boost gods come on in!#$#$#$

[88stangmangt]

ok i am haveing a debate here................................me and 92greengt are arguing about motor combos. I say that if a motor is built with a boost cam to max out at 5500 being the end of the power band(which is my combo).................then your S/C should be at full boost well before that..............he says that if you rev if higher your gonna make more boost....................im saying and maybe im wrong but physics and all the pulley crap we learned about in middle school That once it is done it's done.............now i can see geting maybe 1psi more with more R's but noting worth puting that much stress on the motor to get it right? 12 psi pulley maxed out is maxed right whether it be at 5 or 7k so reveing the piss outta a motor isnt gonna help. yes your gonna be pulling air faster but that doesnt mean your gonna make more boost since the pulley isnt geting any bigger.?????

 

[BlackFox5.0]

I'm confused with what your asking... The faster the blower spins the more boost you get. eventually you will overspin the blower, and it will become inefficient at some point, where, depends on the supercharger.

 

[88stangmangt]

shouldnt that depend on the blower wheel cause what im saying is once you have spun it out thats it its done so if it can be maxed at 5500 why go to 7k?

 

[92GreenGT]

When we were talking, here is what I was trying to tell him and he wasnt agreeing with me.

If you put a 7" crank pulley and a 3.33 blower pulley on, and you shift at 5500rpm and say it makes 8psi. If you had the ability to spin the engine past 5500rpm it would make more boost, thats what I said and he doesnt agree with me.

 

[BlackFox5.0]

Sure it would, but it may not be efficient, and if it's overspinning you risk the chance of killing the supercharger. A supercharger continues to make boost the faster it spins. Just like a turbo would if it didn't have a wastegate.

 

[NightStalkersSO]

Yeah, you're both right. So stop arguing, hug, and go crush a turbo neon!

 

[VG30DE]

Agreed, my 6psi pulley made almost 10 psi at 7100 rpm with the old combination I had in the lincoln, if you keep revvin, it keeps boosting, so your friend is right, if the motor maxxed higher, it WOULD in fact benefit from increased boost and probably run faster down the 1/4.

 

[92GreenGT]

Yeah, we know that. But I wouldnt have a worry with a 7" crank and a 3.33" blower pulley over spinning say an S-trim if it was revved to 6500rpm.

He just didnt think it would make more boost.

 

[VG30DE]

Yeah, you're both right. So stop arguing, hug, and go crush a turbo neon!

LMAO thats awesome
Stupid neons.

 

[BlackFox5.0]

With a 7" crank, and a 3.33" supercharger pulley and shifting at 6500rpm, your impeller speed would be 47,140RPMs The V-1 S-trim maxes out at 50,000RPMs

The V-2 would be spinning at 49,189RPMs, and maxes out at 53,000RPM

If you really need to spin it that fast I would suggest a T-trim as will have less heat, and more power. At this point it's more efficient to use a T-trim.

 

[92GreenGT]

I will never buy another Vortech. Cough*Novi 2000*cough.

But yeah, I know what your saying about that. He just wanted everyone elses opinions.

 

[SmockDoiley]

The faster the blower spins the more boost it makes. A D-1 is rated to make up to 32 psi, but if you get a 14 lb pulley it will get around 14 lbs around 6000 rpms. If you could pull the motor to say 10000 rpms then you would be making more power. The bigger pulleys, just make the boost spool up slower so you dont make too much boost.

 

[Michael Yount]

Any centrifugal compressor will make more boost with more speed -- but only to a point. At some point you'll reach the stall speed of the compressor wheel design, and then both boost and flow will decrease even with increasing speed. There are limits, and they are determined by the design of the compressor wheel. Turbochargers can have the same issue on both sides of the unit - the exhaust side, or the compressor side.

 

[RydeOn]

92GreenGT, did you put money on it, because you are right. Ive made 7 psi on my car just by revving the piss out of it to 6200 RPM. As long as your blower ends up turning under the max RPM, it will make more boost the higher it is revved

 

[88stangmangt]

Any centrifugal compressor will make more boost with more speed -- but only to a point. At some point you'll reach the stall speed of the compressor wheel design, and then both boost and flow will decrease even with increasing speed. There are limits, and they are determined by the design of the compressor wheel. Turbochargers can have the same issue on both sides of the unit - the exhaust side, or the compressor side.

exactly what i was saying................my cam is set for only 5500 rpms so between 2200 and 5500 i should be able to reach the ful boost and then some.............and there after it is gonna fall off.................i think it is a decent boost cam burnt by ED.

 

[Michael Yount]

88 - it's may be more complex than that; even though the cam's naturally aspirated peak may occur around 5500, if boost keeps increasing above that rpm level, boost my push the power peak higher than 5500. I think you and your buddy are trying to generalize things that can't be generalized, uh, in general.

 

[Daggar]

So....now how does it work with a roots blower then. Most of them are making full boost by less than 2000rpm. But spinning them to 6000rpm doesn't increase the boost reading, yet the addition of a smaller blower pulley will increase boost pressure. What gives?

Roots type supercahrgers WILL make more boost at higher RPM. Up to their limit. About the only difference is that screw type blowers are positive displacement. Boost (rated in psi) is gained by the ability of the blower to DISPLACE more air. When you overcome the engines ability to take that air in then that's when you see the pressure increase. Displace more air into the same engine (by running it faster) and the pressure gets higher and higher to the limit of the blowers ability to move air volume.

 

[Gearbanger 101]

So....now how does it work with a roots blower then. Most of them are making full boost by less than 2000rpm. But spinning them to 6000rpm doesn't increase the boost reading, yet the addition of a smaller blower pulley will increase boost pressure. What gives?

 

[Michael Yount]

A positive diplacement type blower (often called roots type) "pushes" a relatively constant volume of gas from the inlet to the discharge at a relatively fixed pressure differential. Increasing the speed increases the volume it can push, but the pressure differential is largely a function of the physical size of the components - rotors and case size. That's why PD blowers produce boost (pressure diff) at low rpm, and why the boost pressure varies little with speed. They don't internally compress the air. So flow through a PD blower is relatively constant regardless of pressure difference, for a given speed of course. Installing a smaller pulley increases the rotating speed of the 'pump' - and usually this results in a pressure increase, but not nearly as dramatic as what happens when you increase the speed of a centrifugal.

A centrifugal compressor is nothing more than a rotating air-foil. It compresses the air in exactly the same way that an airplane wing creates lift. As speed of the rotating foil increases - both volume and pressure increase -- until the airfoil stalls. Then both pressure and flow drop off.

Clear as mud?

 

[92GreenGT]

True.

But this is becomming to technical, yes the blower can be maxxed out and over spun. But we are talking a 3.33 blower pulley and a 7" crank pulley here. I dont see being worried about over spinning a S-trim with that setup. All my point was, if it makes 5 psi at 5000rpm, with the same pulley setup it will make more boost at 6200. That pulley setup will NOT overspin a S-trim. Thats what this whole thread was based upon.