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post #19 of (permalink) Old 01-06-2005, 19:16
Scarlet Fever
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Join Date: Jul 2002
Location: Near Stansted Airport
Car: MGF
Posts: 5,476
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Quote:
Originally Posted by andy@ukcars
Think I've decided to keep the standard haead and simply replace the manifold, cat and induction kit. Upgrade the brakes and suspension and then leave it at that for now. I think spending upwards of 2k on the engine for not much noticeable improvement is a tad silly. I'll start saving for that VTEC conversion
Some homespun, 'potted' wisdom...

Engine tuning is a very personal thing, there are lots of factors involved in what and how you do it, not the least of which is budget and time. But the process can be split into stages - they can be done in any order, but ultimately they need to all work together.

In my case i wanted a reasonable power hike without sacrificing reliability and i did it in small steps over time, here is a full list of the mods done so far:

1 ) ITG Maxogen air induction system
2 ) Trophy (52mm dia) Throttle body
3 ) VVC inlet plenum and manifold (matched)
4 ) MS Stage 1 head conversion (porting only, standard valves retained)
5 ) Janspeed (X-Power) 4:2:1 manifold
6 ) Phoenix cat bypass
7 ) Phoenix rear silencer

So, you can see from the list that i have now completely modified the entire air /fuel / exhaust path. There are still things i can do, but as far as i am concerned this is the 'first step' as they are all efficiency modifications.

Stage 1 - Efficiency (free gains)

As i said in my earlier posting, efficiency is a fundamental part of engine tuning - study the engine, in simple terms: find restrictions and remove them, look at the air flow and smooth it out, reduce turbulence and promote laminar flow. The engine will only perform as well as the narrowest restriction. You are not necessarily looking to speed up the air flow (as moving gases accelerate they have a greater tendancy to become turbulent), in general* you are looking for a free flowing, laminar flow from start to finish - this will allow more of the power produced by the engine to reach the road as less of it is required to suck / blow gases through the engine. It will also promote a more powerful burn as more air can be delivered on demand.

* = There is an argument for turbulence at the point the fuel is injected - although this will reduce the overall air volume in this area (meaning less power), turbulence here will disperse the fuel more thoroughly which also results in more power (and greater fuel efficiency - more fuel is burned, less unburned fuel is expelled).

The other thing to say here is that if you think about the combustion cycle, the engine draws air / fuel in in pulses and the design of the pipework can either aid or hinder the pulsating of the gases. This is not something that is generally able to be worked out by the 'punter' and to some extent you have to rely on the manufacturers' expertise, but you need to know this because it is theoretically possible for one performance part to 'cancel out' another due to the fact that the manufacturer's tend to design thier products for a stock engine (indeed how could they possibly design thier parts for every single possible combination of aftermarket parts, now or in the future?) This is a potential pitfall that is very difficult to predict or cure. Harmony is the key here, but achieving it is very difficult indeed.

These modifications are effectively liberating the potential of the stock engine and as such should not impact too heavily on reliability. I decribed them as 'free' gains because they are available on any engine - they are not free in a monetary sense, rather they are free in so far as they 'come with the car', they just need to be utilised.

Stage 2 - Specification (direct gains)

Difficult subject this, as it encompasses a lot of different items. Basically once you have got the efficiency of an engine to a stage where you are happy with it, the next step is to look at ways of directly upping the power, you can do this in a number of different ways but you need to be aware that they pretty much all come with a reliability cost (to a greater or lesser extent) and also tend to be on the pricey side. I shall elaborate with some examples:

NOS - Nitrous Oxide is injected with the fuel. Nitrous Oxide, or NO2 comprises 1 part Nitrogen and 2 parts Oxygen. This means that in comparison to air, Nitrous Oxide contains substantially more Oxygen. The result is a much more powerful burn, but only when the gas is being injected. This can impact significantly on the wear and tear of the engine - you are moving it's performance outside it's design envelope for brief periods. NOS is fairly safe though, being basically inert when stored and providing you don't go too silly with it, it shouldn't make a dramatic effect on your engine's lifespan. I personally know of one person running a +50bhp shot of NOS on his F with no problems, and i have a +25bhp kit sitting in my garage waiting to be installed (one of these days i'll get round to it! ). The specification change here is the amount of Oxygen in the air. NOS is as far as i am aware the best 'bang per buck' mod you can do, but long term reliability is an issue and you need to be very careful how far you go with it (kit size).

