Flathead Block Relieving for High Performance Flow - How To

Dale, what do you think of "partial releiving", same as Mark Kirby MCF did?

Br
Kjell

.............................
taildragger&fenderless

 

There have been quite a few different relief styles on Harley flatheads. The KR cylinders that I've seen (in my hands or owned) along with the ones that I've seen pictures of used a full relief as a rule. I haven't seen much of a 'stepped' relief in the KR examples - although it sometimes appears as they have them due to how the intake and exhaust seats are done.

I wish I had a flowbench, engine dyno and time to test a bunch of combinations. The only challenge is that the results would probably vary by a considerable amount based on the engine design (say Ford versus Cadillac), where the exhausts were routed (stock in a Ford or 'quick way'), type of cam, whether it is naturally aspirated or blown and the application ( 1/4 mile or Bonneville).

My personal belief is that a full relief is probably the best for higher RPM use and corresponding horsepower (where flow is worth more than compression) in the flathead's case. This may not be the case in a street engine (would also be my guess). For a 1/4 mile engine - probably depends on the car, setup, gearing, etc..

 

I wish I had a dyno, flowbench, about 5 blocks and endless time . . . would probably be able to bring more 'facts' to the table

My gut feel is that a partial relief is probably a pretty good idea for a street motor that has smaller cubes (say 276 and below) and that needs compression for stop n' go usage. A smaller motor needs a smaller combustion chamber to achieve the same compression ratio as a very large stroker flathead with a bigger chamber (like a 304).

For a full-race drag setup, I still believe that a full-relief that enables a straight flow from the valve to cylinder is best. Air doesn't like to bend, so taking the 'Up and Over' bend out of the intake or exhaust flow sure seems to make sense to me.

There are a ton of variables . . . head/chamber design, piston design, cam, intake, exhaust, porting and port flow/volume, weight of the car, gearing, etc.. I'm sure there is a fine balance to be struck between compression and flow (especially on the street). This seems to be less true for full-out race engines -- flow seems to be the winner for higher RPM usage (at least from what many people say).

The only real way to know for a given engine/car combination is to try the partial relief, then the full-relief on the same engine. The only bad news is that once you "go full", you can't go back

 

Thank's for sharing your thoughts Dale
I have done the "partial relieving" on the 276 cid in the modell A.
And same as you, i did not have a Dyno nore a flowbench, so i had to lean on what i had read in the books!?
And it both sound great and pulls fearly good

Br
Kjell

...............................
Taildragger&fenderless

 

thank you thank you for your time
SMRacing

 

Did Ford ever do a factory relieving on ther flat heads

 

There are some Ford blocks that are factory relieved, I've read.

Thanks for the tech, Bored&Stroked; you've inspired me to put up an ad for a junk block to try my first relieving attempt! Thanks again!

 

Yes - it was in certain 59 series blocks (42 - 48), about 1/8" deep and a straight cut that was about 2.5" wide (going from memory here). The typical story was that these were truck blocks and that Ford did it to reduce the tendency to crack in the area between the valves and the bore. Who the heck knows the real story - as there are as many flathead myths as truths out there.

Some say these blocks were special - with designations like '59Z' or '59L', but I have not been able to validate that either (even though I have both of the above blocks).

I have one out in my shop - maybe I'll take a picture this weekend and post it . . . just so you all can see "Henry's Relief"

 

Great stuff, B&S! Deck relief is some of my least favorite work to do on a flathead, or was until I was given a V8-60 block to do for a kickass Kurtis midget that leads a very active vintage-racing life. Up to that point I'd done only blended decks on the few V8-60s I'd worked on, but this customer wanted the new block done just like the one it would replace.

My mentor, Ed Binggeli, gave me an asymmetrical relief pattern he'd gotten from Bobby Meeks in the wayback. I used this to make a Lucite template that seated firmly in the cylinder, permitting me to scribe a consistent profile.

Before this, I'd been carving reliefs by hand,as you do, but the tiny V8-60 intimidated me -- that and it was a very spendy block going into a very spendy car! My shop partner, Kent Fuller had earlier suggested that I use a router to cut reliefs on the French blocks I'd been doing to tidy up their ubiquitous milled relief, but I'm inclined to struggle along rather than adopt a 'revolutionary' technique. The V8-60 looked like a good opportunity to streamline my work.

