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Cambered Rear Vs. Weight Reduction Vs. Power Mods - Help Me Decide!

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296
362
CA
Hello awesome tmo family. I find myself in a bit of a pickle w/my 3v mustang track car.

I need help making a decision on what to do next for my car. My primary goal is to lower lap times. My options for mods are as follows:

  • Weight Reduction - This would entail removing the A.C, gutting the doors, lithium battery, lightweight radiator support, Lexan windows. The result would be a car which is ~160lbs lighter and a wallet which will be ~$2500 emptier. This is a scary one for me as it represents a "full commitment" to making my car a track car.

  • Power Mods - Looking into Livernois Heads w/custom cams to put me at about 350-360whp, which is +50whp from where I am currently. Cost ~$8,000. Also considering a low PSI vortech package for around the same price. This would come with a weight penalty, but would put me at around 400whp.

  • Cambered Rear end - I am reaching out to anyone and everyone who has data on this part. I am seeing anywhere from 0.0s gained to 2s gained. I'd like to think the actual number is somewhere in the middle, but am not sure. All cambered rear end people please come forward! - Cost ~$7,500

Looking for some wisdom from the group! I like the idea of keeping the engine totally stock. But I am also really sick of having the power to weight ratio of an S2000 or E36 M3. At the same time, spending $8000 for power also makes me sick to my stomach.

I know weight reduction will make the car more fun in every regard; better acceleration, turning, braking, but at the cost of "ruining" my car.

The cambered rear end (potentially) represents a bolt on part that should be worth a second or two, all other things being equal.

What would you do? The car currently has tons of cortex suspension, engine bolt-ons. It's a well set up machine.
 
49
41
Exp. Type
HPDE
Exp. Level
3-5 Years
California
If I was in your shoes. I would spend the money on weight reduction then cambered rear. I'm a slower driver than you but I like to have fun and drive loads of laps and drive on canyons all the time. I have plenty of friends that don't enjoy their cars even half as much as I do because they made their cars less reliable with more power. I know there's people on here and all over with boost with no problems either.

Example: I have a close friend with a 600 whp turbo integra. It's got everything, JRZ coilovers, aero, etc. Guy puts similar laps to me but only does like 1/4 of the driving I do and half the time I see him something is broken on it.
 
It's autocross so I can't put a lap time number on the improvement from the cambered axle. It makes the back of the car *much* easier to control smoothly while at the limit which I would think would lead to much better lap times on a road course.

It also halved my tire wear. I don't normally run tires to the ragged end of life, but before I spent a lot of time rotating front to back to keep the edges from cording. That is no longer the case. I ran a set of Re71rs to 130+ runs without ever rotating front to rear.

DaveW
 
296
362
CA
It's autocross so I can't put a lap time number on the improvement from the cambered axle. It makes the back of the car *much* easier to control smoothly while at the limit which I would think would lead to much better lap times on a road course.

It also halved my tire wear. I don't normally run tires to the ragged end of life, but before I spent a lot of time rotating front to back to keep the edges from cording. That is no longer the case. I ran a set of Re71rs to 130+ runs without ever rotating front to rear.

DaveW
Good info on tire wear. I could see it (probably in like 30 years 😂) pay for itself in tire wear. Especially if I ever make the switch to a more expensive tire like a hoosier.
 
296
362
CA
weight > every othe rmod. The dragster guys tell me that 100 pounds is good for over 1/10th of a second, in most autocross tracks, that are point and shoot, those numbers would be applicable, plus the added advantages of helping with cornering, and they are generally cheaper.
I wish I was smart enough to learn how to simulate how much "x" weight loss would impact my lap time. If only I was on an F1 team. LOL.

or... or put a gear and an aluminum flywheel in it.
I have been slightly considering something gearing related, like going to a T-56 and running shorter gears to do a better job keeping the 3v in the power band. But then I worry about if it wouldn't make my faster, as I'd spend more time up/downshifting. I already have a lightweight flywheel on the car thankfully, that was a great mod.
 
296
362
CA
If I was in your shoes. I would spend the money on weight reduction then cambered rear. I'm a slower driver than you but I like to have fun and drive loads of laps and drive on canyons all the time. I have plenty of friends that don't enjoy their cars even half as much as I do because they made their cars less reliable with more power. I know there's people on here and all over with boost with no problems either.

Example: I have a close friend with a 600 whp turbo integra. It's got everything, JRZ coilovers, aero, etc. Guy puts similar laps to me but only does like 1/4 of the driving I do and half the time I see him something is broken on it.
Couldn't agree with you more, I love home simple and reliable the powertrain is on the car, I'd hate to mess with that just to drop a little bit of lap time.
 
