Coupe Head and Valvetrain

The Kit

In 1995 I noticed a pair of carbs and manifold on display at Obert's shop, boy were they cool. At the time I did not own an 850 but I had the plan of building a Coupe once I came across the right one. After looking at these carbs for a couple of months every time I went to Obert's I finally buckled and bought them. Obert acquired them during one of his many trips to Italy and had no history on them at all. I went to several Motto Guzzi and Ducati shops that specialize in Dellortos and even they couldn't identify them. It wasn't until recently that I finally tracked down some literature on the carbs through the Mirafiori Forum. I can't remember who it was exactly that sent me photocopies of the sales literature, so if you're reading this please send me an e-mail so I can give you credit for that! The ad claims "It gives an additional 10 HP, at least 15 HP if used together with a good steel billet camshaft." To my surprise the carbs were part of a kit. The kit came with the manifold, carbs, intake gasket, vacuum lines, throttle linkage and a cam with an unknown grind. I had the carbs on display until 1998 when I finally built the motor.

So according to the ad I should be getting at least a 15 HP gain from these carbs and cam. I haven't dyno tested the car yet so I won't go throwing final HP numbers out, but I will say that a 15 HP gain sure feels like a conservative number. This little motor pulls hard well past 7000 rpm.

The Head

The head is one of the biggest limitations in performance in an 850 (never mind it's size...). There are three major restrictions. The first is the incredibly tiny intake hole cast into the head. The second is the tight 90 degree turn that the intake charge has to take to make it's way into the cylinders. And the last restriction is that two cylinders share one intake port. It's possible to make some decent improvements on the first two restrictions, the last one you'll either just have to live with or drop a couple of dead presidents on a cool PBS 8-port head. Maybe some day. The valve sizes are stock, they are not the problem. Increasing the valve sizes won't buy you much given the previously mentioned issues.

Below you can see how Abarth killed two birds with one stone. Abarth designed an intake manifold that opens up the intake hole to nearly twice it's orignial size. It does so by widening it to look like a big smile. This in turn reduces the sharp 90 degree angle to make the flow considerably more efficient. I did the porting with a dremel tool using the intake gasket as a template . A fair amount of material was also removed around the intake side of the valves to get a straighter shot into the cylinder.

The Intake Manifold and Carbs

The key to all this is of course the intake manifold itself. The manifold is not an Abarth manifold but is of the same design. The manifold and throttle linkage have "ZIOTTI" cast into them. I can only assume they are the manufacturer.

And what better to go with this ultra rare manifold than a pair of sexy Dellortos. Yes, these are dual carbs. At first glance it they can be easily mistaken for a single side-draft. The carbs are FZD 30.24s.

The Camshaft

The cam came with the carbs and was unmarked. I had no idea what it was so my friend Charlie Rockwell offered to have it profiled. The good news was that he found that the cam was not hardened so he had it nitrided. Once installed I profiled the cam myself. Below is the cam data that I got back from Charlie. It's effectively a 275 degree cam and it works extremely well with the porting and carbs. Whoever put this kit together knew what they were doing.

The Exhaust System

The exhaust is an Abarth OT1000 system. There is a company in Italy that was remanufacturing these with the original tooling. The headers are 4 into 2 straight into the can. Coming out of the can are a pair of typically Italian chrome muffling tips. They system works, looks and sounds great, my only complaint being the amount of re-work required to make the system fit and not leak.

The headers and can are two separate pieces. Where the headers enter the can there is a slit pipe with a tightening bolt that is supposed to tighten around the headers and seal. It doesn't work. For starters, if you assemble the system and install it on the car, you'll find that the headers do not enter the can at the correct angle. The can is pressed hard into the oil pan. To remedy both the leakage and the poor fit I ended up having to bolt the can in place and then bend the headers into the correct position. The cute little clamp system was discarded and the headers were then welded to the can at the point of entry.

I bought the system from Obert, but to his credit he warned me that he had never installed the system personally. It turns out that OMP has bought the tooling and is now making the system. I checked it out at Obert's and noticed that even OMP did nothing to improve the poor quality and fit. So do I recommend the system to someone looking for the ultimate 850 exhaust? Yes, as long as you're willing to do some tweaking to make it fit. I am looking into having a local shop look into manufacturing a 'copy' of it for about half the price. This might be a better option

More to come.