VVT Variable Valve timing Questions

gotglasses · #1 (**permalink**) 11-29-2003, 08:58 PM

My 86 Spider has a solenoid operated VVT. I'm not sure it does anything! I confirmed that the solenoid is moving properly.

Should I feel something happening on hard acceleration versus light throttle ? It does make the car idle really rough when I jumper it on. Retarding the cam is a way to gain some top end power , but this may just be set up for emissions. Is it possible to "adjust" it for more power?

BOBCOR used to sell a kit to adjust the cam timing , is something like this available today?

alfa_corse · #2 (**permalink**) 11-30-2003, 04:09 AM

The VVT on Alfas is supposed to be for improved power under acceleration; without sacrificing emissions at idle/low power demand. The problem is that unless you have the factory tool to set the VVT solenoid; you can't be sure that it's doing the job it was designed to do. Maybe someone here on AlfaBB has one (and can give dimension details) or has info on where to get an aftermarket tool.

As far as tweaking it goes; not sure because the L-Jet controls it via various inputs (AFM, Throttle Position, O2). There is a max amount of retard of the cam built into the VVT also; which would limit it's effectiveness.

gotglasses · #3 (**permalink**) 11-30-2003, 12:05 PM

Thanks, Alfa Corse - The Cardisc I have has several Tech bulletins related to VVT adjustment/testing. They don't get into tweaking. The Bobcor cam retard mod was just a plate with holes drilled in at a diferent angle from the factory settings, to give more overlap. Most Alfas in the past ran good with 102 degrees of valve overlap, according to Bobcor. It would be nice if the VVT operated in a range of about 90 to 100. I want to be conservative with this since the possibility of valve interference is very real in a HEMI head engine like this. I lost my GTV engine that way, when an exhaust valve collapsed and went out through the piston.

Any idea what the factory cam timing is , with and without the VVT energized?? My experience at attempting to measure the timing myself is that it requires precision measurement that I cannot duplicate. Moving the cams a couple of degrees one way or the other is a different matter.

A slack timing chain can probably throw off the timing a few degrees, so I'm going to adjust that now. ( before my wife catches me with another project!)

**papajam** · #4 (**permalink**) 11-30-2003, 02:49 PM

Out of curiosity, I looked at the cardisc too and found in 'Shop - Engine Overhaul - Section 6 - Engine (re)Assembly, paragraph 6-10, the procedure for adjusting the VVT solenoid. Seems it's simply a matter of screwing in or out the solenoid until the solenoid end just contacts the plunger. Although the service manual did not mention any special tools for this procedure, the manual does mention special tools to adjust the intake cam timing in para. 6-8.7. Catalog #12 from Centerline, on page 51, says the lobe center on the intake cam from idle to 1650rpm is 118 degrees and 98 degress above 1650rpm.

gotglasses · #5 (**permalink**) 11-30-2003, 03:08 PM

Thanks Papajam - Hmmm - I do have a noticeable clearance right now. I'll have to see if I have a wrench that fits the solenoid nut.

I wonder if someone screwed it out for a good reason?

alfa_corse · #6 (**permalink**) 11-30-2003, 04:44 PM

Hmmm... My factory manual shows a tool you insert between the solenoid and the plunger. You are then supposed to screw the solenoid down until it hard stops against the tool. When you remove the tool the solenoid's actuator then contacts the plunger in the cam cover at proper engagement. I don't have the Cardisc for my Spider since I had purchased the factory manual many years ago.

Is it possible that the VVT self-adjusts on startup? Meaning that it just moves in a little until it detects some change in intake airflow/exhaust O2 and then calls that the zero point?

gotglasses · #7 (**permalink**) 11-30-2003, 09:36 PM

Hi Alfa Corse ! HMMMM - looks like the printed copy may be the winner. I have been confusing valve overlap with Lobe centers - that's the 102 degree number that stuck in my head. Turns out that the actual overlap is only about 44.8 to 51.88 deg. variable ( 7 degrees) versus 66.7 deg for a 1300 Duetto European Spec. Good news is that the VVT changes the lobe centers over a 20 degree range, 118 to 98 above 1650 RPM.

Now we have a four stroke engine here, so the lobe centers are referring to crank movement which is 2X the camshaft movement. On that logic the VVT should alter the overlap by 10 degrees, not the 7 degrees the Cardisc shows.

All this is a long way from the 90 degrees of Overlap that a hot Isky street cam had !

