Here it is! After the first version was 'lost' the guide was started again and is now bigger and better than the first one! Some of the stuff here may be slightly over some peoples heads but once you read it all you start to see things falling into place. Good luck on the strip!

GT4 1/4 Mile Records

GT4 DRAG RACING TUNING GUIDE
By Andy R

Welcome to another instalment of the GT Tuning guide for the ¼ mile.

With GT4 we now have a proper drag-strip for testing of our cars, instead of some random test track, which is quite a nice touch. It is equipped with a Christmas tree for takeoff and a timeboard at the bottom of the track. All very nice, but what about the physics of the cars involved? Well, this time Polyphony Digital have outdone themselves. GT4 is the most realistic simulation of car physics ever, at least in my mind. What this means for us is that with the correct tuning we can get the closest results to what would actually happen if you ran a particular car down the track, with any number of modifications. Before we dip into the tuning guide settings I thought i'd discuss a few new performance options that are now available for use to use while doing or GT4 ¼ mile racing.

SUPERCHARGERS

These compressors run of a car’s crankshaft using a rubber belt or pulley, and are used to force in more air than an engine can normally draw in through normal means. This creates “boost”, thus the engine is “supercharged”. In the GT4 scheme of things superchargers can provide awesome boost response down low and in the midrange of, but are generally inefficient at higher revs (where the boosted air gets hotter), and they also use engine hp to spin in the first place. Even though a turbocharged setup will generally out-power the supercharger up top, there is nothing in the game to make low-rpm torque like a supercharger - not even nitrous (although both go together nicely!).

As example, my SS Commodore with its 5.7L V8 makes 245kW standard, and generally feels a bit “limp” below 4000rpm, after which it hammers. Add the supercharger onto it and it makes 340kW with no other modifications.

This is a good power increase in general (95kW), but it’s the torque increase down low that makes it worthwhile - 510Nm stock (peaking at 4200rpm), vs. 753Nm supercharged (peaking at only 2850rpm!). To really see the increase, have a look at the power and torque charts (in garage) to see what a supercharger does for your torque curve!! You’ll find that a soft, ‘peaky’engine can suddenly fry tyres like a big capacity V8 when given a bit of supercharged boost.

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NITROUS OXIDE

Nitrous (Its not called “NoS” which is a brand name… damn Fast and Furious movies!) is a clear gas (held in a pressurised state in a bottle) that can be injected into a petrol motor along with extra fuel to create an extremely powerful burn in the cylinders. This nitrous “hit” is adjustable, and can be tailored to provide more power assistance, but at a reduced duration - the bottle empties faster when more is used.

As with real life, Nitrous adds hp (which gives mph gains) but in general it is best in its ability to make massive torque gains (which give low ET’s - if you don’t wheelspin). Nitrous-fed cars can suddenly take off in higher gears (to give nice fast launches) without bogging down, which makes for some huge time reductions, and the general hp increase will see good mph (speed) gains.

The real highlight of Nitrous though is what it can do to a Turbocharged car. In reality (and GT4 it seems!), the turbocharger on an engine is driven via exhaust gasses being expelled from the car, and the speed that the turbocharger can turn at is dictated by this restriction. As a general rule, the faster the turbo can spin the more pressurised air it can force into an engine (boost), and the more power and torque can be created.

Nitrous itself contains a massive amount of oxygen molecules in its chemical make-up, and therefore when it is injected into an engine (with more fuel to keep the air/fuel mixture in check) it can generate huge amounts of exhaust gasses, even at low rpm. What this means is that turbochargers can be made to provide massive boost outputs at lower rpm levels where normally they would be lagging, and the final hp output of the engine can be increased over 100%, even on a “full house” modified engine.

Time for an example or two…

1997 Supra RZ, bog stock
~ I won this car - so its brand new - gave it an oil change, it now has 355 hp (most others that make 325 - 330ish). I ran it as it came except I gave it full slick tyres, and the best I could get was a 13.03 at 110mph. After installing Nitrous Oxide (set to 70 hp) I ran again, culminating in a 11.48 at 132mph. The expected gain for a 70 hp increase would have been around 118mph, yet the car ran 132mph - this indicates somewhere in the region of 590hp is being generated…

And for a more extreme example, I have a;

Lancia Delta S4 rally car, 1985 model
~ The Lancia has a 2L DOHC turbo 4 cylinder, and with a stage 4 turbo it makes a very strong 590 hp. As it’s a 4WD it hooks up well with full slicks and is good for running a 9.77 at 147mph. However, as most 4 cylinders have the ability to run a 100 hp nitrous boost, the little 2 litre is suddenly given a massive power increase, and with enormous wheelspin and 3^rd gear takeoffs the Lancia runs 7.882 at an insane 203mph (330kph!). The mph indicates somewhere in the region of 1250 hp out of the 2L engine…

Now onto the setup part of the guide.

