PSRU Ratio and vacuum

[Mike Kimball]

Thanks to everyone for your input on the PSRU ratio question. Bob Masters
at Firewall Forward told me that they have only ever sold a 1.75:1 unit once
and the guy they sold it to wishes he had the 2.118:1. Well, I called him
and he is emphatic about it. "DON'T GET THE 1.75" he tells me. Sounds like
he runs out of ability to push his prop past about 4500 RPM engine speed.
He can't access the horsepower that is available in his engine. Seems like
it's almost unanimous among those responding to this issue. Without fully
understanding all of the variables involved it sounds like I will be much
happier with the 2.118:1. Despite his unhappiness with choosing the 1.75,
the guy is very happy with the CAM 500. Interestingly, he reports only 1000
pounds of thrust from his setup using a Chevy 400 on a test stand. Far less
than the numbers quoted on this list for an LS1 but still plenty for the
2500 pound Mustang replica he's building.

Now for my other question. I was talking to the guy helping me put together
my engine and I mentioned that the PSRU I am getting has a provision for
driving a vacuum pump (or other item such as a prop governor). He said,
"why not just pull your vacuum off the intake manifold". I know this is
done on aircraft engines, but only as a source of "alternate vacuum" to
backup the primary gear driven vacuum pump. I always thought this was
because pulling it off the intake manifold would result in an unacceptable
loss of power from the engine for normal operations which is just accepted
if the primary pump fails. My engine guy says, "Huh? You wouldn't even
notice it, at least with this engine. I can't speak for aircraft engines."
Besides, I've got horsepower to spare. What do you think? (Man, this list
is priceless! I don't care if every one of you turned up in Fairbanks all
at once. I'd buy the beer.)

Mike Kimball
SR #044




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[Mike Kimball]

Thanks Ken. That jives with what my buddy tells my about available vacuum
at different power settings. One of the main reasons I got my instrument
rating was to be able to depart through that dang bay area morning fog that
delayed so many of my flights when I used to live there. Wouldn't do to not
have gyros while climbing out through the soup. Guess I'll stick with a
vacuum pump on the PSRU.

Mike Kimball
SR #044

-----Original Message-----
From: mike.davis@dcsol.com [mailto:mike.davis@dcsol.com]On Behalf Of
klehman@albedo.net
Sent: Thursday, May 29, 2003 6:04 PM
To: murphy-rebel@dcsol.com
Subject: Re: PSRU Ratio and vacuum


Mike
Yup I obviously agree with your psru decision :)
Only trouble with intake vacuum is that you don't have any on takeoff or
for full throttle climbs. I've found the gyro gets wishy washy and then
topples on long climbs on an 0-300. Works fine on the ground and in
cruise and descent. Not good for climb on hazy days.
Ken

Mike Kimball wrote:

Thanks to everyone for your input on the PSRU ratio question. Bob Masters
at Firewall Forward told me that they have only ever sold a 1.75:1 unit

once

and the guy they sold it to wishes he had the 2.118:1. Well, I called him
and he is emphatic about it. "DON'T GET THE 1.75" he tells me. Sounds

like

he runs out of ability to push his prop past about 4500 RPM engine speed.
He can't access the horsepower that is available in his engine. Seems

like

it's almost unanimous among those responding to this issue. Without fully
understanding all of the variables involved it sounds like I will be much
happier with the 2.118:1. Despite his unhappiness with choosing the 1.75,
the guy is very happy with the CAM 500. Interestingly, he reports only

1000

pounds of thrust from his setup using a Chevy 400 on a test stand. Far

less

than the numbers quoted on this list for an LS1 but still plenty for the
2500 pound Mustang replica he's building.

Now for my other question. I was talking to the guy helping me put

together

my engine and I mentioned that the PSRU I am getting has a provision for
driving a vacuum pump (or other item such as a prop governor). He said,
"why not just pull your vacuum off the intake manifold". I know this is
done on aircraft engines, but only as a source of "alternate vacuum" to
backup the primary gear driven vacuum pump. I always thought this was
because pulling it off the intake manifold would result in an unacceptable
loss of power from the engine for normal operations which is just accepted
if the primary pump fails. My engine guy says, "Huh? You wouldn't even
notice it, at least with this engine. I can't speak for aircraft

engines."

