That cam was my go-to hot street cam for a 1.9/2.0 engine. But it idled a bit rougher and needs higher compression to work well.Just saw PJ's 2.4L head for sale on FB and he specs a cam with split specs of 246/242 duration at 0.050", lift of 0.459 intake and 0.435" exhaust, and LSA of 108 which is lower than stock Opel of 110. Opposite the 112 LSA recommended above. Why would this be?
Did you document that anywhere?
This is what we (John Warga and myself) did for our cam gears (and Sterling Rempel's), photos are of my gear and engine. We are running the OGTS Combo Cam, (notionally 0.420 lift, hydraulic grind). Sterling and mine are set up with the 4 degree advance bushing (John's engine is a stroked 1.9 to 2.4, and still a "work in progress"). To the best of my cam degree'ing ability. we both ended up a touch under 3 degrees advanced (after some block and head surfacing)Did you document that anywhere?
Again, it really depends.There is one thing in the info above in post #65 that is usually misinterpreted about a narrow LSA cam: the lower RPM torque band is better. This is only true about the lower end of the mid to high RPM torque band, around 3000 to 6000 RPM in many of these engines. This is where the exhaust scavenging is working, and is the main torque band, where the torque flattens out to within 90-95% of its peak value.
What this statement about narrow LSA cams does NOT mean is that torque at the low RPM's is increased. This would be typically at or below 2500 RPM for many of these Opel engines. This misinterpretation that gets made is that somehow a narrower LSA makes low RPM torque better. The reality is the opposite: a narrow LSA makes low RPM torque worse. This goes hand in hand with the rougher idle of a narrow LSA cam.
The reason that a narrow LSA cam has LOWER torque at low RPM's is that the exhaust scavenging effect dies off once your operating RPM drops below mid range. When that happens, the added intake reversion of the narrow LSA eventually reduces torque as the RPM gets low enough.
The whole way to see how torque works in any engine of this general design is first see how well the cylinders get filled each cycle. Whatever helps cylinder filling increases torque, whatever hurts cylinder filling decreases torque. When the RPM is high enough, exhaust scavenging kicks in and cylinder filling approaches 100%; this is reflected in a number call volumetric efficiency (V.E.) and V.E. is seen in the dyno charts for newer dynos. You will see V.E. approach 100%, and sometimes exceed 100%, in the main torque band of an engine, when the exhaust scavenging is in full swing.
Once the RPMs get low enough however, exhaust scavenging dies off, and then the valve overlap that increases with a narrow LSA, and that is the source of exhaust scavenging, stops being our friend and becomes our enemy. Reversion into the intake increase as RPM's drop lower and lower, reducing cylinder filling (and thus V.E.) and eventually it gets so bad that we end up with a rough idle.
The way to fight this die-off of cylinder filling (and thus torque) at lower and lower RPM's is to to increase LSA and decrease duration. Both of these have the effect of reducing reversion, which allows better cylinder filling and torque at lower RPM's. This is why stock cams and cams for low RPM operations like truck use typically have larger LSA and certainly have smaller durations, than cams in more race or race-like uses.
And if you care about fuel economy, then the same applies: you make the LSA's wider and keep the durations lower.
Our Opel engines seem to fall 'in-between'. With small displacement, the engine needs to operate higher 'up in the main torque band', especially with 70 mph RPMs being in the 3000-ish range, which is mid RPM's and where the exhaust scavengin is starting to work. So LSA tends to be a bit of a compromise for these engines... hence the production LSA ends up at 110 degrees, as opposed to a 112 or 114 LSA for a larger displacement engine.
Travis’ GT autocross car uses an F-306 cam with 106 LSA, and that‘s in a 1.9. As I recall from his chassis dyno run, he had 90% of his peak torque available from 2200-6000 rpms. It had a ridiculously flat torque curve. I drove the car and can attest it really didn’t matter if you were at 2500 or 7500 rpms, it pulled everywhere quite well.Well I have always found it interesting that I can drive my car in 5th gear at about 1500 rpm on level road and it pulls great with a LSA of 108. 10:1 compression, premium gas.
So based on your previous thoughts did it have a rough idle? You recommended a 112 LSA for a big streetable engine. If I understand correctly the wider LSA offers a smoother idle and should move the torque curve even lower?Travis’ GT autocross car uses an F-306 cam with 106 LSA, and that‘s in a 1.9. As I recall from his chassis dyno run, he had 90% of his peak torque available from 2200-6000 rpms. It had a ridiculously flat torque curve. I drove the car and can attest it really didn’t matter if you were at 2500 or 7500 rpms, it pulled everywhere quite well.