Compression

[sfx66]

Getting ready to buy a motor. Can someone let me know what the compression should be on a good healthy 200 motor. The readings were
140, 140, 142, 138, 145, 150, but this was with throttle closed. He re did with throttle open and added 52 more pounds on the #1 cylinder up to 192. Does this make any sense if the throttle is opened or closed.

Thank you

 

[Bort62]

If the throttle is closed, it may restrict the amount of air that is avaliable to the engine while cranking. This can lower overall #'s.

Those numbers sound reasonable. What is more important than the absolute value of the numbers is their relative proximity to each other. Those numbers appear pretty good to me (for a used motor).

 

[deebee53]

If the throttle is closed, it may restrict the amount of air that is avaliable to the engine while cranking. This can lower overall #'s.

Those numbers sound reasonable. What is more important than the absolute value of the numbers is their relative proximity to each other. Those numbers appear pretty good to me (for a used motor).

+1

 

[Bort62]

And welcome to the forum!

I apologize in advance if I may hurt your feelings at some point in the future

 

[CZLN6]

Howdy Back sfx66:

THe advertized compression ratios for 200 sixes ranged from 9.2:1 in 1965 to 8:1 in 1980. To be more specific, I'd need the year of the engine. Casting codes of the block and the cylinder head are more exact.

Guessing from your id, a 1966 200 is rated at 9.2:1 by the factory.

Welcome to the FORUM!!!

Adios, David

 

[sfx66]

Howdy Back sfx66:

THe advertized compression ratios for 200 sixes ranged from 9.2:1 in 1965 to 8:1 in 1980. To be more specific, I'd need the year of the engine. Casting codes of the block and the cylinder head are more exact.

Guessing from your id, a 1966 200 is rated at 9.2:1 by the factory.

Welcome to the FORUM!!!

Adios, David

I do not have that information yet.. but what does your compression numbers mean. I was asking per cylinder, not overall.

 

[Bort62]

David's #'s are compression ratio, which very very loosely correlates with cranking pressure, which is what you are measuring.

Very loosely almost to the point of not.

 

[BIGREDRASA]

The Factory Shop Manual for 1966 lists pressures from 155 to 195 PSI, with an allowable variance of 20 PSI between cylinders. You might try taking new readings with the throttle set wide open, & see what difference that makes.

 

[addo]

Were the compression numbers tested cold?

Compression should be measured hot. By that, I mean pre-running the engine up to where the thermostat is fully open.

This is assuring all parts are expanded to the running dimensions and therefore sealing is at a "normal" level.

All gauges barring extremely high-end ones, have a degree of inaccuracy in the readings. Use them as a guideline, and a good comparative indicator of engine health.

 

[sfx66]

Were the compression numbers tested cold?

Compression should be measured hot. By that, I mean pre-running the engine up to where the thermostat is fully open.

This is assuring all parts are expanded to the running dimensions and therefore sealing is at a "normal" level.

All gauges barring extremely high-end ones, have a degree of inaccuracy in the readings. Use them as a guideline, and a good comparative indicator of engine health.

I'm not sure. The test was redone on #1 cylinder and it gain 52 pounds of pressure up to 192 from 140. so I would assume other would be in this range as well with the throttle open. I'm just trying to determine where this motor is. It runs good.. I just am not looking to rebuild a motor at the moment. Just would like a plug/play. The motor runs strong and accelerates good. It is believed to only have approx. 30k on it. since the rebuild. Is that good for these motors.

 

[60s Refugee]

Those compression numbers are actually pretty good.

Harry

 

[BIGREDRASA]

All things (cyliders) being nearly equal: Looking Good!

 

[Patrick66]

And welcome to the forum!

I apologize in advance if I may hurt your feelings at some point in the future

bort is out resident hater :mrgreen:

jfwy

 

[sfx66]

And welcome to the forum!

I apologize in advance if I may hurt your feelings at some point in the future

bort is out resident hater :mrgreen:

jfwy

So I should just ignore responses I see from him then. No seriously guys., I think I'm ok and will buy the motor. Just did not want something that's gonna need a rebuild. I don't know if tested hot or cold. I know the throttle was closed the first go around.. and the throttle was opened on the re-test of #1 cylinder.. which boosted psi by 52 points. So, maybe were ok considering.

What would the numbers be on a fresh rebuild. That's what I was hoping to get.

 

[Patrick66]

So I should just ignore responses I see from him then.

no, he gives good advice.

you can do another test with the throttle open, but considering the results from the first time, i think your ok anyways.

 

[wallaka]

So I should just ignore responses I see from him then.

no, he gives good advice.

you can do another test with the throttle open, but considering the results from the first time, i think your ok anyways.

He gets hated on because he doesn't BS around. I like it, but some folks like to have their hands held.

 

[Bort62]

Those #'s would be more than enough to make me feel comfortable buying the engine (assuming everything else about it checks out).

There are many factors that will contribute to what a "newly rebuilt" engine will read - which is partially why the absolute value is relatively unimportant.

My relatively newly rebuilt engine reads ~ 150, FWIW.

 

[60s Refugee]

Even if it needs rebuilt, if you have an engine stand, rebuilding these 200's is relatively easy and, dare I say it, fun to do! Besides, you can paint it too, even the spark plugs (sorry Eric! Couldn't help myself ) Parts are sorta' cheap and it doesn't take long. It gives you a chance to do special stuff too, like a better cam, bigger valves, and more. You can just do it stock too. My experiance has been that it's better to build it yourself than buy a reman engine. With compression that good you might even be able to leave the cylinders alone. See, you even have me planning! That's why it's fun...it's good brain exercise.

Anyhow, the one you are looking at will be a good start what ever you decide to do.

Harry

 

[sfx66]

Thanks all. I think I'll get it and run it as is for now. As I mentioned it ran good an dpulled hard in the stang it was in. I was just a little leary about the numbers.. but he did re-test with throttle open and got a higher number, so I think we're ok.

 

[sfx66]

Sorry guys.. one more. I found out the motor has approx. 30k on it since the rebuild. This is still ok.