Lopresti & Powerflow for Cheetah -- good as they say?

[Duane MacInnis]

Hello all,

I may soon be the happy owner of a 78 Cheetah.

I would be tempted to immediately install the LoPresti cowl & rudder cap,
and the Powerflow exhaust.

When the engine croaks I will go for the 160 STC, but in the meantime the
cowl and exhaust combination may extend the cylinder life on these
notoriously hot engines, as well as reportedly yielding some pretty
impressive speed increases and reduction in fuel consumption.

Any experience out there you would like to share?

Thanks

Duane (Vancouver BC)

++++++++++++++
Duane MacInnis
Flight Instructor
Cell (604) 454-7415
www.macinnisaviation.com

[Sydney Hoeltzli]

Duane MacInnis wrote:
> Hello all,
>
> I may soon be the happy owner of a 78 Cheetah.
>
> I would be tempted to immediately install the LoPresti cowl & rudder cap,
> and the Powerflow exhaust.
>
> When the engine croaks I will go for the 160 STC, but in the meantime the
> cowl and exhaust combination may extend the cylinder life on these
> notoriously hot engines, as well as reportedly yielding some pretty
> impressive speed increases and reduction in fuel consumption.
>
> Any experience out there you would like to share?

Duane, you might want to join the Grumman Gang email list
(http://www.grumman.net) and put your question there. I'm not a
Cheetah owner, but a few points. First, the Tiger is a notoriously
hot installation. To my knowledge, Cheetahs aren't particularly
under-cooled and don't have a particular problem with valve wear
or cylinder life. If you have good cylinders to start with, they
should last fine.

Second, I think the general opinion is the best thing you can
do for a Cheetah is top it and do the 160 HP STC. One of the worst
limitations in the Cheetah is poor rate of climb (esp. at high
density altitude), and the word from those who've done it is the
160 HP conversion really really helps out. You won't gain speed
but you'll chew your knuckles less on short-field takeoffs in
summer so you'll definately gain utility.

I don't know what the real-life speed increase from the tuned
exhaust is. I don't know anyone who's done it. The skinny at
last year's convention is that several people had volunteered
a test-bed to produce systematic numbers and the company was
uninterested. Make of that what you will. Ask on the Grumman
Gang if anyone has done it and what they saw IRL

I don't think LoPresti even markets the cowl as producing a
speed increase for the Grummans. From those I know who've done it,
either it doesn't add much or, they did a whole bunch of other mods
at the same time (new paint, fairings etc) so it's problematic to
say which did what. JMO, but I don't think you're going to turn
your Cheetah into a Tiger by throwing a lot of money into a tuned
exhaust and a LoPresti cowl. If you have a Tiger and you're getting
a paint job I think it might be worth the money for the improved
cooling.

If it were my money I'd spend it on the 160 HP mod ASAP.

Without any mods, you'll still be nipping at the tailfins of
Archers and pulling away from 150 hp C172s. Don't be greedy *g*.

FWIW,
Sydney (Grumman AA5B "Tigger")

[The Flynns]

I second the referral to the GG. It's the best place to get info on all
things Grumman. The group's very friendly, responsive and some very
knowledgeable folks including David Fletcher and Cliff Hanson reply with
regularity.

As to cooling, I swapped out the oil cooler for a bigger one with some
positive results and rebuilt the baffling on my Tiger. As part of a
pre-buy, I'd definitely have someone who knows what they're doing look at
the baffling. If you're planning on doing the HC upgrade, why not look for
a Tiger instead? I didn't price Cheetah's so don't know what the price diff
is.
In any event, you'll love the airplane....
As with all recommendations and comments....you got what you paid for!
--
Patrick Flynn
Sammamish, WA
79 Tiger N4543A KRNT

"Sydney Hoeltzli" > wrote in message
...
> Duane MacInnis wrote:
> > Hello all,
> >
> > I may soon be the happy owner of a 78 Cheetah.
> >
> > I would be tempted to immediately install the LoPresti cowl & rudder
cap,
> > and the Powerflow exhaust.
> >
> > When the engine croaks I will go for the 160 STC, but in the meantime
the
> > cowl and exhaust combination may extend the cylinder life on these
> > notoriously hot engines, as well as reportedly yielding some pretty
> > impressive speed increases and reduction in fuel consumption.
> >
> > Any experience out there you would like to share?
>
> Duane, you might want to join the Grumman Gang email list
> (http://www.grumman.net) and put your question there. I'm not a
> Cheetah owner, but a few points. First, the Tiger is a notoriously
> hot installation. To my knowledge, Cheetahs aren't particularly
> under-cooled and don't have a particular problem with valve wear
> or cylinder life. If you have good cylinders to start with, they
> should last fine.
>
> Second, I think the general opinion is the best thing you can
> do for a Cheetah is top it and do the 160 HP STC. One of the worst
> limitations in the Cheetah is poor rate of climb (esp. at high
> density altitude), and the word from those who've done it is the
> 160 HP conversion really really helps out. You won't gain speed
> but you'll chew your knuckles less on short-field takeoffs in
> summer so you'll definately gain utility.
>
> I don't know what the real-life speed increase from the tuned
> exhaust is. I don't know anyone who's done it. The skinny at
> last year's convention is that several people had volunteered
> a test-bed to produce systematic numbers and the company was
> uninterested. Make of that what you will. Ask on the Grumman
> Gang if anyone has done it and what they saw IRL
>
> I don't think LoPresti even markets the cowl as producing a
> speed increase for the Grummans. From those I know who've done it,
> either it doesn't add much or, they did a whole bunch of other mods
> at the same time (new paint, fairings etc) so it's problematic to
> say which did what. JMO, but I don't think you're going to turn
> your Cheetah into a Tiger by throwing a lot of money into a tuned
> exhaust and a LoPresti cowl. If you have a Tiger and you're getting
> a paint job I think it might be worth the money for the improved
> cooling.
>
> If it were my money I'd spend it on the 160 HP mod ASAP.
>
> Without any mods, you'll still be nipping at the tailfins of
> Archers and pulling away from 150 hp C172s. Don't be greedy *g*.
>
> FWIW,
> Sydney (Grumman AA5B "Tigger")
>

