How to limit boost on a supercharger?

[roni87]

I want to run my super around minnesota. Right now I'm running the air to air/ serpentine belt speedwerx setup. I believe around 7 psi at altitude.
Apparently they don't offer a bigger pulley for the supercharger with the serp setup.

Is there a wastegate or blow off valve that can be installed to limit boost to 3psi?

I did run it around the yard for a few miles at the current psi. Put in a gallon of av to about 4 gallon premium and ran fine wot so I know I can get it to work at 3 psi.

Jeremy at sw said I'm on my own to make it work around here as the kit wasn't designed for below 5000ft.

 

[d1100t]

Av gas

What about running straight av gas?
I've ran my turbo charged 800 on 8lbs of boost at 1400ft with no problems on straight av gas.

 

[roni87]

For longer trips or trail rides would be nice not to pack av gas. Also it used way more fuel than my turbo pro at 7 psi. Lowering boost should help me make it between gas pumps

 

[izzni]

Would putting too much weight in the clutch and reducing the top end RPM be an option?

 

[roni87]

Pulleys

I might look into a custom pulley. Per prochargers recommendation 1psi of boost change is generally 1/10" diameter on the small pulley.

 

[roni87]

Ordered up the POD 300 for my sled. This allows the monitoring of a bunch of stuff but mainly reads the boost pressure off the map.
1100 ft elevation

2.0 psi at 4100 engagement
8.5-9.0 psi Just before exhaust valves open ~7200 rpm
6.8 psi at wot 8170 rpm.

I wanted to lower the overall boost and eliminate the spike. I ordered a boost limiting valve and will be installing it via a silicone tee just before the intercooler.
Hope to have it down to 4psi max and it Will still build boost very early in rpms.
A smaller pulley could have got me down to correct psi but would have still spiked before valves open and wouldn't boost as fast off the bottom.

 

[roni87]

Wound up buying a smaller bottom pulley for my sled. 5" instead of the stock 6.5" for high elevation.
Boost is now .2 at idle and around 4 psi max. Should work good for my home range in mn. Went with ibexx weights.
Had the sled in BC this summer and superchargers are pretty responsive when clutched right!

 

[xpturbo600]

Just for piece of mind, I wanted to share an idea. Boost is a measure of resistance to flow, not volume of flow. HP is a direct result of air mass not boost pressure. More flow equals more HP in most cases which leads to questions of detonation as dynamic compression increases.

The reason I say this is because you stated your sled had a boost spike and then it drops. To me, this is less concerning. A supercharger is linear in flow...it cannot spike boost like a turbo. Instead, the sled is simply telling you there is more resistance to flow prior to the exhaust valves opening. If resistance is reduced at the same flow rate, i.e. the exhaust valves opening, the only logical outcome is pressure in the system must decrease. I would not worry about it too much.

Finally, dont drop the boost too much since you bought a boosted sled for a reason. I ran 7 to 8 pounds on a turbo setup all day at 6500 feet on quality pump fuel. However, turbos create resistance to flow vs a supercharger. Happy riding!

 

[Demidoff]

Are you find any solves how to limit supercharger pressure? Can I see you fuel map for low altitude if it possible?

 

[roni87]

I haven't built a map for this thing yet. Just received my autotune and I can't get a afr reading.
Will have one built soon I hope. Are you trying something similar?

 

[Demidoff]

I haven't built a map for this thing yet. Just received my autotune and I can't get a afr reading.
Will have one built soon I hope. Are you trying something similar?

I also became interested in your idea. I think that compressor's pressure at low altitudes it is too redundant for me. I wanted to know your feedback. If I understand you right you want to install a blow off. I still have not been able to find a fuel map for low altitude.

 

[Ajax73]

This thread is a bit old but, did anyone figure out low elevation setting for supercharger? I'm going to ride U.P. Backcountry in a week and would like to try my new to sled there.