Firing Order question

I am helping a friend tuning his 383 stroker with a 471 blower.
The motor starts and runs but under load it's sputtering out of the carburetor. I suggested a timing order check. This is what was found, not a standard order. 18627345. Has anyone any info on this firing order?
Dose it indicate a special crank/cam combination?

 

I've seen on those TV shows where they change the order when they go to heavy boost, etc. If this is a built engine think I'd check with the builder if that's the case. If not, then the thing is def. screwed up timing order wise.

 

I don’t think that’ll work as 6 won’t be on a firing stroke after 8 no matter what you do with the cam

If you want a definitive test. Pull the plugs, turn the engine over by hand and when the rotor arm is getting to firing point check the piston is approaching top for that specific cylinder, put your finger over the plug hole and make sure it’s got compression

 

You MIGHT...tell us... I assume that you are talking a original style, small Chevy ???

Why don't you JUST LOOK IT UP ? The answer is ALL over the internet.
18436572
Been that way since 1955 !

OR...
if he has a 4-7 swap cam ? Then it's -
18736542

Mike

 

Can't be.

Each cylinder sees the piston at TDC twice during the combustion cycle.

You can grind a camshaft to change the function in the cycle when the piston is at TDC, but you cannot change the position of the piston.

You can do a 4-7 swap, because both pistons are at TDC at the same time.

The sequence of piston movement in an SBC, and tons of other V8's is controlled by the fact that two cylinders/rods/piston share a rod journal.

18627345 does not work.

If you start the firing order on one, the next piston up is 8. After that, 4 (which happens to be when 7 is at TDC, too).

It sure ain't 6.

18436572

Even an old-school small Ford has the same firing order, except they name the cylinders differently, and a different cylinder is #1.

18436572
54263781

Despite the differences in the number scheme, those are the same spatial relationships.

Yes, both a custom cam and crank can be made, but that's unlikely.

Viewed from the front, and expressed as the circle they move in, there are rod journals at fixed intervals on that circle.

Yes, you can "move" the cylinder pairings to a different place, but those intervals don't change (except on a flat-plane crank, or weird offset ground rod journals).

Offset grinding of journals doesn't change the firing order, just piston timing.

You'd know if it had a flat-plane crank.

 

"The motor starts and runs but under load it's sputtering out of the carburetor.".....383 stroker with a 471 blower???
That seems like an odd description to me.....are you saying its backfiring? like a typical lean backfire?

 

If you swapped every pair with a custom cam you get:

65721843, which is still the 18436572 sequence, just starting in a different place.

The TDC pairings are:

1 and 6
2 and 3
4 and 7
5 and 8

Those are the only eligible swaps, and they have varying harmonic consequences.

The third timing event can only be 4 or 7.

In order for the #6 piston to be at TDC on the compression stroke, third in the order, #1 would also have to be at TDC on the exhaust stroke, at the same time that it is at the end of the power stroke.

 

Keeping note of the firing order you had at first, what happens when you rewire it?

 

My son has an early 60's inboard ski boat with a rumpity-rump 327. When he first got it, would start and idle fine, under a load it'd pop and backfire through the carb and stumble. We put new Pertronix module in it, among other things, and when I put the new plug wires on the cap, 5 and 7 were swapped. The firing order you describe shouldn't run at all, but I guess stranger things have happened. Try ordering it properly and see what it does, and make sure you're starting by looking at the cylinder numbering properly...

 

How this even starts is beyond me.

You have only two correct spark events, 1 and 8.

You have two sparks as the exhaust valves are opening, 6 and 7. This will light off fuel in the exhaust.

You have two sparks as the intake valves open, 2 and 4. This will light off fuel in the intake.

You have two sparks at the beginning of the compression stroke, 3 and 5. This will light off fuel in the cylinder, pushing on the piston at the wrong time. Low compression ratio and uncompressed mixture may be the only reason that this doesn't stall the engine instantly.

 

Make sure that this is your map.

