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Old 05-07-2020, 02:15 PM   #126
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Agree on the turbo feeding a positive displacement supercharger. But can't agree that a supercharger makes a certain amount of boost. What a positive displacement compressor does is generate flow. The discharge pressure (boost) is a resultant of what is required to move the air through the engine.
Yes, you are describing how boost is created through both turbo and supercharging.

A positive displacement supercharger will generally create a fixed amount of boost pressure, which is what I am describing. Example being that an efficient roots blower will create (as an example) 10psi of boost pressure throughout the rev range, whereas the turbo will create 0 boost at 2000rpm, 25psi at 5000rpm and 20psi at 8000rpm. In a twincharged setup this would mean 10psi at 2000rpm, 35psi at 5000rpm and 30psi at 8000rpm as the roots type blower will increase whatever goes through it by its "fixed" boost pressure that it would create on its own.

We have tested this on about 6 or 7 different setups on various cars with multiple pressure gauges and until you try to get greedy with the blower and make more boost and drop its efficiency or extreme rpm and power levels (as it uses hp to run the blower) it hold true.

With the layout of a subaru this is pretty easy to do, replacing the intake manifold plenum with a roots blower and would allow to use much larger turbos with the feel of an h6.

This was a recent fun build of a friend of mine, photo from a feature, I couldn't find my close up photos.

4.7l v8 with an m112 eaton blower from a cobra and a gtx4508r, has an air/water intercooler plate and runs on methanol for fuel. Makes way too much torque, but is a fun drive.



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Old 05-08-2020, 04:00 AM   #127
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Quote:
Originally Posted by junebugfareast View Post
I am not sure what would happen with a positive displacement supercharger upstream of a turbocharger.
Just so we're clear, I was not talking about a positive displacement supercharger. I was talking about pcampbells' centrifugal supercharger. The compressor map looks kinda like what you'd see from a large turbocharger.
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Old 05-08-2020, 10:26 AM   #128
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Agree on the turbo feeding a positive displacement supercharger. But can't agree that a supercharger makes a certain amount of boost. What a positive displacement compressor does is generate flow. The discharge pressure (boost) is a resultant of what is required to move the air through the engine.
No, you have it reversed, a positive displacement compressor physically compresses air. It captures air just like a piston compressor and compresses a fixed volume per cycle.

A non PD compressor like a turbo, which is nothing but a fan, generates high volume flow and the flow THEN compresses when it is directed into a fixed volume and that volume is removing less mass than is coming in. . .hence pressure rise. It does not compress anything, it adds a ton of energy to a mass flow of air and lets that do the work later on.

These two facts are precisely why a PD compressor has a dead nuts linear boost curve with rpm and a turbo has an exponential curve.
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Old 05-13-2020, 08:33 AM   #129
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Default Vortech supercharger for ~500whp? Si Too big?

Iím now on 5.5Ē (ati) and 2.4Ē pulleys. First try slipped badly. Maxed out at 13psi. I ordered the Gates RPM belt and wow!!! Hit 17 psi on the first try at 6300rpm. Obviously a huge difference. The RPM belts do not stretch due to aramid cords.

Maf Sensor says 344 g/s, sounds pretty nice, but the SC sucks up a lot of power. So Iíd guess ~320 at the wheels hitting 350 whp when I spin it out to 6700rpm which is the stock impellers redline of 55k.

Iíll probably hit the dyno when I get the tune cleaned up.

Iím surprised the exedy ksb04 clutch hasnít slipped yet !



Next up is to get that post IC IAT hooked up. Iím curious to see how hot they are!

One other thing, might be maxing out my MAF setup pretty soon but letís see. 4.66v right now.

Last edited by pcampbell; 05-13-2020 at 11:13 AM.
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Old 05-13-2020, 11:02 AM   #130
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Curious, what do you have for a tensioner on the system? GM actually has a pretty slick hydraulic belt tensioner....thinking about pre-load and belt whip.
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Old 05-13-2020, 11:17 AM   #131
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Curious, what do you have for a tensioner on the system? GM actually has a pretty slick hydraulic belt tensioner....thinking about pre-load and belt whip.