I bought an inexpensive trim router from Harbor Freight, added a larger Lucite platen to span an entire cylinder, and shaped a 1/2-inch ruby porting stone for the relief contour, first cupping the center of the stone to keep it from wanting to 'walk' on the surface.

It was quick and painless, producing consistent reliefs that looked like they were cut on a mill. The finish work with cartridge rolls was a breeze.

Here's the V8-60, monster ports and old-timey relief.




This 1/2-inch ruby porting stone is cupped and shaped for a French flathead V8. The stone for the V8-60 was similar.




The clear Lucite add-on platen permits the router to be moved smoothly over the work area and lets me see what I'm doing.




The compression drop from the finessing of the milled reliefs in this French block is miniscule. Plus, it adds 'sizzle to the steak' in the customer's mind as well as your own.




When finessing the relief in a French block, I set the depth of the stone in the router so it just kisses the face of the milled relief, using the stamped machined depth reference number as a 'witness' mark.



Mike

 

I had a 59Z that was fact. relieved, and one that wasn't; 3 59L blocks that were, one that was not. The 'L' was always thought to be the 'Canadian block', the 'Z' said to be the truck.
My green book doesn't make the case either way.

 

great photos thanks!

 

I still don't have a flathead, I guess it is just a matter of time with all this HAMB influence . A very great post thanks for sharing, I'll let you know the results when the time comes.

 

Mark believes leaving that ramp, or lip, causes turbulent flow, and aids combustion. I believe he has some documentation to back it up.

Of course, you've got to remember, everyone that believes in relieving has documentation, and everyone against relieving has documentation. It is a very hotly contested topic.

One thing to keep in mind, when reading documentation, is the intended application- just because it worked, or didn't work on one application, doesn't mean it won't work on a different one.

We don't need to worry about losing a little compression, we just need as smooth/clear air path as possible. The porting and relief job Dale did should help us immensely!

 

Application plus how the particular combination of components in the system work together. Dynos can be good indicators but drivability and time slips give the final answers.

Ed

 

This is perfect! Thanks Mike!

I finished port work on my block, think Im into it 50hrs, give or a take a couple hours.
Next is relieving... I'd try this myself but time is not on my side.. Im going to farm the initial relief cuts to my machinist and clean it up at home.

Excellent thread Dale.

 

Glad you've tackled it! It is one of those things that makes you nervous to start, really sucks in the middle and makes you happy at the end. Post some pictures when you have a chance.

On the relieving, if you can do the hard work in a mill - that is how I'd do it, then just the rounded blends by hand. I don't have a big mill - sure wish I had one at times . . . like a CNC one!

 

Really nice job plan9.!

Like your tools to
I think i will make a glass/plastic adapter for my jigg the next time i go with partial relieving.

Br
Kjell

.............................
Taildragger&fenderless

 

Thanks for your reply

 

I really feel for you flathead guys, so much time and effort(and $$) for so little HP gain. I love Pontiac V8's and I can relate.. LOL-- just had to throw in some smart ass comment-- sorry :>) PS: I once spent 80+ hours on a set of Poncho heads and was unable to see any real difference in engine performance once back on the street, but I was proud of myself for getting it done.

 

Hmmm, Maybe we both should have just went with SBC's, huh?

 

Well at least with a GMC 6 you start out with OHV's.

 

Close enough for me- I can't wait!

 

Great info in this post!

Thanks to the very experienced contributors.

Mart.

 

I did a 48 merc block in high school auto shop in 1962 & got my coveralls wound up in a half inch drill motor. By the time everyone quit laughing enough to unplug it I had almost denutted myself. True story unfortunately

 

Imagine what that experience would have been like if you were hanging onto a 25K-rpm die grinder with a carbide burr in the collett!

 

Excellent tech post. I have a question about this operation that is bugging me. You scribe a depth line in the cylinder bore but how do you get the proper depth by hand around the valve area and between the valve and cylinder? Take some off and then depth mic it? I think there's a bridgeport at work big enough for my block so I might be able to do mine that way and finish it by hand. Just wondering though.

Thanks for the info.
Scott

 

will do the same

 

I have been doing them in a Bridgeport for years.

 

I'm into the big Lincoln 337 flatties. Getting a complete one that has two cracks between bore and valve that'll have to be fixed. But this'll be part of the rebuild now.
Can you mill heads to recover lost compression?