1,200         14  ( Start of mechanical curve )

Point 5: 2,800         30

Point 6: 3,700         33

Point 7: 8,000         33

 

This will give you a very nice curve with good idle stability, a quick ramp up which is good for Torque and then the slow taper for the last few degrees to avoid detonation. 98 RON should handle this curve well.

 

Note the higher timing figure at 600 RPM. This is to prevent stalling upon quick stops. Especially helpful in Autocross or if Air Conditioning kicks in. On cars without an IAC valve, ( Non EFI )  this is a simple method to stabilize idle. Keep this RPM set point figure set to approx +2 timing degrees more than idle timing degrees.

 

After that you can take some Vacuum readings and let us know what they are and when they are stable.

 

I do not know if your Weber 152's have built in Vacuum ports. Some do have ports for attaching Manometers to each barrel and some don't. The manometer ports are used for balancing carbs, but they can be used as a Vacuum source for other purposes.

 

Edit: Important!! Always verify the programmed timing settings with a Timing light. How the distributor is " Physically " timed affects the total mechanical timing programmed in. ( 123's Website seems to have their Instruction links scattered all over the place ).

 

thanks a lot for your detailed explanation. makes perfect sense. will get that curve onto the dizzy once i have my front fenders back from the paintshop.

less parts on the car means more talking once the police pulls you over

Edited October 1, 2015 by gacksen

[280zex]

This is my current 123 ignition map. My Z is 2.9L turbo carb/blow thru, 280deg cam, .450 lift at the valve....

 

Edited October 4, 2015 by 280zex

[Tony D]

I was going to mention it, but Chickenman got it right, use the MAP/RPM box below your normal idle range to bump timing up 2 or 3 degrees. If the car stumbles off idle, the ignition advances to bring it back up to speed. The old TECII from Electramotive would do this as a supplement to idle air bypass if there wasn't an actual IAC on the engine. It works really well to prevent drop throttle stalling from flogging it off-idle.

[z240]

Another couple of sanity checks for the 123 crowd.

 

First Absolutely (cheap MAP joke...) check the timing with a timing light after you get your timing map filled out. It's easy to not perfectly zero the 123 LED "on" point relative to your mechanical TDC setting.

 

Second, check what the 123 dizzy MAP sensor reads with nothing connected to its port, ie ambient atmospheric. Mine reads -6 inch/hg up here at 935m elevation. Have to factor that into your advance MAP chart. And that may change the map quite a bit when you take the car to the coast...

Edited October 5, 2015 by z240

[Tony D]

Interesting note that they don't have a dual-MAP sensor to altitude compensate.

 

You might want to contact 123 and suggest that for N/A people it's a bigger deal than the boosties.