16v Upgrades?
04-20-2010, 08:11 AM
#62
As to why Porsche designed long runners? I would add on some models only, there is 3 basic types, Euro S and S2 and the US based runner. The longer runners do change the pulses as to when they occur in the rev range, the longer the runner the lower in the rev range they will occur.
The engine above is the 2000 Ferrari F1 engine, to illustrate a point, draw a line from the centre of the trumpet to where the stem meets the head of the valve. The air gets a straight run at the back of the valve, so no losses caused by curves and bends, also to add another level of complexity to this answer, which it probably needs, the air in the Ferrari engine's intake can run at the peak (optimal) possible air speed, around 0.55 Mach.
Now with the Porsche intake, as soon at any point in the runner, the air speed hits above 0.55 mach the runner will not flow any more than that capacity in air volume, a sonic choke so to speak. The reason the bends are bad is that on the short side the air has to travel faster as such the short side hits its peak prematurely and becomes the limiting factor.
The longer the runner, the greater weight of the air in that runner and that can add some ram effect but putting bends in it is not a winner.
Greg
The engine above is the 2000 Ferrari F1 engine, to illustrate a point, draw a line from the centre of the trumpet to where the stem meets the head of the valve. The air gets a straight run at the back of the valve, so no losses caused by curves and bends, also to add another level of complexity to this answer, which it probably needs, the air in the Ferrari engine's intake can run at the peak (optimal) possible air speed, around 0.55 Mach.
Now with the Porsche intake, as soon at any point in the runner, the air speed hits above 0.55 mach the runner will not flow any more than that capacity in air volume, a sonic choke so to speak. The reason the bends are bad is that on the short side the air has to travel faster as such the short side hits its peak prematurely and becomes the limiting factor.
The longer the runner, the greater weight of the air in that runner and that can add some ram effect but putting bends in it is not a winner.
Greg
Last edited by slate blue; 04-20-2010 at 07:04 PM.
04-20-2010, 01:13 PM
#63
Nordschleife Master
Short answer is that I doubt Porsche was aiming very high for its target HP, more like they were designing it to be below some modest level with plenty of room for gains in later models.
04-20-2010, 01:49 PM
#64
Been selling Twinkies on Ebay,
have some extra cash right now.
Rennlist Member
have some extra cash right now.
Rennlist Member
04-20-2010, 02:58 PM
#65
Drifting
Porsche used long runners because they packaged well, allowed access to the spark plugs, and increased torque. This engine was designed in the mid 70s. This is as good as it got back then. Obviously a lot has been learned in the last 35 years.
04-20-2010, 04:12 PM
#66
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Here is my formula for the 16V. All bolt on, expensive, and somewhat hard to find:
85-86 manifolds
free flow exhaust with Y-pipe
Stock 4.5L with top end rebuilt
Powerdyne BD-11 Supercharger
Euro S intake,plenum,runners,TB,"U"
BEGI (fuel management unit)
Magna Fuel (fuel pressure regulator)
Forge (bypass valve)
and a ton of tuning. Should be fun!
85-86 manifolds
free flow exhaust with Y-pipe
Stock 4.5L with top end rebuilt
Powerdyne BD-11 Supercharger
Euro S intake,plenum,runners,TB,"U"
BEGI (fuel management unit)
Magna Fuel (fuel pressure regulator)
Forge (bypass valve)
and a ton of tuning. Should be fun!
05-15-2010, 04:14 AM
#67
Joel, I think in the UK there is a seller of x pipes, blue flame if memory serves me, I think one of the big advantages the exhaust I have is low losses and high velocity. Impossible to achieve without a by pass valve. Have a look at the X pipe and imagine the relevant side closed off, it still works and flows in quite a laminar fashion. Other X pipes may not be the same so you need to examine that before choosing otherwise just make your own. I just put a metal blade in my wood table saw and cut it out like that.
The other thing I wanted was high velocity at the mix point, good pulse interchange, so that means the X pipe is 2.5" not 3" like the rest of the system. So as soon as it mixes, I expand it out to 3" and into one pipe on low engine loads, this keeps the column of air moving quickly and given that is the straighter side the losses are lower. I figured that after the X you also want the gas out, the work the pulses are going to do is basically done, so the lower pumping losses to get it out will lead to best engine performance. The bypass is is not about noise for me, it was about good drive-ability and power.
I will try later to post more info and answer PMs
Greg
The other thing I wanted was high velocity at the mix point, good pulse interchange, so that means the X pipe is 2.5" not 3" like the rest of the system. So as soon as it mixes, I expand it out to 3" and into one pipe on low engine loads, this keeps the column of air moving quickly and given that is the straighter side the losses are lower. I figured that after the X you also want the gas out, the work the pulses are going to do is basically done, so the lower pumping losses to get it out will lead to best engine performance. The bypass is is not about noise for me, it was about good drive-ability and power.
I will try later to post more info and answer PMs
Greg
There are sellers of x-pipes in the UK, I have bought one before from Paul Anderson for my S4, but this time I am going to have a full custom system built by an exhaust specialist for my S2 engined 79.
I have sourced 86.5 manifolds which weigh 3kg each instead of the horrible 10kg cast type it has on there, and look like they will flow much better. Was going to go for a simple Y-pipe, resonator then repackable / removable silencer on the rear so I have a loud or quiet option.
However I am tempted to try and create something like you have done!
Cheers,
Joel
