stupid question but when you go on about a na or vis whats the difference

Vis is simply the later version of the 20v N/A - it's essentially the same engine, but it has a VERY different intake system and ECU

There are also a few trim/cosmetic differences, but I'm not particularly clued up on what they are

Also a minor variation in power, 147 for the N/A and 155 for the VIS, IIRC.

Plastic cam cover.

The Intake system is different which allegedly gives better torque low down and more power further up the rev range you might want to read this http://en.wikipedia.org/wiki/Variable_length_intake_manifold

Variable inlet systems causes the air intake (plenum) to shorten its path from the intake trumpet to the valve bores, again when the engine reaches a pre-defined RPM. This works on the principle that the air intake length is a tuned pipe that when operating at its ideal frequency-in tune with the valves, will allow a smooth and even air flow, and will assist with filling the cylinders efficiently. This works in a similar method to the tuned exhaust system on all modern cars, where the exhaust system creates back pressure to pull spent gasses from the cylinder bores.
The variable intake system uses the cone inside the airbox to reflect negative pressure waves back down the inlet. These waves are used to assist in filling of the cylinders. the variable inlet allows this to take place at different engine speeds.
The notable effect that these two devices have is that the engine will have a linear power deilivery from low RPM up until the red line, without the lack of torque at low RPM, and a kick in power at higher RPM, that is typical of multivalve engines as they come "On cam". (Taken from http://en.wikipedia.org/wiki/Alfa_Romeo_Twin_Spark_engine#Variable_Inlet_Control ) but same principle I believe

4200 rpm the VIS should kick in

20v VIS


20v NA

I thought that was when the Cam Variator switched?

Cam variator operates much lower down rev range certainly well before 2K.
Inlet changes over approx 4-5 K, mine seems at the higher end of this range when you watch the actuator. Joe CC did a really good write up with pictures on the insides of the inlet manifold, worth a search.

Basically VIS feels a lot newer to drive (IMO) compared to NA with the NA feeling a bit more raw, not a bad thing though.
Trim and appearance wise they didn't change to mid 99 so only way you'll spot an early VIS is by lifting the bonnet.

Here's a photo of the VIS system off an Alfa 1.8 Twinspark.


I've put a red circle around the bit that does the work.
It seems to be electrically controlled and vacuum driven.

Underneath this thing there's a rod that moves in and out and connects to a cam type thing that presumably adjusts the length of the inlet tubes.


I'd agree with everything that has been said about the Fiat vis being really noticeably sweeter through the rev range. There have also been comments that Alfa might have switched to a plastic cam cover and overcover to make everything a bit quieter. It is definitely nice & easy to work on.

The only issue with Vis models is that I don't like the wheels. Best to get a set of 16" off a 16VT for a real classic look (all IMHO)

Agree with that one. The original 15" VIS alloys have a rather 'weedy' look to them. I grabbed an old set of 16VTs and had them powder coated for some beef and sparkle. Hooray.

I thought you'd have a set of the later 4 spoke ones on yours which look (IMHO) pretty good. Got a set of those in the shed I'm going to refurb for the next set of tyres, I'm happy with "weedy" 15's