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Question--2 Superchargers 1 motor
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74grand-AM
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PostPosted: Sun Jul 27, 2008 7:46 pm    Post subject: Question--2 Superchargers 1 motor Reply with quote

Hey i have a 1974 Pontiac Grand AM With the 400 in it, ok now im doing twin vortech V4 Superchargers bolth at 6psi per charger how would this run with a carburated motor???

Last edited by 74grand-AM on Sun Jul 27, 2008 9:18 pm; edited 1 time in total
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af2
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PostPosted: Sun Jul 27, 2008 8:24 pm    Post subject: Reply with quote

#1!!!! how do you know what the PSI is???
Ok, I am going to eat dinner then come back. Surprised
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74grand-AM
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PostPosted: Sun Jul 27, 2008 8:53 pm    Post subject: Reply with quote

af2 wrote:
#1!!!! how do you know what the PSI is???
Ok, I am going to eat dinner then come back. Surprised

thes are the specs for the T4 Supercharger and i will not be tuning at 29 psi but just 6psi per charger

Straight cut spur gear
Fits engines up to 1,100 horsepower
Maximum airflow: 1,600 CFM *
Maximum boost pressure: 29 PSI *
Absolute maximum impeller speed: 58,000 RPM
Adiabatic efficiency: 74% **
Available with straight discharge in clockwise rotation
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clay
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PostPosted: Mon Jul 28, 2008 12:40 pm    Post subject: Reply with quote

My guess is they would each have to be pulleyed to turn so slow that they wouldn't be very efficient. Centrifugals build boost in an exponential way. As rpm doubles, boost squares. Centrifugals to me work best if they are running in the high end of their rpm capability. That way, boost doesn't fall off as quick as rpm comes down. If you wanted to run two centrifugals just for the look, I would pick a much smaller head unit and turn them faster. Clay
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Big Dave
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PostPosted: Mon Jul 28, 2008 7:51 pm    Post subject: Reply with quote

Or run a dummy head in conjunction with one functional head.

Have you seen the guy on the web with two roots blowers on top of each other in and old red GTO. Both are hollow with a 2 barrel carb on an old 389 but he puts on a great show. Lots of gear whine and chrome looks intimidating, but runs with none of the headaches of a blower. All show no go.

Is that what you are after?

Big Dave
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74grand-AM
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PostPosted: Tue Jul 29, 2008 1:05 pm    Post subject: Reply with quote

Big Dave wrote:
Or run a dummy head in conjunction with one functional head.

Have you seen the guy on the web with two roots blowers on top of each other in and old red GTO. Both are hollow with a 2 barrel carb on an old 389 but he puts on a great show. Lots of gear whine and chrome looks intimidating, but runs with none of the headaches of a blower. All show no go.

Is that what you are after?

Big Dave
well i might have to stay with one i thought i can use 2 cuas there the same shape as turbos
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clay
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PostPosted: Tue Jul 29, 2008 1:14 pm    Post subject: Reply with quote

They do work similar to turbos. You could probably even get a compressor map to help with head unit selection (although I don't think Procharger will supply one). In the map, both will have an area of maximum effenciency that it is best for both to operate in. By selecting two pretty larger superchargers you could run into the same problem as two very large turbochargers on too small of an engine - sort of lazy and just not the desired output and nowhere as good as it could be. Clay
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Big Dave
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PostPosted: Tue Jul 29, 2008 2:27 pm    Post subject: Reply with quote

With super chargers (includes turbo's) bigger is usually better in racing. You see multiple turbos on race cars because the available units are too small to move enough air. Every year a bigger head comes out so the fastest racers drop back to one big one because of the weight savings.

Just like with carburation you do not want two carbs if one big one will get the job done It makes for four times the work to tune the motor). Multiple turbos or superchargers also doubles the expense with twice the number of pop off valves etc.

