Five Components to a 12 second NA GT

[Bill Putnam]

Before reading on I just want to say that this is basically geared towards drag racers not your average enthusiast looking for 12s on street tires with no real changes to the car. Not that it can’t be applied to someone looking for that but this is geared more towards the people out there looking for 12s and willing to work for it.

1.) Power – If you listen to some old school drag racers they may say you need at least 300+RWHP to hit 12’s in most cars. In some heavier cars that may be true but fact is suspensions are more refined these days and cars don’t weight 4,000 lbs. Most PI headed cars will hit the 245-255RWHP mark with basic mods (Pulleys, Timing Adjuster or chip, O/R H or X, K&N or other type of high flow filter and although not a power mod…gears 4.10s or 4.30s). For a bolt on GT this is enough power to get the car into the 12s after you follow the other steps. Keep in mind more power will make it easier to reach your goal or help offset more weight (see next section) but it can be done with less.

2.) Weight - You basic 5 speed coupe without driver weights 3250lbs. So with an average driver weighing about 180lbs that puts your race weight at 3430lbs. At that weight and a power to weight ratio of .075 you would need 258RWHP to hit 12’s. Power to weight is the power of your car (rear wheel) divided by race weight of the car. Using my car when I broke into the 12’s first time I was making 246RWHP and had a race weight of 3250lb, which worked out to a .075 power to weight ratio or .075RWHP per pound of the car. From what I’ve seen a car can get into the 12s with a .075 to .080 P/W ratio. So if your race weight is 3430lbs then 3430 * .075 = 257.25RWHP. As long as you keep this ratio in the .075 to .080 range you are fine plus keep in mind you can drop weight instead of adding power. An example of this is a car with a 3000lb race weight could break into the 12s with 225RWHP (close to stock power on a GT).

Now I’m sure some of you are asking about weight reduction. Basic weight reduction would be rear seat delete, removal of spare tire, jack, tire iron…these would knock a good 70-80lbs from the car. Add a set of welds or light weight race wheels and you are looking at another 60-80lbs. For more information about specific weights and more ideas look here… http://users.adelphia.net/~mustang-9...0Reduction.htm

3.) Suspension - I feel that this component has the most leeway so to speak. I’ve seen near stock suspension cars get good weight transfer. I honestly believe a car that meets the other requirements could hit 12s on the stock suspension. However those of you that want to get an edge should read on. First thing I would do is look at springs since most of us want a better stance but still want weight transfer. For that look at fox body 4cyl front springs I usually look to the junkyards for these but most buy stock replacements at a local shop (avoid Moog brand though they are taller than stock specs). For the rear end I go with fox body v8 rear springs cut anywhere from a ¼ to 1 coil to level out the car. Just keep in mind that it’s easier to cut too little than too much spring.

Next I would highly recommend a pair of sub-frame connectors welded in to tie the chassis together. Hard launches on slicks will twist the body and this will help keep it straight. Last piece to really help out is struts I went with Lakewoods because they are readily available and affordable but adjustables can be used as well if you have the budget for them. 70/30s and 90/10’s both work well and I stick with fox body specific struts since the car is lowered. Fox body specific springs are ¾” shorter than stock SN-95 springs so the lower fox body specific struts are shorter.

4.) Traction – I’ll cut to the chase here and just skip over street tires and drag radials and go right to slicks. Not that it can’t be done on these tires but it will take more power, more patience and much more writing on my part so we’ll stick to slicks. Cars in this weight range and power level only need a 26x8.5x15 ET Drag for traction. It’s close to stock tire height and is more than enough to make our cars hook on the track. A better suspension will result in better 60 foot times but even on stock suspension a good burnout on slicks will not spin unless the track is poorly prepped or fluids are on the track. Some people opt for cheap steel wheels which I don’t necessarily recommend since you are keeping extra weight on the axles. This opens you up for possible breakage so I would go with a weld wheel instead even if it’s a pair of used ones for track only purposes. Regardless a 15x8 with 5 on 4.5 bolt pattern and 5.5 backspacing will fit perfect, or if you insist on a wider tire like a 10” then a 15x10 with 5 on 4.5 bolt pattern and 6.5 backspacing will also work on our cars.

5.) Practice – This is one component that you can’t buy at any store, you can learn it from a text book and you can’t ask your friends about you simply have to get out there. I’m not saying everyone should be like me and hit every test and tune but don’t expect to make one trip and bingo your in the 12’s. I race on slicks for 3 months before hitting my first 12 second pass. Going to slicks alone was a big change that I had to adjust to before I got the hang of and learned to shift better, etc… Take your time, get comfortable in the car and have fun with it. Do that and you’ll achieve your goal.

