Shoud I relieve my block

[Ol' Ron]

The answer is: absolutely not!!!! The internet as posted several articles on relieving the flathead block. I did allot of this in the early days, untill I went racing, and discovered the fact that very few builders did this. In a conversation with a builder of a few good winning engines , stated there was no real information of the benefits of relieving the block and it was time consuming and a pain in the ass to install the pistons, PLUS no prof that it increased power or economy,
Gramps

[Seth Swoboda]

I would never do it based on the lower CR. Some folks get a big kick out of a relieved block. I had a relieved block and sold it. I was glad to see it go. I agree with you Ron.

[19Fordy]

It's a relief not to relieve.

[V8COOPMAN]

.

I must admit that I would never go to the expense in time or money of relieving a block. But with that being said, I've still gotta ask WHY did those Frenchmen go to the trouble on those beautiful French flatheads (one of which I just sold the last couple of days), as well as the relatively few that Henry Ford produced for buses and other industrial equipment?

Coop

[itslow]

Originally Posted by V8COOPMAN

...I've still gotta ask WHY did those Frenchmen go to the trouble on those beautiful French flatheads (one of which I just sold the last couple of days), as well as the relatively few that Henry Ford produced for buses and other industrial equipment?

Truck and industrial engines which see high load over extended periods of time will often have lower compression ratios. One way of doing this is to relieve the block. GM did this on the 348-409 Chevrolet truck and industrial engines. I'd suspect Ford did the same.

[Jack E/NJ]

Sponsored Links (Register now to hide all advertisements)

Some claim if the exhaust is left alone and the intake relieved a bit, good things might happen.

[Pete]

I would not bother on a mild street engine but I can get well over 1 hp per cubic inch naturally aspirated on gas in a race engine.
The relief is as deep and wide as the block material will permit. The pistons are flat.

[cadillac512]

Originally Posted by Pete

I would not bother on a mild street engine but I can get well over 1 hp per cubic inch naturally aspirated on gas in a race engine.
The relief is as deep and wide as the block material will permit. The pistons are flat.

Is the head flat as well,Pete? Good compression.

[Pete]

Originally Posted by cadillac512

Is the head flat as well,Pete? Good compression.

The head is flat also. The transfer area in the head is adjusted for compression ratio.

I can get 14 to 1 compression ratio for running alcohol.

[Ronnieroadster]

Like Pete wrote for a mild street engine there's no need. However if your interested in getting some more power and economy taking the time to do it correctly is worth the effort. We know Ford did do it on engine's going into Ford trucks makes you wonder why. And as Coop points out the French flathead blocks all had the relief's. Plus as an added point of interest the one flathead design that produced a LOT of power and I would expect economy if needed was the Harley Davidson KR headed flatheads with a relief and that was in the 1960's era.
Like Pete wrote 1 HP per cubic inch out of a Ford flathead is easily possible its being done everyday.

The slight amount of compression reduction caused due to the block being relived in a flathead is actually a good thing considering the poor quality of the gas we have today. High compression and to much timing is a killer for a Flathead unless your burning a good quality high octane gas if your are than your good to go.
Ronnieroadster

[Graeme / New Zealand]

I have a 99A block sitting under a tarp that is factory relieved.

GB

[Tim Ayers]

Originally Posted by Graeme / New Zealand

I have a 99A block sitting under a tarp that is factory relieved.

GB

To add to this, I have three 99A's. Two are relieved and one is not. I'd assume the two that are were in trucks. One of the relieved and the non-relieved are both crack in the #3 intake valve seat.

[Ol' Ron]

I've run some flow test on cumbustion chamber design, and as airflow speeds increas so does the turbulence caused by chamber irregularities. overt 4500 RPN The turblance increase dreamily and the valve bowl is the worst. One reason the torque drops after 4500 rpm. John and I talked about it when he as buildinng his Bvill engine and he came uo with the new guides which helped this area. Photos in his book. I'll post some computer flow graphs, but can't be sure of their accuracy
Gramps

[mcharley40]

I’m no expert however I do have bunch of old literature from early days of Harley Davidson on their development of the side valves. All their successful racing engines had a relief area.
Hopping up Ford Flatties seem to follow suit. Ron you have real knowledge of real testing.
Good enough for me.

[Bored&Stroked]

I have original Harley KR jugs and heads - they were relieved and also had a very different head design. They ran mostly flat-top pistons until later in the 60's when they tried a dome top. The dome top engines didn't make any more HP than the flat-topped piston designs. Of course, these were purpose built racing engines and ran way past 6000 RPM all the time. Flow was everything to their design, with huge ports, big valves, etc.. We only wish our Ford flatheads had anywhere near the type of ports and head-bolt layouts of the Harleys.

