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Discussion Starter #1
I’ve been playing with my 88 Quadrifoglio. The blue pull is with the variable valve timing working. The red pull is with the variable valve timing disabled.

My plan is to use a RPM activated switch (set to normally closed) that will turn off the VVT at 5000rpm. Hopefully that will give me the best of both worlds.

The car is all stock except I added an additional inlet to the air box bottom.

Aaron
 

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It is interesting that the AFR is very well controlled from 3000 to 6000 but then it goes too rich. It looks like L-Jet is not limiting power at at higher rpm and that it can handle more air flow.
100 Hp at the wheels is not bad for a nearly stock motor - a little over 120 at the flywheel.
 

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Discussion Starter #5
I'll be following this with interest.
Why the extra hole in the air box?
For more air. I noticed the stock inlet was pretty small. So I added a second one. It actually picked up 5 whp from that! I’ll try to get a picture tomorrow.

Aaron
 

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Discussion Starter #6 (Edited)
What is the advantage to switching off the VVT?

What happened to the A/F measurement during the 'red pull'?
We think my sniffer think is clogged up.

My car actually makes better power up top with the VVT off, If I can get a working rpm switch I can get the best of both worlds.

Aaron
 

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Trained (ex)Professional, , 1953-2018 RIP,
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What is the advantage to switching off the VVT?
Switching off the VVT maintains a retarded timed intake cam, which decreases valve overlap which can increase high end power (at the expense of low end).
Advancing the intake cam timing via the VVT increases overlap which can aid in low/midrange power (at the expense of high end).
 

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Discussion Starter #10
AFR all over the place... way to rich up high, bit lean midrange.
You probably didn’t notice that is run#55. I’ve been trying a few spring settings on the AFM. Those AFR’s aren’t getting any better than that (on the stock ecu).

Aaron
 

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I have just completed the setup of my new motor which included making multiple runs with three different exhaust timings - 102, 105 and 108 and four different intake timings - 99, 102, 105 and 108. Intake at 99 provides the most overlap, good top end and the weakest low end. 108 gave best driveability at 2500 - 3000 rpm and best AFR control up to about 4800 but was slowest from 4000 to 6700 rpm. In my case 105 was the best compromise but 102 was very similar.

Aaron, are you using the stock one piece exhaust manifold?
 

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Replacing the stock exhaust manifold with a two piece is the best bang for the buck if you are looking for better performance and if you do not have to pass an emissions test. Spiders (and GTV's, etc) built up to 1974 and after 1989 (I think) have the more efficient manifolds.
 

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Richard Jemison
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VVT & cam timing

With the VVT "operative" using an RPM switch to engage it, you should try setting the initial timing to a position just a bit retarded of the factory mark. (1 notch on the sprocket moving the cam reverse of normal rotation) Advancing it at 3000 will result in a lobe center of 102 instead of 99. This will optimize the Valve events on the intake side. (reducing overlap increasing Torque and fuel use)

If the exhaust is timed at 102, move it one hole clockwise to 105 degrees (to 104-105 LC) This will lengthen the power stroke improving Torque & HP.
 

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Discussion Starter #15
Some of you asked about the intake modification. I used about a 2.25 Hole saw and drilled another hole to the side of the original one. Then I addd some flexible hose I had. It’s leftover from a freestyle jet ski project, but I think you can get it at a swimming pool supply store. I’ll get the before and after dynos next week, I forgot to grab them off the dyno computer. But it was a 5 whp gain!!

The first picture shows the front of the airbox from above and the second pic is look at it from underneath the front of the car. This website is rotating the pics 90 degrees, the inlets actually sit on top of each other, not side by side.

Aaron
 

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I have a few questions...

1. What is the sniffer thing you thing is plugged, and what makes you think that? (from post 6)


2. You say run#55 and that you were trying different AFM settings (post 10), so the extra 5 hp is a combination of the extra hole in the air box and the non-stock AFM setting? Can you advise what you have it set to?

3. Do you know what your cams are currently set to?

Thanks
 

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Discussion Starter #17
1. It’s part of the dynojet wide band o2 sensor. It’s a sample tube that you slide up the exhaust as far as you can. It uses shop air and a Venturi to create a suction that pulls exhaust across a remotely mounted wide band O2 sensor.

2. Run 55 was probably my last of the night. I did the AFM adjustments earlier (the wide band was still working then). Basically running the spring a little tighter to lean out the mixture a little.

3. I don’t know. I would assume stock.

I’ll be away from my shop until Wednesday. I’ll get some more of the dynos then to show my progress.

Aaron
 

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Ah. Ok. The sniffer is part of the tester not the car.
Yes. Would be interesting to see other info.
Also curious to hear cam settings.
Happy holidays!
 

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Richard Jemison
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Cam timing

Advancing the intake cam timing via the VVT increases overlap which can aid in low/midrange power (at the expense of high end).
Jim, actually that`s backward.

On the intake side, advancing the cam & increasing overlap reduces the low end fuel load, (out the exh during overlap) reducing combustion pressures (reducing torque) and resulting in late closing of the intake valve which increases reversion into the intake tract and as Jim Steck has pointed out results in a already fuel loaded mass of air passing through the Aux-venturi results in a overly rich mix that shows up on the AFRs at about 3000-5000 RPM depending on intake design.

Retarding the intake cam timing results in less overlap, (more fuel/air mix,in the cylinder, more combustion pressure (torque (& HP) both at lower and higher RPMS.

On the exhaust side, retarding the cam say to 102 LC, will open the exhaust valve later which lengthens the power stroke (more torque/HP).

BUT the factor that cant be ignored is cam lobe design. If the lobes are Typical Alfa factory cams with lots of overlap the cam timing events have to be timed differently to maximize the valve opening where flow is best, with the timing of the piston speed/position so that valve lift is optimized with the draw from the vacuum of the piston`s downward movement.

In the world of single cam engines where intake and exh lobes are fixed on the cam, the rule of thumb is to advance the cams "Centerline" (Center of the cams Lobe Separation Angle (LSA, which when correctly matched will have a larger LSA for long runner intake systems and smaller for short runner systems)
Typically below a 103 LSA (Int LC + Exh LC divided by 2) is considered extremely tight. Most cams built today have Much larger LSAs, 105-112 depending on the lobe design on both and particularly the ramp rate (opening speed the valve.)
That`s why when I suggest abandoning the old factory specified LCs of 102/102 for 104/104 or 105/105 owners report both better power/torque and overall HP.
All my cams typically are best in the 105 LSA range, with LCs of 104/106 or 105/105 etc. depending on lobe & application.

A 99 LC on these VVT engines isn`t getting the optimum from these motors, The VVT is a Emission designed unit with too much advance built into the device. They can be modified with shims to reduce overall advance degrees (from 7 degrees to less advance)
But Idle to 1500 RPM is the target emission point being addressed so they retard the int cam too much(as well as the exh cam at 102LC) to reduce overlap and then advance it too far, so the engine can make enough power to have a sellable automobile, that still barely makes enough power to pull a greasy string out of a cat`s a$$.0:)

Happy Holidays!
 
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