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Tuning an Alpina A4 (long)


JsnPpp

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Hi all,

I've been spending quite a bit of the last several months working on the red car and tuning has been a part of it. It took a bit longer than planned because I updated the "Remove/Configure/Install/Tune an ALPINA A4 Multi-throttle Injection System on a 1973 BMW 2002tii" guide at the same time. I figured I’d capture a summary here for those interested. PM me if you’d like a copy of v2.0 of the guide, happy to send it on.

 

519641919_ScreenShot2019-09-23at8_31_19PM.png.69124c30515f9b795135600c172c2373.png

 

Some backstory research/opinion on stock tii vs Alpina A4 systems prior to the tuning:

Conversations comparing tuning effort of a stock tii injection system and an Alpina A4 system are engaging to me. Now that I have been through the process multiple times for both cars I have reached the conclusion that an A4 system is more simple to tune than a stock tii injection system, despite the additional parts associated with the multiple throttle plates. Why? Once the basics are addressed (points, plugs, timing) and the throttles are sync’d (a work intensive but also infrequent need), the A4 tune up procedure has only 2 variables (sometimes 3) whilst a tii has 3 (sometimes 5). This is a significant reduction in effort. (What are these variables? I’ve included more discussion on this at the end of this post and also in the tuning guide for those interested.)

 

However, the A4’s “simplicity” comes at a cost. The stock tii injection system is like something you would find in a watch-makers shop, while the A4 is more like a sledgehammer at a construction site. Not saying that the A4 isn’t delicate but the goal of it is horsepower (four ~48mm throttle plates instead of one ~58mm plate) and not necessarily refined driving behavior.

 

The A4 is fun but it can be challenging to drive gently since  4X throttles are opening. Dual Webers systems must have similar experience (especially dual 45s).

 

Rabbit hole --> How much more air can the A4 deliver theoretically over a stock tii? Well, at wide open throttle (WOT) this can be calculated easily: 

  • A4 (area) = 4 * (area of individual throttle plate) = 4 * (pi * 24mm * 24mm) = 7,238 sq mm 
  • tii (area) = 1 * (area of throttle plate) = 1 * (pi * 29mm * 29mm) = 2,642 sq mm

 

So, the A4 provides 174% greater throttle area at WOT than a stock tii (100*(7238-2642)/2642). Nearly 3X. This explains why the Kugelfisher needs a new cone (or at least mixture screw adjustment of a stock Kugelfisher). I haven’t done this math before and was surprised by the numbers as well. (Note: I am not saying A4 is 3X the horsepower as a tii, it’s not. There are other factors that contribute to overall power).

  • More fun math --> what percentage of WOT for an A4 equals WOT of a stock tii? Answer = 37% (100*(2642/7238). So about a third of full throttle on an A4 is the same air flow as a tii at WOT. Crazy!

 

Steps for tuning an A4

 

First step is to remove the airbox, snorkel and the two frontmost red horns. This makes it much easier to access linkages.

199496671_photo2.jpg.f560de7759439ce54114f707a5738b57.jpg

 

Set the initial linkage lengths “by the book”. In other words rod “A” is at 194mm (FYI, McCartney lists it as 195mm, debatable difference), lock the enrichment lever in the idle position and the vertical rod “B” length just short enough to remove play. Remove the lock rod.

629422334_Photo3.jpg.1e5b2a3319ae5deeebf9d9f4a9de14a9.jpg

2101677587_Photo4.jpg.c002edbf9e9cd6e2b70a7f9bbe10a745.jpg

 

Some of you may ask, what about the mixture screw? Good question. Adjusting air-fuel ratio (AFR) on a precisely spec’d engine outfitted with an A4 system and a properly matched Kugelfisher has one variable; the idle air screws. However, I have found rod “B” and/or the mixture screw may need to shift to match the A4 system with the engine it is installed on, especially if the engine isn’t the same specification as Alpina A4/S engine (generally accepted to be a 300 cam, 10:1 forged pistons, oversized valves, etc.) But even if the engine matches this specification, I feel all three variables - idle air screws (IAS), the mixture screw and vertical rod “B” - are potentially relevant because of real-world environment conditions. (You may feel different and I'm ok with that, love to discuss it more.)

