V6 vacuum advance curve - Alfa Romeo Bulletin Board & Forums
 
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post #1 of 14 (permalink) Old 07-30-2013, 10:10 AM Thread Starter
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V6 vacuum advance curve

Does anyone have good information on the vacuum advance curve characteristics for the V6 engines?

I have mechanical advance information from the 81-83 Alfa Bosch service manual, but have been unsuccessful in finding the curve for the vacuum advance.

Either distributor degrees / speed or crank degrees / speed would be fine. Just please specify which one it is.

I'm working on building a better "first guess" ignition advance table for my Megasquirt / EDIS set up.

It runs, and I have driven it, but still far from road trip worthy!

Thanks
Mark
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post #2 of 14 (permalink) Old 07-30-2013, 10:47 AM
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On the Milano V6 the max vacuum advance is 12 degrees at 500 mbar. It's in the Milano service manual page 00-34.

But some of the earlier GTV-6s had a vacuum retard instead, didn't they? So it may depend on the year of your car.

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post #3 of 14 (permalink) Old 07-30-2013, 10:56 AM Thread Starter
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Thanks - my set up is so far from normal that precision doesn't matter at this point. I'm just checking for reasonableness (is that a word?)

I'll look at the milano manual. I suspect it is roughly linear?

Thanks a bunch for the directions!

Mark
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post #4 of 14 (permalink) Old 07-31-2013, 03:54 PM
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Degrees advance at vacuum.

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Last edited by ToonRboy; 08-01-2013 at 04:46 AM.
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post #5 of 14 (permalink) Old 08-01-2013, 04:30 AM Thread Starter
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Awesome - thanks guys.

I made a map from the mechanical and vacuum curves. Then backed down on the vacuum advance near idle. The vacuum advance is pretty agressive - at least compared to the megasquirt recommendations.

The car ran OK. I think I can put in some more advance. And I need to increase the fuel in a couple of areas. Slowly getting there.

Mark
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post #6 of 14 (permalink) Old 08-01-2013, 04:50 AM
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This the engine with the Mercedes compressor on it? How much static advance are you running? If so, (boosted motor) What are you using for retard?
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post #7 of 14 (permalink) Old 08-01-2013, 05:04 AM Thread Starter
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Yes, this is the supercharged engine. I need to do an update to that thread.

Initial advance at 1000 RPM 100 KPa (atmospheric pressure) is 8 - which sounds reasonable and starts easily.

Right now I'm using .3 retard for each KPa over 100 as part of the table. I haven't run the engine in boost yet. Still working on idle and part throttle areas of the maps. My goal is to get these dialed in enough that I can drive it to the dyno (20 miles or so - through town) and then get the boost area of the fuel map dialed in there, as well as refining the ingnition map.

The project moves slowly when you only have a couple of hours a week to work on it

Mark
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post #8 of 14 (permalink) Old 08-01-2013, 06:45 PM
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.3 for 1 bar is probably not enough Mark. I think 3 would be more like it. So the stock static ignition timing for the 2.5 is a couple degrees, I run around 8 static on my N/A motor which makes it more lively (with stock '84 emissions retard disabled).

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I would imagine that Mercedes unit won't make 2 bar.
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post #9 of 14 (permalink) Old 08-02-2013, 08:19 AM Thread Starter
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Boost goal is .7 bar, or 10 psi. This equals about 70 KPa. so for .3 for each KPa I have about 21 retard under full boost - where I can. Of course this is all speculation at this point in time.
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post #10 of 14 (permalink) Old 08-02-2013, 09:09 AM
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Quote:
Originally Posted by Mark_toro View Post
Yes, this is the supercharged engine. I need to do an update to that thread.

Initial advance at 1000 RPM 100 KPa (atmospheric pressure) is 8 - which sounds reasonable and starts easily.

Right now I'm using .3 retard for each KPa over 100 as part of the table. I haven't run the engine in boost yet. Still working on idle and part throttle areas of the maps. My goal is to get these dialed in enough that I can drive it to the dyno (20 miles or so - through town) and then get the boost area of the fuel map dialed in there, as well as refining the ingnition map.

The project moves slowly when you only have a couple of hours a week to work on it

Mark
Mark

I have a suggestion, and based on my dyno tuning experiences. Rather than waste time building a map that's definitely going to be changed - I would highly recommend this:

Yes, that's a Uhaul trailer. Trailer it there, have the gurus tune the map all around (and - the added benefit of this - and it's a BIG one - is to do live data logging and tailpipe sniff from a stone cold engine). Helps a lot.

Just my humble suggestion...

WE NEED MORE PICS

Rob
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post #11 of 14 (permalink) Old 08-02-2013, 04:06 PM
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Hey Mark, feel free to send me the map - I can look it over if you'd like. I've done enough cars now to be able to look for obvious trouble spots...

grant at battlegarage-rs dot com

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post #12 of 14 (permalink) Old 08-07-2013, 03:54 PM
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What is the story on vacuum advance for the V6's. My '85 has a vacuum advance canister on the distributor that is connected by a very small vacuum line to the throttle body.

But I hear that on some earlier cars this is actually a retarding device.

However, the diaphragm in the canister appears to have failed, it does not hold a vacuum. I am assume I am running around with mechanical advance only and not benefitting from a little vacuum advance curve.

Is this a vacuum advance canister, and if so is there a way to fix the failed diaphragm?

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post #13 of 14 (permalink) Old 08-08-2013, 07:11 AM Thread Starter
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Rob - that's cheating! The goal of this project is for me to learn as much as I can with the tools and budget that I have. Plus the only time this car has been on a trailer is when it was a stripped shell. Of course I'll need to get it to the dyno to dial inthe ignition map for best power.

Grant - I'll see if I can download the ignition and fuel maps and send them off to you for review. Always good to have a second set of eyes. The challenge with this is that I need to write to a 3.5" floppy disk from the tuning laptop - then transfer to the desktop at home then transfer to a thumb drive to bring it to work and e-mail out. Quite a convoluted path.

The good part is that I have a ignition map based on the info provided here and the mechanical curve that seems to work reasonably well. I added 3 advance over that and things still seem good.

Working on trying to establish the acceleration enrichment and need to clean up the TPS signal a bit. The car drives reasonably at moderate levels. Haven't been hard on it yet.

The sound of the supercharger and the exhaust is inspiring. I need to get video and post it.

Mark
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post #14 of 14 (permalink) Old 09-14-2013, 01:25 AM
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Ignition advance for GTV6 2.5

Hi Mark, just of the top of my head, the ignition timing advance info for my 1984 2.5 GTV6 is as follows:

Static advance @ 950 RPM=7 deg. crank (This would be 2 degrees for the U.S versions with the same distributor. The South African cars had a factory static setting of 7 degrees as there was no real emission concerns in S.A in the 80's..)
Mechanical advance=28 deg. crank @max travel. (14 degrees @ distributor.)
Vacuum advance=10 deg. crank.
I have tightened up my distributor mech. advance springs a tad, and limited travel to 12 degrees distributor (24 deg. crank)
This allows me to now run a static setting of about 10 degrees advance.
Car starts easy and idles real nice.
I plan on tightening the springs a little more, and limiting travel to about 14 degrees crank mechanical advance, and then completely remove the vacuum advance function, and setting up about between 12 and 14 degrees static advance..
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