Hello All,
Can the valves in my 69 Cougar with a 351 W in it handle Unleaded Gas ?
Unleaded gas is better run at lower compression. That allows timing to be in “normal” ranges without preignition. If you have a stock 1969 351W it will ping like crazy with unleaded fuel. Retarding the timing will stop the pinging but the result is red hot exhaust valves. The red hot valves will wear out and cause damage to the exhaust seats in the heads.
A good approach to using modern unleaded fuel is to lower compression to around 9:1 and use cylinder heads that flow more air in order to regain the power lost by low compression.
My 351W was rebuilt in the late 80s. .030 over, hardened valve seats. I have initial timing set at about 12 degrees BTDC. Never any issues with pinging on regular unleaded gasoline.
Likely you had a builder who did a good job. With lower compression and hardened seats you get less power but an engine that won’t ping.
Royce,
My 351c pinged like crazy even using premium unleaded. It didn’t help that the engine overheated too. When I rebuilt it last winter, several rocker arms were cracked at the push rod dimple. There was limited valve recession, but seems it had to have been caused by sticky valves. Could your red hot valve scenario explain this?
Anyway, they installed hardened valve seats, got the cooling passages cleaned out, and I am now running 11:1 compression ratio at factory ignition timing with no pinging using 91 octane ethanol free unleaded.
You probably have a generic piston / ring package that lowered cylinder pressure enough to make it work. Generally weak valve springs and carbon build up on the valve stems / valves are more likely than retarded timing causing valves to stick.
Does the lead substitute additive make a significant difference here?
My experience it makes no difference no matter how much you add to your tank. I added so much octane booster to my tank the spark plug porcelains were pink. The engine still pinged like crazy. Super unleaded, 10.5:1 compression (real, not imagined), stock J code 302.
Good point - I’m still running the original piston rings so no doubt less than factory peak compression. There were no noticeable carbon deposits except for a very small amount on piston tops. I wasn’t thinking retarded timing might cause a valve to stick, but wondered if a red hot valve might tend to slightly weld itself to it’s seat and stick closed.
I was thinking lead substitute (which is not octane booster). Is the substitute still beneficial in some way, even if the valve seats have been re-done w/ hardened ones?
Bottom line - no benefit whatsoever.
Tetraethyl lead is available for purchase on the internet it is not a subsitute but the actual product that was removed from leaded gasoline it works well.
Coming to this chat late & curious…
I’ve had my car now 5 years and put on about 8,000 miles…just crossed over 90k. Never a ping
I changed the plugs and wires to improve starting when I got it back on the road. I use a Lucas zinc additive with oil changes and run only Shell 93 with a Lucas octane boost/ethanol treatment additive.
I don’t believe the 351w- 2v original engine has had any significant work.
Is the lack of pinging something I should fret over? Anything to check?
There are significant difference in combustion chamber shape and influence on knocking with the 351C engines. The 2V is lower compression but will ping on regular. The higher compression 4v does require premium but with that it is not sensitive to pinging. As I understand it the lead also helped with valve seat life hence the advantage in the upgrade to hardened seats. I’ve seen advice that the original valves and seats will survive reasonably well.
I’m basically suggesting the the octane level, independent of whether it is increased by lead or other current blends, is what controls knock.
Lead had another benefit with valve and valve seat life, the degree of which is debated.
I’m sure this will draw out some other information and opinions.
This is consistent with my understanding too. Of course ignition timing and carbon buildup will also influence pinging. I also have read that the 351c with open chamber heads is prone to pinging. My 351c has the wedge chamber heads and has no pinging issues with factory timing spec and 91 octane unleaded. My original 70 Cougar with 351w did require backing off the timing to prevent pinging on regular fuel.
No, you don’t want pinging, I don’t see where you would need 93 and a octane boost with a 351 2V, it should run quite well on regular.
If you’re having trouble with pinging on a “normal” compression engine with proper timing, check for carbon buildup.
I had a 318 (I know, MoPar) that I could not get rid of the pinging in. It was also consuming oil and had 140 +/- 5 PSI all around. I started with the easiest fix which was valve seals. I was 20, so it didn’t take long to get rid of the accumulated carbon. What a difference…
Yup, I think carbon buildup was a big reason my original 70 Cougar with 351W pinged so bad. It actually had chunks of carbon break loose and knock around in the cylinder. I remember using a product called Carb-out that you poured into the carburetor to soften carbon. Made enough smoke to fog up the entire neighborhood. Then you floored it every time you accelerated to blow the carbon out. As a teenager, this was no problem for me! Cleaning carbon out and retarding timing a couple degrees later than factory spec allowed my to run regular gas without pinging. If I wanted peak performance, I would sometimes switch to premium gas and advance timing a couple degrees beyond factory spec. it would then chirp the tires when it upshifted which is something I love about my current Cougar with the 351C!