200ci Degree the cam?
- Thread starter Dustyford
- Start date
This applies only to 200ci
What is your spec for the custom curve? My experience is that 10 degrees initial isn’t enough and that it’ll want to have a bunch more timing soon after you get on the throttle.
For reference, mine is a 1966 200 with the Clay Smith H-6474-0-B camshaft, degreed straight up (within +1 degree). Small log head, stock valves, stock valve springs. I am running a Weber 38/38 on an adapter and an HEI distributor and my exhaust is fairly large with a header but not obnoxious. Oh, also, like you, I’ve got a 5-speed.
I spent a long time figuring out the distributor timing and am settled on +14 degrees initial timing. Vacuum advance is ported and brings on +10 degrees. I curved the distributor with the springs that came with it to add a maximum of +16 advance at around 1200 RPM and it’s all in before 3,000 RPM. This is according to the chart that came with the distributor and I need to check the advance curve numbers with a timing light and a tachometer to confirm.
Just having a look at your cam card, you’ve got a hotter cam than mine. Yours being a bit retarded should be happier to build power further up the rev range than mine too. I can easily pull to 5,000 RPM.
The stock springs are known for being weak and allowing float early so I haven’t purposely pushed it. I shift around 4,500 RPM if I’m driving like a hooligan but mostly in traffic, I’ll shift around 3,000 - 3,500 RPM and cruise around 2,000 RPM.
Since your engine has great compression, my thoughts are give it more ignition timing and see how it responds. These engines will take a terrific amount of timing.
Good luck with it. You’ll figure it out.
By the 0.050 numbers 203/210 the cam is more than stock but I would not consider it a high performance cam. If fact it is a mild cam. It should work very well in your engine. What is your static compression ratio?? This is important!
By the numbers:
LSA = 108
108 - 90 = 18 Therefore 90-18 = 72 to get to Bottom dead center (BDC)
Intake duration at 0.050 = 203; divided by 2 = 101.5; round to 102
102-72 = 30; agrees with timing card intake tappet closing
This is my math check.
Therefore: using the 0.006 timing duration of 252 the intake closing is:
252 divided by 2 = 126
126-72 is 54
or using the 0.002 duration of 272:
272 divided by 2 = 136
136-72 = 64
Usually the 0.006 number is used for effective intake closing. Installing the cam straight up would give an intake closing of 58. Depending on the static compression ratio this intake closing point is important for octane of gas required for dynamic compression ratio. This being a mild cam retarding to use 87 octane indicates a cam that is not compatible with the static compression ratio. If your static compression ratio is over 9.0 then the cam must be retarded to use low octane fuel to get around this, which would be your only option. However, I would think retarding more that 4 degrees is not good.
So to conclude; what is your static compression ratio and what is your quench?
By the numbers:
LSA = 108
108 - 90 = 18 Therefore 90-18 = 72 to get to Bottom dead center (BDC)
Intake duration at 0.050 = 203; divided by 2 = 101.5; round to 102
102-72 = 30; agrees with timing card intake tappet closing
This is my math check.
Therefore: using the 0.006 timing duration of 252 the intake closing is:
252 divided by 2 = 126
126-72 is 54
or using the 0.002 duration of 272:
272 divided by 2 = 136
136-72 = 64
Usually the 0.006 number is used for effective intake closing. Installing the cam straight up would give an intake closing of 58. Depending on the static compression ratio this intake closing point is important for octane of gas required for dynamic compression ratio. This being a mild cam retarding to use 87 octane indicates a cam that is not compatible with the static compression ratio. If your static compression ratio is over 9.0 then the cam must be retarded to use low octane fuel to get around this, which would be your only option. However, I would think retarding more that 4 degrees is not good.
So to conclude; what is your static compression ratio and what is your quench?
I have no idea what the static com
I didn’t get a card with the distributor curve. Dan Nolan set it up for vacuum at 15” and all in at 2800 I believe.
I bought the least aggressive cam they offered. I didn’t build the engine nor do I know anything about building engines. It was a stock build with .040 over pistons.
I ran it a while with stock cam and it never revved over 4000. It struggles to get past 3500. I got new springs with the new cam but they were just regular springs. Sorry for my ignorance.
I consider troubleshooting a checklist. You’ve established that the compression is good and according to measurements, the camshaft is installed several degrees retarded. I would check to make sure the ignition timing is doing what is expected when the engine is running.
If this were my engine, I would fire it up, with a timing light on it and a tachometer so that I could watch what the ignition timing was doing when I open the throttle. It should be at 10 degrees initial advance (or whatever it is most happy at) and then when I open the throttle I want to see it jump when vacuum and then mechanical advance kicks in.
You don’t need to rev the heck out of it but you want to see that it is functioning. To make it simpler to see what was going on, I added extra marks on my damper so that I can see 0 - 14 then 14 - 28 then 28 - 42.
