In, Out and Bang!
Lets look at Induction, Exhausts and setting your timing a little more
Induction
Most people seem to think that shoving a pair of K+N's onto the SU's on their manifold
will increase power. Usually it doesn't. Rover weren't having a laugh when they
put the cast elbows or the air box on, it does actually increase low end torque. Admittedly
there is some restriction there at high revs but most people just don't operate their
engines in that region very much (except me :-
There is an element of pulse tuning and damping present in the designed system which cannot be simply achieved by replacing the whole lot with a couple of air filters. Optimising what you've got is a better and cheaper method. There is a section later discusses this in more detail.
On EFI systems there is a considerable amount of scope for tweaking, depending on what rev range, what torque, what displacement, and how much you want to spend. I'm not going to delve into aftermarket EFI here since that goes from a bolt on system to surreal systems that wouldn't look out of place on an F1 car. It so happens that the standard hotwire and airflap systems can be made to produce enough flow and fuelling to feed all but the greediest of big displacement V8's.
Flapper
With airflap systems the main limitation is the restriction and pressure drop introduced
by the airflap itself. I know of no satisfactory way around this and it will limit
output to around 280BHP. However, to get to this level some other work needs to
be done, as the fuelling will be inadequate. The easy way is to replace or modify
the fuel pressure regulator to give an extra 4-
HotWire
On hotwire systems, the meter also knocks the top end but here it is possible to substitute the meter with a larger part and rescale the fuel map held in the EPROM inside the ECU.
Std Plenums & Throttle size
The standard plenums aren't bad but can be cleaned up a bit and on higher output
engines it may be worth increasing the size of the throttle plate. The Jaguar plates
are commonly used and give a 70mm throttle. Big engines may need up to 75mm and
some even run to 80mm although it's highly doubtful whether the gains for this could
be detected anywhere except on an engine dyno, particularly since it’s really time
to look at a multi-
Twin Plenum
EFI systems with works dual throttle plenums (AKA Twin plenums) are available and have something of a reputation. They were used on Group A Vitesses at one time but really aren’t useful on a normal road vehicle. They have a number of problems, one being that they still need to draw through a single airflow meter and that is the limitation on standard EFI kit. The other is that the throttle progression is wrong and this makes manoeuvring in traffic a bit tiring since the throttle opening increases rapidly for very small amounts of pedal movement. Another issue is that the throttle plates generally are not a good fit and this can make setting the idle tricky.
Finally, there is no room for cruise control and no provision for kickdown on auto's. That said, on a high rpm racing engine or larger displacement high revving engine with a larger airflow meter they do work a bit better and can help noticeably if you are looking for outputs beyond 250bhp.
However, there are even better solutions available (at a price) comprised of much larger carbon fibre plenums with more accurate throttle bodies and better internal shapes, with better spread bore ram stacks and a variety of sizes to suit the application.
Eliots Note: So resist the urge to buy those overpriced units you see on ebay unless you know what you are doing
Trumpets
The ram stack is an area that can affect engine characteristics noticeably since
the rams are tuned to a particular length and high revving engines may benefit from
shorter ones. Additionally, ranges of flared and larger rams are available which
can have a considerable effect at the top end of the rev range. It's also possible
to enlarge the passageways into the manifold to improve breathing at the top end,
but there may be some small negative effect at low revs. The main thing here is
to carefully port the manifold and ram area so the match themselves and the head
openings and provide minimum resistance to flow. This usually means paying a lot
of attention to the area around the injector. If you need big increases in power
at the top end, then after-
Air meter and Filter
It's important to pay attention to the area between the plenum and the airflow meter and the meter and air box or air filter. Firstly, do not ever be tempted to race an engine with no air filter. If you could see what gets sucked in during driving on the road or racing you'd be horrified. The filter also has the privilege of acting as a flame trap in a backfire. Cars have been known to burn without them. Incidentally, if you have a fire here, the secret is to rev the engine to pull the flame in rather than spit it out. In an ideal world, we would collect cold air from directly in front of the vehicle where the pressure is highest. We’d filter it with a low resistance filter, keeping the velocity and pressure constant in a smooth straight duct directly through the meter and into the plenum, with no heat soak from the surroundings and minimal turbulence in the duct. In the real world, we have to fit the ducting into the engine bay and curve it around to make it all fit on to the various bits. We use curly, corrugated flexible hoses which vary in diameter and air filters which introduce pressure drops as well as devices designed to reduce intake noise such as the restrictor and volume recovery device on the nose of the old Range Rover EFI airbox. Worst of all, you may be using an LPG mixer in there as well. Your job is try and approach the ideal. Good Luck.
Exhaust Systems
Now most people would assume that bigger is better or something. It aint necessarily so. Pipe size is important as it influences gas speed. Small Pipes = High Velocity and high velocity is a good thing most of the time.
