What are you trying to do with the car, what head do you have, what carbs, what exhaust manifold (single or dual downpipe), what size exhaust? Also, manual or (unlikely, but you never know) automatic trans?

Stock cam on most B18's that came to the US was the 'C' grind, we were spared the 'A' grind that accompnied the single carb low end models they sold in Sweden. 'C' cam is a rather low RPM cam, won't pull much at higher RPM's, but really, if you have a single downpipe manifold the engine isn't going to flow at high rpms anyhow.

'D' cam was the B20E injection cam, but it didn't really have anything to do with injection. it was based (I've heard) on a 60's B18 rally cam, and the intent of putting that cam on the injected motors was marketing inspired - they needed to put an expensive fuel injection system on the car to meet emissions standards, so to help get the consumer interested in paying extra for it, they included some non-fuel injection performance tweaks (larger intake valves, the 'D' cam) to make more HP to accompany the injection.

With a dual downpipe manifold and a non-restrictive exhaust (my PV came to me with a 1.25" ID exhaust system on it - Midas special) and some SU's, and a manual trans, a 'D' cam will nicely perk up a B18. With very little change in low rpm power, it will extend power up into the 4500 - 5500 rpm range. So you can accelerate in each lower gear a little longer, makes it just feel livelier and peppier.
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'63 PV544 rat rod, '93 Classic #1141 245 (now w/16V turbo)