How important is power to weight when it comes to performance? - Mustang Evolution

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Old 09-21-2017, 07:15 PM   #1
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How important is power to weight when it comes to performance?

So this isn't specific to mustangs (although I have a 14 gt) but I was wondering, how important is a cars power to weight ratio when it comes to performance? For example, my mustang is stock so it has like 420 horse or so. This gives it a power to weight of like 8.5. 8.5 pounds per horse that is. So Say you had that and a miata. A miata only weighs like 2300 pounds (I'm being general for the sake of argument by the way, just sayin). So if a miata had about 270 horse that means it would have a power to weight ratio of 8.5 as well. So would the two cars then be the same performance wise even though the mustang would still have a 150 horse advantage?
Maybe I'm completely off on everything, but maybe that at least puts my question across.
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Old 09-21-2017, 09:13 PM   #2
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Well, like — other things affect a car’s ability to like accelerate. Available traction, gear ratios etc. But like everything else being like equal, think of it like this......two cars, same model but one with much more HP...which one is going to be able to get to 60 quicker?
Your example of the Miata with a lot more HP being equal to your Mustang? Depends on the much lighter Miata being able to put that power to the ground (traction) and how low the gear ratios are.
And, don’t disregard torque as that element is more important than HP in many ways — especially where in the rpm scale the torque peak is. Two equal weight cars with the same HP and torque, but one where the torque comes all in at 2,100 rpm (turbo?) and the other where the torque peak is at 5,500 rpm.....one is going to be way quicker.
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Old 09-21-2017, 09:37 PM   #3
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I understand that. My question is more like, if you have two cars that are identical, including the power to weight ratio, which car will be faster? The car with less power but less weight? Or the car with more weigt but more power?
In theory it seems to me that they would be equal.
Essentially, in looking at a cars performance in terms of speed and acceleration, is it better to have a light weight or more power? All else being equal
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Old 09-21-2017, 11:34 PM   #4
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If you have two identical cars with the only difference being weight and power (with power to weight ratio being the same along with power curves), the lighter car will have an advantage in traction, braking, initial acceleration (think like 60'), handling and fuel consumption. On top of that, wear items like tires, brakes and suspension components will last longer on a lighter car, assuming it's built identically with proper spring rates, valving, etc for it's reduced weight.

The heavier, more powerful car will be able to accelerate from something like 70-100 MPH faster than the less powerful car. Also, the heavier, more powerful car will have a higher top speed because the more powerful engine will be able to accelerate for longer as it's engine will be able to overcome the aerodynamic drag whereas the lighter, less powerful cars engine cannot.
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Old 09-22-2017, 12:21 AM   #5
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So, the short answer is, you want both lighter weight and more power. Ideally.
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Old 09-22-2017, 05:22 AM   #6
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Get a baseball, and then find a ball of lead the same exact diameter. Throw both of the balls with all of the force you are able to give.

Which ball will go the farthest distance?
How fast will both travel?
How much harder is it to push the lead ball to the velocity needed to be thrown?

Weight matters.
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Old 09-22-2017, 06:24 AM   #7
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Not only does weight matter, but where that weight is matters.

Take your miata example again, my NB miata had 15" rims that weighed 13 lbs each, whereas my mustang had 19" rims that weighed 25 lbs each. Even if at the end of the day the car's overall weight was the same, the fact that the mustang rim has double the weight and 4" more diameter means it is going to take more effort to accelerate and decelerate that rim. Same with driveshaft, flywheel, brake rotors, etc...

Also, from a road course standpoint you have to consider weight to MM of tread. My miata ran on 225s, my mustang on 295s. Take the miata's estimated ~2400 lbs / 225 and you get 10.66 lbs per mm of tread. The mustang's ~3600 lbs / 295 = 12.2 lbs per mm of tread.

Take the brakes for example. Miata has 11" rotors and the mustang had 13.2 (no Brembos FTL) 211 lbs per inch of brake disc, vs 272 ... Lighter is always better, regardless of power.

Horsepower is a crutch, because it often times automatically makes things heavier. You need bigger, stronger suspension, bigger stronger brakes, bigger stronger frame, bigger stronger mounting points and braces and brackets ... Its a never ending cycle.
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Old 09-22-2017, 06:26 AM   #8
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Quote:
Originally Posted by Voltwings View Post
Not only does weight matter, but where that weight is matters.

Take your miata example again, my NB miata had 15" rims that weighed 13 lbs each, whereas my mustang had 19" rims that weighed 25 lbs each. Even if at the end of the day the car's overall weight was the same, the fact that the mustang rim has double the weight and 4" more diameter means it is going to take more effort to accelerate and decelerate that rim. Same with driveshaft, flywheel, brake rotors, etc...

