All Small Six Static/Dynamic/Quench

[comet6]

I bought a 250 that has been rebuilt. After inspection it is .060 over with a D0DE-6090-AA head with small (52cc) chambers. I haven't cc'd them but they have been milled.
My options are :
Run it as is at. 8.6:1
Swap in 2.5 rod. 10.7:1
Swap rod and head. 9.5:1

I would also like to run Howard 280108 cam. I don't have valve timing events to calculate Dynamic compression ratio...

I'm tempted to swap rod now, and head later but don't know if it will run on pump gas in the interim.

 

[drag-200stang]

What do you mean swap the head later, to what? An open chamber? That would be going backwards if this is NA.
Best would be 2.5 rod and a custom strong piston with a dish of the compression that you want.
No one has gone faster than that log head NA.

 

[comet6]

What do you mean swap the head later, to what? An open chamber? That would be going backwards if this is NA.
Best would be 2.5 rod and a custom strong piston with a dish of the compression that you want.
No one has gone faster than that log head NA.

Yes, I was thinking the 62cc head has bigger valves too. This D0DE head is fresh but small valve. I like the small chamber for better quench. I am really tempted to keep it but cam timing will make or break it.

 

[drag-200stang]

All large logs have 1.38 exhaust valves. all large logs from 69 to about 76 have 1.649 intake valves. 77 and up have 1.750 intake valves. All large logs from 69 to about 73 has the largest ports, then they were down sized.
What year 62 cc head do you have? Unless someone did something weird.

 

[comet6]

I don't have another head right now. That is why I'm weighing my options. This is going to be a daily driver with ac. I really don't want to go back into the short block after it is in the car. A head swap at a later date is relatively easy. Also can't see spending $600 on custom pistons.

If I run as is it cost $0 .
Rods, ARP bolts , resize $300+ .
Stock pistons to go on new rods $150
I am doing a cam swap in any scenerio

 

[powerband]

suggest :

start by measuring head chambers of the head. If milled already may be less than OEM. to determine projected SCR with the DODE head run the CR' calculators with verified data.

this DODE measures at @ 54 CC chambers' 2Bbl 'Direct Mount" project.

. . .

final machinist head / valve work will check for integrity but not cut / mill head to retain manageable SCR ratings. Milling .040 - .070 is common but may have consequences with CR and Squench .

have fun

 

[pmuller9]

I would also like to run Howard 280108 cam. I don't have valve timing events to calculate Dynamic compression ratio...

Go to the link below and click on the "details tab.

Hydraulic Flat Tappet Street Force 1 Camshaft; 1963 - 1986 Ford 140-250 600 to 4500 Howards Cams 280108-12 | Howards Cams

www.howardscams.com

You can see from that page that the intake lobe has a 259 degree advertised duration and the intake lobe center is set at 108 decrees ATDC when installed.
259/2 + 108 - 180 closes the intake valve at 57.5 degrees ABDC.

 

[comet6]

suggest :

start by measuring head chambers of the head. If milled already may be less than OEM. to determine projected SCR with the DODE head run the CR' calculators with verified data.

this DODE measures at @ 54 CC chambers' 2Bbl 'Direct Mount" project.

. . .

final machinist head / valve work will check for integrity but not cut / mill head to retain manageable SCR ratings. Milling .040 - .070 is common but may have consequences with CR and Squench .

have fun

I disassembled the heads. They are about 53cc. The have guides and seats in all 12. I'm going to have them checked to make sure they didn't hit water. Still had rock hard umbrellas. I'll remedy that while apart.

 

[comet6]

Go to the link below and click on the "details tab.

Hydraulic Flat Tappet Street Force 1 Camshaft; 1963 - 1986 Ford 140-250 600 to 4500 Howards Cams 280108-12 | Howards Cams

www.howardscams.com

You can see from that page that the intake lobe has a 259 degree advertised duration and the intake lobe center is set at 108 decrees ATDC when installed.
259/2 + 108 - 180 closes the intake valve at 57.5 degrees ABDC.

Excellent, according to the Wallace calculator Dynamic is about 8.7 -9.0 :1. depending on final deck shortfall

 

[aussie7mains]

What is all this "dynamic compression" there is no way any real CR can be calculated from cam timing etc. The VE of the engine will determine how much mixture is trapped in the cylinder, this varies so much that it is not determinate without a really sofisticated programme which is not available to us meer mortals. Forget it. You can calculate the CR very easily and that is determinate. You need to out all your effort into improving breathing, especially with anything LOG head. As stock cam with good breathing will work well, check out all the modern 4 valve engines, they have excellent breathing with very mild cam, big overlap is just an excuse for poor breathing.

 

[powerband]

.".. your effort into improving breathing, especially with anything LOG head. As stock cam with good breathing will work well,"

... then it make sense to push a dense charge into the log manifold with forced induction

 

[aussie7mains]

.".. your effort into improving breathing, especially with anything LOG head. As stock cam with good breathing will work well,"

... then it make sense to push a dense charge into the log manifold with forced induction

"Stating the bleedin obvious" as the pommes would say. Its not pushing the charge in, its the increase in charge density, MASS of mixture is what is important, increase that and you have greater BMEP= torque. This can be done a few ways, increase pressure, or cool the charge. Pressure is most common.

