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What Makes The Jap Version Faster Than The Uk?


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Its in the title really, where does the slight extra power and 0.4 of a second quicker to 60 come from with the jap SSII gen6 compared to the UK GT?

The reason I ask is that at Greenam near me, there's a jap import garage that apparently can get hold of jap parts, If the extra power comes from a jap exhaust or somthing, maybe you can just change?

Bare in mind, my knowledge of car internals isn't in any way detailed.

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the ignition timing is mapped for higher octane fuel which gives u more BHP however you'll need to run 100 octane fuel to get the full benefit of an SS2.

optimax is only 98 RON so ud need an octane booster to go with it.

the SS2 is also slightly lighter... no airbags and a space saver wheel

You should be able to get your car set for higher octane fuel by turning the distributer on a rolling road.

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The uk manual specifies 95RON and higher. I use 97RON from (usually from) sainsburys myself. What does that adjustment you mentioned do? Advance the timings? I could probably do with a reference, but the haynes manuals I've found seem to be U.S.

I'm not gonna pretend, I'm ok with looking thick, I don't really know what RON means, and what/why you change engine settings/timings to accomodate different RON petrol. My understanding of engines comes from howstuffworks.com :rolleyes:

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Octane rating

Main article: octane rating

The most important characteristic of gasoline is its Research Octane Number (RON) or octane rating, which is a measure of how resistant gasoline is to premature detonation (knocking). It is measured relative to a mixture of 2,2,4-trimethylpentane (an octane) and n-heptane. So an 87-octane gasoline has the same knock resistance as a mixture of 87% isooctane and 13% n-heptane.

There is another type of Octane, called "Motor Octane Number" (MON), which is a better measure of how the fuel behaves when under load. Its definition is also based on the mixture of isooctane and n-heptane that has the same performance. Depending on the composition of the fuel, the MON of a modern gasoline will be about 10 points lower than the RON. Normally fuel specifications require both a minimum RON and a minimum MON.

In most countries (including all of Europe and Australia) the 'headline' octane that would be shown on the pump is the RON: but in the United States and some other countries the headline number is the average of the RON and the MON, sometimes called the "roaD Octane Number" or DON, or (R+M)/2. Because of the 10 point difference noted above this means that the octane in the United States will be about 5 points lower than the same fuel elsewhere: 87 octane fuel, the "normal" gasoline in the US and Canada, would be 92 in Europe.

Romania is a supplier of "light-sweet" crude oil, which, when distilled, resulted in a gasoline with an 87 rating (DON).

It is possible for a fuel to have a RON greater than 100, because isooctane is not the most knock-resistant substance available. Racing fuels, Avgas and LPG typically have octane ratings of 110 or significantly higher.

It might seem odd that fuels with higher octane ratings burn less easily, yet are popularly thought of as more powerful. Using a fuel with a higher octane lets an engine be run at a higher compression ratio without having problems with knock. Compression is directly related to power, so engines that require higher octane usually deliver more power. Some high-performance engines are designed to operate with a compression ratio associated with high octane numbers, and thus demand high-octane gasoline. It should be noted that the power output of an engine also depends on the energy content of its fuel, which bears no simple relationship to the octane rating. Some people believe that adding a higher octane fuel to their engine will increase its performance or lessen its fuel consumption; this is false - engines perform best when using fuel with the octane rating they were designed for.

The octane rating was developed by the chemist Russell Marker. The selection of n-heptane as the zero point of the scale was due to the availability of very high purity n-heptane, not mixed with other isomers of heptane or octane, distilled from the resin of Jeffrey Pine. Other sources of heptane produced from crude oil contain a mixture of different isomers with greatly differing ratings, which would not give a precise zero point.

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O.k, I'll do my best to do some learning. So with fuel that requires higher compression to burn, you change somthing on the distributor, which as I understand it, controls the timings of the spark plugs? Why would you have it spark at any other time than when the piston is right at the top? I guess knock is an effect where the petrol combusts to early in effect, pushing against the turning of the engine.

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It sounds like you're getting the right idea with regard to why ignition advance is needed. :thumbsup:

Advancing the timing by rotating the distributor changes the ignition timing throughout the entire range of rpm and load points. It is a very crude way of doing things. The shape of the ignition curve is not changed, it is merely offset from the zero point.

Here's a rather crude excel graph as an example:

ign.gif

But it's not even as straightforward as scaling things unfortunately. The curve could a a different shape (although it's probably similar). Toyota will have worked all this out theoretically and experimentally when they mapped the UK and JDM cars. Hence they have come up with maps that have what they consider to be the optimum compromise between performance, and reliability (i.e. blown up engines).

I wouldn't worry about 0.4 seconds on spec sheets. That can easily be made or lost by the person at the wheel. Removing the cat from your exhaust would almost get you back level with a JDM car.

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Greenham .. I'd avoid, or be VERY carefull .. I've been down there often :)

Oh right, what did they do?

