roots blower

[Dixie]

I've had this on my mind before and have just gotten to a point where I think I may try this. I have been wanting to mount a gm roots blower on a 6.2 like a 8v road tractor motor. Until now I was limited with the intake to use. Now I have a friend with a 3d printer capable of making molds for casting an intake manifold from. I'm just wondering what would be best to mount on a 6.2. I realize a 1271 would be way too big but wonder if something like a 471 would be about right with low compression pistons and the like. I'm just not a fan of how the exhaust routs around to the turbo to make the banks set up work. Any ideas Dr. Lee?
gp

[simon]

the 471 roots blower is designed to feed a 2 stroke diesel.
the displacement of a 471 is easely twice that of a 6.2, being long stroke and firing every rotation.
so i think it is giving way to much boost anyway, It will crater that engine in short order, you can't control the boost. besides that you gonna need a good set of earplugs to keep the screeming at bay.

How in the world are you planning to drive that thing ,with a v belt??

i would stick with a stock turbo if i was you.

but do whatever blows your hair back

[Robyn]

I have run the GM type blowers on GM V8 Gassers.

There are drives available and to compensate for the engine size and such one just adjusts the belt pulley ratio.

We used to use 6-71 blowers on 400 inch Rat motors and for the street we set them up about 10% under crank speed.

I am not sure how well it will work but it is feasable.

You could make a manifold using a low rise Hummer manifold and a 1 inch thick aluminum plate and doing some fancy fab work.

I have done this for a small block chevy application years ago.

It takes some patience and a little calculating to get the blower manifold set up so the blower shafts are parallel to the crank.

Normally a blower is run with a 3 inch wide (or wider) gilmer or cog belt to handle the power needed.

This probably is going to be more trouble than its worth.
The old jimmy blower hogs a lot of power at speed and takes up a huge amount of space.

Another idea might be using a paxton huffer thats designed for modern auto applications.

All you need is about 4-6 PSI to wake the little diesel rat right up.

Have fun

Robyn

[gophergunner]

i thought 6-71 blowers were quite common for small block chevs for street rods and such..........if it works on them i can't see why it wouldn't work on a 6.2

i would like to know how that would work out too, that would be somethin quite interesting to see and hear:cool:

[DmaxMaverick]

i thought 6-71 blowers were quite common for small block chevs for street rods and such..........if it works on them i can't see why it wouldn't work on a 6.2

i would like to know how that would work out too, that would be somethin quite interesting to see and hear:cool:

Simply put, VOLUME. Although the CID's are similar, the Diesels turn at ~1/2 the RPM. This means at redline for both, the Diesels are moving 1/2 the air displacement. You could make one work, but I doubt it will be at all practical. The bottom end on these things are fragile as it is. By the time you get a respectible amount of power at the rear of the crank, the front will also be driving the blower. If that's in the neighborhood of 75 HP, that's an additional 75 HP the engine needs to put to the crank. 75 of it won't make it to the flywheel. If your flywheel HP is +50 HP, then the actual engine output will have to be +125 HP. What a waste, and a risk. A turbo is almost free power, by the same standard.

[Robyn]

I agree that the turbo is most likely the best option but I dont think a 671 is going to take anywhere near 75 HP to turn it.

We used to run our race blowers on a test bench to break them in after a rebuild and we used a 1 HP electric motor and run the blowers at about 1800 RPM just to break in the gears and to be sure we did not have any rotor interference issues. ( This was under a loaded condition with the blower working against pressure of about 10 PSI)

Running a stock type GM huffer so it was running 10-15% under crank speed would provide more than enough air for the engine.

To reference another option.
The old Studebakers were available with a paxton supercharger, and it was run with a v belt.

I seriously doubt that one of the little paxtons would pull much more power than a large alternator thats working well or for that matter the cooling fan)

The big blowers like the custom 871 types that have teflon seal ribs in the rotors and that are turning big RPMs are going to pull some big time HP for sure.

The stuff we ran on the BBC's were running 20% over crank speed and the engines were spinning anywhere between 8,700 and 10,000 RPM.
On some rare occassions we did run our little engines (427) up into the land of 11000 RPM's :eek: Having a BBC spinning that sort of revs right near you in a drag boat is quite exhilerating.

