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04-11-2021, 08:55 AM | #1 |
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Highest Reliable Compression Ratio
I want to hear from those who are running 6:1 and 7:1 compression heads on Model "A" and Model "B" engines with babbitt bearings, and stock oiling systems.
Can 6:1 and 7:1 compression ratio heads be run reliably for cars that do a lot of touring? If any, what issues have you experienced?
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04-11-2021, 10:28 AM | #2 |
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Re: Highest Reliable Compression Ratio
I think two major points would be: How good is the bottom end now and how good are you at managing the spark advance lever. I prefer the original manual advance set up because you have total control of the spark setting in any situation. There is nothing wrong with quality babbitt if it is correctly poured, peened, and machined. That being said my present motor has inserts because I didn't have access to a suitable babbitt shop but I do know an excellent machinist. Not an uncommon situation today.
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04-11-2021, 04:01 PM | #3 | |
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Re: Highest Reliable Compression Ratio
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04-11-2021, 05:02 PM | #4 |
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Re: Highest Reliable Compression Ratio
I have Snyders 6.1 with new studs, babbitts, stock oiling. No issues other than less advance is needed.
I have done about 5k per year for the last 2 years and would never go back to a stock head. |
04-11-2021, 06:30 PM | #5 |
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Re: Highest Reliable Compression Ratio
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04-11-2021, 06:47 PM | #6 |
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Re: Highest Reliable Compression Ratio
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04-11-2021, 09:33 PM | #7 |
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Re: Highest Reliable Compression Ratio
For what it is worth, I ran a little over 10 to 1 on a babbit engine for about 7000 miles. The bearings were still like new when I sold it. There were 2 hill climb meets on it besides the usual street driving. It had a Dan Price head and a 404A radius lifter cam.
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04-12-2021, 07:07 AM | #8 | |
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Re: Highest Reliable Compression Ratio
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Ron |
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04-12-2021, 07:33 AM | #9 |
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Re: Highest Reliable Compression Ratio
I have run 8,000 miles on an engine with babbitt bearings, stock oil system, with a 7:1 Thomas fin head. No issues, no knocks, no oil drips.
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04-12-2021, 07:37 AM | #10 | |
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Re: Highest Reliable Compression Ratio
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What about those of us who are running 8:1 compression? Don't we get to comment?? When we stop to analyze why there would be a failure, lets begin by determining what would not cause the failure;
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So why do some people experience failures whereas others do not? IMO there are several key factors that when they are followed, the longevity will rival or exceed that of using an insert bearing. To begin with, the proper composition of bearing material must be used. Ford originally used a mixture of Tin, Copper, and Antimony, -with over 90% of that being Tin-based. With certainty, failures come when a Lead-based material is used instead. Lead was used by many rebuilders in the 50s - 70s because it was easier to obtain and much cheaper -however, its use also gave a bad rep. for Model-A cast bearings. Next, the casting process is one that must be done correctly, -and thoroughly. A huge key to success for longevity that is often omitted is the peining and burnishing process. Without these two steps, the material is not as dense which leads to faster wear. Additionally, the burnishing process makes the bearing harder and during the burnishing process it momentarily becomes fluid where it conforms to the shape of the journal pin. How this burnishing is beneficial is because the load-bearing surface of the bearing is now greater which leads to slower wear. The biggest reason why cast bearings fail is because the cast material gets hammered-out. When the clearances become excessive, it fails fast. For example, when you use a 5# hammer and hit a piece of solid copper wire, which will flatten it quicker? Lifting the hammer ¼" and striking the copper, -or lifting the hammer 1" and striking the copper. The same can be applied to loose bearings. The reason insert bearings seem to last longer is because the babbitt-like material is much thinner and has been placed onto the shell properly. When a block uses cast (babbitt) bearings installed correctly, they are equal in strength to the insert bearing, -and will actually give longer service life since there is a greater (thicker) amount of material. Ohh, ...and regarding the controlling the timing, I have found this should not to be a huge deterrent for having higher compression ratios. If someone is concerned, then buy a higher octane fuel at the gas pump when refueling. Then, there are many Model-A hobbyists that subscribe to the theory that if a little advance of the timing lever is good, then more advance must even be better. Most Model-A engines are operated with more advance in the ignition timing than what is optimum. Operate it at an advanced timing level just under the point where detonation is found, and the cast bearings will be happy. |
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04-12-2021, 07:41 AM | #11 |
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Re: Highest Reliable Compression Ratio
Original Winfield red head,7 to 1 compression on 'hard' babbit. Babbit does not fail from compression it fails from torsional vibration of a stock crankshaft and improper timing. Any increase in compression reduces the engine tolerance for improper timing, I prefer running a mechanical advance distributor for consistent proper timing at all speeds. To combat torsional vibration I use a murray horn harmonic balancer and have a mitchell OD to keep the rpm down.