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SUSPENSION SETUPS - GAINS TO BE MADE

Depending on the make, model and age of a car in GT4 you can see either a small gain or a massive gain when changing and tuning the suspension for drag racing. The reason behind this comes down to what the standard suspension/tyres/weight bias and power delivery is like to start with, and thus how effective the vehicle is putting power down already.

To explain, a late model Mazda RX-7 can run a low 10 second quarter mile with its standard suspension setup (factory stock) when given all other mods. It does this due to its wide tyres, its 50:50 front to rear weight bias and its smooth power/torque curve that rises in a fairly linear manner (a nice rising curve as the revs go up).

Conversely, I have a 1969 Corvette which sports similar power and weight bias to the Mazda but cannot match its times on standard suspension, even with all other mods being done This is due to the Corvette being equipped with narrower tyres and the fact that the modified (supercharged) V8 delivers a massive amount of power and torque early in the rev range, making the car wheel-spin too much, and hard to balance on the throttle.

For all my GT4 drag cars I have adopted a setup that will return results no matter what - they are as follows:

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TRANSMISSION AND DRIVETRAIN CHOICES - WHAT TO RUN?

Depending on a few factors you should pick wisely when it comes time to buy transmission/ drive-train parts. This goes for all parts except for clutches (triple plate always) and Differentials, which can be any of the 4 types available (no difference in a straight line).

Flywheels
~ The more torque you generate, the quicker the engine will be able to rev, and possibly wheelspin. Makes big torque engines hard to balance on the throttle, especially when trying to setup the revs for launching off the line.

Gearbox
~ Fully Custom box - no matter what!! Spend that 10,000cr and make your car run any amount of gears over the ¼ mile that you want - my 1969 Corvette runs a three speed setup (monster torque) whereas my S2000 runs a tightly-packed 6 gear setup (low torque).

Carbon driveshaft
~ Same principle as the flywheel (less rotating mass means faster acceleration), but I generally make this one change to all my cars, as it only becomes a factor once you launch the car - it does not affect the vehicle before you takeoff. The gains will be larger for low torque cars that struggle to accelerate with a standard shaft, whereas for some supercharged V8's you can’t tell the difference.

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BALLAST FOR TRACTION - ADD SOME MORE!!!

For all the vehicles in GT4 that are only powered by one set of wheels (ie everything except for AWD) its crucial to add some form of ballast to provide extra grip (traction). This weight is used to pin the tyres to the road surface more effectively and will help you to launch a vehicle that would otherwise wheel-spin copiously.

The amount of weight you add will be dependant on a few factors, but generally speaking I run my rear wheel drive cars at about 80-120kgs of ballast, and my front drive cars closer to 200kgs of ballast. The reason for the difference is that when a RWD car accelerates a lot of weight is transferred to the rear - a front drive car conversely has weight taken off its drive wheels, hence the maximum amount of weight is needed.

Some cars will benefit a lot more than others by having weight added. Large capacity/supercharged or torque productive cars can be made to launch extremely fast where normally they spin the wheels, and for hi-rpm /low torque cars they can be geared shorter in the lower gears to provide faster launches.

The only real downside to all this is that weight can cost Mph (speed), in that you will generally see a 3-5mph loss for every 100kgs you add into your car. However, this is offset by the fact that most modified street cars in GT4 cant get enough traction - there isn’t enough tyre to transmit the power they put down, and in some cases you may actually see a gain in speed due to the vehicle being able to transmit full power to the ground earlier on.  This is especially relevant for cars using nitrous, where the hp and torque gains are mainly lost through wheelspin.

Please see my example below for the reasoning behind this.

Pontiac GTO Coupe, 770 hp
~ The Pontiac has a considerable torque peak in its rev range, around the 3500rpm area that makes the car prone to wheelspin in the lower gears. With all normal ¼ mile mods and adjustments done the car runs 10.62 @ 140mph over the quarter mile… I then added 90kgs, which brought times down to 10.30 @142mph, and finally 170kgs which gave me 9.97 @ 141.

