Dear inliners, my name is Torsten and i live in germany. some years ago,i started building me an oldscool streetrod and swept a 235 chevy from 1957 in my 1931 chev roadster. now the engine is warn and i have to rebuidt it. so far. I have read alot about souping that chev but my english is not so good. My main question is how to port the head? here are lot of threads but i dont find any pictures how a good port is looking.I plan to handgrind it with some reamers and grinders. Can you please send me some pictures of sucsessfull heads. And how big can i bore the side intakes? Is 40mm diameter too big? I plan to customgrind the cam also. in the moment noone has cams in stock, so i need specs for my mashineshop. the car should still be rideable on road. Would be nice when you would help me.
Your English is as good as most people who were born here. There ar not many pictures on our forums here. It is too difficult to post new ones and most of the old ones have disappeared.
Fred Clymer & California Bill Fisher both wrote book on Souping up Chevy sixes. If you can find those they will help.
Here is a link to a thread on the HAMB website. There are a lot more pictures there. This thread has a lot of good information for you. I'd like to see pictures of your Chevy roadster. HAMB LINK
"I wonder if God created man because he was disappointed in the monkey?" Mark Twain
Thanks, I know the books and the link already, I thougt i found some more informations. In the books and also on hamb the portinginformations and the specs for cams are not sattisfying. Ore i am to stupid or want to much.
Personally I think that the porting ideas from the now 70 year old speed manuals have not stood the test of time and engineering knowledge.
The intake side of these heads is limited by the valve opening - not the port. So what is to be gained by increasing the size of the port? The answer is nothing. And in fact we give up velocity through the port when we "hog out" like the Fisher speed manual suggests.
On my 216 build I focused on removing the ridges from the floor of the port and smoothing the back wall: Frankly if I had to do again - I would raise the floor to the level of these ridges. Not sure what a suitable fill material would be.
Moreover, the biggest gains from porting on these heads comes from focusing on the exhaust port - with particular attention to matching the port size with the gasket - followed by a thorough smoothing.
Good advise, that is why a new Speed Manual for these & the GMC is needed. A lot has been learned since '54 and a lot of new parts are available. There were no small block valves or springs when that book was written.
"I wonder if God created man because he was disappointed in the monkey?" Mark Twain
W/r/t "The intake side of these heads is limited by the valve opening - not the port" I disagree. The ratio of the intake valve area to the cylinder displacement is comparable to many high performance V8 engines. Using the std. 1.875" valve in the 235: Valve area in square inches 2.76" Cylinder vs. valve area = 7.0% For comparison, a 350 with the std. 2.02" intake valve: Valve area in square inches 3.20" Cylinder vs. valve area = 7.3%
In my opinion, the port is overworked, and not nearly large enough since the common pair of cylinders causes constant pressure changes, reducing the efficiency and making the port “feel” smaller. This is why the siamese intake ports of the later Gen-3 engine of similar displacement are wider ovals with far more cross-sectional area. According to author A. G. Bell (https://tinyurl.com/yb7uahxr), a siamese intake port’s area should be slightly larger than its intake valve area. Using the common 1.875” valve, the port should be approximately 1.900” ID (3% larger area than the valve), which is 91% larger than the existing 1.375" intake port. Of course, this is impossible due to the casting’s limited wall thickness. My conclusion: the port cannot be made too large.
Its times like these that I really really wish I owned or had access to a flow bench. Being a hot rodder at heart, I have always increased the intake and exhaust valves and hogged out the bowels under the valves just a bit to accommodate the larger valves. I do this out of habit these days because I have been doing it for 45 years. I have also hogged out the intake port, and have not hogged out the intake port. It would be really interesting to know what mods do what, if anything, and at what flow and potential rpm. Man would that be interesting.
A bench test of a siamese port is less representative of actual running conditions than that of a single port. Not only does pressure cycle due to what the twin is doing, but the interval between paired ports is different for all 3 pairs.
Agreed but in terms of flow, and the horrendous short side radius, and near flat back wall, it would still be interesting to see what effect the changes actually make to potential air flow.
Kirby experimented with lumps in the Stovebolt head. The gains were similar to what is experienced in the later Chevy 194-292 siamese heads. I'd start there.....
The intake ports aren't very similar. The 250 is much larger in area, and benefits from higher velocity, while the 235 is already too small, both in absolute terms and in proportion to its intake valve. The 235 shape probably will improve with an insert to re-direct the short side flow, but how much effect without reducing CFM? How to attach an insert without a bolt?
The most comprehensive cylinder head research on a siamese port engine that I've read is Vizard's work on the B.M.C. Mini. Unfortunately, it's an L4 with very different port sharing and time elements than an L6. I've been looking for work on a siamese L6 (Ford Zephyr, etc.) with no results.
Panic, the bolt-in lumps do use a bolt in the latter 194-292 head. Since Kirby/Sissell is renowned for brazed lumps, I'm sure there were formed in the port by that method and then shaped manually by hand/grinder.