Also, from a road course standpoint you have to consider weight to MM of tread. My miata ran on 225s, my mustang on 295s. Take the miata's estimated ~2400 lbs / 225 and you get 10.66 lbs per mm of tread. The mustang's ~3600 lbs / 295 = 12.2 lbs per mm of tread.

Take the brakes for example. Miata has 11" rotors and the mustang had 13.2 (no Brembos FTL) 211 lbs per inch of brake disc, vs 272 ... Lighter is always better, regardless of power.

Horsepower is a crutch, because it often times automatically makes things heavier. You need bigger, stronger suspension, bigger stronger brakes, bigger stronger frame, bigger stronger mounting points and braces and brackets ... Its a never ending cycle.
A very accurate answer.
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Old 09-22-2017, 07:02 AM   #9
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Ish416 you pretty well answered my question exactly. I'm sorry if it wasn't very clear. But that's kinda what I was wanting to know. So a lighter car may initially accelerate faster but a more powerful car, given the same parameters, will have the power to keep pushing despite the weight difference.
I do realize that ideally you want both low weight and high power, I just was curious which was more important. Sorta. Which makes sense. A veyron weighs a good thousand pounds more than most of it competitors but still held the title of the fastest car for awhile
okay. Well that really does kinda answer my question. Thanks
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Old 09-22-2017, 07:55 AM   #10
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Now, compare the Veyron to a Hennesy Venom GT. Both cars are quick, but that modified Lotus can walk all over a Veyron.
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Old 09-22-2017, 07:57 AM   #11
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Quote:
Originally Posted by Lgarretto View Post
Ish416 you pretty well answered my question exactly. I'm sorry if it wasn't very clear. But that's kinda what I was wanting to know. So a lighter car may initially accelerate faster but a more powerful car, given the same parameters, will have the power to keep pushing despite the weight difference.
I do realize that ideally you want both low weight and high power, I just was curious which was more important. Sorta. Which makes sense. A veyron weighs a good thousand pounds more than most of it competitors but still held the title of the fastest car for awhile
okay. Well that really does kinda answer my question. Thanks
I disagree with this. Power to weight ratio... by definition if the cars are equal in power to weight then their accelerations will be similar. You can argue that the higher horsepower car will have more available power to over come drag, but at the same time you have to acknowledge that car is also carrying more weight...

We're getting way off topic and it becomes very subjective at this point, but when talking outright top speed you also have to start factoring drag and aero in. A hard top miata is a hell of a lot more slippery than an S197 mustang... But then you come back to gearing; does the car physically have enough gear to go that fast... its a slippery slope.
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Old 09-22-2017, 07:58 AM   #12
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Old 09-22-2017, 09:35 AM   #13
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That is true of the venom and the veyron, however, the venom makes more power than the veyron and is also lighter. 1244 horse vs 1200 horse. And 1200 pounds lighter as well.
A better example may be an agera r. 3000lbs and only 940 horse compared to a venom which is 2700lbs and has 1250 horse. But the agera achieved a higher top speed than the venom.
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Old 09-22-2017, 09:39 AM   #14
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Honestly voltwings is right. When you start talking thousands of horses and minimal weight difference I think it has to be a completely different ballgame. Not to mention obviously gearing and drag coefficients and whatnot.

I am curious as to the whole query because I am considering getting rid of my mustang for something else. I like my mustang but I see 10-20 exactly like it every day. I want something a bit different. It's just a play car anyway. And one of my choices is the brz. Which is why I was curious about how much power to weight ratios come into play. I want to end up with comparable performance.

Either way all of this has been helpful I'd like to say. Thank you
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Old 09-22-2017, 09:39 AM   #15
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Quote:
Originally Posted by Lgarretto View Post
That is true of the venom and the veyron, however, the venom makes more power than the veyron and is also lighter. 1244 horse vs 1200 horse. And 1200 pounds lighter as well.
A better example may be an agera r. 3000lbs and only 940 horse compared to a venom which is 2700lbs and has 1250 horse. But the agera achieved a higher top speed than the venom.
Gearing and aero. Lets bring this back down to more realistic terms.

Take a hellcat for example. 707 hp, 4500 lbs = 6.3 lb/hp.

For a miata to be at 6.3 lbs/hp it would have to make 380 hp ... Imagine almost 400 hp in a miata, i'm pretty sure it will be able to match the hellcat (gearing aside.) Or another way to look at it would be essentially taking a 5.0 and stripping 1000 lbs out of it... a 2600 lbs 5.0 ...

