Standard Firing Order or H.O./351 in a 302 ??

Anyone have any input on losses or gains using a H.O. firing order on a carburated 302 base engine ? Spoke with a pretty slick engine builder who said that he always see's less bottom end with the H.O. firing order on a carburated 302. Just wondering as I have a H.O. order cam and thinking of going mech flat tappet.


Thanks, Coop

 

i didn't dyno on the 302 firing order, but I tell you, I really like the sound of the 5.0 firing order on my cam.

don't mean crap for power, I agree. But sounds great.

Dyno numbers weren't all that shabby, considering the build I have.

 

I`ve never heard of it making any difference power wise

 

The chevy guys have talked this stuff up for years. Lots of guys keep saying that going to a 4-7 swap camshaft picks up a few HP. BUT..keep in mind that since they're swapping camshafts, the lobe profiles may (and usually) are not the exact same as the one that's coming out. Stock 1-8-4-3-6-5-7-2 Chevy firing order is exactly the same as the 1-5-4-2-6-3-7-8 order of our early 302's and 289's. The 5.0/351w firing order (1-3-7-2-6-7-4-8) is identical to the LS1 firing order....which is 1-8-7-2-6-5-4-3, a.k.a "4-7, 2-3 swap"---which is why LS1's sound a little like Ford engines (cause the firing order is the same).

GM numbers they're cylinders differently. Theirs are 1-3-5-7 from front to rear on the driver's side and 2-4-6-8 on the pass. side.

I believe R-M did a back-to-back test on a 4-7 swap cam and a standard cam in a BBC and there was less than a 1hp difference between the two. Going off of memory-might want to check into it for yourself. R-M is Reher-Morrison Racing Engines.

Reason for the change in firing orders-the engine runs smoother. The whole NVH thing.

 

Running smoother sounds like a good enough reason. Would seem to help with longevity

 

It is my understanding that the change in firing order was to eliminate a harmonic vibration that could occur with the original firing order. Harmonic vibrations can break cranks and cams but it seems iffy that swaping one set of adjacent cylinders to another is going to do more than put the vibration in another place.
??? maybe it works ???

 

Did some more searching and found Ford made the change to take load off the block and what not. Im really thinking of a cam swap and looking into a Mech Flat Tappet. Guess Ill keep the 351W order that mine is now. If anything I wont have to change the wires around on the cap...LOL

 

Thanks for that great info. I have always heard that the reason was so the engine ran smoother too. I have also heard that it helped prevent Plugwire crossfire between 7 and 8 firing right behind one another.
Also It is said to reduce crankshaft and block stress by not having two cylinders fire right next to each other.

Chevrolet has shamelessly integrated ALOT of fords designs into the LS engines....making them great engines witthout a doubt.:16suspect

 

So instead of 7-8 firing together you have 6 - 5 firing together.
When I first looked at the change (years ago) I figured it was stupid because now you had two cylinders firing together further from the flywheel which would cause more crank twist - (more hamonics). as far as putting less load on the block... exactly how? Same torque, same side, different place.

 

Not sure about power ... but I'm running a 1995 HO motor in my Grabber ...

It sounds more like a late model car than an old school V8 ... has to be the firing order that makes the different sound.

 

When Ford was developing the 351W they originally tried using the old 289/302 firing order. Along with NVH it also caused durability problems with the 351's front main bearing, so they changed the firing order. When the 5.0 came out they used the 351W firing order. Some say because Ford originally fitted the 5.0 with a 351W cam, others say strictly for NVH reasons.

 

Seems like that with the old firing order, 1 & 5 fire 90° apart, which would tend to twist the crankshaft because those are the two front cylinders, and both rods are attatched to #1 journal.

New firing order places 4 & 8 at 90° apart, which places the load on the #4 rod journal-which is in the rear obviously-which would reduce crankshaft "whipping".

Also-some cam guys have been experimenting with a Ford version of a 4-7 swap (without the 2-3 swap). Basically it would be 1-5-4-8-6-3-7-2 firing order on a Ford engine because of the way the cylinders are numbered differently. To my knowledge, not enough people have played with it to know whether or not it does anything advantageous as far as intake pulse tuning and exhaust scavenging. I'd certainly like to try it-so long as the cam guy gives the cam to me. $400 + gaskets and fluids is quite a bit to swallow for R&D. The sound, though, would definitely be different. I know that on the BBC, going from the standard firing order to a 4-7 swap definitely changes the tone-and many say that the 4-7 makes the engine smoother running. Some have experienced gains in HP and TQ but as I mentioned, those are the folks that have actually changed the lobe profiles.

If we were "really" serious about pulse tuning, exhaust scavenging on a race engine, we would be looking at a special camshaft and a "flat" (180°) crankshaft-although-the sound of it would definitely be an attention getter