The two different firing orders questions

[olddog]

Thanks guys.

At first I thought there could be know differance in performance. Then I thought it could change the exhaust scavenging (SP?) and even smooth out flow in the intake. So then I thought it was possible that it could impact performance, so I had to ask.

I sure would like to hear both engines side by side, just out of curiosity. I'll have to pay attention at some car shows.

Is that factory cast iron cranks that tend to break? I wouldn't think anyone would stroke and build more Hp with the smaller mains of the 5.0 block if the larger mains 351 block already soves the problem. If the cranks are a known problem, I will rule a 5.0 completely out right now. However if steel cranks are OK then I may keep it on my maybe list.

[Dennis Kelley]

There are no problems with the stock 5.0 crank or block up to 400 fwhp. the only time you run into problems is with power adders and poor tune. the standard 5.0 rotating assembly from 86 thru 92 is very durable. I have a stock 86 motor in my mustang that has 300000 mile on it. I seen motors sprayed at 150hp level on a conservative tune last for several years. You can break the block with boost or spray but I would think that you would be hard pressed to destroy one naturally aspirated.

later

dennis

[Sizzler]

In the late 70's, Ford engineering basically went down the tubes.

We ended up with the modular engines, bigger dimensionally, severely limited internally. The engineering plan was apparently to design and build a motor bigger than the biggest big-block Ford made, to install in vehicles (someone, I hope) they forecast were going to get smaller due to the gas shortages. The 'plan' was to take up a larger percentage of the available volume in these smaller vehicles?

These same engineers, when faced with developing the H.O. 302, which didn't roll over and die for the modulars, were looking for more HP. So, they pulled a existing cam out of a 351W performance catalog and used it in the 302. More power from that cam; cheap 'development' costs. That's all the reason for the change in the 302's firing order. As for the 351's firing order? Petty change for pettiness sake? Just to make it different from GM's firing order? Maybe to take some load off of the front main bearings which in the old firing order were hit bang bang in sequence while the new order gives them a little rest between hits?

Anything Ford has done since 1970 has not impressed me.

[Woodz428]

As has already been posted, it was indeed main bearing loading that Ford was re-distributing. I would have to look at the early order, but think it had to do with not having 2 firing pulses (one after another) on the same main. The other comment about the early H.O. cam is also correct, the original cam used in tests was a 351 marine cam. That neccesitated the 302 change, although the initial change made in the new (at the time) 351W was main loading.

[DSGcoupe]

Originally Posted by Woodz428

As has already been posted, it was indeed main bearing loading that Ford was re-distributing. I would have to look at the early order, but think it had to do with not having 2 firing pulses (one after another) on the same main.

I know this is an old thread and I am newer to this forum, but not to the automotive world. I am curious about the theory behind the above quote. When looking at the two firing orders, it appears they just moved the load to the rear two cylinders instead of the front two (front crankpin journals to the rear crankpin journals)

Old FO= 1-5-4-2-6-3-7-8
H.O. FO= 1-3-7-2-6-5-4-8

this leads me to believe that it was more of a bean counter move to save on production costs.

(I will sit back with my bucket of popcorn now. )