If i had 4 different size pulleys with the same diameter step change
will boost keep increasing more ?

eg, the 1st smaller size pulley gives 2psi more will the second give 2 psi above the first step , or will it be more because the centrifugals are non lineair in boostbuildup ?

example :

original blower pulley size = 4.0 inch
how will the boost buildup look like ?

3.8- +2psi
3.6- +2psi (4psi extra form baseline)
3.4- +2psi (6psi extra from baseline)
3.2- +2psi (8psi extra from baseline)

or :
3.8- +2psi (= +2 psi from baseline)
3.6- +3psi (= +5psi from baseline)
3.4- +6psi (= + 11psi from baseline)
3.2- +10psi etc etc..

 

I'm not a boost wizz, but I'm decent with numbers. At least mathematically, in theory, it should be exponential, all you're doing is increasing impeller RPM relative to the motor RPM by the ratio provided by the combination of the crank and blower pulley. How much boost did you see max, at say 6500 rpm on the 4" pulley? From that, if it is exponential, you should be able to get an accurate boost reading for any size pulley only limited by the blowers max CFM.

 

i dont think boost is necissarily linear, but i do think that CFM output is linear. Therefore I believe the power is linear as well.. which is really what matters isnt it

 

In my experience, after playing with 7 blower pullies and 3 different head units, your first model is more accurate. Just remember as you get smaller, slippage issues increase. On my T-trim, I went slower with a 2.75 blower pulley than I did with the 3.12. Finally settled on a roughened, hard anodized 2.85 which has set my peak boost record at 12.87.

Jim

 

You have to also remember that centrifugal blowers are only "efficient" to a certain rpm turned. You have to plan your "max efficiency" point to coincide with your max rpm or your mid to peak powerband, and pick your pulleys accordingly. That, or you'll end up spinning your blower past the point where it is making anymore useful "boost" and/or overboosting -if thats at all possible in the advent of blowoff and dump valves.

 

Uhh, Ok.

Blowoff valves are only used to prevent compressor surge on decel. Dump valves are used when you can't think of a proper word for a wastegate!!!
Wastegates are not used on Centris.
Many people overspin their Centri's and the boost is "useful"
The biggest concern when overspinning the blowers seems to be the bearings ability to handle the additional load.

 

You can overspin a blower to where you have maxed out the airflow capacity of the blower, and you'll end up with excessive heat and basically airflow cavitation. Each blower has it's sweet spot where it is the most productive. Bob

 

thanks, guys, i installed the biggest pulley that would spin the centri to it's max rpm at max engine rpm and got a bit better boostpressure, but still not nowhere near i thought i would be

it was as delta T said, it looked much like my 1st example and was not very lineair as i hoped it would be

 

Uhh, ok... then dispite displayed ignorance, you know exactly what I'm saying. If you disagree, then that is what you need to say. You can save the pinhead comebacks and snide remarks for your elementary classmates. When you spend your time trying to make other people look stupid, you only succeed in displaying your own stupidity. People like you are aggrevating at best.
A "wastegate" is a device exclusive to a turbocharger system. It bypasses EXHAUST gasses on the ENGINE EXHAUST side of a turbocharger system to reduce the speed of the impeller (boost) side when necessary. Ergo, I DID NOT call what I have a "wastegate".
I'm setting my Paxton Novi2000 up to hit advertised max rpm right below 6000engine rpm. I have two (whatever you wish to label them) valves set up in the system. One is to recirc the boost backed up in front of the throttle when I shift or suddenly lay off the throttle (that which you labeled a 'blowoff"). The other is to bleed off any excess PSI over what I set the pressure release for. I set my system up the way I did to get the blower to max efficiency as low in the rpm range as possible. After all, it is a centrifugal and not a roots blower.
When I called Paxton, I asked VERY SPECIFIC QUESTIONS. One of which was: Is the 55,000 rpm limit where the unit will shell out, or will it spin to the 62,000rpm that it might possibly see with my chosen 8" crank pulley and 2.7" blower pulley? The answer had LESS than nothing to do with bearing failure. I was told that the unit would hang, but after 55,000 rpm, the impeller would not make any more usable boost than it would at or below that level. Bob almost paraphrased what Paxton techs told me.
If anything, I will need to go to a larger blower pulley and smaller crank pulley to avoid boosting at the advertised max 29+ psi (that the Novi 2000 is capable of sustaining) the majority of the time. The trick with these centrifugals is to keep the boost at the level where you want it in the rpm band you can use it.

 

Did you not see what Bob said. If you are spinning the blower to its max RPMs, excessive high intake temps are mostly likely killing the power. Have you monitored the IATs?

 

i said nothing about power or the killing of power.
but my post was about boost pressure, thats a big difference, you can have one without the other

it's not that difficult, if it is not making the boost i would like, i have to spin it more to get more airflow.
nothing scientific about that

and obviously doing this in a higher efficiency range / island is more desirable

 

There is nothing scientific about it if you just buy a "kit", follow the directions, and then brag about what a engineering genius you are (like some people who will remain unnamed). But the rest of us have to learn theory and application to avoid grenading an engine. You need to apply some cooling method to the boost (air or water intercooler, meth, E85 tune, CO2 or Nitrous across the face of the intercooler, etc.) to avoid detonation and increase/densify the fuel air charge for power. It does you no good to create "boost" just to lose the power you are trying to generate to latent heat attached to it.

 

o you are waaay off

who said anything about a kit ?
there is absolutely NOTHING available for the engine which i installed the centri on.
not even off te shelf low compression pistons / forged rods / stong headgaskets.

EVERYTHING from building the complete low compression engine with special made forged components and wireringing the headgasket myself to making my own pulleys and making my own mounting system for the centri and special tensioner and making my own wireloom for the fully programmable injection system , welding my own intercooler, rewelding an aluminum inlet manifold from a different engine to make it fit and more performance oriented.

to the point of something simple like completely altering an alternator so it could fit below the centri .

and at least another 50 things i won't even mention.

basically changing a distributor engine with a carb (without any of the sensors i need to get it running distributorloss on the progammable injection system) to a fully forged distributorless race engine with fully prog engine management running 100% propane

so if there are any "bragging rights" (which i don't give a ****) about this build i think they are due to myself

 

Sorry JeeJee. The "kit **** and braggin thing" wasn't about you. I have a beef with BlownBlueZ06. I have a problem with people who have more money than common sense. That wasn't about you and I should have been more specific.

Now that you have been more specific about your setup; Sounds like you have an obstruction in your blower/ intercooler line to the throttle, your blow off/bypass valve is bleeding your boost off (if you are running one), overlap in your cam may be bleeding the boost off (that usually only happens at low to mid rpm though), leak in the boost lines (but it sounds like you covered that one). Sounds like you did your research so this is really remote; Maybe the blower is too small for the engine cid. In which case, its running out of *** on the top end.
Or, if it has nothing to do with the boost itself, the air fuel mix with the propane conversion may be off. I've never run propane myself, but the mix has got to be WAY different than gasoline or even e85.

Again, I apologize for the misunderstanding.

 

Where can you find this info? I have yet to see a compressor map for any Procharger.

 

cfm output is linear.

 

I couldn't find one anywhere for my Paxton Novi2000 either. That is the primary reason I just broke down and called them.

 

108dragon : it's okay. i guess the misunderstanding is partially caused be the fact that english is not my native language .