Would anyone be interested in a set of forged pistons (improved copy of the Jahns Dome top "Dog Turd" to fit an 848 head) and performance rods (stock length or longer length possibly to reduce weight of the pistons)? I have been working on a couple things and have two resources that I used when I did a lot of VW work over the years and have been entertaining the idea to do a couple sets for myself as no one really has anything on hand. Thoughts or interest?
IIRC Ross still offers HC pistons, CR not known. A pop-up piston must be made in 2 handed sets of 3, since the exhaust bump is on the other side for paired cylinders. I would guess that a piston would be the bigger seller. If the pin boss is made thick enough the same casting could be finished to either 235 or 261 pin size. I doubt a forging is needed for the conservative engine speeds. There is no available piston to use with the GMC rod, both for compression distance and pin size. There is a huge minimum to be sold before the costs are recovered. As said or light bulbs: the first one cost $100,000,000., after that they're $1. each
IMHO a new rod is going to fall outside the budget of most builders. More length requires a new piston, $$. The 261 rod is apparently safe for moderate performance use, the only defect being the pin size, which means custom pistons or only use in bores 3.75" and larger. All of the other existing rods that look useful have the wrong journal size, length, or width.
Pop up pistons in the stovebolt cylinder head do really bad things to the flame travel across that weird-shaped combustion chamber. It's a lot simpler to use a shorter rod with the same flat top piston and increase the stroke length to get more cylinder displacement and compression. The H-beam rod I'm using is rated for 900+ HP, and allows me to change the 235/261 stroke from 3 15/16" to 4 5/16". With a little bit of overbore, the 261 becomes a 300. With the same rod and stroke, a 235 goes to 270. A set of those rods costs less than $400.00. What is the point in inventing ridiculously expensive "solutions" to situations that can be addressed with simple machine work? 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!
Due to the recessed exhaust valve and generally flat chamber surface, the easiest way to significantly reduce chamber volume (more than a head or block mill) is to add material to the piston dome directly below the exhaust recess. IMHO the many different 18 bolt head castings may not have the exhaust pockets exactly matching as to location, shape, and depth. From the photos and drawings I've seen, the bump is an irregular rectangle, but some completely fill the recess (but not to full depth), some are taller, some have a "flame notch" to address HRL's excellent point of flame travel interference. What I don't know (don't laugh!): Are these bumps made larger than needed, and supposed to be hand-fitted to the actual chamber? A bump 1/2" tall (example only) will begin to enter the recess 37 degrees BTDC, where does the recess volume (mixture on the compression stroke, mixed gas on the exhaust stroke) exit? My guess: the exhaust valve will be partially open during the overlap period near TDC with any hot cam, especially with late exhaust closing. For highest CR change should the bump almost touch the valve?
Concept would be to maximize the bump without the need to require grinding on the dome after the fact using an 848 casting. I have a Faro arm and plan on scanning the block, head and gasket as well as other parts to put together a 3D model of the engine with three blocks and 4 848 heads that I can scan. Getting the piston closer to the deck surface will reduce chamber volume (adding a valve pocket will add, but allow for valve clearance for higher lift and longer duration cam profiles). Every 0.010" of piston to deck height = 0.17 point of compression (calculated with a 3.780" bore size) and every CC that can be eliminated in the chamber volume increased the compression by 0.08 point. Basically adding a 6 cc dome (spread out over the available space will increase the compression by 0.50 point. Eliminating 1 cubic inch (16.3871cc's) will raise the compression by 1.54 point. If I can the the dome to bump a stock block / stock head (unmachined) to 9.5:1, that would be my goal. Anything higher I can live without for this project.
Key is not interrupting spark path, quench (or improving it) and keeping weight down. I have a set of forged 235 pistons and had a set of Jahns. Understand that only a couple companies will do a semi custom cast piston (adding dome material for you to finish machine). The rest will sell forgings (JE, Wiseco, Ross, Arias, Diamond, etc) for you to machine (I don't have the equipment for this.
"There's no substitute for cubic inches"- - - - - -unless you're a train driver- - - -then you use "cubic dollars" to try to achieve the same result! How about adding 5 cubic inches to each cylinder without messing with the piston shape? 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!