Besides, I've got horsepower to spare. What do you think? (Man, this

list

is priceless! I don't care if every one of you turned up in Fairbanks all
at once. I'd buy the beer.)

Mike Kimball
SR #044

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[klehman]

Mike
Yup I obviously agree with your psru decision :)
Only trouble with intake vacuum is that you don't have any on takeoff or
for full throttle climbs. I've found the gyro gets wishy washy and then
topples on long climbs on an 0-300. Works fine on the ground and in
cruise and descent. Not good for climb on hazy days.
Ken

Mike Kimball wrote:

Thanks to everyone for your input on the PSRU ratio question. Bob Masters
at Firewall Forward told me that they have only ever sold a 1.75:1 unit once
and the guy they sold it to wishes he had the 2.118:1. Well, I called him
and he is emphatic about it. "DON'T GET THE 1.75" he tells me. Sounds like
he runs out of ability to push his prop past about 4500 RPM engine speed.
He can't access the horsepower that is available in his engine. Seems like
it's almost unanimous among those responding to this issue. Without fully
understanding all of the variables involved it sounds like I will be much
happier with the 2.118:1. Despite his unhappiness with choosing the 1.75,
the guy is very happy with the CAM 500. Interestingly, he reports only 1000
pounds of thrust from his setup using a Chevy 400 on a test stand. Far less
than the numbers quoted on this list for an LS1 but still plenty for the
2500 pound Mustang replica he's building.

Now for my other question. I was talking to the guy helping me put together
my engine and I mentioned that the PSRU I am getting has a provision for
driving a vacuum pump (or other item such as a prop governor). He said,
"why not just pull your vacuum off the intake manifold". I know this is
done on aircraft engines, but only as a source of "alternate vacuum" to
backup the primary gear driven vacuum pump. I always thought this was
because pulling it off the intake manifold would result in an unacceptable
loss of power from the engine for normal operations which is just accepted
if the primary pump fails. My engine guy says, "Huh? You wouldn't even
notice it, at least with this engine. I can't speak for aircraft engines."
Besides, I've got horsepower to spare. What do you think? (Man, this list
is priceless! I don't care if every one of you turned up in Fairbanks all
at once. I'd buy the beer.)

Mike Kimball
SR #044




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[Reed, Britt/FSC Salt Lake]

Mike - In needed to correct the post where I mentioned that Chris had the
1.5 ratio on the LS1 - It was Chucks engine and he said this weekend that it
was the 1.7 ratio Stinger PSRU - What Prop(type, pitch and length)/Engine
combo did the was the guy who bought the 1.7 but wished for the 2.1? It
seems like the 2.1 needs 5700 rpm to get going which seems like it would be
better for a Subaru engine than a Chevy-

Britt - SR194

-----Original Message-----
From: Bill Delcambre [mailto:bdelcambre@cox-internet.com]
Sent: Friday, May 30, 2003 6:48 AM
To: murphy-rebel@dcsol.com
Subject: Re: PSRU Ratio and vacuum


The manifold vacuum thing might actually work with an auto conversion.
Airplane engines operate at extremely high manifold pressures (low manifold
vacuum), compared to auto engines. I'm guessing this is due to cam profile
and relatively retarded ignition timing. An auto engine might just maintain
enough vacuum, throughout the range of throttle positions to pull it off.
If you know someone with a LS-1, try to talk him into doing a temporary
install of a vacuum gauge and go run the dog crap out of it (stand on the
throttle on a steep uphill climb) and note the vacuum. If it runs below 8
or 9", I doubt if it would work. My dad used to have a vacuum gauge in a
motorhome, but I don't recall how low it could go...

If you've got in mind a turbo, at any point, all bets are absolutely off!

