Flathead Block Relieving for High Performance Flow - How To

Okay gang, many of you know that I'm a bit obsessed with flatheads (of all sorts) and racing. I sometimes take for granted all that I've learned and the many folks who have helped me learn . . . I'm forever in their debt.

What the Hell is a 'Relief' or Relieving Anyway - and Why Would You Do It?

There are as many beliefs and opinions on flathead relieving as there are bung-holes . . . no shortage of debate, myths, examples, etc.. So read this if you want one mans opinion, if you don't believe in 'relieving a flathead' block, then what are you doing here anyway

1) General Theory Behind Relieving: If you look at the valve locations on flathead engines (Ford, Cadillac, etc) - you'll see that the valves are canted toward the bore . . . the angles differ between manufacturers and even years of manufacturer. What the canting does is it requires a depressed "pocket" on the cylinder side of the valve . . . usually about 1/8" to 3/16" deep. The most important flow area of the valve (by the cylinder) is buried below the deck surface. This means that the intake charge has to go up/over the area between the valve and the cylinder and make two turns --> once to go up, then another time to turn back into the cylinder. This is bad for flow.

Henry Ford accounted for it by making a rounded trough in the head - to let the gas go up, over and around. Now - look at every high-compression head out there . . . do you see that trough? Nope . . . it is gone! So - while the high-compression head achieved some compression, it actually hurts the flow in the "transfer area" - which is the area between the valves and the cylinder.

This is what relieving is all about -- to ADD a new transfer area between the valve and the cylinder bore. Not only is it to give space for flow, it is also to enable the intake charge to take as straight as path as possible to the bore (no going up, over and around as is the stock designs).

2) Relief Types or Styles: There are quite a few different styles of reliefs - from what I'll call 'partial' to 'full', "stepped" (where there are different depths on the intake versus exhaust side), etc.. I'll show you a few examples before I detail what I did on the FlatCAD Bonneville engine:

a) Partial or Blended Relief:

This is typically done on a high-performance street flathead - where you want to improve the flow, but don't want to lose the compression or move the power band up too high. This is an example from my friend 'RustyBucket' (fellow FlatCAD member) - it is from his very cool 276 cube full-house street flatty. He did all the port/relief work himself . . . and still swears, cusses and bitches about it to this day (it is a dirty ass job!).





b) Stepped Relief:

This is where there are different relief depths between the intake and the exhaust. I've seen this most often on some of the flathead Harley street engines - it was NOT used on the KR race bikes to the best of my knowledge. The main reason for not doing a full relief was to preserve some compression . . . but in my mind, the amount is so minuscule, who cares. Here is an example I collected form someplace - seems to be a work in progress (at least I hope so ):



c) Full Relief:

This style is at a consistent depth from side to side. On flathead Fords, I've seen the typical depth vary between 1/8" to 3/16". The shape follows a gasket line. Here is an example that I did on my 59L Ford Flathead block - this block uses stock size valves, with a relief depth of .187:



3) Okay - Time to Get Dirty and See Some Details

Subject/Victim: FlatCAD 1942 Cadillac V8 - Bound for Bonneville in the 'Medusa' Car

The following describes how I do it (at least this week!) - and should give some good ideas to think about and follow. Again - every flathead guru has his own beliefs . . . these are mine.

Warning: You should ALWAYS plan to do a complete valve job after a relief operation! Also, if you happen to gouge a critical area (or go too deep), it is possible to ruin a good block or be in for a costly repair. With all these warnings said, I did my first relief when I was 15 - so don't be afraid, just be smart, plan well, learn to use your tools BEFORE you attack your block . . . or pay a professional!


a) Tools Needed:

Different people use different tools --> everything from a high-speed die grinder (me), to milling machines, to routers . . . to drill motors. I always use a high-speed air grinder . . . but I'm also pretty good at controlling it, obtaining a uniform depth, etc.. Use tools that you're comfortable with -- if you need to practice on something first, by all means do! Take a junk block and hack away -- get the process down, experiment a little - then tackle your pristine racing block . . . or not.


