Firing Order

[02vettekiller]

Ok guys. This is probably a dumb question but here goes. The motor in my 91 5.0 is out of an old cougar or some crap but regardless has a 15426378 firing order. It runs like a champ and I have no problems but want to install a new FMS cam which are designed to use the new 351 firing order which is 13726548. I pulled the intake already and it is a roller motor, hence the spider and the tie bars on the lifters. Can I just put the new cam in and change the firing order or do 302's have different crankshafts which won't allow me to do this. I thought a 302 was a 302 when it came to cranks rods and pistons. Please help.. I am ready to get rid of my wimpy cam this weekend. Thanks, and please help

 

[71swing]

yes, the crank will determine the firing order. you can not change the firing order by just changing the cam. It will keep the same fireing order but dapending on the cam specs you may still be able to use it.

 

[blkcobra50]

I thought all 82 - up 5.0 HO's had a 13726548 firing order the same a 351W's?? And pre-late 80's non HO 289/302 had the 15426378 firing order which I think are flat Tappet blocks? I'm not saying you are wrongbaout the firing order on the cougar motor but never heard of a HO motor with a flat tappet firing order. correct me if i'm wrong someone

 

[jrichker]

yes, the crank will determine the firing order. you can not change the firing order by just changing the cam. It will keep the same fireing order but dapending on the cam specs you may still be able to use it.

Wrong answer.

The crankshaft is the same for plain 5.0's and HO engines. The camshaft determines the firing order. Putting in a HO cam makes a plain 5.0 use the HO firing order.

A V8 crankshaft has to be laid out with the crank throws at 90* to work. Each throw will have an intake, compression, power, and exhaust stroke determined by the camshaft. The relative position of the each pair of camshaft lobes to the other pairs lobes determines the sequence when these events will take place for each cylinder.

Don't forget to use the HO computer, or the engine won't run at full potential.

How to verify that it is indeed an HO engine: remove the #1 & #3 spark plugs. Put your finger in #1 spark plug hole. Crank the engine over until you feel compression on #1 cylinder. Slowly turn the engine until the TDC mark and the timing pointer line up. Mark TDC on the balancer with chalk or paint. Put your finger in #3 spark plug hole and crank the engine 90 degrees. You should feel pressure trying to blow past your finger. If you do not feel pressure, repeat the process again. If you feel pressure, it is a HO engine.

No pressure the second time, remove spark plug #5. Put your finger in #1 spark plug hole. Crank the engine over until you feel compression on #1 cylinder. Put your finger in #5 spark plug hole and crank the engine 90 degrees. If you feel pressure now, the engine is not a HO model, no matter what it says on the engine.

Using a small carpenter or machinist square to mark the harmonic balancer off into 90 degree sections may be helpful here.

A 15/16 deep socket & breaker bar or ratchet may be used to turn the engine.

The HO firing order is 1-3-7-2-6-5-4-8.
Non HO firing order is 1-5-4-2-6-3-7-8

 

[71swing]

The crankshaft is the same for plain 5.0's and HO engines. The camshaft determines the firing order.

Is that not what i said.

 

[JChalfan]

Is that not what i said.

Um, no not really.

You said the crankshaft determines the firing order, which is not entirely true. The camshaft determines the firing order.

The crankshaft does dictate what firing orders are possible. You could not have 1-2-3-4-5-6-7-8.

In a 302, you CAN change the firing order with just the cam, no need to touch the crank.

Jeff