Changing firing order..
Turbo Mini Forums

I was looking at the swiftune DC5 crank thinking what a great idea it is, not because I'm about to buy one, but just out of general interest. Then I thought about firing order.

Wouldn't it make more sense, if going to the trouble of designing a completely new crank, to change the firing order to 1324 or 1423? Would need a cam with lobes in the appropriate places, but seems like a good idea for those using a 5 port cylinder head, either for nostalgia or some competition rules etc. My brain and scrap of paper can't work out if that would mean a crossplane crank but that makes no odds does it..

Thoughts? or a link to someone that has tried it?

its been done,

WWW.FORCE-RACING.CO.UK PLEASE CLICK HERE

THeres been a few posts on here about it too....

AlexF

BMW K head conversion firing order is different

I think you'll find the BMW firing order is 1243 - a straight reversal of normal 4 cylinder 1342. Anything else would need a special crank with big ends 1 & 2 on the same level, and 3 & 4 likewise - resulting in a balancing nightmare.

1971 Austin (Healey) Sprite - running turbocharged since 1993
My Car thread: http://www.turbominis.co.uk/forums/index.php?p=vt&tid=448825

Quite right - but it is fine with the standard crank - it's just a case of fitting the plug leads in the right order to match the order dictated by the cams. But to go to 1324 or 1423 (to make alternate pulses on the inlet ports of a five port head) would require a change of crank, to something horrible!
As an aside, in the vintage world, some of the serious Bugatti Type 35 racers do change the firing order of the straight-eight engines, to make more efficient pulses in the intakes - but I believe this is again without changing the crank. I also found this - where Yamaha have uneven intervals... http://www.autoblog.com/2008/09/08/yamaha-...g-firing-order/

1971 Austin (Healey) Sprite - running turbocharged since 1993
My Car thread: http://www.turbominis.co.uk/forums/index.php?p=vt&tid=448825

What would be the benefit of changing the firing order? Would you not suffer from any crank flex or similar if it were 1423 due to no.4 firing straight after no.1 which is at the opposite end of the crank? With 1342 you never have more than 1 cylinder between firing cylinders, if that makes any sense?

The only difference I can see affecting anything is exhaust tuning on the shared centre port?

www.topcatcustom.co.uk

topcat, it would be to eliminate charge robbing in the inlets

I seriously doubt it!

Ah of course, pretty obvious now...

www.topcatcustom.co.uk

Stupid idea.

It would totally fuck up the inner cylinders by having the two exhaust valves open at the same time on the siamese exhaust port. One opening just as the other is going into overlap.

Dead end.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

As Paul said

I seriously doubt it!

That is the answer I needed. Cheers, saved me a lot of paper and pens..

you could go "big bang" requiring only a camshaft change

turbo 16v k-series 11.9@118.9 :)

Denis O'Brien.

remember when youre messing with the timing order in this way it is possible to get crank/cam conflict!
so you'll have to consider different rods.

never said it was a good idea

turbo 16v k-series 11.9@118.9 :)

Denis O'Brien.