It is just stock on the 5 rib outer belt.

It might be that with the RPM (low/no stretch) belt there is no need for a dynamic tensioner. From what I understand youíre supposed to put it on as loose as possible.

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Old 05-15-2020, 07:58 AM   #132
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Welp, now I canít repeat my results hitting 17psi. It seems to slip/grip/slip/grip repeat.

Any chance the SC is surging (off left side of compressor map)? What would this look/feel like?
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Old 05-15-2020, 08:01 AM   #133
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surge of any kind is usually easily detected....loud fluttering noise. Or it may be visible on logs if you had a pressure sensor close to the inlet of the blower.

Slippage will be belt routing, tension etc etc.
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Old 05-15-2020, 09:06 AM   #134
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Thanks, I guess I don't think it is surging... it is not fluttering at all, and at partial throttle it pulls hard, no slippage. It is when I go full throttle that it starts doing the boost/slip stuff.



I asked ATI if there is a larger pulley that'll bolt to the front of my ATI crank pulley. Might be able to run a significantly larger pulley combo in 6 or 8 rib that way. They said yes, but I'm waiting for specifics.

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Old 05-15-2020, 04:23 PM   #135
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No, you have it reversed, a positive displacement compressor physically compresses air. It captures air just like a piston compressor and compresses a fixed volume per cycle.

A non PD compressor like a turbo, which is nothing but a fan, generates high volume flow and the flow THEN compresses when it is directed into a fixed volume and that volume is removing less mass than is coming in. . .hence pressure rise. It does not compress anything, it adds a ton of energy to a mass flow of air and lets that do the work later on.

These two facts are precisely why a PD compressor has a dead nuts linear boost curve with rpm and a turbo has an exponential curve.
Are you saying a roots blower discharging into an open pipe will be at positive pressure?
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Old 05-15-2020, 04:26 PM   #136
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Are you saying a roots blower discharging into an open pipe will be at positive pressure?
Which is impossible....because there is no restriction.

Regardless of how anyone describes each compressor....unless it is discharged into some sort of restriction, you arent going to see any positive pressure or boost.
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Old 05-15-2020, 04:58 PM   #137
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Are you saying a roots blower discharging into an open pipe will be at positive pressure?
What they are saying is that the twin-screw superchargers are different from a roots or centrical in that it doesn't simply move air until it hits a restriction to create boost. It actually has sealing between the screws that create its own restriction as the air moves from one end to the other until you touch the throttle and release the boosted charge into the motor.

Basically if you wanted to tap into the housing on all three options just before the discharge and you let it discharge into an open pipe only one will have an internal boost reading.

There is a reason a twin-screw is by far the most efficient supercharger style, also why it is basically regulated out of a lot of drag racing classes.
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Old 05-15-2020, 06:31 PM   #138
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Agree that a twin screw is a fundamentally different beast than a roots machine but roots was what was mentioned as a PD machine in a prior post. Just showing my age I guess - superchargers were classically a 6-71 sticking through the hood.
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Old 05-23-2020, 07:54 AM   #139
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2.4Ē pulley off to get carbinited. I think in the end Iím going to need both of whatever crank and SC pulley I use to be treated. But Iíll do one at a time for now.
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Old 05-24-2020, 08:37 AM   #140
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Do you guys think Iím less likely to have belt slip the lower I ďgearĒ the SC? That is to say , for example hitting 52k rpm at 6300rpm should be more resistance and more slip likely than at, say 6700rpm even if the manifold pressure is the same?

(Putting aside the fact that lowered geared can use larger pulleys)
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Old 05-24-2020, 04:38 PM   #141
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I think so. You can also think of that as getting more engine RPM (thus more air going into the engine) for a particular compressor RPM. I'd expect the manifold pressure to go down a bit as a result.
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Old 05-24-2020, 05:40 PM   #142
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If you reduce the gearing and load/speed on the blower, there should be less chance of slip

But verify you are getting slip first, create a tooth on the blower pulley and log speed.
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Old 05-27-2020, 08:16 PM   #143
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It really seems like revving it out is going to be the way to go in this application.

