Camshaft specs for LPG engine

[greenval]

The cam in my engine has a few lobes vanishing, the possible result of the last mechanic putting a solid cam in with hydraulic lifters. So im looking at a replacement hydraulic cam, and I am considering an LPG grind.

The engine is a Chrysler 360, with about 10.5:1 compression, Keith Black Pistons (therefore with notches in them), heavy duty valve springs with dampeners, standard rockers, gearbox has a little bit of extra stall in it, roughly 2200 I can estimate. It ran a 13.25 with that combo. I only want the cam to perform the same or better than the previous one.

Im unsure what kind of lift the last cam had, but figure if I stick to around .500 lift Id be safe.

Any advice in the area is appreciated.

 

[franzh]

Since the engine is obviously performance oriented, I assume streetability is not a concern. I would use any of the aftermarket grinds for gasoline in the range you wish, with a little more emphasis on lift rather than duration. Your choice of grinders, no plug-ola here.

Also, I have used hydraulic lifters on a solid grind many times with no problems, however, using solid lifters on a hydraulic grind will lead to problems as the cam profile does not have clearance ramps. I suspect other problems leading to lobe failure, such as, used lifters, switched lifters, valve float allowing lifters to bounce, used camshaft, and so on. The 360 engine is not particularly known for cam wear.

Franz

 

[greenval]

interesting...thanks...

 

[strokersix]

Franz, Will you please elaborate on the lack of clearance ramps causing trouble in a solid lifter/hydraulic grind combination?

Thanks.

 

[patprimmer]

As hydraulic lifters remain in constant contact with the lobe surface, even on the base circle, there is no need for a gentle take up of the slack, as their is no slack.

With a solid lifter, there is always some slack, that must be taken up gently, so if the cam has say a specified .020" tappet clearance, there might be .030 or .040" of the initial lift that has a much slower acceleration rate, to minimise impact damage. As hydraulic cams do not have this ramp, they damage solid lifters. A hydraulic lifter does not need this ramp, but it does no harm, other than loseing a tad of performance at lower speeds.

On the other hand, a solid lifter can tolerate a little bit of valve float, whereas a hydraulic lifter will take up the extra clearance created by the float and then hold the valve off the seat when on the base circle, so hydraulic cams are generally gentler over the nose so as to reduce the chance of float. Regards
pat

 

[franzh]

Pat:
Well done, beat me to the punch! Thats what I get for traveling a couple of days!

Franz

 

[bikejeremy]

hello
I have an old toyota pick-up that i run stricktly on LPG..I want to build a street motor for it and am looking for advice. I want fuel mileage primarily, but would also like it to be able to pull. The 20, 22 r series motor was available originally with a hemi- head, reverse tumble flow set up..Toyota later switched to closed chamber, swirl design..Which do yall think would be better, and what type of cam profile should I invest in.. What do you think would be the maximum compression ratio I can use??

all advice is MUCH appreciated

 

[patprimmer]

I would go for the head with the highest CR. If both heads give high CR, I would go for the biggest inlet port and valve size.

LPG can tolerate bigger ports tha petrol because the fuel is in gas form and does not "puddle out" in the manifold and ports. Also as the gas occupies more volume than liquid pertol, the VE of the engine drops off a little, and bigger inlet system helps compensate.

I expect that 11:1 is a safe upper limit if the fuel is butane, propane mix.

If it is pure propane, over 12:1 can be used, that is if you can get 12:1 without going to very expensive pistons Regards
pat

 

[evelrod]

I am surprised that no one is old enough to remember putting solid lifters on hydraulic grind cams. In the early 50's when hydraulics were just coming in the rev range topped out at 5000 or so and the guys like me were putting early Cad and Olds engines in Fords and trying to race them. Performance parts were very scarce so I switched tappetts to get a bit higher rev range. (it sounded ok, then) The combo made a LOT of racket but I don't recall any other problems. You just didn't put a lot of miles on a car in those days. The first performance grind for my 52 Olds (46 Ford Coupe) was a McGurk with 'high lift' rockers. What a change. The complete kit was $75 !!! Ahhhhhhh. The good old days. Phooooooy!
Everybody has to start somewhere. I look back and am continually amazed that I made it this far!

Rod

 

[bikejeremy]

Thanks for the reply...
The fuel I will use is alleged to be minimum 90% propane. The pistons are equally expensive in the 11:1 and 12:1 versions... For the closed chamber head, the 11:1 pistons are flat, and the 12:1 ones have a small dome in the middle that I hope would induce turbulance..
What do you think???
And as far as camshats???

Thanks much