engine advice

[Timnmelinda]

From my decipher this thread You have told me what exactly I had just purchased

"looks like you have a 1968 200 block with a 1970 head."
Thank You grocery getter, fo rthis help.

If you saw this thread the engine was supposed to have been rebuilt 10,000 miles ago. So the plan is to pull the pan and see how things look.
If it looks like a fresh rebuild, I plan to change cam and timing chain and put it in. My first question is without dissasembley is their an accurate way to determine what compression this engine was set up with?

Now If the engine does not look fresh from rebuild, I am going to do the whole thing, bore, new masterkit, a cam/lifter/timing chain upgrade. What I am after is a nice running reliable package that if I can control throttle, get reasonable milage. I am hoping to measurably increase pep in the process between the upgrade in gear ratio and the planned enginge upgrades I think it should fill my needs.

Rebuild or not, I am planning the following combination

200 possible bored out
I believe my compression goal is in the 9.0 to 1 range.
32/36 or 350 holley 2 barrel, (I allready have 32/36)
one of the following cams:
Classic Inlines - Clay Smith Cams - USA
264S-110: 264/264 - 214/214 - .450/.450 - 110* - 1400-5000
264S-112: 264/264 - 214/214 - .450/.450 - 112* - 1600-5200
DUI Ignition (I allready have)
Split headers feeding 2 inch dual exhausts turbo mufflers with crossover
(allready have)
Auto trans rebuilt w shift kit
8 inch rear 3.25 ratio

I would love to run offy 3x1 but for simple reliability I feel I am better with 2 barrel

If I have to redo "new engine" I am going to get 3 angle valve job, hardened seats, etc. If I am doing this I will also direct mount carb as well.
For what I am after should I go after a 78 to 1980 head, will it really make much difference and be worth the added expense of getting another head, considering what I am after? Or should I just use the 1970 head?

Yes I would love nothing better than to have one of Mike's new heads, but economics will have to put that into the hopefully down the road category.

Any other suggestions or reccomendations, or modifications for my package?
Anything I am not thinking of that I should be?

While the pan is off, should I install new oil pump as a precaution?

I was also looking at this cam
268D-108: 268/274 - 208/218 - .455/.480 - 108* - 1200-4800
But it seems from much I have read on here The 264s are highly spoken of.

Looking forward to your thoughts
Tim

 

[rocklord]

A compression check would give you a ballpark figure of the CR. Just divide the readings by 14.8.

135psi / 14.8 = 9.12 CR

 

[FalconSedanDelivery]

Where did that math come from ??

 

[wsa111]

I have a compression ratio of 10.25 & my cranking compression is 190#

This is with a camshaft @224 degrees @ .050.

The cranking compression is dependent on the intake closing.

That formula is bogus. The camshaft is the X factor. Bill

 

[fordconvert]

With that formula my well used 200 is well over 12:1. It CC's and measures out to almost 8.2:1 (due to some odd pistons and machine work).

 

[rocklord]

http://en.wikipedia.org/wiki/Compression_ratio


Measuring the compression pressure of an engine, with a pressure gauge connected to the spark plug opening, gives an indication of the engine's state and quality.

If the nominal compression ratio of an engine is given, the pre-ignition cylinder pressure can be estimated using the following relationship:

p = p0 x Cr^y

where p0 is the cylinder pressure at bottom dead center (BDC) which is usually at 1 atmosphere, Cr is the compression ratio, and γ is the ratio of specific heats of the working fluid, which is about 1.4 for air, and 1.3 for methane-air mixture.

For example, if an engine running on gasoline has a compression ratio is 10:1, the cylinder pressure at top dead center (TDC) is

p(TDC) = (1 bar) x 10^1.4 = 25.1 bar

This figure, however, will also depend on cam (i.e. valve) timing. Generally, cylinder pressure for common automotive designs should at least equal 10 bar, or, roughly estimated in pounds per square inch (psi) as between 15 and 20 times the compression ratio, or in this case between 150 psi and 200 psi, depending on cam timing. Purpose-built racing engines, stationary engines etc. will return figures outside this range.

Factors including late intake valve closure (relatively speaking for camshaft profiles outside of typical production car range, but not necessarily into the realm of competition engines) can produce a misleadingly low figure from this test. Excessive connecting rod clearance, combined with extreme oil pump out (rare but not impossible) can sling enough oil to coat the cylinder walls with enough oil to facilitate reasonable ring seal artificially give a misleadingly high figure, on engines with compromised ring seal.

This can actually be used to some slight advantage. If a compression test does give a low figure, and it has been determined it is not due to intake valve closure/camshaft characteristics, then one can differentiate between the cause being valve/seat seal issues and ring seal by squirting engine oil into the spark plug orifice, in a quantity sufficient to disperse across the piston crown and the circumference of the top ring land, and thereby effect the mentioned seal. If a second compression test is performed shortly thereafter, and the new reading is much higher, it would be the ring seal that is problematic, whereas if the compression test pressure observed remains low, it is a valve sealing (or more rarely head gasket, or breakthrough piston or rarer still cylinder wall damage) issue.

If there is a significant (> 10%) difference between cylinders, that may be an indication that valves or cylinder head gaskets are leaking, piston rings are worn or that the block is cracked.

If a problem is suspected then a more comprehensive test using a leak-down tester can locate the leak.

 

[CZLN6]

Howdy All:

Thanks Dan for sharing that info. Just be clear that you are talking about cylinder pressure, not compression ratio. Another variable would be the elevation at the locale of the pressure test.

Tim- As far as a static compression ratio without disassembly, I'm afraid you're out of luck. The formula Dan shared will give an indication of engine efficiency if you're able to turn it over to get cylinder pressure readings. A pressure check of each cylinder, for comparison will give you another glimpse at the condition of this engine.

The only way to determine CR is to disassemble and to carefully measure all of the critical deminsions and do the math.

About the only advantage of the later head over your '70 would be hardened valve seats, but you can have them installed in the head you have. The later head will have a larger diameter carb hole, but if you're modifying for a direct mount two barrel that won't be an issue. The last issue is intake tract volume. The later head will have almost 200 ccs greater internal volume. That would be a slightl asset at higher rpms. Given your criteria, that's not much of an issue.

I'd like to see you use the dual pattern cam from Mike. I have a 260 single pattern cam, which works fine in similar uses as you're planning. But, I'd like to hear from some actual users of the dual pattern cam for comparison. I like the theory and concepts behind a dual pattern cam.

Also, please consider back-cutting the intake valves, lightening the reciprocating mass, and balancing the whole assembly. ARP rod bolts would be cheap insurance and worth considering. Decking the block to zero and using one of Mike's new head gaskets @ .038" and then unshrouding the valves to attain your goal CR will be worth the time and effort. IF you do maximize combustion efficiency you could realistically go for a higher CR goal- say 9.5:1 without much worry.

That's my two cents, for what it's worth.

Adios, David