turbo or s/charger.

There is a popular misconception that superchargers don't heat up the intake air this is completely wrong, in fact in most instances a supercharger (roots type) with its inherrent inefficiency will heat up the intake air more than a turbo.
The reason roots type blowers aren't intercooled is the fact it's very difficult to fit an intercooler between the blower and the inlet manifold.
Other blowers like vortech, paxton, powerdyne etc lend themselves well to intercooling and in most instances will outperform the roots type ones.
Regards Andrew.

Any compression will heat the air....

Roots or screw type are more efficient than the belt driven fan they use on the commodore...
Roots and screws are positive displacement so there is no lag and no overun....

Talk to CAPA in the riverland...capa.com.au

I can not agree with Andrew that the belt driven fans out perform the roots type...its all about how much pressure one wants to pump

i'm with you tuff60....hate turbo lag too!

the belt driven fans are not really supercharger nor a turbo....I like to think of them as a mule (hybrid)...not quite a turbo and not quite a supercharger...but they do work......but as you say not efficient at what they do

Nude, I am not saying the centrifugal blowers don't work, they just are not as enjoyable as PD blowers. Had a blown VS commodore a few years back that started with a centrifugal blower, and was ditched in favour of a roots type. Awesome to drive afterwards, power from idle to red line, compared to power from 3400rpm upwards with the centrifugal blower. I will admit that total rwkw was down by almost 60kw, it didn't matter as the car did not spend alot of time over 5000rpm where the centrifugal had more power. The hairdryer did sound better, great for making people wonder what was in it. PS. the PD ran cooler as well.

Tuff 60.. great explanation you know your stuff, but just like to add something so as not to confuse some less experienced in the diff between a blower and a supercharger.

The GM used a roots blower but its not really classed as a supercharger due to it not ever raising the intake pressure above atmoshere. On the two stoke diesels the blower was there to just clear the combustion chamber. Like on the GM 6V53 the blower isnt an add on its a nescessity, on later versions of this engine they then added a TURBO!!!!

I think the definition of a blower as apposed to a supercharger is related to the valve or port timing, if the intake closed before the exhaust then its a blower, otherwise pressurisation is achieved and its a supercharger!!

But like I said great explanation!!

Matt.

Theyre both a play on words
the "turbo" in turbo-charger ...relates to the centrifugal impellors which do the pumping and the driving.

Superchargers generally relates to belt driven pumps....

But the dyne etc is only a belt driven impellor...so could it also be a turbo?

Lets face it, they both compress a higher fuel air ratio into the engine.
Any thing which raises the manifold pressure above the normal aspirated pressure, even if it still in a vacuum has been blown!

I believe that most engines would have to have the valve timing altered to take full advantage of the extra fuel air mixture

Nah Nude you have missed my point, on a GM 2 stoke diesel the blower isnt an add on or an extra power addition, it is essential, otherwise the engine will not clear the waste gasses without it. It will not run at all!

"Boost" isnt there because the intake pressure never gets above atmoshere and couldnt because the intake ports are covered before the exhaust ports...all done by the piston position in the cylinder, no adjustments possible there!! (there are no valves, the pistons movement opens and covers the relative ports in the cylinder wall!)

On any other 4stroke application the exhaust valve closes before the inlet, so if the charge is pressurised from a turbo or a supercharger then before the inlet closes that boost pressure is also now inside the combustion chamber. Hence (what I was led to believe)the major difference between a blower and a supercharger.

There isnt a play on words the two terms are dictated by the drive method used, if it is exhaust driven its a turbo if it is engine driven its a blower or supercharger depending on its application.
Matt.

I didnt miss your point...you missed mine
I reiterate
Any thing which raises the manifold pressure above the normal aspirated pressure, even if it still in a vacuum has been blown!

Are you telling me that the engine your describing here runs at the same psia before and after the blower is fitted? note PSIA which for the uninitiated begins at zero or 32 inches of vacuum (approx -15psig)...if that is the case why have it!!?

