Compression and flow

[3W Hank]

About compression in a FH.
Old speedparts heads had high compression as the Canada heads and to Kogel both cast iron and aluminium.
So idea must have been that compression got a stronger engine.
But this engines had a terrible flow around the piston so one can questionise if not a lower compression get more flow to spark, so more power in reality.

I has a set of the ’10 to 1’ L&S heads and Ross domed pistons.
Heads is at 59 CC and measure 10.5 mm or 0.413” deep chambers.
They get 10 in compression with 1/8” bore and a 4” stroke and a 0.04” thick gasket in a 59BA.
My cam is a Potvin 425 ( 425” lift ) so I might get away with this.
But I might has to mill the chambers or go with a thicker gasket.

-So the question is, do this engine like compression or do they make more power less compression.
That would cure all piston to head and valve to spark plug issues aswell.

In my case I’m not after max power, just like the sound and feeling and old parts.
So question is more technical.

[Ol' Ron]

WOW!!!
Gramps

[Brian]

It's the age old question; flow versus compression. Everyone has their own theories. Some things work better than others. Real serious racers keep their combustion chamber designs secret. I very much doubt that anybody on this board will tell you how to achieve the holy grail, it's up to you to experiment and discover what works best for you, in your case..Enjoy the challenge.

[3W Hank]

Whats the big secret today, competition is out since 1955 and this engine might give 150 HP or maybe go for it at Bonneville ( +300 ) but its no money or glory.
My idea was technical if someone had it on a dyno and tested 10 or 6 in comp.
As far as I know the old Harley racing design is hard to beat.
I has documents but question was just overall.
Its open to text me private.

[Ronnieroadster]

Originally Posted by 3W Hank

Whats the big secret today, competition is out since 1955 and this engine might give 150 HP or maybe go for it at Bonneville ( +300 ) but its no money or glory.
My idea was technical if someone had it on a dyno and tested 10 or 6 in comp.
As far as I know the old Harley racing design is hard to beat.
I has documents but question was just overall.
Its open to text me private.

Hank your question is not that simple to answer. Since your only building a traditional hot rod for the cool factor just use the parts you have and you will have at least 125 HP and maybe even up to 150. Certainly enough HP to hurt the Ford flathead three speed and twist the early Ford axle tips as well.

You know what it takes to make power you told me some time back you were involved with Super Stock Hemi stuff. To be fast with that engine it takes a lot of skill/secrets.
If someone was to ask you how to modify a Hemi to compete against you in drag race competition I think you would be hesitant to give away any information.

I will say to get the power needed to make decent HP with a normally aspirated flathead on gas is difficult but can be done. Many hours have been spent by me and a few others to figure things out. But to just give pointers on what to do is not so easy considering the time and Benjamin's each of us have invested to figure some things out.
Ronnieroadster

[Brian]

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There is a wealth of information about this matter in both printed form and on the internet. Ronnie above makes a valid point which backs up my comments....[Hemis] . Obviously, if one could achieve both flow and compression, that would be the ultimate, wouldn't it? Where do you want the flow? Considering that with a naturally aspirated engine, you are relying on atmospheric pressure to fill the cylinder[s], but the exhaust is 'blown' outta the cylinders by the rising piston, I'd say you need to concentrate on filling the cylinder[s]. And all this gibberish is only MY thoughts on the matter....The majority of aftermarket cylinder head manufacturers make pretty finned heads with combustion chambers which closely resemble those on stock Ford heads. The combustion chamber sorta resembles the shape of the head gasket, and to raise the compression we simply 'lower the roof'. what does this do to potential breathing? I reckon it restricts the flow. So, we need to narrow the passage from the intake valve to cylinder, but raise the roof. This will still give us a small combustion chamber [compression] but permit a good flow. Now, where do we locate the spark plug? Ford Located the plug sorta over the ex valve, is that the best location? Tubman swears by the location in Edmonds heads....I agree with him. When you've discovered the ultimate , please, by all means, report your findings on here. We all want to know. Good luck.

[3W Hank]

Brian, please send me the information on internet.

Yes as all things it is related to experiance and R&D.
My knowledge on Hemis in NHRA stock is work on friction, get oil down from head, good ringseal and get out max on compression and max cam lift.
I dig out 200 HP more than on the 80’s but its no real secrets going on here as company sell cams, rings etc and its more or less totally open but why cars go faster now is new speedparts is allowed ( or new tech ) so the RPM is higher and transmissions, converters and tires are way better than before.
Its actually most about the money and less any secrets.

My idea on this hotrod is classic parts and as Ron said ex 100 HP on the rear wheels is enought ruin all the parts after the engine… ;- )
But I will never do a burnout in this car.

I guess back then the gas was not as good even from our pump gas so I think this kind of engines might like a better flow than high compression.

The chamber that has both flow and ’high’ comp is ideal but that mean one need make new heads and a flow path and still has the CC down plus roof has high as needed.
But this question as I said was more technical as its more a basic test people must has done to classic hotrod set up and the finned heads that was out before and now.
I’m not talking on going deep and set records.

[Ol' Ron]

I've been in this area fo the Flathead almost all my life, and there isn't really an answer to your question. Application controls most of it. My experience is in small engines on a 1/3 mile track and drag racing. with no rules, you can do anything you can afford. that's why their are rules./ I prefer to modify the stock head, price wise it offers more. I thinl the Grancore head is probably the best after market one, But if you run a blower , boost wins ask RR. The best thing about racing is!!!! Competition!
Gramps

[Ziggster]

Came across this vid yesterday on YT. Gives a great insight as to what happens in a flathead/ L head combustion chamber.


https://youtu.be/xflY5uS-nnw?si=gmPmfZw5ipeLsPB_

[panic]

The bore to stroke ratio is a factor favoring longer strokes

[Bored&Stroked]

The problem with a definitive answer is that the only one that is accurate is "it depends".