Herm Kohnke felt the torsional vibration would push the center main journal .001 off center at 2400 rpm. Counterbalancing helps. Folks hear about racing upgrades like cross drilling the crankshaft and fully pressurizing the engine and invest big money into doing it,not necessary for a street car..Fords stock system works fine,the hydrodynamic principle (crankshaft floating on a film of oil) maintained by gravity in the A engine is capable of sustained high rpm (2400).. |
04-12-2021, 11:18 AM | #12 |
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Re: Highest Reliable Compression Ratio
Thanks to all of you who have shared your experiences. Brent & Pete, I admire your hi-compression experiences.
Is there a stock-looking 7:1 head available?
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04-12-2021, 11:31 AM | #13 |
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Re: Highest Reliable Compression Ratio
Bob,
There is another aspect to the equation, the shape of the combustion chamber will have a large effect in the resistance to detonation, not just the CR. Brett and Pete are spot on with their explanations. The Babbitt material and process of installation is key. FWIW, I do insert bearing installations in "B" motors and 4 out of 5 blocks will have inadequate lead based babbitt, just beat out. John
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04-12-2021, 11:34 AM | #14 |
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Re: Highest Reliable Compression Ratio
Tod Buttermore makes one.
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04-12-2021, 12:02 PM | #15 |
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Re: Highest Reliable Compression Ratio
My personal opinion is that crypto-HC heads (heads that are HC but look stock) are OK but one needs to be extra-careful to document them. You won't own the car forever, and whomever you pass it on to will need to remember that their car will behave differently than one with the stock head. A 5.5 head can probably pass without documentation, but certainly once you get to 7 you should either mark the head visibly or keep good records.
That's one reason I like the Winfield head – it keeps the stock shape, but it says Winfield on it and the spark plug locations are different, so anyone buying the car will be able to identify that it's a 6 or 7 head without taking the head off. Also I painted mine fire engine red, but that's just me. |
04-12-2021, 12:20 PM | #16 |
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Re: Highest Reliable Compression Ratio
There are some very good answers above! I ran a 7.5:1 Cyclone flathead for years with no problems. Included were several trips from SoCal to Las Vegas to visit Ed Winfield. The engine was a B/C, stock oiling, babbitt by an unknown guy but done at Trade Tech school in L.A., so of unknown quality. It is not compression, but detonation that will ruin babbitt. Something to think about, ... when 2 Model A's are traveling down the street together at the same speed, one totally stock, the other with high compression, dual carbs, etc., they are both using the same amount of power, so both have the same amount of pressure in the cylinders. At that point they are totally equal. Now if they both put the pedal to the metal, the non-stock A will put more pressure on the bearings and will pull away from the stocker. With oil as a cushion, the bearings will not be harmed.
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04-12-2021, 12:37 PM | #17 |
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Re: Highest Reliable Compression Ratio
Yes, ...before Tod, Larry Brumfield offered the Super Brumfield which was 7:1. I have two of them, and can send you photos of you like.
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04-12-2021, 02:01 PM | #18 |
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Re: Highest Reliable Compression Ratio
Hi Brent. Please post pictures of the Brumfield 7:1 head.
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04-12-2021, 03:46 PM | #19 |
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Re: Highest Reliable Compression Ratio
I am amazed with all the interest in high compression heads. How fast do you really have to go in a Model A? My Victoria has a touring cam and it idles lousy. With the fast steering and bias ply tires, my car is made for secondary roads doing less than 50 mph. One of the pleasures of the car is getting there eventually and enjoying a 1930s motoring experience safely. Ed
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04-12-2021, 04:37 PM | #20 | |
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Re: Highest Reliable Compression Ratio
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A typical 'touring camshaft' should never make an engine idle lousy. The Stipe camshafts typically have more lift (generally a minimum of 0.030" more) than a typical reground 'Touring Cam'. The new Stipe cams including the IB340 and under all idle very nicely, -so I am believing you have other issues that are causing your poor quality idling. |
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04-12-2021, 04:46 PM | #21 | |
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Re: Highest Reliable Compression Ratio
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If your "touring" cam idles lousy, it was either ground by the wrong guy or installed by the wrong guy. A quality "touring" cam will idle SMOOTH at 400 rpm. |
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04-12-2021, 04:56 PM | #22 |
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Re: Highest Reliable Compression Ratio
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04-12-2021, 06:02 PM | #23 |
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Re: Highest Reliable Compression Ratio
Maybe in Maine and alot of other spots in the country a stock model is adequate..here in suburban Northern CA A stocker running without convoy protection is at the mercy of the yahoos..