**papajam** · #8 (**permalink**) 12-01-2003, 05:42 PM

But which printed copy! This is getting confusing. Alfa Diass pub. PA3748, dated May '85 with supplements to Nov '87, is what's on the Cardisc cd. Maybe Alfa changed the VVT solenoid adjustment procedure? Or the procedure's different for the Motronic cars? Hmmmm.......
The Centerline specs are for the '80-'85 VVT and unfortunately, don't agree with the '85-'89 Alfa specs. Not to detract from Centerlines monumental efforts to provide this kind of info but if push comes to shove, I'll go with Alfas specs.
The first pic is the valve timing specs which show the valve overlap to be (about) 45 - 52 degrees. Certainly not the best on the planet but not the worst either.
The second pic is the cam timing. Just when I get used to lobe center timing marks, the marks are changed to angular degrees. Sheesh!

**papajam** · #9 (**permalink**) 12-01-2003, 05:43 PM

...cam timing marks.

alfa_corse · #10 (**permalink**) 12-01-2003, 06:41 PM

Quote:

Originally posted by papajam
But which printed copy! This is getting confusing. Alfa Diass pub. PA3748, dated May '85 with supplements to Nov '87, is what's on the Cardisc cd. Maybe Alfa changed the VVT solenoid adjustment procedure?

gotglasses · #11 (**permalink**) 12-01-2003, 08:58 PM

Fabulous PapaJAm! Looking at those cam duration numbers you can see why the later 2000cc motors don't have the free revving quality of the early - pre- emmissions motors. I put webers and euro cams in my GTV 2000 and it drove like a different car - actually it revved like my GTV-6 !

Back on the subject of VVT adjustment and the various shop manual interpretations. These Alfa manuals are pretty terrible. In the past I would use the Mitchell's and found them better. Factory Shop manuals always seem to pre-suppose that the reader attended the annual three week course where they tell you all the little secrets they should have put into print in the first place.

There are some issues that the manual does not address. Like -should the car be running when these adjustments are made ?. The tool that is referered to probably is used on a cold engine. When my engine is off there is a gap. When running there is no gap, but movement can be seen when engine is revved.

I'll try it both ways and see what happens. Thanks again!!

gotglasses · #12 (**permalink**) 12-01-2003, 09:20 PM

The performance cam that International sells is starting to look very attractive to me at 290 deg duration with 73 deg overlap and 11 mm lift. The VVT should allow a decent idle with this. Anyone have experience with this on L-Jetronic cars?

**papajam** · #13 (**permalink**) 12-02-2003, 06:54 AM

Well, well well!! I'll be dipped in chocolate! While the cam and timing specs I posted did come from the PA 3748 manual, the VVT solenoid adjustment procedure did not. Not knowing that there is more than one manual on the cardisc, I just searched for a VVT adjustment procedure. After actually READING the fine print, the procedure I found, and posted, is from manual PA8777 dated May 1990! That would be for the Motronic cars, wouldn't it?
Thanks, alfa_corse, for teaching this old dog a new trick; read before barking!

I guess the questions are, what do you set the high performance cam timing to with a VVT? Is the cam compatable with the VVT? If you toss the VVT in the bin, what happens to the emissions?

gotglasses · #14 (**permalink**) 12-02-2003, 09:23 PM

Hi papajam ! New York State tightened up the emmissions standard this year to 50% of previous years. Very few older cars pass now without new converters. This is one reason we are seeing decent cars in the wrecking yards. One of the reasons I bought my car was that it did pass this year and has a fairly new converter. Since my car is not old enough for Historical plates I would have to be tested in NYC area - and would probably fail after any mods. Cars registered outside the Metro area, like mine, don't get the full dyno treatment but they are looking to see if the emmissions equipment is there. If it looks modified , or has a test pipe mounted, you will fail and have to bring it back in factory condition in order to pass. This rules out most "exciting" mods. I also would not brag to the mechanic about having fitted a "racing cam".

I don't believe that my inspection station would notice a missing VVT but I'd rather not tempt fate. I'd like to get more power but will keep all the emmisions stuff functional. Is a performance cam a way to do it?

So here is the IAP Cam-
Item No. Description Price On Hand
92644000 Camshaft Set $375.00

Installation Notes
Fits fuel injected engines with variable valve timing
Not legal for highway use in California
11mm of lift, valve timing is 30/80-67-43, duration is 290 degrees
overlap is 73 degrees.

Oh well - it's still not a slug and it does idle very smoothly in stock form.

**papajam** · #15 (**permalink**) 12-03-2003, 05:33 PM

Actually, those cam specs look pretty decent for an 'emission' engine. I'd give IAP a call and ask if there might be any concerns about passing a state emissions test with these cams. And are the cams a stand alone performance mod? Or are additional engine mods recommended to be used in concert with these cams and would those additional mods, if any, affect emissions or hurt the cat?