Bill
----- Original Message -----
From: "Mike Kimball" <mkimball@gci.net>
To: <murphy-rebel@dcsol.com>
Sent: Thursday, May 29, 2003 8:54 PM
Subject: PSRU Ratio and vacuum

Thanks to everyone for your input on the PSRU ratio question. Bob Masters
at Firewall Forward told me that they have only ever sold a 1.75:1 unit

once

and the guy they sold it to wishes he had the 2.118:1. Well, I called him
and he is emphatic about it. "DON'T GET THE 1.75" he tells me. Sounds

like

he runs out of ability to push his prop past about 4500 RPM engine speed.
He can't access the horsepower that is available in his engine. Seems

like

it's almost unanimous among those responding to this issue. Without fully
understanding all of the variables involved it sounds like I will be much
happier with the 2.118:1. Despite his unhappiness with choosing the 1.75,
the guy is very happy with the CAM 500. Interestingly, he reports only

1000

pounds of thrust from his setup using a Chevy 400 on a test stand. Far

less

than the numbers quoted on this list for an LS1 but still plenty for the
2500 pound Mustang replica he's building.

Now for my other question. I was talking to the guy helping me put

together

my engine and I mentioned that the PSRU I am getting has a provision for
driving a vacuum pump (or other item such as a prop governor). He said,
"why not just pull your vacuum off the intake manifold". I know this is
done on aircraft engines, but only as a source of "alternate vacuum" to
backup the primary gear driven vacuum pump. I always thought this was
because pulling it off the intake manifold would result in an unacceptable
loss of power from the engine for normal operations which is just accepted
if the primary pump fails. My engine guy says, "Huh? You wouldn't even
notice it, at least with this engine. I can't speak for aircraft

engines."

Besides, I've got horsepower to spare. What do you think? (Man, this

list

is priceless! I don't care if every one of you turned up in Fairbanks all
at once. I'd buy the beer.)

Mike Kimball
SR #044

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[Bill Delcambre]

The manifold vacuum thing might actually work with an auto conversion.
Airplane engines operate at extremely high manifold pressures (low manifold
vacuum), compared to auto engines. I'm guessing this is due to cam profile
and relatively retarded ignition timing. An auto engine might just maintain
enough vacuum, throughout the range of throttle positions to pull it off.
If you know someone with a LS-1, try to talk him into doing a temporary
install of a vacuum gauge and go run the dog crap out of it (stand on the
throttle on a steep uphill climb) and note the vacuum. If it runs below 8
or 9", I doubt if it would work. My dad used to have a vacuum gauge in a
motorhome, but I don't recall how low it could go...

If you've got in mind a turbo, at any point, all bets are absolutely off!

Bill
----- Original Message -----
From: "Mike Kimball" <mkimball@gci.net>
To: <murphy-rebel@dcsol.com>
Sent: Thursday, May 29, 2003 8:54 PM
Subject: PSRU Ratio and vacuum

Thanks to everyone for your input on the PSRU ratio question. Bob Masters
at Firewall Forward told me that they have only ever sold a 1.75:1 unit

once

and the guy they sold it to wishes he had the 2.118:1. Well, I called him
and he is emphatic about it. "DON'T GET THE 1.75" he tells me. Sounds

like

he runs out of ability to push his prop past about 4500 RPM engine speed.
He can't access the horsepower that is available in his engine. Seems

like

it's almost unanimous among those responding to this issue. Without fully
understanding all of the variables involved it sounds like I will be much
happier with the 2.118:1. Despite his unhappiness with choosing the 1.75,
the guy is very happy with the CAM 500. Interestingly, he reports only

1000

pounds of thrust from his setup using a Chevy 400 on a test stand. Far

less

than the numbers quoted on this list for an LS1 but still plenty for the
2500 pound Mustang replica he's building.

Now for my other question. I was talking to the guy helping me put

together

my engine and I mentioned that the PSRU I am getting has a provision for
driving a vacuum pump (or other item such as a prop governor). He said,
"why not just pull your vacuum off the intake manifold". I know this is
done on aircraft engines, but only as a source of "alternate vacuum" to
backup the primary gear driven vacuum pump. I always thought this was
because pulling it off the intake manifold would result in an unacceptable
loss of power from the engine for normal operations which is just accepted
if the primary pump fails. My engine guy says, "Huh? You wouldn't even
notice it, at least with this engine. I can't speak for aircraft

engines."

