jr69187

You want the constant boost. That and the cfm should increase as the rpms raise i think this correct but please some one more well versed int he subject correct me. This comming along nicley sterling faster than mine but that is due to a blown motor and several other things that are blocking my path but by the weekend they should all be removed.

faster7

You'll be TRYING to accomplish constant boost, but you know it won't quite be perfect. Air pulsing with waves flows differently at different pressures and rpm's through the motor, changing VE all the time. But it should be close!

True, you'll be under boost at idle but the ideal volume of water injected at that point would be vastly different than at 8krpm and under boost. Ballpark cob-job I'd shoot for would be switched on past 2500rpm and past 1/2 throttle.

Peejay's right on with the water injection. There are different things that can be accomplished with water/alchy injection. Depending on what you're wanting, you may be shooting for "atomization" or "vaporization." I like a little bit of both. ;-)

That's why most water inj. rigs ARE setup to run high pressure water, so that it's finely atomized when it comes out of that TINY orfice.

Most normal fuel injectors won't hold up to water, but there are a few people working on some stuff they're secretive about, soon they'll be sharing what they find for doing a nice aux injection setup on the cheap giving the most benefit. They're going for both the atomization and vaporization side, it should be interesting.

Anyone care to hear more about the different things water inj. can do? Yell at me off list and I'll send you some archives I have.

Sterling

If these things are'nt too expensive, I'm thinking it's a worth-while investment.
...Anything to prolong engine life. And more power, too. Seems almost foolish not to do it.

Are there any drawbacks?

mar3

iTrader: (8)

Alcohol will eat your rubbber alive. If you don't stay on top of keeping your water tank full, you'll probably lunch your engine if its running under good boost when the water stops. Detonation doesn't take long to impart serious damage.

Sterling

...I'd be inclined to keep my boost level safe, and retard the ignition...set it all up as if I did'nt have the water injection.
If I were to start messing around, in order to insure that I don't run out of water, I would use the float mechanism found in the window washer or brake fluid container. I would hook it up to the annoying seatbelt light on the dash. Easy to do without yanking the dash.

Sterling

so, getting back to the topic title, all of my failed attempts at calculating the probable boost from my M-62 Eaton were based on a max blower RPM of 14K. That's what Eaton has on their charts.
But when I visit Mangusons site, their charts go up to 16K.

Now, I don't expect to be ripping along at redline (engine) all the time - especially with a supercharger...I would hope I don't have to!
But could'nt I simply change the pulley ratio so make the SC redline hit at, say, 7000 engine RPM?
I mean I love the fact that my beer keg redlines at 8400, but with a supercharger, it becomes a different animal. Seems to me nothing's to be gained from going that high once you force feed it. Both SC efficiency and engine efficiency start to drop at a certain point, right?

So then, in everyones opinion, just how fast do you think I can occassionally spin that SC without killing it?

...And I've decided that, though everyones responces about boost psi #s not mattering much (...it's how ya use it.) does make sense, I still want to know figures. If I can't quantify, I go crazy.
And this is all hopefully going to end up on a street ported engine someday, too. It's a big project for a little fish like me!

peejay

M-62 is one liter per rotation, right?

And max revs on the blower are 14,000, max revs of the engine are 7,000. (Going by the numbers you've given me)

With a 2:1 pulley ratio so that max revs of the engine and blower coincide, you're looking at a mass flow difference of roughly 2:1. I say 2:1 because the engine (I'm assuming stock port?) will not actually take in 1.146 liters of air per revolution due to the V.E. boing max at about 80% or so. So let's say one liter of air per revolution actual just to make the numbers pretty.

This would seemingly be 14.7 pounds of boost at sea level. However in reality it will be slightly *higher* because the blower is only 70% or so efficient at moving air, it heats it up more than what you would expect from a 100% efficient compressor. Heated air expands, so having twice the mass of air will result in more than twice the pressure. I don't have the formulae handy but let's say about 18psi.

Assuming my general SWAG's are accurate.

Personally, I'd put 1.25:1 pulley ratio's on it and go from there. Better too small and not build enough boost, than too large and kill the engine the first time you open the throttle. (Boost builds as a function of throttle position with a blower!)

Sterling

My Yaw dyno sheet shows a best of 88.8% VE.
The Eatons are better than 70% efficient, but I don't know by how much.

My calcs:
For each rev,
Engine needs 85% of 1.146 liters = .974 liters...Call it one liter.
Blower gives 1 liter.

If ratio 1:1 is like atmospheric 14.7 psi,
Then if I want to start out with 8 psi of boost, I figure I add that to 14.7 to get the pulley ratio.

