Final Dynamic Compression Ration Check Assistance

Matthew68

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My dilemma with fuel is I can get ethanol free fuel at 91 octane, or I can get fuel with up to 10% at 93 octane.

I’m having the aluminum head ported and polished. The issue I run into is if I use a dished piston by SCR drops significantly to mid 9s, even if I dropped the chamber size to 50. I’m thinking flat top with 53cc is good.

Which fuel is recommended, 91 corn free or 93 with corn?
 

pmuller9

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Stay flat top with 53cc chambers.

Corn free gas has more energy per volume and will produce more power and slightly better gas mileage.
Obviously 93 octane corn mix has higher octane than a 91 octane fuel and will have higher resistance to detonation.

The two fuels may require different jetting using a carburetor so it may be a matter of setting up for one or the other.
 

Matthew68

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I also talked to Jerry about a 270/270 cam. That would push my intake close ABDC to 63* and hence lower my DCR to 8.14-8.18 depending on overview (either 20 or 30 over).

That might make me feel a little bit better.

On the fuel, with the SCR being right at 10:1 and flat top pistons am I better off setting up for 91 corn free or 93 with corn? I realize the higher octane will help combat any detonation but am I doing more harm than good with the added ethanol?
 

pmuller9

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The 270/270 cam would be a much better match for the ported head and having a lower DCR would give you more margin for tuning.

Ethanol is harder on the older gaskets and seals, absorbs moister and is more prone to vapor lock.
Ethanol Free gas has higher energy content and will yield better gas mileage.
 

xctasy

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Use the Snow Performance Anti Detonation injection, and get a better EDIS or TFi ignition. The lowest octane gas with the highest methylene window cleaner will work best if it doesn't freeze up.

The cam and compression ratio can live in a make believe 120 Sonnoco world of pre 1971 11:1 bliss.
 

Matthew68

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pmuller9":2ubl2kml said:
The 270/270 cam would be a much better match for the ported head and having a lower DCR would give you more margin for tuning.

Ethanol is harder on the older gaskets and seals, absorbs moister and is more prone to vapor lock.
Ethanol Free gas has higher energy content and will yield better gas mileage.

Thanks P. I’ll stick with the 270/270 cam then. Schneider tries to grind with 2 degree advance built in. I’ll have my builder degree, but would you recommend advancing or dot to dot (assuming everything matches up perfectly after degree).
 

CNC-Dude

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It will still have to be degreed to assure accuracy because of machining tolerances/errors in the timing set gears and crank keyway.
 

pmuller9

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Matthew68":34qobhdc said:
Thanks P. I’ll stick with the 270/270 cam then. Schneider tries to grind with 2 degree advance built in. I’ll have my builder degree, but would you recommend advancing or dot to dot (assuming everything matches up perfectly after degree).

Try to get the cam close to 2 degrees advanced which means the intake lobe center will need to be close to 108 degrees ATDC.
If it falls between 108 and 110 ATDC that will be ok.
If not then you will need a multi key timing chain set which will let your machinist move the cam by 2 degree increments to get it right.

Clay Smith PP-200-DRC Dual Roller Timing Chain Set
https://www.claysmithcams.com/ford-200- ... red&page=3
 

Phase3

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Following along, id like to add that pump 93 or e10 fuel has a lower stoich than ethanol free as in it will need to run slightly richer. Ethanol free is 14.6 to 1 and e10 is near 14.1. Just thought id bring this up as if you tune it for e10 you will be safe using ethanol free. If you go through gas like i do, i would rather pay the 3.70 for 93 than the 5.00 for ethanol free. You will most likely experience vapor lock with 93 e10. If the prices are no matter, i would surely run ethanol free in anything with carburetor.
 

Econoline

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I think you'd be just fine w/ 8.1-2 dcr. Probably a bit more like the 8.4 from the other cam, but I don't know maybe it will be borderline. I say this b/c I'm running almost 8.1 dcr with my 250 and a log head, which should be much more prone to detonation than your 200, esp with better quench and combustion chambers with the aluminum head. I had a pinging issue, but that's been resolved. It was due to too much total advance. I've got 12 initial and 26 mechanical now for 38 total and everything is fine on 91-92 octane.
 

62Ranchero200

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Just a reality check for my own education - if the OP now has a head with 53 cc chambers, there is no reasonable way to decrease the volume of the chambers, right? Milling the head, but that would increase SCR and DCR.

Thanks
Bob
 

CNC-Dude

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It has a lot to do with the ignition timing and distributor setup. You can still be well under the DCR recommendation and still ping and rattle if you have too aggressive of an advance curve or incorrectly set up distributor. My reaction would be to push the DCR a little higher to maximize output and justify your expense for the cylinder head.
 

chad

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it seems the shoe is on the wrong foot (my fav metaphor right now on ford6).
Instead of starting w/the rpm'n octane 1st step Qs (cam selection) things have turned around.
'S OK tho, I am the first one to state I do not have automotive engineering understanding. Perhaps
Y I 'go by the book'...
 

Matthew68

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What impact does advancing/retarding the cam have on DCR? For example, the cams I am looking at are a Schneider 264 or Schneider 270 (intake durations both with 110 LSA). With the 264 that puts me at 8.3 DCR and the 270 puts me at 8.1ish. They claim to grind 2 degrees advance in.

I’m looking to calculate DCR taking into consideration advance/retard decisions into my calculations.

Thanks
 

chad

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"...They claim to grind 2 degrees advance in. ..."
my understanding - they do anything U want for same price
 

cr_bobcat

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I can run the numbers for you again if you'd like. Or I can just post the script. It runs on a freeware version of an engineering program called Octave. Well, I wrote it on Matlab, but Octave runs most Matlab scripts. I ran it on both to ensure I got consistent results.
 
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