 

[powerband]

"Pressure is most common".

good to clear that up ...

 

[aussie7mains]

"Pressure is most common".

good to clear that up ...

We could talk about N2O!

 

[Cox Custom Mechanical]

One of the most important numbers I find in these builds is quench. When I start any build, I work from 0.030-0.045 quench and then go from there, 9 times out of 10 it’s my starting point. It's also something generally overlooked due to the fact these engines mostly ran dish pistons from the factory.


Just by running a flat top piston with approximately 0.040 quench with a 62 chamber yields 10.8:1, while that is high having a good/tight (but not too tight) quench helps control detonation. Static compression and quench are only 2 parts to a 3-part equation, the third being dynamic compression which is greatly dependent on your camshaft.

After all that if your quench is right but your static compression/dynamic compression ratio is too high you can machine a small dish in the centre of the piston. When I do this, I only relieve the chamber area to take advantage of all that squish. The other way is to get a cartridge roll and relieve the chamber in the head just by doing a quick clean up and smoothing out some areas yields 1-2cc's. I won’t go into re profiling the chamber for now as that's a whole other topic.

These are just a few aspects to look at when planning your build, I hope this help and like always please feel free to message me if you have any further questions.

 

[pmuller9]

What is all this "dynamic compression" there is no way any real CR can be calculated from cam timing etc.

As stated above from Cox Custom, the DCR is strictly used as an indicator for detonation tolerance of pump gas octane.
It has nothing to do with anything else in the context of this thread.

Because the smaller 144 to 250 sixes have a smaller diameter bore than the big six, they will tolerate about a 1/2 point more DCR than the big six.
The big six works with a DCR between 7.0 to 7.5 for 87 to 91 octane pump gas respectively.
If the tolerance is improved by better quench distance, it is used for more margin rather than pushing the DCR higher.
All of this is based on data from the many engine builds on this sight.
In almost all cases, when the DCR limit for a certain octane pump gas was violated, there was detonation and in some cases engine damage.
That's why new engine builds on this forum check the Static Compression Ratio versus the camshaft intake valve timing to determine the DCR.

 

[Cox Custom Mechanical]

As stated above from Cox Custom, the DCR is strictly used as an indicator for detonation tolerance of pump gas octane.
It has nothing to do with anything else.

Because the smaller 144 to 250 sixes have a smaller diameter bore than the big six, they will tolerate about a 1/2 point more DCR than the big six.
The big six works with a DCR between 7.0 to 7.5 for 87 to 91 octane pump gas respectively.
If the tolerance is improved by better quench distance, it is used for more margin rather than pushing the DCR higher.
All of this is based on data from the many engine builds on this sight.
Almost in all cases, when the DCR limit for a certain octane pump gas was violated, there was detonation and in some cases engine damage.
That's why new engine builds on this forum check the Static Compression Ratio versus the camshaft intake valve timing to determine the DCR.

Well said pmuller9 you are bang on with the Dynamic ratio for regular (Pump Gas), our "premium" pump fuel in Australia is 98 RON, which is the equivalent 93AKI(USA) you can sneak 8.0-8.25, but for that you want good quench and reliable fuel.

In theory you can have have as much static as you like if you have enough cam duration to compensate.

I have a 9.380 deck 144ci I am putting together as time allows and the problem with it is I can't get enough static compression into it for methanol, let alone dynamic due to the size of the camshaft.

 

[comet6]

Finally got some parts in hand. Ended up with E63E rod that measured 6.045" . Pistons are 3332H Australian 250. They have 28cc dish. Since the rods are NOT 5.99" it pushed piston above deck about .050" . After cutting crown to meet deck, dish will be about 23cc. All this with 54cc head puts me at 9.25 cr . If the rods had been published length it would have worked out perfect. I suspect this is what went awry in Lavrons build.

 

[Cox Custom Mechanical]

Finally got some parts in hand. Ended up with E63E rod that measured 6.045" . Pistons are 3332H Australian 250. They have 28cc dish. Since the rods are NOT 5.99" it pushed piston above deck about .050" . After cutting crown to meet deck, dish will be about 23cc. All this with 54cc head puts me at 9.25 cr . If the rods had been published length it would have worked out perfect. I suspect this is what went awry in Lavrons build.

Normal 250ci rods are 5.88, what are your 6.045 rods out of?

Just out of curiosity, were your rings imperial?

 

[bubba22349]

Those aren't the right set of Rods that they sent you, the correct ones will measure at 5.99 to 6.00 center to center long, I would send those back. By the way Lavron's Rods were the right ones 5.99's there used to be lots of pictures showing all this (now missing since he passed away a couple years ago) and they fit into his 250 Six block perfectly with only a light .010 Block Deck cut for a Zero Deck. Rods were E63E-B1A from a 2.5 Liter HSC/HSO Taurus 4 cylinder rod is 5.990" long. He then used with those the Silvolite 3332H pistons .030 oversized, dish measured 2.843" and .276" deep (equals 12.863cc) the Compression height = 1.530.