I've done some reading about Z guys pushing 10psi on their HKS SC kit by using 85mm pulley. After ordering an waited anxiously for it to arrive, guess what? As the title says, it went off the efficiency range. Not only I'm not getting higher boost, its dropping off after 5500rpm. The boost gauge reads 0.5bar of boost at 5500rpm. After that, it just falls all the way down. At 6500rpm, I'm only at less than 0.3 bar.

Anyone who knows what exactly went wrong please advise. It felt so crappy now. I'd rather just go back to stock pulley compared to what I'm having now.

 

seems you know what went wrong... centri superchargers have pressure maps just like turbos. go off scale the efficient goes as well.

unless something is leaking/slipping, which probably isnt the case as you'd have other issues.

 

I've checked all the joint so I'm sure its not air leak. My guess is the SC ran out of efficiency range. But how did the other HKS SC guys get 10psi from their system? Mine is already dipping far from there.

 

Please help. Any suggestions? I wouldnt mind sending it to a pro dealer but the problem is, I'm like 20 hours away from states.

 

hmm, I am seeing 12 psi peaking at 4500, but it does start to dip after 6000 rpms. I can tell you that with the HKS SC, you cannot just put on a smalley pulley and get significant increase in boost. There is much more too it than that, but it is achievable, as my setup shows. My suggestion is to contact SAM@GTM (who customized my kit), he is most knowledgeable about maximixing power with the HKS SC kit.

 

I know that GTM modded the charger housing. Anyone with experience who help out.

 

Do you have a GTM kit?

 

Do you mind sharing what other mods you did to get achieve such boost? It feels like the SC just lost traction at high speeds

 

I wish I had it. I bought the SC from a HKS dealership.
Appreciated all the feedbacks given.

 

Cosworth plenum, Nismo Headers, Power Enterprise metallic HFC's, Tanabe y-pipe, Amuse R1 titan exhaust, FCon vpro, AFK, ATI damper crank pulley (slightly OD--adds a little more boost I think) GTM spec "stage 5" HKS SC kit, etc.

 

I think that's the problem. I don't think a smaller pulley on a stock HKS SC kit, will give you the results you are looking for. You need the GTM modifications. Also make sure your belts are the right length for the new pulley and that they are tight.

 

My setup is around there. Just didnt have the ATI pulley. Do you know if Sam@GTM could be generous enough to give me some pointers and advise? Thanks.

 

I got 7PK1030 belts and they are tight. I understand there are certain things being done by GTM to achieve such boost. Mind helping me out? I would love to send my car to them but due to the distance, its impossible.

 

Call them up and ask or pm them on the forums. Won't hurt to ask.

 

GTM probably changed the sun gear out of the S/C? I could be wrong.

 

^where would they even source that? Thier upgrade package isnt that expensive which means it must be a straight forward modification.

can you two HKS owners share photos of your setups? At least any external differences would be noticable...

 

physical appearance should look rather identical. Just written to Sam@GTM. Hope he have a solution for my problem.

 

Anyone else who rectified this problem please help me out here. Thanks in advance.

 

No one knows? Anyway, I will be sending the compressor housing to a machine shop to try out different things. Not too sure if it works but its worth a try. I'll post my results later.

 

On the original HKS SC kit the smallest pulley size you could use in theory was about 89mm from the OEM 95mm based on a 142.6 crank pulley size and 6600 rpm cut. This kept the pulley rpm at 10453 rpm and the impeller at 99131 rpm which were just under the warranty limits.

Formula as supplied by rotrex:

I = E x ((Dc+2.8)/(Dp+2.8)) x 9.483


I = Impeller speed max
E = Engine Speed max
Dc = Crank Pulley Diameter
Dp = S/C Pulley Diameter

Pulley(mm), Impeller RPM, Pulley RPM

95 93049.76 9812.27
94 94011.01 9913.64
93 94992.34 10017.12
92 95994.37 10122.78
91 97017.76 10230.70
90 99166.89 10457.33
89 99131.44 10453.59
88 100223.20 10568.72


Michael