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Final Dynamic Compression Ration Check Assistance

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Matthew68
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Final Dynamic Compression Ration Check Assistance

Post #1 by Matthew68 » Fri May 10, 2019 12:55 pm

Hi Folks,

Finalizing the camshaft for my motor and just got off the phone with Jerry from Schneider Cams. Below are the specs for my build. Am I in the "safe zone" for compression ratios? Based on the tech articles and other calculators I seem to be, but wanted another set of eyes on it.

Engine Build Specs:

Aluminum Head/Intake
Either 350cfm 2100 or 480cfm 4100 (undecided, will see which runs better I have both)
Piston Dish = 0
Deck Clearance = 0
Combustion Chamber Size = 53cc
Stroke = 3.126"
Rod Length = 4.715"
Gasket Thickness = .044" (Victor)
Gasket Bore = 3.81"
Cylinder Bore = EITHER 3.70" or 3.71" (awaiting feedback form machinist)

Camshaft Specs (Hydraulic):

Intake Duration = 262 (at .050" = 208)
Exhaust Duration = 270 (at .050" = 214)
Intake Valve Lift (1.65 rockers) = .462"
Exhaust Valve Lift (1.65 rockers) = .480"
Lobe Separation = 110
Intake Valve Close ABDC = 59

Static compression is coming out to be right at 10:1. I run exclusively premium 91-93 octane. I have 91 ethanol free around me, I plan to use that.

Dynamic compression I'm finding multiple calculators that are giving me different results. One says I'm right at 8.37:1 which is in range per the tech articles on static vs dynamic. Others I've been in the 7s. Does anyone have a tool to calculate dynamic CR based on my build?

Cheers,
Matthew
1968 Mustang Coupe 200ci - Pertronix + Coil
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cr_bobcat
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Re: Final Dynamic Compression Ration Check Assistance

Post #2 by cr_bobcat » Fri May 10, 2019 3:08 pm

Double check what I put in for the inputs, but this is what my handy-dandy little homebrew tool came up with. Oh, I ran it the first time with the ground-in advance set to 0deg. Assuming the cam card gave you the intake closing value, it would appear that there is 2 deg of advance ground in. I'll assume this means it's a Schnieder cam?

Anyway.....
================================================
INPUT - BUILD PARAMETERS
================================================
Block Specifications:
Cylinder Bore = 3.71 in
Centerline to Deck Height = 7.808 in
Rod Length = 4.715 in
Stroke = 3.126 in
Piston Dish Volume = 0 cc
Piston Compression Height = 1.51 in
Cylinder Head Specifications:
Combustion Chamber Volume = 53 cc
Intake Valve Diameter = 1.8 in
Exhaust Valve Diameter = 1.5 in
Rocker Arm Ratio = 1.65:1
Cylinder Head Gasket Dimensions:
Gasket Diameter = 3.81 in
Gasket Crush Height = 0.044 in
Camshaft Specifications and Events:
Intake Duration = 262 deg
Exhaust Duration = 270 deg
Lobe Separation Angle = 110 deg
Cam Intake Lift = 0.28 in
Cam Exhaust Lift = 0.291 in
Ground-in Advance = 2 deg
Camshaft Installation Advance = 0 deg
Intake Opening Angle = 23 deg BTDC
Intake Closing Angle = 59 deg ABDC
Exhaust Opening Angle = 63 deg BBDC
Exhaust Closing Angle = 23 deg ATDC
Intake Valve Lift = 0.462 in
Exhaust Valve Lift = 0.48015 in
Valve Overlap = 46 deg
================================================
OUTPUT
================================================
Engine Displacement = 202.76 in^3
Rod to Stroke Ratio = 1.51:1
Rod Angle = 19.36 deg
Resulting Deck Height = 2.394e-16 in
Squish Distance = 0.044 in
Static Compression Ratio = 10.0:1
Dynamic Compression Ratio = 8.41:1
Block: Stock C8 Block/pistons, C9-M head, 1.75/1.5 valves, dual spring, 1.65 RAU Rockers, port divider, direct mount Holley 4412-500, HEI w/20* advance, manifold vac, dual-out Arvinode exhaust, Clay Smith 264/274 110* installed w/ 4* advance, adjustable dual chain timing, C4 w/ shift kit, 3.20 (TBC) rear ratio, 9.44 SCR / 7.97 DCR

Build that Six with parts from http://www.vintageinlines.com

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Re: Final Dynamic Compression Ration Check Assistance

Post #3 by cr_bobcat » Fri May 10, 2019 3:15 pm

Minor correction. I forgot to adjust for the piston compression height. Most the new pistons come with a 1.500" compression height. The numbers don't actually change, but here is the output for the corrected calculation. This is with the same 0.030" overbore that I forgot to mention previously as well.

