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Valve Timing


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12 replies to this topic

#1 automan1223

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Posted 24 January 2004 - 06:55 PM

Curious if any of you tune'rs out there have messed with valve timing. I am concerned with increasing power in the upper rpm range as engine is on aircraft. 5000+5500 range.

I know most tuning books recommend 8 degrees max before or after but I am wondering how much improvement can be had. Any thoughts ?


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#2 Legacy777

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Posted 26 January 2004 - 08:58 AM

You didn't mention whether you're looking at using an ej25, ej22, etc.

You may want to contact cobb tuning www.cobbtuning.com as they make cams for the 2.5 May also want to contact Paeco http://www.paeco.com/

#3 blitz

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Posted 26 January 2004 - 12:33 PM

I speculate that some meat could be added to the lower end of the torque curve by advancing the stock cams a couple degrees, which would benefit a relatively heavy, 4EAT equipped vehicle, but the tradeoff would be a power fall-off above 5000 RPM.

I don't see any benefit of going the other way (retarding the stock cams) in hopes of finding better breathing up top. As Legacy777 mentioned, your best bet to get the motor to breath freely is the Cobb street cams combined with an intake, Cobb header, and a decent exhaust. If you want to go further, have the heads done. Further yet? ...Cobb club-racer cams.

There's a lot of power to be had, at the expense of some engine longevity.

#4 automan1223

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Posted 26 January 2004 - 12:52 PM

Ok, this engine is in a gyro, and turns a Propeller a steady 5000-5500. I forgot to mention that the cams are a slightly high po stratus grind, which I figure due to their low cost is just a simple base lobe regrind. The motor does have a slight lope at idle, but turns no less than 1200 rpm. Head work will be done, currently working on a mild port, polish, and 5 angle valve job. I think that might wake it up but I feel there is more to be had with a more agressive cam profile.

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#5 blitz

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Posted 26 January 2004 - 12:56 PM

Just noticed the aircraft requirement, so I guess the Cobb header is out, but I'd imagine that you've already got a decent-flowing custom exhaust installed.

The only disadvantage to the Cobb cam (or any other stage 1 cam) is the higher lift which works the valve springs harder. This I think might neccesitate a periodic valvespring changeout interval to retain reliability in flight.

The engine might respond to a little bit of cam-retard if you combined it with having the heads done (including a multi-angle valve job).

The only way to know for sure would be to have access to some dyno time. A dozen pulls to try different combinations would show you the way.

#6 blitz

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Posted 26 January 2004 - 01:31 PM

Had some more thoughts. Not sure what kind of altitude you routinely see in that sort of craft, but I would think that as atmospheric pressure drops as a consequence of altitude, accelerative velocity in the manifold and ports will suffer proportionately ...so if the air lags, make the cam lag too. You might be onto something.

Also, continous full-throttle operation at 5500 RPM seems like it would place a fair amount of strain on stock internals as well as generate a butt-load of heat into the piston crowns, ring-lands, oil, and exhaust valves. Part-throttle operation at 4500 RPM on a continuous basis shouldn't pose a problem.

#7 automan1223

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Posted 26 January 2004 - 04:46 PM

I got news for you guys. Experimental aircraft builders use subs going back to the ea 81, 82, ej 18, 22, 25, & eg 33. There are great little engines and they run full open all day long. If they do go its because the aircraft builder took the easy way out and got a bit too high mileage one out of a junkyard and just bolted it up and away they went. Never checked anything and either the mix was so off it burned it up after hours of abuse or they ran really bad gas or av gas thinking they were doing it a favor. I have pulled apart engines from running junk yards donors with 110,000k miles and the insides look brand new except for some burned oil here or there. The weak spot with the 2.2s seem to be the exhaust valves. Pitting, some metal transfer from the valve seat to the valve ! Once in a while an oil pump will let go, or act funny enough to get replaced. These engines are a lot better than they get credit for. While most blow head gaskets after years of cooling system abuse, they can and do run for years happily at 5500 rpm. usually 5200 with stock cams, 54-5500 with high po regrinds. Except for vw & corvair engines, subaru is the most popular auto conversion out there.

#8 calebz

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Posted 26 January 2004 - 05:02 PM

You still haven't said what engine you are using in the gyro.. that would be helpful.

#9 automan1223

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Posted 26 January 2004 - 05:12 PM

I am using a EJ 2.2 l . But it has been fitted with a custom manifold for a holley carb and an electronic distributor.

