Help finding my compression ratio.

65coupei6

Famous Member
Staff member
VIP
The time has almost come to swap the OZ250 head with the CI aluminum head.
I finally cc'd the aluminum head @ 54cc
I don't remember what pistons are installed. Most likely sealed power dish.
Engine has been bored over .030

I am not sure which head gasket to use felpro or Corteco. I do have a c9oz-6079-a gasket set.

I don't think the block has been decked. It's been awhile.

Any wisdom or guidance is appreciated.
 

Attachments

  • IMG_20180201_154416.jpg
    IMG_20180201_154416.jpg
    3.1 MB · Views: 232
Use the Carquest Victor headgasket. It is .004" thinner than the Felpro. Advance Auto Parts can get the gasket.
Zero deck the block. Get the chambers down to 50cc's. That will get you close to 9.5-1.
I don't know how far you want to go, but flat top pistons will get you close to 10.5 area.
The aluminium head can handle higher compression than the Iron head.
Thats about the limit cause you guys on the west coast are stuck with 91 octane fuel.
You need 1.65 rocker arms to get your lift as high as possible. The CI head flows all the way up to .600" lift.
If you go with flat top pistons, upgrade the camshaft to the Schneider 270-80H.
Manual trans 110 L/C, C-4 112 L/C.
Now you will need more than the 7448-350 Holley.
Get your wallet out.
 
What are your plans with the OZ250 head? I am interested if you are not going to use it!

Edit: sorry, not sure why this was posted twice. Can’t seem to delete this one!
 
65coupei6":3m6vpsl2 said:
The time has almost come to swap the OZ250 head with the CI aluminum head.
I finally cc'd the aluminum head @ 54cc
I don't remember what pistons are installed. Most likely sealed power dish.
Engine has been bored over .030
I am not sure which head gasket to use felpro or Corteco. I do have a c9oz-6079-a gasket set.
I don't think the block has been decked. It's been awhile.
Any wisdom or guidance is appreciated.

Tried an on-line caculator?
Hit up cr_bobcat yet (may B a PM?)

static'n dynamic difference too don't 4get...
good luck!
 
65coupei6":2397pgjp said:
The time has almost come to swap the OZ250 head with the CI aluminum head.
I finally cc'd the aluminum head @ 54cc
I don't remember what pistons are installed. Most likely sealed power dish.
Engine has been bored over .030

I am not sure which head gasket to use felpro or Corteco. I do have a c9oz-6079-a gasket set.

I don't think the block has been decked. It's been awhile.

Any wisdom or guidance is appreciated.

With 3.710 bore
3.126 stroke
Sealed Power .030 over Pistons have a 1.500 pin height (stock pin height was 1.511) so an extra .011 down the hole if block hasn't been decked. They have a 2.320 diameter dish .105 depth about +6.5 CC dish volume?
Deck clearance is .030 (down the hole) stock is .019
FelPro head gasket .050
C.I. Aluminum head 54 CC
So I get an 8.4 to 1 compression ratio! You be giving up quite a lot of compression from the optional, good luck (y) :nod:
 
Howdy Back Marco and All:

Are you going to rebuild the short block too? What cam will you be using? What is the intended us for this engine? Bill seems to be more in-the-know about what you have and your future plans so maybe I'm chewing old cabbage. If I am, sorry. Please bring me up to date?

Thanks.

Adios, David
 
Thanks for all the input.

This will be a street motor. I was hoping to use my current cam. Schneider 260 intake / 270 exhaust, 110 lobe sep. , .420 /.440 lift.

Instead of the YT 1.65 rockers i was going for the 1.6's

I also have a Fitech which will replace the Holly 350. Not, sure about a total rebuild. I still have to find someone to do the work. Not enough room to do a rebuild in my garage. I already had a tight squeeze doing all my suspension work and brakes.

Also, i will be doing a compression check this weekend. I am burning oil thru the PCV. Not sure if it is the valves or rings. If it is the rings, i might as well swap to the 2.3 HSC pistons.

This is all in front of a C4 with an 8" 3.0 tracloc.
 
Eric m":33aqs4z6 said:
What hp did you have with the oz head and what do you expect with the aluminum head?

I do not know what to expect with the aluminum head.

But for reference. I dyno'ed the stock 200. It came up around 80 rwhp. After the Oz250 head, cam, single out headers, DSII (not recurved) Holley 350. It came up to 135 rwhp.

Now this is with two different dyno machines. So, the results may not be perfect. I have to go look for my old dyno sheets.
After my new build I will bring it back for another session. Hopefully the last place that did it is still in business.
 
