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Old 02-14-2008, 08:11 PM   #16
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..............................THIS GUY KNOW WHAT HE'S TALKING ABOUT,,,,My 871 coming off the line a 600 idle had 11# as fast as I could stomp it,and 16# at 7000...It had aprx. 11# at less then 1500 rpm,and then about 1# more every 1000.....OLDHEAD
Then your blower must be junk, or my data logger sensor is fucked up. My boost doesn't change.
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Old 02-15-2008, 12:54 AM   #17
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9:1 with 7PSI is a good starting point. It's mild and won't hurt parts. You can sneak up on it from there.
If you start out with a 9:1 compression ratio and 7 lbs of boost what will you do when you want to swap pulleys on the blower/crank to make 14-15 lbs of boost? Change pistons? Run alky on the street? Retard timing so much your EGT's go through the roof and kill power? Run C-16 race gas on the street at $13+ a gallon? Remember, a roots type supercharger is an awesome looking piece, but it creates a lot more heat than the centrifugal supercharger and therefore can't utilize the same compression ratio. It can make serious power.


Once you get more serious about it, most of the blown alky motors are 11.3 to 11.7 to 1, with up to 40 PSI.

I think you're comparing apples to oranges. This guy is talking street motor. An alky blower producing up to 40 PSI is most likely a retro with hi helix rotors, a delta outlet and down ports. You can't even turn a new 18 point stripped alky blower over by hand it's so tight. Think of much heat that would create on the street.

Then your blower must be junk, or my data logger sensor is fucked up. My boost doesn't change.

I don't think oldheads blower was junk. I think as RPM increased, his supercharger ("positive displacement pump") was producing more air/fuel than the engine could use so it became backed up in the intake manifold. That's called boost!
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Old 02-15-2008, 11:34 AM   #18
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In relation to UR's post above..

1. You have "X" theoretical compression available based on octane rating, head efficiency and air density without having detonation.

Whether the motor is 7:1 with 20 PSI or 9:1 with 7 PSI (just throwing out numbers), the same end compression is all thats available.

A higher static compression motor with less boost will run better than a lower compression motor with more boost. Why? Because it has more snap of it's own, and only uses the blower (which uses less power due to less overdrive) when you put your foot in it. When you put your foot in it, there's less boost, and as such, less heating of the air charge in the compression chamber (intake plenum), thus giving a greater net power increase.

2. It might be apples to oranges, but the stripping on a blower has nothing to do with heat creation after the blower is broken in. The seals will wear down within the first 30 street miles to a point where there is no contact being made, but a very good seal is formed by minimizing clearances within the blower. B&M did this on their 2 lobe roots blowers and it worked great. Teflon/Nylatron seals are just fine for street use.

3. His blower either has excessive clearances, or the heads don't flow enough air. If the blower has excessive clearances for the application, it's beating the air to death and actually losing power. If it doesn't, and he's getting increased boost as engine rpm increases, it's not called "Boost", it's called "Boost stack". Boost stack is excessive boost above and beyond what the motor can flow, and does nothing but to heat the air and LOSE power.
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Old 02-15-2008, 12:45 PM   #19
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I also am a fan of having 9:1 and lower boost. Like WJ Birmingham said with more compresion your not working the blower as hard and keeping the discharge temps cooler, and all that makes more power. And with a centrifical I like more then 9:1
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Old 02-15-2008, 01:02 PM   #20
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You wouldnt have that problem if you ran one of them aftercoolers under the supercharger would you. Thats what im looking to do. I dont care about hood clearence there is no hood.
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Old 02-15-2008, 01:16 PM   #21
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You wouldnt have that problem if you ran one of them aftercoolers under the supercharger would you. Thats what im looking to do. I dont care about hood clearence there is no hood.
Yes, but the after cooler typically requires an ice box... How are you going to keep a continual supply of ice on hand for street cruising? They typically aren't too cheap either. Typical costs of after coolers for roots blowers run in the 1500-2k range for just the plate that sandwiches between the blower and manifold.