Big Dave
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d2180sx
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PostPosted: Sun Sep 28, 2008 11:24 am    Post subject: Reply with quote

Have you thought of going the twin-charger route of using the supercharger for your low end and a bigger turbocharger (or twin turbo) for the high end? It's something that worked well in the 80's and it's something some guys are playing around with again. Even VW, ahem..., has a production Golf 1.4 l that utilizes this concept of a mechanical supercharger and a turbo. It does make sense to have instant forced induction from zero and then have the supercharger cut out at your predetermined boost level/RPM and then have the turbocharger take over the boosting duties from there.

Some reasons for it:
- No need to sync up the superchargers; just dial in when you want the blower to kick out and the turbo to take over
- limited drag and making efficient use of your exhaust flow (for the turbo)
- space savings; two superchargers sound like they would take up a lot of space (I am sure someone will say the same about a turbo or two turbos)

Just food for thought

Oh! On the carb, what type are you using? It would work best with a smaller carb. Is the system utilizing a draw-through or blow-through configuration? I am gonna assume you want to take the charged air and run it direct into the carb and that you have a carb hat like on Holley-double pumpers. This would be the blow-through system [better throttle response and better cold starting(fuel doesn't fall out of suspension too easily)]. 6 PSI isn't a whole lot, but I know that you will be like most people who experience forced induction, you will want more power and run more boost, which will require the addition of the intercooler (5 PSI is ok without intercooler, but more and then you will have heat soak) and BOV is essential for a pressurized system running higher boost. Since you are using a carb system, this is essential since you don't want boost spikes to ruin inner seals and gaskets in the carb.

I love forced induction, but from the sound of it, many would think you would benefit from going more modern EFI and using that as your base for forced induction, but to each his or her own. I would love to see how it turns out for you.



vw-golf_tsi_airflow.png
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VW Golf Tsi airflow diagram for supercharger and turbocharger combo

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clay
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PostPosted: Tue Sep 30, 2008 12:47 am    Post subject: Reply with quote

Blow through carbs don't work.......

This emoticon is too cool not to steal from 10sec.et and use...Clay

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d2180sx
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PostPosted: Tue Sep 30, 2008 4:14 pm    Post subject: Reply with quote

clay wrote:
Blow through carbs don't work.......

This emoticon is too cool not to steal from 10sec.et and use...Clay


Well, no... they do work if you address pressurizing the carb fuel bowl(s) and venturi, as well as ensuring you have adequate fuel flow for the increased air flow forced induction will provide. Show me where it does not work and i will show you where the mistake lies.
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clay
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PostPosted: Wed Oct 01, 2008 12:10 am    Post subject: Reply with quote

Holley double pumper, airhorn removed, centrifugal supercharger setup, around 3000 - 4000 rpm, squeezing in throttle lightly as the tires are spinning (street tires) and there is a slight pop back through the carb. Other than this one flaw, it works perfect. What could be some causes of this? Clay
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PostPosted: Wed Oct 01, 2008 12:46 pm    Post subject: Reply with quote

clay wrote:
Holley double pumper, airhorn removed, centrifugal supercharger setup, around 3000 - 4000 rpm, squeezing in throttle lightly as the tires are spinning (street tires) and there is a slight pop back through the carb. Other than this one flaw, it works perfect. What could be some causes of this? Clay


Same here, although it will happen coming off idle also. I switched to a Pro-form body, no help. My theory is that the accelerator pump discharge is fighting the slight boost pressure (above throttle plates) in the tip-in mode. I have put in a .035 squirter, (in place of the .031) but have not road tested yet.

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Paul P
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PostPosted: Wed Oct 01, 2008 2:01 pm    Post subject: Reply with quote

It could be related not only to the nozzle but the accelerator pump cam profile too. Have you or Clay tried different cam profiles? Just curious. 50cc pump?

yes...

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big_G
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PostPosted: Wed Oct 01, 2008 2:26 pm    Post subject: Reply with quote

Paul P wrote:
It could be related not only to the nozzle but the accelerator pump cam profile too. Have you or Clay tried different cam profiles? Just curious. 50cc pump?

yes...

I put a red cam (middle profile) in at the same time I did the nozzle upsize. Had the small white cam (lowest profile) on originally ...I will road test it this week-end. May need the 50cc. pump if this fails. Gary

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