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Lopresti & Powerflow for Cheetah -- good as they say?
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 |
#2
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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") |
#3
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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") |
#4
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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 |
#5
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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 |
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