Swapping from a 15% pulley to 17% pulley

[Jaw_F430]

Hi all

Having fitted my new head the boost pressure has dropped and now I am thinking of upping the boost more by switching to a 17% pulley.

Just to get a collective answer does anyone see any disadvantages from switching to a 17% pulley? (or advantages apart from more power)

I initially went for the 15% as this is at the top end of the operating scale for the s/c before excessive heat is produced and it seemed the safer option as I had stock I/C.

James

[sam_a156]

Keen to hear comments on this too. I also saw a tangible drop in boost.

My -17% Alta v2.0 is already on its way. Going to swap my current JCW & +3% crank setup to oem crank and -17%.

Personally I would think that going for bigger reduction might not allow to raise the rev limiter so much as -15% due to overspinning the s/c. Suppose 7400/7500 should still be ok though(?)

Sam

[Jaw_F430]

Quote: Originally Posted by sam_a156 (original)

Keen to hear comments on this too. I also saw a tangible drop in boost.

My -17% Alta v2.0 is already on its way. Going to swap my current JCW & +3% crank setup to oem crank and -17%.

Personally I would think that going for bigger reduction might not allow to raise the rev limiter so much as -15% due to overspinning the s/c. Suppose 7400/7500 should still be ok though(?)

Sam

Thats what I was thinking Sam as my map may end up at 8k redline. Boost shown on gauge after fitting few parts is 14-15psi

[GRSmotorsport]

Quote: Originally Posted by Jaw_F430 (original)

Thats what I was thinking Sam as my map may end up at 8k redline. Boost shown on gauge after fitting few parts is 14-15psi

I'm running a 17% pulley with no problem at all (touch wood!). Wouldn't worry too much about the slight loss in boost. You want maximum BHP with the minimum amount of boost. I'm peaking at 15.5psi but still seeing 250-256bhp. I'm not running a lighter crank pulley either.....

[Jaw_F430]

Quote: Originally Posted by GRSmotorsport (original)

I'm running a 17% pulley with no problem at all (touch wood!). Wouldn't worry too much about the slight loss in boost. You want maximum BHP with the minimum amount of boost. I'm peaking at 15.5psi but still seeing 250-256bhp. I'm not running a lighter crank pulley either.....

Cheers GRS

Do you have a big valve head fitted? And are you running air to air or chargecooler?

[GRSmotorsport]

Quote: Originally Posted by Jaw_F430 (original)

Cheers GRS

Do you have a big valve head fitted? And are you running air to air or chargecooler?

Yes I have a West Tuned big valve and flowed head, I'm also running a charge cooler

[MINI-Morgan]

Have you still not got that 17% on yet?? Come on....some of us are even running one with the stock intercooler without any probs!

[Silent1]

Quote: Originally Posted by sam_a156 (original)

Keen to hear comments on this too. I also saw a tangible drop in boost.

My -17% Alta v2.0 is already on its way. Going to swap my current JCW & +3% crank setup to oem crank and -17%.

Personally I would think that going for bigger reduction might not allow to raise the rev limiter so much as -15% due to overspinning the s/c. Suppose 7400/7500 should still be ok though(?)

Sam

Revving the engine to 7500 RPM with a 17% pulley would spin the supercharger to ~19313RPM that's 3313 RPM over the maximum safe limit of an M45, the thermal inefficiences you're going to encounter at that RPM would almost certainly negate any benefit from spinning it that fast.

At the very least you're going to encounter a drastically shortened service life for the supercharger as well as the fact if it does let go spinning that fast i wouldn't like to guess what else it will take out.

[MINIMANIAUK]

As above comment , but if you dont run to the red line all the time then the only issue could be the premature water pump drive fails and possible cavitation ,again only if very high rpm maintained.

Boost pressure itself is not and indication of how much power you will make -the flow and volume of air is ,what you need is quality of boost not size of boost .
You could for example shove a cork into the intake manifold with a hole in the middle- result would be far higher boost pressure!!! but far less power!!

Quality boost = lowest temp, thus greater density , at the optimum speed of airflow, with minimum turbulence, and drag.

The charger also uses less power to turn when providing quality boost and more power when not

[Jaw_F430]

I think I will stick with my 15%. (looked on NAM as well and a lot of them use 15% with good power made)


If I can make around 230WHP with my current spec I will be happy (thinking of going back to stock exhaust as well as JCW with Janspeed mani is quite loud IMO)

Cheers for all your comments guys

[MINI-Morgan]

You have to consider your end result. 17% will be faster if you maintain good temps and dont rev as high. 15% will be better at higher revs. You decide if you want more torque or higher revs I voted torque as I hate driving type-r's