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04-12-2021, 06:53 PM | #24 |
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Re: Highest Reliable Compression Ratio
X3 here in Cali, lunatics...
But, it does go noticed when you pass a BMW on the freeway, or pull up next to him. J
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04-12-2021, 07:32 PM | #25 |
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Re: Highest Reliable Compression Ratio
Thank you for your comments. It peaks my interest to find out what kind of cam is in my car. Ed
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04-12-2021, 07:45 PM | #26 | |
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Re: Highest Reliable Compression Ratio
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I have the B engine out of my 2 door right now and have a 450 hp crate engine in it. It will do 155 and is just like a Sunday drive on the freeway. |
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04-12-2021, 10:23 PM | #27 | |
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Re: Highest Reliable Compression Ratio
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I don't know about where you are, a Sunday drive on the freeway down here is playing miss all the bumper cars and don't get run over... J
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04-13-2021, 09:28 AM | #28 |
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Re: Highest Reliable Compression Ratio
Ed In Maine, I am driving my Victoria to the 2021 New England Meet in Newry, Maine from Long Island, so I need to cruise along the interstates to get there. 50-55mph is a must do, and a hi-compression head improves the efficiency of the engine to do it. There are thousands of Model "A" drivers who drive to out-of-town functions, and they must be able to do it on main roads. Do you drive your Victoria anywhere of significant miles from home?
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04-13-2021, 11:15 AM | #29 |
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Re: Highest Reliable Compression Ratio
I agree with Brent, plus gas mileage goes up with higher compression. Compression and a bigger carb are the two quickest and easiest ways to more power, cam is next but not near as effective per dollar and time invested. The very latest B cam has more lift and slightly more duration than a normal B, and makes a great touring cam.
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04-13-2021, 02:56 PM | #30 | |
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Re: Highest Reliable Compression Ratio
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My point was that while a stock model A body has an extremely poor drag coefficent and lots of frontal area especially with fenders on, it will handle very good at speeds over 100. If your car wanders or shakes at 65, something is worn out or out of adjustment. |
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04-13-2021, 09:50 PM | #31 |
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Re: Highest Reliable Compression Ratio
[QUOTE=BRENT in 10-uh-C;2006434]
A typical 'touring camshaft' should never make an engine idle lousy. I agree. I have a "Touring cam in a B engine with a 6.0:1 head and it consistently idles very smooth at 350 RPM. If I go up into the mountains where the air is thinner, it will idle at 290 RPM. Chris W. |
04-14-2021, 07:47 AM | #32 |
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Re: Highest Reliable Compression Ratio
Its important to note making these changes on a stock model a engine raises the engines efficiency. Higher compression, adding fuel, using a mechanical advance distributor and making it breathe better results in better economy and a cooler running engine. That's something most model a guys don't get, they feel you are ruining the engine 'hotrodding' it. banging the bearings out of it, causing it to run hot and increasing wear..
Actually the opposite is true, raising efficiency extends engine life, upper cylinder issues decrease as well,rings seat better, less exhaust heat due to a better burn saves valves..Alot of the common issues with a stock engine disappear...exhaust manifold drooping, burned exhaust manifold gaskets,engine temperature issues...gone. |
04-15-2021, 12:00 PM | #33 |
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Re: Highest Reliable Compression Ratio
Camshaft choice I have a story to tell about that. Many years ago I got a phone call from a guy wanting to buy one of my cams. He had a (heavy) fordor, all stock but wanted more power. We talked for quite awhile and I thought I had convinced him to not change his cam, he was running a B cam at the time. Well ... a month or so later I get a call from a guy complaining about one of my cams having no power. It took me awhile to realize it was this same guy. He had gotten one of my cams from another source, I have no idea which grind it was. He had a test site that he uses, up a steep hill, in high gear, starting from 5 mph, said it was slower with my cam than before. When I finally realized it was this same guy, I said "didn't I recommend staying with your B cam". There was a long silence on the phone after that!
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04-15-2021, 12:55 PM | #34 |
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Re: Highest Reliable Compression Ratio
As early as 1933, stock V8s were shipping with poured bearings, mechanical advance, and a 6.3:1 compression ratio. If anything, the A was under-compressed for its time.
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04-15-2021, 01:04 PM | #35 |
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Re: Highest Reliable Compression Ratio
Look no further than the 'new and improved' 4 cylinder engine introduced in 1932..other than just a mild compression increase it incorporated all the upgrades Ford engineering noted as necessary from 28 to 31
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