Having higher compression is a big benefit in a flathead for normal off-the-line performance, cruising a hotrod around town, etc.. Flow becomes much more important at higher RPMs - which very few flatheads will ever see on the street.

Also, consider that compression has a LOT to do with the overall bore/stroke and cubic inches. You pick up a lot of compression in a big cube engine - without doing anything to the head at all - it is all based on the size of the cylinder you're filling and how far it travels up on the compression stroke before you hit TDC. Your engine is on the smaller side - 276 cubic inches - so you'll need to keep the chambers smaller than you would on a 304" plus flathead.

For what you're building, compression will be your best friend. It is a lot cheaper to chase compression than it is to experiment with max flow. Which takes years of experience, dyno work, track work, lots of parts, etc. To achieve higher flow potentials, you get into heavily ported blocks, big valves, special chamber work, etc -- and what works for one engine combination may not be right for another. Also, in order to USE all that port work, valves, etc - you need a lot of flow from your carbs and manifold. How many carbs do you plan to run and which ones?

Also, squish/quench is a big deal on any flathead. You'll want to achieve about .040 to .045 above the pistons as your final clearance dimension (with a head-gasket on). Most head-gaskets are about .050 to .052" thick - so factor that into your measurements.

In the end, unless you're looking for sustained higher RPMs and max high-RPM horsepower, you're better off keeping the compression high and putting flow as a secondary concern.

[tubman]

I like your way of thinking; especially the last paragraph. Lately, I have found that if you can get the quench right, everything else follows and little extra work is required. There are exceptions, like the case where one of my blocks had been decked .030" more on one end and required an end to end angle mill of the head. (That was a bugger to figure out, but became obvious with a little thought.)

[Ol' Ron]

Another problem with compression is the lame from and detention. A 9:1 Cr can detitinate when when the flame front is too long. this comes when the piston to head clearance is too large. This can be solves with higher Octane fuels, but that cost more money. I like to run 87, not much sense in a higher octane fuel in a "street engine) I hope to get somes pics of the head modifications at the welders. I have two intakes for the engine a Merc bored for the 2GC and an offy 4Bl witha holley 390, This has a very small primary port.
ramps

[3W Hank]

I was not try to get into full serious race HP here to make new chambers ( maybe new heads ) instead just old classic speedparts and if people has tested going with a 0.04” gasket that get say 10 to one and then try a 0.100” gasket get ex 7.5 to one.
As I said, the question is more technical but related to peoples test.
It was not asking for years of Bonneville R&D.

In this case I has my heads, cubic is set, intake set and carbs and cam and distributor.
The idea and parts I will do ( out of the box ) is I like light lifters, light valves, less crank shaft weight and a aluminium flywheel and a light pressuare plate.

Shore, I could use quench at 0.045” ( 0.045” copper MLS gasket ) and mill chambers in the valve area to get more CC, and maybe make flow areas, but I’m not plan mill my old heads.
So if thicker gasket the quench will be more.

[Ol' Ron]

I don't see what lighter valves and aluminum flywheels have to do with compression. This isn't necessart in a "street engine" especilly a light flywheel.
Gramps

[Brian]

Assemble your short block, then machine the heads to achieve the desired .040" odd thou quench. Getting that clearance from top of piston at TDC to head to within .040-.050" is paramount for optimum performance. This is pretty well the last step in building your mighty power plant, you need the short block assembled, then modify the heads to suit. I hear you say you don't want to mill the heads; you may well have to! Or, as you say, machine over the valves to achieve clearance, again, you may well need to. Putting all that lightened stuff into the engine is all well and good, but a waste of time if you don't prep the heads...

[3W Hank]

Ol’ Ron.
No a light flywheel has nothing to do with the compression, just mean the topics was not real race orianted but mention my combo and some ’out of the box’ as light crank and light valves. Light crank rew up faster and light valves/lifters read cam better and less material to drag around.
I came over a NOS set 8AB lifters and a used CSB titanium valves for free.
Lifters and valve is 90 grams. I think my 425 eliminstor cam like it.
Plus I will not modify my old speedparts.

-Allot of good info has come.
But is still miss if any had a combo going higher in comp, had valve clearance and sparkplug clearance on the edge but still work - but then add a way thicker gasket and see what reaction was ( lower compression )
Again I’m not into research on flow or try go 200 MP on a NA FH pumpgas.

[3W Hank]

Brian,
Yes I guess that what it will be, quench at 0.04” by ’gasket thickness’, not machine then make shore valve and sparkplug has clearance.
Again, topic was technical.

[petehoovie]

Originally Posted by 3W Hank

Ol’ Ron.
No a light flywheel has nothing to do with the compression, just mean the topics was not real race orianted but mention my combo and some ’out of the box’ as light crank and light valves. Light crank rew up faster and light valves/lifters read cam better and less material to drag around.
I came over a NOS set 8AB lifters and a used CSB titanium valves for free.
Lifters and valve is 90 grams. I think my 425 eliminstor cam like it.
Plus I will not modify my old speedparts.

-Allot of good info has come.
But is still miss if any had a combo going higher in comp, had valve clearance and sparkplug clearance on the edge but still work - but then add a way thicker gasket and see what reaction was ( lower compression )
Again I’m not into research on flow or try go 200 MP on a NA FH pumpgas.