================================================
INPUT - BUILD PARAMETERS
================================================
Block Specifications:
Cylinder Bore = 3.71 in
Centerline to Deck Height = 7.808 in
Rod Length = 4.715 in
Stroke = 3.126 in
Piston Dish Volume = 0 cc
Piston Compression Height = 1.5 in
Cylinder Head Specifications:
Combustion Chamber Volume = 53 cc
Intake Valve Diameter = 1.8 in
Exhaust Valve Diameter = 1.5 in
Rocker Arm Ratio = 1.65:1
Cylinder Head Gasket Dimensions:
Gasket Diameter = 3.81 in
Gasket Crush Height = 0.044 in
Camshaft Specifications and Events:
Intake Duration = 262 deg
Exhaust Duration = 270 deg
Lobe Separation Angle = 110 deg
Cam Intake Lift = 0.28 in
Cam Exhaust Lift = 0.291 in
Ground-in Advance = 2 deg
Camshaft Installation Advance = 0 deg
Intake Opening Angle = 23 deg BTDC
Intake Closing Angle = 59 deg ABDC
Exhaust Opening Angle = 63 deg BBDC
Exhaust Closing Angle = 23 deg ATDC
Intake Valve Lift = 0.462 in
Exhaust Valve Lift = 0.48015 in
Valve Overlap = 46 deg
================================================
OUTPUT
================================================
Engine Displacement = 202.76 in^3
Rod to Stroke Ratio = 1.51:1
Rod Angle = 19.36 deg
Resulting Deck Height = 2.498e-16 in
Squish Distance = 0.044 in
Static Compression Ratio = 10.0:1
Dynamic Compression Ratio = 8.41:1
Block: Stock C8 Block/pistons, C9-M head, 1.75/1.5 valves, dual spring, 1.65 RAU Rockers, port divider, direct mount Holley 4412-500, HEI w/20* advance, manifold vac, dual-out Arvinode exhaust, Clay Smith 264/274 110* installed w/ 4* advance, adjustable dual chain timing, C4 w/ shift kit, 3.20 (TBC) rear ratio, 9.44 SCR / 7.97 DCR

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Re: Final Dynamic Compression Ration Check Assistance

Post #4 by cr_bobcat » Fri May 10, 2019 3:17 pm

And here is what I come up with if the machinist only does a 0.020" overbore for a 3.70" bore. Not significantly different, but here they are anyway :beer:

================================================
INPUT - BUILD PARAMETERS
================================================
Block Specifications:
Cylinder Bore = 3.7 in
Centerline to Deck Height = 7.808 in
Rod Length = 4.715 in
Stroke = 3.126 in
Piston Dish Volume = 0 cc
Piston Compression Height = 1.5 in
Cylinder Head Specifications:
Combustion Chamber Volume = 53 cc
Intake Valve Diameter = 1.8 in
Exhaust Valve Diameter = 1.5 in
Rocker Arm Ratio = 1.65:1
Cylinder Head Gasket Dimensions:
Gasket Diameter = 3.81 in
Gasket Crush Height = 0.044 in
Camshaft Specifications and Events:
Intake Duration = 262 deg
Exhaust Duration = 270 deg
Lobe Separation Angle = 110 deg
Cam Intake Lift = 0.28 in
Cam Exhaust Lift = 0.291 in
Ground-in Advance = 2 deg
Camshaft Installation Advance = 0 deg
Intake Opening Angle = 23 deg BTDC
Intake Closing Angle = 59 deg ABDC
Exhaust Opening Angle = 63 deg BBDC
Exhaust Closing Angle = 23 deg ATDC
Intake Valve Lift = 0.462 in
Exhaust Valve Lift = 0.48015 in
Valve Overlap = 46 deg
================================================
OUTPUT
================================================
Engine Displacement = 201.67 in^3
Rod to Stroke Ratio = 1.51:1
Rod Angle = 19.36 deg
Resulting Deck Height = 2.498e-16 in
Squish Distance = 0.044 in
Static Compression Ratio = 9.99:1
Dynamic Compression Ratio = 8.37:1
Block: Stock C8 Block/pistons, C9-M head, 1.75/1.5 valves, dual spring, 1.65 RAU Rockers, port divider, direct mount Holley 4412-500, HEI w/20* advance, manifold vac, dual-out Arvinode exhaust, Clay Smith 264/274 110* installed w/ 4* advance, adjustable dual chain timing, C4 w/ shift kit, 3.20 (TBC) rear ratio, 9.44 SCR / 7.97 DCR