Besides, I've got horsepower to spare. What do you think? (Man, this

list

is priceless! I don't care if every one of you turned up in Fairbanks all
at once. I'd buy the beer.)

Mike Kimball
SR #044

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[klehman]

Mike

I'd suggest getting the vacuum pad but perhaps holding off on deciding
what to put on it. Seeing as how you are going to have an engine that
needs electric power to run, some guys stick a B&C permanent magnet
alternater on the vacuum pad. If wired properly even one alternator and
one battery gives two sources of electric power which are each more
reliable than a vacuum pump. A second alternator gives you unlimited
range though. It's getting so it almost seems a shame not to use an
electric horizon or one of the new electronic displays such as Dynon.

I committed to a vacuum pump (and possible intake manifold backup or
intake manifold fed T&B) because at the time it was several thousand
dollars cheaper. However now that there are electronic alternatives I
would probably go all electric if making the decision again. If you need
an electric horizon for IFR you can price in a replacement vacuum pump
or two (500 hrs each??) into the equation. If VFR you can compare the
cost of a Dynon type display to all the individual instruments in a
conventional panel. I think prices on displays like the Dynon will get
even more competitive and two of such units will eventually even be
worth considering.

Yet another option might be intake manifold vacuum supplemented by an
electric vacuum pump...

Ken

Mike Kimball wrote:

Thanks Ken. That jives with what my buddy tells my about available vacuum
at different power settings. One of the main reasons I got my instrument
rating was to be able to depart through that dang bay area morning fog that
delayed so many of my flights when I used to live there. Wouldn't do to not
have gyros while climbing out through the soup. Guess I'll stick with a
vacuum pump on the PSRU.

Mike Kimball
SR #044

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[Reed, Britt/FSC Salt Lake]

Rick -
You may need to take into consideration the large RPM variation on the "auto
engine" side i.e. run the engine at 4800 rpm and then drop to 2800 ?? the
Prop side Hi/Low will be about half the variation -

I clipped the following from -
http://www.casa.gov.au/avreg/aircraft/A ... /1-098.HTM

5. Overspeed
Exceeding engine redline is another proven method for trashing your vacuum
pump. Most pumps begin to provide useable suction (or pressure) around 1,500
rpm and provide optimal life at engine rpms below 2,000. (Not surprisingly,
this is the speed chosen by designers of electrically powered backup pump
systems.) The maximum continuous operating speed of Airborne pumps is 4,000
rpm (rotor shaft); for Edo pumps, 4,200 rpm. Lycoming pump pads generally
turn 1.3 times crankshaft speed. Continental pump pads, however, turn 1.5 to
1.545 times crank speed, which means that any time a Continental operator's
engine rpm exceeds 2,588, the Airborne pump limits are being busted; and any
time a Continental owner turns up more than 2,700 rpm, Edo's rpm limits are
violated. combine high rpm with high demand (as in Continental-powered
Cessna P210 with deice boots flying at 20,000 feet), and you can begin to
see why some operators experience so many problems with pumps. Add a
bonafide prop overspeed incident to the scenario (whether intentional or
unintentional), and you've got real trouble.

Britt - SR194


-----Original Message-----
From: rickhm@mindspring.com [mailto:rickhm@mindspring.com]
Sent: Friday, May 30, 2003 12:04 PM
To: murphy-rebel@dcsol.com
Subject: Re: Re: PSRU Ratio and vacuum


Why not connect a traditional aircraft vacuum pump as an accessory and drive
it with a belt. Yes one would need to figure out the right ratio's so the
pump spun at the proper speed for a typical engine RPM. Is this a good
option or am I nuts?

