I have a 1979 C3 with a 1969 327 block with 350 heads from a 71. I bougth this car last year and am now just getting a chance to work on it. The car runs and drives fine but has some considerable grey smoke coming from drivers side exhast and seems underpowered. Smells alot like fuel when started. I did a compression test yesterday and here are the results, 1-70, 2-35, 3-120, 4-130, 5-120, 6-130, 7-90, 8-72. Could this be valve issues or a ring issue. The car has brand new plugs and the low compression cylinders have considerable carbon on them already. I would love some guidance as to what steps to take next. Thanks for the help.

 

If you are lucky, the low readings could be from carbon build-up on some of the valves. It's interesting that the four cylinders that read low are the two at the front of the engine and the two at the back.

The first thing you should do is get a can [or two] of SeaFoam and attempt to get rid of as much of that carbon as possible. When you do this, park the car in a place where cr@p coming out of the exhaust won't make a big mess! Then remove the air cleaner, fire up your [already warmed up] engine, hold the throttle at about 2500 rpm or so, and start pouring {slowly} the SeaFoam into the carb primaries. You may have to 'feather' the throttle or rev it more while the engine ingests the SeaFoam, but it will start blowing carbon cr@p out the back pretty quickly.

If the exhaust output cleans up and you have more SeaFoam left, just pour it in your fuel tank (if it's half full, or more). It will continue cleaning the engine/valves as that fuel is used.

Then you need to check compression again to see if those low numbers have gotten [significantly] better. If there is more than 15% difference in the compression numbers, rings and/or valves are the culprits. By the way, a 327 engine with '71 [base engine] heads will have a compression ratio in the area of 8.0 to 1. That engine should run fine, but it won't make much power.

 

A 327 and 350 block both have 4.0" bores as standard. A 1969 block should easily accept a 350 crank; why not pull the engine and rebuild it?

If it's a daily driver, rebuild any worn out 350 to your desires and swap out the 327 when done.

 

I will try the seafoam tonight and see if that makes a difference. I really wanted to see if this engine would pan out. I am not opposed to replacing the 327 with a new crate or rebuilt 350 either. Thanks for the suggestions and let me know if there are any other thoughts. I hope I am not on here next weekend asking about rebuilds or crates but if I am thanks in advance for your suggestions.

 

I rarely even pull out a compression gauge because it doesn't tell you much. Do a leak down test. It will tell you whether it's heads or rings and the condition of the motor

 

SeaFoam first, recheck next, leakdown test...if you have the equipment and can do it; then repair or drive as necessary.

There is nothing wrong with the 327 block/engine. With the low-power set-up you have now, you have a great driver car with better mileage than 350 engine will do.

 

I do a compression check first, but a leak down provides a bunch more information. It's easy to do, and the tool is pretty cheap at Harbor Freight.

 

I did the sea foam flush last night and had to stop after one can because my neighbors thought my house was on fire. Took the car for a test run and after 20 minutes of driving it was still putting out the same grey smoke. I will do the cylinder leak down test this weekend. Thanks for the suggestions and I will post the cylinder stats later. Thanks for the Harbor Freight suggestion, I will pick up the tool this week. Larry, I will give you a call this week to talk about a possible rebuild.