V8 firing order/exhausts

[Ralphh85]

why does the rover V8 have a 18436572 order, as down 1 bank its the equivilant of a 1234 firing order and on the other bank its a 1324 (same as ford S4).

just seems very ilogical? but ig uess there must be a reason.

main reason for askign is im gonna be building an exhaust soon and need to know best way to link them.

the range rover links them different on each side, which it hink is best, tho expect a good exhaust would have much longer primarys as the 100mm ones are gonna do nothing good.


Ralph

[mgbv8]

You trying to sort out a pulse tuned exhaust for the RV8 Ralph?

I'm pretty sure you have to swap the middle two of each bank to get it right.

There will be others along soon to give you the full griff.

[Ralphh85]

yeah, i have a mate who did motorsport engineering, an he made up a spread sheet for the rover k series engine which was what i had before, which gave points of power for what ever primary/secondary lengths. and the opposite way round.

shouldnt be to hard to adapt it tot he V8, just need the cam duration.

the inside 2 will be swaped but only one one side.

Ralph

[ChrisJC]

That's a big subject Ralph. Basically, the Rover V8 (along with most other V8's) has a dual plane crankshaft. This gives the best engine balance, but it means that each bank does NOT work like a four cylinder engine.
So on the odd bank, you get the following firing *--*-**- and on the even bank you get -**-*--*. You can see that you don't have exhaust pulses evenly spaced in time.

If you want exhaust pulses evenly spaced in time, you need the end two from one bank and the inner two from the other bank. This is very tricky unless you've got a GT40 where the exhausts are behind the engine rather than below.

Performance engines use a flat plane crankshaft which is the same as a four cylinder crank, so you get two four cylinder engines. The engine balance is as bad as a four cylinder, but you can do decent exhaust tuning. All high performance V8's are flat-plane. Of course a flat-plane engine sounds like a four cylinder, it doesn't have the nice burble of a dual plane V8.

See this
http://www.cowdery.org.uk/cranks.php for some animations.

Chris.

[ian.stewart]

I run a tri Y system, basically because of the lack of space, but it seems to work 1,5/8ths primaries about 200/220mm long, and are linked 1-5, 3-7, 2-6, 4-8,

[Ralphh85]

thanks for the infot here, of course power is the main point of my convertion, but i would give up a 100bhp to keep the V8 burble!!!

will look in to it more tomoz.

cheers
Ralph

[RoverP6B]

The cylinders numbered from the front of the engine on the nearside are 1,3,5,7 and on the offside 2,4,6,8.

Using the Rover 180 degree dual plane low rise inlet manifold fitted with twin SU carburettors, the offside carburettor fuels cylinders 2, 3, 5 and 8. The near side SU fuels 1, 4, 6 and 7.

Ron.

[ChrisJC]

Using the Rover 180 degree dual plane low rise inlet manifold fitted with twin SU carburettors, the offside carburettor fuels cylinders 2, 3, 5 and 8. The near side SU fuels 1, 4, 6 and 7.

Ron.

This means each carburettor sees four equally spaced induction cycles. Of course it's much easier to do this on the inlet side as it's all close together.

Chris.

[Ralphh85]

ahh just looked at chris's linkt here, so thats why the V8 is suposed t be more balenced as you never have 2 pistons goign int he same direction, unlike the staight 4.

interesting. i like V8's even more now!

im guessing if you where to link the same pipes as what the carbs do that would help.

tho most of this is sayign i should just make up an exhaust and not worry about it!


Ralph

edit, does anyoen have any idea what kind of pipe diamitor is good for the V8, 1.5inch primarys/secondarys, 2inch thirds and maybe a 2.5inch pipe back to the silencer?? or is 2.5inch over the top?

[ChrisJC]

ahh just looked at chris's linkt here, so thats why the V8 is suposed t be more balenced as you never have 2 pistons goign int he same direction, unlike the staight 4.

Not quite.

You would think that a straight four is balanced because for each piston going up, there's another one going down. But the piston going up isn't going at the same speed as the piston going down, so there's a net imbalance. This isn't obvious, but if you draw out the crank, con-rods & pistons for two cylinders 180degrees apart (e.g. at 45deg ATDC), you can see that the crank angle is different for the two pistons.

For a V8, the maths is complicated (and beyond me) to show that you can get perfect (I think) balance. The problem is that you need huge counterweights on the crank to do it, and this fact (along with the near impossible exhaust tune) means that as a rule, V8's aren't high revving highly tuned motors.

Chris.

[Ralphh85]

yea, they go different speeds due to the piston moving fastest while its at the top, as the conrod gets shorter (in height) as well as the crank moving down, if the conrod was only a tad longer than half the stroke it would hardly move lower 180degree's.

i dotn quite get whyt he V8 is any better but i guess it is! the longer the conrods the less this will be apparent i would think.


Ralph

[TVRleigh]

ahh just looked at chris's linkt here, so thats why the V8 is suposed t be more balenced as you never have 2 pistons goign int he same direction, unlike the staight 4.

interesting. i like V8's even more now!

im guessing if you where to link the same pipes as what the carbs do that would help.

tho most of this is sayign i should just make up an exhaust and not worry about it!


Ralph

edit, does anyoen have any idea what kind of pipe diamitor is good for the V8, 1.5inch primarys/secondarys, 2inch thirds and maybe a 2.5inch pipe back to the silencer?? or is 2.5inch over the top?

On the TVR's 400SE it 1&3/4" headers into a 2" that goes into a central box, and a 2.5" single out.

[Ian Anderson]

1.5 inch (The 1960's GT40s running 5l engines also ran 1.5 inch headers)
numbers 2 and 3 from each side crossed over to the other side and then into a 4 into 1 collector and 2.5 secondary wit a 1 in ch silencer on each side.

This then gives one pulse down each of th 2.5 inch secondaries in perfect timing

Loud and a great sound

Now this is possible on the rover and some TVR cars have had the cross over popes run forwards around the fan belt pullies!

This cross over system s said to give an extra 15 to 20 hp

I believe you are looking between 23 ans 27 inches on 1.5 inch promaries for best results depending on where you want the sweet point to be in the rev range.

Ian

[Ralphh85]

well due to easiness and room im goign to go with making something up which follows the current layout.

cheers for all the replyes an may put something more technical inplace at a later date.


Ralph

[TVRleigh]

1.5 inch (The 1960's GT40s running 5l engines also ran 1.5 inch headers)
numbers 2 and 3 from each side crossed over to the other side and then into a 4 into 1 collector and 2.5 secondary wit a 1 in ch silencer on each side.

This then gives one pulse down each of th 2.5 inch secondaries in perfect timing

Loud and a great sound

Now this is possible on the rover and some TVR cars have had the cross over popes run forwards around the fan belt pullies!

This cross over system s said to give an extra 15 to 20 hp

I believe you are looking between 23 ans 27 inches on 1.5 inch promaries for best results depending on where you want the sweet point to be in the rev range.

Ian

The TVR don't have cross over exhausts though they just bring the whole lot forward to a 6" dustbin.

I think the Tuscan Race cars had forward facing Exhausts with real cross over.

I've done a in between job, using the griff headers. due to limits of the engine bay size.

My custom install











and some Tuscan Race Car ones