Rick Muller
SR70

-------Original Message-------
From: klehman@albedo.net
Sent: 05/30/03 09:37 AM
To: murphy-rebel@dcsol.com
Subject: Re: PSRU Ratio and vacuum

Even with a somewhat restrictive oem intake and filter and a venturi

(carbuerator) I've never seen a car engine that pulled more than about
an inch (hg) of vacuum at wide open throttle even at high rpm. If it did
pull significant vacuum you'd be losing a lot of power for want of a
good intake. The vacuum at wide open throttle is strictly a function of
pressure loss through the filter, carb or TBI, and manifold so it should
be minimal regardless of cam, volumetric efficiency, etc. OTOH this is
certainly workable IF you were prepared to take off, climb, and cruise
at part throttle when you were counting on the gyros. The more you close
the throttle, the more vacuum... Think you need at least 3" of hg to
spin gyros and preferably 4" or so. Another option might be to
supplement with an old external venturi hanging out in the breeze. I
love the options we homebuilders have :)
Ken

Bill Delcambre wrote:

The manifold vacuum thing might actually work with an auto conversion.
Airplane engines operate at extremely high manifold pressures (low

manifold

vacuum), compared to auto engines. I'm guessing this is due to cam

profile

and relatively retarded ignition timing. An auto engine might just

maintain

enough vacuum, throughout the range of throttle positions to pull it

off.

If you know someone with a LS-1, try to talk him into doing a temporary
install of a vacuum gauge and go run the dog crap out of it (stand on

the

throttle on a steep uphill climb) and note the vacuum. If it runs below

8

or 9", I doubt if it would work. My dad used to have a vacuum gauge in

a

motorhome, but I don't recall how low it could go...

If you've got in mind a turbo, at any point, all bets are absolutely

off!
Bill



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[Mike Kimball]

I was thinking it was starting to resemble a mathematics forum. I've run
out of fingers and toes a long time ago. All the numbers, variables, and
possibilities are giving me a migraine. Unfortunately, I'm at the stage
where it's got to be done. Thanks everyone.

On another subject, just for curiosity, I asked Brian Godden at MAM for his
opinion of my plan to put a 400 HP V8 on what is essentially a stock SR2500.
I told him my major concern was with the tailfeathers. He said he would
never put more than 300 HP on an SR2500, but his focus was on "Vne and
structural dive speed". He also played down the amount of work done on the
tailfeathers. It sounds like there were some small cracks from the hinge
bolt holes appearing due to the use of the M14 and the big prop so they
added some extra doublers here and there. Well, I think I'm going to press
on with my plan anyway with the following cautions. 1) Avoid exceeding the
179 mph Vne for an SR2500. 2) Regular, careful inspections of the
tailfeathers. I can do that.

Mike Kimball
SR #044

-----Original Message-----
From: mike.davis@dcsol.com [mailto:mike.davis@dcsol.com]On Behalf Of
klehman@albedo.net
Sent: Friday, May 30, 2003 1:06 PM
To: murphy-rebel@dcsol.com
Subject: Re: PSRU Ratio and vacuum


It has been done. Tim England (think I have the name right) even did it
with a little flat belt running on the prop shaft without a pulley. Of
course you need a bearing assembly that will handle all pulley loads and
a female spline or some other method of connecting to the wobbly shaft
on the pump. I'm betting that direct drive off a camshaft will put the
pump speed in the general ballpark and work just fine with a psru
equipped engine. It's a lot of work though if the psru manufacturer
already offers a pump pad ;)

The old smog pumps that I looked at were a bit on the large and heavy
side. This is starting to resemble an engine list...

Ken

rickhm@mindspring.com wrote:

Why not connect a traditional aircraft vacuum pump as an accessory and

drive it with a belt. Yes one would need to figure out the right ratio's
so the pump spun at the proper speed for a typical engine RPM. Is this
a good option or am I nuts?

Rick Muller
SR70

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[rickhm]

Why not connect a traditional aircraft vacuum pump as an accessory and drive it with a belt. Yes one would need to figure out the right ratio's so the pump spun at the proper speed for a typical engine RPM. Is this a good option or am I nuts?

