Piston/compression/fuel combinations for O-360 and O-320

[SHIPCHIEF]

Sure;
Longer stroke would use a shorter connecting rod if the same piston was used; Block deck height and cylinder/head being the same.

[C-GRVT]

interesting thread and good information from Mahlon on how to achieve certain results.
It is probably obvious to most (but it wasn't to me, hence this post for those like me who might benefit) that engine modifications (and not only to compression ratio) can substantially affect other important choices such as propeller and have consequences to the build.
My experience in building my RV is that decision points arrived when I was not really equipped to make a fully informed decision. As has often been said in various contexts, it is not knowing what we don't know that can create problems.
For example, Van's asks for an engine selection to be made at the time of ordering the finishing kit. I selected a constant speed vertical induction 0-360from the form. I did not know that Van's plans and finish kit did not support that option. Not fatal, and I am happy with the choice I made, but it troubled me that I only figured that out later.
The next point - I ordered an engine. I chose an AeroSport engine, fuel injection, one mag and one Lightspeed. A good engine choice, I think, from a very good engine builder. It was only later, when I needed to decide on and order a propeller, that I discovered that Hartzell, for example, has a list of tested and approved engine/prop combinations that do not include the engine that I ordered (and would not include an engine with high compression pistons, to bring this post back to the thread). After some research and discussions with knowledgable people I have a Hartzell prop and am happy with the choice. But again I found myself having configured the engine without benefit of all the relevant considerations.
So, for anyone like me doing this for the first time and thinking of speed and power mods, like electronic ignitions, porting and polishing, playing with compression ratios, there are considerations down the line other than horsepower and engine performance.
Bill Brooks
Ottawa, Canada
RV-6A finishing kit

[flyboy1963]

Bill,
I feel your pain! Every descision made along the way, whether informed or not, has that dreaded domino effect!
I'd like to know if there is some way to know if, for example, I run 94 octane mogas in my lo-comp 0-320, or the future avgas, what hp I can expect?
perhaps we should be re-doing flight testing, as we would if we installed a 125 hp engine instead!
the new t/off distance over 50' obstacle is..........?? feet
rate of climb at gross is now...........fpm?
etc etc.

[chaskuss]

Originally Posted by SHIPCHIEF

Sure;
Longer stroke would use a shorter connecting rod if the same piston was used; Block deck height and cylinder/head being the same.

Scott,
"Block deck height" is not the same when comparing a 320 to a 360. The 360 cylinder is 0.500" longer to complement the extra .500" of stroke. The easy way to tell a 320 cylinder from a 360 cylinder is to count the fins on the steel barrel. A 320 will have 15, a 360 will have 19.
Charlie Kuss

[SHIPCHIEF]

Thanks! I didn't know the combination, just the relationships!
I have an RV-9a project on the back burner waiting for me to finish the RV-8.
So I have to keep my eyes open for the right powerplant choices.

[NDrv8r]

I talked to Gibson in OK about higher compressions. His take was that it was asking for blown heads. Have there been any issues of cracking associated with higher compressions?

Also, is the LW-15357 9:1 piston applicable to parallel and angle valve engines?

[frewjm]

The Type Certificate line of logic is from FAA/FAR's. For review by this panel but found on another GA website.

FAR 1.1 General Definitions? which (as extracted from current FAR?s) states that:
?Major alteration means an alteration not listed in the aircraft, aircraft engine, or propeller specifications--

(1) That might appreciably affect weight, balance, structural strength, performance, powerplant operation, flight characteristics, or other qualities affecting airworthiness; or
(2) That is not done according to accepted practices or cannot be done by elementary operations.?

And conversely

?Minor alteration means an alteration other than a major alteration. ?

The overarching fact is that the alteration of the engine to type O-320H, to which the minor change will reference as the changed engine, is clearly listed in the governing engine specification control document which is ?Type Certificate Data Sheet No. E-274 Revision 21?, refer Appendix 3

The Type Certificate Data Sheet No. E-274 is the FAA certification document for the 0-320 engine. All engine models listed in the document lie within 0-320 engine specifications. In the TC block on each engine data plate ?274? appears for all 0-320 engines listed in the E-274 document. Revision 20 to E-274 dated August 10, 2009 lists 59 engine models that fall within this engine specification, including 0-320-E2A and 0-320-H3AD.

Therefore converting an ?E2A to a ?H3AD is a change within the engine specification and qualifies as a minor change as all engineering issues were considered when the type certificate was issued, or else a new seperate type certificate would be needed.

[LifeofReiley]

Blah Blah... in the experimantal market Who really cares??

[C-GRVT]

Reilly,
"Blah Blah doesn't really address the point.
A "major alteration" as defined by the FARS is relevant to what we do. The FARS definition reflects physics and safe practice. We may be exempt from FARS but not from what the FARS are trying to address. We ignore that at our peril. To bring this back somewhat to the thread, changing to high compression pistons, for example, has consequences to things that matter such as suitability of propeller.
Bill Brooks
Ottawa, Canada
RV-6A finishing

[SHIPCHIEF]

SO I've been reading about the O-340 currently offered by ECI and others.
This is not the O-340 used in the twin Navion, rather, an adaptation of a 4.125" stroke crankshaft, O-320 cylinders and standard 4 cylinder crankcase?
My 'research' indicates that a custom connecting rod might be used?
Stock 5.125" pistons, as used in O-320 & O-360?
Or, is a stock length connecting rod, and a low compression piston used, to result in a higher compression ratio?
What is the parts combination? Can a O-360 crank be offset ground to reduce the stroke, and be reliable?
Any antecdotal stories on custom O-340 engines and their history?
Can an "engine guy" reasonably build his own experimental O-340?