Does anybody know what the rocker arm ratio happens to be on a stovebolt engine, and is it the same for both the intake and exhaust valves? I'm getting another brainstorm- - - - - -how about fabricating a fixture to accept individual rocker arm studs to replace the rocker shafts for a 216/235/261 engine, and using roller rockers for a big block V8 with a 1.7:1 ratio? By the time I'm done with building my Rube Goldberg engine, about the only original parts are going to be the block, cylinder head, and sheet metal! Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
Just measure the distance from the center to the pushrod and the distance from the center of the other side. Divide the longer distance by the shorter distance. Boom: rocker arm ratio. Next up for the Rube Goldberg Stovebolt: Roller cam bearings.
OK- - - -I was about to do the "measure the offset" procedure, but drawing on the collective wisdom of the forum usually gets an answer quicker, and more accurately. The 1.5:1 small block rocker arms sound like a better choice. I'm thinking of installing a piece of flat steel in place of the rocker shaft with screw-in studs aligned with each valve stem, then using a roller bearing rocker at each stud to move the valve. The studs for the exhaust rockers will probably have to be installed at a different angle than the intakes to keep the geometry right. The end result should be a valve train with a lot less friction loss than the old shaft system and lighter weight components- - - - -especially if aluminum roller rockers are used. Hardened steel custom-length pushrods from Comp Cams, and pushrod guide plates should keep everything aligned properly. If I use hollow pushrods and modern design lifters, it will probably also make it possible to eliminate the antiquated rocker oiling system the stovebolt engine uses. Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
The stock 235 rocker arm ratio is nominally 1.5:1, same for both intake and exhaust. The 216 is nominally the same, although I calc 1.48:1 from some old published data on cam and valve lift.
I have an old, NOS set of Fenton high lift intake rockers I picked up, years ago. Never tried to install, since the set I have is the Powerglide-specific PN. They had a different set for standard transmission cars, and presumably the difference was for hydraulic vs solid lifters. Image is from the instruction sheet. I don't see the spec on the instructions, but the Fenton box says the rockers increase the valve lift by 0.065". That calculates to just over 1.7:1 rocker ratio, depending on what cam info I use.
So, your seems like you brainstorm is on the right track, especially if you can improve exhaust breathing. Interesting the old Fenton parts don't include improvement on the exhaust side...
Edit: I see while I was typing, the factory data at 1.477:1 was published. Thanks!
Has anybody ever tried running roller lifters on a flat-tappet cam? I'm just full of oddball ideas this morning, and I'm only drinking coffee!
"I know the voices in my head aren't real- - - - -but boy, do they come up with some good ideas!"
LOL! Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
I just ordered one stamped steel big block V8 rocker arm to use for comparison measurements with a stovebolt rocker. If it looks like the geometry is close to right, I might proceed with doing a mockup mounting bracket for screw-in studs on one cylinder of a junk head I have on hand. If the measurements look good, I'll scavenge up some used big block roller rockers from one of my hotrodder friends. Assuming I can get the right pushrod length, mounting position, and angle of the studs, and an acceptable vertical angle of the pushrods, then I'll proceed to make a fixture to hold all 12 rocker studs and pushrods. With a stud mounting plate about 1/2" or 5/8" thick and an inch or more wide, pushrod guide slots could be incorporated into the same part. The mad scientist sitting on my shoulder is whispering stuff in my ear with a vaguely Teutonic-sounding accent! "Yessss- - - - -ve can rrrrreallllyyyy make thisssss vorrrrkkkk!" Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
Wellll- - - - -this one's going to take a lot of R&D before it's a go. Eventually, I plan to fabricate a valve system involving roller lifters, custom made hollow pushrods that oil the valves, stud-mounted roller rocker arms, and an increased rocker arm ratio. The big block rockers have a higher ratio than the stovebolt shaft-mounted ones, but the distance from the center pivot point is also much shorter. That will mean the pushrods will be angled toward the middle of the engine as they exit the lifters instead of pointing straight up. That's not uncommon- - - -the 1st. generation MOPAR hemi V8's had a similar pushrod angle, but it is a bit of an unusual arrangement. I'm going to get a prototype big-inch 216 going with a conventional valve arrangement, and keep tinkering with a modified valve system as "Phase 2" of the project. Stay tuned! Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
My pushrods are going to end up about 9.5 degrees. The pushrod people told me that was no problem. I don't know what angle you are talking about or what the limit is. Mike Kirby (Sissle) made a cantilever set up for extreme angles with an intermediate lifter.
The fulcrum (the stud in the BBC) must be where it places the pallet end on the valve stem tip. If the rocker's overall length is too short, its pushrod socket will be too far away from the pushrod relief hole. The stock BBC rocker arms are 1.65" (stud to pallet) and .97" (stud to pushrod) for 1.7:1 ratio. Length of both arms is 2.62". The stovebolt rocker looks like 3.41".
Yes, those figures agree with the measurements I've made. The next step is to mock up a single cylinder valve train on a head and block I've got on the stand to see if the angle of the pushrods created by moving the rocker pivots inboard to get the proper sweep of the rocker tip across the top of the valve stem can be accomplished without interference with anything. The different angle of the intake and exhaust valve stems on the stovebolt head is going to be an important consideration. The modification would be a lot simpler on a GMC head. Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