The site was owned by another company, who then fled leaving everything .. dodgy so-n-so's .. then this new place took over and i've had a nose about ..

MotoCars Ltd (www.motocars.co.uk)

Most of their stuff appears tatty ..

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You could always get the ECU chipped to give it a more aggressive ignition curve.

This also gives more horses. Mine is running 12bhp over stock. Impressive, given that the car is 12yrs old.

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Bugger, typing away and my computer crashes. Must be the heat. :ffs:

Just been reading around and mulling over that graph, I finally get it, the spark advances more the faster the engine goes, finally got that there is a delay between the spark and the mixture igniting and reaching full pressure, hence the need to advance the spark slightly (and also to advance it more at higher engine speeds).

I guess the reason you advance it more with higher octane is that its harder to burn, so you give it that energy earlier to reach full pressure at the top?

So, given that I run 97ron, is it worth tweaking? Its tempting because it might be relativly simple for a complete novice like myself, I guess it wouldn't cost anything. On the other hand, If it could do alot of damage or dramatically effect my mpg (I'm not sure how it could, it'd be injecting the same amount of fuel, just getting more energy out of a higher octane right?) then maybe its not worth the risk?

I am also tempted by other mods, air filter, ecu, de-cat, trd shocks springs and anti-rollbars, and some 17's, but their all money items for the future at the moment. Can you get high flow cat-converters so you don't mess with emissions but get the same benefits of de-cat?

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Yeah, you're getting the idea. Just remember that combustion is not an instantaneous 'explosion', but a very fast burning of a near perfect mixture of air/fuel. The flame front/pressure wave takes a finite (regular but dependent on mixture) amount of time to travel from the spark plug to the piston crown. At higher rpm, the piston will have moved further on its downward stroke by the time the pressure hits it, meaning wasted effort.

With perfect fuel you can set the timing so that the flame front meets the piston at the optimum time (15 degrees after TDC iirc). But with less than perfect fuel, igniting at this point will cause knock (not det/preignition). When the combustion is initiated at the spark plug tip, the cylinder pressures rise dramatically. If they get too high they will cause a second combustion somewhere else in the chamber (from a hotspot). When these two flame fronts meet, you get the 'knocking' sound. To avoid this with poorer fuels, ignition timing is retarded from the perfect point giving a lower cylinder pressure at the initial combustion.

It might be worth advancing the timing a fraction. If it is too much for the engine the knock sensor should pick it up and pull some timing anyway (so you end up back to square one). In theory more advance should make your engine more efficient (up to a point), and you would gain mpg, but I doubt it will make a noticable difference in reality.

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Thanks for the help everyone, mikeb in particular :thumbsup:

Now all I need is a guide on the specifics of doing it. I had a look at the link to the manuals at the top for the gen6, but alot of the links are either broken or clearly for the american car. I spose I could follow the spark plug leads back to the distributor, but I'm not gonna change anything unless I'm clear on what I'm doing and how much of an adjustment to make :unsure:

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You need a strobe to set the timing. There should be a notch on the outermost bottom pully and some marks on the cam cover to line it up with.

Run the engine up to temperature, then bridge TE1 to E1 and put it in diagnostic mode. This locks the timing at a known value (probably 10 degrees BTDC, but you should double check that). Then you slacken the distributor (the bolts are a pain to get at) and rotate it until the timing is correct. I'd recommend turning off the engine while moving the distributor in small increments then rechecking it.

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or just try advancing the dissy a little and giving it a try. probably need to be in diagnostic mode first though.

a few degrees makes a massive difference too.

probably best for an expert on a rolling road to do it for you tbh.

mike anyideas if diagnostic mode disables the knock sensor?

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spotipus asked

whats its bhp at the wheels frodo? just askin out of interest cause mine is 142 with no ecu adjustment or upgrade just a k&n

Can't remember to be honest. Got the bit of paper somewhere. Standard for my gen 5 is 154bhp with the cat, or 158bhp without the cat.

So, with the cat removed, a better flowing backbox, k&n 57i, and the chip tuned on the rolling road, it managed 166.1bhp.

Considering most cars lose bhp over the years due to wear and tear (I would have expected mine to be 140bhp tops stock as its 12yrs old) I was pleasantly surprised.

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my 162 GT was 'bang' on stock BHP... I was very impressed.

with exhaust and filter it 'lost' 5BHP top end, but gained torque bottom end.

lets not even mention what happend when it was dyno'd with the nitrous - the gain was immense as it began using the additional bore size...

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Hmm, as much as I like the idea of getting into this and tweaking my car, I can imagine messing it up, and obviously I don't have a rolling road, I don't even understand every other bit of terminology. Think your right cooki, I'm safest just saving up and leaving it to a mechanic to get stuff done. I know eventually I want more of a shove throughout the rev range, rather than more peak power, though I wouldn't want to lose much in the way of peak power.

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