Basic V8 tuning

V8 Tuning.....The Exhaust

The exhaust....If we didn't have any ears we could do without them and easily get some more horsepower from our engine. Because the exhaust gases create some resistance in the piping which has to be overcome by the engine any exhaust system causes power loss (apart from shockwave tuning at some specific rpm points... but that's another story). The more backpressure an exhaust system generates the more power will be lost. The standard SD1 system is not very restrictive but if any serious tuning is considered the exhaust system should also be looked into.

The existing cast iron exhaust manifold is quite reasonable and not a very bad flowing design, but it really can be improved upon by installing a tubular system....however these are a bit pricey. The main exhaust system can easily be improved by just deleting the first silencers. If you have a mild steel system which is in a bit of a bad state than you really should consider a stainless steel system, especially if you plan to keep your car for longer than four years.

There are various suppliers of stainless steel exhaust systems for the SD1, some have the same diameter as the standard system, some have a bigger diameter. Stainless steel systems come in a great variety...here we look more into one particular exhaust system. The system described here is the Stainless V8 Sports System from Rimmer Bros.

This is serious stuff 4 exhaustpipes made by EPS Hoogezand

The latest Sports System of Rimmer Bros has the advantage that it can be used with the original manifold and downpipes. So it is possible to fit the stainless tubular manifold in a later stadium when the financial situation permits. Rimmer claims a power gain of around 10 to 15 hp can be had....although I think the last figure is a bit optimistic...The standard system really isn't that bad!

So.....is it difficult to install???.....well yes and no. Adriaan Briene ordered the complete package including tubular manifolds, fitting kit and a manifold fitting kit. The whole lot comes without any instructions....some info how the piping should run would have been handy. Now it is a bit of a puzzle first what comes where...

Rimmer was phoned to ask if it was suitable for LHD and they confirmed that it was suitable for both LHD and RHD. However in reality this is not entirely the case!!! On my LHD the tubular manifold piping for cylinder no. 1 just touched the lower steering coupling!!.... The remedy??

Rimmer Bros Sports Exhaust 8,1 kB
Rimmer Bros Sports Exhaust

Stainless steel
The Sports System is a complete Stainless steel system. It is made of grade 304 stainless steel. Although 316 is more corrosion resistant the advantage of a 304 system is that the steel has a bit less chromium, Molybdeen and Nickel added and thus is a bit more flexible. Because especially an exhaust system can shake and vibrate a lot a 304 system is less likely to break than a stiff 316 system. Stainless 304 systems can still show some light surface corrosion, however this forms like aluminium a layer after which the corrosion process virtually stops. This is why on some systems the piping is made of 304 and the silencers and the visible parts of 316.

The tubular manifold was put on a metal plate and holes were drilled into the plate. Then the manifold was bolted onto the plate. This to make sure that later on the manifold still would fit onto the cylinder head. Then the tube for cylinder no. 1 was heated and bend about 1,5" inwards on a hydralic press, this to make sure it wouldn't touch the coupling anymore. After this modification the system fitted perfectly. However it proved sometimes to be very difficult to get the nuts onto the studs screwed into the cylinder head. This because sometimes there is very little room around and behind the pipes!...some redesigning here certainly could do no harm!!

The manifold touched the steering coupling 15,4 kB

After this delay the tubular manifold was clothed with Thermotec insulation. This to prevent to much heat production in the engine compartment. However later I thought if this really is the case because cast iron (the standard manifold) gives off it's heat a lot better than stainless steel! this is a bit compensated because the surface area of the stainless system is a lot bigger but still I wonder if the Thermotec really is necessary. However it really looks the part....soo racy!! Getting it onto the piping isn't that difficult. If you wet the insulation a bit it becomes a lot more flexible and can easily be wrapped around the tubing. On some points however the piping runs so close to eachother that you have to wrap around two pipes simultaneously..not such a beaufiful sight but not that much visible from the top. The strap kit is very easy to use. On starting up the insulation gives of a lot of fumes and really smells terribly!!!! but after a few miles the smoke goes away. The smell stayed on for week or so!!