65coupei6":18qtk74h said:
Eric m":18qtk74h said:
...for reference. I dyno'ed the stock 200. It came up around... After the Oz250 head... It came up to...
Now this is with two different dyno machines. So, the results may not be perfect. I have to go look for my old dyno sheets.
After my new build I will bring it back for another session. Hopefully the last place that did it is still in business.

Hopefully this is not too personal a Q but: how much have these sessions cost?
How many runs at each session R allowed?

Thank you, good luck w/this newer build!
 
chad: The first time i did the dyno was with a Mustang Club I belong to. So they gave us a group discount. $60.
The second time, with the Oz head, was $120. Both were for 3 pulls. The second time i did a little tuning.
 
thank you
(WoW, that;s nice...twice that here, but guy comes 2 U).
 
Update:

Well i found a machine shop. They will pull the engine and rr it. I am on his waiting list. Nice clean and organized shop. He said his dad used to build 200's and 250's back in the day. Lots of equipment for everything. He showed me some Nascar heads, one off mopar heads. He was also showing me some 5 and 6 angle valve jobs, etc...

Now to come up with the $$$.

Plus they also have a chassis dyno!

I will probably start a new thread to cover the build, parts, etc...
 
Been busy lately. I'll try running your numbers later today and see what I come up with. That Pat Kelly article looks like he's using the exact same research article I found for computing DCR. The wording is extremely close.
 
With 3.710 bore
3.126 stroke
Tempo HSC .030 over flat top pistons, 1.500 pin height
Deck Recess 0.030
FelPro head gasket .050 compressed thickness
C.I. Aluminum head 54 CC

Compression ratio calculates to 9.1:1.

Zero the deck, and the compression jumps to 9.75:1

This compression is manageable with the aluminum head.

Hope this helps.
 
So I think I got the block and head data in there correctly. I don't know about the camshaft profile though. I assumed you have a 110* lobe separation angle. Didn't even take a guess at the lift numbers so I've left in the ones I have on my cam.

================================================
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 = 6.5 cc
Piston Compression Height = 1.5 in
Cylinder Head Specifications:
Combustion Chamber Volume = 54 cc
Intake Valve Diameter = 1.76 in
Exhaust Valve Diameter = 1.5 in
Rocker Arm Ratio = 1.6:1
Cylinder Head Gasket Dimensions:
Gasket Diameter = 3.81 in
Gasket Crush Height = 0.042 in
Camshaft Specifications and Events:
Intake Duration = 260 deg
Exhaust Duration = 270 deg
Lobe Separation Angle = 110 deg
Cam Intake Lift = 0.2946 in
Cam Exhaust Lift = 0.3 in
Ground-in Advance = 0 deg
Camshaft Installation Advance = 0 deg
Intake Opening Angle = 20 deg BTDC
Intake Closing Angle = 60 deg ABDC
Exhaust Opening Angle = 65 deg BBDC
Exhaust Closing Angle = 25 deg ATDC
Intake Valve Lift = 0.47136 in
Exhaust Valve Lift = 0.48 in
Valve Overlap = 45 deg
================================================
OUTPUT
================================================
Engine Displacement = 202.76 in^3
Rod to Stroke Ratio = 1.51:1
Rod Angle = 19.36 deg
Resulting Deck Height = 0.03 in
Squish Distance = 0.072 in
Static Compression Ratio = 8.51:1
Dynamic Compression Ratio = 7.11:1
 
A 0.030" deck mill will get you here. Note the ~0.040" squish. This puts you in the right zone. I'd have to go back and read again on what is allowable for aluminum vs cast iron. You might be able to go with even further of a mill and have the piston reach TDC slightly proud of the deck surface.

================================================
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 = 0.042 in
Static Compression Ratio = 9.10:1
Dynamic Compression Ratio = 7.59:1

A 0.030" deck mill and 50 cc chambers (~0.020 head mill) gets you here. The squish distance will obviously remain the same, but you get a bump in compression ratio.

================================================
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 = 0.042 in
Static Compression Ratio = 9.60:1
Dynamic Compression Ratio = 8.00:1
 
Well, I guess thee machine shop did not want any new work. Called them and it always went to full voicemail boxes. So i could not leave a message. When I finally got a hold of them. They said oh yeah. We forgot. Call us back.

So, I found a new place. Actually, a Mustang shop who uses and outside machine shop. But, the Mustang place does the tear down and reassemble themselves.

I dropped it off Saturday. They are closed Sunday & Monday. But, I got a call already today saying they already pulled the motor and dropped it off at the machine shop.

They said it was already bored over .040 not the.030 I thought. I am pretty sure it is ok to go up to .060. What do you guys think?
 
Back
Top