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Unread 04-08-2007   #1 (permalink)
HalfPackLX is offline Apprentice

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Default what compression ratio is my 1989 Mustang 2.3l?

What is the compression ratio on my 1989 2.3l mustang?
How much do i need to have the head milled for 10:1 compression?
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Unread 04-08-2007   #2 (permalink)
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Bone stock most EFI 2.3s that were non-turbo had about 9:1 to 9.5:1 compression depending on year.

As far as how far to have it milled, you'd have to talk to a machine shop.
 
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Unread 04-11-2007   #3 (permalink)
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Thanks, for the info. I thought it was around 9:1. When I bring the engine in for machining I'll just tell them what I want.

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Unread 04-11-2007   #4 (permalink)
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OK, I'll take a stab at this one, just follow the bouncing ball....LOL

Basicly, "static" compression ratio is the ratio of the "swept volume"(stroke) divided by the "volume at TDC". Also taken in consideration is the "head gasket volume", "dish/dome volume"(dish is positive volume, dome is negative), "head volume", and "deck volume".

Assuming your stock compression ratio is 9.0-1 and you have a 2300 cc or 140cuin motor and "deck volume" is the only thing you want to changeby shaving the head....

Each cyl displaces 35 cubic inches. Using the above formula (and knowing the bore and stroke of a 2.3l/140cuin is 3.44" x 3.70") we can calculate the "volume at TDC".

"volume at TDC"= "swept stroke volume"(pi X r2 X H) divided by Compression ratio
= [3.1416 x (1.72" x 1.72") x 3.70"] / 9.0
=3.82 cuin "volume at TDC" stock 9.0-1 compression ratio (A)

to get the "volume at TDC" in a 10.0-1 compression ratio, substitute 10.0 into the formula
= [3.1416 x (1.72" x 1.72") x 3.70"] /10.0
= 3.43 cuin "volume at TDC" with 10.0-1 compression ratio (B)

to get to 10.0-1 compression ratio, substract B from A and you need to lose .39 cuin.

By shaving the head, the only place you can "lose" "volume at TDC" is in the "deck volume"...

"Deck volume is (pi x r2 x "deck height" Or "deck clearance")

Now, we can substitute and calculate how much "deck height" you must lose.

[3.1416 x (1.72" x 1.72")] x "deck height"= .39 cuin
"deck height"= .39 cuin / [3.1416 x (1.72" x 1.72")]
=.39 cuin / 9.29inin
=0.041981"
or rounded off, "deck height" loss to achieve 10.0-1 compression ratio from 9.0-1 is 0.042" . (or 1.1mm for the metric geeks)

A shop manual is necessary to know how much "deck height" can be safely removed from a 2.3l. .042" is quite a bit and you may wind up "out of service limits". If you do have it shaved, be sure to turn the motor over by hand after assembly to insure proper piston/valve clearance. Also, make sure the head bolts (I assume the 2.3l has head bolts and not studs) are not "bottoming out" to insure a good head gasket seal.

Note: As I said before, this will give you the "static" compression ratio. You must also take your cam into consideration because extended valve opening/overlaps can reduce your "effective compression ratio". "Static" compression ratio and cam choice must be considered as a system!

good luck!

Hope I ain't bored everyone by doing the calculations (which I did not double check) on line, but I aint had that much fun in years and it shore brought back memories.........

Memories of when I didn't check piston to valve clearance by hand before firing off an engine.........
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Unread 04-14-2007   #5 (permalink)
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well thanks for all the calculations. I should copy it to a word document so I don't loss the info. I will have to think it over and do the calcs. I do plan on putting a higher lift cam in it.
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Unread 04-19-2007   #6 (permalink)
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Please notice I said....Assuming your stock compression ratio is 9.0-1...

Do not take these figures litteraly. It is to only show you how to calculate amount of material to be removed. Since you are adding a cam into the mix, I would only remove enough material to bring the head to factory specs (flat) and think about increasing the compression ratio in another fashion......such as dish/dome pistons. You can also add a stoker crank, but you would probably have to have some machining on the block to create rod clearances. Either way, be sure to check piston-valve clearances. I think I stated in another thread that .100" piston-valve clearance for straight shifts and .070" for automatics. (I will check on myself there). The extra clearance for the straights is that if you miss a shift and the valves float, you won't wind up with an oil pan full of scrap metal.
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Unread 04-19-2007   #7 (permalink)
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yeah I figured I'd find out my compression for sure first then do the math. I will be buying forged pistons. Probably from racer walsh. So I may as well call them when I'm ready to buy and ask them about what they know also. They deal with a lot of 2.3l and 2.5l setups.
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