When ordering the package it was also recommended that the standard clutch hose should be exchanged for a stainless steel braided one. It fitted without any problems but I think it was a bit on the long side. The rest of the system didn't give any problems although it required a lot of fiddling to get the piping to fit.....instructions would have been helpful here I got left with quite some clamps and nuts and bolts, where are they needed for??
My car is also equipped with airconditioning. The compressor had a bracket which connected to the old iron manifold. With the tubular manifold you have to make a clamp yourself to give the bracket the neccesary support.

The rear DTM styling 9,5 kB

Once completed the system looks quite good from the back with that 3" DTM exhaust however I would have liked to see it to be a bit more upwards as a whole....now it hangs a bit too low for my liking. The sound is good!!!! it really gives a very dark brown burble. The old exhaust system could not be heard above 60 mph (100 km/h) now you still can just hear the engine burble through the exhaust and it really isn't that obtrusive....However on lower speeds (in town driving) I thought the bassy sound a bit on the heavy side. This is why I added some barifold sound insulation in the luggage compartment. The insulation was put on the plywood boards and against the backside of the car. This made it just perfect giving a modest V8 burble on town driving and the exhaust is still audible enough at autobahn speeds.

Power????....you will certainly know that you've installed a different exhaust system!!!....Previously the engine ran noticeably out of breath when reaching 4500 rpm.....now it pulls easily towards 5500 rpm. And it certainly has improved power output...the quoted 10 hp being quite reasonable. In the lower rpm regions any improvements are not obvious to me. Above 3500 rpm you can notice that the engine is pulling stronger. Further I wasn't able to see any changes in fuel consumption, for better or for worse.

Tubular manifolds
The standard cast iron manifold of the SD1 isn't a bad affair. When you are considering mild tuning you can still use the standard exhaust manifolds. After all the silencers (mufflers for our american readers) are the main restrictions in the exhaust system. When a faster cam is installed things get more complicated.

A faster cam gives more overlap between inlet and outlet. This means that the inlet and outlet valve are opened both for a short period. The chance that a cylinder sucks in exhaust gases from another cylinder during the inlet stroke increases with more overlap! (read, a wilder cam). Making the exhaust pipe longer before it is connected with the exhaust from another cylinder prevents this from happening or at least reduces the effect. It is also important which cylinders should be connected first. Whe should not directly connect cylinders where one has an exhaust stroke and the other one has an inlet stroke because this would result in exhaust gases from one cylinder flowing into the other one. To give a few examples for our V8.

If No. 1 has exhaust No. 7 has inlet
If No. 8 has exhaust No. 2 has inlet
If No. 5 has exhaust No. 3 has inlet
If No. 6 has exhaust No. 4 has inlet

So No.1 shouldn't be directly connected to No.7 etcetera. Based on this the best tubular exhaust for a V8 with the firing order of our Buick/Rover should look like the figure below. Note that the exhaust for left and right hand side are different!

The best way to construct a tubular manifold would be to make two 4-2-1 tubular manifolds. Four cylinders dump their exhaust gases in four individual pipes, then two and then into one, as shown above. Now take a look at the cast iron exhaust manifold for cylinders 2,4,6 and 8. If you look closely you already see it is of a 4-2 design! and as such quite good! The other one is less good directly connecting 1-3 and 5-7.

Have you ever looked at the available space around the V8 in an SD1? there is almost none. So a 4-2-1 system is not that easy for the SD1 although it would be the best. The Rimmer system is a 4-1 system where all four pipes of one cylinder bank come together in one pipe. Not too good to prevent backflow but the long piping already helps a lot. Actually more than the standard manifold.

The connection of the four pipes into one is quite critical for good performance. It should have a narrow angle and a smooth transition into one pipe. In this respect the Rimmer system is reasonably good, the transition should have been made smoother.