Theory
I'm not going to deal with all the intricacies of exhaust design here as it's a massive
topic and difficult to explain for all possible engine set-
Backpressure
The first thing is that unless you have a wild cam and are looking for ultimate top end power without regard for low speed torque, some exhaust back pressure is useful and desirable. This is because even if we can't utilise the return pulse in the exhaust, we can still use it to prevent inlet fuel and air from being drawn excessively into the exhaust system during the valve overlap around BTDC at the start of the compression stroke. Conversely, it's also extremely useful for obtaining reasonable low speed torque on an otherwise wild cam without sacrificing huge top end gains. Back pressure introduced by using a restrictive silencer isn't really the right way to go as it will cause extra losses at the top end so the correct route is to use narrower pipes at the manifold end to slow down the escaping exhaust and use pipes of the correct length with a relatively open silencer. On a V8 (and some other configurations) it's possible to use the pressure generated by other cylinders to provide the "stopper", and this is why a balance pipe or a connection between pipes on all cylinders is extremely helpful. Unfortunately it's extremely difficult to plumb a V8 in an ideal manner since it requires linking pairs of cylinders from side to side in a horrendously complex manner, so a compromise must be reached. In practice, the production system used on 90's Classic 3.9 EFI range rovers is almost ideal in terms of layout but as usual, suffers from productionising. Here, cylinders firing as near to 180 degrees apart are paired via a short runner and connected to two long primary pipes each side of the engine, then to a collector then on as a single pipe each side to another final collector that serves as the balance pipe. The lengths are correct for the design power and torque and work well with the production camshaft.
4 into 1
A four into 1 on each side can barely improve on the std manifold described above. If the dimensions are equivalent and serves mainly to massively increase cost and complexity. Good gains can be had from using an improved version of this standard arrangement and have been proven in competition down the years.
However generally speaking, the standard manifold and collectors are rather too restrictive and the pipes are a little narrow for engines where big increases in midrange torque are expected. If the cam is changed and peak torque and power are further up the range then the pipe lengths should be altered to suit. The headers need to be shortened a small amount as do the intermediate pipes. There is a formula for calculating the resonant length a pipe needs to be from valve head to open end and it's diameter but I can't remember it or find it. However, it's usually the case that if you measure the primary pipe it will be somewhere between 34 and 39 inches on any engine, with the longer lengths increasing torque lower down the rev range and vice versa. Do bear in mind that using a pipe that has an excessive diameter will reduce gas speed and lose torque at the bottom end although good gains may be had at the top end and vice versa. Also bear in mind that the majority of hydraulic cams have generous exhaust timings to allow narrow pipes to work well and increasing the pipe size may actually produce less power and use more fuel as well as increasing the pipe temperature.
Setting ignition and camshaft timing
Ignition timing
The crank pulley has a TDC mark and several 4 degree marks either side of it, plus either a raised arrow or a pointer at the top on the timing cover to help you. The engine and dizzy both normally turn clockwise, so the 8BTDC mark will be two divisions to the right of the TDC mark. Turn the crank to about 8 BTDC. Turn the dizzy so that the vac. unit is at 9 o'clock and terminal 1 (cylinder1) at 6 o'clock. Turn the rotor arm so it's at about 4 o'clock. Insert dizzy in hole noting that it probably won't go completely in cos it hasn't engaged with the oil pump. Check that the rotor arm is nearly pointing at 6 o'clock. Fit securing plate and tighten till you can still just turn the dizzy without force. Spin engine. Dizzy will engage oil pump and drop down. Check rotor arm is at 6 o'clock or 12 o'clock when engine is at 8 BTDC. Tighten retaining bolt. Start engine. If nothing happens then timing is 180 out so turn engine to 8 BTDC, check position of rotor arm, if at 12 o'clock, remove dizzy and repeat operation above so that it's at 6 o'clock, otherwise turn crank 360 degrees, remove dizzy and repeat operation. Clear as mud? Easy when you actually get hands on. It's not as bad as it reads but you have to think about what's going on a bit cos there are two engine rotations for every dizzy rotation and the firing stroke for cylinder 1 and 6 are 1 rotation apart so it's possible to time it up for the wrong cylinder. Try it and see what happens.
Cam Timing
If the engine is on the bench with the timing cover removed... Don't worry about turning the crank to TDC, it may be difficult or inconvenient at times and this method avoids that. Take the timing gears and chain and fit the gears and the chain together while holding the camshaft (larger) gear so that the crank gear dangles on the chain. The cam gear has a small raised arrow on the front, this should be at 6 o'clock. The crank gear has a small dot on the front and this should be at 12 o'clock. In other words, the arrow and dot should line up with eachother and through the shaft centres. Slide the assembly onto the crank and camshaft making sure the chain doesn't jump. Now rotate the camshaft and gears until the gears locate on the keys in the shafts. Slide the gears uniformly onto the shafts until they go completely home. That's it. Note that this won't work if your chain is badly stretched and in need of replacement. You should double check at some point anyway, by rotating the engine clockwise until the arrow and dot line up at 6 and 12 o'clock. It's usually easiest to fit the front pulley and bolt and turn on that. T
DC and Dizzy at No.1 Check.
Before fitting the rocker covers, turn the engine to TDC and so that the followers are on the back of the cam lobes for cylinder 1 and in between the inlet and exhaust lobe on cylinder 6. This TDC for cylinder 1 and the rotor arm should point to cylinder 1 when you fit the dizzy. It's very easy to set the timing 360 degrees out otherwise.
Final adjustment
Actually, the freehand approach to ignition timing is best once you've got the thing so it starts and drives. If you're happy the vacuum advance and mechanical advance work correctly then advance it as much as you can without any pinking. Usually thie worst spots will be sudden acceleration at low revs after idling , due to higher air intake temperatures, or mid range high load situations like towing or full throttle on steep hills, just advance it until it pinks and then back it off until it goes away, then back it off another two degrees for safety. That will give you optimum timing. Expect to be able to get as much as 4 degrees extra advance if using super unleaded over regular unleaded. Initial advance is not critical as long as it falls somewhere between 0 and 16 degrees