98
143
Exp. Type
Autocross
Exp. Level
20+ Years
Olsburg, KS
If I ever blow up the engine in my Bullitt I'll take a long hard look at upgrading to a 5.0. Significantly more powerful (even in stock form) and I don't know that they're any less reliable. They also give you more RPM to work with. To start with, I'd be looking at losing weight. It takes stress off of everything and is the cheapest thing to do. As someone with a supercharged car, I'd stay away from that if you can. If you do supercharge it, make sure it has a LOT of cooling capacity. In spite of the shortfalls, I do really enjoy the supercharger on mine.
 
61
118
Exp. Type
Time Attack
Exp. Level
20+ Years
Melbourne Australia
This is a scary one for me as it represents a "full commitment" to making my car a track car
Just read through your full car build. Looked at the photos and came to a conclusion. Who the hell has been telling you your car isn't a track car. Damn. I'm sure it isn't a daily driver.
I'm with @blacksheep-1 on this even before seeing his comment.
weight > every other mod.
As someone who club raced a very under powered 4 cylinder, weight loss was the greatest gain. Unfortunately its also the least glamorous so tends to be the last thing people look at.
For every pound you can dump out of your vehicle, its a pound you don't have to accelerate, brake, stop sliding through a corner. Suddenly your brakes work better, your tyres last longer, less stress on the engine, gearbox, the cooling system, oil temps, diff temps. HP whilst fun kills components. Less component stress equals less costs overall. The exact reason my GT engine is staying stock.

Real world example.
Winton Racetrack here in Australia. 1.86 mile handling circuit.
1200kg 944 Porsche normally aspirated 120Kw @ engine on 225/50 R15 Bridgestone 540S tyres, my best time 1-39-8
1780kg Mustang GT 306Kw on 285/305/30 R20 Cup 2's, my best time 1-36-6 whilst praying it would stay on the black stuff through corners. I couldn't believe the feel of so much weight compared to my previous track car. It honestly scared me the first time tracking the GT.

I'll go one further and say, rotational weight > weight but that's a costly one.
I know weight reduction will make the car more fun in every regard; better acceleration, turning, braking, but at the cost of "ruining" my car.
How are you "ruining" your car making it "more fun in every regard". Delete/"unbolt" as much as you can before "cutting" anything out. You can do that latter when you realize you have a track car and its a truck load of fun. My 944 was a tin can, full cage, 2 race seats, harnesses and still had number plates on it. Still the most fun thing on 4 wheels.

In the words of Colin Chapman - Adding power makes you faster on the straights. Subtracting weight makes you faster everywhere.
 
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341
Maybe I'm missing something but reading through your build thread.... if your primary goal is better lap times and you are ready to spend some dough why are you insisting on using 200tw street tires? You could shave seconds with a set of GY 3Rs, Hoosiers, or whatever. You list weight, power, and cambered rear end... why not tires?

All mods are Purchased Speed, it's really just a question of how much ROI you get for your money. Nothing beats tires. You have a really nice track car, now put it on some properly fast tires if ultimate lap times is your goal.

And if like others of us you are trying to keep it street legal, then your next mod should be a tire trailer imo.

Again, gorgeous build and I enjoy following your adventures, nice work!
 
174
298
Utah
Totally agree. Weight beats all. @stevbd is spot on about the tires. I have taken my 2014 down to 3400 with driver (TT2). In March I was running the Toyo RR and put in a 2:09.144 on the UMC Outer (Horsepower layout, 3.2 miles). In May I ran the Hoosier R7 on the same track, warmer temps and put in a 2.06.009 and improvement of over 3 seconds. I was blown away.

I thought it would take me some time to make up the time on the Hoosiers, but I was wrong. At your skill level, you will see instant results with a change to the R7.

I am running full Cortex everything including front SLA (except the cambered axle) with the 315 R7 on an Apex 11".

Nice build by the way. I went from a 2006 S197 to my current 2014 S197 so I know the horsepower draw. I am so glad I solved that problem with the 2014 car.
 
51
20
Exp. Type
HPDE
Exp. Level
5-10 Years
New England
Looking back on past projects, many of them made it into the “one mod too many” category. Of course this is with the benefit of looking back with hindsight.

The point being is the answer may be to do nothing. It sounds like your current project has fulfilled its original goals. If you are truly down to chasing lap times then it maybe time to consider another platform. Or maybe a more updated mustang. S550 or at least a coyote car.

Also if you are not on a race slick or r-comp that will be he closest thing to a cheat code with your current setup.
 
6,288
8,019
Looking back on past projects, many of them made it into the “one mod too many” category. Of course this is with the benefit of looking back with hindsight.

The point being is the answer may be to do nothing. It sounds like your current project has fulfilled its original goals. If you are truly down to chasing lap times then it maybe time to consider another platform. Or maybe a more updated mustang. S550 or at least a coyote car.

