351 Cleveland timing
Thread Starter
Joined: Jul 2006
Posts: 3
From:
351 Cleveland timing
Hello all,
I am relatively new in this forum. I'm from Spain so I apologise for my english. I own a '70 Mustang Coupe with a 351 Cleveland engine and Shaker hood.
My dad and I took the engine apart and did an overhaul restoration on it. We replaced valves, springs, push rods, pistons, bushings, segements, timing chain and wheels, oil pump, and some other parts I don't know the name in english for.
The engine runs fine, but before and after the restoration, it behaves wierdly. For a start, at about 4000 rpm it seems as if the engine would not deleiver any extra power... don't know if that is normal. What is more annoying is the following. Running at normal speed and about 1000-2000 rpms, if I kick the throttle, the engine starts to rattle (you can even see the shaker hood vibrating wildly) and don't deliver any power. It doesn't stall. However, if I push gently on the throttle, the engine speeds up fine with a nice acceleration.
We suspect of the timing advance, but we are unsure as the Ford Manual only state the advance at idle (~600 rpm). I have made a chart of the timeing advance. At idle it is 6ยบ, and at 3000 rpm it is 36ยบ with the vacuum advance connected and 24ยบ or so with it disconnected and plugged. Does anyone know what the timing should be for different rpms? Is too much or too little we have at the moment?
The vacuum advance can be regulated and I suspect it could be that it is too "loose" so that when we kick on the accelerator, it advances too much, producing the rattle. Does this make any sense? Could the problem be somewhere else?
Thank you in advance for any help.
Di4l
I am relatively new in this forum. I'm from Spain so I apologise for my english. I own a '70 Mustang Coupe with a 351 Cleveland engine and Shaker hood.
My dad and I took the engine apart and did an overhaul restoration on it. We replaced valves, springs, push rods, pistons, bushings, segements, timing chain and wheels, oil pump, and some other parts I don't know the name in english for.
The engine runs fine, but before and after the restoration, it behaves wierdly. For a start, at about 4000 rpm it seems as if the engine would not deleiver any extra power... don't know if that is normal. What is more annoying is the following. Running at normal speed and about 1000-2000 rpms, if I kick the throttle, the engine starts to rattle (you can even see the shaker hood vibrating wildly) and don't deliver any power. It doesn't stall. However, if I push gently on the throttle, the engine speeds up fine with a nice acceleration.
We suspect of the timing advance, but we are unsure as the Ford Manual only state the advance at idle (~600 rpm). I have made a chart of the timeing advance. At idle it is 6ยบ, and at 3000 rpm it is 36ยบ with the vacuum advance connected and 24ยบ or so with it disconnected and plugged. Does anyone know what the timing should be for different rpms? Is too much or too little we have at the moment?
The vacuum advance can be regulated and I suspect it could be that it is too "loose" so that when we kick on the accelerator, it advances too much, producing the rattle. Does this make any sense? Could the problem be somewhere else?
Thank you in advance for any help.
Di4l
5th Gear Member
Joined: Mar 2005
Posts: 3,566
From: Marquette Mi
RE: 351 Cleveland timing
The rattle is preignition, spark knock, or detonation. All of those are different ways to say the same thing. The fuel air mix is being ignited before the spark plug fires. A 70 Cleveland with 4V heads will have compression that is too high for cheap gas. You need fuel with a higher octane rating to run your engine and get power out of it without putting holes in pistons, breaking crankshafts, or flattening rod bearings. That is what happens when an engine knocks severely, it pounds on all the parts from the piston to the crank like a large hammer hitting it repeatedly.
I assume you have 4V heads because you mention a shaker, I dont recall ever hearing of them being installed on a 2V engine. 4v and 2v refers to the carbuertor, 4 venturii and 2 venturii or 4 barrel and 2 barrel. 4v heads have much larger ports than do 2v heads, also 4v heads in 1970 had small combustion chambers for high compression. High compression and low octane fuel dont mix well. try running the premium in it, or if you can find some race gasoline with an (USA) octane rating of 100 or more, use it in a 50/50 mix.
Clevelands are known for high rpm power because of the large ports, so why doesnt yours turn over 4000 rpm? Valvesprings would be my guess. If the valvespring doesnt have enough pressure to controll the valve, at high rpm the valve will bounce off the seat when it closes. That limits power because the valve timing is off, its called floating the valves. The cure for it is stiffer springs that controll the valve better. It should be turning 6500 rpm no problem, just dont do that much for long periods of time with a stock Cleveland. It wasnt built to rpm that high that long distance, but with modifications it can handle it easily.
As a shift point 6000-6500 is okay as long as the bottom end is fresh and was balanced for new pistons. Cruise rpm should be 3500 or lower, but with 4v heads, you want to keep it over 2000 rpm to keep the engine running clean. and not loading up. If the plugs come out looking black or fuel soaked, and black smoke comes out the exhaust, it is running rich (too much fuel) or loading up. When puddles or fuel form in the intake or the intake becomes saturated by fuel because the air isnt moving fast enough to keep it in suspension, the engine loads up and dies or idles very rough. If it runs great when cold, then starts belching black smoke and idling rough, its probably doing just that.
Valvesprings have a lifespan, doesnt matter if its a BMW, an Audi, a Pontiac, Ford or Honda. They all lose pressure over time and use. Higher rpm requires stiffer springs, lighter valves helps but this is a relatively large V8, it needs large valves to flow enough air to make it run and make decent power.
