Exhausting question.

[dikko]

it's only a lowly Kent Formula Ford engine but I have noticed there is quite a step-out in the opening of the exhaust on the pipe manifold.

The pipes are a much larger bore than the outlets on the head.

Q. Would this step create enough turbulence to result in power loss by creating back pressure and upsetting exhaust flow?
Q If so how much? Anything significant?

I wonder if there is an advantage in funnelling out at that point or am I whistling in the wind and just need to put my foot down further and close my eyes more...

[zefarelly]

Hi Dikko . . . . just seen this . . . . if the flange holes match the port and the tubes are bigger, this is no bad thing . . . . it helps prevent any reversion, although with such a tame cam it will be minimal . . . . overall header length is more important for HFF.

[dikko]

Ta Joe, just trying to eek another BHP out of it. Best brake later I suppose!

[IsabellaKelly1979]

Q. Would this step create enough turbulence to result in power loss by creating back pressure and upsetting exhaust flow?
Q If so how much? Anything significant?

In my opinion it may result in power loss quite substantially, but I will ask my friend who is abroad at the moment and knows a little bit more than me

[Gungebucket]

Originally Posted by dikko

it's only a lowly Kent Formula Ford engine but I have noticed there is quite a step-out in the opening of the exhaust on the pipe manifold.

The pipes are a much larger bore than the outlets on the head.

Q. Would this step create enough turbulence to result in power loss by creating back pressure and upsetting exhaust flow?
Q If so how much? Anything significant?

I wonder if there is an advantage in funnelling out at that point or am I whistling in the wind and just need to put my foot down further and close my eyes more...

Having spent a lot of time building FF Kent engines and doing exhaust development I can tell you ( fact not opinion) that you should leave the primary pipes with the step to the exhaust port. Any attempt to provide a taper simply results in lower power output.

[FastDB2s]

in 2002 we had our 1st alloy Aston Martin DB2/4 head ported by Motorman, he tapered the port out to the same size as the manifold, we never got great power of that head whatever engine it went on, whatever cams we ran.
In 2004 or 5 we had another guy port our heads, ex Cosworth, he tidied the exhaust port but left the step in as he said it was worth over 10 bhp, he was right, same spec engine, same inlet airflow, little or no improvement in exhaust flow but 10 + bhp up on a 2.9ltr 6 cylinder.

[dikko]

Cheers guys for an interesting and surprising answer - wasn't expecting that.....

Another 10 hp for my Formula Ford engine would be rather good too...(( ^ :

[Gerard C]

@ FastDB2s: do you remember the exhaust port diameter and the step size, please?

@ dikko: I dont think you can expect 10 hp more from a FF engine though, but almost all the small displacement engines I saw (4 cylinder bikes 600 cc and 1000 cc) had this step between the exhaust port and the manifold (sometimes in the head itself). Any attempt to remove the said step gave very bad results in terms of power and torque, as confirmed by Gungebucket.
May be it does not sound "logical" but the power sheets dont lie.