Cam shafts / valves - Alterations to the timing affect the breathing of the engine, you can do this with larger valves (normally as part of a porting job on the cylinder head), VVC timing gear or altering the profile of the camshafts. They all do the same job - they let more fuel / air in per engine cycle. Valves do it directly, VVC mechanism slows the rotation of the camshaft during the valve open stage (meaning it is open for longer) and reprofiled cam shafts also alter the valve open duration, but in a more direct manner. The beauty of the VVC mechanism is that it also speeds the rotation up at lower engine revs, meaning there is a fuel efficiency benefit. Camshafts represent good value for money, but fitting can be costly and setting up the timing is tricky. You also need to note that if you go too wild with the cam profile you can encounter idling and starting problems.

Direct to head, multiple throttle bodies (DTH-MTBs) - These replace the entire induction system, inlet plenum, manifold and fuel rail - they are basically short trumpets, one for each cylinder that draw air directly with a fuel injector in each. The specification change here is the fueling and delivery to the engine. DTH MTBs dramatically simplify the air way into the engine and they also are capable of flowing greater amounts. This, coupled with a greater fuel delivery results in a 'bigger bang', but at the expense of fuel economy and emmissions (which is why manufacturers don't fit them to road cars these days). Generally they are trouble free (simple technology) and reliability isn't too much of a concern. They are also a pretty cost effective way of liberating a nice hike in bhp.

Forced induction (turbo / supercharging) - The expensive option Compressing the air entering the engine results in a higher density of Oxygen for a given volume producing more power. How this is achieved is the difference between Turbo and Supercharging. Both are very complex, compressing the air also produces heat (hot gases are less dense so contain less oxygen - ergo counter productive), so to be efficient will require an intercooler (to cool the compressed air). Intercooler are heat exchangers so produce heat that needs to be expelled from the engine bay (a problem in the F/TF) and Turbo chargers compress air using a turbine sited in the hot exhaust system (producing even more heat, that needs to be gotten rid of). There are also ancilliery items like changes to the fuelling system (more air = more fuel) and compression ratio, plus if a big hike in power is required (and if you are going to spend mega bucks on forced induction you want a BIG hike in bhp to justify it), then you need to improve the reliabilty of the engie directly and this usually means forged pistons, uprated liners, steel crank etc = more money. Forced induction on an F/TF is on the limits of what the engine is capable of and this is reflected in the costs. Large gains yes, but value for money?

Increasing capacity - The 1.8 K4 is basically a 1.4 sized engine with larger bore liners and a longer stroke on the pistons - effectively it is already 'tuned' from new as these two items are 'standard tuning options' on most other engines. You can buy 1.9 and 2.0 litre capacity K4 engines from people like Scholar and Judd - but these are highly specialised engines and as such have a question mark over them (for me at least).

Chip tuning - I feel there is very little gain available on the 1.8 K4. This engine is naturally aspirated (not forced inducted) and as such there is a limit on how much you can achieve by advancing or retarding the ignition timing without causing problems (pinking etc). Some gains are available, but they are small and the potential for problems is great enough to require the chip to be programmed on an RR (or on the fly using a laptop from the passenger seat). RR time cost money and this normally makes chip tuning a non-cost effective option. Replacing the MEMS with a complete engine management system is only really justified when the stock MEMS is having trouble keeping up with the modifications done - and if you go down this route you need to be aware that you are setting the management system up to suit the engine and mods and this means that every time you modifiy the engine futher you need a new map to compensate, meaning more RR time (and more s).

Stage 3 - Engine swap (cheating! )

There comes a point where the engine just isn't capable of producing the required gains cost effectively or reliably. When this happens it is time to consider an alternative power source and in the case of the MGF/TF, there are 2 options out there at the moment - Mike Satur's Honda iVTEC conversion and the KV6. Neither are straightforward, both of them will alter the handing charateristics of the car (so you need to look at this too - but with this kind of power hike common sense says you should look at the handling and stopping performance of the car), and both of them are specialist, relatively expensive options. But the gains from this kind of work are huge, so should be seriously considered.

Why spend 6K on the 1.8 K4 and get a highly tuned engine that is potentially unreliable when you can spend 6K on an engine swap and get more power reliably?

----------------

As for me, well i've got my eye on some TF 135 camshafts and as i said earlier i have a +25bhp NOS kit sitting in my garage. I am in no hurry to fit either of them, as i am perfectly happy with the way the car is driving at the moment, but sooner or later i'll feel like a bit more power and then they'll be fitted - you can never have enough power, over time you get used to the performance of the car and then want more. Hence the Star Wars 'Dark Side' anaolgy - "Once you start down the Dark Path, forever will it dominate your destiny" (and bank account!! )

Last edited by Scarlet Fever; 02-06-2005 at 17:44.
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