Mr.FRU-T-Pants

...to be able to tell me the differences if any, and specifically, how they move the power band/boost in a 20v motor versus the stock cam. This might be one for you, James...not sure.

Thanks,
Patrick

squidix9

I think I have the Lehmann cam in the Coupe, but I'm not entirely sure. The PO couldn't give me a lot of details when I bought it.

I called John B, but he was rather vague too. It's supposed to be an identical twin to his Coupe.

For sure I've got a Lehmann ECU.

I haven't done a teardown yet to do a complete inventory of what's inside.

Mr.FRU-T-Pants

I guess you never had another installed to which you could compare it.

squidix9

No, both cars are VERY different

Mr.FRU-T-Pants

I know, I meant in the CQ.

fusilier

It didn't have numbers on it, but It was visually inspected by a friend who knows cams better than me who could tell it wasn't a stock cam and he's seen 7As, 3Bs and RS2s. Totally useless info, but thats all I know.

Mr.FRU-T-Pants

Worth a shot...thanks, anyway.

Rich L.

But my understanding is that the RS2 and 7A exhaust cams have different lobe shapes to change the valve timing and affect the overlap and duration they have the valves open. The AAN and 3B motors' stock cams are setup to have no overlap, meaning the exhaust valves shut before the intake valves open. This prevents any unburned fuel from escaping the cylinder and hurting emissions and fuel economy.

What the RS2 exhaust cam does, and the 7A cam to an even greater degree, is leave the exhaust valve open longer and perhaps even leave it open a tad after the intake cam opens. This increases flow through the cylinder, getting a little more old stuff out and a little more new stuff in. This hurts low RPM torque while it helps high RPM horsepower. Not exactly sure why, but it's similar to using larger intake runners, again this allows more air at high RPM but makes the air move slower at low RPM, same affect of less torque but more power.

Anyway, that's a very rudimentary explanation and I hope it makes sense. I'm running a 7A cam and expect this to be making my boost come on a little bit later, higher in the RPM band, but making the horsepower curve a little bigger and a little higher in the RPM band. I have no proof of this myself, but it's what my engine builder explained to me from his significant amount of testing back in the day.

HTH,
Rich

P.S. That engine running, Man? How's it go?

M1LL10N

I don't have either cams nor a 20vt, but what you said makes perfect sense.

Mr.FRU-T-Pants

I guess I was more after a comparo between the two cams, Lehmann and RS2. I have both, and I'm trying to figure out if I want to use either.

Odd, though. I've heard that the RS2 cam lowers the boost threshold, and cuts power up top. Makes sense to me since the RS2 was/is known for quick low mph acceleration. Javad elaborated a bit when I asked him. The overlap bit is consistent with what he said, though.