 

Prior to the final tuning it is helpful to me to have a visual of the relationship between linkage adjustment and AFR. Here is one way to think about how the three variables provide this impact:

 

Mixture screw: The mixture screw controls the overall fuel delivery across all throttle and rpm settings, universally. The mixture screw can be thought of as the master fuel spigot of the pump. Clockwise turning (CW) of the mixture screw (“in”) increases the amount of fuel output (the curve shifts up). Conversely, counter-clockwise turning (CCW) decreases the amount of fuel output (the curve shifts down). See the figure below.

1187504679_Photo5.png.37965d27d70614d02f4d32e1916de5e2.png

 

 

Vertical rod “B”: The vertical rod “B” controls the position on the fuel delivery cone in the pump (this is similar to the adjustment screw on the D-cam lever on a tii). Shortening the length of the vertical rod moves the horizontal rod A “away from idle”. The result is more fuel at each throttle position, which in turn decreases the AFR (and decreases idle speed). This is illustrated in the following figure as shifting left.

1537045680_Photo6.png.4efb647a2d41a3654876de8313f51e1c.png

 

 

Idle Air Screws (IAS): The IAS restrict air flow into the individual throttle bodies at idle (i.e., no throttle pedal input). Tightening the screws reduces air flow, which decreases idle (AFR goes up). Loosening the screws increases the air flow, which increases idle (AFR goes down). Remember by definition this only impacts idle. 

 

Summary of initial settings: 

  • Mixture screw to a bit less than 1cm exposed (optional, depends on your comfort level of changing this)
  • Turn in the idle air screws (IAS) and then backed out each 1 turn. 
  • Loosen the warm up regulator “hat” so that you can use it to change the mixture screw settings easily (no tool required). (Once the system is running properly you can lock down the mixture screw setting based on the regulator hat position.)
  • Vertical rod "A" should be at 194/195mm length.
  • Vertical rod "B" should be "just long enough" and not locked.

 

Once the linkages and screws are at initial settings, here is the long/short on the tuning. (Ignore the mixture screw adjustment recommendations if your pump is set as you wish it to be.)

 

Target: The goal is idle between 850-950RPM, the mixture screw as “lean as possible but still rich enough” and the vertical linkage length to as close as possible to idle spot on enrichment lever. Idle AFR about 13.4. Timing has a huge impact on runtime behavior; make sure to have the system within spec and consider making modifications along the way (additional guidelines in the manual).

 

  • First obtain a stable 850-950RPM idle. In my case the engine started but idle was high and wandering. I needed to drop the RPMs down. I tightened the idle air screws about ½ turn and sync’d them. This reduced the idle and the wander but I found when blipping the throttle linkage that it heavily bogged - not enough fuel or just misalignment of AFR. 
  • Use the warm up regulator hat to press on the mixture linkage (forces the mixture lever up). This enriches the mixture (and lowers rpm) and moves the mixture screw in a non-permanent way (see figure below). Sync the four IAS to bring the idle where it needed to be. This seemed to be the better approach but a slight change in rod “B” length could still help should I want to go there at some point.
  • Iterate between adjusting idle air screws, mixture screw (using the top hat warm up lever), and a bit of vertical rod "B". Takes time.

 

Throttle response is a key part of evaluating tuning success. It will be “snappy” when set right, but remember those are big throttle plates dumping open so it isn’t necessarily easy to achieve (keep in mind that most driving is off-idle). After a few iterations of the above procedure I started to find the right place for both IAS and mixture hat. Once it was "good enough" I adjusted the mixture screw length to match the warm-up regulator hat distance and tightened all lock nuts.