Rick Muller
SR70

-------Original Message-------
From: klehman@albedo.net
Sent: 05/30/03 09:37 AM
To: murphy-rebel@dcsol.com
Subject: Re: PSRU Ratio and vacuum

Even with a somewhat restrictive oem intake and filter and a venturi

(carbuerator) I've never seen a car engine that pulled more than about
an inch (hg) of vacuum at wide open throttle even at high rpm. If it did
pull significant vacuum you'd be losing a lot of power for want of a
good intake. The vacuum at wide open throttle is strictly a function of
pressure loss through the filter, carb or TBI, and manifold so it should
be minimal regardless of cam, volumetric efficiency, etc. OTOH this is
certainly workable IF you were prepared to take off, climb, and cruise
at part throttle when you were counting on the gyros. The more you close
the throttle, the more vacuum... Think you need at least 3" of hg to
spin gyros and preferably 4" or so. Another option might be to
supplement with an old external venturi hanging out in the breeze. I
love the options we homebuilders have :)
Ken

Bill Delcambre wrote:

The manifold vacuum thing might actually work with an auto conversion.
Airplane engines operate at extremely high manifold pressures (low

manifold

vacuum), compared to auto engines. I'm guessing this is due to cam

profile

and relatively retarded ignition timing. An auto engine might just

maintain

enough vacuum, throughout the range of throttle positions to pull it

off.

If you know someone with a LS-1, try to talk him into doing a temporary
install of a vacuum gauge and go run the dog crap out of it (stand on

the

throttle on a steep uphill climb) and note the vacuum. If it runs below

8

or 9", I doubt if it would work. My dad used to have a vacuum gauge in

a

motorhome, but I don't recall how low it could go...

If you've got in mind a turbo, at any point, all bets are absolutely

off!
Bill




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[klehman]

Even with a somewhat restrictive oem intake and filter and a venturi
(carbuerator) I've never seen a car engine that pulled more than about
an inch (hg) of vacuum at wide open throttle even at high rpm. If it did
pull significant vacuum you'd be losing a lot of power for want of a
good intake. The vacuum at wide open throttle is strictly a function of
pressure loss through the filter, carb or TBI, and manifold so it should
be minimal regardless of cam, volumetric efficiency, etc. OTOH this is
certainly workable IF you were prepared to take off, climb, and cruise
at part throttle when you were counting on the gyros. The more you close
the throttle, the more vacuum... Think you need at least 3" of hg to
spin gyros and preferably 4" or so. Another option might be to
supplement with an old external venturi hanging out in the breeze. I
love the options we homebuilders have :)
Ken

Bill Delcambre wrote:

The manifold vacuum thing might actually work with an auto conversion.
Airplane engines operate at extremely high manifold pressures (low manifold
vacuum), compared to auto engines. I'm guessing this is due to cam profile
and relatively retarded ignition timing. An auto engine might just maintain
enough vacuum, throughout the range of throttle positions to pull it off.
If you know someone with a LS-1, try to talk him into doing a temporary
install of a vacuum gauge and go run the dog crap out of it (stand on the
throttle on a steep uphill climb) and note the vacuum. If it runs below 8
or 9", I doubt if it would work. My dad used to have a vacuum gauge in a
motorhome, but I don't recall how low it could go...

If you've got in mind a turbo, at any point, all bets are absolutely off!

Bill

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[rickhm]

Well, lets see.

If my max pump speed is 4k and the max engine is say 5k the ratio is 0.8. If I need 1500 pump speed to produce vac, then the engine needs to turn at 1875. If I am using a 2:1 gear box up front then my prop is spinning at 937.5 and if I am using a 1.7:1 gear box my prop is spinning 1103. I think I might be ok here.

On the other hand. For "optimal" I need a pump speed of 2k and at a 5k engine speed this suggests a ratio of .4. If I need 1500 pump speed to produce vac then then engine needs to turn 3750, with a 2:1 gear box the prop is spinning at 1875 and with a 1.7:1 the prop is spinning at 2205. A litte hot for an idle speed.