Also if you are not on a race slick or r-comp that will be he closest thing to a cheat code with your current setup.
Easy button on lap times is a set of A7s. I've posted the T2 runoff race from the runoffs. The blue car is of course lightened, but a cage puts a lot of that back in, so I'm saying 3500 pound..ish. and last I checked they still had to run 275 or 295 rubber, not a big tire, but you can plainly see what a slick tire will do in the video.
 
184
281
Exp. Type
Time Attack
Exp. Level
10-20 Years
75024
Some thoughts on this.

Weight savings - At your level I don't think it would get you the speed delta you want. I would not gut the doors without a full cage, loss of that side intrusion protection is significant. Maybe make the door glass removable. Lexan f&r will help, but it not a huge weight savings. Lithium batteries will fail, always. You have built a very reliable car over the years, don't miss sessions or events because of a 20lb lighter battery, or be sure to have a spare.

I would add power. Those prices seem high, but I'd look at larger NA or Coyote swap to get to 400+ whp. This gives you easy 10ths down every straight. Boosted carries a lot of durability baggage and weight.

With your aero I don't think the cambered rear would be a big delta, mainly just help wear.
 
296
362
CA
Just read through your full car build. Looked at the photos and came to a conclusion. Who the hell has been telling you your car isn't a track car. Damn. I'm sure it isn't a daily driver.
I'm with @blacksheep-1 on this even before seeing his comment.
weight > every other mod.
As someone who club raced a very under powered 4 cylinder, weight loss was the greatest gain. Unfortunately its also the least glamorous so tends to be the last thing people look at.
For every pound you can dump out of your vehicle, its a pound you don't have to accelerate, brake, stop sliding through a corner. Suddenly your brakes work better, your tyres last longer, less stress on the engine, gearbox, the cooling system, oil temps, diff temps. HP whilst fun kills components. Less component stress equals less costs overall. The exact reason my GT engine is staying stock.

Real world example.
Winton Racetrack here in Australia. 1.86 mile handling circuit.
1200kg 944 Porsche normally aspirated 120Kw @ engine on 225/50 R15 Bridgestone 540S tyres, my best time 1-39-8
1780kg Mustang GT 306Kw on 285/305/30 R20 Cup 2's, my best time 1-36-6 whilst praying it would stay on the black stuff through corners. I couldn't believe the feel of so much weight compared to my previous track car. It honestly scared me the first time tracking the GT.

I'll go one further and say, rotational weight > weight but that's a costly one.

How are you "ruining" your car making it "more fun in every regard". Delete/"unbolt" as much as you can before "cutting" anything out. You can do that latter when you realize you have a track car and its a truck load of fun. My 944 was a tin can, full cage, 2 race seats, harnesses and still had number plates on it. Still the most fun thing on 4 wheels.

In the words of Colin Chapman - Adding power makes you faster on the straights. Subtracting weight makes you faster everywhere.
All very good points here. My car currently is not a street car in the typical sense, but it does have functioning AC, functioning windows, current license and registration. But it is zero fun to drive on the street, it's rough, loud and too capable to have any fun on normal roads without tripling the speed limit. I no longer get any rush or satisfaction from speeding on public roads. So the car never leaves my enclosed trailer other than to go on the racetrack.

Maybe I'm missing something but reading through your build thread.... if your primary goal is better lap times and you are ready to spend some dough why are you insisting on using 200tw street tires? You could shave seconds with a set of GY 3Rs, Hoosiers, or whatever. You list weight, power, and cambered rear end... why not tires?

All mods are Purchased Speed, it's really just a question of how much ROI you get for your money. Nothing beats tires. You have a really nice track car, now put it on some properly fast tires if ultimate lap times is your goal.

And if like others of us you are trying to keep it street legal, then your next mod should be a tire trailer imo.

Again, gorgeous build and I enjoy following your adventures, nice work!
I had multiple reasons for not going to a faster tire, most of which revolve around the following:

1.) Running costs
2.) Class restrictions

But, my ultimate goal is to compete at a national level with this specific Bullitt mustang, and when I reach that point I will be running on a hoosier or something even faster. My overall mentality is to make the car as fast as possible on 200tw tires, and then once I feel the car is ready, and my skills are ready, to bolt on slicks and compete in NASA. I did not want to waste $$$ doing chassis R&D with tires which are $2k and only last 3 track days.


After reading through all of your posts, and doing a couple weeks of soul searching on my own, I have decided that I am willing to take things to the next step of "full racecar" for the sake of competing at a national level. I have quite a to-do list, but I do think that with weight reduction, slicks, better aero and perhaps that cambered rear end, I can get the gap awfully close to the hot shots in nasa. All while using a stock, unopened "truck engine" of a 4.6L 3v. This should be fun. You all have been a massive help.