#10 blitz

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Posted 26 January 2004 - 06:08 PM

Originally posted by automan1223
I got news for you guys. Experimental aircraft builders use subs going back to the ea 81, 82, ej 18, 22, 25, & eg 33. There are great little engines and they run full open all day long. If they do go its because the aircraft builder took the easy way out and got a bit too high mileage one out of a junkyard and just bolted it up and away they went. Never checked anything and either the mix was so off it burned it up after hours of abuse or they ran really bad gas or av gas thinking they were doing it a favor. I have pulled apart engines from running junk yards donors with 110,000k miles and the insides look brand new except for some burned oil here or there. The weak spot with the 2.2s seem to be the exhaust valves. Pitting, some metal transfer from the valve seat to the valve ! Once in a while an oil pump will let go, or act funny enough to get replaced. These engines are a lot better than they get credit for. While most blow head gaskets after years of cooling system abuse, they can and do run for years happily at 5500 rpm. usually 5200 with stock cams, 54-5500 with high po regrinds. Except for vw & corvair engines, subaru is the most popular auto conversion out there.




Nope, hardly news to me. I've been to the Eggenfeller site many times. www.eggenfellneraircraft.com Here's a direct quote from their site regarding typical operational RPM. Take it for whatever your life is worth::eek:

"QUESTION: Are there any placarded "non-operation" RPM zones? You mention that you typically run 3800-4200 RPM for continuous operation--and for takeoff and emergencies, you can run 5300 RPM for short times. If I choose to run the higher RPM for "longer" times, do I jeopardize engine reliability (i.e., does reliability drop off quickly) or does it just shorten the TBO?"

"ANSWER: No placarded zones. Reliability and TBO is reduced by drawing more than 75% continuously in any engine."

"QUESTION: If my car ran at 5600 RPM I would be concerned. The Subaru is essentially an auto engine even after it has been converted for aircraft use. Should I be concerned about this?"

"ANSWER: We don't operate @ 5600 RPM but high RPM is an excellent way to get power from a well balanced engine with a short stroke for a SHORT DURATION such as for takeoff and initial climb. In the GlaStar, we get plenty of power @ 5300 RPM. This RPM is used for takeoff, and climb is @ 4800-5000 RPM. "

"The Subaru is no ordinary car engine. There is a main bearing every 2 inches and this, together with a balanced flywheel and lightweight pistons, provides for an easy turning engine. It is not a coincidence that we only work with Subaru engines. Drive a Subaru and wind it to 8,000 RPM, it will be smooth as silk and you will understand that 3800-4200 for continuous use is not a problem."

#11 automan1223

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Posted 27 January 2004 - 11:00 AM

Gyros are draggy rotorcraft, and they take A LOT more power to keep going than any fixed wing aircraft. I have been a gyro enthuiast since 1998. Believe me when I say good old boys just yank em from the junk yard and swap some parts and go flying. I am an ASE Master certified tech since 1990. Some of the stuff I have seen some do gave me chills. I am not going to argue with someone elses data, or facts, you do what you want to. but I can tell you what I know from 1st hand experience not some writing on a wall.......

and that is if you dont run them too lean, or to agressive a timing curve, they run like timex watch. Now you can overheat them on a summer day with a poor cooling system or too small a radiator but as long as your egt stay below 12-1300 deg I dont care what you turn. He might have them set up for max power at 4500, I dont know I can only tell you what the gyro crowd runs them at. I am curious what failures he has had.

I guess nobody has messed with cam timing.

#12 blitz

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Posted 27 January 2004 - 02:05 PM

Originally posted by automan1223
Gyros are draggy rotorcraft, and they take A LOT more power to keep going than any fixed wing aircraft. I have been a gyro enthuiast since 1998. Believe me when I say good old boys just yank em from the junk yard and swap some parts and go flying. I am an ASE Master certified tech since 1990. Some of the stuff I have seen some do gave me chills. I am not going to argue with someone elses data, or facts, you do what you want to. but I can tell you what I know from 1st hand experience not some writing on a wall.......


Relax dude. no one wants to see you fall out of the sky. :D Being conservative at 10,000 feet is generally not considered to be some form of character weakness. :cool:

and that is if you dont run them too lean, or to agressive a timing curve, they run like timex watch. Now you can overheat them on a summer day with a poor cooling system or too small a radiator but as long as your egt stay below 12-1300 deg I dont care what you turn. He might have them set up for max power at 4500, I dont know I can only tell you what the gyro crowd runs them at. I am curious what failures he has had.



The quote was for a stock 2.5 which is pretty much what Eggenfeller has been using as of late. Other than a hand-built intake manifold, they don't soup 'em up. They offer a supercharger option, but it's setup to compensate for altitude rather than increase HP over stock by boosting over Bar.

I guess nobody has messed with cam timing.



Most of the companies that make adjustable cam gears for Hondas and Toyotas, etc. don't cater to Subaru. This is the only source I've been able to find to date: www.speedstash.com/camgears.html#subaru, but there's nothing there for a 2.2 tho.

#13 automan1223

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Posted 27 January 2004 - 02:35 PM

I can understand why, the crank and cam sprockets have points for the pickups for the sensors and moving them might negate any improvement unless you compensate. For now I am stuck with 4 degrees max before or after. To mfg such a part is more involved than the hondas or toyotas.




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