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Re: Final Dynamic Compression Ration Check Assistance

Post #5 by Matthew68 » Fri May 10, 2019 3:42 pm

Steve - THANK YOU! Looks like we’re spot on.

In terms of the aluminum head, does the DCR ranges still apply as linked for the iron heads? Or do the ranges shift (up, I would assume)?

ci/CompressionR.html
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Re: Final Dynamic Compression Ration Check Assistance

Post #6 by Econoline » Fri May 10, 2019 3:53 pm

Looks like he may be using 2.5 pistons. If so they have a compression height of 1.556"

Edit: Never mind, I was thinking this was a 250, not a 200. It is 1.5 for the 2.3 flat tops.
Last edited by Econoline on Sun May 12, 2019 1:56 pm, edited 1 time in total.
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Re: Final Dynamic Compression Ration Check Assistance

Post #7 by wsa111 » Fri May 10, 2019 7:57 pm

Matthew68 wrote:Steve - THANK YOU! Looks like we’re spot on.

In terms of the aluminum head, does the DCR ranges still apply as linked for the iron heads? Or do the ranges shift (up, I would assume)?

https://fordsix.com/ci/CompressionR.html

The aluminium head can handle 1/2 higher compression than an iron head.
The best thing you can do is get rocker arms at least 1.6 or higher. The CI -VI head flows so much batter than an iron head.
You are leaving at least 15HP on the table with 1.5 rocker arms.
67 mustang,C-4, with mod. 80 hd, custom 500 cfm carb with annular boosters, hooker headers, dual exh.-X pipe, flowmaster mufflers, DSII dist. MSD-6al & MSD-Blaster 8252 Coil. Engine 205" .030" over with offset ground crank & 1.65 roller rockers. 9.5 comp., Isky 262 cam.
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Re: Final Dynamic Compression Ration Check Assistance

Post #8 by Matthew68 » Fri May 10, 2019 8:47 pm

wsa111 wrote:
Matthew68 wrote:Steve - THANK YOU! Looks like we’re spot on.

In terms of the aluminum head, does the DCR ranges still apply as linked for the iron heads? Or do the ranges shift (up, I would assume)?

ci/CompressionR.html

The aluminium head can handle 1/2 higher compression than an iron head.
The best thing you can do is get rocker arms at least 1.6 or higher. The CI -VI head flows so much batter than an iron head.
You are leaving at least 15HP on the table with 1.5 rocker arms.


Bill, I have 1.65 YT rockers I’ll be using.
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Re: Final Dynamic Compression Ration Check Assistance

Post #9 by pmuller9 » Fri May 10, 2019 9:58 pm

Take advantage of the heads breathing capability and run a larger cam.
Move up to the Schneider 270-80H
It will also drop the DCR to just under 8.2

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Re: Final Dynamic Compression Ration Check Assistance

Post #10 by wsa111 » Fri May 10, 2019 10:11 pm

pmuller9 wrote:Take advantage of the heads breathing capability and run a larger cam.
Move up to the Schneider 270-80H
It will also drop the DCR to just under 8.2

I agree & get the chamber cc's closer to 50.
67 mustang,C-4, with mod. 80 hd, custom 500 cfm carb with annular boosters, hooker headers, dual exh.-X pipe, flowmaster mufflers, DSII dist. MSD-6al & MSD-Blaster 8252 Coil. Engine 205" .030" over with offset ground crank & 1.65 roller rockers. 9.5 comp., Isky 262 cam.
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Re: Final Dynamic Compression Ration Check Assistance

Post #11 by Matthew68 » Sat May 11, 2019 8:08 am

Jerry and I decided on that cam since I am mostly using this car as a cruiser and not really a racer. RPM range matches my street driving with limited highways.

