If a stock 92 LT1 makes 300/hp at 5000/rpm with a stock cam's maximum lift of 4470/4590 and 1.5 rockers where are they getting the rest of the rpm's to flow to 5k when the cam stop making power at 4xx

same scenario with the LT4 330/hp at 5800 with a cam's maximum lift of 4760/4790 just where/how do they get the difference in rpm's needed if the cam doesn't flow all the way upthere???? Unless rpm's are determined by duration rather than lift I have no clue!!!

 

Camshaft duration, and its relationship to the Lobe Separation Angle, are generally more indicative of where (at what RPM) the cam will make usable power, and eventually 'peak'. The camshaft's LIFT will usually be a product of what the cam manufacturer/designer feels is 'optimal' for the cam's application. They will take into account, of course duration, but also the typical capabilities of the engine family's cylinder heads (in our case the 23 degree head of a SBC) and what type of cam/lifter is being used (hydraulic roller, flat tappet, solid, etc.). This is an oversimplified explanation, but for the most part we are relying on the cam makers to grind us a good, usable camshaft that will work with our engine displacement and cylinder head flow.

Speaking of cylinder head flow, this is what we usually look at to decide how much lift we want, or need, our cam to have. But to keep things 'optimal' for a particular application (street, race, emissions compliance, etc.) we can only have as much lift as our duration will allow. This is a physical restriction based on valvetrain components and their geometry.

As for the maximum RPMs for different camshafts, the manufacturer can 'ballpark' the RPM range (based mostly on duration), but the actual RPMs and peak power will also be dependant on many other factors related to how the engine was built-- stroke and displacement, head flow capability, intake choice, exhaust design, etc. Changes to any one these engine specs can move max/peak power up or down in the engine's RPM range.
If one of your questions is "Will an LT1 engine's max HP peak at a higher RPM if one were to install a 'larger' LT4 cam?" The answer is "Maybe, just a little bit". In this case, the LT4 cam is not that much 'bigger' duration wise, than the LT1 cam. The LT4 cam's higher lift helps power, but affects RPM very little. The big difference, again in this case, is the LT4 head's design. The larger runners require greater engine speed (more RPMs) before it reaches its max power potential. Another by-product of this, of course, is more overall HP (330 vs 300). Conversly, though, you could install a camshaft that has noticably more duration (and lift) than either GM/LTx cams, into a LT1 engine that will increase HP, and cause this HP to peak at a higher RPM. However, once you go beyond the capabilties of the stock heads and 350 cubic inches, too much duration (and lift) become counterproductive, whether or not it increases the RPMs at which peak power is achieved.

 

I was talking to a forum member the other day who races a vette (don't remember the yr, but know it was an alum. head L98) in Super Stock class. He said the rules prohibit a cam w/more lift, but duration is not. He is running a custom grind w/250*/260 *duration at .050 and stock lift at .415"/.429", Stahl headers, 4.88's, and stock heads, and intake. It turns 10.83, but can't remember the mph. Obviously it is lightened to specs, and I don't know the CR but it has to be quite high. I can't imagine putting out enough HP or torque configured that way to turn those numbers. Anyone have any feelings or smarts to verify that it would be possible to do that, not that I am questioning him, but w/the stock intake and 113 heads, how could it flow well enough to turn in the 10's? I am baffled.

Rich K

 

Running Super Stock drag classes takes great ingenuity, and sometimes tons of experimentation and testing.
With that much duration on a TPI motor, you can bet it has a huge amount of overlap, but a relatively narrow, higher RPM powerband. With those 'trick' headers and big exhaust you can take advantage of potential exhaust scavenging with such a long duration, narrow LSA cam. This can help with the somewhat restrictive TPI intake, and extend the engine's powerband/RPM slightly. I would assume he is running an automatic with possibly as much as 4,000 RPM stall speed. He can probably now make power up to 5,500 RPM, and might shift the transmission around 5,600-5,700 RPM. With those screamin' 4.88 rearend gears, and the high stall convertor, he is able stay in his "relatively narrow powerband" after each shift. The long duration camshaft is only good for making power in the higher RPMs, so as long as the engine stays in these higher RPMs, he will continue to accelerate the car via the aggressive gearing. The extremely long duration (for the mild lift requirements) allow the small heads and intake to flow the maximum amount of air they are capable, relying on greater 'valve open time' instead of greater valve lift. An unported stock head will benefit very little from a higher lift camshaft, as opposed to maximizing duration.

This specially ground cam is obviously only good for a very limited race application, and would not idle or supply sufficient vacuum for a typical street engine. These supposedly impressive 10 second times can be attributed to a lightweight car with maximum gearing, almost perfect traction and launch technique, and just enough engine to last for 1,320 feet. A smart chassis set-up and an excellent driver is assumed for this type of racing with these fast times.

 

according to super stock class rules 2005/07 any flat-tappet cam can be used maybe he choosed to use the one you described plus he has the option to stroke his engine to 362ci as well but as far as the heads there are some vortec bowtie large port iron heads allowed by ssclass capable of supporting well over 600hp and at 3200lbs limit it is possible to turn 10.81 at 126mph in a fairly track only car as 500hp mentioned. by the way thanks 500hp for answering my question