Shoud I relieve my block
- Thread starter Ol' Ron
- Start date
Jack E/NJ
Well-known member
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...ing-back-a-hudson-6-performance-head.1242895/
.
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...ing-back-a-hudson-6-performance-head.1242895/
.
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Bored&Stroked
Well-known member
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:
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:
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
BANNED
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.
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
BANNED
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
Well-known member
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
Well-known member
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?
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?
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Pete
BANNED
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.
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
Well-known member
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
Ronnieroadster
cadillac512
Well-known member
Those are just casting divots. Some Ford heads have them too, in varying size and depth.
Bored&Stroked
Well-known member
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):
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
Well-known member
Jack E/NJ
Well-known member
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?
Yes. Very interesting indeed! Could we perhaps get a better side view of the crown profile please?
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Bored&Stroked
Well-known member
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).
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).
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jplutz
Senior Member
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
Well-known member
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!