If I take the head down to 50cc my SCR will jump. I’m already at 10:1 with 53cc and flat top pistons.
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Final Dynamic Compression Ration Check Assistance

Post #12 by chad » Sat May 11, 2019 9:14 am

almost seems like tryin to choke dwn the advantages ofa alu head'n that intake.

I remember U said a trailer'n hi altitude drivin, no? Also not-quite-DD but used like one (sits w/o use then driven), yes?
What is the rest of the picture?
"Big thing is only make one change at a time. Change 2 or more things at a time it becomes difficult to figure which change helped or hurt" turbo2256b » 1/16/2017
Chad - '70 LUEB on '77 frame (i.e. PS, D44, trapezoidal BB 9", 4.11), 250, NV 3550 & DSII to B transplanted, "T" D20/PTO, 2" SL, 1" BL, 4 discs, 33"X15", tool boxes, etc. Seeking: Hydraulic gear motor for Koenig pto. chrlsful@aol.com (413) 259-1749

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Re: Final Dynamic Compression Ration Check Assistance

Post #13 by Matthew68 » Sat May 11, 2019 11:47 am

chad wrote:almost seems like tryin to choke dwn the advantages ofa alu head'n that intake.

I remember U said a trailer'n hi altitude drivin, no? Also not-quite-DD but used like one (sits w/o use then driven), yes?
What is the rest of the picture?


What do you mean trying to choke down? 10:1 compression and 1.65 rockers with a decent cam...not sure what I’m choking down and still have it for the style of street driving I’m doing.

No trailer hauling and no altitude issues. I’m about 450’ of elevation with just stop and go traffic mostly. Not a daily driver, maybe take the car out 1-2 times a week depending on the weather in the Midwest (Ohio).
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Re: Final Dynamic Compression Ration Check Assistance

Post #14 by chad » Sat May 11, 2019 12:06 pm

sorry, must needa read whole threads
looked like leavin some on the tabel mabel,
("... increased LSA's that bleed off cylinder pressure...")
back to my nap
:(
Last edited by chad on Sat May 11, 2019 1:26 pm, edited 1 time in total.
"Big thing is only make one change at a time. Change 2 or more things at a time it becomes difficult to figure which change helped or hurt" turbo2256b » 1/16/2017
Chad - '70 LUEB on '77 frame (i.e. PS, D44, trapezoidal BB 9", 4.11), 250, NV 3550 & DSII to B transplanted, "T" D20/PTO, 2" SL, 1" BL, 4 discs, 33"X15", tool boxes, etc. Seeking: Hydraulic gear motor for Koenig pto. chrlsful@aol.com (413) 259-1749

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Re: Final Dynamic Compression Ration Check Assistance

Post #15 by CNC-Dude » Sat May 11, 2019 12:26 pm

Matthew68 wrote:Jerry and I decided on that cam since I am mostly using this car as a cruiser and not really a racer. RPM range matches my street driving with limited highways.

If I take the head down to 50cc my SCR will jump. I’m already at 10:1 with 53cc and flat top pistons.


The DCR is more meaningful and what the engine actually sees based on the cam selection and other variables. The static compression is not really relevant in today's world because it doesn't take into account more meaningful engine parameters and data. Many newer factory performance V engines have static compressions of 11:1 or more and still use pump gas. Its all in the cam selection and cam timing that makes the engine more manageable. If you ever see in a cams description that increased compression is required, its because it usually has increased LSA's that bleed off cylinder pressure, and needs higher compression to help compensate, but can still has low enough DCR to be driveable on pump gas. So don't let the static compression number fool you as to the engines true rating.
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Re: Final Dynamic Compression Ration Check Assistance

Post #16 by wsa111 » Sat May 11, 2019 1:37 pm

Make sure you degree the cam. In your usage i would advance it at least 2 degrees.
67 mustang,C-4, with mod. 80 hd, custom 500 cfm carb with annular boosters, hooker headers, dual exh.-X pipe, flowmaster mufflers, DSII dist. MSD-6al & MSD-Blaster 8252 Coil. Engine 205" .030" over with offset ground crank & 1.65 roller rockers. 9.5 comp., Isky 262 cam.
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Re: Final Dynamic Compression Ration Check Assistance

Post #17 by Matthew68 » Sat May 11, 2019 1:40 pm

CNC-Dude wrote:
Matthew68 wrote:Jerry and I decided on that cam since I am mostly using this car as a cruiser and not really a racer. RPM range matches my street driving with limited highways.