Now that you know the key components to get into the 12’s you have to keep it all together.  In the above situation I would highly recommend an aftermarket shifter just to help keep the transmission alive longer. The biggest weakness in the above is the differential and axles. Not to say they can’t take some abuse because they can, mine went almost a full year of launches on slicks before breaking. I would look at a set of 31 spline axles and an Eaton or Ford 31 spline differential beefed up to keep the back end in one piece.

Bill

[Starkie]

Amen.

Starkie

[Kurgan]

Took me 6 months to hit 12's

[D.K]

Excellent write up Bill!

[DARKHRSE99]

Yes, another good write up Bill

Bill Rocks. :hail:

PS Bill, doesnt rotating mass (wheels) have more bearing than chassis weight?

[Kurgan]

Originally posted by ChickInHer01GT
PS Bill, doesnt rotating mass (wheels) have more bearing than chassis weight?

Ding ding ding, we have a winner!

Last I heard, the best estimate was about .1 seconds for every 100 lbs of total vehicle mass lost, and about .1 seconds for every 10 lbs of rotating mass lost.

[Wayne S]

Originally posted by Kurgan
Ding ding ding, we have a winner!

Last I heard, the best estimate was about .1 seconds for every 100 lbs of total vehicle mass lost, and about .1 seconds for every 10 lbs of rotating mass lost.

.1 for 100LBS sprung weight
.1 for 10LBS unsprung weight

[Jackie Chan]

weight for the verts:
I weighed my vert at Orlando Speed World during the World Streets and it came to 3390lbs w/o driver
that is without spare/jack/lug wrench/front swaybar/no cats(prochamber)
the car had an 1/8 tank of gas
bullitt wheels
leather
mach460

[AutomaticWeapon]

i said it before, ill say it again... thanks to Bill's patience, i got the shorthand version some time ago on StangNet... and im grateful as hell.

it took me 55 passes to hit 12s, i know it would have taken alot longer without his advice.

Bill, you da Man.

-Mike

[madmike]

Great info. I read it a while back at SN too.

BTW, it took me two months and 21 passes to get in the 12s. Actually, only six 1/4 mile passes before the 12. All the others were at the 1/8th mile track.

As Mike said though, if it weren't for a lot of the info that others had already found, I wouldn't have been able to get 12's that quick. Thanks Bill!

Mike

It took me one pass to get from 13.7's into the 12's

*poops hood* hey how did that blower get there

In all seriousness, I have so much respect for you N/A guys. Your running better times than some (most) PA guys. Good job

Makes me want to put my coupe(and driver) on a diet. At the moment race weight with driver is 3601(im 180lbs)

[DARKHRSE99]

Originally posted by Jackie Chan
weight for the verts:
I weighed my vert at Orlando Speed World during the World Streets and it came to 3390lbs w/o driver
that is without spare/jack/lug wrench/front swaybar/no cats(prochamber)
the car had an 1/8 tank of gas
bullitt wheels
leather
mach460

Damn, your Vert is Heavy. Mine weighs about 300Ibs lighter then yours. You better get that Vert on a diet quick.


Jason

[AutomaticWeapon]

hey, Jason. is that with you in the car? 3090#?

i always thaught verts were alot heavier... besides the usual stuff, what the heck did you ditch?

-Mike

[wiz]

these steps worked for me! thanks again bill!

Damn good, I kinda went overboard in the power department.. now it's time to balance the car and get some slicks on it. You guys almost make me wish I went N/A.. simply sick times for your power.. A lot of the Fox Body guys can't understand why we can't get our times down to where thiers are and you guys are showing that it can be done.

[Wayne S]

Originally posted by CTGrey02
Damn good, I kinda went overboard in the power department.. now it's time to balance the car and get some slicks on it. You guys almost make me wish I went N/A.. simply sick times for your power.. A lot of the Fox Body guys can't understand why we can't get our times down to where thiers are and you guys are showing that it can be done.

Can be done but they still rape us pretty good in the 60ft time department

[Steps]

I could not agree more there....

My brother is cutting 1.9 60's on street tires in his 92...

[Jackie Chan]

i know plenty of guys pulling 1.9s with 99+ on street tires

[DublOVert]

Originally posted by DARKHRSE99
Damn, your Vert is Heavy. Mine weighs about 300Ibs lighter then yours. You better get that Vert on a diet quick.


Jason

Vert=pig