How much boost can you safely run with a stock motor and ecu? All i have is a smaller pulley, catch can, dual intake, muffler delete and a tune, looking to put a smaller pulley on. im not sure the exact size pulley im running but im pushing around 15-16lbs...suggestions for a smaller pullley without damaging anything? or other options for more power? Thanks

 

read...read...read....some guys are cranking 21-22psi but you get heat issues
you go 62mm SC pulleys on Stock Crank
or 65mm pulleys on 181 cranks - extreme
or stock 75 on 185 crank
not sure if someones running a 62 with a 185
I think there's a 178 out there as well.....

see attached picture - although this assumes linearity of psi with rpm and I dont think that is the case - but I stand corrected.

Note also - boost isnt everything - density is everything....but density is promoted by boost sure
- but low AIT's also promote density
and on that....
The lower you can get your pre supercharger air temps and humidity the more efficient it'll run.
That's why people talk about altitude, track temps and humidity and its effect on AIT's

Humidity is your enemy - H2O vap is useless - in and out as H2Ovap - it takes up space
Although H2O (liq) is another thing.
People spray water into their intakes or post charger, but although its evaporation can cool temps to down as low as wet bulb temps the resulting H2Ovap (now useless) displaces available O2 for burning. Others spray it on their IC during WOT to bring SC operating temps down.

Most people cool post supercharger.

 

what size is the stock crank pulley? thank you for all your help as well

 

75mm......
- and some extra characters to keep the fun police happy....

 

i ran a 65mm s/c pulley on a 178 mm crank pulley. it was spinning in the 16500 rpm range. much more and you will be way past the effiecient range of the blower. heat was an issue but ran 11.9 in 86* heat so it can work

stock s/c pulley is 74mm and stock crank is 154mm

 

Welcome by "Oh Porsche One"...
figure below updated

An afterthought....it should be linear since the blower is pumping in at X and the pots are sucking it in at Y - both are "fixed displacement" volumes and both are linked to the crank....so the "inventory pressure" within the plenums is only influenced by any changes in the ratio between the two - ie: speed the charger up and you increase the inventory pressure because the SC is puming it in faster than the pots can take it way.

hmmm...need more afterthoguhts

 

I have no real knowledge on this only a gut feel, hopefully it's not just gas.
As the SC speed increases the efficiency will go down. So after a while there will be no increase due to blow back and the inefficiency of the SC to compress more air.

The design will limit the max pressure obtainable. Less efficiency due to increased clearances will make the SC last longer and not need to be torn down for repair every few runs.

 

Heres some math gratuitously stolen from a BrianBrave post:


155 / 74 = (2.10) * 5.8K = 12,180 SC RPM (Factory)

178 / 74 = (2.41) * 6K = 14,460 SC RPM

181 / 74 = (2.45) * 6K = 14,700 SC RPM

185 / 74 = (2.50) * 6K = 15,000 SC RPM


Code 3 pulley = 65mm (so I've read) although waldig hinted it may be 63mm(?) can someone measure?

155 / 65 = (2.38) * 6K = 14,280 SC RPM

178 / 65 = (2.74) * 6K = 16,440 SC RPM (Stacked)

 

That's how fickle I am.....Table now Updated and Aligned
I've higlighted the Waldig Figures in red

b22b

 

i have hit 19 lbs with just a c3 and 22 lbs stacked. refigure your tables

 

the "boost calcs" in post #2 (and 9) don't seem correct.

to find the gross effect of changing a crank pulley, you divide manifold pressure by original pulley and then multiply by the new pulley size .... HOWEVER you MUST factor in the atmospheric pressure of 14.7 psi

so if you have a car with a 155 pulley and you replace it with a 181 .... your calc goes like this
beginning boost 29.2 (14.5 +14.7) divided by 151 times 181 equals 34.1 psia

now subtract 14.7 from 34.1 and you get 19.4 psig .... this is your new boost (gross calc of course as pumping losses will vary slightly)

then .... assuming all of the over-drive values are correct in 32Krazys post (I have no reason to doubt brian brave or steve on this) ... then you could apply the overdrive values to this equation to find the gross boosts for the various pulley combos ....
example:
beginning boost (including 14.7 atmospheric pressure) divided by 2.1 and then times 2.41 (and then subtract out 14.7 atmospheric pressure) will give you the gross boost for the 178/74 pulley combo.
etc etc ...



Chris

 

its an engineering thing chris. to much time playing with numbers not enough time wrenchin and racin!!

 

okay updated.....
took poetic license and updated the others ....you know - change history and all that stuff.....

b22b

 

Some more information on various pulley size combos here:

https://www.crossfireforum.org/forum/691690-post81.html

 

Love your work.....!

 

Mine? Thanks!

 

where are you getting the 48 hp gain from the Rudy Pulley?
If I've calculated correctly.....
370cfm cylinder displacement/requirement ( minus fuel vol) at 6000rpm
stock 14.5psi = 690cfm intake required at atm.
eg: rudy 62mm pulley at 20.2psi = 825cfm intake at atm. = +20% (70hp?)
You got some losses factored in? SC eff etc.

 

Yes. I went about it differently though.

I multiplied the blower overdrive % by the HP level (350 or 400) and by a unit-less empirical factor that I derived to calculate the HP gained (boost) column. I similarly multiplied the accessory overdrive % by another factor I derived to calculate the HP lost (accessory overdrive) column. I subtracted the losses from the gains for the total HP gained.

Deriving the empirical factors is where the wild approximations come in.
I took the HP gains Eurocharged has published for their pulleys (which seem to be generally accepted as accurate) and adjusted the factors until the results generated matched up close to what Eurocharged has published. Initially I focused on the 65mm pulley and found the HP gained factor because there was only one to adjust since the 65mm has no losses from overdriven accessories. I then found the factor for the accessory losses that lined the 181 and 185 pulley results up with what Eurocharged has posted. I checked the numbers for reasonableness, and then played with graphs.

We know that above around 20% overdrive the supercharger efficiency starts increasingly limiting the HP gained. I made no attempt to factor for that reduced efficiency.


I ordered a 62mm pulley, so I am hoping your estimate is right and not mine!

 

yes - I'm also thinking of selling the Code3 (I havent yet put on) and going for a 62mm + killer chiller and maybe the pulley saver kit and see where that gets us.
Injectors and fuel rail+pump then be next.