Bits: I use an assortment of high-speed solid carbide "double-cut" rotary flies for all my porting and relief work. I am just not a big fan of 'stones' - I like to make the metal fly! With that said, you need to know HOW to use these rotary bits - they eat shit up in a hurry and if you can't control them, then you should not use them. The good news is that I buy a couple sets for EVERY porting/relief job. I buy an assortment on eBay - some short ones and ALWAYS a set of the longer ones with 6" or so shafts (which I cut back to about 4.5"). Typical costs per job are about $65 -- not cheap, but not bad when you consider what it would cost to have somebody port/relieve a block.


Sand Paper Rolls and Mandrels: I go to McMaster-Carr and order sand paper rolls in bags of 25 or so. I use the 'ZA' compound ones - as they have longer life and cut better. I use 1.5", x .5" with a 1/8" mandrel. The grits I use are 60, 80, 120, 150, 240 -- then I hand roll my own 320 and 600 grit ones. I will probably use about 1/2 of the above for a big port/relief job - but they're always handy to have arouns.

Blue Die Chem: You need a bottle of blue die-chem to mark the block deck surface and the top of the bore - to you can mark where you're working, etc..

Safety Stuff: You don't need cast iron in your lungs and you may need your ears and eyes are nice to have. I have a good set of ear protection, eye-protection goggles and a breathing mask. Also, I've found that a good set of mechanics gloves helps your hands take the vibration and abuse of the job - so buy a pair.

b) Planning the Job:

Clean the deck surface with fine sand paper or Scotch Bright. Clean the top 1/2" of the bore as well. This helps the Die-Chem stick. Apply Die-Chem to the whole block area between the valves and the bore. Also go around the valves and do the top 1/2" of the bore - next to the valve area. You'll use a scribe to mark the relief location.

Use an old head gasket or head pattern to mount to the deck surface. Take a scribe and scribe the gasket pattern onto the deck. The following shows a lexan template that we made of the FlatCAD head profile - we used it to fit the head, check alignment, etc:



Here is the block/deck surface with the gasket shape scribed in:



c) How the heck to mark the bore depth?

I've created a little "trick" tool that makes it easy -- just came up with it today! Take an old piston (that fits your bore) and drill a hole in the top of it. Then make a steel bar that is about 1" wider than the piston and drill a hole in the center of it. Then, given the design of the piston (flat top, dome, etc) - you may need to add "shims" to set the height. Basically I want the edge of the piston to be DOWN in the bore at my relief depth. Then I can easily scribe the depth line. Also, I can place the piston in the bore and visually check my relief depth at any time -- cool stuff here!





In the block - scribe your lines, use it to check relief depth while "in process":



d) Making Your First Cuts:

First - stand back, select a good 'flame tip' rotary bit and THINK about what you're about to do. Imagine in your mind where you'll start, what process you'll use, etc.. The planning you do and "imagineering" in your mind will always help the process - never be in a big hurry, you can ruin a good block!

What I do in all my porting and relief work is try to get the "boundary areas" done first - to whatever width, shape or depth I need. I find that having the edges done make it easier to do the bulk work in the middle and still have a guide to follow.

On the picture that follows, I made two guide cuts at just about full .170 depth. I was initially pondering a 'step relief', then changed my mind. What you should have seen below was TWO side cuts - each that followed the gasket line and went down to the scribed depth line in the bore. You have to be REALLY careful when you make these first cuts - make sure you control the air grinder with both hands. You do NOT want the cutter jumping around and damaging the deck surface or other areas.



e) Roughing It In - Let the Cast Iron Fly Baby!:

Once I do my boundary cuts, then I start doing the heavy roughing work. Again, I tend to work toward one boundary at a time. I'll get the full-relief depth kind of close, then take a lot of care to blend in toward the valve seat. You don't want to be gouging the seat areas - you want to gently work the grinder - taking nice smooth side-to-side cuts until you're just touching the top of the valve seat area. You do the same on the bore side (paying attention to your scribe mark).




f) Quality of the Finish Work With a Rotary File:

You can manually create a pretty decent finish with a rotary file . . . if you get used to using a consistent and fine pressure, keep the cutter moving and gently shave off fine cuts at a pass. I've found that certain cutters can do a finer job than others -- depending on how centered they are, sharpness, etc.. I try to find a good 'flame' shape that really cuts smooth and use it for the finish work. If you're having a hard time, then you might want to use stones for all finish work, buy better equipment, get some better skills . . . or stop drinking . . .



g) Sand Paper Rolls - Boundary Areas First:

Again, I always do the rounded relief edges first - getting them nicely blended, smooth and consistent. It isn't a bad idea to have some SMALL sand paper rolls that are about .250 or .375 diameter for the relief edges. I bought a few 'porting kits' that had some nice small ones that I use. I get all the fine edge work done first - then progress toward the middle.

h) Sand Paper Grits:

As I'm pretty good with rotary files, I start will 80 grit on the relief areas, then go to 120, then 150, then 240, then 300 then 600.

i) Completed Work . . . Not to Bad for a "Hand Job"







So there you have it . . . and what a RELIEF it is . . .