I guess fundementally, there is a relationship between prop speed and pump speed, regardless of the engine (LS1, Lyc, Cont., Franklin, etc.). You would like the idle prop speed to provide adequate vac (1500 pump speed) and at high prop speed you would like to have the pump below its max. There is no perfect answer here. But a compromise between 0.7 and 0.4 should get one there I think? If you select a min prop speed of say 1200 then the ratio would be .625 (2:1 gear box) or .73 (1.7:1). This gives you an upper end pump speed (5000 engine RPM) of 3125 (2:1) and 3676 (1.7:1). I think it will work?

Did I miss something?

Rick Muller
SR 70
-------Original Message-------
From: "Reed, Britt/FSC Salt Lake" <BReed@slcrail.com>
Sent: 05/30/03 11:17 AM
To: murphy-rebel@dcsol.com
Subject: RE: Re: PSRU Ratio and vacuum

Rick -

You may need to take into consideration the large RPM variation on the
"auto
engine" side i.e. run the engine at 4800 rpm and then drop to 2800 ?? the
Prop side Hi/Low will be about half the variation -

I clipped the following from -
http://www.casa.gov.au/avreg/aircraft/A ... /1-098.HTM

5. Overspeed
Exceeding engine redline is another proven method for trashing your vacuum
pump. Most pumps begin to provide useable suction (or pressure) around
1,500
rpm and provide optimal life at engine rpms below 2,000. (Not
surprisingly,
this is the speed chosen by designers of electrically powered backup pump
systems.) The maximum continuous operating speed of Airborne pumps is
4,000
rpm (rotor shaft); for Edo pumps, 4,200 rpm. Lycoming pump pads generally
turn 1.3 times crankshaft speed. Continental pump pads, however, turn 1.5
to
1.545 times crank speed, which means that any time a Continental
operator's
engine rpm exceeds 2,588, the Airborne pump limits are being busted; and
any
time a Continental owner turns up more than 2,700 rpm, Edo's rpm limits
are
violated. combine high rpm with high demand (as in Continental-powered
Cessna P210 with deice boots flying at 20,000 feet), and you can begin to
see why some operators experience so many problems with pumps. Add a
bonafide prop overspeed incident to the scenario (whether intentional or
unintentional), and you've got real trouble.

Britt - SR194


-----Original Message-----
From: rickhm@mindspring.com [mailto:rickhm@mindspring.com]
Sent: Friday, May 30, 2003 12:04 PM
To: murphy-rebel@dcsol.com
Subject: Re: Re: PSRU Ratio and vacuum


Why not connect a traditional aircraft vacuum pump as an accessory and
drive
it with a belt. Yes one would need to figure out the right ratio's so the
pump spun at the proper speed for a typical engine RPM. Is this a good
option or am I nuts?

Rick Muller
SR70

-------Original Message-------
From: klehman@albedo.net
Sent: 05/30/03 09:37 AM
To: murphy-rebel@dcsol.com
Subject: Re: PSRU Ratio and vacuum

Even with a somewhat restrictive oem intake and filter and a venturi

(carbuerator) I've never seen a car engine that pulled more than about
an inch (hg) of vacuum at wide open throttle even at high rpm. If it did
pull significant vacuum you'd be losing a lot of power for want of a
good intake. The vacuum at wide open throttle is strictly a function of
pressure loss through the filter, carb or TBI, and manifold so it should
be minimal regardless of cam, volumetric efficiency, etc. OTOH this is
certainly workable IF you were prepared to take off, climb, and cruise
at part throttle when you were counting on the gyros. The more you close
the throttle, the more vacuum... Think you need at least 3" of hg to
spin gyros and preferably 4" or so. Another option might be to
supplement with an old external venturi hanging out in the breeze. I
love the options we homebuilders have :)
Ken

Bill Delcambre wrote:

The manifold vacuum thing might actually work with an auto conversion.
Airplane engines operate at extremely high manifold pressures (low

manifold

vacuum), compared to auto engines. I'm guessing this is due to cam

profile

and relatively retarded ignition timing. An auto engine might just

maintain

enough vacuum, throughout the range of throttle positions to pull it

off.

