Relieving 8BA Block

This relieving the block has always been fascinating to me. I have done it on a few blocks in the past and I've heard the negative comments. Just with common sense thinking, you know there is pressure in the combustion chamber. Granted it is forced against the top of the head as the exhaust valve is open, and works it's way around the valve into the port. If you have a relief that pressure will also have an open path to under protruded valve directly into port which seems to me would reduce the pressure on the top of head. For the minimum compression loss you can always take some material of the head surface.
The French blocks are nice castings with more nickel for strength and a better exhaust path then Ford. All the ones I've seen are relieved.
I would like to see a dyno test between two naturally aspirated engines, one with relief and one with out. My money is on the relieved engine!

cdan34
 
All of the SUMB French engines were army truck engines. Near all of the engines that were purposed for big trucks were relieved. Trucks always needed some help in keeping them from self destructing under hard use. Since gearing made up for the lack of horse power, they needed a change from the stock automobile design to improve long term work performance. Relieving was the fix that FoMoCo engineers settled on since the flathead is so limited with respect to what can be done to it that won't take more away from it's capability to function in order to effect a change. In later years they did more modifications to the heads. The 8RT heads are a good example of a low compression head but when pulling a full load in the old F6, it really made the difference between the roughness of detonation or running smoothly. It was all about warranty consideration and reliability to keep the customer coming back for a new truck every so often. The big F7 & F8 trucks were the first Fords to get the new 317 Lincoln Y-block in 1952 so that they could get away from the flatheads. Even the Lincoln 337 wasn't up to the task well enough for the big trucks so it was finally dropped for the OHV engines.

Relieving was such a mainstay for the old aftermarket aluminum heads with crow foot chambers(that are still available to this day), that it's been viewed by so many to be the performance way to go that it is doubtful that there will ever be an agreement between folks that are all for relieving and those that don't use large reliefs.

Barney Navaro was one of the guys that played with the bent 8 long after most folks were adjusting there rocker arms. He preferred a small relief that basically just made a smooth ramp from the valve seat edge to the edge of the cylinder wall. After all those years of both seat of the pants experimentation and using science to effect meaningful changes, this was what he settled on.
 
panic: Thanks for your post. Maybe some here don't realize how much you know about this stuff. Please continue!


Terry
 
Panic please repost. That was great info. Obviously you have some special knowledge on the WR/KR. This forum has all types please don’t take any post personal as there are many readers & for everyone that may not be interested in your post there’s possibly many that are. Thanks so much for the opportunity to at least read it once but would love to read again & retain as much of your knowledge as possible.
Cheers
Tony
 
"panic" - I think you're reading this wrong. My post was to explain to "Ronnie" what was happening, not to criticize you.

I will however, suggest you develop a slightly thicker skin if you are going to post on internet message boards. There are some that are a lot worse than this one.

As to your post, I found it quite informative.
 
Well . . . seems 'Panic' came and went. He might be the same guy that I've seen on other forums (in the past) - most likely the HAMB. Hopefully he has some good information to share, he'll repost it. If he some information about the Harley KR - would love to hear it as my neighbor built many of them for flat-track, Daytona, side-hacks, etc..

There is always more to ponder, learn about, debate, etc -- if one isn't willing to debate ones 'facts' that one posts . . . then it seems a waste to post them.

I didn't get to read the infamous post . . . maybe he'll rethink . . .
 
He deleted his post after several of us tried to explain what happened and invited him to stay and contribute. Probably not a greatr loss.
 
Engine:
305 ci. Naturally aspirated. Dry sump.
14.5 to 1 compression.
FLAT TOP 2 ring pistons.
307 hp @ 6300 on 118 race gas.
.200 deep relief.
 

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Pete said:
Engine:
305 ci. Naturally aspirated. Dry sump.
14.5 to 1 compression.
FLAT TOP 2 ring pistons.
307 hp @ 6300 on 118 race gas.
.200 deep relief.
Click to expand...

Just curious: What might the horsepower be if the block were not relieved but instead the same amount of material were taken off the roof of the combustion chamber in the transfer area?
 
Pete said:
Engine:
305 ci. Naturally aspirated. Dry sump.
14.5 to 1 compression.
FLAT TOP 2 ring pistons.
307 hp @ 6300 on 118 race gas.
.200 deep relief.
Click to expand...

Pete, you should know that nobody can make horsepower with a relief . . . you should not have tried. I'd fill that relief back in with JB Weld and get your compression up to 16:1 and run regular pump gas. This should give you 308 hp @ 8000 rpm. LOL :D:D
 
At 14 CR on a 307 ci engine, The combustion chamber would be so small, not much air would be in there
 
What does JWL say about recieving a Flathead block in his book? Did he run Dyno comparisons? What were the results?

Whoop's, just went back and saw his previous post. Never mind :o
 
Last edited:
40 Deluxe said:
Just curious: What might the horsepower be if the block were not relieved but instead the same amount of material were taken off the roof of the combustion chamber in the transfer area?
Click to expand...

It did not work as well because of the longer path.
 
B&S, how come you didn't place the spark plug in the transfer area on the new heads.Just curious./ That
s really a long flame front??
 
Pete said:
It did not work as well because of the longer path.
Click to expand...

Thanks for the interesting reply! I didn't think of the longer path as being detrimental. I was focused on the loss of air flow due to the sharper turn from valve to cylinder, caused by the lower roof of the combustion chamber. Always more to think about!
 
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