 

No matter how far you get in the driveway you aren’t done until you get it out on the street. Tuning the engine for optimum performance and fuel economy involves drive time to feel how garage settings impact real-world.  It is easy to find yourself with a nicely running engine but fuel economy in the basement. Tune, measure, drive, tune, measure, drive, tune, measure, drive... Keep iterating the mixture screw if you permit this variable in your effort to bring this to where you want it. Once you get near optimum it will feel like it has near instant throttle response, a mile of pedal travel while decent fuel economy (my definition is >24mpg during brisk highway driving, city driving "depends").

 

Tools
I've listed the tools required for a complete removal/installation in the manual. For the most part the tuning can be completed without exhaust % CO monitoring (wide band meter). I’ve done it, just takes more time to reach the results. A wide band 02 sensor will help shorten the tuning time. Alpina indicates the target idle % CO is 3.0 % (about the same as stock tii). This translates into an AFR of 13.4. Keep in mind that a high AFR (lean) is more dangerous to an engine (as has been said on this forum “Too fat is better than too lean!”), so best to err on the side of rich at least while getting to know the engine. From the magic of the interwebs are the following guidelines (http://www.afrplus.com/AFRplus-unit-functionality.asp):

 

AFR Values & Characteristics in Four Stroke Engines

  •  6.0 AFR - Rich Burn Limit (engine fully warm)
  •  9.0 AFR - Black Smoke / Low Power
  • 11.5 AFR (0.77 Lamda) - Best Rich Torque at Wide Open Throttle
  • 12.2 AFR (0.82 Lamda) - Safe Best Power at Wide Open Throttle
  • 13.3 AFR (0.91 Lamda) - Lean Best Torque
  • 14.6 AFR (1.00 Lamda) - Stoichiometric AFR (Stoich)
  • 15.5 AFR - Lean Cruise
  • 16.5 AFR - Usual Best Economy
  • 18.0 AFR - Carbureted Lean Burn Limit
  • 22.0+ AFR - EEC / EFI Lean Burn Limit

 

During acceleration you are targeting mid-11’s to 13’s.

 

Thank you for reading. For those of you interested in a copy of the “Tune an ALPINA A4 Multi-throttle Injection System on a 1973 BMW 2002tii - v2.0” guide, shoot me a PM with your email and I’ll send it over. 

 

Cheers,

JasonP

1015804273_38-Last.jpg.63ad76d6001a905309cdd5c7259da4a8.jpg

 

The A4 test mule: The red car, (originally aka., "The Tomato")

