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The best thing you can do is check out the Fastest DSM Drag Times page, maintained by James Heck, and compare your times to the times posted by other members.
As a very rough guide, you should expect the following 1/4 mile
times, given a good launch and decent driving on your part:
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Auto cars can add about 1 second to any of the above times. Check Club DSM Automatic for another list of auto times.
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Quick answers:
- stock fuel system, pump gas: 15 psi, or an O2 sensor reading of 0.85V minimum, or an EGT reading of 1650 degF maximum.
- upgraded fuel pump, stock turbo, pump gas: same as above.
- upgraded fuel pump and injectors, stock turbo: same as above. You will probably hit fuel cut first. Here's why.
- turbo upgrades: varies, but typically lower than 15 psi. You'll need a fuel management system before you can do much of anything more than that. Here's why.
Owing to individual variations between cars, the 0.85V O2 reading mentioned above should be treated with extreme care. Most people prefer 0.90V or better.
Detailed answers:
By changing the intake pressure in your car, you are changing the mass of air entering the engine. In order to maintain
a proper air/fuel mixture, more fuel must be delivered to the engine to compensate. Therefore, the 'safe' amount of boost on any DSM is primarily determined by the fuel delivery system in the car. Also, local factors will change the actual mass of air entering the engine, which again changes the required fuel.
Under all circumstances, remember this simple rule: intake air pressure does not equal intake air flow. Flow is what matters.
The amount of boost pressure you can run without risking damage to your engine depends on the following factors:
There may be other factors that affect maximum intake pressure. Those interested in a more detailed discussion can read Morgan D'Antonio's post about what limits boost levels on DSMs.
In the above list, the fuel pump and fuel injectors determine the amount of fuel that can be delivered to the engine in a given time. Aftermarket pumps and larger injectors increase fuel delivery capacity.
Turbo and intercooler efficiency determines the temperature of the air going into the engine at any given pressure. Lower temperatures reduce combustion temperatures, but also increase the actual mass of air entering the cylinders. Colder ambient temperatures also increase air mass. Higher altitude cars, though, have less dense air to push than sea level cars, meaning less air mass enters the engine.
MAS modifications introduce an additional element of error into the mass air calculations done by the ECU. Because the ECU, under some conditions, does not check to see that the amount of fuel provided is adequate to safely operate the engine, the operator must monitor the engine operation. Most 'free' mods do not change the MAS operation enough to cause problems, but there is always a small possibility of engine damage, as well as idle and misfire problems.
Gasoline octane is important in that it also reduces the occurance of knock. Running too much boost on bad gasoline with leave your engine pinging like crazy, forcing the ECU to cut boost and reduce timing, thereby losing power.
The rule, accoding to leading DSM performance authorities, is to run at least 0.85V from the oxygen sensor at all times. This corresponds to exhaust gas temperatures of about 1650 degrees F maximum. Failure to observe these limits will often result in melted engine parts.
As a general guideline for those without air/fuel or EGT gauges, sea-level cars may safely run 15 psi (1.0 bar), with the stock fuel pump and turbocharger. The addition of other mods does not generally change this figure, provided the intake pressure remains at 15 psi maximum. This is the level that most owners run in their cars, at least until further upgrades are possible.
For those not operating near sea level, the 'safe' boost you can run seems to increase by about 1 psi (0.07 bar) for each 1000' over sea level. For example, a car at 3000' over sea level can safely run as much as 18 psi of boost. This rule is less reliable than the above 15psi rule, though, since high-altitude owners are understandably reluctant to repeat the boost-related engine damage experienced by some unlucky sea-level owners.
Those owners with upgraded fuel pumps may also run higher boost levels than 15 psi. If you want to do this, presumeably you have installed air/fuel (A/F) and/or exhaust gas temperature (EGT) gauges in your car to monitor the engine operation. Moving to higher boost levels without at least one of these instruments can be hazardous to your cars health. Provided you meet the above-mentioned 0.85/1650 rules, there is no limit to the boost you can run until you hit fuel cut.
It should be noted, however, that the stock DSM turbochargers are pretty much incapable of making more power somewhere around the 15-17 psi level. Above this limit, the turbocharger heats the intake air so much during compression that any power gained from additional air density is lost. Many people have reported this effect, which leads to less power at higher boost pressures.
Also, higher boost pressures exact more stress on the engine components, regardless of the air mass. After all, 18 psi is still higher than 15 psi. Owners that run pressures higher than 15 psi may experience failures on other components that cannot take the stress. One good example is the intake manifold gasket, which was made of rubber in 1990-1992 cars, and sometimes cannot handle the increased pressure. (Fortunately, the replacement 1993-1994 gasket is metal.)
Those interested in the factors responsible for limiting boost should read Morgan D'Antonio's take on what really limits your boost levels on a DSM.