See you all at Bonneville!

 

Killler! You are king

 

Damn Dale, nice work! Thanks for taking the time to add pics, great job.

 

COOL! Excellent pics and enjoyable write-up too!
How much compression do you lose doing this?

 

Nice job!!

Do you have any flow numbers to compare before and after?

J

 

Awesome post..

Can I add a hint?

when you are doing the relief cutting with a die grinder, get an old head gasket, and tape it on and leave it there, then if you slip, you should hopefully not damage the deck surface, just an old gasket. also gives you a good visual reference for how wide to go, assuming your new gaskets are the same shape as the old one (they do vary a bit from brand to brand)

 

Awsome work! i am rebuilding my flatty now and have been kicking the idea of releaving around. It is a scary thought to attack your engine with a grinder. you made mention of using a router? i have not heard of this but i can see the advantage of depth control.

 

Great tech Dale - thanx for taking the time to share !!

Wish I was a B-Ville with ya all.....

Good luck and keep us posted !!

Rat

 

That's magnificent! In actual fact, it's art... Looking forward to attempting to apply these skills you have offered to us all on my Flathead build!

Also, is it the same process if you were to relieve a 4 Banger? Any alterations in the process?

Thanks Dale.

HC.

 

Great info here thanks for sharing. Releived an 8BA about a year ago and I gotta say it was pretty nerve racking stuff with a die grinder attacking a mint block.

 

Excellent stuff great pics you must have patience of a saint.

I would love to see what the relief relates to in rear wheel HP I am sure it flows better on the bench but there is a compression reduction, Compression has an effect on HP and torque right accross the rev range my guess is relieving will only show a benefit at high revs. Be interesting to see a dyno sheet with a motor of the same spec relieved and none relieved.
Just looking an answer for the HP/20 Hours with a die grinder equation.
Rich

 

Great tech piece, Dale! You obviously have more patience than I do!


QUOTE=HOTRODDICKIE;6624174]Excellent stuff great pics you must have patience of a saint.

I would love to see what the relief relates to in rear wheel HP I am sure it flows better on the bench but there is a compression reduction, Compression has an effect on HP and torque right accross the rev range my guess is relieving will only show a benefit at high revs. Be interesting to see a dyno sheet with a motor of the same spec relieved and none relieved.
Just looking an answer for the HP/20 Hours with a die grinder equation.
Rich[/QUOTE]

Well, since the engine Dale did was for Bonneville, the high revs are where we need the power! Also, it is a blown engine, so being able to breath is more important than the static compression.

There are specs out there showing relieved vs non-relieved. If you look into it , you'll find two very different lines of thought on it- kinda like the Ford-Chevy thing!

 

Are you going to make it to Bonneville this year with the car ?

 

[FONT=Arial, Helvetica, sans-serif][/FONT]Haha!

Well, I'm glad you asked this week, instead of last week. Last week, I was having an anxiety attack over getting this finished. After talking with everyone, and 'tweaking' some of the ideas we had- basically forgetting them until next year, I feel better again!

The level of commitment on the team is extremely high, and everyone is working every spare moment to make this happen. I just can't brag these guys up enough!

We will be there!

 

B&S you have a gentle touch to do that kind of work, it's beautiful..With a touch like that I bet your wife is a happy women..LOL...
Duane..

 

Great write-up and pictures. Thank you.

 

Always been good with my hands . . . and I'm one lucky SOB to have my girl Amy (a true hotrod partner in every way!).

I find that having good tools is key, but the ole' "practice, practice, practice" sure comes into play. Also, I'm a perfectionist - can't stand my work being of lesser quality than what I see others can do. There is always room to improve . . . always.

You really have to have good eye/hand coordination for this type of precision work -- same with TIG welding . . . some have it naturally, some develop it over time . . . some will never.

My Uncle used to say "I can't do that crap, I shake like a dog shitting razor blades!"

