H pipe exhausts on V8 - are they quieter?
Discussion
Does anyone know for certain if an H pipe exhaust reduces noise levels on a V8 exhaust (the H pipe being a pipe whihc links the two banks?)
I think the answer is YES on a two plane cranks V8 such as an SBF or SBC, but what does it do for an engine with a flat plane crank such as an F355 engine - anything?
I think the answer is YES on a two plane cranks V8 such as an SBF or SBC, but what does it do for an engine with a flat plane crank such as an F355 engine - anything?
I know them a balance pipes, but I think its mildly performance enhancing on certain cranks and firing order combinations. The logic is along the lines of:- Ideally, you would have two of the header pipes from each bank going into each collector, but because this isn't very practical, the balance pipe helps make up for it. My tuning bible is out in the garage, so I can't tell you which cranks etc benefit. I might remember to pick it up tomorrow.
I think it works on SBF and maybe SBC. X -pipe defo works on SBF as thats effectuively what the GT40 had.
Thye purpose is to even out the pulses from a firing order which is imbalanced on the individual banks.
Theb heart of my question is that an exhaust manufacturer has told me a flat plane V8 can be made to sound like a V12 using an X-pipe. I'm trying to figure if tis is true or not.
Thye purpose is to even out the pulses from a firing order which is imbalanced on the individual banks.
Theb heart of my question is that an exhaust manufacturer has told me a flat plane V8 can be made to sound like a V12 using an X-pipe. I'm trying to figure if tis is true or not.
Two plane cranks have three exhaust layouts:
A cross plane crank will never quite have the power potential of a flat plane due to the balance weights. A cross plane requires extra weights as neighbouring cylinders are not going to cancel each other out as on a flat plane. More weight means more inertia which means slower revving.
There is however a layout that gives a high revving cross plane eight. The flat eight. The crank is less complex than a flat six as an eight does not need to "box". If the first two throws are in one plane and the last two in the other plane then you can have minimum counter weights for fast revving. The exhaust layout can be a four-two-one layout on each side which gives nearly the power from a flat crank V8.
- H layout as on a GT40. The middle cylinders on one side are linked to the end cylinders on the other side. This is the high power layout for a two plane crank. regarding noise this will minimise the burble but go big every where else. The actual noise will depend on a lot of other factors as well.
- 4 into 2 on each side with cylinders 1/2 and 3/4 on one side and 1/3 and 2/4 on the other side. This is a compromise high power layout. The cylinders are not at 180 degree firing intervals, they are at 270 which is theoretically not as good but in practice there is more space to actually get the pipe in around the engine. Some burble but often a crackle as well.
- 4 into one on each side. Low power, big burble.
- four into one on each side.No burble.
A cross plane crank will never quite have the power potential of a flat plane due to the balance weights. A cross plane requires extra weights as neighbouring cylinders are not going to cancel each other out as on a flat plane. More weight means more inertia which means slower revving.
There is however a layout that gives a high revving cross plane eight. The flat eight. The crank is less complex than a flat six as an eight does not need to "box". If the first two throws are in one plane and the last two in the other plane then you can have minimum counter weights for fast revving. The exhaust layout can be a four-two-one layout on each side which gives nearly the power from a flat crank V8.
OK, Established opinion supports Any's theory (the longer the better) and that an X pipe arrangement between the two banks will reduce the sound level and give a flat plane engine more of a wail like a V12. This is very good for my use case.
So researching the web, a company called Gothspeed have stuck a silencer which incorporates an X-pipe on YouTube here http://www.youtube.com/watch?v=aaVqYjWcbxo .
Now in designing my silencing I have some space restrictions - The chassis makes it easier to have one silencer (like that Ferrari above) in the space behind the traansaxle - a space measuring 27" x 13" x 13" overall. I think I can get a box of 2800 cubic inches in that space (for comparison an F355 box is about 2000cu) whihc will get the noise really low for track use in the UK.
The car I am building has 4 exhaust outlets - I paln to build the whole silencer in 2.25" pipe and run an unsilenced path out and into the box where I can install some Capristo like valves. Thsi gives me a volume control for when I want the more realistic noise (liek when not on a track, and not at 7.00am on Sunday morniongs near my own (read neighbours)house !)
Cramming all this in means some pretty tight radius bends. For a 2.25" system running a 400bhp 3.5 litre V8 (so 1.7litre per bank) what is the reccomended min pupe bend radius to avoid power loss. There are likely to be 6 x 90 deg bends for each bank in the box.
I'm thinking an centreline radius of 4" - is this too tight for decent flow??
Rough sketch of ouside shape is below. Ideas welcome, as well as an quotes to make!
So researching the web, a company called Gothspeed have stuck a silencer which incorporates an X-pipe on YouTube here http://www.youtube.com/watch?v=aaVqYjWcbxo .
Now in designing my silencing I have some space restrictions - The chassis makes it easier to have one silencer (like that Ferrari above) in the space behind the traansaxle - a space measuring 27" x 13" x 13" overall. I think I can get a box of 2800 cubic inches in that space (for comparison an F355 box is about 2000cu) whihc will get the noise really low for track use in the UK.
The car I am building has 4 exhaust outlets - I paln to build the whole silencer in 2.25" pipe and run an unsilenced path out and into the box where I can install some Capristo like valves. Thsi gives me a volume control for when I want the more realistic noise (liek when not on a track, and not at 7.00am on Sunday morniongs near my own (read neighbours)house !)
Cramming all this in means some pretty tight radius bends. For a 2.25" system running a 400bhp 3.5 litre V8 (so 1.7litre per bank) what is the reccomended min pupe bend radius to avoid power loss. There are likely to be 6 x 90 deg bends for each bank in the box.
I'm thinking an centreline radius of 4" - is this too tight for decent flow??
Rough sketch of ouside shape is below. Ideas welcome, as well as an quotes to make!
I have to say I dont like the idea of X traps, to me it seems that there is going to be some restriction on flow.... my chamber brought together the 2 pipes flowing the same way so the gasses could mix without clashing.
Now my 'thoughts' are purelly based on my ideas of how gasses are going to flow rather than any physical experience making exhausts and testing them, so I'd be very interested in actual results produced
Beware large silencer boxs, in my experience these blow the wadding out and end up just a resonance chamber.... I personally would try to build 2 silencers in the space you have and run length around them in a similar manner to what I have done on my Noble.
Now my 'thoughts' are purelly based on my ideas of how gasses are going to flow rather than any physical experience making exhausts and testing them, so I'd be very interested in actual results produced
Beware large silencer boxs, in my experience these blow the wadding out and end up just a resonance chamber.... I personally would try to build 2 silencers in the space you have and run length around them in a similar manner to what I have done on my Noble.
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