If I take the head down to 50cc my SCR will jump. I’m already at 10:1 with 53cc and flat top pistons.


The DCR is more meaningful and what the engine actually sees based on the cam selection and other variables. The static compression is not really relevant in today's world because it doesn't take into account more meaningful engine parameters and data. Many newer factory performance V engines have static compressions of 11:1 or more and still use pump gas. Its all in the cam selection and cam timing that makes the engine more manageable. If you ever see in a cams description that increased compression is required, its because it usually has increased LSA's that bleed off cylinder pressure, and needs higher compression to help compensate, but can still has low enough DCR to be driveable on pump gas. So don't let the static compression number fool you as to the engines true rating.



That’s fair, but today’s engines have things like variable valve timing and other features that can help deal with higher SCR that our little old sixes can’t replicate.

But if I’m going to go to 50cc chambers my SCR becomes 10.54:1 and my DCR becomes 8.81:1. Do I need that high for a cruiser on 91 pump gas? Do I risk pinging. I’m asking bc you guys are smarter than me and I’m looking for advice. This is going to be a grocery getter, date night, etc. I’m not looking to drag race or street race whatsoever.
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Re: Final Dynamic Compression Ration Check Assistance

Post #18 by CNC-Dude » Sat May 11, 2019 2:35 pm

With the extra bump in compression, the larger cam that was suggested can lower the DCR lower. So can advancing/regarding the current cam. Do you have the actual cam opening and closing events to calculate the DCR accurately?
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Re: Final Dynamic Compression Ration Check Assistance

Post #19 by pmuller9 » Sat May 11, 2019 5:37 pm

Matthew68 wrote:But if I’m going to go to 50cc chambers my SCR becomes 10.54:1 and my DCR becomes 8.81:1. Do I need that high for a cruiser on 91 pump gas? Do I risk pinging. I’m asking bc you guys are smarter than me and I’m looking for advice. This is going to be a grocery getter, date night, etc. I’m not looking to drag race or street race whatsoever.

You are correct in being concerned about increasing the SCR any higher than 10:1 with a resulting 8.4 DCR.
There comes a point where you have to back off ignition timing and richen the mixture to prevent detonation which decreases power over having a lower compression having and some margin for tuning.
If you have to detune it will also affect gas mileage.

I feel that an 8.4 DCR is on the high side.
I would polish the combustion chambers smooth and install the cam straight up for an 8.3 DCR.

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Re: Final Dynamic Compression Ration Check Assistance

Post #20 by CNC-Dude » Sat May 11, 2019 8:41 pm

For the last few years, I have been heavily involved with quite a few LS racers and have been performing a lot of custom mods for them. I thought I remembered you saying you were using both 91 and 93 octane gas, so if you pushed your DCR into the upper 8's, you would be fine with that. The LS guys are running 8.8-8.9 DCR with 93 octane and aluminum heads comfortably with their combos. They also are running as high as 8.5 DCR with 91 octane. So if you are considering only 91 octane, then I'd agree with pmuller in that you are pushing the high side of 91 octane and should stay where you are.
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Re: Final Dynamic Compression Ration Check Assistance

Post #21 by Matthew68 » Sat May 11, 2019 9:37 pm

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?
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Re: Final Dynamic Compression Ration Check Assistance

Post #22 by Econoline » Sat May 11, 2019 9:46 pm

Ethanol free is always better fuel, especially with a carb and heat soak ect
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Re: Final Dynamic Compression Ration Check Assistance

Post #23 by pmuller9 » Sat May 11, 2019 9:59 pm

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.

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Re: Final Dynamic Compression Ration Check Assistance

Post #24 by Matthew68 » Sat May 11, 2019 10:13 pm

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?
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Re: Final Dynamic Compression Ration Check Assistance

Post #25 by pmuller9 » Sat May 11, 2019 11:19 pm

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.

