recurving distributor

[adm22]

Thanks for all the information have almost too much here and my brian is beginning to hurt.

I do not want to try going to fuel injection or anything that requires too much moodification to stuff since if it breaks down and I am far from home can find someone to fix it. It went with the petronix instead of a electronic box since it could be easily be changed to points if needed real quick.

My engine has about 40k mile on it. I repalced it a few years back with one that was a NAPA rebuilt one. The owner had it in a barn for years since the car he had intended to put in in crashed a couple weeks after he bought the engine. He said he bought it in the early 90s, but I think it might have been older as I had to replace the heads a coupel years after it was put in due to unleaded gas screwing up the valves. The engine that had been in the car had over 300k miles on it and was starting to burn oil. I found the replacement engine relatively cheap- about $1100 less than a rebuilt one from Autozone so I jumped at getting it.

I have however not been able to read the timing marks so I have no idea how close to the right settings. When the timing is advanced adn the engine is warm it does not start easily- meaning ti does not even want to turn over. I melted a batetry cable once when trying. I backed the timing off and this does not happen anymore but the MPG has suffered. Before this on one road trip I git 28 MPG I consisder this real nice.

Before I put in the overdrive the car was getting about 18 on the highway. My calculations showed me that the engine with overdrive should be running .6 as fast which is about right and also I hoped would get 1.67 better gas mileage whihc would be 30 whihc it did not. As set right now it gets on average in the low 20s (city and highway). Someone told me that the engine was no lober at max torque or performance whihc is why the change upwards was not as great. Before I backed things off- I generally set the timing to where the engine sounds best at an idle. The average was aroudn 23-24.

I have the 2.75 rear end. I am not looking to set any acceraltion records but also do not want the 0-60 to be a "YES". I have had no problems with acceleration as things are although I do sometimes get some pinging if I hot a hill in overdrive at less than highway speeds 40-45 MPH.

The distributor is the one that has been in the car since I got it meaning it has around 475k miles on it. So perhaps it might be wearing out. It is about the only thing on the car that has not been repalced me- so like having somehting original left.

What I would like to have is to ahe the engine at best possible performance in the 1800-2200 rev range and haev it so that it will still work well up to about 3000 as this is what hiway speeds were at a 1:1 3 speed and 4th speed now- so if needed could donwshift in adverse situations- mountains and like.

 

[72HCODE]

the 2.75:1 was the tallest rear end ford had for 71-73 cars, my car was equipped with one as well. tallest gear meant best few economy at highway speeds since at 55-75mph the rpms were as low as possible.

Low rpms meant throttle plates at much lower possition, there for less air, less fuel, higher vacuum at cruise.

now consider this, a modern mustang runs 3.51-3.71 ish rear end ratios.

the modern transmission is also going to be geared internally to meet an rpm range for each gear with a narrow range for the rear end ratio. you could very well be overgeared for application and a lower ratio rear end is going to bring you more into spec with what the newer transmission was designed to handle.

remember those tall gear ratios in old cars compensated for the lack of a 1:1 overdrive.

-----

now you mentioned a pinging at mid throttle engine.

First you need to reproduce the ping and figure out what your doing on the pedal at that point.

example: your at cruise holding pedal steady at 45mph. you approach the hill without touching the pedal as you climb load goes up, and the engine pings, then you know it isn't the accelerator pump circuit. now increase throttle slowly, does the ping stop as speed increases slowly, adding additional load usually makes the power valve turn on. cruise jets could need to come up 2 sizes, or you need to look at your power valve.

power valve would be the first thing to look at since the car does not appear to surge. for that you need a vacuum gauge.

The power valve compensates when you don't use the accelerator pump shot for a fast acceleration. as load goes up(climb hill) the Vac drops, when it reaches a certain point the Power valve turns on to add more fuel then as the engine recovers and VAC goes up it shuts off.

general rule of thumb, MAX HG at Idle divided by two plus one.

So say your making 17HG at idle you then want a 17/2 + 1 = 9.5HG power valve. Stock 99% of the carbs come with a 6.5 HG valve. Carb makers err on the side of MPG.

but this calculation is for performance not MPG.

lowering the Power valve threshold from 6.5HG to 3.5HG saves fuel because you or forcing the valve to turn on when the engine vacuum gets very very low (very high load). You are leaning out the engine, in your case too lean mid throttle.

so first you hook up a vacuum gauge and find that hilly section that you know the car pings on, reach steady cruise before it then do not adjust the throttle let the engine load and ping starts then look at the vac gauge and note the ping.

in theory if your car has a 6.5HG valve you should see the ping happen above this point like 9-7HG because you are right on edge. so you could install anything from a 9.5HG to a 7HG valve. the 7HG would be leaner then a 9.5HG valve because it turns on extra fuel later rather then sooner.

but you need a little more to compensate mid throttle.

now if ping occurred always under heavy acceleration then your attention would be accelerator pump or power valve, accelerator pump would would be more likely.

----

Thing to remember is the engine could care less about what you want, it wants what it wants. It is very possible with the combination of parts you have that you will never see the MPG you want because the engine will not tolerate it. Hot start issues, fuel boiling, detonation, etc....

there is also the reality of what you put into the fuel tank makes a difference in MPG

First did your state switch to Ethanol, because Ethanol drops MPG 33% in some cars. ethanol has a higher flash point but the energy content is 1/3 less then real gas.

Octane level is actually a big deal. a higher octane level actually allows you to run an engine leaner because of high detonation level, so if you think your saving money running 87 octane you might not be because you have to flush more of it down the engine compared to 97 octane to compensate for engine detonation(ping) when these cars were new even after lead was phased out, you had 107 octane levels in gas.

so imagine coming off 107 octane down to 87 and the problems that causes.

more food for thought really.

but first take care of any tuning issues on the engine involving detonation. have to make sure the engine is happy first.

a worn distributor would show other ignition issues that you don't seem to have. you could pull the plugs and have a look at things, you don't seem to have misfire or jumped timing.

I would think about looking into your rear end ratio and the possibility you are over geared for application, more isn't always better its like a bell curve, too much or too little doesn't work.

Before I put in the overdrive the car was getting about 18 on the highway. My calculations showed me that the engine with overdrive should be running .6 as fast which is about right and also I hoped would get 1.67 better gas mileage whihc would be 30 whihc it did not. As set right now it gets on average in the low 20s (city and highway). Someone told me that the engine was no lober at max torque or performance whihc is why the change upwards was not as great. Before I backed things off- I generally set the timing to where the engine sounds best at an idle. The average was aroudn 23-24.

I have the 2.75 rear end. I am not looking to set any acceraltion records but also do not want the 0-60 to be a "YES". I have had no problems with acceleration as things are although I do sometimes get some pinging if I hot a hill in overdrive at less than highway speeds 40-45 MPH.

The distributor is the one that has been in the car since I got it meaning it has around 475k miles on it. So perhaps it might be wearing out. It is about the only thing on the car that has not been repalced me- so like having somehting original left.

What I would like to have is to ahe the engine at best possible performance in the 1800-2200 rev range and haev it so that it will still work well up to about 3000 as this is what hiway speeds were at a 1:1 3 speed and 4th speed now- so if needed could donwshift in adverse situations- mountains and like.