1973 BMW 2002tii Hardy&Beck Alpina A4/S (Early '73, VIN 2762913)

 

~~~

 

PS: How do the tuning variables of stock tii injection system and an A4 system compare?

 

As referenced above, the stock tii injection has five variables - three primary locations for adjusting air and fuel:

  • Idle speed adjustment screw - one screw on the “tuna can”.
  • Adjustment screw for butterfly - air delivery
  • Adjustment screw on lever - fuel delivery

Also the following two, which most don’t modify but are part of the equation, especially for motors not matching factory specs:

  • Pin hole edge - Stopping point for the d-cam, adjustable.
  • Kugelfisher mixture screw

 

2081946582_Photo7.jpg.a9ee71ef24e214fcc54a08d21535aa28.jpg

The A4 system has three variables. Two primary locations:

  • Idle air screws (four of them, all accessible)
  • Vertical rod “B” - air and fuel alignment

And one additional:

  • Kugelfisher mixture screw

 

1319988494_Photo8.jpg.54b9319c87d66ad8913d6fa73bca3fa0.jpg

While variables don’t capture the entire tune-up effort (example, the stock tii injection doesn’t involve sync’ing butterflys), it is still relevant! There is less to adjust on an A4. (More on this topic in the manual)

 

 

 

 

 

 

 

 

 

 

 

 

 

Edited by JsnPpp
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1973 2002tii (2764167), Baikal, sunroof, A/C, 5spd OD, 3.91 LSD, etc. Rebuild blog here!

In the past: Verona H&B 1973 2002tii (2762913); Malaga 1975 2002; White 1975 2002

--> Blog: Repro tii cold start relay;   --> If you need an Alpina A4 tuning manual, PM me!

 

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1 hour ago, markmac said:

Nice job on this Jason, i need to re-re-read.  By the looks of the coloring on your injection lines, you have been putting some fuel through there....good work!

Thanks Mark - I'll send you a copy. 

 

Yes, I was surprised to see the delta of color too, you can ell which photos are new and which are from the earlier manual..

 

Jason

1973 2002tii (2764167), Baikal, sunroof, A/C, 5spd OD, 3.91 LSD, etc. Rebuild blog here!

In the past: Verona H&B 1973 2002tii (2762913); Malaga 1975 2002; White 1975 2002

--> Blog: Repro tii cold start relay;   --> If you need an Alpina A4 tuning manual, PM me!

 

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  • 1 year later...

Thank you for this article! I have the same engine A4s in my Touring.

I am constantly tuning...;) 

The engine runs well and I have lots of fun with it....

The only thing that i want to improve is the throttle response!! Like you said, I want it more snappy..... ;)

The throttles are in sync and the idle is nice and stable.

I am experimenting with ignition and get some results, but still think it could be more “direct”.....

At idle it runs a bit lean but is about 3,5% CO

If I make it more fat, CO will go up dramatically.

O2 is about 2

CO2 is just under 10...

 

Do you have an idea what i could try?

I would also be interested in that pdf!! :)

 

All the best from Vienna. P

 

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  • 1 year later...
7 hours ago, a4s said:

Hi I would like to get one of your tuning guides if you have any available. Thanks 

 

Blast from the past article! You bet, shoot me a message through the forum with your email and I'll be glad to send a pdf to you.

 

~Jason

1973 2002tii (2764167), Baikal, sunroof, A/C, 5spd OD, 3.91 LSD, etc. Rebuild blog here!

In the past: Verona H&B 1973 2002tii (2762913); Malaga 1975 2002; White 1975 2002

--> Blog: Repro tii cold start relay;   --> If you need an Alpina A4 tuning manual, PM me!

 

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  • 2 months later...
6 hours ago, StefanA4Stouring said:

 

Hi Jason,
if it is still possible, I would also like one of your tuning guides.
All the best 

 

info@imago-lupus.de

You bet! I'll shoot you an email.

 

~Jason

1973 2002tii (2764167), Baikal, sunroof, A/C, 5spd OD, 3.91 LSD, etc. Rebuild blog here!

In the past: Verona H&B 1973 2002tii (2762913); Malaga 1975 2002; White 1975 2002

--> Blog: Repro tii cold start relay;   --> If you need an Alpina A4 tuning manual, PM me!

 

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  • 1 year later...

Nice write up Jason,

 

One thing that I will add with the A4 system, at idle make sure that the throttle plates are completely closed. The idle speed is set by the 4 idle air screws only with closed throttle plates. Many high mileage A4 systems can have worn throttle body bores passing too much air at idle making it difficult to lower the idle speed. The throttle plates and screws are the same as Solex PHH carburetors and are available from some eBay sellers like Alfa1750 https://www.ebay.com/sch/i.html?_trkparms=folent%3Aalfa1750%7Cfolenttp%3A1&_trksid=p3542580.m47492.l71970&_ssn=alfa1750

 

Shops restoring Porsche 356, 912 and 911 Solex carburetors can probably oversize bore a A4 throttle body set.   

 

Most A4 and A4s throttle body have a 45mm bore, I have heard rumors of some competition 48mm sets but have never seen one, you are very lucky to have one. 

 

Jeff  

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