Wow Scott, I thought that stuff was sold. How close would your 4 cylinder head come to fitting one of these? It's just metal. Starting with a raw casting……...
I think i'm all in with both feet now. I think the main issue with my 4 cylinder head is going to be the bore spacing between the middle pair of cylinders. I also have the intake you sent me for this engine on my first project list to make patterns for when my mill arrives, so a specific application head wouldn't be out of the question or to far out either if its wanted.
I have a '25 Olds head here. I guess they were the hot set up in the day. I have had a Morton & Brett OHV head for the Dodge here, but it's gone. Lately a younger more energetic guy has been using my tools to work on adapting an aluminum Chrysler 340-360 head to the Dodge. He has posted many pictures here on the HAMB.
Scott, if you need an Olds 3 Port or a spare '28 or earlier head to look at, let me know- you're only a couple hours away!
That's good news Scott. My son that was looking into your foundry setup just bought a mill and we are thinking of moving mine down the hill to a friends shop. Neither are CNC though. If you can make it on small runs I think there are parts needed.
Mac, that is what i'm seeing that is a desirable upgrade for these engines. I don't think that its necessary to re-invent the wheel on a lot of projects, since the Olds head is a known upgrade, why not use that as a starting point and improve from there if needed. Maybe collectively we can create a better mousetrap and provide goodies that are otherwise unobtainable. I'll definately hit you up Mac, thanks.
I'll be using mine mostly to create patterns for the backlog of projects i've been waiting to complete. Then I can begin casting them.
When thinking of using 270 GMC pistons in the Chevy 4 you have to remember that the 270 had two different piston styles. The early 270s had a dome chamber and the later one had a D shaped chamber. The early piston might work better here depending on the pin height. Here is a Venolia from a set I have. https://picasaweb.google.com/sixpics/GMCRod?authuser=0&authkey=Gv1sRgCPTToLGl4_z_eQ&feat=directlink
This is from an Email I received. I also note in another thread speculation about swapping a Willys/Jeep crankshaft into another 4 banger (Chev 4?). The Willys/Jeep crankshaft has the 3 main bearings spaced approx 8.375" between them. Years back I checked the potential for swapping this crank into crank into the early Chev, Ford and Overland 4 but it is too short, unfortunately.
Rich, thanks for the answer on the Willys crank! CNC-Dude, will see if there is a day over Thanksgiving break that I can get up to you for a visit
Well, I don't know that I would call it a lot of experience, but here is what I remember. The pistons that I started with were the later style (just because we had a set of takeouts from a rebuild of my sons duce and a half. Stock, they are for a 3.781 bore. As I recall, I had to enlarge the pin hole, because I was using Ford A rods, with a 1'' pin. Next, because the hump in the piston was on the side where the spark plug was, considering the expansion slot in the piston skirt, I had to heli-arc the slot to change the thrust side of the piston--then turn the piston to 3 3/4'' (removing .030'') to suit the block that they were going in. Next, with clay, I found that I had to cut valve reliefs in the ramp going up to the ''dome''. Cam had more lift and duration than stock. The idea behind all this was for the top of the dome to act as a squish area, opposite the plug, but it (the piston dome) didn't come close enough to the head to be very effective at this. Ended up with a compression around 8 1/2 to one. Combustion chamber ended up with a poor shape, with a large area away from the spark plug, between the piston hump and the cylinder wall. Worked, but only slightly better than a flat topped piston, and then only better IMO because of the slightly higher compression. Certainly not worth all the trouble. compared to one of the pistons that I made from a billet top and tube skirt, welded together. Herb
I don't have pin height on these but the distance from the top ring to top of piston is much more than the later flattop and a better shape that the lump one. These don't have a split skirt. That and the little knob on top makes me wonder if they are finished. They are new Venolia never installed. Unfortunately they are .030" over making them 3.81125". I can measure them if anyone cares. Where would these be with Durant rods? In the bottom of the pan.?
I got the Durant rods out today and did some measuring. These are not exact some were done holding the part and caliper in one hand and the camera in the other. I also made a rough measurement on the 270 Venolia's pin height 2.5". The rod center to center is 8". So this combo total length is 10.7". What is the deck height of the '28 Chevy? More pictures: https://picasaweb.google.com/sixpic...authkey=Gv1sRgCKWp84rS6J3y1AE&feat=directlink
I think I noted these figures from posts earlier in this thread. Chevy rod centre to centre distance is 7.375" and the piston compression height is 1.9375". If these figures are correct, stock total length is 9.3125" quite a bit less than the Durant/270 piston combo.
If the above numbers are correct wouldn't that put the stock piston 1.1875" down the hole? Some of this is discussed on pages 4 & 39 of this thread.
Even when ignoring the gasket thickness that would give a compression ratio of 4.37:1 when using a swept volume of 42.72 cu. inch and a "combustion chamber" i.e. 1.1875" height of cylinder @ 12.68 cu. inch volume. Isn't the published compression ratio 4.75:1 on the '28 motor?
The bore above the piston travel is larger than where the rings travel by about .050''--but this would work to lower the ratio, unless taken into account--which was probably not the case- in the above calculations. The manufactures were not above lying back then---or even now. Herb
She must be! That is cool. Herb, The cylinder is larger above the rings? How far can we push the rings up before we get into that. Well if we take it out to 3.75? that will get fixed. You believe the cylinder walls a 1/4" thick? What is the thinest that you think would hold up on a naturally aspirated driver? Is there a way to check for core shift before you cut through a wall? I did a chart of rod-piston combos from data here but I can't get it to post. I'll try again later.
If you go past 3.75", you won't just be worrying about thin walls, you will run out of any wall space between cylinders 1/2 and 3/4! It's an unfortunate flaw by the designers- we just need to find the right balance of crank/rod/piston for getting the most out that bore
Maybe to recap, can someone post the stock bore and stroke of this engine for me. I feel like i'm late to the party, but have been drawn into this discussion and am very interested. Thanks!
Six ball-- I was guesstamating on the .050 over. I will measure both the distance the overbore goes down and the actual overbore size later this PM. I have heard of the blocks being bored to 3.875'' and Ford A pistons being used, but don't know if the bore centers of #2 and #3 were shifted to keep the deck distance from being any less than stock. Of course, this also cuts down on the wall thickness at the front of #2, and the rear of #3. I determined the 1/4'' by sectioning a blown-up block--it may well have been the thickest one they ever made, so YMMV/ The only way that I know the wall thickness before boring would use ultrasonics, which they determine the thickness of boilers--a rather expensive process. Herb
My Howard head GMC, which was 4.125 X 4 had pistons .300 down at TDC. Maybe tomorrow I will measure my Chevy with the model A rods.
Thanks for the info Rich. From my experience in overbores, most all mildly prepped race engines can safely have bores as thin as .125" thickness as long as the bore doesn't have a lot of core shift. But, it can always be bored out and have thick Darton style flanged sleeves installed to get a beefier cylinder wall. Even with the compression as low as it is, if you were able to bump it up to 8 or 9:1, it would still not have any questionable head gasket sealing issues at that level with 4 sleeves.
Wow, That's down there. Thanks Rich. It lets you know that we'll have to carefully measure our engines before we start ordering parts. Using the numbers in the thread if I use the 270 GMC Venolias I have with a Stock Chevy rod it would be .425" below the deck. With a Model A rod it would be .30". The pistons are .030" over so the bore would have to be 3.81125" unless I could turn the pistons down some.
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