Shoud I relieve my block

[Jack E/NJ]

Maybe B&S meant with a corresponding flat recess up into the head too?

[Tim Ayers]

Originally Posted by Pete

No. When you are trying to get maximum compression, why do something that
decreases compression.Two flat mating surfaces are the minimum area attainable.
Also, the flame front travels faster over a flat surface rather than one with
humps, valleys and corners..

So to confirm what you are saying, Pete. Your thoughts on an ideal chamber is a flattop piston that does not extend past the deck surface and a corresponding flat chamber in the head?

[Pete]

Originally Posted by Tim Ayers

So to confirm what you are saying, Pete. Your thoughts on an ideal chamber is a flattop piston that does not extend past the deck surface and a corresponding flat chamber in the head?

Yes.

[Ol' Ron]

I can understand why relieving the block works do well. most of the cylinder heads have very little transfer area so relieving is there to make up the difference. I was just looking at my Hydro engines, They rak well over 5K and when they came out of the water Pegged the needle, Somebody here suggested Monkey see, monkey do, Yes, I can see how it might work My Grancore heads used apopu piston In my Bvill engine I used 3 3/4 stroke pistons on a 4" crank

[Jack E/NJ]

Pete >>>When you are trying to get maximum compression, why do something that
decreases compression.>>>


I'm confused. How does a flat popup that kisses a correponding flat recess reduce compression?

[Bored&Stroked]

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Originally Posted by Jack E/NJ

Pete >>>When you are trying to get maximum compression, why do something that
decreases compression.>>>


I'm confused. How does a flat popup that kisses a correponding flat recess reduce compression?

It shouldn't as long as the squish is the same. There would be a tiny bit of loss around the perimeter of the pop-up - as it obviously can't scrape the chamber. You can see on my piston design for the FlatCAD, I have a tiny "relief" in the area of the pop-up.

[Pete]

Originally Posted by Jack E/NJ

Pete >>>When you are trying to get maximum compression, why do something that
decreases compression.>>>


I'm confused. How does a flat popup that kisses a correponding flat recess reduce compression?

I guess things got jumbled in the interpretation somewhere.
Two flat surfaces mating will have the smallest area between when brought together.
Add a dome or pop up and you INCREASE area and reduce compression.

[Tim Ayers]

Pete,

How much "squish" do you aim for when you run the flattop set-up?

Tim

[Bored&Stroked]

Originally Posted by Tim Ayers

Pete,

How much "squish" do you aim for when you run the flattop set-up?

Tim

On the FlatCAD, I always tune the squish for .040. If your bores are good and you don't have excessive clearance, then piston rock is at a minimum and you might get away with as low as .030. Also, depending on whether you're running NA or boosted, this can certainly come into play.

[Pete]

Originally Posted by tim ayers

pete,

how much "squish" do you aim for when you run the flattop set-up?

Tim

.035

[Jack E/NJ]

B&S>>>shouldn't as long as the squish is the same. There would be a tiny bit of loss around the perimeter of the pop-up - as it obviously can't scrape the chamber.>>>


Pete>>>Two flat surfaces mating will have the smallest area>>>


OK. Thanks. Makes sense.


Another thing. Smooth arching reliefs into the heads seem like they would be better for flow drag reduction than 90 degree reliefs in the deck. Even though a bit of turbulent mixing might be lost, charge might be greater?

[Ol' Ron]

I don't think the charge over the piston is immportant. It should be in the combustion chamber with the spark plug.
Gramps

[Jack E/NJ]

Well yeah at ignition time. But first gotta fill the hole with as much charge as possible before ignition happens.

[Bored&Stroked]

One also had to think about flame travel and in the end, the charge has to force the piston down - so how the flame travels and if it travels toward the back of the piston top does come into play. Some of the more modern CFD software packages can do simulations that are pretty dang good as they relate to cylinders and combustion chambers and the various cycles of an IC engine.

[Jack E/NJ]

No CFD simulation needed for watching a flame-front travel in an early Ford glasshead v8. Gotta blink fast though. Or may be use a high speed camera. Interesting how the flame looks hotter down the hole than in the combustion chamber.


https://www.youtube.com/watch?v=-PYaJW_jQW4

[Bored&Stroked]

As this is the "Mother of all Threads" on the subject of reliefs. Here is a "stepped" relief that I did on my own "experimental" 284 cubic inch engine that is in my 32 Cabriolet.

I did this to mimic some of the Harkey KR race jugs that I happen to have. I've used this engine to try some different ideas, concepts and parts out on.

It has a big-ass roller cam (huge duration and .420 lift), coatings on pistons, valves, cometic MLS head gaskets, etc..

A guy needs to have a flathead "playground" to have some fun in. LOL

SteppedRelief1.jpg

DeckComplete.jpg

[petehoovie]

Originally Posted by Bored&Stroked

As this is the "Mother of all Threads" on the subject of reliefs. Here is a "stepped" relief that I did on my own "experimental" 284 cubic inch engine that is in my 32 Cabriolet.

I did this to mimic some of the Harkey KR race jugs that I happen to have. I've used this engine to try some different ideas, concepts and parts out on.

It has a big-ass roller cam (huge duration and .420 lift), coatings on pistons, valves, cometic MLS head gaskets, etc..

A guy needs to have a flathead "playground" to have some fun in. LOL

Attachment 531943

Attachment 531944

[Pete]

You give up a LOT of intake port area with those old raised surface blocks.

I have never heard of anyone machining the raised surface off before porting. Have you??

[Bored&Stroked]

Originally Posted by Pete

You give up a LOT of intake port area with those old raised surface blocks.

I have never heard of anyone machining the raised surface off before porting. Have you??

Hey Pete - I have not either, but I can't see there being an issue doing so. What I have not tested (with a sonic tester) is there any difference in the amount of material below the raised intake surface? Interesting thing to ponder!

[Pete]

Originally Posted by Bored&Stroked

Hey Pete - I have not either, but I can't see there being an issue doing so. What I have not tested (with a sonic tester) is there any difference in the amount of material below the raised intake surface? Interesting thing to ponder!

I have never owned one of those blocks so no test data available.