Currently on the 5.5" crank and 2.62" pulley, both untreated pulleys, redline @ 6500 and hit 15 psi, ~310g/s , no slipping to be concerned about. I'll just keep doing it 100 rpm at a time for now.

Need to start worrying about stock valvetrain though. I'll probably only go up to 6900 for now.

I was reading a post that I think was by Joe from ASF machine, he said you can use Supertech SOHC 9.5mm spring seats with Brian Crower 257 springs for a relatively cheap spring setup ($200-$230 depending on Crower vs OEM retainers).

I'm not sure yet if I needed to get into inconel or ferrera exhaust valves.

Last edited by pcampbell; 05-27-2020 at 08:54 PM.
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Old 06-01-2020, 06:41 PM   #144
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Back on 5.22x2.4, this is a nice jump in low end boost over 5.5x2.62. and seems like it could be the sweet spot.


Last time I was on the dyno with the same pulley setup I hit 14psi @ 6258rpm...now I am at at the same MAF voltage and boost @ 5839rpm after getting the pulley treated.
All I have done , basically is have the 2.4" pulley coated, and add a larger idler for more wrap on the crank pulley.

I still have the Gates RPM (Kevlar) belt if I need to go there.
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Old 06-02-2020, 04:40 PM   #145
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I did back to back runs, and the second run to higher RPM yielded less boost. (This was the first run).

Sorry my axis labels are swapped, you get the idea.



I'm going to throw on the Aramid RPM belt now, unfortunately I have to make the Crank idler smaller to fit this K050705 but It think it'll be worth it.

Really want to see 20 psi because, nice even number!
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Old 06-02-2020, 07:19 PM   #146
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Well, The RPM belt is challenging, either that or the Belt wrap isn't enough . Inconsistent results, weird curves. It does this "grip/slip/grip/slip" thing in huge ups and downs, or it slips a lot and then it grabs, or vice versa.

At least the standard belt slips just a little when it slips. It is more consistent overall.

Back to regular belt.
So far my best is 18psi, 375 g/s. On this path it should hit 20psi and over 400g/s (again not sure how accurate this is, but closeish) at around 7000-7100.

Sort of interesting, you can see a few degrees of timing changes on the boost graph. There is some false knock around 5400, which clears up around 6400.

Last edited by pcampbell; 06-02-2020 at 07:32 PM.
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Old 06-02-2020, 09:20 PM   #147
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Every supercharged car I've seen on the dyno or owned by friends that had belt slip, its always the tensioner in the end
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Old 06-03-2020, 12:00 AM   #148
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Is there any chance you could go to a wider belt?

I know it's a lot of pulleys to replace, but it might solve the slip problem. C5 blower kits start at 6-rib (stock) and go up to 8- and 10-rib.
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Old 06-03-2020, 08:39 AM   #149
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Ideal would be to bolt another pulley into the front of the ati or fluid pulley for a separate belt that would just run the SC. It wouldnít be that hard it I could find a pulley that would bolt up to these crank pulleys. Ideally itíd be large, then I could run 2 fairly large 6 rib pulleys and have lots more belt wrap. I donít know if I have the clearance for an 8 rib. But 1 additional rib plus significantly bigger pulleys Iím sure would make a difference.

Ati says they donít sell anything. All of their supercharger pulleys are supposedly a different spacing. I wouldnít be surprised if there is something out there off the shelf I just havenít found yet.
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Old 06-03-2020, 08:46 AM   #150
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Default Vortech supercharger for ~500whp? Si Too big?

Here is an example


http://www.vdamper.com/30-V6-TSI-Supercharged_p_42.html

These though are certainly application specific. The SC pulley recesses into the crank pulley. Itís not just flat bolted to it.

Last edited by pcampbell; 06-03-2020 at 08:53 AM.
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