Wayne did it about 75 years ago or more. There are still a few of them around. There's also a you tube video that's been posted here several times showing how ridiculous some people can get about modifying a stovebolt engine. Crossflow aluminum head, turbo, etc.
"You really can make a silk purse out of a sow's ear- - - -but it makes the pig look funny, and it doesn't hear very well!"
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!
How about just installing a dual overhead cam Toyota Supra engine? The engineering and dyno testing has already been done on that one. A 3.8 liter Jag would also work well if you prefer a period-correct "dumb" engine without a computer. I'm wasting my own time by adapting a DOHC PT Cruiser head to a Model A Ford block.
My stroker crankshafts for 235 and 261 engines have 1/2" machined off the counterweights for piston skirt clearance, which lightens them up a little. 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!
If it's just for yourself, a new stock Barra or Atlas engine will deliver the power of a 12 port at 20% of the cost. As a marketing strategy, the best return on investment is: don't spend another dime, it's a dead end.
My 261 runs a set of 302 GMC rods so I had to order forged pistons which I did from Venolia. Pretty good lump on the pistons. But the rub was that they were not inexpensive and they were only semi finished. You had to final grind them to fit. I actually do not have the skills to do that so had to farm it out so more expense. Pistons had a valve relief cut in the top. The thing is, the motor runs better with a bit more compression. To have access to some stock rod pistons for a 235 and 261 with near zero deck height and a lump to get the compression into the 9.75 - 10 range would be really great and supportable on today's pump gas.
IF HRL has a way to stroke these motors, and lighten the crankshaft, along with the higher compression pistons, jeez, you might really be able to build something that runs really well. What fun!
It's nothing but simple machining and an ability to use a micrometer and a calculator. Right now I'm in the process of installing a 235 rotating assembly into a 216 with all the modifications hidden so the engine looks like a bone-stock 216. The next couple of projects will be the "235" with 270 CID, and an "almost 300" 261. All of them will use original equipment type flat top pistons, and they'll have compression ratios of 9:1 or more.
The only reason to use a higher static compression ratio would be to compensate for a stupidly radical camshaft that doesn't close the intake valve until the piston is way up the compression stroke, requiring the remaining cylinder volume to be squeezed tightly enough to get back to the original compression pressure. Using popup pistons with a mild camshaft gets into cylinder pressures that limit the timing advance to a tiny amount to avoid preignition and detonation. One of my customers learned that the hard way when he insisted that I install 12:1 compression pistons in a Morgan +4 (Triumph TR-4 engine) without using a radical cam. Detonation melted the pistons. "There's no free lunch!" 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!
A very long (310 degree) intake duration has been used successfully with low static compression ratio (5.5:1), by advancing the intake lobe to 90 ICL. IO 65 BTDC, IX 65 ABDC. With its long rods, this point captures 76% of the full stroke length. This shifts the remaining duration into overlap, resulting in very bad manners, poor low speed torque, bad fuel mileage, weird jetting, etc. but a necessary compromise for maximum power in a race engine.
IMHO the same method could be used in a stovebolt to keep acceptable CCP with a big cam... if the huge overlap symptoms can be managed with skillfully selected and adjusted carburetion. This would be tough with any plenum manifold; 3 separate individual carbs would be my choice. This would have to be a new cam blank, AFAIK the lobe clocking is far beyond any regrind.
I have a Faro arm and plan on scanning the block, head and gasket as well as other parts to put together a 3D model of the engine with three blocks and 4 848 heads that I can scan.
I went down this rabbit hole about a dozen years ago so I'll share where it led me. I had the ways and means to investigate improvements to the head and set about to digitized and cut up several. I figured comparing McGurks mods to a stock head would be a good place to start. All my expertise is in metalcutting so I beat the bushes at the local race engine builders to locate a flow bench and someone who knew how to use it. This led me to a fellow machinist who did a great deal of port work and was interested in my project. Even an adapter plate to mount the head to the flow bench had it's challenges. I'll briefly summarize results:
1. He told me opening the ports from the side to the intersection was detrimental as it reduced velocity. 2. The exhaust ports are very restrictive and there's not much that can be done other than basic smoothing. 3. There's a bump in the combustion chamber wall that shrouds the exhaust valve...removing it helps a bit. 4. Reworking the short side turn (1/8" radius), bowl and guide shaping, bigger valves, blah, blah, blah, are all of limited benefit due to #5 5. Nothing would improve flow substantially due to the "T" shape of the port even when he tried clay wedges, bumps, etc. that would be impossible to mount in the port anyway. 6.In conclusion it was a dead end and we reached the same conclusion others have... throw the tractor head in the bush and start from scratch.