Still looking for anyone who has before/after lap time data with the cambered rear end.....
 
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6,288
8,019
All very good points here. My car currently is not a street car in the typical sense, but it does have functioning AC, functioning windows, current license and registration. But it is zero fun to drive on the street, it's rough, loud and too capable to have any fun on normal roads without tripling the speed limit. I no longer get any rush or satisfaction from speeding on public roads. So the car never leaves my enclosed trailer other than to go on the racetrack.


I had multiple reasons for not going to a faster tire, most of which revolve around the following:

1.) Running costs
2.) Class restrictions

But, my ultimate goal is to compete at a national level with this specific Bullitt mustang, and when I reach that point I will be running on a hoosier or something even faster. My overall mentality is to make the car as fast as possible on 200tw tires, and then once I feel the car is ready, and my skills are ready, to bolt on slicks and compete in NASA. I did not want to waste $$$ doing chassis R&D with tires which are $2k and only last 3 track days.


After reading through all of your posts, and doing a couple weeks of soul searching on my own, I have decided that I am willing to take things to the next step of "full racecar" for the sake of competing at a national level. I have quite a to-do list, but I do think that with weight reduction, slicks, better aero and perhaps that cambered rear end, I can get the gap awfully close to the hot shots in nasa TT3. All while using a stock, unopened "truck engine" of a 4.6L 3v. This should be fun. You all have been a massive help.

Still looking for anyone who has before/after lap time data with the cambered rear end.....
Look up " blacksheep hates watts linkages" and read the entire article
 
51
20
Exp. Type
HPDE
Exp. Level
5-10 Years
New England
But it is zero fun to drive on the street, it's rough, loud and too capable to have any fun on normal roads without tripling the speed limit. I no longer get any rush or satisfaction from speeding on public roads.
This is it in a nutshell. To move forward this car will forever be a dedicated track car. It some ways this is more liberating. I have tried many times to build the perfect hybrid (street/track) vehicle, and it never works out, the balance always tips in one direction. Of course I will keep trying...

For you, I would prescribe an aggressive weight reduction strategy. Its like adding more tire, brakes and power all at once. I like the idea of maxing out your setup with the 200TW tires. Its like running with a parachute. I look forward to seeing how this turns out for you. Enjoy the ride!
 

cortexracing

Supporting Vendor
41
132
Weighing in here and trying to be objective as I'm naturally going to be a bit biased. First, the feedback above is top notch. This community is as you probably know, a phenomenal place to get a variety of input. Having seen hundreds of these builds, and having sold hundreds of cambered axles, I have a two different suggestions for you.

Is it a street car that races or a race car that is driven on the street?

If it's a street car that races; you can selectively trim weight (rear seat deletes, potentially removing the sound system but leaving door panels) and for gods sake leave the A/C (my streetable track car becomes unbearable in the summer and I'm now trying to add driver cooling back into the car.) Add grippier tires as others have mentioned, this will be your single largest time gain for the money spent. The cambered rear and a coyote swap are both likely similarly expensive endeavors. Our data points indicate that most customers will see roughly 1.5-2 seconds in improvement around a ~1:30 per lap track. I do not have similar data points for a 3V to coyote swap change but am doing that on a personal car and am eager to see the time difference. I suspect it will be similar or slightly more than the cambered rear. With that said, the coyote is going to be much more noticeable on the street so it would benefit you to do this first and will likely give you the greater satisfaction. You can then follow that up with a cambered rear to get as much time as possible out of the car when your budget allows.

If its a race car that streets the formula is fairly simple: gut the car. With that said, I'd really encourage you to evaluate the dollars spent in weight savings. The factory aluminum hood and fenders are quite light and going to a carbon fiber panel is probably not worth the dollars spent. Lexan front and rear windows can help but become miserable to drive on the street as they get fine scratches (forget about using your windshield wipers.) By fully gutting the doors, A/C system including the compressor & under dash box, and remaining interior you can very realistically shave 160 pounds out of the car and spend next to nothing. There is 90lbs that can easily and cheaply be removed from the doors alone. The whole A/C system is another ~25 lbs. Carpet, trim, and headliner is ~15. The factory stereo and all speakers are another 10lbs. From there you will still want to add the grippier tires as the next step. The order for the cambered rear and coyote is again largely a matter of personal preference. If the 3V works and you dont feel it's holding you back, put the cambered rear in and run the 3V until it blows up. This gives you plenty of time to prep your coyote swap and divide the budget up over time.

One thing not mentioned here is safety. Please continue to invest in quality safety gear (fire system, driver clothing, belts, etc) throughout your build. You can always build another car or delay mod purchases but you can't get your life back.

Feel free to give us a ring as you keep working through your project. We're happy to help however we can.

Hope this helps.
 

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