A more cost effective means to cool the intake charge would be to use a small 1 gallon tank filled with methanol, and use a hob switch to turn on a small pump/solenoid when you're beyond 4 PSI of boost. Methanol works as a great, cheap intercooler as well as an octane booster (it burns slower than gas).

At the same time you could also have the same circuit hooked into a MSD timing retard, pulling out "X" degrees of timing to further assist in detonation control.

Again, if you can afford it, the Screw blower is going to be the best solution if you want that big roots look hanging out of the hook.
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Old 02-15-2008, 01:47 PM   #22
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I like the big roots look
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Old 02-15-2008, 01:48 PM   #23
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You know like this....
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Old 02-15-2008, 01:55 PM   #24
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Quote:
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You know like this....
I hope you're kidding... That looks stupid, imo... But to each their own.
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Old 02-15-2008, 01:57 PM   #25
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Now this on the other hand....

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Old 02-15-2008, 02:09 PM   #26
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I was overexagerating.. Its going in the car thats my avatar.
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Old 02-15-2008, 02:30 PM   #27
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http://www.rbssuperchargers.com/Page...D=3921&Search=

You might want to check with RBS about their used blowers. JR used to work for RCD, but started his own company (He's an RCD dealer).

They have the ability to rebuild and tailor blowers to your needs in house. My old 10-71 Mooneyham is listed on their page @ 2100.00. It'd be a good gas blower for you.
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Old 02-15-2008, 02:42 PM   #28
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1. You have "X" theoretical compression available based on octane rating, head efficiency and air density without having detonation.

Actually, there are allot more factors involved and to be more precise, static compression is not as encompassing as dynamic compression which additionally takes into consideration camshaft profile and rod length.

Whether the motor is 7:1 with 20 PSI or 9:1 with 7 PSI (just throwing out numbers), the same end compression is all that's available.

That's where your thinking is wrong. a 15:1 500+" BBC engine will require race gas and not make 2000+ HP. Steve Morris Racing Engines just built and dyno'd a blown 500+" BBC that made 2000+HP that ran pump gas! He had to experiment by raising boost while lowering compression to avoid detonation so he could utilize pump gas. Do you really think he could have ran say 12:1 compression and approx 15 lbs of boost instead of the 7.5:1 and 27 lbs of boost he used? No way! It's been known for ages, lower compression coupled with high boost WILL make more HP requiring less octane.

3. His blower either has excessive clearances, or the heads don't flow enough air. If the blower has excessive clearances for the application, it's beating the air to death and actually losing power. If it doesn't, and he's getting increased boost as engine rpm increases, it's not called "Boost", it's called "Boost stack". Boost stack is excessive boost above and beyond what the motor can flow, and does nothing but to heat the air and LOSE power.

If the motor could flow everything the blower could throw at it, there would be no measurable boost in the intake manifold! As engine rpm increases and subsequently blower RPM increases there is less time to fill the engine's cylinders. The roots type blower is a positive displacement pump and will continue to pump roughly the same amount of air per revolution. A typical street/strip engine can not keep up.

Teflon/Nylatron seals are just fine for street use.

So your saying a blower with 18 point (strip) Teflon and Nylatron is good to run on the street? I disagree and so does BDS. (Actually so did Mike Kuhl when he owned Kuhls Superchargers) Teflon the lips of the rotors maybe fine, but no to the nylatron in the valleys. Call Craig Railsback (owner) at BDS and ask him how much heat a 18 point teflon and nylatron blower creates.

B&M did this on their 2 lobe roots blowers and it worked great.

Funny you should mention B&M blowers. We did some R&D for them (then B&M President Jim Davis, Bob Spar was the owner) on their mini blowers back in the late 80's. They had a hell of a time keeping the Teflon strips in place. Actually, one of my motors is in their black supercharger hand book and was in one of their advertisements.
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Old 02-15-2008, 02:43 PM   #29
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I was thinking more of the 8-71
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Old 02-15-2008, 02:44 PM   #30
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Quote:
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I hope you're kidding... That looks stupid, imo... But to each their own.

That does look goofy!
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