Dyno results
After completing the air box mods and fitting the exhaust system I had the engine output measured on the rolling road. The data showed about 133BHP at the flywheel, 101.5BHP at the wheels and a peak torque of 129 lb-ft. This confirmed that the engine was in healthy form.

Since the air box modifications had produced little noticeable change in power I started to wonder where the restrictions were. It's already known that modifying the inlet valves/head can yield up to 12% gains. After that there are three suspects: air flow meter (sprung flap design), throttle body and inlet manifold. The throttle body has a diameter of approximately 58mm which is slightly larger than the 56mm value given by A Graham Bell in his book "Modern engine tuning" as being suitable for 150BHP. So that's probably OK. The spindle can be flattened off to gain 2-3% extra there. The inlet manifold is a strong suspect since the Irmscher manifold is available. The air flow meter is a major restriction, but replacing that with a hot-air meter would take some serious homework. The most elegant solution to the air flow problem is to fit a throttle body conversion and this might well happen.This entails replacing the air box, single throttle body and inlet manifold with 4 ganged individual throttle bodies, one per cylinder. The ecu is replaced with a competition item that uses the throttle angle and engine speed as input parameters rather than air flow and engine speed.

The results show a healthy 133BHP at the flywheel (spec is 128 or 130 depending on source) and 129 Lb-ft (spec is 130). The power at the wheels is 101.5BHP. I really wish that I'd had the power measured before starting on the mods. It might be that the modifications have lifted a sub optimum engine up to specification, or that they've had little effect. It's entirely plausible that the engine wasn't quite making the specified power, say 128BHP. Therefore I might have gained 4-5BHP.

At first I was disappointed with the figures. On reflection, however, I came to the conclusion that there were pretty good. Bill Blydenstein told me that 101.5BHP at the wheels was good. The rolling road people told me that these engines don't normally make the specification. Looking at the power curve, it's making more than 130BHP for a rev range of almost 1000rpm. That's a nice fat power band. And don't forget that the engine felt more lively as well.

There is a noticeable flat spot at about 3700rpm. It's noticeable when driving as well. Then engine picks up at about 4000rpm and from then on it really pulls.

There's a deliberate mistake in the graph. The torque at the wheels should be larger than the values shown. It should be multiplied by the gear ratio from flywheel to wheel since the wheels are turning more slowly than the flywheel. I used the flywheel speed to calculate the torque. It'll have the same shape though,

After a few months with the car at this output I learnt what it could and couldn't do. I went through a phase of thinking it wasn't fast enough. If flooring it all of the time it didn't seem lively enough, but when I backed off a bit I started to appreciate it more. It really is quite a rapid car. It was most noticeable when my brother took it for a test drive with me as passenger. It felt fast then as it pulled me into the seat. Still, could do with being a bit faster.

Whatever the results mean, at the end of the day I have a true 133BHP to play with in a good condition engine that runs fine.

From the graph above it would appear that this engine matches the 20SEH. However, its code is SER . The exact specification of the 1990-1992 performance Vauxhalls is a bit of a minefield.