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Discussion Starter · #1 ·
I've noticed how often newbies (and not so newbies confused by the multi-voiced claims of the marketplace) seek help in determining which mod to start with, add on, or benefit from. Trying to find a logical method of quantifying in some way all these diverse mods is difficult, but I think I've come up with a method that will often work.

The Augus issue of MMFF features an column by Richard Holdener that contains some simple math one can use to compute the effect of a given modification on a given car. The logic goes:

1. Compute the number of g's (gravities) you car produced in current form. The example he used was a 5 speed car with 400 lb feet of torque, a 3.27:1 final drive and a 2.95:1 first gear ratio. Drivetrain efficiency was set at 87% (average for a 5 speed - automatics would be lower) to compensate for lossed in the clutch, transmission and rear, and the tires had a rolling radius of 1.1 foot (racing slick, but close to that of many 315 drag radials as well). The car in the example weighed 3000 pounds. Here is the formula:

2.95 x 3.27 x 0.87 x 400 / (divided by) 1.1 = 3,356.98/1.1 = 3051.80 pounds of thrust. Next divide the thrust by the weight of the car:
3051.80 / 3000 = 1.017 g's of acceleration.

Changes to any of the variables will rais or lower the acceleration number, ie, add 100 lb/ft of torque with a nitrous kit, and you get 1.27 g's.

Change to 4.10 gears, and you get 1.278 g's.

Reduce the weight of the car by 600 lbs, and you get 1.271 g's.

Obviously you can also dollarize the equation, assigning the cost of the modification to the g's, ie:

Nitrous kit costs $1200, you gain .25 g's, the cost is $300 per .1 g gained.

Gears cost $600, you gain .25 g's, the cost is $150 per .1 g gained.

As you can see, the better investment purely from this standpoint are the Gears - more "bang for the buck". Lets say you could gain 33hp from a $400 throttle body and intake. This would be equal in value to the nitrous, at about $300/.1 g gained, though still inferior to the gears.

The article contains many caveats regarding things like aerodynamic drag not being factored into the equation - and this is true. But this forumula is at least invaluable in prioritizing the various modifications in at east a quasi-scientific manner.

If you can find it, seek out the article and read it (he has a similar write-up in the July issue regarding lateral acceleration, ie, handling and braking, that has similar potential in determining which handling modifications to do first.

I think aerodynamic loads get discussed next month. I for one am all ears.

tripleblack
 

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Discussion Starter · #2 ·
Math errors

I think there are some math errors in my post. The equation should result in a cost of $480 for .1 g with nitrous, $240 for gears, and so on.

Old age, pure and simple.

tripleblack

tripleblack said:
I've noticed how often newbies (and not so newbies confused by the multi-voiced claims of the marketplace) seek help in determining which mod to start with, add on, or benefit from. Trying to find a logical method of quantifying in some way all these diverse mods is difficult, but I think I've come up with a method that will often work.

The Augus issue of MMFF features an column by Richard Holdener that contains some simple math one can use to compute the effect of a given modification on a given car. The logic goes:

1. Compute the number of g's (gravities) you car produced in current form. The example he used was a 5 speed car with 400 lb feet of torque, a 3.27:1 final drive and a 2.95:1 first gear ratio. Drivetrain efficiency was set at 87% (average for a 5 speed - automatics would be lower) to compensate for lossed in the clutch, transmission and rear, and the tires had a rolling radius of 1.1 foot (racing slick, but close to that of many 315 drag radials as well). The car in the example weighed 3000 pounds. Here is the formula:

2.95 x 3.27 x 0.87 x 400 / (divided by) 1.1 = 3,356.98/1.1 = 3051.80 pounds of thrust. Next divide the thrust by the weight of the car:
3051.80 / 3000 = 1.017 g's of acceleration.

Changes to any of the variables will rais or lower the acceleration number, ie, add 100 lb/ft of torque with a nitrous kit, and you get 1.27 g's.

Change to 4.10 gears, and you get 1.278 g's.

Reduce the weight of the car by 600 lbs, and you get 1.271 g's.

Obviously you can also dollarize the equation, assigning the cost of the modification to the g's, ie:

Nitrous kit costs $1200, you gain .25 g's, the cost is $300 per .1 g gained.

Gears cost $600, you gain .25 g's, the cost is $150 per .1 g gained.

As you can see, the better investment purely from this standpoint are the Gears - more "bang for the buck". Lets say you could gain 33hp from a $400 throttle body and intake. This would be equal in value to the nitrous, at about $300/.1 g gained, though still inferior to the gears.

The article contains many caveats regarding things like aerodynamic drag not being factored into the equation - and this is true. But this forumula is at least invaluable in prioritizing the various modifications in at east a quasi-scientific manner.

If you can find it, seek out the article and read it (he has a similar write-up in the July issue regarding lateral acceleration, ie, handling and braking, that has similar potential in determining which handling modifications to do first.