Brazed lumps, even epoxy lumps for a 235 is pretty exotic for us backyard hackers. Like I said, I would love to have a flow bench and see what effect certain things have on air flow through the valve. For example, in 1950 when GM introduced the powerglide to the Chevy line, they apparently had concerns about parasitic loss and thus used a 1 15/16 inch intake valve to increase air flow. This continued until 1952. I think it would be interesting to know what effect just installing that valve has, and then how much hogging out of the valve bowl is needed, if any, to maximize the use of the larger valve. In other words, what is needed, and where is the point of diminishing returns.
Same for the intake ports. I always thought the intake port itself was theoretically large enough to support a pretty good amount of flow, at a good velocity, for lower rpms (say 1500 to 5000 rpm). I would love to know what effect on velocity enlarging that port a bit would have on velocity and air flow through the valve. Maybe negligible maybe not, might be a balancing act between the two.
Same on the exhaust side. You can get nice one piece stainless 1.6 exhaust valves, with nice cut down stems and swirl polished under heads that will fit. It would be very interesting to see what the larger valve will do all by itself, and then what has to be done in terms of relieving the exhaust chamber pocket to make use of the larger valve.
I know we can discuss this and offer opinions and thoughts on theory, but actual numbers would be the most fun. But again, without owning a flow bench, having to farm out my curiosity to a third party might get pretty expensive pretty fast.
I've noticed that many cams for the 235, including some OEM, feature longer exhaust duration. The bias ranges from a few degrees to 12 or so longer. In general, intake ports are sensitive to increased lift, either by lobe height or rocker arm ratio, but exhaust ports are more sensitive to the crank position where the exhaust valve cracks open (in degrees BBDC). This is partially due to much higher pressure at the exhaust valve (up to 70 psi), which quickly vents the cylinder once the valve opens, while the intake port pressure may not rise above 3.5 psi even with a tuned exhaust system.
I thought I had been involved in several discussions with members that are no longer here on the forum. I found one discussion that was started in Sept. 2008 regarding a joint 848 head porting and flow bench project with one member that was in Canada. I did some port work and flow bench testing to both the Stovebolt head and a GMC head for comparison. Results were posted but so far I can't find them because you can only search back 10 years, and those discussion predate that time.
I thought I had been involved in several discussions with members that are no longer here on the forum. I found one discussion that was started in Sept. 2008 regarding a joint 848 head porting and flow bench project with one member that was in Canada. I did some port work and flow bench testing to both the Stovebolt head and a GMC head for comparison. Results were posted but so far I can't find them because you can only search back 10 years, and those discussion predate that time.
The hard part here for me was the "Newer Than" setting. I could get rid of the 1 but in the drop down box where the default is"weeks" above it is "days" and above that is " ". I did not know there was a blank to choose. That opened up the "past". Narrowing the search or divine the "older than" further back gets you to the beginning of our time.
Also if it is a thread that you have been part of, like CNC said above, you can go to your profile page and search your old posts. You can do that in someone else's posts if you know they were in a post you remember or you know they discuss certain things or are interested in certain engines.
"I wonder if God created man because he was disappointed in the monkey?" Mark Twain
That is a good option Beater. One thing I did discover that was disappointing from looking back through some old discussions is how many of those people involved in them are no longer on the forum. Nexxussian, Sixinarow, CurtB and many, many others have found other interests maybe, or passed away even....
There are a lot of options for them. Many have moved on to sites that are more specific to their interests and some to sites easier to use and better maintained. Keeping this website up to date is a big job as you well know.
"I wonder if God created man because he was disappointed in the monkey?" Mark Twain
W/r/t "The intake side of these heads is limited by the valve opening - not the port" I disagree.
My conclusion: the port cannot be made too large.
But doesn’t this depend on a lot of other variables?
The basics suggest that at low lifts <.15” or <.20” (depending on the author) – the “flow through area” between the valve and the seat is the limiting factor – not the port. And this article suggests that port flow efficiencies don’t begin to kick in until valve lift exceeds 20% of valve diameter: https://www.motortrend.com/how-to/sucp-0902-chevy-engine-port-variations-measuring/ With a 1.875” in intake valve that’s (.20x1.875) or.375 lift. The stock camshaft lifts in the neighborhood of just .30x” on the intake. The corvette cams a bit higher but not much.
And then there is the basics for intake runner volumes – which suggests that for low RPM torque - runner size should be focused on velocity not volume: https://www.racingheadservice.com/head-runner-volume Stovebolts are the epitome of low RPM torque by design.
And then there are the more complicated questions that abound when looking at the design:
Where does the intake runner end and intake port begin? How does the volume of the opposing valve pocket play into a port volume calculation? Does the center runner/port (with even 360/360 intake pulses) somehow demand different treatment then the outer runner/ports (with uneven 240/480 intake pulse events)?
