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one of the resons I am useing the roller , but you can change the rocker arms from the last year lima , its a diffrent ratio but brings in a tad of lift and a few more degres of duration and I am going to pull in a much advance as I can for lowi end torque , the max RPM will never see over 2700 , it will be swinging a 74 inch wooden propellor , yep it going on a airplane ,

I've heard a lot of differing aspects regarding the rocker ratio change. I SOOOooo wanted to take one of each rocker and test them side by side. Virtually ever article I've read is all "talk" and I can't recall anyone giving proof.

 The only thing that changes is the position of the roller as it relates to the ratio. It would have to move closer to the lifter to improve the ratio. BUT, - and this is assuming the stock roller sits directly centered under the high point of the cam (we will call it 6 O'Clock) at full lift, then the greater lift rocker would be inclined towards 5 O'Clock at its full lift. It then becomes a factor of does the greater ratio give equal or greater compensating lift..., or does the high lift occurring at an angle (5 O'Clock)  therefore only be equal or less? I  did a drawing (limited skills) to illustrate the point.

BTW, why a Lima engine in a plane? It is one of the heavier 4 cylinder engines.

The cam and rocker set up I got from a write up on Routh 66 hot rod high , has a listing for what year cam and rockers , and what changed when you swap parts , Got both of them and also going to check to see if the industral 2.5 cam is any diffrent , ( got one of those also ) as for why the lima engine in a airplane is because they are very reliable and there is one airplane that will work with it , only is was built back in 1928 with the ford model A engine , yep only forty HP on a good day but it worked , not fast but it did work well , many engines were put in that aircraft but I wanted to keep it all ford , (model A engines are getting hard to find ) but I will be useing the 2.5 with the duel plug head so I will have a secondary ign like real aircraft , the ford industral book list the LRG425 at 65 HP @ 2700 rpm so power is enough and the weight of the engine is about the same as the model A engine , just need the low end grunt to swing the prop , as for how lnog it will last , it will out live me , I work at the airport and most of the tugs here have that engine in them , I look on the hour metter (HOBBS) they have over 6 to 7K on them , they overhaul the piston engines in aircraft at 2K some go more but not often ,


--- Quote from: pinto_one on July 07, 2020, 08:13:02 AM ---The cam and rocker set up I got from a write up on Routh 66 hot rod high

--- End quote ---

Not that site again....

The 2.3 cam and rocker information on that site is entirely wrong and at this point I would argue entirely responsible for the roller follower "ratio upgrade" myth refusing to die. There is no difference in ratio between early and late roller followers.

What ! I thought everything on the internet was true  :o  , but good thing I did not go out and buy thinking they would work , have to double check that mith myself , but still do not know if the industral cam is any better , the head casting is diffrent also , it was made as a duel plug head but the extra hole for the spark plugs are not machined out at all , and has the small valves and valve seats , this one had a propane carb on it , thanks for the info , guess typos always waste time and money when they look to be legit , at least I can run the engine on a test fixture with the prop and swap out the cams to give me max rpm static and find out which one is the best ,


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