I will only be scanning the head to fit the Piston dome to an average size and shape, no head development. Any data on scan will be for modelings 12 port head (dimensions and constraints) in relation to the original design.
It's one head for a Ryan Falconer V-12 aircraft racing engine. They are used primarily for aircraft pylon racing but he will make you one for your car. The engines are custom built. V-12 part #1291. It's covered in the latest printing in Leo S. book on page 126. Ryan and his son Erik run the company and the are great guys and very helpful. His V-12 engine is based on 2 Chevy inline 6's so the bore spacing is the same. A complete head will run about $6k. It's nice that my blower will be on the passenger side so I can still see and the headers are on the driver side far away from my intake. This should help with charge temp. They do not bolt up.
I really don't understand the motivation for many of these projects. If the idea is to "think outside the box", someone already did that (many times). Re-inventing the wheel proves nothing. If the idea is to go fast, using a Chevy 235 or 393 L6 instantly doubles the budget and halves the return.
I really don't understand the motivation for many of these projects. If the idea is to "think outside the box", someone already did that (many times). Re-inventing the wheel proves nothing. If the idea is to go fast, using a Chevy 235 or 393 L6 instantly doubles the budget and halves the return.
If you want cheap power, get an LS. But people do that all the time.
I have certainly done projects in an unusual way just because I wanted to be different.
Only the first person is "different", everyone else is following what they saw. Or is there a particular modification that you never heard of used on this engine? 12 port head dates to 1950 (approx.). Example: I applied these features that (AFAIK) had never been done to a H-D "UL" big flathead engine 4.750" stroke crankshaft (1978), original is 4.28125" 8.750" shop-made connecting rods, original is 7.90625" intake nipples removed, 1-1/2" copper DWV tube extensions silver-soldered to port face intake manifold fabricated from DWV 2 IR Mikuni HS40 carburetors exhaust cams reground to Indian Chief profile 2nd gear row added to return pump to double scavenge capacity pressure oilers added to valve covers for spring cooling modified breather timing stroker plates for correct deck height include pressure oil to piston skirts
Isn't the guy who originated most of these ridiculous-looking modifications named R. Goldberg? Improving the performance of a stock-appearing engine without throwing truckloads of dollars at the project makes a little sense. The rest of it is just eye candy to feed an overactive ego. (At least in my humble opinion!) 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!
Improving the performance of a stock-appearing engine without throwing truckloads of dollars at the project makes a little sense.
Doesn't your stock-appearing 216, larger displacement engine project fall into that category, Jerry? Where are you keeping those truckloads of dollars?
Kevin 1951 Chevy 3100 work truck Follow this saga in Project Journal Photos 1929 Ford pickup restored from the ground up. | 1929 Ford Special Coupe (First car) Busting rust since the mid-60's If you're smart enough to take it apart, you darn well better be smart enough to put it back together.
I'm actually building it on a budget- - - - -other than applying 60+ years of experience at building "cheater" race engines. The custom crankshaft grinding is the most expensive part, since my own crank grinder isn't in running shape yet. Most of the other parts are straight off Ebay- - - -they're just for "non-stovebolt" engines. I'm making them fit in my own machine shop, and evaluating performance with my own dyno, instead of shoveling cubic dollars into the pocket of a builder of exotic race engines.
Once I'm done building and testing, I'll be happy to share the specifications and modifications with any other stovebolter, free of charge, if he wants to build one like it. At my current state of age and health, there's not much point in keeping any secrets or getting mercenary about it. I fully intend to stick around for another 25 years, unless the next man-made health crisis manages to kill me. It almost happened this time! 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 do things for myself that I could never do for a customer: too $$$. My first adventure, 1970: porting the interior of a cast iron Chrysler "B" engine (350, 361, 383, 400) factory dual quad manifold. Must have 10+ hours in it before I was satisfied, but you can't charge $500 for something that only shows .02 ET and 3 mph increase. If it had more cam it might have picked up bit, but that's what I had at the time.
