Building for Torque Porting Question

JWL said:
FoMoCo never decided to broach the transfer area because it was a performance enhancing technique. It was done to help prevent crack formation at the upper level of the eyebrow. The only debate is about whether or not it was helpful in that regard.
Click to expand...

I haven't had experience with factory relieved blocks. Do they crack any less often than non-relieved blocks?
 
40 Deluxe said:
I haven't had experience with factory relieved blocks. Do they crack any less often than non-relieved blocks?
Click to expand...

Instead of the narrow top area between valves and cylinder the wider area you get from the relieve is distributing the heat better and cracks don´t have a good sharp edge to start from.
 
Porting and relieving is usually not worth the effort, and only then if you have experience in doing it. Last year a customer brought in his T-Bird that he bought on line. It didn't run right, particularly at low speeds. We pulled the heads and found that someone had relieved the block so far that the top piston ring was exposed! The only "fix" was finding a different block, not an easy or cheap proposition.
 
That had to be one hell of a decking job if the top ring was exposed. Something does not add up. How would you ever get an intake manifold to fit if it was a Y block.
 
Last edited:
This is the second time supereal has posted something about a T-bird having what sounds like a flathead engine problem. Wish he would elaborate.
 
Last edited:
Is there not some debate over why the truck blocks were relieved, this is in regards to the 99a engines.
Lawrie
 
Lawrie said:
Is there not some debate over why the truck blocks were relieved, this is in regards to the 99a engines.
Lawrie
Click to expand...

Two reasons come to mind right away...less risk for cracks and to lower compression driving them hard with the less good fuel back then.
 
Why would the relief lessen the chance of cracking,would you not be better off with more metal in that area,also if they wanted to loose some compression why not use a cyl head with a larger chamber,like 81T or the like.and the relief only takes a small amount out off the chamber
Lawrie
 
I wouldnt relieve it for an even simpler reason ....
Its tough to get the pistion rings in the bore.
Double tough if have metric rings ( which i would use)
 
Lawrie said:
Why would the relief lessen the chance of cracking,would you not be better off with more metal in that area,also if they wanted to loose some compression why not use a cyl head with a larger chamber,like 81T or the like.and the relief only takes a small amount out off the chamber
Lawrie
Click to expand...
The sharp small area between valve and cylinder heats/cools faster then a larger flat area.
Any small area heating up faster then the rest of the block under load is a potential problem.
And the difference in heat gives tension in that narrow strip which becomes an excellent place for a crack to start.
Machining nice radiuses on every sharp edge would probably help some to.
 
I don't think there is a very good reason for relieving, Yes blending in all the surfaces mighr do the same think and not reduce the CR. BUT!!! These are street engines. Think??
 
I have had, through the years, four flatheads. I have relieved them all and the compression was brought up in other ways. I know there is a debate on this one. Here are my thoughts; on the exhaust stroke the pressure is towards the top of the combustion chamber. Likewise the top and side of valves. When relieving you open an area that would let some of the exhaust out 90 degrees
to the valve. I think this would help relieve pressure. Wouldn't that be a good thing ? I don't know about the horsepower gain and some of you guys are much more involved in this then I am.

So what is lost by relieving the block ? I would think the engine could breath better.

cdan34
 
Scotty
Another thing might be to rethink the transmission. Maybe the std truck 3 speed would be a better option, unless you really need that real low 1st gear?
 
I have seen only a few factory relieved blocks. Probably a dozen or less. A few(I think 3) were cracked This might be a slightly lower percentage than non-relieved blocks.

When the exhaust valve opens there is a "blow-down" of pressure because the entire chamber contains combustion pressure. That is why the exhaust has such a loud sound. There can be 80 or more PSI blasting out of the chamber(depending on the engine).

After conducting more than 400 flow tests I find no reason for relieving unless there is a desire to increase residual exhaust gas contamination or lower the CR.
 
There are two things that I don't even consider anymore when building a flathead : relieving the block and exhaust dividers. BTW, I have a nice, new pair of the latter in their original packaging; anybody want 'em?
 
Kahuna, I don't really NEED the granny gear. I have only used it starting out on hills when I loaded the heck out of the truck. The engine is really tired though. I may not have to use it when I have a fresh engine.

I have thought about a T5. The T98 works and is paid for so it'll have to do. I may gradually collect what I need to swap another trans at a later date though.

I trying to keep it a freshened up old truck more than turning it into a street rod. I have to admit, an overdrive would really be nice though.

Budget is a big concern. It's taken me two years to go through all the systems as I drove it. A little at a time as I could afford. It's time to tear it down for body, paint and engine rebuild.

Thanks for all the replies.
 
You must log in or register to reply here.
Back
Top