Relieving 255 merc flathead

dennis

dennis

Member
Made a jig for my bridgeport to rough out .100 relief
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Its important to be aware of cutter rotation and feed direction so the cutter does not chip the edge of the cylinder
 
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Machined a depth gauge and marked each cylinder so the depth does not go below top ring.

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Leaving my options open . Will run NA initially .Lots of good and bad with relieving but I thought I would give it a try.
 
Because turbos are generally ugly and not particularly traditional. Where as even a small modern blower with some time spent on it looks right on a flatty.

The relief looks good! With some aluminum heads you should still have a nice reasonable compression ratio and good transfer.
 
dennis said:
Ive seen lots of flatheads with blowers but has anyone ever seen a turbo flathead .Ive only seen one or two on the net under construction . Wonder why this type application wouldnt be a more popular solution to making the flathead breath.
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Yes, the only real reason to run a flathead is to have a traditional motor. Turbos are not traditional for pre 60's engines. If you are building a motor merely for horsepower, you could make most any other choice other than a flathead.
That said, "Flatheads forever!!!"
 
Relieving will increase aie flow but also drops compression a fair bit. Not a good idea for normally aspirated flatheads. Usually only done with a blower.
 
Agreed early Frenzel or McCulloch blower very traditional but hard to find. Big Donaro I would presume
 
Relieving

flatcat said:
Relieving will increase aie flow but also drops compression a fair bit. Not a good idea for normally aspirated flatheads. Usually only done with a blower.
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I guess as long as you dont go to deep and loose all the squeeze it should be okay I would think. Seen this on the factory N/A 337 truck flattys as well as the little french Simcas flathead v8s.
 
There are literally hundreds of examples to prove transfer is more important than compression on a flathead. On a Ford a relief is the only way to make this happen due to the stupid way the valves are recessed into the deck.

Spend some time reading about Harley flathead race bikes. 7:1 compression and out running overhead valve machines.

A friend has been building flathead fords for decades and has ove 300,000 miles on his 51. Big chamber 53 heads. Isky cam, un shrouded valves and less that 8:1 compression due to a good relief and 4" crank. Gets over 20 mpg and runs freeway speeds without problems.
 
Torqstorm.Com,If the dollar wasnt so crappy id get one of these.Cool traditional look,V-belt driven but new.
 
The factory reliefs on the truck engines were done to reduce the tendency to crack the block from heating due to the thicker iron in that area. The milled relief is not the best way to increase flow, it takes out too much iron.
 
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