In TVR world we have our Cerbera, it too has a fearsome reputation. it could bear no other name than that derived from the mythical Greek beast but is it also so unruly that it won't respond to traditional tuning methods? Well yes and no.

The Cerbera AJP8 is in a simple form two conventional four cylinder engines joined at the hip, this would in itself bring with it several advantages but as we now learn more and more about tuning this engine the advantages were not fully taken advantage of.

The main reason for making a V8 engine behave as two four cylinder versions is in the exhaust tuning options that this opens up. By making the engine in this way with a flat plane crankshaft you make equal exhaust pulse spacing down the exhaust on each side of the engine. You can take advantage of the equal spacing firstly to allow the exhaust gases to exit without intereference of one pulse over another in the pipework and also by using the momentum of the individual gas pulses to pull a vacuum behind them which can scavenge the next combustion chamber to open it's exhaust valve on that side of the engine, this scavenging can cause inlet charge to enter the combustion chamber earlier than would normally be the case so improving volumetric efficiency. TVR choose to fit a relatively efficient pair of manifolds in principle, but packaging restrictions mean that the primary pipes are too short and of unequal length thus rendering any equal pulse spacing and exhaust scavenging effects almost useless. The manifold is also designed in such a way as to partially block of part of the exhaust port as it exits the cylinder head .. this is traditionally a bad idea on any engine but especially so on an engine using a cam with lots of valve lift on overlap, as the step in the exhaust exit creastes a situation whereby the exhaust gas pulse is hindered in it's exit from the head, so exaggerating any camminess in the engine by not allowing efficient scavenging of the chamber to take place. It's bad for emmissions, bad for hp and bad for driveability. Or so I thought, and here's where one of the multiple brains of our own Cerberus decides to do something rather odd.

Here at TCS I have my own rolling road dynonometer, a piece of equipment which allows me to measure the hp output of a car to a repeatability of less than 1 percent, as such it's invaluable in finding out what works and what doesn't work when tuning cars. What it has taught me is that the Cerbera exhaust manifold in it's larger-bore 4.5 form is actually nowhere near as bad as it first appears, in actual fact it's pretty good. This came as somewhat of a surprise as initially I had thought they were very compromised because of the limitations mentioned in the previous paragraph .. but we now know that even with a set of bespoke manifolds fitted (and i've now tried 3 different versions of manifold for the cerbera) the gains are always less than 10lb.ft of torque, that's a minimal 2.5 percent improvement, and usually at isolated parts of the rev range ie not across the whole range. If you're on a mission to extract the outright hp of your engine, or have a need to replace existing cracked manifolds there is merit in going for something different, but the outright HP gains are very small. I have many remapped Cerberas now in the 420-440bhp bracket on standard large bore 4.5 exhaust manifolds and those aren't the sort of figures you get from a restrictive manifold system.

One thing that these high hp Cerberas do have in common though is they have all had modifications to the rest of the exhaust system.

One thing that is immediately obvious from the hours, days, weeks of testing that I have done is that when it comes to the rest of the cerbera exhaust system then big is good and bigger is better! The standard system is a fair size but it's not the best it could be, useful gains are easy to make on high hp cars.

You will often hear people talk about how an exhaust system should be properly sized and more importantly not be sized too large or you will lose low/midrange hp for little gain elsewhere, well this is where another of Cerberus' brains decides to behave strangely going smaller in cross section pipe area will most certainly harm top end hp, but going larger only results in gains until the pipe itself is no longer a restriction in any way. I have run Cerberas on my dyno with a pair of 3 inch perfectly straight pipes in place of the conventional exhaust and compared the results against the best flowing aftermarket exhausts and there are no losses anywhere in the low to mid parts of the rev range. The Cerbera really doesn't seem to react as conventional thinking would suggest with reference to exhaust system sizing and i suspect this is down to the design of the manifolds not allowing anything downstream to affect what occurs in the combustion chamber. The only effect taking place is the negative effect of too small a pipe size restricting absolute hp because of limited outright flow rating.

So, we know the standard system is pretty good, the factory back box for example is very high flowing and certainly not worth changing until you are chasing hp outputs north of 400hp, but how can the Cerbera exhaust system be improved? Well if you're going to keep most of the original system, or you have already fitted some expensive stainless sports pipes on your car which are going to be on for a long time then by far the best thing you can do for hp is to link the two separate pipes which makes up the under-car system together, and link them together as early as possible. By linking the two sytems together you create a situation whereby the individual exhaust pulses travelling down the pipes have opportunity to transfer across to the other pipe in the system ... this wouldn't usually happen in a flat plane V8 engine as you would normally have pulses travelling down the two pipes in unison, however the Cerbera has another quirk to it's make-up and this is the 75 degree V angle. The 75 degree angle means that the pulses travelling down the two systems pipes are not adjacent ie if there's a pulse travelling down one exhaust pipe the corresponding pulse in the other pipe will either be slightly head or slightly behind therefore you have a series of almost-alternate pressure pulses travelling down the pipes, and this allows for some sharing of the pressure between the two system pipes. This pressure sharing is a good thing because it allows for a more consistent flow to the rest of the exhaust system, for it is here where the real restrictions in the system are.

The main restrictive parts of the standard system are the bends they are often not proper mandrel formed therefore they reduce in cross section gases don't respond well to flowing round bends so if you are to pursuade gas to move freely with no flow loss you really should be making the bends larger in section area not smaller. One way to improve the flow rating of the system is to smooth the flow out so that instead of the bends trying to pass individual large pulses of exhaust gas we share these pulses in the link pipe upstream, the bends then see the same total exhaust gases as before but are now presented in a smoothed way which reduces hp pumping losses.

If you have an exhaust which is ready for changing then there is no reason not to go for the largest pipework in there that you can fit, with TVR production tolerances this can often mean having something made up bespoke for your car and the cars which have bespoke large bore smooth flow pipes make very high hp indeed, and you will know that your exhaust will not be a restriction to power in this configuration. Even the best HP producing off the shelf exhausts are still too narrow in my opinion so go large! having said that, by far the best off the shelf exhaust that i have so far tested is marketed by Silverstone Peformance who took the TCS linked decat pipe idea and utilised it during the design of their road and track sport exhaust system and coupled it with a high flowing but very quiet rear silencer assembly, it isn't cheap but it is beautifully made and is fitted to three of my most powerful remapped cars, it works well! Whatever you do don't be tempted to fit some of the cheaper sports type tailpipes as they have smaller bore pipes than standard and will instantly sap 20hp or even more for the very worst versions from a very powerful cerbera!

The other wonderful thing about having a proper free flowing exhaust system is the sound! Fantastic!

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