Dad always commented if it blows just remember, "Parts never go up, they go down" (as in you get wet)

The 500 + inchers never run much over 7500 RPM with the blowers on them right at crank speed.

Our play boat had a 396 with a 671 on it and that little beastie would turn happily all day at 8500 .
This engine had a static comp ratio of 5.75 :1 and the blower was at 40% over crank speed.

Dont ask why that wierd combo, cause it would take a week to tell the story :D

I agree with Maverick though, the blower, however kewl looking is not a practical thought for the 6.2/6.5

Might be kewl to put a 6.5 with a Huffer on top in a little T bucket roadster though just to gather stares :D

Get a Banks turbo and save yourself a lot of work and $$$$

Robyn

[gophergunner]

too bad these engines are that fragile.......i'd like to have one with a lot of power but i hate wasting my money on it if i know it can't handle it

[DmaxMaverick]

I agree that the turbo is most likely the best option but I dont think a 671 is going to take anywhere near 75 HP to turn it.

We used to run our race blowers on a test bench to break them in after a rebuild and we used a 1 HP electric motor and run the blowers at about 1800 RPM just to break in the gears and to be sure we did not have any rotor interference issues. ( This was under a loaded condition with the blower working against pressure of about 10 PSI)
......

The 75 HP was just a number I threw out there for discussion. I'd bet it's not far off above 75% output, though. 1800 RPMs at a static 10 PSI is very different than actual application (Fluid Dynamics 101). I suspect the blower will have to be overdriven, not underdriven, for the low RPM range of the Diesel engine of discussion. Otherwise, it will have a similar lag we see with a turbo. At any rate, the dynamic CFM at desired pressure has to be calculated. Although a roots blower is a positive displacement pump, internal clearances, even in new condition, make them inefficient at low RPMs. I don't see any advantage for a daily driver. At the track with specific demands, it could be done well.

Turbos work so well on Diesels because the engines are fuel modulated. Turbo output is fuel (exhaust gas) modulated. Blowers work well with gassers because the engine is airflow modulated. A blower moves air dependent on crank speed, which is positive displacement of air in/output for both the engine and blower.

[Dixie]

Thanks for the info. I was just pondering something detroitesque. I won't go turbo. Don't like the exhaust routing. Might just stay na. gp

[Robyn]

Maverick

Remember though that the GM blowers (6-71) were for a much larger engine that was a 2 cycle and used a large volume of air of scavenge the cylinders.

The 6-71 is 426 cubes and is using the blower to air each cylinder every time the piston drops below the ports.
So basically its pumping air for an engine thats twice as many cubes as the 6.5/6.2 if you figure the firing pulses.
The air box remains charged under running conditions (Above idle) and the flow of air is huge through those engines.

My old 8V running on fast idle at 1000 RPM would really put some velocity
out the twin tail pipes and that was all off the blower as there is no pumping action from the pistons.

I really think that the under drive would do fine even at the low RPM
The Old Detroits were a 2100 RPM engine at max speed.

The old two strokes did get a turbo added to the mix in addition to the blower.

My 8V-71 in my GM coach had a turbo that fed into the blower and there was a bypass valve to let more air into the engine past the roots huffer.

The aftermarket makes some cute little GM type blowers for street toys that will make a 350 just howl and would probably do fine on the 6.2/6.5
Some are even V belt driven and cant use all that much power.

I agree though that the turbo is by far the best way to get power.

Grandpas Studebaker Hawk with the Super charged 289 was no slouch in its day. :D

later

Robyn

[gophergunner]

in my opinion............i haven't heard a diesel engine yet that can make as sweet a sound as an old detroit.:cool:

[Colorado Kid]

After 6 years of driving a Bluebird All American school bus with a 6V53 sitting right next to me I can't hear any of the other diesels well enough to notice, at least not out of my right ear!

[Craig M]

A few Hummer H1 owners have installed Paxton or similar superchargers on their 6.5's. They appear happy with the results. Claim good bottom end torque. Some loss on fuel econlmy, but one does not buy a H1 for fuel economy.

[Robyn]

The detroits that I always liked the sound of was the old 12V-71

The venerable old "Buzzzin Dozen" what an assembly that was.:eek: