Shoud I relieve my block

[Ronnieroadster]

Originally Posted by 38 coupe

Is this a decent summary of the information in this thread?


1 - Below 4500 rpm there is no benefit to a relief.

2 - For motors built for competition use a relief can help, but must be carefully designed. The rpm range of competition will heavily favor whether a relief is helpful or not.

3 - For all out high rpm use such as land speed racing a relief is necessary.

My thoughts are what Pete said.
Ronnieroadster

[Jack E/NJ]

Pete >>> 1 - "Below 4500 rpm there is no benefit to a relief." Wrong.>>>


Maybe this is a companion question that should be kept in this thread.

Since most of us seem to have unrelieved blocks --- and since block relieving seems so drastic especially if something goes wrong --- should I somehow relieve my head instead?

Well, sorta. Fill in most of the dead zone over the hole? Examples below from a hamb thread. I can almost see the swirlies happen as the mixture gets sucked into the hole.


https://www.jalopyjournal.com/forum/...-head.1242895/

















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[Bored&Stroked]

The question comes back to the application and usage of the engine. In a performance built engine, a relief will help - especially if you have good port/valve work done, cam, heads, etc.. In a stocker type engine, it will reduce compression and there is not a huge amount of benefit. Also, what RPM do stock engines usually run at?

Pete, Ron and I probably relieve every engine we build - as we do not build stock type engines. I've not built a stock engine in 40 years.

If I was building a stocker or mild performance type engine, I'd probably do more of a blend of the transfer areas around the valves - more of a 1/2 relief to improve flow out of the valve pocket. Also, consider that stock type engines are already suffering from low compression - do you want it any lower?

Here are a few pictures of what I'll call a 1/2 relief - it was done for a 276 cubic inch street engine running dual carbs and a Potvin 3/8 cam. Stock valves sizes, street porting and guide work (on the tops). This is kind of a "tweener" - improved ports, a 1/2 relief - not a competition style engine, but surely an improvement over stock. It ran extremely well in a street driven Model A roadster:

PortsFinished1 copy.jpg

ReliefWithRadiusBoreEdge copy.jpg

GuideInPort1.jpg

[Tim Ayers]

Originally Posted by Bored&Stroked

The question comes back to the application and usage of the engine. In a performance built engine, a relief will help - especially if you have good port/valve work done, cam, heads, etc.. In a stocker type engine, it will reduce compression and there is not a huge amount of benefit. Also, what RPM do stock engines usually run at?

Pete, Ron and I probably relieve every engine we build - as we do not build stock type engines. I've not built a stock engine in 40 years.

If I was building a stocker or mild performance type engine, I'd probably do more of a blend of the transfer areas around the valves - more of a 1/2 relief to improve flow out of the valve pocket. Also, consider that stock type engines are already suffering from low compression - do you want it any lower?

Here are a few pictures of what I'll call a 1/2 relief - it was done for a 276 cubic inch street engine running dual carbs and a Potvin 3/8 cam. Stock valves sizes, street porting and guide work (on the tops). This is kind of a "tweener" - improved ports, a 1/2 relief - not a competition style engine, but surely an improvement over stock. It ran extremely well in a street driven Model A roadster:

Attachment 531548

Attachment 531549

Attachment 531550

Dale,

Looks great, as usual. This is close to the type of relief that Barney Navarro used on his engines.

I've curious about the "eyebrow" above and 1/2 way between the valves. Any thoughts on if this metal impedes, improves or is indifferent to flow?

Jack E/NJ,

Thanks for posting the heads picts. Curious about head combustion chamber shape and how to improve that area as well.

[Pete]

If you are going to modify your engine to ANY degree, you must understand the basics of what works as "stand alone mods" and grouped mods.

Stand alone mods are things that improve performance by themselves, such as a computer type ignition.
More compression.
More cubic inches.
More flow exhaust.

Any one of these by itself will improve performance.

Grouped mods are any combination of the above including a performance camshaft, big valves, dry sump, port work, relief, modified heads and many other things.

You DO NOT relieve a block and not do something to raise the compression back to at least where you started.
That is like having a bad set of spark plugs and only replacing half of them.

[Pete]

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Originally Posted by Jack E/NJ

I can almost see the swirlies happen as the mixture gets sucked into the hole.

The mixture is not sucked in. It is forced in by atmospheric pressure. The intake vacuum does enhance the flow though.

Pressure and vacuum flow systems behave differently.

[Bored&Stroked]

Originally Posted by Pete

If you are going to modify your engine to ANY degree, you must understand the basics of what works as "stand alone mods" and grouped mods.

Stand alone mods are things that improve performance by themselves, such as a computer type ignition.
More compression.
More cubic inches.
More flow exhaust.

Any one of these by itself will improve performance.

Grouped mods are any combination of the above including a performance camshaft, big valves, dry sump, port work, relief, modified heads and many other things.

You DO NOT relieve a block and not do something to raise the compression back to at least where you started.
That is like having a bad set of spark plugs and only replacing half of them.

Very well said Pete! I like the way you elaborated on "grouped mods" - which was what I was trying to convey in my earlier posts.

[Jack E/NJ]

TA>>>Curious about head combustion chamber shape and how to improve that area as well.>>>

Yeah, me too. While a better-designed slug crown seems like it might help fill the compression void, reducing the dead zone as in Hudson's vortex head might be the next best thing?

[Pete]

I always welcome data on twiddle diddling with any engine component that will make the dyno reading go higher.
Even if it is only 1 or 2 hp.
I had a friend in the 50's that was a Boeing engineer and owned a Kurtis 3000 series Indy car.
As a side project once in awhile he would help us with race car math problems that were more easily solved on the Boeing analog computer rather than with a slide rule.
He and I both met Smokey Yunick at a race we went to watch once. Smokey was running Hudsons at the time. From a short talk after the race we were able to get enough info to reverse engineer what he was doing with the Hudson combustion chamber which was similar to what we had been doing to the Ford's except on a bigger scale. We went bigger on the relief and went faster.
Little humps and pathways in either the block or heads never worked for us.

[Ronnieroadster]

Pete its been my experience the more I opened up the combustion chamber in the head and the relief as well we continued to make more power. No humps or pathways needed as far as I have determined.
Ronnieroadster

[jplutz]

Jack, why are there holes directly over the piston in the Rocket head?

[cadillac512]

Those are just casting divots. Some Ford heads have them too, in varying size and depth.

[Bored&Stroked]

Originally Posted by Ronnieroadster

Pete its been my experience the more I opened up the combustion chamber in the head and the relief as well we continued to make more power. No humps or pathways needed as far as I have determined.
Ronnieroadster

Generally, I'd agree - though when you're running a supercharger/blower or any forced induction, it is a different beast than a NA situation. The quest is how to increase flow and also maintain or increase compression.

If you look at the Harley KR's, they were ALL about flow and compression was not the bigger issue. BUT they had huge duration/overlap in their cams, tight lobe centers, fantastic ports, huge valves and very specifically designed chambers. They were also very high RPM flatheads - they spun them at 8,000 rpm all the time, so low-end power was really not the issue . . . higher RPM horsepower (which means flow) was the issue.

One thing I believe in as it relates to the Harley KR design is the flow-ramp across the cylinder. If you look at the pictures I've posted, the flow comes across from the intake to the bore. I suspect this is a very important aspect of the design - and resulting performance.

The intake charge had a very easy path down the cylinder (and it swirled the charge) and the bore was not covered up by the head chamber. Also, as the design used a pop-up, the chamber was "out of the way" of the flow once the piston was 3/16" down the bore.

The pop-up opened up the opportunity for flow, without sacrificing compression. To me, this is the beauty of the design. This is exactly what I did in the FlatCAD design - following the specific design notes of Jerry Branch with his Harley KR mods.

Another thing I've done is to put a heavy radius on the leading edge of the pistons for two reasons. 1) to reduce the tendency for the edge to overheat. 2) It helps flow get over the top of the piston as the piston starts to move down the bore. Here is what the pistons/deck look like presently - as I'm currently getting the engine ready for Bonneville (flathead Cadillac):

IMG_0076.jpg

69307476044__EA44891C-31EC-4D17-B161-C71AAB3869D1.jpg


For those who are interested, do some searches for the articles that Jerry Branch published on modifications to the Harley KR (back in the 60's).

[petehoovie]

Originally Posted by Bored&Stroked

Generally, I'd agree - though when you're running a supercharger/blower or any forced induction, it is a different beast than a NA situation. The quest is how to increase flow and also maintain or increase compression.

If you look at the Harley KR's, they were ALL about flow and compression was not the bigger issue. BUT they had huge duration/overlap in their cams, tight lobe centers, fantastic ports, huge valves and very specifically designed chambers. They were also very high RPM flatheads - they spun them at 8,000 rpm all the time, so low-end power was really not the issue . . . higher RPM horsepower (which means flow) was the issue.

One thing I believe in as it relates to the Harley KR design is the flow-ramp across the cylinder. If you look at the pictures I've posted, the flow comes across from the intake to the bore. I suspect this is a very important aspect of the design - and resulting performance.

The intake charge had a very easy path down the cylinder (and it swirled the charge) and the bore was not covered up by the head chamber. Also, as the design used a pop-up, the chamber was "out of the way" of the flow once the piston was 3/16" down the bore.

The pop-up opened up the opportunity for flow, without sacrificing compression. To me, this is the beauty of the design. This is exactly what I did in the FlatCAD design - following the specific design notes of Jerry Branch with his Harley KR mods.

Another thing I've done is to put a heavy radius on the leading edge of the pistons for two reasons. 1) to reduce the tendency for the edge to overheat. 2) It helps flow get over the top of the piston as the piston starts to move down the bore. Here is what the pistons/deck look like presently - as I'm currently getting the engine ready for Bonneville (flathead Cadillac):

Attachment 531719

Attachment 531720


For those who are interested, do some searches for the articles that Jerry Branch published on modifications to the Harley KR (back in the 60's).

[tippa77]

This is very interesting !

[Jack E/NJ]

B&S>>>The intake charge had a very easy path down the cylinder (and it swirled the charge) and the bore was not covered up by the head chamber. Also, as the design used a pop-up, the chamber was "out of the way" of the flow once the piston was 3/16" down the bore.>>>


Yes. Very interesting indeed! Could we perhaps get a better side view of the crown profile please?

[Bored&Stroked]

The pistons are in the engine - so this is the best I can do. They are flat-top, with a .040 squish to the head, the radius is done by hand and then I balance the pistons to the same gram weight. The radius on the leading edge follows the shape of the relief - a bit of an angle (notice that it is clocked off of straight up - four pistons go one way, four go the other way.

Also, keep in mind the level of porting in this block (extreme) and the port sizes are a whole lot bigger than a Ford. Both intakes and exhausts exit out the top - the exhausts don't "snake" through the block like on a Ford. All in all, a much better flowing design (and bigger cubes) than a Ford. BUT - not easy to design, build and work on.

I moved the ring pack down for this iteration of the piston design (as it is blown and under quite a bit of boost) - we're running metric rings (which is all I run if I have a chance).

IMG_0004.jpg

IMG_0005.jpg

IMG_0039.jpg

IMG_0040.jpg

[Jack E/NJ]

Thanks! What are those speckles that seem to be on the seats? Pits?

[jplutz]

B&S, The polished ports are beautiful, like jewlry. I had a 40 LaSalle coupe' in high school. It sounded great with straight pipes! My dad would chew me out when the old bat across the street called to complain at supper time! I had a cable cut-out����! JPL

[cadillac512]

Originally Posted by Jack E/NJ

Thanks! What are those speckles that seem to be on the seats? Pits?

Pretty sure these pics were taken before the final finishing of the seats was done,hence the pits. Beautiful work!