FI intake question for you guys.

[kc95sc400]

Refresher: I have an SC400 with a V-9 Vortech supercharger.

The supercharger inlet is 3.5 inches. The intake pipe (suction side) that I am using is only 3 inches in diameter. Both times I was on a dyno, the car made LESS power and boost with the intake pipe and filter removed.

Anybody have any ideas on how / why this could be?

Used the same Dynojet both times. The only thing I can think of (something I've suspected about the Dynojet) is that the dyno can't load the car, possibly causing it to make less boost than it does on the street anyway.

KC

 

[JustenGT8]

Dynojets suck for sure. Could be that but an SC is not load dependant for boost production like a turbo..it's purely revs.

More likely the air flow into the SC is improved by the intake pipe and filter...even if a small dia. Air flow around the bare entrance is probably quite turbulent?

 

[-Nemesis-]

Didn't you go from 3" to 3.5" earlier? How'd the power difference go there?

I've found the smaller the sc feed pipe, the lower the boost made.

 

[kc95sc400]

So with the turbulent theory, a bigger pipe might be better than a smaller pipe but both would be better than nothing at all.....

I haven't yet come up with the guts to try running down the track without the pipe. Doing so could help tell the story though.

KC

 

[kc95sc400]

No, I haven't tried with a larger pipe. Just with the 3 inch and with nothing at all.

KC

 

[kc95sc400]

BTW, a supercharger (mine anyway) is very much load dependant. It won't even make boost in neutral. Also, I can be at redline with very little throttle opening and not have any boost. Or on the other side, I can be at low revs and WOT and have a few psi.

KC

 

[JustenGT8]

BTW, a supercharger (mine anyway) is very much load dependant. It won't even make boost in neutral. Also, I can be at redline with very little throttle opening and not have any boost. Or on the other side, I can be at low revs and WOT and have a few psi.

KC

That's not the SC that's the bypass. With no bypass it's simply revs turning the comp wheel.

 

[kc95sc400]

That's not the SC that's the bypass. With no bypass it's simply revs turning the comp wheel.

Nope.

Does the same thing without the bypass although the map readings are higher. Still doesn't make boost at high rpm low throttle though.

Took the bypass off last night after running at the track. I am trying to see if it feels any different on the low end. Doesn't really seem any stronger, I'll have to test it at the track.

I suppose it might be worth buying a piece of 3.5 and / or 4 inch pipe and trying it. Could track test. Run with the current pipe and no filter, run with 3.5 and / or 4 inch pipe without a filter and see if traps increase at all. If an improvement is seen, I could then spend the money on a filter for which ever size works best.

KC

 

[JustenGT8]

You still need throttle opening or a turbine won't move air Trust me it's not load dependant,, they are purely an rpm driven device.

A turbo is essentially the same...the only thing 'load' does for a turbo is provide more exhaust gas to drive the comp wheel.

Testing some different pipes is easy enough but i suspect just using a 3.5 inch inlet pipe will be as good as it gets?

 

[striker]

with the correct radius flare on the end, that's the trick!

Grtz Thomas

 

[neal]

Sorry justenGT8 a turbo is load dependant. How do you think the turbo on a stationary constant speed diesel engine (ie generator or pump engine) works. they dont have a throttle the pump just adds more fuel.
It is not really the flow of gas that gives boost it is that under load there is more air fuel combusting and as the piston cant go down fast enough (due to load) the gas is still expanding as it exits the head and push's harder against the comp wheel giving more boost

 

[spf_lexus]

Hey KC, I am with you on this. My P1SC has a 4'' inlet, and a NEVER run anything, just a fine screen T-bolted. I have a chop-welded 4'' radius with a high flow 4'' cone filter and I couldn't get into boost for ****, the revs climbed much slower and 7psi felt weaker, revs are crucial for the centri. Took it off and went back to screen method and all power was back. I thought about getting a .010'' smaller pulley to compensate but never tried.

I thought my restriction was the tight engine compartment, almost no air delivery to the filter.


I also noticed that I can run my car w/o a BPV at all and the idle never chaged. Once I replaced my fouled plugs that were causing me trouble the BPV issue never came back and all it seemd to do was bleed pressure on decel, keeping me from shredding more belts.

 

[JustenGT8]

Sorry justenGT8 a turbo is load dependant. How do you think the turbo on a stationary constant speed diesel engine (ie generator or pump engine) works. they dont have a throttle the pump just adds more fuel.
It is not really the flow of gas that gives boost it is that under load there is more air fuel combusting and as the piston cant go down fast enough (due to load) the gas is still expanding as it exits the head and push's harder against the comp wheel giving more boost

Err dude, read carefully before posting eh ;-) I was referring to SC's not turbos.

 

[MWP]

BTW, a supercharger (mine anyway) is very much load dependant. It won't even make boost in neutral. Also, I can be at redline with very little throttle opening and not have any boost. Or on the other side, I can be at low revs and WOT and have a few psi.

It is, its just you are not seeing it... you are measuring boost in the inlet manifold which is controlled by the throttle body.
Measure pressure between the SC and the TB to see what the SC is really doing.

 

[neal]

Sorry justenGT8 I read your comment "A turbo is essentially the same...the only thing 'load' does for a turbo is provide more exhaust gas to drive the comp wheel" as saying a turbo is essentially the same.. as a supercharger and driven more by RPM.

 

[JustenGT8]

No probs mate, a lazy post on my part didn't help Just need to convince KC that a centrifugal SC is an rpm driven device ;-)

 

[XR8tt]

Its very hard for any compressor to flow or compress air under vacuum !!
As in part throttle..
Filters tend to smooth airflow. A rollled pipe or trumpet would cure this. Also maybe sucking in HOT air ?? From engine bay..

 

[Zuffen]

Most centrifugal blowers have the t/b after the the turbine so it should make the same boost at any rev point regardless of throttle opening.

In fact on little or none it should make more until the bypass opens.

 

[XR8tt]

Yes ...
After compressor.. Sorry to be pedantic..
They generally don't full off boost as rpm climbs..
Depending on s/c size no matter what type..

 

[stevechumo]

I thought my restriction was the tight engine compartment, almost no air delivery to the filter...

The air is still there because your supercharger sucks in the air with much greater force than a NA engine with just vacuum. Unless you completely close the supercharger inlet or block part of it, then the air will be reduced. But then your compressor will have a big problem of the resistance to the point that it can't turn no more, or may be much slower. The reason you lose power is because of the air/oxygen is less densed when it's soaked in the heat. With colder air, the air is more densed thus has more oxygen to burn and that turns into power.