Did a compression check....how did I do?

[shadango]

Finally got around to doing a compression check....

As a refresh, its a 76 318 engine with j heads, eddie 750 carb and manifold.

In theory internals are stock.....that what I was told.

cyl

1  starts at 75...pumps to 125  (in just 2 or 3 rotations)
2  starts at 75...pumps to 125
3  starts at 75...pumpls to 125
4  starts at 80 or so....pumps to 140
5  starts at 75...pumps to 130
6 starts at  75...pumps to 123 or 124
7 starts at 75....pumps to 123 or 124
8 starts at 100...pumps to 136

All cylinders hold pressure for at least 20 seconds or so

All plugs are dry except for plug 8 which is a little damp with fuel...all are running rich

So, I know the desire is high compression and EVEN compression across the board....should I be worried about 5 and 8? Are they abnormal or are the others too low?

Please tell me I am ok....LOL  (We need a "praying hands" emoticon!!)

[Oldschool]

I think you are fine...  No more than 10% difference from the lowest to the highest.  Might be slightly low, but it is probably a low compression engine to start with being from the mid '70's.  Drive it..............             

[spitnl]

Hi,

I agree with Oldschool, although the numbers are somewhat low they are close enough.
Perhaps you did the test with the throttle closed, and cold engine?

Frederick

[shadango]

Hi,

I agree with Oldschool, although the numbers are somewhat low they are close enough.
Perhaps you did the test with the throttle closed, and cold engine?

Frederick

Actually....yes.....cold engine, throttle closed......

Let me guess, shoulda done it with a warm engine and throttle wide open?  (Can I just wire it open?)

Should my numbers go up if I do it that way?

[moper]

Yes, go hot and wire it open, with all the plugs removed. I think you might be low too, and hot it wil go up a bit. Or should...

[shadango]

Ok...will have to wait til I get my exhaust on....too loud to run for very long to get hot.

Bottom line though is that these numbers are OK  considering its cold?   Any chance the number will go DOWN?

[72bluNblu]

Those numbers are pretty good for cold with the throttle closed. With the engine warmed up you should see better ring sealing, and with the throttle open you should be able to pull more air in when you're turning it over. Both should increase the numbers you're seeing. Either way, the numbers aren't horrible, considering its likely a low compression engine anyway (for a '76 you'd be doing well to have 8:1). Its unlikely that the numbers would be lower once the engine is warm, but just about anything is possible. The high numbers aren't anything to worry about either, they're not abnormally high.

Warm the engine up, even 5 minutes should be fine. Then either wire the throttle open or put a brick on the pedal, you want the throttle open but you don't want to pump it each time you do a hole otherwise you'll flood it with fuel. Pull all the plugs so it spins over faster, usually 3-4 cranks should give you the highest numbers. But it sounds like you should be good to go already! 

[shadango]

Thanks Bryan!

Does it matter if I pull all the plug at once or do one at a time?

[Oldschool]

Thanks Bryan!

Does it matter if I pull all the plug at once or do one at a time?

Pull them all out at once....       

[shadango]

SO...looks like I was hosing up the test from the beginning......LOL!

(Thanks for getting me straight guys.....will post the results when I redo it......

I may try and "warm her up" again this weekend.......I need an excuse to here her run every few days...LOL

[72bluNblu]

Pull them all out at once....   

It'll spin faster with all the plugs out. Not as much work for the starter, plus it should give slightly better/more accurate numbers.

[shadango]

I guess my thought was that the engine has the plugs in when it is running so keeping them in would be the most accurate?

..........now I feel dumb..... LOL

Side note:  I just spent about an HOUR changing a LIGHT BULB in the third tail light on my wife's 06 Hyundai SOnata....talk about RIDICULOUSLY STUPID engineering from a maintenance standpoint....love the car, really, but geezuz!   

I searched the web for a how to and plenty offools just like me....I ended up making some modifications to make it easier in the future.....

Thats why I love the fish.....seems like back then things were so simple.....they almost fix themselves!  LOL  Ok not really....otherwise, this forum wouldnt be so active and I wouldnt be making so many posts with questions....but man, the Sonata is a real pain to do routine bulb changes on....!!!!!!  Would much rather be under the fish!! 

[moper]

See, that's a Hyundai... If it was a Mercedes, it would have changed itself .    I can't believe we'll all be driving Fiats soon. God I hate Fiats...

[BarracudaDave]

FIAT (Fix it again Tony)