liqidvenom

iTrader: (6)

so i will start this by saying i am tired and i had a long day doing calculations so if this is off a bit then forgive me....

i have been reading alot about people being afraid of overspinning their blowers and the like so i decided to pull up the formula and do some calculations for myself.

first you would need the gear ratios for the blowers we tend to use for vq30's which are the

blower name gear ratio max impeller speed
V1 3.45:1 50,000
V2 sq-s 3.6:1 50,000

those by itself arent to important just yet. and im going on an assumed 6.25 for the crank pulley diameter ( i no longer have the stock pulley on my car so i can ensure its accurate, but that can be easialy changed in the formula)

the impeller calculation that pertains to us is this

crank pulley diameter x gear ratio x max rpms to be spun/ supercharger pulley diameter

ie: for a v2 it would be 6.25"(crank pulley dia) x 3.6 x 6500/3" (supercharger pulley) and that would give you 48750 rpm's at the impeller. 48750 is below the max 50,000 rpms our blowers should see.

now its simple math to understand that if we go smaller in pulley size that we will climb higher very quickly in impeller speed and thats due to the large size of our crank pulley.

here is where i was thinking of this and i might probally get laughed at or something. if you reduce the diameter of the crank pulley that would allow us to be able to run a smaller pulley without being anywhere near the 50k impeller limit.

for example: 5" (underdrive crank pulley dia) x 3.6 x 6500/3"=39000 as an impeller speed.

note i used 5" as a possible size...its raining and hot and im lazy to go measure my underdrive pulley

now some of you guys are saying, but if we make the crank pulley smaller we wont make any boost since its spinning so much slower....

I am thinking that with most compresors, running it near its max impeller speed does 2 negaive things to it:
1) heat up the air a great deal and also lowers the adiabatic efficiency
2) puts un needed stress upong the bearing in the compressor.

I am thinking that our blower are able to build boost even being spun only at 39k at redline and with our new abilities with EU and such would allow us to increase our redline and run a smaller pulley and still be way below our 50k max impeller limit. this is all just a hunch since i am tired and just going over this in a long winded thread.

this would allow their possible max of 20psi ( which is more theoretical then anything imho) and still be below the the impeller max( which i beleive is a gross understatement of how hard their blowers can spin, since many cars that run v2's have giant crank pulleys compared to ours and still run a 3" pulley with ease).

so the cliffs for those who cant stand to read all that much, running a smaller crank pulley should allow us to be able to run more s/c boost while keeping under vortechs impeller speed limit.

so what do the gods off bost have to say on this

The Wizard

iTrader: (43)

I don't get what you're saying. By going with a smaller crank pulley, you just lost boost. Putting on a smaller blower pulley will only get you back to where you were psi wise, but also spinning the blower at much higher revolutions. If anything, you would want a slightly bigger crank pulley to get a little more boost while maintaining the same blower pulley speed/revolutions.

If you're worring about how hot the boost gets, get a AWAC/ intercooler/meth injection setup.
If you're worried about wear and tear on the compressor, don't run a small pulley. You gotta pay to play.

Someone please correct me if my thinking is wrong.

SPiG

iTrader: (7)

Yes over reving the blower will start to get out of its efficiency and make the intake charge heat up, but changing the actually pulley diameters while keeping the ratio between the pulleys the same or close will not affect that. It is not each pulley's diameter that matters but the ratio of crank to SC that will determine boost.

The main disadvantage of running smaller crank and SC pulleys would be that there is less contact area on both pulleys to the belt and thus it would be easier to slip. Then you have to run more belt tension and that is what really wears on the bearings. As the wizard said you really want a bigger crank pulley since it would give you more belt contact and give a higher crank/SC ratio and thus more boost.

Realistically there are so many other more important mods to be done with a boosted car like tuning, piping, fuel setup, etc. that an UDP is probably not going to account for a large enough gain to negate the trouble of the belt contact, pulley size, and even crank dampening issues.

liqidvenom

iTrader: (6)

what i was getting at was that we could run a smaller crank pulley and use the larger s/c pulleys we have available to use already....but like i said this idea seemed like it wasnt going to somethin that would work in actuality.

i under5stand that other mods were important as well, i was just focusing on the blower and what drives it.

also i doubt that the blowers listed efficency is that anywhere near its 50k impeller limit, hence why i mentioned that spinning it less but reving a bit more would give us back some of the lost efficency that would be worth the belt slipping issues.

SPiG

iTrader: (7)

Are you talking about revving the engine higher, but spinning the SC less?
The same could be done with the stock crank pulley and a smaller SC pulley, and an extended rev limiter. If this helps get more psi, that I don't know.

I am not sure where vortech gets its max psi level from. It is probably for a different sized engine, but I am not sure if more displacement would help it get more pressure or less.

I think they have compressor maps for the Vortech units somewhere on their site or something. That would be the best thing to check if you really wanted it to be in its peak efficiency.

liqidvenom

iTrader: (6)

yeah spig, you kinda see where i was going with this.

i just spoke to a guy named randy and he told me that first off the 20psi max is somethign thats dependant upon the car, which i am sure lots of you guys already know. ( things such as the engines ability to flow lead to that)

what i really asked him for was if thy have maps that show the impeller rpm vs theortical boost but he said they get those numbers from just lots of testing per car they build kits for i assume.

he also said that the max rpm that you want to spin a v2 is around 45,000 and after that you being to loose a good deal of efficency.

my idea was hopefully to get a hold of a boost vs. impeller rpm chart and find the max efficecy and be able to hit that right at redline, seemed like an easy thing to figure out to me but we are lacking some extra info i would needto do the calculations.

ill probally look more into this later though