 

Here is my setup for saving about half the time for a relief job.
Finishing is same as Dale does it.

 

Story of my life Pete . . . I need a "bigger tool"! I only wish I had a mill big enough to put a full block into! Someday my friend . . . someday!

 

Great job! I've been following over on the Flat Cad thread but good to see the details here.

 

Most excelent work as allways Dale!
Your threads will help alot of us guys making flatheads go faster!
And as said before, all this is good for a new flathead book!!?

Br
Kjell

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

 

Great work.... I am dissecting all of this for my future flathead hop up......Thanks

 

Nice work. Just wish I had half of your talent.

 

Great post Dale , here's where my block is at, getting closer.

 

Went back at it this evening - finished the other side. Now that I'm up to speed on the FlatCAD, takes me about 1 hour per relief total . . . start to 600 grit finish. That isn't too bad for all hand work.

Couple More Pictures to Help the Newbs:

1) Small Assortment of Tools: Here are the actual tools that I use for a Relief Job. I haven't shown some of the finer grit sandpaper rolls (as I "roll my own" big Bob Marley's for the 320 and 600).





a) I only use the two carbide rotary files shown for relieving. The one with the straighter sides is used to do the "boundary cuts" on the gasket edges (which again, I always do first). Then I switch to the other one to "Hog Out" all the stuff in the middle and I get it about .020 or so from final. Then I switch back to the straight sided one for the final shaping and to get the relief as flat and consistent as possible. Again, you can get a pretty consistent finish with a rotary file - it will be a bit rough, but there should be no gouges, obvious grooves or un-blended areas. Just practice a bit on ANY piece of cast iron!

2) Couple Technique Pointers:

Some of you are probably wondering "How the hell does this Wanker get the relief areas so flat looking . . . with a dang hand grinder and round rotary bits". Maybe because of the obvious 'wanker' reference . . .

Here is what I do -- can't say that I ever had any instruction on porting and relieving, just self-taught. So, since it works for me - might work for you.

a) Notice that my little high-speed air grinder is not that big. I can use both hands to guide it pretty well. What I do is place the bottom side of it against the deck (down below the cylinder) and kind of brace it against the deck as a rotation point.



b) Use the Deck as a 'Steady Rest': Basically, I hold it against the deck and apply even pressure then use my hands to rotate it in an arc -- to cut a little layer off the relief area each time. I just keep going back and forth and shaving the cast iron away. Yes, it is a bit repetitious, but that is exactly what you want --> a consistent, easy to replicate motion that you use over and over again. Kind of like a "Human milling machine" - making small cuts per pass.

c) Hand Blending: I will lift it off the deck and hand blend all the areas that roll into the gasket edges, corners, etc. --> but this is small work compared to the major "hog out" operations.

d) Sandpaper Rolls: I have a couple mandrels -- one that is about 6" long. I like the long mandrels to polish the relief -- as they allow me to keep the sand paper roll "flatter" or more parallel to the relief (due to their length). I use a similar motion for all the coarser grits as noted above. This gives a consistent finish and doesn't make all those "dig marks" that are so easy to make with sand paper rolls. Keep the rolls moving - even when you're blending the corners.

Take your time, practice a bit . . . any flathead caveman can do this

 

Great looking job . . . nice to see some more port and relief work! Are you going to be at Bonneville in August? Hope to meet you!

 

I'm sure you have as much if not more . . . all of this work just takes a bit of research, some fairly inexpensive tools (except a big compressor) and practice.

I think with just a couple hours of work on an old block, that just about anybody can get this technique down and be on their way. In a single day, you can do a really nice relief.

Porting takes a bit more skill and time (and knowledge so you don't "hit water" ) - but it is all similar in the end . . . so go for it!

 

Amazing work. If not using a blower like Buddy mentions, which relief is best for all-round street use ? The stepped relief or the full relief ? I can Imagine the HD type stepped relief must have some advantage ? Any knowledge about this?

 

This is Great Tech!

I, like most guys learn by actually seeing things in action and your pics help put the text into perspective.

Thanks for taking the time to post up this great article,


moe



.

 

I've read this post a few times over the last couple days. It's been inspirational....I've got a junk block that I'm going to practice on first. I think when I build my motor for the coupe, I'm going to step it up a notch and build the baddest flathead I can....all because of this thread.