Cylinder Head Compression?

[Deleted User]
[Deleted User]
edited June 2011 in HUDSON
I have a 7.25 to 1 head that I found for the 41 212cu splasher 6. The one that is on there now is 6.50 to 1. When I checked the clearance on the block to the cylinder head I didn't hear any noises, pistons hitting, so I think it will work. I wanted to know if there may be any problems running with this? Can anyone tell me how much more I may get out of the old girl with this cylinder head? Thanks

Comments

  • Park_W
    Park_W Senior Contributor
    edited June 2011
    See later post 6-13-2011.
  • Marconi
    Marconi Senior Contributor
    I would check the part number on that head before I did anything with it. All the 212s listed in the Motors Manual show 6.00 or 6'50 comp. ratios, the only engine that shows a higher one is the 175 engine at 7.00 or 7.25 to 1. With that head on a 212 the comp ratio would go to the moon considering the stroke difference between the two engines, 7/8"! The part number is usually cast into the top surface of the head but it kinda looks like a stamping,it will be 6 digits and usually starts with 15xxxx. Hey Walt, if I'm off base here feel free to jump in here and correct me on this!
  • terraplane8
    terraplane8 Senior Contributor
    I bumped up the compression on my '36 Terraplane to around 7.3:1 with excellent results, the relevant threads are here:

    http://www.classiccar.com/index.php?option=com_kunena&func=view&catid=13&id=69962&Itemid=152

    http://www.classiccar.com/index.php?option=com_kunena&func=view&catid=13&id=114333&Itemid=152
  • [Deleted User]
    [Deleted User]
    I agree with you, but today's owners know more than we do. That is why they have engine problems. They try to get more out of it than what it was built for. Torque a 212 more than 45 ft lbs and a stud will pull right out of the block. Hudson gave up on high comp heads, blew head gaskets. OH. Well, to each his own. Walt.
  • Marconi
    Marconi Senior Contributor
    If you want a little more oomph out of your 212, I'd take the original cyl head and have it milled .030 or .040, that'll give you a little extra power and won't blow the crankshaft out the bottom of the block! Also you won't have to worry about how you can torque the head studs any tighter, remember, they're only 3/8" studs!
  • Park_W
    Park_W Senior Contributor
    edited June 2011
    Sorry ... my initial response was based on a faulty recollection that the 7.25 ratio was offered in the 212 engine as well as the 175. Not so.

    Marconi said the CR would be "to the moon" if you put this head on a 212. Well, if my "figgering" is right, it wouldn't be quite to the moon but it might as well be. It comes out to about 8.8:1. Hardly practical under any circumstances.
  • Marconi
    Marconi Senior Contributor
    7.25 to 1 would be fine. The only head that is listed in Motors 1947 manual that is 7 or 7.25 to 1 is for the 175 engine. That head on a 212 would put the comp. ratio up somewhere near the moon! A 7.25 to 1 head for a 212 should be fine though, I was just cautioing him to check and make sure he had a 212 head and not one for a 175 cid engine. Just check the part number and be sure.
  • [Deleted User]
    [Deleted User]
    We have way better head gaskets now. I have had zero problems running the high comp heads. I am sure that back in the day it may have been a problem with the older style gasket.

    And the Hudson engineers tested every head combo you could think of. I have the complete engineering docs from Hudson and they tested high comp heads for failure, performance etc. They sure did know what they were doing.
  • Park_W
    Park_W Senior Contributor
    Marconi wrote:
    With that head on a 212 the comp ratio would go to the moon !

    Well, not quite to the moon, but if I figured right it would be about 8.8:1 on a 212 engine. Definitely not advisable for a number of reasons. [My original response was based on a faulty recollection that the 7.25 ratio was offered on the 212 as well as the 175 engine. It wasn't. Mea culpa!]
  • Park_W
    Park_W Senior Contributor
    edited June 2011
    51hornetA wrote:
    They sure did know what they were doing.

    They definitely did. See my revised entry on Page 1.
  • terraplane8
    terraplane8 Senior Contributor
    51hornetA wrote:
    We have way better head gaskets now. I have had zero problems running the high comp heads. I am sure that back in the day it may have been a problem with the older style gasket.

    And the Hudson engineers tested every head combo you could think of. I have the complete engineering docs from Hudson and they tested high comp heads for failure, performance etc. They sure did know what they were doing.

    I'd be interested in seeing this info. specifically w.r.t. the 212" engine, and the potential head gasket & stud problems that Walt alludes to. Is there anything you have on this? Hudson did say in one of their blurbs pre-war that when better fuel became available that their engines could handle 9:1 or even higher compression. They were trying to say that their engines could foot it with more modern engines designed for the better fuel. I assume they would not be lying. I think that referred to the Eight.