[Sydney Hoeltzli]

Peter Gottlieb wrote:
> I just flew a Cheetah to Oshkosh and back to New York. It just got back
> from the shop after being repainted and getting the Powerflow exhaust.
>
> The Powerflow exhaust will not make a dramatic difference. I think maybe I
> noticed a little more power and climb but definitely didn't blow my socks
> off.

The lower drag of a new paint job (esp. if all control surfaces were
balanced and put into rig) can add a little bit of climb and speed

Does the plane have a 4 cyl EGT/CHT by any chance? Any info on
if the spread was about the same or any narrower, afterwards?

Cheers,
Sydney

[Dan Luke]

"Sydney Hoeltzli" wrote:
> The lower drag of a new paint job (esp. if all control surfaces were
> balanced and put into rig) can add a little bit of climb and speed

I've heard that this is an OWT (nothing personal, Sydney).

How does a new paint job reduce drag if even rough paint barely penetrates
the bottom of the boundary layer?
--
Dan
C172RG at BFM

[Sydney Hoeltzli]

Dan Luke wrote:
> "Sydney Hoeltzli" wrote:
>>The lower drag of a new paint job (esp. if all control surfaces were
>>balanced and put into rig) can add a little bit of climb and speed

> I've heard that this is an OWT (nothing personal, Sydney).

Nothing personal taken. It's a fact that several people I know
have seen this. You might note that I didn't specify it
was the paint itself; if the control surfaces were a bit out of
rig and put right, that could easily account for it. Another
factor is weight. 2-3 paintjobs with some patching and overspray
can easily add 30-40 lbs or more. Strip it off and replace with
one even coat, lighter plane.

> How does a new paint job reduce drag if even rough paint barely penetrates
> the bottom of the boundary layer?

Beats me. Your guess is as good as mine.

Cheers,
Sydney

[Duane MacInnis]

Thanks to you all for the kind posts.

I know I cannot make a Tigger out of a Cheetah on the cheap (w), but the
price differential is so great up here in Vancouver BC (known to some as
West Canuckistan) that it would be worth spending a few bucks to eak
whatever performance and longevity possible out of the Cheetah.

The aircraft in my sights has a low time airframe/engine, so if the cam
ain't rusted from underuse, it should go for many hundreds of hours before
needing an overhaul -- then I go for the 160. In the meantime, if the
LoPresti cowl and Powerflow improved cooling and performance significantly,
they may be a good investment now to help extend engine life and later too.

In any case, your many suggestions to join the GG and AYA have not fallen on
deaf ears -- I will do that when I get the plane, then think about mods with
their doubtless good advice.

Thanks again -- great group.

Duane



"Duane MacInnis" > wrote in message
. ..
> Hello all,
>
> I may soon be the happy owner of a 78 Cheetah.
>
> I would be tempted to immediately install the LoPresti cowl & rudder cap,
> and the Powerflow exhaust.
>
> When the engine croaks I will go for the 160 STC, but in the meantime the
> cowl and exhaust combination may extend the cylinder life on these
> notoriously hot engines, as well as reportedly yielding some pretty
> impressive speed increases and reduction in fuel consumption.
>
> Any experience out there you would like to share?
>
> Thanks
>
> Duane (Vancouver BC)
>
> ++++++++++++++
> Duane MacInnis
> Flight Instructor
> Cell (604) 454-7415
> www.macinnisaviation.com
>
>
>

[Sydney Hoeltzli]

Duane MacInnis wrote:
> In the meantime, if the
> LoPresti cowl and Powerflow improved cooling and performance significantly,
> they may be a good investment now to help extend engine life and later too.

I know three local pilots with Cheetahs. Two have 4 cyl CHT/EGT,
one only one cyl (hottest). None of the three seem to have a problem
with engine cooling. All of the three have meticulously maintained
baffling. One gets flown all over the place at high DA in summer.
One has the 160 HP mod, the other 2 don't. Guess which one.

I don't think cooling is a major issue with the Cheetah. Your
#1 priority should be making sure that the baffling and baffle
sealing is in tip-top shape.

Peformance? You'll have to count the legs on those horses
yourself.

> In any case, your many suggestions to join the GG and AYA have not fallen on
> deaf ears -- I will do that when I get the plane, then think about mods with
> their doubtless good advice.

Duane, I would strongly recommend you to run don't walk and join
both groups NOW. Both will be an invaluable resource to you in terms
of things to inspect and look out for, BEFORE you buy the plane.

Good luck,
Sydney