It seems to me that would be actually just reducing the duration. If it comes to that I'll just get another cam. I'm trying to get this dialed in before adding the Man A Fre manifold.
I have an Engle roller in the hemi in my dirt modified. It didn't have any paperwork, so I called Engle. I had about the same experience "Roothawg" did. They essentially told me that anything between .015 and .035 would work, and that very experienced tuners run them tighter or looser depending on the situation. Not being an experience tuner, I set mine at .016 intake and .018 exhaust and the engine has always run good and strong.
I read something somewhere, they claimed .016" is a good place to start with an unknown cam. It's just on the high side of "tight lash" cams and a little on the low side of more typical factory lash. Iron block/Iron heads anyway. Then maybe play around with it a little checking vacuum. There is a procedure maybe to determine optimum lash for a cam using a degree wheel? That stuff is like voodoo to me.
After all these years and many moves before returning to my childhood home 50 years ago. I doubt still having it, but many years ago, I had a hrm special publication that had a pic of Chet working on his bonneville car, a GMC powered '41 Hollywood Graham, seated in a wheelchair out on the salt flats. First dirt racer I built in '67i used a solid flat tappet cam from Chet, IIRC, it cost $39.95
I’ll update my results so far. I set the cold lash at.018” I and .024 E and with the engine fully warmed up, I had a “whisper “ in the right side exhaust pipe. After setting overnight, I reset the lash to .017 I & .025 E. I think I can go a little tighter on the intake. Exhaust is good. Sent from my iPhone using H.A.M.B.
The usual way to find the clearance settings of an unknown cam is to degree it at 2 degree intervals and then plot the numbers to a graph. You can see instantly what the proper setting is. Most early Herbert cams (50's) had quite close valve settings, like .008 and .010.
there are guys running roller cams that suggest very tight lash and bigger springs on the street. lash as tight as .004-.005 hot. this is to prevent damage to the cam. the rollers can pound the cam lobes to the point of damaging them. for racing the lash is returned to normal specs. i personally dont do this. i do have a hot and cold setting i use. my block and heads are aluminum and the grow as the engine pics up temp. it grows about .008
I always used the valve lash to see what the engine wanted, if the specs called for .016 & .018 I'd get enough passes at the factory spec to know how fast the car would run then I'd tighten the intake lash a couple thou, if the car ran faster then I'd know the cam wasn't big enough. You do the intake tighter then larger; the exhaust tighter then larger; then do both and give your numbers to the cam grinder and he'll know what to do.
I've always read with Iron heads and Iron block, to add .002" to the cold lash. The manual for my slick sez .019" cold and .018" hot. I never bothered before to set them hot, though made sure they were set accurately cold and checked up on them once in while. A while back I checked & adj one bank hot like the book says. Seems to me the intakes were all spot on, but 2 or 3 of the EX valves had grown about .001" or .002". About a week or so later I checked the other bank hot, same thing. Everything set .019" cold was spot on at .018" hot, except 2 or 3 mostly EX valves were .020" maybe. I'm not persuaded one or two thousandths matters anyway. I'd like to think it idles smoother for my trouble. Setting the lash hot is kind of a pita.
I used to tune up" hot rod" cars for a used car dealer. I would warm up the engine. With it idling I would tighten the valve lash, without a feeler gauge, until all valves were quiet. Then with engine still idling I would back off an intake adjustment until it would just barely tick. I would then check that setting I would do the same on an exhaust until it too would barely tick. I would then set all valves to those two settings. I never heard of any problems from using this somewhat crude method Greg
a good thing to do on a engine with stiff springs is to run the lash twice when first setting up the engine. having all the push rods in on one side only will flex the cam giving a false reading. putting them all in loose then running the lash works better.
My experience with this engine is that the exhaust valves grow about .004” when hot and the intakes about .001”. I have installed lash caps when the engine was built. I don’t think that is a factor. Sent from my iPhone using H.A.M.B.
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