In addition, the diagrams from the Bill Fisher book appear to be notional as opposed to a blue print. The 216 based diagram suggests that the port is going to be hogged out beyond the diameter of the alignment rings (1.40625) but the text describes a straight plunge with 1.375 shell reamer - leaving some room for the alignment ring intact. Interestingly – this takes the 216 runner up to the 235 spec.
But I think it is counterproductive to maintaining velocity and ramming effect.
That’s why I restrained my attention to the floor of the runner where it branches into the port blending it down into the valve pocket (yellow) – but it still sharp turn.
I've noticed that many cams for the 235, including some OEM, feature longer exhaust duration. The bias ranges from a few degrees to 12 or so longer. In general, intake ports are sensitive to increased lift, either by lobe height or rocker arm ratio, but exhaust ports are more sensitive to the crank position where the exhaust valve cracks open (in degrees BBDC). This is partially due to much higher pressure at the exhaust valve (up to 70 psi), which quickly vents the cylinder once the valve opens, while the intake port pressure may not rise above 3.5 psi even with a tuned exhaust system.
The stock cam in the 216 is dual pattern grind. I am running a regrind based on an ancient Isky specification (DP#2) Inliners Post circa '04 Isky advertised it as a 250/280 affair. Stock spec is 220/231. I asked the guys at Delta to regrind a cam to the Isky DP#2 spec. The cam doctor report for the stick indicates: 248/264 @ .020 205/233 @ .050 Theoretical Lift is .41/.40 with stock 1.5:1 rockers. Add lash & rocker retreat - it's more like .39x.
The idea is to promote exhaust scavenging. In the stovebolts the combustion chamber is unswept. Holding the exhaust valve open allows exhaust gas velocity to empty the chamber.
Moreover, it's counter productive (for compression ratio) to open the intake too early or keep it open to long - hence the dual pattern.
(updated the '04 forums posting with links to the new home for photos - Isky description is there.) Should also say stick shift only.
Cam doctor says 107.4 lobe separation with 40 degrees of overlap at .020 and 3.4 degrees at .050.
The .020" split is 16 degrees, the .050" is 28. Never seen that before, the .050" is always shorter. The 235 chamber is flushed by the slightly recessed deck relief leading away from the intake seat. Opening the intake early affects compression?
Incomplete response. Holding it open affects CR. Opening it early results in reversion/dilution of intake charge (not to mention negative impacts on vacuum).
Jack Clifford sold dual pattern cams for years. The scuttlebutt then was that Erson ground his cams. With all of the corporate changes, my guess is that Erson, to the extent it still exists, does not have those patterns any longer. Would be fun to know if they do still have them.
As to the theoretical discussion, I stick to my guns that we can discuss till the cows come home but that real numbers on a real flow bench would be the very best and most fun. Frankly, we would even be able to sort out what effect that tiny little outward bump in the exhaust chamber has on flow, and at what lift that effect occurs, and the best way to minimize it, among other interesting information re port size, hogging the intake runner at the alignment ring lands, thinning of the guide, how much relieving is best to make use of a larger exhaust valve, all kinds of stuff.
When Erson ground the cam for my son's Studebaker they did it using specs we had gotten from John Erb. They were pretty much operating from the back door of the Mallory Ignition building in Carson City, NV. When Mallory left Erson moved to Mound House, NV between Carson & Dayton. Near the end of their time there Steve Tanzy was in charge. Steve sat down with me to design a cam for my 153 four cylinder. He worked up 3 grinds based on my roadster build. He gave me a tour of the shop. The interesting part to me was that their machines were converted crank grinding machines that were run by a real machinist. The lobes were ground individually with the machine following a bolt on lobe pattern which could be changed lobe to lobe. So any profile could be in any place on any cam. When Erson moved back east those machines & patterns did not go with them. It would be interesting to know if they still exist and where they are. A huge stash of roller rocker parts & material ended up in another shop in speed equipment shop in Carson City. I don't know if Steve is still around or not.
I agree about how interesting it would be to be able to test your head work on a flow bench. Nothing is a perfect test for performance except the timing lights but flow tests can help.
"I wonder if God created man because he was disappointed in the monkey?" Mark Twain
John Erb was one of the good people at KB-Silvolite until his retirement, and wrote much of the tech literature on that site. We exchanged some e-mails, he was very knowledgeable and helpful especially about nitrous. Also a Studebaker fan IIRC!
You are so right. One of the smartest men I've ever known! When my son was in high school we were building his '54 Stude Conestoga. He bough a McCulloch supercharger and looking for a rebuilder lead us to John. (one of his sidelines) After an hour or so visiting John offered him a part time job. Jake worked for John for summers through college. John is the reason Jake is a mechanical engineer now. John & Sandy were good to him. We will miss him.
"I wonder if God created man because he was disappointed in the monkey?" Mark Twain
