Researching supercharger, need advice

[MGBpilot]

After test driving a MINI Cooper and a MINI Cooper S (and buying a Cooper S) I have come to appreciate the extra kick that can come with supercharging.

Got me to thinking about bolting the Moss supercharger kit onto my '77 B.

I've spent several hours reading information on the 'Net about supercharing MGBs, and I'm still a little confused. Could use a little advice to help me make my final decision.

I rebuilt my B's engine three years and 13,000 miles ago:
- 30-over "high-compression" pistions (I think it gave me 8.8:1 compression ratio).
- 5-under on the crankshaft.
- heavy duty valve springs.
- mild road cam.
- Eurospec dizzy with Lucas Sport Coil.
- double row timing chain.
- Ford Type-9 5-speed transmission.
- Weber DGV carb, which I put on the engine before the rebuild.

I've been reading how the Moss kit works best on low-compression (8:1) engines.

My question, given the build described above, is the Moss kit an appropriate add-on for my particular application?

Would also appreciate a recap of the pros and cons on supercharging.

At this point my choices are going to be either leave things alone (everything is running smooth)or pull the Weber and replace it with a Moss supercharger.

Appreciate the input. Thanks for the opinions.

Ken V.
'77 MGB
Safety Fast!

 

[Steve_S]

The SC kit works best on lower compression engines only because you can use more boost. It will work fine on high compression engines but it won't give quite the performance gain. The advantage of the SC is the wide torque band. power is available pretty much wherever you need it.

I'm ordering a kit right now for my '65 but I'm lowering compression to allow for more boost so long as the engine is apart.

 

[swift6]

The boost that the supercharger gives is not dependent upon the compression ratio of the engine. The supercharger boost is determined by the diameter of the pulley for belt drive and then the pop-off valve (if it has one) to keep from 'over-boosting'.

They recommend supercharging lower compression engines because as the air is crammed into the engine (the main job of a supercharger) the compression ratio effectively increases. If you start with a higher compression ratio then the higher the effective ratio under boost. If you go too high then you begin to see ignition related problems and blown head gaskets at minimum, grenaded engines at worst. The higher the compression ratio that you start with then the higher the effective compression with the supercharger. Which could reduce the longevity of your engine.

Performance cams for a naturally aspirated engines can sometimes offer less performance for forced induction. Especially if they have long durations with intake/exhaust overlap as you end up pushing fresh air/fuel mix directly out of the cylinder and into the exhaust.

Depending upon your altitude in Kansas, having an 8.8:1 engine might not be that big of deal for supercharging. As you increase your altitude, ambient air pressure decreases and effectively lowers your compression ratio as the air is less dense. Along the front range in Colorado, average of 5,000 feet, we effectively lose one full point of compression just due to the altitude. We sort of look at low boost superchargers (like the Moss unit) as 'altitude equalizers'. /bcforum/images/%%GRAEMLIN_URL%%/wink.gif

 

[PC]

... then the pop-off valve (if it has one) to keep from 'over-boosting'....

You don't want to pop-off a suck-through system. It tends to spew high volumes of fuel and air at an ideal combustion ratio.

Eaton blowers use a bypass valve to limit boost.


PC.

 

[PC]

...Would also appreciate a recap of the pros and cons on supercharging. ...

Benefits to a direct drive positive displacement supercharger:
more power
instant throttle response
more torque
no mods to exhaust required
more power
cool whining noise
did I mention more power?

Drawbacks to a direct drive positive displacement supercharger:
expensive
less efficient than exhaust driven supercharger (turbo)
added complexity (more to break)
prone to detonation/grenading unless tuned and controlled correctly
must use really good gas
annoying whining noise


.

 

[tony barnhill]

I don't know much about it but I have ordered 1 supercharger kit for a customer & 1 fuel injected kit for another customer....they both seem happy with their setups.

 

[PAUL161]

This might be a little drawn out, hopefully not too much. It might help you decide on what type of blower is for you.Forget the fact that I'm referring to diesel engines with blowers and just concentrate on the type of blower. Detroit Diesel by GM, originally designed the double roller, DIRECT DRIVE, blower many years ago for their diesel engines. (I know that this is not the one for your application, but just bear with me on a direct drive blower). It was such an excellent design that it has been copied and modified numerous times to except carburetors, fuel injection and Lord knows what else and used on drag racers, hot rods and street cars from way back when. The direct drive blower will take a tremendous amount of abuse and can be shut down at high engine speed without harming it's bearings due to the fact that engine oil pressure is still evident until the engine completely stops. NOT SO with an exhaust turbo! A turbo blower must be slowed down by idling the engine to it slowest speed before shutting down and really should be allowed to cool slightly as the bearings can be ruined if shut down at high speed. A turbo blower will "windmill" after the engine is shut down. The bearings are not lubricated during this time if the engine is not running. It is "windmilling" on hot drying bearings. Never shut down a turbo engine at high speed! Don't get me wrong and think I'm against Turbo blowers. They are excellent blowers but require a little different maintenance procedure. I know of some direct drive blowers that are at least 30 years old, never been apart and are still running. PJ