Mechanical fixes to the spark knock would be dished pistons to lower the compression ratio. That means changing pistons and tearing the engine down again. If you dont want to run the best fuel you can find and pay a premiun price for it, change the pistons so they have a dish in them. You want around 9.0:1 to run the really cheap gas.
I assume you have 4V heads because you mention a shaker, I dont recall ever hearing of them being installed on a 2V engine. 4v and 2v refers to the carbuertor, 4 venturii and 2 venturii or 4 barrel and 2 barrel. 4v heads have much larger ports than do 2v heads, also 4v heads in 1970 had small combustion chambers for high compression. High compression and low octane fuel dont mix well. try running the premium in it, or if you can find some race gasoline with an (USA) octane rating of 100 or more, use it in a 50/50 mix.
Clevelands are known for high rpm power because of the large ports, so why doesnt yours turn over 4000 rpm? Valvesprings would be my guess. If the valvespring doesnt have enough pressure to controll the valve, at high rpm the valve will bounce off the seat when it closes. That limits power because the valve timing is off, its called floating the valves. The cure for it is stiffer springs that controll the valve better. It should be turning 6500 rpm no problem, just dont do that much for long periods of time with a stock Cleveland. It wasnt built to rpm that high that long distance, but with modifications it can handle it easily.
As a shift point 6000-6500 is okay as long as the bottom end is fresh and was balanced for new pistons. Cruise rpm should be 3500 or lower, but with 4v heads, you want to keep it over 2000 rpm to keep the engine running clean. and not loading up. If the plugs come out looking black or fuel soaked, and black smoke comes out the exhaust, it is running rich (too much fuel) or loading up. When puddles or fuel form in the intake or the intake becomes saturated by fuel because the air isnt moving fast enough to keep it in suspension, the engine loads up and dies or idles very rough. If it runs great when cold, then starts belching black smoke and idling rough, its probably doing just that.
Valvesprings have a lifespan, doesnt matter if its a BMW, an Audi, a Pontiac, Ford or Honda. They all lose pressure over time and use. Higher rpm requires stiffer springs, lighter valves helps but this is a relatively large V8, it needs large valves to flow enough air to make it run and make decent power.
Mechanical fixes to the spark knock would be dished pistons to lower the compression ratio. That means changing pistons and tearing the engine down again. If you dont want to run the best fuel you can find and pay a premiun price for it, change the pistons so they have a dish in them. You want around 9.0:1 to run the really cheap gas.
Thread Starter
Joined: Jul 2006
Posts: 3
From:
RE: 351 Cleveland timing
Thank you very much for your help.
Surprisengly enough, my engine is a 2V rather than a 4V. I will defenetly try using a higher octane fuel. Here in Spain we can choose between 95 or 98 octane. No lead in any case. I am currently using 95 octane plus an "add-up" product to compensate for the lack of lead.
About the 4000 rpm thing, my dad had told me he suspected of the srpings, but was unsure. Your post confirms his thought. However, he said that one solution would be to fit an extra inner spring to each of the valve springs, having two for each valve rather than just one. This would have the same effect as having one stiffer spring, if I'm not wrong. Do you know if an extra spring would fit into the "valve rods"?
I'm not willing to get the engine up to 6000 rpm for long periods of time. in fact, I've never gone beyond 4000.
Thank you again for everything. I'll let you know how it all goes with your suggestions.
By the way, I can't help to upload pictures of my car. The interior is all being done, since the brown color does not suit the blue body color.
First image is to show the engine. Second one shows my mum, dad, brother at back doing funny faces and some friends. You can see myself on the left of the car on the last picture
Di4l
[IMG]local://upfiles/44143/5D91403946F14B9A80C246C6D653C549.jpg[/IMG]
[IMG]local://upfiles/44143/D10314BC722B49EDA2BE5CDA52417F9D.jpg[/IMG]
[IMG]local://upfiles/44143/62347F58E5AE46C9AC974E324162D459.jpg[/IMG]
Surprisengly enough, my engine is a 2V rather than a 4V. I will defenetly try using a higher octane fuel. Here in Spain we can choose between 95 or 98 octane. No lead in any case. I am currently using 95 octane plus an "add-up" product to compensate for the lack of lead.
About the 4000 rpm thing, my dad had told me he suspected of the srpings, but was unsure. Your post confirms his thought. However, he said that one solution would be to fit an extra inner spring to each of the valve springs, having two for each valve rather than just one. This would have the same effect as having one stiffer spring, if I'm not wrong. Do you know if an extra spring would fit into the "valve rods"?
I'm not willing to get the engine up to 6000 rpm for long periods of time. in fact, I've never gone beyond 4000.
Thank you again for everything. I'll let you know how it all goes with your suggestions.
By the way, I can't help to upload pictures of my car. The interior is all being done, since the brown color does not suit the blue body color.
First image is to show the engine. Second one shows my mum, dad, brother at back doing funny faces and some friends. You can see myself on the left of the car on the last picture
Di4l
[IMG]local://upfiles/44143/5D91403946F14B9A80C246C6D653C549.jpg[/IMG]
[IMG]local://upfiles/44143/D10314BC722B49EDA2BE5CDA52417F9D.jpg[/IMG]
[IMG]local://upfiles/44143/62347F58E5AE46C9AC974E324162D459.jpg[/IMG]
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