    I guess O-ringing the block would be an option too if there is room between the relevant studs and the bore. The Railton Light Sports Tourer had 7.75:1 compression and won many races, hillclimbs and time trials in England pre-war. I haven't heard that they had head gasket or stud problems. Ivan Zaremba who races his Railton LST Replica would be one to ask also.
  • [Deleted User]
    [Deleted User]
    When I hear 6 more HP it sounds exciting but not a the risk of being stuck later down the road. I'm about to do a valve job and put new rings in the 212 6 cylinder. I found what I thought were some rare finds. The cylinder head being one of them. Currently I have a aluminum intake manifold that I came across so I ported and polished it along with the exhaust manifold. I removed the exhaust manifold butterfly to get better flow. I am trying to get a little extra to make it up some of the hills. My compression was super low in all cylinders so I know after this valve job and new set of rings I might just have to hold on anyways without putting on the cylinder head. But if it will work, why not? Of course that's why I come to the forum to get all of your great feedback.
  • Park_W
    Park_W Senior Contributor
    edited June 2011

    Based on my experience drag racing ages ago with a splasher eight, the most productive thing you can do to increase power is install a dual exhaust manifold. Even though Hudson enlarged the manifolds in '37, it appears the exhaust was still somewhat restrictive.
  • [Deleted User]
    [Deleted User]
    With that 175 head you will be changing the center main often. That is the weak point in the 212 engine, as it's the last thing to receive oil from the splash system. Ivan has the 8 in his Railton with a pressure oil system he designed and rods and mains get oil on the first turn. Walt.
  • [Deleted User]
    [Deleted User]
    As much as I like the idea of running the higher compression head it sounds like a lot of extra work is necessary to keep the old girl on the road. I'll stick with 6.50 to 1 head. Thanks Walt.
  • ivanz62
    ivanz62 Expert Adviser
    Well I run 8.2:1 with an Edmunds aftermarket head on my big port Hudson 8. It runs fine on premium pump fuel. Must be careful to not have too much spark advance at low RPM to avoid "pinging" if you have a heavy foot.
  • ivanz62
    ivanz62 Expert Adviser
    And I want to agree with Park--the best thing you could do is anything to improve the exhaust flow.
  • terraplane8
    terraplane8 Senior Contributor
    In 1949 Hudson said that the Eights were good for 9.3:1 compression with 100 octane fuel and up to 12.5:1 with suitable fuel. Methanol perhaps?

    The attached file refers.
  • terraplane8
    terraplane8 Senior Contributor
    In 1949 Hudson said that the Eight was good for 9.3:1 compression on 100 octane fuel.

    This is from the 1949 Sales Fact Sheet Hudson vs. Oldsmobile Engines.
  • Park_W
    Park_W Senior Contributor
    terraplane8 wrote:
    In 1949 Hudson said that the Eight was good for 9.3:1 compression on 100 octane fuel.

    Would be interesting to know if they were looking at just feasibility of that compression ratio at the top end ... detonation resistance, etc., or the larger picture including ability of the lower end to handle the added stress.

    Some experimentation on the dyno by some experts in the fifties showed that you reach a point of diminishing return at, I think it was, around 9:1 or a little lower. As you reduce the size of the combustion chamber in the head, you generally "lower the roof" there, so the transfer passage from valves to cylinder bore gets squeezed down, restricting the breathing capability. Going further than the optimum point produces more compression, but the ability to get fuel-air mixture into the cylinder is compromised even more.
  • terraplane8
    terraplane8 Senior Contributor
    Good point. You would think that the combustion chamber would have to be filled in on the opposite side from the valves to stop that airflow restriction if you were shooting for 9.3:1 or something that high.

    Ivan has 8.2:1, no doubt he would have made it higher if there was benefit in doing so! Although the Edmonds head he's using is probably not ideal either - I wonder what happened to the aluminium head that Ivan and Pat were working on a few years back? I remember a few pictures were posted on here and it looked good.
  • ivanz62
    ivanz62 Expert Adviser
    Once again, Park and I agree, I think. The transfer window from the valves to the bore is the limit with normally aspirated engines. I do not have experience with the 8 cylinder at higher compression ratio than 8.2. My past experience with the 308 6 cylinder seems to show around 8.7:1 as a limit with 92 octane. Definitely 9.2:1 was too much for that fuel.

    Back to the 8 cyl--the compression is limited by machining to give 1/8" clearance in the chamber above the fully open valve which is then blended into the roof of the chamber to increase that transfer area. This a trade off of compression for breathing that has worked for me.

    The cylinder heads that Pat McDonald and I have worked out together have never been used here although I think there are some running in England. Mine are in the collection of parts to one day build a full pressure oiled Hudson 8. The combustion chamber design and spark plug placement copied from Clifford's 6 cylinder head. The head also takes water out a multiple ports over all the exhaust valves rather than at the front through a single thermostat housing requiring the fabrication of a tapered tube water log running along the top of the cylinder head to the top of the radiator. Same as Hudson did on their 1930's Indy 8 cylinders.
    Photo attached is the early engine with the side of the block cut off and the ports reversed.
  • [Deleted User]
    [Deleted User]
    After a little more research I've found that the cylinder head is from a 3" x 4-1/8" engine bore. This is from a Hudson parts manual for 1940-1942. I thought that if you guys had more information it might change the result for me to run this cylinder head 7.25 to 1 ratio. Then again, maybe not. :unsure:
  • Park_W
    Park_W Senior Contributor
    We knew it was for the 4 1/8 stroke 175 cu. in. engine for some time. See Marconi's post on the 13th.
  • [Deleted User]
    [Deleted User]
    With all the feedback I was confused if this was a good idea or not. Of course I wanted to run this cylinder head but not at the risk of doing serious damage. Especially when I don't know what shape the bottom end is in. I wasn't aware that the 4 1/8 stroke was the 175 cu. in. engine. I'm learning a lot about thank you. This is a great forum!
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