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How to calculate Powerdyne internal rpm 

 

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 Post subject: How to calculate Powerdyne internal rpm
Posted: Wed Jan 30, 2008 10:56 am 
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I've been reading and the Powerdyne blower seems to have a maximum impeler RPM of between 38,000 to 43,000 rpm (depending on what parts have been used in it).
Does anyone know how I would calculate what rpm it would be doing with different sized pulleys on my EF I6?
The pulleys listed on CAPA's site are: 3.15, 2.9, 2.7 and 2.5 (http://www.capa.com.au/prices_power...e_superchargers).

 

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Posted: Wed Jan 30, 2008 1:44 pm 
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Have you actually got the blower? If you do just turn the pulley once by hand and note how many times the impeller turns. From there you can work out the gearing inside the blower and what sized pulleys will give you your desired impeller speed.
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Posted: Wed Jan 30, 2008 2:40 pm 
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Hi,
Max. Safe impller RPM=42500.
Ford Falcon I6 engine @6000RPM
-Pully Dia. 3.15 your impeller RPM=37320
-Pully Dia. 2.9 your impeller RPM=40537
-Pully Dia. 2.7 your impeller RPM=43540
--Pully Dia. 2.5 your impeller RPM=47023

If you give me your engine RPM @ shiffting gear, will give you other calculation.

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Posted: Wed Jan 30, 2008 3:12 pm 
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Hey boost, cheers a bundle for that. The ECU and that is standard (standard XR6 automatic ECU), so the factory rev limiter and such is all still in place.
So I guess I need it so that at redline it is still under the maximum safe impeller RPM - although it would only be at redline for a very short period of time and it's very rare for me to actually have my foot flat for that long...
Off my memory redline is 5500 rpm, so that would mean that I might be able to go the 2.7 diameter pulley without exceeding the maximum safe impeller RPM.
What is the formula you used to calculate those? I assume the size of the harmonic balancer is considered etc.?

 

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Posted: Wed Jan 30, 2008 7:10 pm 
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twr7cx,

Internal setup on Powerdyne is 1.0 to 3.15, Max Safe RPM is 42500 But I recommend Max.39000
You may calculate the Impeller speed as following.
(Crank Pulley Diameter x 3.15 Eng. r.p.m)/Supercharger pulley Dia.

by the way I have Powerdyne supercharger in my Ford EF I6 works V.Very fine, I using Pully size 2.9 and 3.15

I recommend that you start with pully size 3.15 that will give you 6psi of boost if you go for more boost you need FMU, Exaust system, intercooler,....
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Posted: Wed Jan 30, 2008 7:19 pm 
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Heres how I did it.

--------------------------------------------------------------------------

Crank pulley dia (eg 6")

Divided By

Supercharger pulley dia (eg 3")

Times 3 (internal cog ratio)

Times engine RPM (eg 6000)

Equals internal RPM (eg 36000)

-----------------------------------------------------------------------

Max internal revs using standard bearings and belt is 36000rpm with short stints of 40000 - 42500 (It varies who you talk 2).

If you want 2 upgrade the bearings and belt to 60000 or a better impeller http://stores.ebay.com/928-Motorsports are the guys I used. Went together fine.

 

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Posted: Wed Jan 30, 2008 9:55 pm 
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boost wrote:
I recommend that you start with pully size 3.15 that will give you 6psi of boost if you go for more boost you need FMU, Exaust system, intercooler,....


I'm currently running the 6 psi pulley, so that would be the 3.15. I'm halfway through installing an intercooler, so once that's in I want to bump it up to 9psi. I just wanted to see if I could run any more than 9 psi, but clealy not then.

 

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Posted: Wed Jan 30, 2008 9:59 pm 
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Mac Winter 76XB351GS wrote:
If you want 2 upgrade the bearings and belt to 60000 or a better impeller http://stores.ebay.com/928-Motorsports are the guys I used. Went together fine.


