So just for general knowledge, if a camshaft rated at an rpm rang of 1000rpm-5000rpm, you would want a stall converter designed to lock at 1000rpm to math the camshaft so the engine will be able to push the car off the line without the engine stalling at low rpm under load correct? Thanks guys.

 

Alot of misunderstanding about converters. Assuming you are talking about a 700r4 you want 2,400-3,000 rpm stall speed with lockup for a cam about that size. You want the engine to get quickly up into its torque curve, rise to peak HP relatively quickly and not drop much below peak torque when the trans upshifts.

 

Even more misunderstanding about camshaft "ratings".

Consider for a moment:

EXACTLY WHAT does that "rating" mean?

Does it mean that the engine's output is absolutely uniform across that RPM band? Is it ±10? Is it ± 50%? does it mean that the engine is simply CAPABLE OF running those RPMs successfully? if you took a cam from one mfr that was "rated" "1000 - 5000 RPM" and one from another mfr that was "rated" "1500 - 5500 RPM" would there be a difference? Which one would be "bigger"? can you be sure? do you know?

Don't feel bad; I don't either.

They're AD COPY. Nothing more. Intakes are even worse; some one of those I've seen says, "idle - 7000 RPM". Really???

If an engine produces the same torque at 1200 RPM as it does at 2400 RPM, then it's producing twice as much HP at 2400 RPM as it is at 1200, since HP = torque x RPM x a constant. And, since HP is the time rate at which the engine is producing energy, that also means that it will accelerate the car twice as fast, all else equal.

THAT is the first reason you would want a higher stall converter.

The other reason is, if the camshaft is designed for high-RPM power (long duration) then it extracts a penalty at low RPMs because the valves essentially "leak" compression and render it inefficient. So it's entirely possible that an engine can produce ALOT more torque at some higher RPM than at some lower RPM, in which case, having a converter that pins the RPM down low, will force the engine into a band of RPM where it struggles to produce any meaningful power at all. OTOH if the cam is designed for good low-RPM efficiency (short duration) then its torque curve will fall off rapidly starting at some RPM, which if the car's gears and converter try to force the engine into THAT RPM range, no meaningful power will be produced either... think, a stock LG4 with 3.73 gears, where the car will launch like a bat outta hell but takes 2 miles to pass a semi on a 2-lane highway at 55 mph because it doesn't produce any more power when you shift it down than it does in high gear. The downward-sloping torque curve resulting from peak torque coming at some low RPM means that the engine doesn't benefit from running at the higher RPMs.

Stock stall for the converter in these cars is in the 1450 - 1600 range. Too low really, having been designed for gas mileage and emissions and such as that, as much as for "performance".

A cam "rated" for "1000 - 5000 RPM" is going to be pretty much about like The RV Cam. Peak torque is probably going to be at around 2600 - 2800 RPM and peak HP no higher than 4000. Which means the car will probably go the fastest on the drag strip with about a 2600 RPM converter and shifting at around 4000 RPM or maybe just slightly higher depending on the spacing between gears (in a 700 that might mean for example shifting at 4500 from 1 - 2 and 4200 all other gears). But without knowing what cam you're actually talking about, it's difficult if not impossible to cut through the ad copy to get at the underlying facts, if any.

 

Another thing too, is the "rating" is based off what ever car/weight that the manufacture uses for their benchmark as stated in this video by Boss hog.


As stated above, there are many variables that affect the "rating"