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07-23-2014, 06:43 AM
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Join Date: May 2014
Location: KBVY Massachusetts
Posts: 1,100
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Upgrading Engine in a -4 vs -8 - which is harder?
Hi all,
I'm in the market for a -4 or a -8. There are a lot of variables in my mind and I'm trying to sort them out/eliminate them by getting answers to questions. This particular question is a big one:
There is a "Build or buy?" thread in the -4 forum. The consensus seems to be that if you are going to buy, find a good airframe and then customize it the way you want.
If I buy an a/c with an O-320 FP, and I want to upgrade to an O-360 C/S, the questions are:
1) Is there any difference in the amount of work and/or expense doing this in a -4 vs a -8?
2) In either case, would I need a new engine mount? New cowling? New anything else?
3) Aside from routing the prop control to the cockpit and modifying the throttle quadrant, is this sort of engine upgrade a difficult proposition if you have not built an airplane?
Thanks for any insight.
Last edited by Saville : 07-23-2014 at 08:46 AM.
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07-23-2014, 08:15 AM
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Join Date: Oct 2008
Location: Punta Gorda, Fl
Posts: 325
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That change on a -4 would require:
New gear legs matched to new motor mount
New cowl and obviously prop and spinner
The governor would need a recess cut into the firewall.
Relocation of the battery and any other tricks to move the c of g back away from the nose.
__________________
Jesse
'89 RV-4, N2626C - purchased flying
Converted to Fastback - Sliding Canopy - Tall Gear
Dynon Skyview w/ acc. & VP-x Sport
Catto 3-Blade (gen. 1)
Based: KPGD
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07-23-2014, 08:25 AM
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Join Date: May 2006
Location: Houston
Posts: 2,012
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Quote:
Originally Posted by southtarnation
That change on a -4 would require:
New gear legs matched to new motor mount
New cowl and obviously prop and spinner
The governor would need a recess cut into the firewall.
Relocation of the battery and any other tricks to move the c of g back away from the nose.
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You sure the mount would change?? I just changed my -8 from -320 to -360 (parallel, Dynafocal to Dynafocal). Only substantial change was the baffling. I did keep the same CS prop. Just put the cowl back on and go.
The dimensional change was the width of the engine. This would likely be a slightly greater concern with a -4 (stuffing everything into the smaller cowling space).
Whether or not one has built a kit plane isn't really the measure, IMO. Whether or not you're familiar with maintaining/installing/modifying things forward of the firewall in a small plane is. And a swap as you describe puts you back in the complexity of original firewall forward kit construction.
Last edited by Low Pass : 07-23-2014 at 08:27 AM.
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07-23-2014, 08:52 AM
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Join Date: May 2014
Location: KBVY Massachusetts
Posts: 1,100
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Low Pass,
From what you write, you make it sound as if it's easier in a -8 than a -4.
And yes there is also the question as to what an O 360 really buys you in a -4. According to Van's performance charts, we're talking a little over 7 mph difference.
Thanks!
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07-23-2014, 09:06 AM
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Join Date: Jan 2005
Location: albuquerque, nm
Posts: 1,167
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In addition to the comments above:
There is very little room between the engine and the firewall on an RV-4.
There is a lot of room between the engine and the firewall on an RV-8. The 8 doesn't need a recess for the governor--In fact there is probably 6-8" between my governor and the firewall.
Best,
Guy
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07-23-2014, 10:00 AM
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Join Date: Mar 2005
Location: Dallas area
Posts: 10,768
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The -4 also used a different cowling for F/P vs C/S.
F/P cowlings were designed for a 4" extension. Later the cowlings were changed to use a shorter extension so the same cowling could be used for both.
__________________
Mel Asberry, DAR since the last century.
EAA Flight Advisor/Tech Counselor, Friend of the RV-1
Recipient of Tony Bingelis Award and Wright Brothers Master Pilot Award
USAF Vet, High School E-LSA Project Mentor.
RV-6 Flying since 1993 (sold)
<rvmel(at)icloud.com>
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07-23-2014, 10:05 AM
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Join Date: Jun 2006
Location: Freericksburg, VA
Posts: 624
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Quote:
Originally Posted by Mel
The -4 also used a different cowling for F/P vs C/S.
F/P cowlings were designed for a 4" extension. Later the cowlings were changed to use a shorter extension so the same cowling could be used for both.
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Not sure when this change was made but I expect the majority of kits for sale out there have the latest cowl that uses the 2.25" extension for the FP prop.
I expect the change would be easier on an -8 given it has more room but there are a ton of -4s fling with an O-360 up front so it ain't rocket science to cam one in there.
__________________
Richard Bibb
RV-4 N144KT
Fredericksburg, VA
KEZF
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07-23-2014, 04:25 PM
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Join Date: Oct 2008
Location: Punta Gorda, Fl
Posts: 325
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Quote:
Originally Posted by Low Pass
You sure the mount would change?? I just changed my -8 from -320 to -360 (parallel, Dynafocal to Dynafocal). Only substantial change was the baffling. I did keep the same CS prop. Just put the cowl back on and go.
The dimensional change was the width of the engine. This would likely be a slightly greater concern with a -4 (stuffing everything into the smaller cowling space).
Whether or not one has built a kit plane isn't really the measure, IMO. Whether or not you're familiar with maintaining/installing/modifying things forward of the firewall in a small plane is. And a swap as you describe puts you back in the complexity of original firewall forward kit construction.
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Yes you are right, I'm not thinking clearly. Motor mount and therefor legs could be reused, sorry bout that. 
__________________
Jesse
'89 RV-4, N2626C - purchased flying
Converted to Fastback - Sliding Canopy - Tall Gear
Dynon Skyview w/ acc. & VP-x Sport
Catto 3-Blade (gen. 1)
Based: KPGD
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