I've heard good things about 928 Motorsports from some other pages I've read on the net.
So what exactly need to be upgraded to get a 60000 rpm rating? I assume the belt and bearings - anything else such as impeller or impeller shaft? I'm not looking to rebuild the blower at the moment as it's still under 1000kms on it, but it's nice to know for the future.

 

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Posted: Wed Jan 30, 2008 10:48 pm 
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boost wrote:
twr7cx,

Internal setup on Powerdyne is 1.0 to 3.15, Max Safe RPM is 42500 But I recommend Max.39000
You may calculate the Impeller speed as following.
(Crank Pulley Diameter x 3.15 Eng. r.p.m)/Supercharger pulley Dia.

by the way I have Powerdyne supercharger in my Ford EF I6 works V.Very fine, I using Pully size 2.9 and 3.15

I recommend that you start with pully size 3.15 that will give you 6psi of boost if you go for more boost you need FMU, Exaust system, intercooler,....


Dont meant to be a smart a***, but the BD-11A Powerdyne has a step up ratio of 3.05, not 3.15. Which is only 3% i know, but its still true, and can be a fair bit at these speeds.
I wouldnt waste my time intercooling a BD powerdyne either,they struggle to make the boost they prommise without putting an intercooler infront of them.


Here is my response from the 'other forums', for your interest.

To calculate Impeller Speed the formula is:

(Crank Pulley Dia / Blower Pulley Dia) x Blower Step Up ratio x Engine RPM = Impeller Speed

Powerdyne step up is 3.05.

‘SC step up ratio’ is the number of revolutions of the impeller for one revolution of the SC pulley (a ratio 3.05:1 built into the SC by Powerdyne).
Engine RPM is the maximum engine RPM.

The Powerdyne impeller doesn't move as much air as a lot of other blower manufacturers impellers.
It tops out at 42500 rpm.
After that it's just spinning too fast to efficiently capture and compress the air.

Max Blower Impeller Speed 42500 RPM
Max Efficient Impeller Speed 40600 RPM

I also remember reading somewhere that CAPA rate the Powerdyne Blower Impeller to 39000 rpm.
They have a tendency to throw the internal drive belt after this, so I guess its there limit to avoid warranties.

Interesting to see that 928 Motorsports rate the bearings to 38000 rpm as well with a normal operating range of 26000rpm (and 138 Deg C)

Example calculations.

(7.25 / 3.45) x 3.05 x 6000 = 38456 rpm

or

(7.25 / 3.33) x 3.05 x 6000 = 39842 rpm

or

(7.25 x 3.33) x 3.05 x 6250 = 41502 rpm


Internal Blower Ratio for blowers are.

ATI P-600 3.05=1
ATI P1-SC 4.10=1
ATI D1-SC 4.10=1
ATI D1-SC 4.10=1
ATI D1- (all) 4.44=1
ATI F- (all) 5.10=1
Paxton SN 4.44=1
Paxton NOVI 3.54=1
Paxton GSS 4.40=1
Vortech V-1 3.45=1
Vortech V-2SQ 3.61=1
Powerdyne DB11 3.05=1

 

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Posted: Wed Jan 30, 2008 11:37 pm 
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dodgie wrote:
The Powerdyne impeller doesn't move as much air as a lot of other blower manufacturers impellers.
It tops out at 42500 rpm.
After that it's just spinning too fast to efficiently capture and compress the air.

Max Blower Impeller Speed 42500 RPM
Max Efficient Impeller Speed 40600 RPM


Have you seen the 928 Motorsports replacement impeller (http://cgi.ebay.com/ebaymotors/Powerdyn ... 0194717382)? Reckons it's 20% more efficent and able to handle up to 60,000rpm.

 

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Posted: Wed Jan 30, 2008 11:41 pm 
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So what is the crank pulley/harmonic balancer size on the EF I6?
I somehow came to 6.22 using algebra on the equation with crank pulley as X, it's been 5 years since I've done maths but, don't suppose this is correct?

 

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Posted: Thu Jan 31, 2008 12:03 am 
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I've done some calculations based on two assumptions:
1. the correct crank pulley/harmonic balancer size for my EF I6 is 6.22.
2. the redline and gear shift point of the automatic transmission of the EF I6 is 5,500rpm.

