302 vs. 351 firing order

[billysboat]

I've read the posts about the firing order differences in these two engines. My 66' champion which I just bought has had the original 302 swapped out with a 351. As far as I can tell, it's a 351 and brand new too, plus all the accessories. I was also told by the former owner the motor has only about 10 hours on it. It has a 351 eldebrock intake and I am guessing that this manifold will not fit on a 302 block. It also has a Holley marine 750 double pumper which I know is another issue all on its own.
I took it to the R.Y.C. yesterday (we call it the redneck yacht club) and man... did it turn some heads. So after it started right up with a nice idle we all thought it was going to set the water on fire. Limping it back to the dock, we all wondered why it seemed like it was not firing on all cylinders.
I came home and started looking on the net and discovered it had a 302 firing order. Looking at the posts on this site I then seen that fords will run on both firing orders, but a 351 running on a 302 firing order will crap out, backfire, and spudder when giving it throttle.
.... so I changed the firing order to a 351's and it wouldn't start. Changed it back to a 302 and it started right up. but it wouldn't rev and backfired through the carb. Now here is my question. Should I stick with the 351 firing order and just would need to adjust the distributor and reset the timing to get it started? Or, are there any other than the two firing orders that I've seen posted on this site or others for marine cams or ford motors?
Thanks, and even though I am a newbie, I'm still a redneck with a computer.

 

[bomar76]

Re: 302 vs. 351 firing order

1. Most people have no idea Ford Small Block V8's are numbered thussly:
Transom
4 8
3 7
2 6
1 5
Front of boat

2. Most people are unaware the dizzy spins Counter Clock Wise

Fix the firing order using the above info and you will most likely find your troubles.

 

[zbnutcase]

Re: 302 vs. 351 firing order

And it is the camshaft that determines the firing order. And as cams are fully interchangable, It could be either. If you want to get technical, there are four possible firing orders, two for standard rotation engines and two for counter-rotation.

 

[Bt Doctur]

Re: 302 vs. 351 firing order

Not to mention some 302`s use the 351 firing order too.

 

[Bt Doctur]

Re: 302 vs. 351 firing order

 

[billysboat]

Re: 302 vs. 351 firing order

O.K. now it is getting tricky. I see from the diagram that the distributor always rotates in a counterclockwise direction for either a R.H. or L.H. motor.
Would it hurt the motor if I try all four firing orders? And would it even run if it was reversed ?

 

[Bt Doctur]

Re: 302 vs. 351 firing order

you need to tell us the direction the pully or flywheel turns when you hit the starter

 

[Bifflefan]

Re: 302 vs. 351 firing order

if its a single motor then its most likley a standard rotation. start with the firing order for the engine 302 or 351 which ever. if it runs ratty then switch to the other. you wont hurt it if you try the wrong one. it just wont run well.

 

[billysboat]

Re: 302 vs. 351 firing order

I figured out it was a standard rotation. Took off the valve covers as was mentioned in another post. Took out #1 and found tdc. Watched the valves and #5 was the next one to fire. Then used the 302 firing order 1-5-4-2-6-3-7-8 , it started right up. I do need to check or adjust timing cause I moved the distributor around some. No backfires and rev's a little better now.
.... so now do I check dwell or timing first?
My next post will be about Holley Carbs

I appreciate your help and can't wait to post a pic of this boat.

 

[Fishermark]

Re: 302 vs. 351 firing order

.... so now do I check dwell or timing first?

You set the dwell, and then the timing. The dwell affects timing, but not the other way around.

 

[billysboat]

Re: 302 vs. 351 firing order

Dwell it is then sir.

BTW what would the dwell setting be?

 

[Fishermark]

Re: 302 vs. 351 firing order

point gap should be .017
dwell 26-31 degrees

 

[billysboat]

Re: 302 vs. 351 firing order

Got the dwell at 27. And now a little closer. Timing later when I get a light, but the fun was killing a dreary east coast Sunday to be ready for next weekend.
Out

 

[bryanboonelake]

Re: 302 vs. 351 firing order

302,351W is 15426378

351C is 13726548

so I guess it could be either one. Im not familiar with Ford marine, but I restore old mustangs, so try both of those

 

[jtybt]

Re: 302 vs. 351 firing order

Merc used the 351 cam on at least some of their 302 engines.

My '72 888 (302) has 351 firing order because it has a 351 cam

 

[haulnazz15]

Re: 302 vs. 351 firing order

The 351C was never used in marine applications, so disregard anything related to that engine. 351's use a 351 firing order, unless someone put a 302 cam in it. The 351 firing order is better balanced.

I thought only the later 302's used the 351 firing order, I know the 302 H.O. did.

 

[billysboat]

Re: 302 vs. 351 firing order

.... so if it is running now using the 302 firing order, My question would be, will it run on a 351 firing order? And what would the benefits be of using a 302 camshaft?

 

[haulnazz15]

Re: 302 vs. 351 firing order

There aren't any benefits to running a 302 cam.

 

[billysboat]

Re: 302 vs. 351 firing order

....so I was still wasn't happy with the way it was running. Popping out the carb when trying to throttle it too fast. The dwell was on and timing too, I was thinking the carb was next and I took my mechanics advice to check the firing order again, he said, an easy way to tell 302 vs. 351 firing order is to take the number one, three, and five spark plugs out, disconnect the coil and turn it over to find TDC on number one, the next cylinder out of number three and number five to reach the compression stroke will tell you which firing order to follow. Mine was the 351 firing order after all. The timing still marked the same after checking it. The motor started right up and now no pop and rev's up fast.
I think this theory will work on all motors if you have enough fingers to plug the spark plug holes.