A twin-screw or roots will always draw unless it has a bypass, positive displacement blowers don't have any other choice, and it's always going to try to compress whatever it can suck even at idle, that's why the use bypass valves to help prevent the charger from having to work at idle (take a look at the damn thunderbirds setup if you need). A centrifugal isn't compressing enough to even make a drag at idle, which is why almost none use them unless they're setup pre-TB.

 

Again not true. Take your positive displacment blower and put an absolute pressure gauge on both sides, intake and output. Now start the engine, read the gauges. What do you notice? The intake gauge has a higher pressure then the output gauge.
What does that tell you? The blower is not compressing anything, you might even say that it is being sucked along. In fact if it is loose enough it will be spun along without a belt.
The atmos pressure is higher then that below the blower.
These are not compressors they are pumps, althogh the screw has some internal compression. It is basicly a pump.
Why does it not make boost? because it is on the inlet of another positive displacment pump

 

hey richard, i think you've got this argument all tied up so why don't you get back to work on that supercharger so i can buy one NOW..... hehehehehe

 

I have more vacuum between the charger and the throttle body (with no bypass) than I do the engine and the charger, as I've said before. Without a belt (and bypass), you won't get enough air through the lobes for it to even run (and the twin-screw surely won't turn on its own like that). Have you even done what you suggest above? Ever even built a twin-screw setup? Better yet, have you built any non-centrifugal setups at all?

(Oh, and why do top dragsters with roots blowers keep being dragged into this? There's a pretty severe difference in a car driven down a track 5 times every other weekend than a daily driven vehicle that has to be somewhat tolerable)

Oh, and I've seen the Camden units produce boost revving in neutral, hell I'm sure if you went over to the rx7club and bugged Tech_Greek he'd make a video of his (though with his gauge who knows, that and if he can even get it hooked up after the charger)

 

[QUOTE=SonicRaT]I have more vacuum between the charger and the throttle body (with no bypass) than I do the engine and the charger, as I've said before. Without a belt (and bypass), you won't get enough air through the lobes for it to even run (and the twin-screw surely won't turn on its own like that). Have you even done what you suggest above? Ever even built a twin-screw setup? Better yet, have you built any non-centrifugal setups at all?


With the tb closed yes but only enough to produce the energy to turn the blower. That's a roots. And it will turn the rotors without a belt. I can't say all will but I've done it.
With the axial flow you can drive the car without a belt and the blower will keep spinning after you shut it off. Mine is not a centrifugal by the way. Yes I have built just about every kind of set up there is except the screw. By this I mean I've built engines using them, the only kind I've designed and built myself is the Axial Flow.
I've been doing it for 40 years. My first job was at Paxton when I was 20.

I did design and build a multi stage centrifugal once around 1976-7 but never ran it on an engine. That is now in a private collection.

Look it up if you want. Beside the obvious AxialFlow thread in this forum you can search Latham Axial Flow Supercharger which was my old company or just put it together with my name and search.

I only bring up the dragsters because that is most radical example to show there is no boost in the manifold at idle.
(

 

As was said before, boost will never been seen at idle unless the charger is EXTREMELY oversized and forces enough air through the 'closed' throttle body, though the engine would stall long before that ever happened from all of the load.

But, regardless, as you said yourself, a positive displacement is just a pump, and generally it's a larger pump than the engine. It doesn't take too much science to understand that a larger pump will draw more air through the same restriction than a smaller one. Obviously, this isn't a very large ammount (at idle with the plates closed), however it does exist. The result is the air pumped out of the supercharger is more than the engine would pull on it's own, and the result is 'positive pressure', nothing near 0", but it's still positive over the engine without the charger. I've seen this on well over 70 blown cars in the past 3 years.

 

This is past the point of being stupid. You guys have to get this.
Lets start over, if your engine had 15 inches of manifold pressure at idle then it will have 15 inches at idle after you put the SC on. Why? Because that is how much power it needs to over come internal friction to run. There will be a little more load because of the blower but it is not enough to change the manifold pressure by that much that it will read on the gauge.

If the "Extreamly" large blower were so big that it made boost at idle then that means the engine would not have run before because it would not have made enough power to overcome its own friction. This is an impossable senario.

I hate disagree with your personal experiance because you seem to grasp most of it but you did not see 70 engine produce this phenomonon.
If the blower was making more air flow in then the engine would be running faster then idle so you would have to close the throttle more to bring the idle down by decreasing the manifold pressure.

