V2Rocket

i was thinking that not having a throttle before the blower would mean it was always trying to compress some air and taking power off the crank drive, even if there was a bypass it'd still get some feed air.

there has to be a reason why all OEM-level cars with positive displacement blowers have the throttle before the blower then...the GM 3800 L67 even has the bypass integrated in the blower housing but between the throttle blade and the blower inlet. same with the supercharged ford modulars. and the t-bird this blower came off of.

Paulyy

As far as i know -

The throttle before the blower, the blower won't be producing boost because the throttle is closed not letting any air in.

The throttle after the blower, the blower is producing pressure before the throttle, but the by pass valve is venting the pressure and recycling it though the system so theres atmospheric pressure before the Trottle body.

DarrenD

From what I've read, it can be done either way. In an intercooled setup it is advantageous to have the TB after the blower to reduce lag. I've also read about quite a few people talking about having surging issues with the TB before the blower due to lack of air and cavitating the blower at low throttle conditions. I looked at it like a blow-through turbo setup and used a bypass valve, so far so good!

V2Rocket

you may be right about it being a moot point, but i think if there was an issue with pre-blower throttle i dont think any of the OEMs would do it that way, but they all do even with the flexibility of making anything in any shape they want. again, GM even cast the bypass valve into the SC housing on their 3800 cars after the throttle plate, and the Ford SuperCoupe has a small bypass valve between the throttle body and the lower intake manifold behind the supercharger.

from what ive seen the blower with real cavitation issues is the M112, not the M90, because they made that blower larger by lengthening it but leaving the opening in the back the same size so it cant feed itself at high RPM.

ZR8ED

Man! I am going to have to swing by there sometime and see this thing completed!
Congratulations on a successful test drive!

MB968

If the throttle body is before the roots type/air pump, when you are not asking for boost, the air pump will be operating in a partial vacuum depending on how far the throttle plates are open or closed. You can think of air as a fluid (which it is from a purely scientifically standpoint). So when the throttle body is mostly closed, the air pump sees very little resistance from the air since the density of air molecules is low. It will take little energy to drive the blower under these conditions a key factor in mileage requirements.

If the air pump is constantly working against back pressure with the throttle body after the air pump, a lot of energy will be wasted with the air pump fighting against the back pressure. And it will be a lot tougher duty for the air pump, affecting its long term reliability.

In either design, the bypass allows air that is pumped by the unit and not used by the engine to be reused by the pump, somewhat equalizing the air pressure at both the outlet and inlet of the air pump. And of course if the throttle body is after the pump, the bypass, which will open if the throttle body is closed serves to keep the output of the air pump from being slammed up against the throttle plates (again, think of air as a fluid).

This is not necessarily the complete picture, but are most of the key factors at play.

Noahs944

DarrenD, VERY NICE WORK!!

DarrenD

For sure, anytime.

Thanks. It looks better in pics, the car has really high kms which meant it was rough enough to be cut up for this build but overall I'm happy with the results.

DarrenD

I went to look at another blower this morning as it looks like my current one needs at least a snout rebuild. The guy was touting it as being like new but sadly it too was leaking oil and not nearly as nice as he described it. Looks like I'll rebuild mine, delaying the project yet again.

V2Rocket

luckily the snout is super-easy to rebuild if you have access to a press, a freezer and an oven.

DarrenD

Yes. I watched some stuff on youtube and I have experience rebuilding industrial gearboxes, shouldn't be an issue.

Volhv_944

Smells like Speed/Reference sensors. Mine engine would cut out when shaking the car.... or poking at the wiring. It was easy for me to diagnose it, since they were the last things I had touched.

V2Rocket

is it loud with the throttle after the blower? reading on other sites would indicate that the case.

DarrenD

I don't really have a reference point, but it is very loud, I absolutely LOVE the sound it makes.

I pulled the supercharger out tonight, and I'll hopefully get my snout rebuild kit this week and rebuild it at a friends shop this weekend. In the meantime I'm trying to clean up and improve all the little issues that need to be addressed: wiring, hose routing, clamp direction, rad mount, guesset the sc belt tensioner and the list goes on. I'm also hoping to clean up and paint the SC as well as much of the body behind the front bumper. I'm also planning on moving the K&N filter, I think it's too low where it is.

And on it goes...

MB968

Given your experience, you should find it quite easy to rebuild. As I recall, the fits are such that there is one fixed and one floating bearing (with a coil spring in between to keep a light preload on the bearings and to deal with the thermal growth of the drive shaft). Make sure you get the same seal, or a direct replacement. My M90 was off a GM 3.8l. As I recall the exact part number seal was no longer available from Chicago Rawhide, but a replacement was. Due to the oil in the drive being synthetic, make sure you get the Viton seal which is what the original would have been made of.