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Re: Final Dynamic Compression Ration Check Assistance

Post #26 by xctasy » Sat May 11, 2019 11:37 pm

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.
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Re: Final Dynamic Compression Ration Check Assistance

Post #27 by Matthew68 » Sun May 12, 2019 8:28 am

pmuller9 wrote: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).
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Re: Final Dynamic Compression Ration Check Assistance

Post #28 by CNC-Dude » Sun May 12, 2019 10:04 am

It will still have to be degreed to assure accuracy because of machining tolerances/errors in the timing set gears and crank keyway.
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Re: Final Dynamic Compression Ration Check Assistance

Post #29 by pmuller9 » Sun May 12, 2019 11:36 am

Matthew68 wrote: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

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Re: Final Dynamic Compression Ration Check Assistance

Post #30 by Phase3 » Sun May 12, 2019 1:28 pm

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.
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Re: Final Dynamic Compression Ration Check Assistance

Post #31 by Econoline » Sun May 12, 2019 2:02 pm

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.
It ain't gonna fix itself

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Re: Final Dynamic Compression Ration Check Assistance

Post #32 by 62Ranchero200 » Thu May 16, 2019 8:08 am

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
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Re: Final Dynamic Compression Ration Check Assistance

Post #33 by CNC-Dude » Thu May 16, 2019 9:53 am

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.
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Final Dynamic Compression Ration Check Assistance

Post #34 by chad » Thu May 16, 2019 12:26 pm

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'...
"Big thing is only make one change at a time. Change 2 or more things at a time it becomes difficult to figure which change helped or hurt" turbo2256b » 1/16/2017
Chad - '70 LUEB on '77 frame (i.e. PS, D44, trapezoidal BB 9", 4.11), 250, NV 3550 & DSII to B transplanted, "T" D20/PTO, 2" SL, 1" BL, 4 discs, 33"X15", tool boxes, etc. Seeking: Hydraulic gear motor for Koenig pto. chrlsful@aol.com (413) 259-1749

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Re: Final Dynamic Compression Ration Check Assistance

Post #35 by Matthew68 » Tue Jul 09, 2019 8:53 am

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
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chad
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Re: Final Dynamic Compression Ration Check Assistance

Post #36 by chad » Tue Jul 09, 2019 9:27 am

I've not been there 4 awhile but most answ R at above "tech archive":

ci/SparkTech.html

ci/CamDegree.html

ci/SelectCam.html

and so on...
"Big thing is only make one change at a time. Change 2 or more things at a time it becomes difficult to figure which change helped or hurt" turbo2256b » 1/16/2017
Chad - '70 LUEB on '77 frame (i.e. PS, D44, trapezoidal BB 9", 4.11), 250, NV 3550 & DSII to B transplanted, "T" D20/PTO, 2" SL, 1" BL, 4 discs, 33"X15", tool boxes, etc. Seeking: Hydraulic gear motor for Koenig pto. chrlsful@aol.com (413) 259-1749

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Re: Final Dynamic Compression Ration Check Assistance

Post #37 by Econoline » Tue Jul 09, 2019 11:28 am

Advancing the cam will raise the DCR, retarding it will lower it.
It ain't gonna fix itself

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chad
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Final Dynamic Compression Ration Check Assistance

Post #38 by chad » Tue Jul 09, 2019 12:14 pm

"...They claim to grind 2 degrees advance in. ..."
my understanding - they do anything U want for same price
"Big thing is only make one change at a time. Change 2 or more things at a time it becomes difficult to figure which change helped or hurt" turbo2256b » 1/16/2017
Chad - '70 LUEB on '77 frame (i.e. PS, D44, trapezoidal BB 9", 4.11), 250, NV 3550 & DSII to B transplanted, "T" D20/PTO, 2" SL, 1" BL, 4 discs, 33"X15", tool boxes, etc. Seeking: Hydraulic gear motor for Koenig pto. chrlsful@aol.com (413) 259-1749

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Re: Final Dynamic Compression Ration Check Assistance

Post #39 by cr_bobcat » Tue Jul 09, 2019 11:54 pm

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.
Block: Stock C8 Block/pistons, C9-M head, 1.75/1.5 valves, dual spring, 1.65 RAU Rockers, port divider, direct mount Holley 4412-500, HEI w/20* advance, manifold vac, dual-out Arvinode exhaust, Clay Smith 264/274 110* installed w/ 4* advance, adjustable dual chain timing, C4 w/ shift kit, 3.20 (TBC) rear ratio, 9.44 SCR / 7.97 DCR

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