Timing/advance curve question

[travis]

While I’m saving my peso’s for a bulletproof trans and rear end for my new project, I’m thinking about throwing some of mine and my buddies leftover parts onto my ‘84 Cougar…because that thing is gutless as hell. Perfect running 302/CFI/AOD car with 2.73 gears and 140-ish stampeding shetlands…the early 80’s must have been depressing times.

Highway cruise engine speed is really low (1.83 effective final drive ratio!). My question is…what kind of approach do you take for the timing curve with a sub 2000 rpm cruise speed? A bunch of initial with a very short curve, and a bunch of vacuum advance? And try to keep a functioning EGR system to help prevent detonation? Between us we have some stock mustang 5.0 cams, shorty headers, off road H-pipe, ported E7TE heads (that will also bump the compression up to the high 8’s), assorted 600cfm and bigger carbs, etc. Not expecting “fast” but right now it is almost dangerously slow for traffic around here. The sad thing is that it mechanically runs perfectly fine. I know gears might help a bit but no sense putting the money and effort into the 7.5” stock rear.

[rebelrouser]

Generally an advance cure is tied to the rpm of the engine. The fuel burns at the same rate while the speed of the piston increases, so you have less time to develop maximum pressure in the chamber, so you ignite the mixture sooner as RPM increases. Most engines are more prone to detonation at lower RPM, so you may pull a little timing to protect the engine at slower RPM's. One issue I see in a lot of combinations like you have is that a camshaft is picked to increase HP, but the increase is at higher RPM than stock, and since they usually have more duration, cylinder pressure is reduced as well. So you have a rear axle ratio that does not keep the engine in the torque curve the cam is developing, and you have reduced the engines efficiency at lower RPM by killing cylinder pressure. I have seen this scenario a hundred times. Then they come to my shop and say, I think it just needs the carb tuned. And I don't know how many times I have said it is not all about the engine, it is about the combination. Spend the money on the rear axle, that way you have something that will hold up when you increase the torque from a good engine. One way to look at this is NHRA stock eliminator, those guys do a lot with the confines of basically a stock engine, apply what those guys do to a street car.

[HDBD]

First thing I would do is get a 94-98 mustang rear end under it. Probably 3:08 gears and even that is an improvement. A combination of a proper advance curve mechanically with full vacuum advanced also tuned to the combination will work best all around. I would not use EGR at all, just tune the curves to match the load and engine requirements without pinging using pump gas.

[BobbyB]

While I’m saving my peso’s for a bulletproof trans and rear end for my new project, I’m thinking about throwing some of mine and my buddies leftover parts onto my ‘84 Cougar…because that thing is gutless as hell. Perfect running 302/CFI/AOD car with 2.73 gears and 140-ish stampeding shetlands…the early 80’s must have been depressing times.

Highway cruise engine speed is really low (1.83 effective final drive ratio!). My question is…what kind of approach do you take for the timing curve with a sub 2000 rpm cruise speed? A bunch of initial with a very short curve, and a bunch of vacuum advance? And try to keep a functioning EGR system to help prevent detonation? Between us we have some stock mustang 5.0 cams, shorty headers, off road H-pipe, ported E7TE heads (that will also bump the compression up to the high 8’s), assorted 600cfm and bigger carbs, etc. Not expecting “fast” but right now it is almost dangerously slow for traffic around here. The sad thing is that it mechanically runs perfectly fine. I know gears might help a bit but no sense putting the money and effort into the 7.5” stock rear.

I,m not recommending it for the long term, but, if you only want to increase acceleration performance with the engine parts you currently have... you might just try some higher gears in your 7.5" axle... I know a guy that beat the daylights out of one with a pretty stout 351 & never broke it. If you keep street tires on the car you might be OK for a while.

It really comes down to the money you can afford to spend on it now. Many ranger truck had 7.5 inch axles with 3.45 gears. 3.73s & 4.10s are out there too.

If you break the 7.5", what have you lost?

[travis]

I was actually looking for a fox mustang 8.8 rear end that was already built with some sort of posi and 3.73’s. A few years ago you could find them everywhere. Now, not so much. I’ve literally had 2 sell minutes before I could snag them here locally. My understanding is that the fox mustang rear end is a bolt in deal, you just have to reuse the Cougar (or T-bird) axles and brake assemblies for the wheels to set right under the car. And the SN95 mustang rear is supposed to bolt in and be the correct width, but then there is the whole rear disk brake thing to deal with, different wheels, and converting the front to bigger brakes and 5 lug as well.

