Initial timing question

[concobra]

Thanks for the response. Let's look at the information you have supplied and see what we come up with.

1. 9:1 compression. Given that this is an accurate measurement. The cam you have selected will yield around 150lbs. or more of cranking compression. If installed straight up. Try to verify this. If you find that it is below 120lbs. your cam could be retarded and therefore your are not developing enough cylinder pressure to create adequate vacuum at 14 degrees. Remember that you need to run this test with the engine cold, carb. open all the way, & allow the motor to turn over at least 5 revolutions.

2. Vacuum reading. Your measurement of 16-17 inches is low considering the timing you are using (25 degrees) and the engine RPM of 1000. Should be around 20. Therefore the ignition timing may not be your actual problem. (After all 25 degrees is 25 degrees.) It could be other things. More on this in the conclusion.

3. What intake and carb? The Edelbrock Performer and 600 carb. are very good street units and exhibit excellent idle and throttle response. The standard calibration of the carb. is close enough to allow your engine to run well with only minor tuning required. ( This stated based on your cam selection and assuming you are using standard porting) Keep in mind that a carburetor's calibration is relative to the CFM flow more than the CID of the engine. Probably not the problem.

4. Running temp is great. No problem here.

5. Problem existing since new. Given this truth you may wish to look at other problems that can occur during assembly that can contribute to this problem. More on this during the conclusion.

6. Distributor off a tooth or so. Seems a reasonable option but is not an issue. The motor has no idea where the distributor sets relative to exciting the plug verses piston position. To explain further. Even if the distributor was pulled and turned 180 degrees but the wires were placed correctly on the cap relative to timing order the motor would not know the difference. As you said earlier the timing is at 25 degrees. Thats when the timing light indicates the plug is sent a signal and that is exactly when the plug can ignite the cylinder fuel charge. If it's 25 degrees then it's 25 degrees. Since the motor will not run well at 14 degrees (and it should) and it only runs well at 25 degrees then the conclusion would not be an ignition timing problem. Advancing to 25 degrees is just hiding the real problem.

7. Your camshaft selection and how it effects this stiuation. I looked up your cam and if I am correct it is Comp Cam's # 35-414-3. Based on high performance as a gauge, this is a mild cam. This cam should idle easily at 750 RPM and pull 17 to 20+ inches of vacuum.

By the way a side bar thought. If the heads are not ported to flow 75% exhaust to intake which stock Ford heads never due. Then you are not running enough exhaust lift and duration to compensate for this poor exhaust flow. You might consider a dual pattern cam with more exhaust lift and 10 degrees more duration @0.050 than intake.


OK enough facts let's draw some possible answers.

1. Your cam is retarded. You can make a reasonable deduction to this by the cranking compression as listed in item #1.

2. Your hydraulic lifters are slightly holding the valves open. Don't laugh it can happen. This holds very true with Fords and the non-adjustable rocker arms on rebuilt motors. If you surfaced the heads, had the valves done, are running a cam with a different base circle or any number of variables this can happen. Did you verify the preload? This will show up during the cranking test as a low cylinder pressure.

3. An intake air flow leak. Probably manifold located. I would consider looking here first. This seems to be the most likely. All of the problems you have mentioned would exhibit themselves with this situation. Do you know how to test for this?

There are other possibilities but let's start here and good luck.