kstills

Hey there,

The red line on these engines is around 5800-6200, somewhere in there, no?

What is the limiting factor for running higher rpms with the 2v engines? Is it the lower end, valve train or both?

Does the 4v setup rev higher, and if so why?

Thanks in advance.

72MachOne99GT

As far as I know, the reason our redline is so 'low' (compared to a cobra or 5sp mach) is the head flow.

The heads on our cars don't flow well enough, especially up high. So the cam is (not sure the word here) 'designed'? to make the most effective use of the rpm range where the engines making good power.

Since there's little to no need for a 6500-7K power band in our cars, the cams and valve springs arent really designed to sustain rpms that high.

That's most of it in a nutshell. Obviously as you can tell, I don't have all the specifics and such, but basically a lack of necessity is why we redline where we do in our 2V motors.

If I made any mistakes, somone PLEASE correct me.

Trmachuno

Mach's and cobra's rev to about 7k rpm.

MJH78

Well a Cobra is DOHC and 32 valves. might be the heads, I don't know, but when you have 32 smaller, lighter valves compared to 16 heavier valves, the 32 lighter ones are obviously going to function more efficiently. you can put 32 valves in a SOHC engine, but it's not ideal. weight of the smaller 32 valves combined might be close to the weight of the bigger 16 valves, but you can't really operate the 16 heavier ones at the same RPM as you can the lighter 32 because they are heavier and the springs would be stiffer and such.

72MachOne99GT

On a V8, that would be one f-ed up looking camshaft.

I'm not sure, maybe you're rigth mjh, but are the valves in our SOHC engines actually larger than the DOHC ones?

Seems like that would defeat half the purpose, but I don't know for sure. As I said in my first post, most of that is just what I've read and learned from this site and other sources.

35thAnni99GT

I don't think so. It would look like 2 sets of regular pushrod cams. You couldn't fit that many valves in this tiny head though.

2 valves of smaller size vs one larger valve is actually not defeating the purpose. The actual valve "curtain" (ie - surface area x lift) is much larger with the two smaller valves. For example a stock PI head vs a "C" head, the "C" head with a .450 lift cam covers the same amount of curtain as the PI head with an .800+ lift cam, IIRC.

ZW99GT

Plain and simple answer, you won't be making any power higher than 6250(stock rev limit), so why bother? The more RPM you turn, the more stress on the engine. So why put that extra stress on it if you it's gonna make you slower?

35thAnni99GT

What if we now bring a set of Comp Stage 3 cams into the equation. With a higher (7100 RPM) shift point, assuming you've replaced the valve springs, why not?

72MachOne99GT

No, I understand that, I just was not sure how close in size they were etc.

I understand that two smaller intakes will be larger than one big one.

I just never thought about the actual sizes of the two (dohc vs our sohc)

as for the 32v sohc, how messed up it would look in OUR heads is what i was getting at.. it'd be a mess

35thAnni99GT

lol have two .5 inch valves per intake/exhaust. Sweeet.