When I designed our FlatCAD chambers, heads and pistons (flathead Cadillac Bonneville engine) - we used as much of the 'KR' design as possible - including the custom mods that Jerry Branch made for his modified KR's.

Branch (and my neighbor 'Snuffy Smith') made some of the highest HP KR's of the day. I learned a LOT from Snuffy! Snuffy built a KR for use at Daytona for a rich guy back in the early 90's - was making about 60 HP on a 45 cube KR on gas. The guys running the dyno were really surprised about the HP he was able to achieve on the good ole' KR sidevalve motor.

[Bored&Stroked]

Here is a picture of a KR head - for flat top pistons - the piston popped up about 3/16" of an inch into the chamber. This was very important for flow:

KR.jpg

Here is a picture of the Navarro Hi-Flo head - which used some of the KR type design (stepped relief):

DSC00521.jpg

Here is a Tony Baron "Pop-UP" head - using a very tall pop-up piston design:

BaronPopUp.jpg


Here is a picture of the 3D CAD Model for the FlatCAD chambers:

HEAD-Final9b_CNC_mockup.1.jpg

Here is the actual FlatCAD Head Chamber:

Chamber.1.jpg

[Ol' Ron]

Well I guess I'm wrong. I'd like to see a flathead that makes one HP per cubic inch flathead on gas. I nolonger have the eqipment I used for my testing, so I can't comment on these reselts with any acury. I agree with the HD engine design as we looked at it back then. The Grancore heads were similar with a pop up piston. someone out there has them, Ford factory relieved blocks didn't last long and were designed to limit detention. I was told. But they never included it in the late engines or the 337. The French were just copying it.
Everybody has an excuse for their actions and beliefs , I stand corrected.
Gramps

[Bored&Stroked]

Originally Posted by Ol' Ron

Well I guess I'm wrong. I'd like to see a flathead that makes one HP per cubic inch flathead on gas. I nolonger have the eqipment I used for my testing, so I can't comment on these reselts with any acury. I agree with the HD engine design as we looked at it back then. The Grancore heads were similar with a pop up piston. someone out there has them, Ford factory relieved blocks didn't last long and were designed to limit detention. I was told. But they never included it in the late engines or the 337. The French were just copying it.
Everybody has an excuse for their actions and beliefs , I stand corrected.
Gramps

Actually, you were not wrong - it is all about the application and usage of the engine. Relieving a Ford Flathead does nothing of value before about 4000 - 4500 RPM . . . actually it hurts low end power as it reduced compression (with everything else the same). Also, relieving is just one small piece of the overall puzzle - you have the ports to worry about (they take serious amounts of work), you have the cam to worry about, you have the valves, the chambers in the heads, etc.. As Pete noted - when all the things are specifically designed to work together (for racing) - then relieving is part of the "combo" that was typically used.

Also, typically these naturally aspirated engines were fuel injected - which surely adds horsepower over the typical Stromberg setup. And truth be told, the classical Hilborn flathead injector is too small for max HP. Guys like Don Ferguson Sr. cast their own injectors way back in the 80's - with big port/butterfly sizes more like a SBC injector (to get the flow they needed).

Then, one can start talking about oil-control, dry-sumps, crank scrapers, vacuum pumps, low-tension rings, straight-cut cam gears, etc.. A lot can go into one of these engines - and it is not for those "on the cheap".

[John R]

Originally Posted by Bored&Stroked

Actually, you were not wrong - it is all about the application and usage of the engine. Relieving a Ford Flathead does nothing of value before about 4000 - 4500 RPM . . . actually it hurts low end power as it reduced compression (with everything else the same). Also, relieving is just one small piece of the overall puzzle - you have the ports to worry about (they take serious amounts of work), you have the cam to worry about, you have the valves, the chambers in the heads, etc.. As Pete noted - when all the things are specifically designed to work together (for racing) - then relieving is part of the "combo" that was typically used.

Also, typically these naturally aspirated engines were fuel injected - which surely adds horsepower over the typical Stromberg setup. And truth be told, the classical Hilborn flathead injector is too small for max HP. Guys like Don Ferguson Sr. cast their own injectors way back in the 80's - with big port/butterfly sizes more like a SBC injector (to get the flow they needed).

Then, one can start talking about oil-control, dry-sumps, crank scrapers, vacuum pumps, low-tension rings, straight-cut cam gears, etc.. A lot can go into one of these engines - and it is not for those "on the cheap".

Dale, Thanks for a very balanced and informative discussion of the topic!.
John

[Bored&Stroked]

Originally Posted by John R

Dale, Thanks for a very balanced and informative discussion of the topic!.
John

This has been a good thread - based on a lot of the folks contributing who have many years of experience with these goofy engines (not only Ford, but many other variants).

Like anything else, there is no one "right" answer . . . the answer is the usual "well, it depends".