14.7 + 8 = 22.7
22.7 divided by 14.7 should give me the engine pully size...
1.54 : 1

...Oooohh - You are good, peejay!

At 8K engine RPM, the blower will then spin 12,320 RPM.

And THAT is absolutely PERFECT.
It's exactly the starting point I want, with room to go up to 14 psi. if I make the blower spin at 16K @ engine redline (8K).

This is very exciting...But is it really that simple?
If it is, then I'm ready to start talking about air mass and temperature!

peejay

1.54:1 gearing will give you more than 8psi of boost because of compressor inefficiency.

Huh?

Yep. Remember a ways back where I was explaining that a 1.5:1 pressure ratio only made a 1.3:1 density ratio (only putting in 1.3 times as much air instead of 1.5) because of compressor inefficiency? Well, blowers are a wee bit different than turbos, so the math is a little backwards. Turbos are typically controlled with wastegates that limit manifold pressure, so pressure ratio is fixed and density is variable with compressor efficiency. Well, with a positive displacement supercharger that is directly driven by the crank, DENSITY is fixed (because it works by just shoving more and more air in) and PRESSURE is variable with efficiency.

So that 1.54:1 is going to give you more than 8psi. In fact that's about on par with the density ratio that I calculated for a 70% efficient turbo giving me 15psi of boost. So, ah, you are probably better off starting with pulleys in the 1.3:1 range to be safe.

BTW I know Eatons can get up as high as 85% efficiency, which is absolutely incredible... but it is still something that is significant enough that you have to take it into account.

Sterling

Thanks alot, peejay...and certainly everybody else, too!

That clears an awful lot up! And it makes perfect sense.

So my blown engine is much more likely to suffer from detonation than a turboed engine because of air expansion that happens after the air comes out of the SC?

In order for me to understand a few things, let me throw some strange ideas at you, and you can explain why they won't work...

What about having the outlet on the SC really big? I always see the same size plumbing going into and out of the SC. Does it make any difference where the actual "bottle neck" is located, or does the air heat up within the SC no matter what diameter the plumbing is?
Reason I ask is that an awful lot of effort goes into flow-dynamics for manifold and such...even the Eaton blower itself. Should'nt I be real concerned with the transition from the blower outlet pipe to my carb box?

What would happen if you could put an IC in every body panel in your car, and have the outgoing air travel all the way around the car and back into the carb?
(Don't laugh...I'm tryin' ta freakin learn, here!)
Maybe the hose would start out a larger diameter, and very gradually become smaller to the appropriate diameter for the carb box entry.

I've read about people in Australia that weld together two 2nd gen. ICs.
I've also read where others use a custom made IC, or a racing IC, and the boost drops about 1 psi. Is'nt that a good thing? It says to me that the damn thing is working, right?
Why can't I make my own IC from two stock radiators soldered together? (not in tandem; I mean sandwiched.) I'm a silversmith, and I make big tea sets and ****. It would be a cake job for me.
Would it work? It would certainly fit like a dream!!!

And finally, is'nt it much better to have 7 psi of nice cool dense air than 8.5 psi of freakin hot air, even though the mass, or oxygen count per pound is the same? I mean it seems to me that the 7 psi.er will kick the others *** if for no other reason than that #1 the engine is using power to heat up the air through inefficiency, and #2 the engine is trying harder to disapate heat energy. Also, is'nt the 8.5 pounder engine trying harder to compress the mixture?

Am I on the right lines of thought?

peejay

Air will be hot no matter if compressed by a turbo, blower, or a piston or a rotor or that matter. Diesel engines ignite their fuel solely on the heat generated by compressing air. The question is, do you see anybody running 8 psi without an intercooler?



The heat comes from the actual compression of the air... and the way positive-displacement superchargers work, the compression isn't done in the blower itself (like a turbo works), the compression is generated because of the high backpressure between the blower and the engine. Optimizing the exit could make things a little better, but few people know how to port a Roots blower properly and I'm not one of them. However go to www.theoldone.com and you will probably find information (not too detailed though) on modifying Eaton superchargers. I say not too detailed because he doesn't say what exactly he does, but he does provide pictures and there's enough theory in there to keep a team of engineers boggled for a lifetime.



Waitaminute... you plan on making this blow-through? I say DON'T DO IT. What happens when you shift at 8k and let off the throttle? The blower is trying to force 12,000 liters of air (or whatever you decide for pulleys) per minute into a closed pipe! At the very best, this will result in blowing the hose off or breaking the belt. At the worst... well the E-shaft snouts are pretty weak on our cars and are known to bend/break when you put a blower on.