Now based on those using the formula you guys gave given me I should be able to step down to a 2.7 pulley for the supercharger.

If the internal step up ratio of the supercharger is 3.05 then at redline the rpm of the blower would be 38644.6296.
If it is 3.15 then 39,911.6667rpm.

Both of those figures are below the max blower impeller speed (42,500rpm) and the maximum efficient impeller speed (40,600rpm).

The 3.15 is a big higher than CAPA rating (39,000rpm), but not by much (911.6667rpm).


Now when you consider that the car is a daily driver. Most of the time when my foot is flat it'll be traffic light drags (i.e. between 60 - 80kmph -obviously these are on special private safe purpose built roads and not the public streets) so the throttle is lifted prior to 1st gear redline. Therefore it would be extremely rare for the engine to be taken to redline and the blower reved so hard - so the blower wouldn't be getting pushed to it's maximum.

Therefore based on that I could almost risk going to the 2.5 pulley. 3.05 gives 41,736.2, and 3.15 gives 43,104.6. Now 3.15 goes over the maximum impellor speed and both go over the maximum impeller efficency speed, but that's only at redline which would barely be seen.

For now I'm considering going to the 2.7 to hopefully get the blower to start boosting earlier and improve my low down torque.

Any mistakes in my logic?

 

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Posted: Thu Jan 31, 2008 9:05 am 
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twr7cx wrote:

Have you seen the 928 Motorsports replacement impeller (http://cgi.ebay.com/ebaymotors/Powerdyn ... 0194717382)? Reckons it's 20% more efficent and able to handle up to 60,000rpm.

its not just the impeller that limits the rpm, you also need to consider the shaft, balancing and the bearings
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Posted: Thu Jan 31, 2008 1:15 pm 
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It doesn’t surprise me that CAPA rate the Powerdyne Internal Blower Ratio at 3.15, instead of the actual 3.05.
As this would put their 39000-rpm limit to 37761-rpm, which is just under what ‘928 Motorsports’ rate the bearings at (38000 rpm).
Again probably a warranty thing CAPA uses.

Your crank pulley math is correct, but I would physically measure the crank pulley if you can, just so you’re not guessing, and maybe someone can confirm your pulley size too.

And I would also take the maximum engine rpm in the calculation to mean what the rev limiter cuts the engine out at, and not your shift point. But that’s just me being safe, and thinking about accidental over revving (i.e. wheel spin).
Also, your shift point naturally aspirated, may be lower than it will be under boost. Your not going to find out what it would be untill you drive it supercharged.

I think the biggest issue with the Powerdyne blowers is with the bearings, as when they go, that’s when the belts break.
This is why 928 Motorsports, have cooling vents for the blower casings, as well as bearing and belt upgrades, etc, etc.

So basically, the higher and how often you rev the blower, will determine the likelihood of damaging a bearing, causing belt breakage.

What rpm your willing to risk is up to you.

I would start modestly, and change to a smaller blower pulley if your not happy.
Remember how happy your gona be when the blower fails.
Not that its a huge drama to change the bearings and belt (provided thats all that gets damaged), but it is an a** pain to do just the same.

 

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Last edited by dodgie on Thu Jan 31, 2008 6:30 pm, edited 3 times in total.

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Posted: Thu Jan 31, 2008 1:42 pm 
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dodgie wrote:
Vortech V-1 3.45=1
Vortech V-2SQ 3.61=1


Thats interesting!
We swapped a mates V1 S-Trim for my V2SQ, at the same time we fixed up some dodgy joins in his cooler piping, and made a new intake for the blower.
He runs a 2.95" pulley with I *think* a 7" crank pulley, and could only ever get 5-6psi.
When we put the V2 on, hes now making 8.
We put it down to possible boost leaks in his old piping and s**t intake.
Could the 2000 odd rpm difference in compressor speed account for that difference in airflow?

Sorry for O/T too twr7cx.

 

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