The V8 Owners Forum -

There are a few GMC/Detroit 6-71 and 4-71 blowers on ebay in the States and some say- needs to be converted for gas- so you can use it on a typical suck through setup, I thought these were made to run wet?
Anyone?

GMC blowers are in fact designed to be suckers, they are attached to the exhausts of uniflow 2 stroke diesels and suck the exhaust gasses out the exhaust port, by doing so they suck the new charge in the top pas the inlet valve. That link you posted earlier explains in the bit about sizing them for their 2 stroke aplication.
Mike

Ohh! More trivia lol thanks for that, they dont look very black then considering the diesel fumes and soot that has gone through them..

So can one assume that they are pretty well sealed against fumes etc and no conversion has to be done before they can suck a pre-mix of petrol & air?

most of the ones you see on petrol v8s are bought new so don't ever see the original application . they are converted by the aftermarket suppliers with new seals and machined cases for tighter tolerances so they will give you boost at lower engine speeds. this is why I was advising you to buy one that was of known history when you posted the link off ebay. They looked as if they had come off a diesel engine application . If you have the kit to machine the case and end plates it is not a problem to convert them then the information is out there to do the conversion, if not you have just bought two big paper weights (not so trivial).
Mike

Lol dont need any more paper weights!!! Thanks for all that

kiwicar wrote:GMC blowers are in fact designed to be suckers, they are attached to the exhausts of uniflow 2 stroke diesels and suck the exhaust gasses out the exhaust port, by doing so they suck the new charge in the top pas the inlet valve. That link you posted earlier explains in the bit about sizing them for their 2 stroke aplication.
Mike

Not picking holes but I always thought they were used to blow the exhaust gas out by pressurising the inlet on the two stroke diesel, hence the term 'blower' ?

Mark

Hi Mark
the term Blower is because they were originally designed as a method of shifting grain into a grain store (or flour) (have a look on the back of any truck transporting flour or bulk powder load), they have no internal compression in their operating cylce so they don't pump a fluid in the normal sence, they "blow" it (handy if that fluid is not compressable).
Yes in many deisel aplications they are also used as a conventional supercharger, but this is normally a four stroke diesel appication, on the 2 stroke they are generally used to scavenge the exhaust out the cylinder (this way there is less mixing of inlet air and exhaust gas).
I will now pop off and have another read of my copy of "Italian postal service cancellation numbers 1977 to 1981"
Mike

kiwicar wrote:GMC blowers are in fact designed to be suckers, they are attached to the exhausts of uniflow 2 stroke diesels and suck the exhaust gasses out the exhaust port, by doing so they suck the new charge in the top pas the inlet valve. That link you posted earlier explains in the bit about sizing them for their 2 stroke aplication.
Mike

Hmm, the 8, 12 and 16 cylinder two stroke V GM's (Detroit diesels) I've worked on all had the blowers in the centre of the V, and they pumped air into the cylinder, through piston ported ports at the bottom of the cylinder sleeve. The exhaust then passed out through the four exhaust valves in the head. Never heard of a blower 'sucking'. They'd be getting awful hot.

Some Detroits have turbos on as well, that feed into the blower, and thence into the cylinder, for extra power.

If they only have the blower they are called a 'naturally aspirated' motor. But basically they wouldn't run without a blower on, as there is nothing to force the air into the system to start with.

They don't build them any more, as they are so horribly inefficiently, dirty, and unreliable.

Hi Paul
I've found both arrangments on uniflow 2 stroke diesels reading around both with the valves at the top used as inlets and as exhaust valves. If the GMC's you worked on had the roots blower forcing the air in through the ports on the cylinder then I stand corrected for this case.
I am still certain that roots blowers were used to scavenge the exhaust aswell (napier delitic junkers aero diesel various marine designs).
Mike

kiwicar wrote:Hi Paul
I've found both arrangments on uniflow 2 stroke diesels reading around both with the valves at the top used as inlets and as exhaust valves. If the GMC's you worked on had the roots blower forcing the air in through the ports on the cylinder then I stand corrected for this case.
I am still certain that roots blowers were used to scavenge the exhaust aswell (napier delitic junkers aero diesel various marine designs).
Mike

I might have it back to front actually, intake might be through the head valves, exhaust through the piston porting. Been ten years since I spannered on a Detroit smoker.

As I said Paul I've seen both arrangments, Bl***y odd things 2 stroke diesels the designers seem to get all worked up about temperature gradients and keeping everything flowing in one direction and forget about getting enough air in there in the first place! . I do like the design of the deltic http://en.wikipedia.org/wiki/Napier_Deltic
Mike

kiwicar wrote:As I said Paul I've seen both arrangments, Bl***y odd things 2 stroke diesels the designers seem to get all worked up about temperature gradients and keeping everything flowing in one direction and forget about getting enough air in there in the first place! . I do like the design of the deltic http://en.wikipedia.org/wiki/Napier_Deltic
Mike

Fascinating. I've never seen one before. It makes you just want to stare at it.

Ew! Amazing in a kinda "why?!" way!!! 3 Cranks too...