I think aerodynamic loads get discussed next month. I for one am all ears.

tripleblack
 

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Well, my 02 GT I have now is my 3rd stang I've owned but is the first I' ve decided to modify.:happyhapp After searching websites, reading magazines, and just talking to other mustang owners, it seem to me (esp. on my budget) that making the most of the horsepower I have is the way I need to go. Of course I will start with giving it a breath of fresh air with K&N intake system, X pipe, and Flowmasters. ( I like the rumble, had em on my 94 cobra) Next will be 4.10s ( the car only sees about 3 to 4 thousand miles a year), and of course the Superchips flash tuner. Subframe connecters to reduce the "off the line" flex. Suspension upgrade to get the power to the ground. And like you said, reduce the weight. Light weight rims such as the Steeda offerings though I haven't decided yet. Ilike the idea of a 10.5 in rim in. the back with a drag radial to get some good bite. Aluminum drive shaft, and a rear seat delete. Already stripped the trunk. After all that, then I'll start really tearing into it. Forged pistons and rods, cam, injectors, fuel pump and haven't decided on the Procharger P1sc or Kenne Belle 1700.:eyepoppin But like I said, I just want to wake up what I have now:sleeping: . Then we'll go for broke!:kooky:
 

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Discussion Starter · #4 ·
Using the formula, gears are almost always your best "bang for the buck", with exhaust near the bottom (though a perrenial favorite due to the visceral need to advertise the muscle under the hood).

My own priotizing would be:

1. Brakes - OE brakes stink. Upgrade to Cobra kit brakes will set you back about $500 or so. Logic: If you can't stop, you are endangering yourself and all those expensive mods you just made - so make the brakes #1.

2. Shifter - OE shifter sucks. Upgrade to Steeda or MDW. $180. Shifter is worst peforming oe part on the car. Missing gears can ruin your whole day (and your transmission).

3. SCT tuner (Diablo a good 2nd choice). Tune will allow you to control many downstream mods, and yield immediate gains of response, hp and torque. $400.

4. Gears. 3.55 if you're going after a Kenne Bell or Whipple SC - 3.73 or 4.10's other wise. Depending on mileage of your car, may need complete new set of bearings, too. $600+ installed. Best "seat of the pants" change you'll make short of major engine build, sc, turbo or nitrous.

5. Forking of the decision tree. If you're going with a naturally aspirated build, best investment here is the biggest one. Cams, springs, & ported/polished heads. You can add about 60hp here - and cost about $3000+, including labor and misc. parts. Expensive route. This DOES NOT INCLUDE lots of other expensive bolt-ons you will probably want, like bigger tb, intake, injectors, maf, cai, etc, etc.

5.a. Other fork: Power adders. I've chosen the Kenne Bell kit, which includes just about everything you need to make the install - and costs $4300+. Adds about 100hp to a stock 02 GT (maybe a little more with other bolt-ons).

Got to go - will add to thoughts here later.

tripleblack

Storkdork said:
Well, my 02 GT I have now is my 3rd stang I've owned but is the first I' ve decided to modify.:happyhapp After searching websites, reading magazines, and just talking to other mustang owners, it seem to me (esp. on my budget) that making the most of the horsepower I have is the way I need to go. Of course I will start with giving it a breath of fresh air with K&N intake system, X pipe, and Flowmasters. ( I like the rumble, had em on my 94 cobra) Next will be 4.10s ( the car only sees about 3 to 4 thousand miles a year), and of course the Superchips flash tuner. Subframe connecters to reduce the "off the line" flex. Suspension upgrade to get the power to the ground. And like you said, reduce the weight. Light weight rims such as the Steeda offerings though I haven't decided yet. Ilike the idea of a 10.5 in rim in. the back with a drag radial to get some good bite. Aluminum drive shaft, and a rear seat delete. Already stripped the trunk. After all that, then I'll start really tearing into it. Forged pistons and rods, cam, injectors, fuel pump and haven't decided on the Procharger P1sc or Kenne Belle 1700.:eyepoppin But like I said, I just want to wake up what I have now:sleeping: . Then we'll go for broke!:kooky:
 

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Well, before I go the super charger route, wouldn't it be a good idea to go with forged pistons and crank? I've heard a lot of horror stories about stock pistons and and crank not being able to handle the added pressure, so I'd like to upgrade the bottom end first. thoughts??
 

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Discussion Starter · #7 ·
AOD, etc.

Blower build to support BIG blower definitely needed (in the case of the Kenne Bell twin-screws, 2.2 or 2.4 models recommend forged internals).

Small blower does not require this (Kenne Bell 1.7), though you MUST control the urge to up-pulley it to the point she blows up (in general terms, you CAN add pulleys to max out a smaller sc and get big gains - until the rods exit the motor). Keep within the manufacturer's recommendations (they are all very specific as to boost levels for given blocks), keep a good dyno tune on the car, and you'll be fine.

Main decisions to make with a blower is, first of all, do you want the screaming high rpm hp gains you get from the centrific guys (VorTech, Paxton, etc) or the low end torque you get from the twin screw guys (Kenne Bell, Whipple, Saleen)? Once you decide this, you are indeed looking at whether or not to build a forged small block or not - all of which depends on the hp goals you set. If you need 600hp, build the block and go for the gold. If you'll be content with less than 400hp, bolt on the small sc and go about your business.

tripleblack

Storkdork said:
Well, before I go the super charger route, wouldn't it be a good idea to go with forged pistons and crank? I've heard a lot of horror stories about stock pistons and and crank not being able to handle the added pressure, so I'd like to upgrade the bottom end first. thoughts??
 

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Discussion Starter · #8 ·
Intercooler

Forgot to mention - good streetable setup benefits from an Intercooler (also sometimes known as an aftercooler or precooler - depends on the setup). This will allow better tuning, more power, and cooler charge temps, and more dependable operation. All it does is cost about $1200 more than the same sc without one.

tripleblack
 

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Discussion Starter · #9 ·
Math lesson

Just ran across this old math method for mods.

Still looks like another way to figure out which mod comes first!
 

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wow that was way too much math. Im a fan of dollar to HP ratio lol (w. the exception of gears)
 

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very insightfull! you learn something new everyday!
 
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