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What should the compression be on a '74 260 L26 engine. I tested it and it was from 150 to 160 psi, is this the right range?

thanks
 

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What crank?

Usually you take compression readings on three cranks. (Remember to block the throttle WIDE OPEN during compressions checks, and have a good charge in the battery.)
First crank (your cranking compression) should be in the 100-110 range.
thrird crank (around 150)
Fifth crank (higher than 150, and stable, not continually climbing)
My 260 with an N47 head on it cranked 100/110 first, 145/155 third, & 175/186 fifth crank. This is for 110,000 miles, with freshly lapped valves and clean combustion chambers. That is good.
Yours seem fine. If the first crank nets you less then 85-90# the valves or rings may be going away. Put some oil into the cylinder and recheck it ("wet test") if it dramatically increases, the rings are going away. If it doesn't increase, the valves are most likely in need of a clean up.
 

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Re: What crank?

When i tested the compression of my engine i did it with the carburetors off and when the engine was cold, so im hoping the compression will be a bit higher than what i recorded in those tests
 

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Yes.

Warm, with piston rings oiled up, likely to get higher comp reading.

Agree w/ TonyD - block throttle open. Tony's a lot fussier than me about watching the gauge. I crank it untill the pressure stops rising (maybe ten cranks) then record the reading. Don't think N47 was stock 260 head. Maybe motor is pumped up some (shaved head or such for higher compression).

My experience w/ stock 260 is 140-150 is right-on. Run great on regular! Forget about 1/4 times (especially w/ 2.34 diffy), but enjoy a high speed cruise and smile the whole way to the low test pump!

Good luck!
Al
 

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ME? "pump up" a motor? NOOOO!

N47 head CC's compared to E88? any guesses?
Marginal emissions reading with E88, swap N47 with inserts, that really activate the AIR injection---like if you are running non-stock needles....
Adjustable cam gear, for retarding the cam 4 degrees, making it pull strong to 7000 (albiet killing the bottom end altogether...) and swapping in a 3.70.
ME? What, ME Pump Up a motor. NAH! It's all stock parts. Stock if anyone else asks.

The rate of rise of the compression tells you how the rings are seating. In all reality on a well-seated engine, three to five cranks should be all it takes to get to max compression. After that, no matter how long you crank it wont rise.
If it takes 10 cranks to get to a stable point, that's a bit long. The important thing is that the engine hits 100 to 110 psi on the FIRST crank. If it doesn't, find out why, as something is amiss.
 
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