I'm getting 12.9 psi on my 2006 JCW with JCW pulley, 2% overdrive crank pulley and OBX header with stock cat. Was at ~12.4 psi before crank pulley. I don't know if its good or bad. Pressure measured through OBD 2.

What pressures are you guys seeing?

 

I tapped the line below the intercooler and have like 14-15 lbs. The Detroit Tuned BPV is supposed to add between 1/2 and 1 lb of additional boost.

 

I get 13 to 14psi. Taken off my Scangauge. No mods to pulleys but I have 380cc injectors. I am going to install a vacuum operated gauge moving forward. Currently looking for one with a tattle tale needle like to one in my old 930. At least with this I can see what my max boost was after the run rather than having to look at the Scangauge while under boost.

 

did you see a boost difference with that DV ?

 

I forgot to mention I have a DT BPV. It was installed at the same time as the 2% crank pulley. Sounds like I should have 1-2 psi more boost.

 

My JCW is bone stock and I see just a tad over 11 psi

 

I would see at WOT over 14psi depending on where I started in that gear for WOT.

 

I have a 15% SC pulley, a 2% crank pulley, a DT bypass valve and an RMW tune. I have a mechanical boost gauge and see 15/16 psi of boost. at WOT.

 

and to clarify, I have the stock JCW pulley and Way's 2% ATI crank pulley. I do not have the Detroit Tuned bypass valve.

 

You installed a Dominator cam so you boost will be lower. I differ that DT BPV will not add peak boost pressure. It only closes the bypass sooner.

 

I cannot resist the opportunity of spamming this thread with the evidence of my SC has higher boost. Bone stock MCS with 15% pulley. 15 PSI boost. The boost gauge is very useful for me to review my driving if I accelerate hard enough at different part of the track.


Boost pressure alone is not a reliable indication of power output without taking into account the engine aspiration differences. Else is just apple vs orange comparison.

 

As the boost with a supercharger would appear to based on crank revolutions that thereby rotate the belt that spins the SC, how would a cam within the engine impact boost?

On the Detroit Tuned BPV, need Chad or Nick to speak up here. From what I have read on the matter is that the seal on their valve is tighter and therefore the pressurized flow is kept in the flow and not able to leak back through the backcheck.

 

Cam lift, duration and overlap on a cam will affect manifold pressure.

If you open the intake valve further or longer you flow more volume past the valve, hence it takes more volume to achieve the same "pre-cam" manifold pressure. In simple terms the air is leaving the intake manifold before it can be pressurized.

I'm not going to get in to overlap, do a google search it's an interesting read.

If the output volume of the supercharger is linear per rpm then you will see a lower manifold pressure.

If you have a turbo, it can compensate by opening the wastegate later the boost will remain the same or be slightly less.

Just because you see a drop in manifold pressure does not mean you have lost any performance. You are actually getting more air in the cylinder giving you the ability to make more power.

 

Ah that now means we have to get into total, dynamic and static pressure albeit this is a gas and not a liquid.

 

Correct

 

In all of our testing thru the years, we always see a touch more boost out of the cars. it can be UP TOO 1 psi but always more. but again we are testing it with a mechanical gauge and etc. etc. but as soon as the BPV shuts, it's building boost, the sooner it shut the more boost the system can make int he given RPM band. given small, but it will make more, and each car is different in how it reacts to any mod you add to the car.


Chad
Detroit Tuned

 

Read somewhere a MCS should see higher boost as the head is not "ported" like the JCW. With ported heads people see a drop in boost.

 

Do you mark your BPV's with anything to identify it as being a Detroit Tuned unit? Reason I ask is I'm going to be doing a clutch on our JCW and if it doesn't already have one I would like to install one. Thanks for any information Chad and sorry to OP for the slight highjack

 

I pressure tested the system at the throttle body and found a leak between the supercharger and the intake tube, the green gasket. After fixing that and the car idles better and has ~0.5 psi more boost @ WOT.

 

Nice job! Did you smoke test the system?

 

No, I made a device out of 2.5" silicone hose, abs pipe cap and some pipe clamps. Similar to this , shoved it onto the throttle body and pressurised the system to ~20 psi. I could hear the leaks.

As for the dt bypass valve you should be able to tell by the spring tension. The stock one that came out of my car was as stiff as a spring loaded ball point pen and the dt was maybe x3 stiffer. If my valve was busted then i'm talking out of my as*.

 

A+ on creativity! Spring on my BPV is fairy stuff But with no baseline who’s to say if it’s a “pimp” version. Good to hear you’re getting your car sorted.

 

Late to the party here, but also take into consideration your altitude. If you above sea level elevation then your boost will be lower.

 

16-17psi max

 

The use of boost in many instances could be replaced with back-pressure as it better explains what is happening ie: more air being supplied than being used.

I have worm drive clamps on my by-pass valve connections as the euro type clamps were leaking at 5 psi. I made a similar type pressure tester.