 

Your Chevvie should be 18436572 clockwise. Cylinders 1,3,5 and 7 are on the drivers side, 2,4,6 and 8 are on the passenger.

Your cam may be a 4/7 swap, but most likely not.

-Abone.

 

Gimpy was kind enough to post a picture. Go with that and you will be fine. Once you get this figured out, we will help make sure the distributor is in the right spot.

-Abone.

 

Pull all the sparkplugs. The engine should turn over by hand.
You didn't say what you have for a distributor but line the rotor up with the #1 cap/wire while also determining that the piston is at TDC.
Then just roll the engine to clock the rotor to the next cap/wire in the firing order and check the piston to see if it's a yes or a no for TDC.
You should be able to tell right away which firing order you have, the usual Chevy order or that one in the first post, without tearing anything apart.

Try googling "1862734 firing order" and see if you get any hits.
..

 

I think the distributor is wired correctly, your friend has just numbered the cylinders wrongly.

If you thought the cylinders were numbered 1-4 down one bank and 5-8 down the other, the 18436572 firing order would look like 18627345.

18627345
8 ........... 4
7 ........... 3
6 ........... 2
5 ........... 1
(front)

18436572
8 ........... 7
6 ........... 5
4 ........... 3
2 ........... 1
(front)

 

Genius!!! Good call

 

It took Kiwi ingenuity, that's exactly what has happened. Even the wire tags had it wired with the wrong numbers.
Going by SBC firing order it is correct. It is a case of bad timing and carburetor tuning.
Thanks for your input. Cheers Mate from Texas.

 

Thank you , problem solved

 

Start all over with what the members have shown. Get the ignition sorted so there is no question. Then, take the carb off and check it over fully. If it's got a power valve (Motorcraft or Holley), double check that to make sure it wasn't blown from the sneezing.
Under load is when issues start. The ignition is under more load (and a blown application should have less gap), and the fuel system has to provide more fuel although the carb isn't seeing a different signal due to the blower. You need to check each part of the system and confirm it's in good working order before tuning.
EDIT: you answered before I hit post. Glad that was the answer, but you aren't out of the woods yet.

 

To all who took the time to give an answer to this question, thank you.
Problem, incorrect cylinder numbering.

 

Well I can guarantee that he isn't the first one who ever did that. When I put my T bucket together I wired it just like I always wired my 69 Cutlass S with a 350 R in it. I don't think the neighbors appreciated it one night at 02:20 when I woke up from a dead sleep with the That I had wired it totally wrong, went out in the garage in my robe, rewired it, fired it up let it run for a few seconds and shut it off and went back to bed. That was in Texas too.

 

The way I have seen this done is to take the ceramic out of a spark plug put a balloon over the metal bit, screw in plug hole turn engine over, when balloon is blown up to max check here rotor arm is. I would draw a circle on a bit of cardboard with a reference point of the distributor, then mark 8 points on the circle. Where the rotor is at full compression mark the appropriate place on the card. Just noticed I was a bit late for the party. Might help someone in the future though,

 

Now that you have a understanding On timing,, You can Use any poll on cap As
# 1 TDC & piston @ TDC ,& rotor lined up with that poll , & start firing in order on Standard sbc firing
18436572 & if was a 4-7 swap 18736542,

Asking about your 383 combo with
4-71?
What stage /case 4-71 you have?
Cam size spec ? Where Initial timing
set ? & total ?
Plug heat range ?
Boost psi ? Under or over drive ?
Belt type ?
Carb or carbs sizes ? what fuel ?
Jets ? Squirter? Pv ? Cam pump?
Fuel psi ? Size fuel lines ? Tank to carb or carbs ? Fuel pump ?
How many RPMs you plan or trying to turn ? How heavy is vehicle?
Trains Stick or AT?
Yes many Questions before you melt pistons ,Kick rods , burn a block , heads,

Just going back to the 4-7 swap ,
High Hp ,Big CID ,boost / Nitros use & center counter weight bouncing to spread load across mains more evenly