If this were my engine, I would fire it up, with a timing light on it and a tachometer so that I could watch what the ignition timing was doing when I open the throttle. It should be at 10 degrees initial advance (or whatever it is most happy at) and then when I open the throttle I want to see it jump when vacuum and then mechanical advance kicks in.
You don’t need to rev the heck out of it but you want to see that it is functioning. To make it simpler to see what was going on, I added extra marks on my damper so that I can see 0 - 14 then 14 - 28 then 28 - 42.
It doesn’t get a vacuum response until at least 15” so probably only at cruise. I have seen the mechanical advance at work. I have a digital timing light that shows rpms and advance in degrees so I can watch while revving. I don’t understand why it doesn’t rev. I wish there was a Ford/Mustang six guru near me. I can’t even find another six banger to compare to.
A correctly working ported vacuum advance system will begin advancing with a few degrees of throttle opening. There will be 0" vacuum at idle, and by the time the transition circuit comes in, the vacuum going to the distributor closely equals intake manifold vacuum from then on at all throttle positions. When testing with the timing light you should see the idle base timing at idle. As soon as the throttle is opened up even slightly the timing mark should instantly advance the full amount of advance built into the vacuum canister. If this is not happening there is an issue with some part of the vacuum advance system.
Frank, Thanks for joining my nightmare. My VA is set to allow vacuum at 15” or higher. When I open the throttle the ported vacuum raises to about 10” immediately. I don’t see over 15” until about a steady 2000 rpm. Max idle I can get without engaging ported vacuum is about 520 rpm. Base timing is 10* which is spec for my altitude. 5300’
As previously mentioned somewhere above, one of the reasons for the engine hitting the wall at a certain high rpm is weak valve springs.
Even though they were replaced, they may not have been the correct springs for the cam lobe profile.
Also, the base timing with this cam needs to be more than with the stock cam.
Even though they were replaced, they may not have been the correct springs for the cam lobe profile.
Also, the base timing with this cam needs to be more than with the stock cam.
AH! the altitude info is good. 15" of vacuum = 17.3" vacuum at sea level. If your vacuum can does not advance till 15" of vacuum, this is your key problem. You will rarely have 15" under load at that altitude. You're basically driving with the timing 15* late at all times. And as Mr. Muller said above, more base timing is needed. Even more so at altitude.
P, The cam company sold the springs and lifters and cam together but that doesn’t mean anything. I am intrigued by the idea of weak springs. Would shimming the springs help? Then I go back to the fact the engine did the same thing with stock replacement cam, springs, lifters. Interestingly enough, I haven’t read about anyone having this issue or resolving this issue.
I didn't realize that the engine did the same thing with the stock replacement cam.
Did it hit the wall at the same rpm with the stock replacement cam?
You don't have the ignition timing to allow the engine to spin up.
These 200's are gluttons for timing and your vacuum advance canister is not doing you any favours. I don't think my vacuum can requires such a high vacuum but I will have to read the spec on it. As @Frank mentioned, as soon as ported vacuum is initiated, the timing mark should jump ahead the prescribed amount.
I have experienced a similar situation with mine when I first put the new engine in my car. I didn't have enough initial timing and I chose to plug my vacuum advance and depend on mechanical advance (bad theory). It was a hard pull to get it to spin up and it fought me. As soon as I added port vacuum advance, it took right off.
Edit: The topic of valve springs is an aside to what’s going on with your engine. The stock springs are well known to be sub par for camshafts that need a fast spring. Cam manufacturers like Clay Smith offer springs that will match the requirements of the camshaft or you can use 302 and 289 springs depending on the spec of the camshaft. In your case, I am more than certain it’s timing so I wouldn’t suggest going down a shim or heavy spring rabbit hole until you get your ignition timing sorted out.
These 200's are gluttons for timing and your vacuum advance canister is not doing you any favours. I don't think my vacuum can requires such a high vacuum but I will have to read the spec on it. As @Frank mentioned, as soon as ported vacuum is initiated, the timing mark should jump ahead the prescribed amount.
I have experienced a similar situation with mine when I first put the new engine in my car. I didn't have enough initial timing and I chose to plug my vacuum advance and depend on mechanical advance (bad theory). It was a hard pull to get it to spin up and it fought me. As soon as I added port vacuum advance, it took right off.
Edit: The topic of valve springs is an aside to what’s going on with your engine. The stock springs are well known to be sub par for camshafts that need a fast spring. Cam manufacturers like Clay Smith offer springs that will match the requirements of the camshaft or you can use 302 and 289 springs depending on the spec of the camshaft. In your case, I am more than certain it’s timing so I wouldn’t suggest going down a shim or heavy spring rabbit hole until you get your ignition timing sorted out.
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