So why is a turbo charger a exhaust driven impellor compressor and why is a positive displacement compressor a supercharger and why a belt driven impeller compressor is also a supercharger?..i reckon its a play on words

Ahh Nude, you have missed it again, it is a restriction that creates pressure, if a vessel is open and you blow air into it there is no pressure build up, thats why there is no 'pressure' if the INLET closes before the EXHAUST. Any 'pressure' (if any) will equalise back to atmosphere while the Exhaust is open. I do agree that the blower pumps, as does a turbo, super etc, they all pump but depending on the design of the engine, dictates whether the intake charge actually is allowed to build up significant pressure above atmosphere. This does not happen in a two stroke GM diesel until much later when the designers then descided to add a TURBO before the blower, but I wont even go there!!

The reason for the blower is clearly stated, the GM engine will not run without it, it is the SOLE reason the exhaust gases are cleared and the fresh air replaced. That is the design of the GM 2 stoke. I do believe some 2stroke diesel can run without a blower but I guess that is all in design, Im having a guess that once a GM blower is installed the piston displacement cannot move the air past the blower, hence if you snap a blower shaft (easy to do if you keep tapping the trottle) the engine just stops!!
As for 'super' and 'turbo' I thought that was industry standard for how the forced induction is aquired. If the impellor is driven by the engine (paracitic horsepower) it is a Supercharger. If the impellor is driven by waste product of combustion like exhaust (no paracitic horsepower) then it is classed as a turbo. I dont believe it has anything to do with the compressor type ie positive displacement or not! Hence why I didnt think it had anything to do with 'playing' on words, just definitions of application types.

I hope that is clear I dont know any other way of describing without diagrams etc. But I am more than happy to drag out my old text books and look into it again and maybe refresh myself and help explain it a tad better, it was nearly 13 years ago!!! So I apologise if Im rusty with my explanations and have caused confusion!

Thanks Nude
Matt.

Sorry guys, didn't mention the GM diesels for how they operate, but to prove how robust roots type blowers are, they passed US Mill Spec so they must be tough. I agree with you Nude on the fact that the GM diesels were/are blown but have to also agree with Matt that without the blower the motor would not even pump air. The reason being is that like a regular read valve two stroke when the inlet is open so is the exhaust, so it does not create it's own vacuum. Vacuum in a regular two stroke is created in the crank case when the piston goes up, as the piston comes down it forces the trapped air into the cylinder. The GM diesels were twin overhead valve engines(they had to be to get the compression required to ignite diesel), with wet sumps, so as the crank case is not used to force air into the cylinder a blower must be used. As both valves are open together no real boost is achieved, but I guess that before the valve opens there would be slight positive manifold pressure(never checked, but will now have to) This makes for an engine that lasts a lot longer and is more economical as it does not burn/waste vast quantities of oil in the fuel mix. When a blower is placed on a four stroke it's purpose goes from a necessity to a combustion aid, as in more air more bang. I do completely agree with Nude on the play on words thing, in my opinion, they are all superchargers as the all push more air in therefore supercharging it.
Hope this all make sense. Let me know if it doesn’t. I am a big fan of the early GM diesels, interestingly enough by just changing the cam gear and blower drive they can be made to run in reverse.

Gee Tuff you know your GMs, what are you a Diesel fitter!! I love em too, especially the sound they make at 3000rpm, sounds like they are doing 10 000rpm! Thats the 2stoke for you!
Matt.

so, do we all agree that the puropse of the blower on the GM is there for two reasons.....& not neccessarily in this order...to supercharge and to clear waste gases...

Ahh Nude, its cool, forget it!!
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Take it easy
Matt.

GM's didn"t have inlet valves they had ports in the cylinder liners and most had 4 exhaust valves. We use them in road stabilizers with twin turbos on 8v 92 's they also give Denning buses that great sound.