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Owners of newly upgraded turbochargers often find, to their dismay, that they experience a severe loss of power at the same boost levels they ran with the old turbo. This is because that the upgraded turbocharger has better flow rates and efficiency than the old turbo - that's why it's an upgrade - and the stock ECU/fuel system cannot handle it. Too much air is entering the engine, leading to low O2 sensor readings, high EGTs, even severe knocking under acceleration. The only solution to this problem (besides lowering boost, or removing the turbo upgrade) is to purchase a fuel management computer of some type. These devices allow the owner to 'trick' the ECU and manually adjust the fuel delivery back to correct levels.
Owners which already have a fuel computer installed should run a mimimum of 0.85V from the O2 sensor, and a EGT maximum of 1650 degrees F. Exceeding these values may result in engine damage. See above for why.
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Read this entry in the Top Ten FAQ.
FWD owners will also want to read these posts from Brett Nashlund, Jim McKenna, and John Hindle.
Automatic owners should note that power-braking their cars too much will build a fair amount of boost. This may cause the BOV to open while you are still standing still, leading to a crummy launch. The moral of the story is there is such a thing as too much boost, at least at the line. Taking it easy will not only save your tranny, it will give you a better launch.
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What is wheel hop? My front/rear end goes "whump whump whump" when I launch. What's going on? |
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This is generally wheel hop, also known as a convenient automatic windsheild wiper activation feature. Both AWD and FWD DSMs apparantly suffer from this, in proportion to other mods; FWDs tend towards front wheel hop, AWDs prefer rear hop.
Not really caused by wheels bouncing, wheel hop occurs when the tires are getting/loosing grip in rapid sucession. Wheel hop tends to stress transmissions, differentials and other driveline components quite badly, as described in this post by John Werner. It has also been posted that the majority of center differential failures are directly related to wheel hop. Slicks, stiff suspensions, hard launches and burnouts promote wheel hop, and the resulting driveline failures.
Those who suffer from wheel hop should read Mark Purney's page on reducing wheel hop. Mark's solution (provided by Road Race Engineering) involves filling the stock engine mounts with polyurethane rubber to make them stronger.
Other FWD solutions include: equal tire pressures (left to right), lower tire pressures, softer suspension, a front sway bar (not strut tower brace) and less drastic launch techniques. AWD solutions include: equal tire pressures, softer suspension, and less drastic launch techniques.
Also look at this post by Scott Willard, which describes his experience with a loose driveshaft striking the bottom of his car. This is not the same as wheel hop but has the same symptoms - he describes a test to differentiate between the two conditions. AWD cars which exhibit a thumping from the rear are likely to have this problem, which is caused by worn carrier bearings. The solution to this problem is listed on the FAQ Locator; the $5.00 Carrier Bearing Fix page has the details.
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Since this can change at any time, current record holders are not going to be listed here. However, the top shop cars in 1998 were from Buschur Racing and Extreme Motorsports, both of whom have already run 10.xx 1/4 mile times without the use of nitrous oxide.
Dave Buschur also has a phenomenal 9.67 @ 139.4 MPH timeslip for his most unique creation: his rear-wheel-drive Eagle Talon. No nitrous here, either, and it is DSM powered. (Apparantly there are two other purpose-built DSM-based drag cars, but neither has the original Mitsubishi engine block.)
Several others have also broken into the 10s. Various other people hold records for 1G, 2G, AWD, FWD, stock turbo, etc. etc.
[Note: From time to time, debates on the definition of a 'DSM' emerge on the Digest. These debates usually center around a record-breaking car which, because it does or does not have a certain component or feature, 'should' or 'should not' be considered a 'DSM' in the 'true' sense of the word.
Such judgements are entirely subjective and cannot be resolved, except by arbitrary rules; resist the temptation to reopen any such debate on the Talon Digest, as the moderator (and membership) are tired of hearing about it. All race results that can reasonably be deemed related to DSMs are reported - whoever is king in your own mind is best kept to yourself.]
James Heck keeps track of who is the fastest in Club DSM; check it for the latest information.
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This depends on a number of things, including:
Owing to the large variety in desired performance and spring/shock combinations, there are few well-established guidelines as to how to set up the car. Most people agree that DSMs benefit from a somewhat stiffer suspension, especially in the rear, but most shocks have no difficulty providing that. Lowering the car seems to be more important to improved handling.
Drag racers have noticed that a stiff rear suspension seems to promote wheel hop in AWD cars. The same may hold true for stiff front suspensions and FWD cars. On the other hand, dedicated autox racers usually desire the stiffest, lowest, most balanced suspension package available.
Cars which are lowered a great deal demand stiffer suspensions to keep the car off of the bump stops. A setup that is too soft will have the car always bottoming out, leading to an uncharacteristically harsh ride.
Here are some quick searches that will provide other opinions on how to select and/or set shocks:
And, on a related note:
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Maintained by Sean Costall. Changes and suggestions are welcomed! If you have any information on the answers to any of these questions or wish additional questions, please mail me.
This page is an extension of Club DSM .