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http://www.ffcars.com/ubb/ultimatebb.php/ubb/get_topic/f/1/t/064307/p/1.html#000000

i got the info from the above post. i originally had the 1-3-7-2-6-5-4-8, and the engine ran terrible.

i changed it around to the 1-5-4-2-6-3-7-8.

the frist one is for an HO engine, so the post says. i had a '90 donor, now i have carb, accel distributor, and edelbrock cam.

with the second firing order, it runs like a top! it's the same crank, so what is going on? even though it works perfectly, i would still like to learn.
 

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Beautiful engine, Eddie.
 

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Originally posted by Bill G:
It's the cam not the crank that controls the firing order.
Bill G
Half correct. The cam and the crank need to be matched to each other. If you had a cam with one firing order and a crank with another your engine will never run right, if at all. Imagine a cam that opens the intake valve on a compression stroke :eek:
 

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2savage,
For the 302 he is 100% correct. They all have the same crank arrangement. The cam simply has the lobes for the 3-5 and 4-7 cylinders out by 180° which is 360° of crank rotation. So the piston is in the exact same location but is on the compression cycle vs. exhaust (or vice versus).

Cheers, Rod
 

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Discussion Starter #7
NOW IT'S MAKING SENSE

the header on the #5 cylinder got so hot it turned red/orange, and i could swear it looked CLEAR, like you could see thru it.

i the engine off immediately, and it cooled in 1 second.
 

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Just think of it another way. The crank doesn't know if it's the compression or exhaust stroke. The cam tells the engine which it is.

Bill G :D :D
 

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Nice Guy:

STOP POINTING THAT FUC&*ng GUN AT MY DAD, LARRY! (now I get it, you man-made lake dog, you!)

Edelbrock's cam (PN2221 as memory serves and which I am absolutely positive you have), for the roller 302, as you have learned (as I did) the hard way, is not a cam that was made for the late model 5.0 HO engines. It was made for the early model blocks to allow the use of roller lifters and as such had the old firing order: 1-5-yada yada yada.

As Rod correctly points out, on the HO motor they switched the lobes on the cam for exhaust and compression on 3-5 and 4-7 and as such the crank remains the same.

My Ford guru here in the thriving metropolis of Yuba City told me that one theory of why Ford made the change was that because both front cylinders (1 and 5) fired BANG BANG, there was too much stress put on the cranks and as such they were experiencing too many cranks failures. Ergo the new firing order.

BUT (and if you take nothing else away from this, remember I talked about a big BUT) there is another issue that you need to be aware of: Cam base circle size.

The issue here is that the Edelbrock 2221 has a smaller base circle than that of an HO cam. The base circle is the diameter of the cam lobes MINUS the lob itself. Think of what the diameter would be if the cam didn't have an egg shape, but was completely round and you've got the right picture. On the HO cams the base circle is bigger and as a result the lifter sit higher in the lifter channels.

What this means to you is that your Edelbrock cam allows your lifters to sit lower in the lifter channel than a normal HO cam.

IF A LIFTER SITS BELOW THE DOG BONE ON THE DOWN SIDE OF THE CAM LOBE YOU'VE GOT SERIOUS ISSUES AS THE LIFTER COULD SNAG ON THE RECESS OF THE UNDERSIDE OF THE DOGBONE AND "KA-BLOOEY" THERE GOES A LIFTER, A CAM, AND QUITE POSSIBLE A WHOLE LOT MORE!!!!!

Once I determined that Edel's 2221 was a pre HO cam, which was after my motoer was completely assembled and I couldn't get it to run because of the firing order, I chose to yank the manifold to check out each lifter to ensure I had proper clearance. Fortunately, I did and so I did not have to replace the cam. But every block is different and I would not be a responsible member of this forum and a fellow snake charmer if I did not advise you to make sure you are in the clear.

As an alternative to yanking the manifold, you can remove your valve covers, pull your rockers and remove your push rods; and if you have a boroscope, can check each lifter on the bottom side of the stroke. As long as each lifter is at or above the top of the dog bone, you're cool. if not, well...have you seen the scene in Train Planes and Automobiles where Steve Martin is at the car rental counter? Remember what the woman told him? Yeah "You're Fu&^ed!"

Believe me, I spent hours with my engine guy, with COMP Cams, and hammering Edlebrock on the phone demanding they provide me the base circle size of 2221 and demanding that they change their marketing materials to more accurately inform people on what they are buying.

Okay, I'm off the soap box and want to wish you and everyone else who reads this a very Merry Christmas!
 

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Discussion Starter #11
perfect! i am going to print this out and add it to my bathroom reading material... the perfect place to read and let it all soak in.
 

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Eddie, I think you still have a problem. You now have a spark order than matches your cam order, but the fact this cam works at all shows that you accidently installed a crank from a 2-stroke motor! :D

Mike
 

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Originally posted by Eats 'm Whole:


My Ford guru here in the thriving metropolis of Yuba City told me that one theory of why Ford made the change was that because both front cylinders (1 and 5) fired BANG BANG, there was too much stress put on the cranks and as such they were experiencing too many cranks failures. Ergo the new firing order.
I thought the best firing order for crank strength (with no consideration for vibration or intake balening would be straight down the crank for one end to another. The 1-5 followed by the big diagonal 5-4 was replaced by a simillar 4-8 on the other end of the block following (instead of followed by) the 5-4 cross block order (cross engine is best for balence but hardest on the crank by what I've always been told). I'm not sure the explanation of your Ford guru is complete. May not be wrong, but not compelete. Possibly the crank support is stronger at one end of the engine that the other.

Mike

PS. I poked around the net and found the answer. As I suspected it is not the crank, but the journals, with the front main journal being considered a weak point on the Ford blocks. While the 1-5 (or 4-8) puts less load on the crank, it does load the front journal heavilly, while the 4-8 does the same to the rear main journal, it is considered stronger. You'll notice that previously the "cross block" orders were 1-5, 2-6, and 3-7 (everywhere but 4-8 at the back of the engine). They are now 2-6, 3-7, and 4-8 (everywhere but the front) stressing the front main journal less.

[ December 21, 2005, 02:51 PM: Message edited by: Michael Stora ]
 

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I think you will find that the reason for the firing order change was because of the extra load on the front main from the large accessory load on the later engines. Early ones only ran a few acc. on the front.

Bill G :confused: :D :D
 
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