The engine doesn't know if it has a SC on it or not. It only knows how much air is forced into it. That's right I said forced into it. Ah you say, forced into it. Yes all air is forced into it with or without the SC. In reality the engine does not "suck" air into itself, it get forced in by mother nature at 14.7 psi. That is if your at sea level.

Adding artificial pressure does not change what the engine "sees". It only takes what it need to do it's work up to the point where it can no longer get enough to do the work you ask. So idleing is what you ask of it so that is all the air it will take.

I have a 30hp CNC milling machine back there but say I want to engrave my name in a piece of aluminum with a 1/16 inch end mill. How much HP will the motor draw when I cut the part? A very small fraction of a HP, right? What if I bought a 50 HP mill, or a 1HP mill? It would still use that same HP to cut that part.

If you ingest more mass then more power is produced and it has to go someplace. If not to some load then to more RPM untill it uses that amount of HP to overcome whatever friction there is to match said power.

Either you honestly can't see it or you flat *** will not belive me. If the later is the case find someone who knows more then I that you will belive.

 

Well you have to admit though that more air flow is needed since the engine needs more power in order to be able to drive the supercharger as well as itself.

 

Ah yes, but what do you think it would take? Say less then half HP. Would a 1/2hp motor turn the thing at idle speed? Picture it as on the bench with a 1/2hp electric motor. You know it would turn it at low speed when the intake is blocked off. Consider also it has a high vacuum on it's discharge. I submit that it is less then 1/2hp and will not show up in manifod pressure. If it does it is one hell of a inefficeint blower. Like maybe a 8-71 on a Honda would show up but not an Eaton.

 

I definitely have learned a lot from RP. When can I put one of these sc'ers on my vehicle?

*sits back with a bucket of popcorn and watches the show*
*munch munch*

 

You've seemingly come to a misunderstanding on just about everything I've said. A supercharger will do work at idle. There are a few results of this, ASSUMING all things the same. Either the superchargers parasitic drag will be greater than the result of it's additional air and the engines original idle speed will decrease (or simply not run at all, an example of which is the Camden units), the drag and additional power provided by the additional air of the supercharger will be similar and the engine speed will remain the same, or in the case of a rather efficient blower with little drag, their will be more air provided than parasitic drag resulting in an idle increase (again, assuming all things to be equal). Now, afterwards, this can be adjusted to obtain a similar to 'stock'. Now, I know you're trying to say that regardless, atmospheric is only going to push air through the plates at the same pressure. This is true, but don't forget that the blower is a larger volume than the engine and is under less pressure which presents less resistance. This allows atmospheric pressure to push more volume. It can be argued that this is extremely negligible, and short of spending a week measuring volume and flow and so forth there's not much in the way of an answer to that. But regardless, the result is the same, the charger does work at idle, with one of the above results.


I'm not even sure how to reply to this. An engine uses any ammount of air it is provided up until atmospheric unless forced into compression. The result is an increase in engine speed and power, the only thing that determines how much the engine is 'forced' are the throttle plates, or something else controlling the air fed to the engine.

And for curiosity sake, are you selling any units outside of a complete kit yet?

 

Is it odd that the picture of the Blitz kit does not show an inter-cooler?

 

I don't think it comes with one (i guess thats the way they do it) . I think if you want the intercooler it would be a seperate purchase from blitz. Just read that this kit runs on a stock ecu, so no ecu upgrade with the kit.

 

Wee this thread is getting more interesting with every day.

 

i've been reading up on this thread. been having fun reading. KEEP GOING AT IT!. my day goes by that much faster =)

 

Apologies for getting back on topic, but I wrote to these fellas about their listing and FYI the answer:

"Do you have abit more detailed information, a web reference site with more info, dyno graph you can actually read, install manual, history of product, how long has it been available, things like that? These are the minimum I would want to read before ever making an offer in this $4000 price range for something so major a mod to my MT RX-8. Thanks."

Finally got a reply:

"Sorry about the delays, there are no other information avaliable on either the US or JP website. nor dyno graphs. this unit has been on sale for about 1 year now without problems. This kit is a complete upgrade and will work with both factory &/or aftermarket ECU. This kit on the factory ECu will give you 40HP more. With aftermarket ECU there is more potential. This item is in Japan Tokyo and is ready to go."

Might be fun trying to get tech help or warranty on such a well documenting thing as this after a year out and still in this condition.