It'd *work*... but it would be very inefficient because the blower would have to work extra-hard to force it through the small flow area of the fins. And since you HAVE to draw through the carb with a blower, this also means that you'll be sending air and fuel through it... it's generally accepted that you can't use a traditional intercooler with a draw-through setup because the fuel puddles in places.

Yes! The demonstration that I remember most vividly is a certain engine throwing 45psi into an engine without an intercooler, heated up the air to 400-something degrees. With an intercooler temps dropped to 280 or so degrees but pressure also dropped to 35psi boost. HOWEVER... the intercooled engine made more power because it was taking in 5% more actual MASS, despite being at lower pressure, it was cooler enough that mass into the engine increased.

Sterling

YES!...This is gonna be a blow-thru deally.
Boost sensitive valve? Something I can set to a particular pressure level so that the valve opens when there's a surge...like a steam safety valve.
Is this what a "blow-off" valve is?
This was an initial idea I had, but then thought that I would'nt need one.
I was gonna put a manually operated bypass valve on there anyway, and use a pressure sensitive fuel regulator. So I could limit the wear n' tear on the engine and supercharger.

And the sandwiched radiators...are'nt they basically the same design as an IC? So they will allow 15-17 psi of water to circulate through one, pushed by a piddly little impeller, but I can't expect 10 or so psi of air to go through them when they are spliced together, and the volume is doubled?...How's that?
(I'd rather buy one anyway, but I was certain it could be done.)

REVHED

There's no reason you can't make it blow through. Just install a blow-off valve.

Sterling

This will insure a steady "fixed" pressure...regardless of air density changes, right?

If I install a light that comes on when the blow-off valve opens, then it would come on every time I shift, correct? It would also tell me when the charge was getting too hot, because if I set it to 8 psi @ (whatever normal) temperature, and the light comes on, it's because the air expanded, yes?
I dunno how I would use that info...just that there's a space on the boost gauge where I can install a LED, and fabbing a switching mechanism should be easy enough. (I love to tinker.)
But with a blow-off valve, the boost gauge alone would'nt tell me when it's working, right? Ideally, it would read the same boost, provided the valve was doing its job smoothly.

Are these blow-off valves adjustable? ...Expensive?
And using a pressure sensitive fuel regulator...Is the responce time of these devices fast enough for carb application?
(Not so worried about a little backfire as much as a lean condition occurring when I thrash the pedal again on the up-shift.)

I could also make an ignition-cut system using a relay hooked up to the potentiometer that acctuates the RPM buzzer...very easy to do. (Just a thought...if I need to do that.)

My questions are being answered so well! Thanks so much...Had I not had your input, I might just well have grenaded my engine!!!

So let's move on to timing...(not that we've exhausted everything else quite yet!)
I've read that I can simply retard my timing, alot, and that'll keep me from having optimum power, but will keep my engine safe.
Right now, I run no VACUUM advance, though my mechanical advance is stock. This is per Yaws instruction.

I know very little about timing advance, and how/why it affects performance in applications like this.

The vacuum advance is set up ideally for idle for smog, isn't it? And then the advance moves up as the RPMs increase, until centripital force is great enough in the dizzy (at about 3500-3800 engine RPM) that it forces the ignition to be advanced at whatever the mechanical setting is.
What I don't understand, is why it is'nt advanced continually up the RPM range. Why is the advance stopped at 3800 RPM?

If I don't want to mess around with expensive advance computers and crap, and I fix my advance to a safe point, how do I do it, and what do I lose?

I do know from experience at least enough that when the timing is done correctly, it makes a big difference in power just with a carbed stocker 12A. So, though it's critical that attention is paid to the timing of a blown engine...so it does'nt eat itself; will I even notice a difference between "safe" timing, and "optimum" timing with a supercharger?

You can all tell I'm not looking to spend alot of money on this set-up, but I'm not a tight-wad...I will spend money on "smart" essentials and fail-safes.

REVHED

A blow-off valve isn't an "overboost" valve as such. They are used on forced induction engines to vent the intake charge ONLY when the throttle is shut. On a turbo engine this prevents the air from reversing back towards the turbo and slowing down or damaging the compressor. But, on supercharged engines they're even more important. As the throttle is shut the compressor mechanism will not be stalled as the crankshaft is still driving it. The massive pressure spike can be enough to severely bend the throttle butterflies or break the drive belt. Obviously blow-off valves are only needed in blow-through systems as in a draw-through setup the turbo or blower will happily continue to spin away in vacuum when the throttle is shut.