Traction is the biggest factor in getting a modified car down the strip quickly. When you add ballast over the driving wheels you are attempting to make the tyres rotate at the same rate as the ground beneath them, hence the vehicle accelerates at a faster rate.  Without ballast (even when running super slick tyres) a high-powered car can wheel-spin most of the way down the track.

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WEIGHT REDUCTION - GOOD OR BAD?

In my previous guide for GT3 I noted that for fast times with a FWD car it was generally best to leave some weight on the car - this helped the lower traction FWD setup grip the road, resulting in less wheelspin (and lower times). This rings true in GT4 as well, but only for certain types of cars. The kinds of vehicles that need to retain weight for fast times are generally those with huge torque figures (large capacity, supercharged etc) and cars that have narrower tyres (most pre-1990 road cars have narrow tires). These vehicles will benefit from having some extra mass to help them with making that sudden launch off the line - suspension tuning and race tyres can only help so much!!  But enough storytelling - here’s yet another example…

My 1970 ‘454’ SS Chevelle
~ With 7.6L of  V8 under the bonnet it makes 685Nm of torque just off idle (2600rpm), so even with slicks it can light the tyres easily, especially if it drops into the next gear at these revs. I then added a supercharger to the mix, which gave me +365 hp, but added a massive 503Nm - a total of 1188Nm - I now had major traction issues even in 3^rd gear (and I only run 4 gears for ¼ mile setup in this car!).

This car had already had all its weight taken out (from 1850kgs down to approx. 1440kgs), so I couldn’t put this back in. Even with all mods for suspension, longer gearing (to try to tame the torque curve) and 200kgs of ballast I could ‘only’ run a 10.91… So this car was taken off drag duties, converted to N/A stage two and setup for circuit racing (still very sideways circuit racing!), and another Chevelle was then modified.

This car was built identical to the previous one, except for the weight reductions, which were never touched. With exactly the same settings to the other car (but minus the 200kgs ballast) this SS ran a 10.55 straight away. I still found that the car had traction issues, so I added weight slowly until I had an additional 135kgs. With this I’ve run 9.88 @ 152mph - over a second quicker than the old car, with more weight rather than less.

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COMMON PERFORMANCE CHARACTERISTICS OF AN ENGINE

When viewing an engine’s “type” in the garage you can get a fairly good idea of how the car is going to drive. This relates mainly to the capacity of the engine and the valve-train (fuel/air inlet) setup of the vehicle. Here’s a list of terms and a basic understanding of what they mean for that engine.

OHV - Over-Head Valve
~ Although this configuration is the oldest and most basic of all the setups it is used on some newer cars (mainly V8s). In general terms these cars will build torque well in the low-midrange and have a power curve that flattens out up top. Most standard cars with this setup don’t make much power beyond 6000rpm unless excessively modified, or of a late model design.

SOHC - Single Over-Head Camshaft
~ Having no pushrods or rockers to operate the valves, this configuration sees the camshaft on the very top of the cylinder bank. The single cam itself operates all the valves (inlet and exhaust) and it generally allows for higher RPM than a OHV setup as there is less moving parts. This was developed for use (in production road cars) during the late 60s/early 70s, mainly for use on 4/6 cylinder engines.

DOHC - Double Over-Head Camshaft
~ Having twin camshafts mounted over the cylinder head allows for individual cams to run the inlet and exhaust valves, which means the ability to change the timing of each to allow for both good low rpm response and then allow for hi-rpm cylinder filling (large horsepower output for capacity). This setup uses a 4 valve per cylinder arrangement, so nitrous, turbos and superchargers will see more of a top end power gain than those put on a similar engine with a non DOHC arrangement - this setup flows better than anything else.

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SUMMARY

The only real way to get any car to perform over a ¼ mile (even a simulated one) is to follow the oldest racing approach - test and tune. With only the right parts and the right settings will you be able to get those low ET’s and high MPH numbers, so keep modifying, chopping and changing until you find what suits your chosen vehicle best. The info enclosed in this guide is just that - a guide to hopefully assist you. It is in no way the be-all and end-all for GT4 drag racing, but it should help you to understand a few of the more complex theories and principles behind getting a good ¼ mile result.

Thanks for reading, and keep sending Mustang-man your ¼ mile submissions!

Andy R :D

GT4 1/4 Mile Records

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