Supercharger Help

[danielbrookes]

If I disconnect the outlet it works fine - no squeal and that’s the bit I don’t get.

For the boost side, based on my pulley ratio I should be producing 12psi (ish) at max RPM. 
 

[richyb66]

So the charger is generating boost. When it's all piped up, this boost is acting against a closed throttle on the plenum at idle and if this boost isn't bled off, the charger is going to get hot. 

When you say you have a bypass, is the function of this to pass air from the inlet to the outlet side of the charger to allow airflow at idle? 

[richyb66]

Also do you have a boost gauge connected so you can monitor what's happening in real time. The boost pressure isn't linear according to revs. 

[danielbrookes]

Thanks for taking the time to reply.  The bypass is to pass air from supercharger inlet to supercharger outlet via a pipe that bypasses the charger.  My understanding is that at idle the bypass valve is open and the supercharger is bypassed, avoiding heat build up.

Boost gauge is on the shopping list...maybe I should bump it up! I was planning on getting one after I had got her running.

[richyb66]

So it sounds like you have nothing controlling boost. 

Eaton is positive displacement so the boost level is similar at all speeds. If it's generating boost at idle and the plenum throttle is closed, you'll get pressure backing up in to charger which will cause heat build up and possibly belt slip. 

Ideally you'd want the clutched pulley and actually stop the charger when you don't need the boost but for now, I'd be putting a blow off valve between the charger and the intercooler to stop the pressure and heat build up. If the charger overheats it will basically kill it. 

Your bypass valve needs to operate based on inlet manifold vacuum. 

I'd also only be using the throttle and TPS on the charger inlet. Having a second one on the plenum seems an unnecessary refinement / complication at this stage. The only refinement I'd add would probably be an idle air control valve on the plenum throttle body so you have some tunability to your idle. 

[danielbrookes]

Thanks, that also explains why I have issues with the plenum connected. I did wonder but wrongly assumed that my bypass valve took care of that.

I have an IACV from when I built the car but I could never get it to idle properly with one and the tuner I used didn’t rate them.  I think I’ll dust it off once this is sorted.

Tomorows job then will be to get it running with outlet disconnected and of course to research blow off valves.

Thanks again!

[richyb66]

The other thing you need to remember is that the Eaton produces boost through external compression. What this means is that the air isn't really compressed inside the charger and they only work if the pressure differential across the charger itself is relatively narrow. The ideal situation is to be moving a large volume of air, but still at ambient pressure.The actual boost is generated by this increased volume of air downstream of the charger.

This probably isn't what you'd expect but it does help to explain why having pressure back up in to the charger (and at the same time a closed throttle on the inlet) causes a large pressure differential, which leads to heat, rotor expansion and failure.

If you're particularly bored, there's plenty on the internet that goes in to more detail.

[danielbrookes]

Richy - you are a star! You mentioned a BOV and it got me thinking about the bypass valve.  I went back to basics and it seems so simple now, the fault was no vacuum at bypass valve.  The butterfly wasn’t opening at all because there was no vacuum - I assume because I have a throttle at plenum.

Hooked up a vacuum hose from plenum and voila, issue fixed! Thank you so much for your help.

Now I need to work on my tensioner alignment as it’s 1mm off, easy fix.  I am so happy and as usual Rhocar produces the goods :).

Have a virtual beer on me.

[richyb66]

Good news! We're all here to help if we can. 

[danielbrookes]

Went to get the car tuned yesterday and we had a problem with the belt again, at 3.5-4K it slipped.  The tuner said it was strange how the power came all in at once, however, he removed my pre charger throttle so I now only have a single throttle on plenum.

He tuned the car but said he had to compromise the map slightly because of the belt slip, told me to sort slip, put it in auto tune and see how I go then bring it back to be finished.

Well I fixed the belt slip and oh my - the car is transformed!  I’ve made other changes, lightened flywheel being one of them, but it’s night and day.  I’ve always felt disappointed in the cars acceleration - not anymore. It’s positively frightening when you plant it.

I have a small list of things to complete before I return it for it’s final tune. I’m replacing my bypass valve with a brand new one as he suspected it could be faulty.  I’ve also got some tidying up to do with vacuum cables and need to fit a barbe/swage to the end of fuel rail.  Easy stuff.

Anyone who is thinking of fitting a charger - do it! At the moment I’m “only” pushing 200bhp/200ftlbs but I can’t stop smiling!