If you know someone with a LS-1, try to talk him into doing a temporary
install of a vacuum gauge and go run the dog crap out of it (stand on

the

throttle on a steep uphill climb) and note the vacuum. If it runs below

8

or 9", I doubt if it would work. My dad used to have a vacuum gauge in

a

motorhome, but I don't recall how low it could go...

If you've got in mind a turbo, at any point, all bets are absolutely

off!

Bill



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[BCairboat]

If everyone wants a cheap vacuum pump on their V8 why not just use the
standard anti pollution pump that came with the engine.
They are a positive displacement rotary vane pump capable of pulling any
amount of vacuum you want. They run off the same belt as the alternator which you
need anyway and last forever.
Grant.



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[klehman]

It has been done. Tim England (think I have the name right) even did it
with a little flat belt running on the prop shaft without a pulley. Of
course you need a bearing assembly that will handle all pulley loads and
a female spline or some other method of connecting to the wobbly shaft
on the pump. I'm betting that direct drive off a camshaft will put the
pump speed in the general ballpark and work just fine with a psru
equipped engine. It's a lot of work though if the psru manufacturer
already offers a pump pad ;)

The old smog pumps that I looked at were a bit on the large and heavy
side. This is starting to resemble an engine list...

Ken

rickhm@mindspring.com wrote:

Why not connect a traditional aircraft vacuum pump as an accessory and

drive it with a belt. Yes one would need to figure out the right ratio's
so the pump spun at the proper speed for a typical engine RPM. Is this
a good option or am I nuts?

Rick Muller
SR70

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[Rickhm at home]

Mike,

I have been traveling and am just now catching up. This is essentially
what he told me a while back. When I inquired about the strength of the
firewall. He didn't express concern about the firewall only Vne. If it
were a float plane where there is more drag, I recall he felt comfortable
with 300 hp.

RIck Muller

-----Original Message-----
From: Mike Kimball [SMTP:mkimball@gci.net]
Sent: Friday, May 30, 2003 3:59 PM
To: murphy-rebel@dcsol.com
Subject: RE: PSRU Ratio and vacuum

I was thinking it was starting to resemble a mathematics forum. I've run
out of fingers and toes a long time ago. All the numbers, variables, and
possibilities are giving me a migraine. Unfortunately, I'm at the stage
where it's got to be done. Thanks everyone.

On another subject, just for curiosity, I asked Brian Godden at MAM for his
opinion of my plan to put a 400 HP V8 on what is essentially a stock
SR2500.
I told him my major concern was with the tailfeathers. He said he would
never put more than 300 HP on an SR2500, but his focus was on "Vne and
structural dive speed". He also played down the amount of work done on the
tailfeathers. It sounds like there were some small cracks from the hinge
bolt holes appearing due to the use of the M14 and the big prop so they
added some extra doublers here and there. Well, I think I'm going to press
on with my plan anyway with the following cautions. 1) Avoid exceeding
the
179 mph Vne for an SR2500. 2) Regular, careful inspections of the
tailfeathers. I can do that.

Mike Kimball
SR #044

-----Original Message-----
From: mike.davis@dcsol.com [mailto:mike.davis@dcsol.com]On Behalf Of
klehman@albedo.net
Sent: Friday, May 30, 2003 1:06 PM
To: murphy-rebel@dcsol.com
Subject: Re: PSRU Ratio and vacuum


It has been done. Tim England (think I have the name right) even did it
with a little flat belt running on the prop shaft without a pulley. Of
course you need a bearing assembly that will handle all pulley loads and
a female spline or some other method of connecting to the wobbly shaft
on the pump. I'm betting that direct drive off a camshaft will put the
pump speed in the general ballpark and work just fine with a psru
equipped engine. It's a lot of work though if the psru manufacturer
already offers a pump pad ;)

The old smog pumps that I looked at were a bit on the large and heavy
side. This is starting to resemble an engine list...

Ken

rickhm@mindspring.com wrote:

Why not connect a traditional aircraft vacuum pump as an accessory and

drive it with a belt. Yes one would need to figure out the right ratio's
so the pump spun at the proper speed for a typical engine RPM. Is this
a good option or am I nuts?

Rick Muller
SR70

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