When someone ports & relieves a flathead.........what is the relieve part? How is it done. I've never been inside a flathead (but I have a lawnmower engine!!!) 6sally6
The relief is where the deck area between the valves and the piston is ground down a certain amount,,,usually about .060 to .100 thousandths. It lets the pistons have a little better direct shot to pull the fuel charge in and get the exhaust pushed out. I am new to this,,,but have seen them for some time. I will probably do some to mine as well. Tommy
Conventional wisdom says that relieving a block is counter productive on all but large cubic inch racing engines. It cuts compression you will need.
Who wrote it in a book? Was it Tardell? I can't recall, but "someone" put out a how to on it, and as I recall was a trade off between compression and flow. I also think I recall in the book it was best done (as said before) for stroked/large CU engines. Anyone recall the book I'm speaking of? It was way more in depth than "how to rebuild your flathead V8".?
This may or may not be a reliable source, but the author indicates that the power loss from the minor compression loss is more than offset by the increased flow efficiency. Myself, I really can’t say. https://www.google.ca/url?sa=t&rct=...thead-myths/&usg=AOvVaw2bsLmuyd31T9pad8pVqYCV
My C69 block has the factory relief. It was a truck engine used for an industrial purpose. I can't see them relieving the block if it resulted in less power if used on trucks.
big trucks typically had less compression so they wouldn't detonate (ping) with heavy loads going up hills ... double benefit from the relieving for them as they want lower compression anyhow
Thinner metal, weak area, less heat sink, more temperature variations, all this increases the possibilities for cracking the valve seats in a street engine. A street engine sees more severe duty than a race engine.
With a 4" Merc crank, that's at 276 ci, which is getting up there where relieving can be beneficial. With a longer stroke, even more so. It would be interesting to see comparative dyno runs between relieved and non-relieved engines running everything else the same. BTW, the "weighs half what it used to" is a bit of hyperbole, now, isn't it?
It seems simple to me, even though I have 5 flatheads, I haven’t driven one in forty years. But the relieving helps at high rpm and hurts at low rpm, due to lower compression. It’s a trade off, less power down low....more power up high. Since a street engine sees a whole lot more low rpm, I would forgo all but a very little relieving on a street engine. Just my .02 Bones
It still weighs a ton! It is merc cranked and 471 supercharged, Navarro blower heads. Relieving the block was never an option, just obediently and attentively followed the commandments handed down in the good book...
Mike Bishop's porting and relieving guide is on the net and should be the bible for any flathead guy.
My 296 ci motor was extensively ported (intake and exhaust) and the block is a factory relieved 59L block. Some unshrouding around the valves to take advantage of the all the porting.
It also was believed to help reduced the heat caused by detonation which caused the intake seats to crack into the bores.
Our experience has been you would not be able to feel any negative difference from relieving a block if its a small street engine the reason being the additional breathing gained by the relief will add more set of the pants acceleration. Typically why we put Hot Rodded engines in our cars in the first place. As for the thoughts the removed material will add to the possibility of cracking that also is not true. The area located below the valves is extremely thick some blocks I have measured more than 1/2 inch thick this amount of iron will easily crack due to the cold/hot fast changing cylinder temps taking place. The only way to stop this problem is by flooding the block with coolant to keep the location from getting extremely hot. Most of the cracks we see are actually located on the intake valve seat area see lots more by the intake than by the exhaust. The colder incoming air charge from what I see is the main reason for the cracks removing the small amount of iron for the relief will never help eliminate a crack. My two cents worth of info. Ronnieroadster
Found this old Hot Rod Network article. Seems relieving offsets any reduction in CR. https://www.google.ca/amp/s/www.hotrod.com/articles/0905sr-ford-flathead-myths/amp/
In my opinion, adding a supercharger to the mix changes the rules. I am talking normally aspirated street engines.
Hey Thanks were already working on the next Flathead engine for Speedweek 2020 and hope to have another ARDUN running as well for a different class record if things go right. Only takes about 8 months to get the engine ready LOL
I'm with Ronnie - I tend to always put in relief work . . . sometimes more, sometimes less - depending on the engine block, the usage, etc.. If I'm starting with a factory relieved block - then it will always get a full relief and I make sure to create a much nicer relief than the factory. Every factory relieved block I've seen looks like they did the work with a crude grinder of some sort -- kind of the worst quality machining of the whole block. I have no reason as to why Ford did this so crudely . . . must have been a manufacturing after thought! On some street engines, sometimes I do more of a 'street relief' - kind of half way between a full and non-relieved . . . to keep compression up (especially on a smaller engine - say a 276). The discussions around "flow" are worth thinking about in that unless you have designed the engine to be able to REV in the upper RPM ranges, you'll probably see no benefit from relieving the block. I'm talking about flows and RPMs above 4000. If all you're doing is babying the engine and really don't rev it up much (or have an ignition that can handle it), then relieving is probably just for bragging rights.
Just to add some more fun to the discussion - Joe Abbin's book and horsepower claims. Personally, I don't tend to put a lot of merit in the technical analysis and HP/Torque numbers that Ron Ceridono quotes in this article (or that book in general). My opinions are formed by actual work, racing, dynos and other such madness - like my buddy Ron's are. Also, I take particular notice of the work Harley Davidson did on the KR race flatheads - the most advanced racing flathead ever built. Here is a little sentence (from that article) that you should ALL read carefully when you look at that article, the HP claims, etc: "In the Roadrunner Engineering study, published in the December 2002 and March 2003 issues of STREET RODDER article "Revival of the Fittest," the computer analysis was based on a 276 cubic inch Flathead with a "3/4 race" cam and typical intake and exhaust systems at sea level conditions. Actual flow test data and combustion chamber volumes for representative test head configurations were then used for input into Engine Analyzer Pro." You see the last 3 words 'Engine Analyzer Pro' - that is a SOFTWARE program . . . it is not an engine dyno. I have that software - it is a simple tool that can help one with decisions, but it just that - a tool. It can't possibly truly understand how a flathead works . . . versus a Hemi . . . versus an LS motor, etc.. The numbers it generates are based on simple extrapolations - not actual dyno results for our goofy flatheads. So when you see big ole' claimed horsepower numbers out of this "software dyno" - you should really be skeptical as to if your engine will even be close - at any RPM. Truthfully - your actual HP will usually be a lot less than what that program calculates . . .
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