I have a 351w to drop in, with probably somewhere in the 350-400hp range. The 7.5” rear may take it on street tires, but no way the trans will. And beefy AOD’s are not cheap. I’ll probably end up going to a 4R70W anyway so I can retain the lockup function

[travis]

I think first I’m going to try the shorty headers and off road H-pipe, and see if the CFI will tolerate it.

[jeff swisher]

I ran a 6000 lb 1984 E150 with 306" Ford I built.
Big single exhaust. Small valve ported heads, plenum ported 2V intake and I ported the exhaust manifolds.

Goal was 20 MPG. First up was stock cam advanced 4 degrees.
That helped but not there . I then went with a 260H comp cam and it was more powerful everywhere and 2 MPG more.

Averaged 17.6 MPG with spirited driving AOD was in it and 9" with 3.50 gears.
Too heavy to use the OD.
Best MPG was mid 19's really trying to get MPG.

It ran 18.0 in the 1/4 mile.

Now I played with timing curves and bought an adjustable vacuum advance canister and could not make any vacuum advance show any gains in MPG.

My curve was all in my 2200 rpm 18 initial and 35 total.
Vacuum stayed high when adding some gas pedal to pass someone. Not flooring it just adding more throttle.
11" of vacuum during passing.
That way I was not in the power circuit in the carb. But vacuum would not drop out and I got pinging if timing was higher than 35 total.
Yes even at part throttle.
In the van with quiet exhaust you can easily hear the engine.

I built my own vacuum advance pot and tried as little as 3 degrees more and 10 degrees more and NO more MPG was noticed.
I had it set up to drop out at 12" vacuum and normal cruise vacuum was in the 18+ area.

I settled on 35 total all in by cruise RPM.
I drove that thing 30,000 miles a year most years and 15,000 on light years.
I kept it for 13 years.
Had a 3" lift on it and double overload springs on the rear I installed and 4 shocks up front.

I had a 350" chevy in a much lighter car 1978 Nova and 9" in it and I had some 2.29 rear gears Yes 2.29 ratio I stuck in it.
I had pulled my 370 gears and was getting 15 MPG with a small amount of spirited driving.

I had high hopes for the 2.29 gears but was rewarded with 8 MPG.
Timing curve was not in by cruise RPM so I made it all come in by 1600 RPM and got 18 MPG.
270H magnum cam and 750 carb with ported 186 heads.

That was a fun one. Shift into second gear at 95 MPH and bark the tires.

[BobbyB]

I think first I’m going to try the shorty headers and off road H-pipe, and see if the CFI will tolerate it.

Travis, How are you going to use the cougar? Daily driver? Weekend cruiser? Test bed ?

The 260 cam Jeff mentioned provided many smiles for me... I used it in a low compression 302, home ported heads, headers, 600 holley, small dual plane, 125 hp shot of nitrous, c4 with shift kit... tried 3.25, 4.11 & finally 3.00 gears with traction lock. All in a 3000 poundish 63 comet hardtop.

[hoodeng]

Engine ignition advance is specific to a vehicles application, you can have the same engine fitted to a number of weight and load vehicles that will have completely different load characteristics for given RPM's/road speed, as in say, a non performance 351C in a Mustang through to a F250 fully loaded and dragging heavy trailers etc.
What will be factory different in these engines will be, 1, Carburetor and settings, 2,more importantly will be curving of the distributor.

A dyno operator versed in mechanical/vacuum advance distributors should be able to curve the unit to give safe advance under all operating conditions.

[travis]

Travis, How are you going to use the cougar? Daily driver? Weekend cruiser? Test bed ?

The 260 cam Jeff mentioned provided many smiles for me... I used it in a low compression 302, home ported heads, headers, 600 holley, small dual plane, 125 hp shot of nitrous, c4 with shift kit... tried 3.25, 4.11 & finally 3.00 gears with traction lock. All in a 3000 poundish 63 comet hardtop.

It’s going to be primarily a weekend toy, maybe drive it to work once in a while, and the occasional long weekend trip. The car is a very comfy cruiser as it sits…I originally wanted to build it into something that would run deep into the 11’s but after driving it a while I really don’t want to ruin the comfort level of the car. Sheesh…I must be getting old

[Dan Timberlake]

What is it like driving around in 3rd, which should be about like changing the gears to 2.73s ?

There are stories on the internet that there is a certain amount of converter lockup in third gear. If correct that should be worth a few mpg too.