sublime

Just to show whats the difference: 9A and most PL engines have a head with intake ports like this: The intake ports of an KR usually look like this:

Sorry for having kept you waiting.... As modifing an exhaust camshaft to an intake camshafts involves adjusting the timing, I guess something went wrong. The exhaust camshaft is far from beeing aggressive. Even a Schrick 260° is somehow mild, it provides widespread torque an peakpower increases smoothly around 2500-3000rpm. But talking about 16V, using a 1.8l PL it makes a big different if you use KR ignition controller oder PL ignition controller. If you use KR modell, you loose knock controll, but you gain a far more ballanced power output. Using the 2.0l 9A Modell, a modified Chip does the job. To answer your question, mildly open the intake ports at the bottle neck, but driving a 1.8l it isn't necessary while using an exhaust camshaft as intake. I whould advise you reconsider replacing the mod. intake camshaft by a mild sportscam or checking again if the modifing job has been done propperly. Oh, damn, i just realised something. Of course I always spoke of the 1.8 KR cylinderhead, whose intake ports are somehow quite well contrukted. While having a narrow 2.0l cylinderhead, widen up the ports isn't that wrong. But I whould advise going for a 1.8 KR head, I saves a lot of work. Greetz Chris

What LowG has said matches the experiences I've made so far. Generally, the way a port has to look like depends on the camshafts you're going to choose. The inlet port diameter behaves antiproportional to the air speed. Opening up the diameter means reducing the air speed at the same rpm. The optimal airspeed is reached at a higher rev. (Keep in mind, after reaching the optimal airspeed, burning efficiency (or the equivalent, torque) will start to drop and bhp rising will start to slow down. When torque is dropping faster than the rev, bhp starts to drop). While going for a mild street race camshaft (speaking of arround max. 268° and max. 0.45in of valvelift) it's good advice to avoid opening up the port too wide. I whould concentrate on optimising bottlenecks, as it is with the valveseats (get the 3-angle vlave seat cut, although you should get noticeable benefits with a 2-angle cutting job, without the last 5° cut) and the area arround the valveguides. The original vw head layout isn't that bad, at least the inlet. If you plan on using camshafts above approx. 276° and 0,49in valvelift (which I whould not recommend while using the original KE-Motronic/Jetronic), you can consider widen up the inlets. Those camshafts open longer and earlier and therefore need a greater air speed to be able to use those gas dynamic effects generated by the mass inertia of the airflow. Yes, on the first view, it looks like opening up the ports and reducing the airspeed is the wrong thing to do. But as the port opening results in an optimal airspeed appearing on a higher rev and the sharp camshaft pushing up the ideal airspeed even higher ('cause it needs those gas dynamic effects), the max. torque lies on a rev a lot higher. And as bhp is a product of rev and torque, this is the reason why sharp camshafts and wide inlets often lead to high bhp numbers. So where's the drawback? It the rev range below the ideal airspeed. It's way wider than the rev range on mildly modified engines. That's why those race engines need to be operated permanently in high revs. Low rev torque drops a lot on those engines (at least with OEM injection/ignition and intake manifold). The air is to slow and in addition to that, the intake valves close to late. So gas-fuel mixture is lost that whould otherwise be burned. It's a little complicate to explain without any pictures. For those who do have some experiences with engines I whould like to recommend the book "Four Stroke Performance Tuning" by A. Graham Bell. I've read a lot of books in the last years, but this is definitly the most detailed one and reads like Mr. Bell really knows what he's talking about. A short comment on a personal experience I've made: if you do not modify the outlet and use a very mild intake camshaft, even with modified intake ports (at least on the 1.8l 16V) you can go on without changing the OEM outlet camshaft. It doesn't effect the max. bhp a lot, just about 1-2hp and it slightly lowers your bottom rev torque up to mid range rev. Just my personal erperience. Greetz Chris