[lovehamr]

Originally Posted by olddog

So the best cam choice for a turbo verses a blower is a bit different.

I only said that because of its use in this thread and think we need to be on the same terms if we are going to be understood in our technical usage. The term "blower" is commonly used to define a device placed on engines with a functional need for additional airflow. The term blower is applied to rotary screw, roots-type, centrifugal compressors and turbo-superchargers when utilized as part of an internal combustion, forced induction, system. What I mean is that writing something like this is kind of silly because a "turbo" IS a "blower" regardless of the colloquialism that a mag like HRM might apply at any given time. And here it is again:

Originally Posted by olddog

A twin screw compressor and a roots blower are totally different technologies. Note the names compressor and blower.
Twin screw compressors are used in industry to compress air, well over 100 psi. A roots blower cannot get anywhere near that pressure. Anything a roots blower can do, a twin screw compressor will do with less hp consumed and less temp rise in the air. Not to mention the compressor can generate pressures that the roots cannot get to.

Here again, the verbiage is misleading at best and wrong at worst. A supercharger is an air compressor used for forced induction of an internal combustion engine. Those methods vary but that IS what they are. I will agree that a twin rotor old style roots SC cannot match the efficiency of a Lysholm (twin screw.) But to say that it’ll do anything that an older roots type will do is equally wrong because the Lysholm, though capable of higher PSI cannot match the older roots in volume. And you only have to look as far as your own post to see an example:

Originally Posted by olddog

If this is an absolute fact in all circumstances, then why is Top Fuel running blowers?

I’m assuming that you’re referring to roots or twisted lobe roots types here. Of course they aren’t running Lysholms, turbos, centrifugal, sliding vane or scroll types. Of course there is a reason for that. The oxygen content of nitromethane enables it to burn with much less atmospheric oxygen and the cooling effect of all that fuel attenuates a good bit of the compression heat. For those so inclined here you go: 4CH3NO2 + 3O2 → 4CO2 + 6H2O + 2N2. In short, what they need is a whole lot of intake charge moving fast and at boost pressures approaching 75psi. That’s right, 5.0 bar.

All that stuff is not really applicable to us but the simplicity of the design IS VERY applicable as the manufacturing of a roots type is easier and thus less expensive than any other type. In this case, what are we talking about? 15psi and up for expected boot pressure? Or are we most likely talking about 5-10psi? If it’s a street car but you’re still going for the ultimate power or something like that then there are other choices. However, if it’s a street car and you are looking at moderate boost levels (say 7psi or less), on an otherwise unchanged engine, you can still expect a 40%+ increase in power with an old reliable roots without breaking the bank. Then your back to “will it fit under my Cobra’s hood?” I know a roots would never fit under my BB Cobra’s hood.

But on a SBF? Hmmmmmmmmm, could be……………

As a side note, I may be jaded because I just put a TRD roots type SC on our newest Toyota truck and the difference is amazing!

Steve