old 302 firing order vs. 302 HO and 351 order. - Ford Mustang Forums : Corral.net Mustang Forum
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Old 11-04-2002, 04:14 AM   #1
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old 302 firing order vs. 302 HO and 351 order.

Why did the HO's go to the 137 firing order? Any reason for this?

I'm asking becuase I'm eyeing a cam with the "old" 154 firing order. I currently have the 137 firing order. It is a carb setup, so I just need to swap plug wires.


And most importantly.. will it sound different? :P
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Old 11-04-2002, 07:45 AM   #2
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The 'old' 1-5 firing order puts more stress on the end of the crank.

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Old 11-04-2002, 08:03 AM   #3
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154--137

Zackly!! the 5.0 "peanut" cranks break at 1-5 journal!! 'cause there so light and weak ( the trick is to get an early 302 crank), so Ford changed the firing order to help!

Cam grinders say " the 154... firing order will make MORE power than the 137 firing order", but then there is that cranshaft thing again!!

Just me.................

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Old 11-04-2002, 08:28 AM   #4
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The firing order changed from 15426378 to 13726548 because the camshaft dictates the firing order and the camshaft was chosen for the then-new H.O. 5.0L in '82 due to time contraints and availability, nothing more. Engineers in charge of developing the H.O. 5.0L engine for the Mustang wanted to afford it a better camshaft than what was currently being used but could not justify tooling a brand-new one so they sourced one from a previous 351W application (D3OE-6250-AA which is a '73 Torino application, NOT marine).

Last edited by FoxChassis; 11-04-2002 at 03:51 PM.
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Old 11-04-2002, 11:17 AM   #5
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I was told by the then SVO techline that it was due to trying to eliminate the stress on the crank and bearing wear.
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Old 11-04-2002, 12:48 PM   #6
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Then why change sequential firing of opposing cylinders from the front to the rear? Look at the old firing order and the new firing order; sequential firing of opposing cylinders changes from the front (cylinders 1 and 5) to the rear (cylinders 4 and 8). Any coincidence that rear main seal failure seems to happen often? If there was this alleged stress on the crankshaft and/or bearings why did they wait until '82 to address it?
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Old 11-04-2002, 12:58 PM   #7
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firing order..

Go with FORD!! they did it for the crankshaft and bearing failure!!
Retooling??? Sourced up old 351 Cams?? really dont think so... but hey, it was cool??

Just me.........................

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Old 11-04-2002, 04:12 PM   #8
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It's fairly common knowledge that the H.O. 5.0L flat-tappet camshaft is an old 351W grind. The Service Part Number is D3OE-6250-AA (D3O = 1973 Torino).

There were factory 289 and 302 engines producing more factory-rated HP than what the '82 H.O. was rated at (157 HP) that were using the 15426378 firing order and CERTAINLY many more that were modified and producing power levels far beyond what the factory ever offered, most of which still employed the factory cast iron crankshaft and certainly the factory firing order. Where are all the crankshaft and bearing failures in those engines?
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Old 11-04-2002, 04:50 PM   #9
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Quote:
And most importantly.. will it sound different?
Good question. The 5L cars seem to have a distinct growl... which turns into a droan when you open up the exhaust.

Maybe it was changed so it would sound a little meaner with the restrictive, catalytic exhaust?

Foxchassis' explanation seems plausible... platform sharing & parts interchanging saves money. But why not use an old 302 cam, or change the 5.8's firing order?

Maybe the rear of the thin-walled casting was designed to be a little more solid? (for the flywheel, bellhousing, etc)?

And why was the waterpump & distributor rotation reversed?
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Old 11-04-2002, 05:57 PM   #10
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Distributor rotor rotation has always been counter-clockwise.

The reverse rotation water pump was dictated by the serpentine belt-drive system.
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Old 11-04-2002, 08:54 PM   #11
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I have herd the storys about the standard 302 Firing oder being hard on cranks and Bearings, But what I don'r understand is why they only used it on the 302HOs? if it was hard on things you would think they would have switched it on the Non-Hos to??
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Old 11-04-2002, 09:11 PM   #12
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Needed more duration in a hydraulic flat tappet cam. The 302 with conventional fireing order was too short duration. The 351 cam fit the bill, saved developing a new cam. Stress had/has nothing to do with it.

The original Ho engines, ie the solid lifter 289 had no problem... but also required a little more tunning than the hydraulic flat tappet.
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