Also, in the drag equation, the velocity factor is squared. Meaning doubling the speed quadruples the drag, so at high speeds aero matters a heck of a lot more than HP.
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Old 09-22-2017, 09:50 AM   #16
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So essentially, if you were to give a lighter car enough power to be equivalent to a heavier car it should be pretty much equal yeah? Mostly anyway? I mean, gearing and aero mean a lot. But I'm talking more generally than that
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Old 09-22-2017, 10:04 AM   #17
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Yes, that's why it's a ratio. Any given weight divided by any given HP, if the ratios are the same - all else equal - acceleration "should be" the same. This is kind of a purely theoretical discussion at this point though.
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Old 09-22-2017, 10:08 AM   #18
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Well it's been pretty interesting and it's given me some good points. So thank you.
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Old 09-22-2017, 06:33 PM   #19
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It's called bop balance of power . All race organization use this so car of different size and structure can race against each other.
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Old 09-23-2017, 11:50 AM   #20
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Old 09-23-2017, 12:33 PM   #21
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it matters almost as much as the drivers skill level.
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Old 09-24-2017, 11:20 PM   #22
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Originally Posted by Lgarretto View Post
Honestly voltwings is right. When you start talking thousands of horses and minimal weight difference I think it has to be a completely different ballgame. Not to mention obviously gearing and drag coefficients and whatnot.

I am curious as to the whole query because I am considering getting rid of my mustang for something else. I like my mustang but I see 10-20 exactly like it every day. I want something a bit different. It's just a play car anyway. And one of my choices is the brz. Which is why I was curious about how much power to weight ratios come into play. I want to end up with comparable performance.

Either way all of this has been helpful I'd like to say. Thank you
Voltwings has some extensive knowledge as well as praticle experience.
As with any theoretical calculations, sometimes what is written on paper doesn't always translate to reality in the real world. I had a 95 Spec Miata that made 120rwh and 2385lbs with me in the car...the fastest lap at Thunderhill was 2:09. A friend had an EV09 with just shy of 300rwh and 3285lbs with driver and his lap was almost exactly the same 2:09. Yes, chassis setup and driving skills come into play and that can make a big difference, just as a lighter car with more HP and a poorly setup chassis can lose to a heavier car with less HP and well setup chassis in drag racing.
Just a thought. If you have a GT Mustang and want something lighter with comparable performance and are talking a BRZ you are going to fall a little short. A Mini JCW is comparable to the BRZ although neither are going to have performance comparable to the GT. One of the reasons I sold my TrakPak was because of my age and the other is that I wanted to take more than two people with my on trips. The car I now have has the same performance as my old Mustang, can take 4 people on short or long trips and carves corners with the best of them...although my Mini Clubman is much more fun to drive...even driving 1275 miles in two days.
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Old 09-25-2017, 04:31 AM   #23
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Just did a test drive of the WRX and BRZ. If they would put the TC engine in the BRZ that would be a contender....nice car but to me it seemed overpriced. The WRX I liked but wasn't as much fun as the older one I've drove, bigger than I thought it was going to be (but with real room in back seats) but my car and 18K I didn't like it that much.
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Old 09-25-2017, 06:31 AM   #24
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Just did a test drive of the WRX and BRZ. If they would put the TC engine in the BRZ that would be a contender....nice car but to me it seemed overpriced. The WRX I liked but wasn't as much fun as the older one I've drove, bigger than I thought it was going to be (but with real room in back seats) but my car and 18K I didn't like it that much.
This, i REALLY wanted to like the BRZ/ FRS twins... It's a phenomenal chassis, but they are just sorely under powered. Everyone i have talked to absolutely loves them however, i imagine there is just something about it, but when you're coming from a high HP car like a mustang it's just going to be really hard to cope.

That being said, i'd look into an ND miata, as it outperforms the brz in almost every single aspect. You want to talk about a car that's over priced though... i firmly believe the miata market is a used car market, because no one in their right mind should be paying 30k for a miata... you can get a heck of a lot of car for that money.
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Old 09-25-2017, 10:27 AM   #25
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I won't fit in a Miata.....I did ask on a Miata forum for someone with racing seats to let me try one one but no takers. Thinking about the BRZ I realize that there is no way to pass anyone...it is fun but if you got behind someone on a 2 lane blacktop you would be stuck unless there is a long passing zone.

Setting up appointment to drive GTI and I will also look at new GT. The GT I am sure I'll like but idk if I'll like it enough to be my car AND 18K which seems to be a good deal.

side note: at the WRX dealer they asked about my V6 when I was trying to get a price quote (the 3 sites I looked at all said 12K) and they asked me "is it a Shelby or Boss 302?" I considered saying yes.
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Old 09-25-2017, 11:00 AM   #26
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I won't fit in a Miata.....I did ask on a Miata forum for someone with racing seats to let me try one one but no takers. Thinking about the BRZ I realize that there is no way to pass anyone...it is fun but if you got behind someone on a 2 lane blacktop you would be stuck unless there is a long passing zone.

Setting up appointment to drive GTI and I will also look at new GT. The GT I am sure I'll like but idk if I'll like it enough to be my car AND 18K which seems to be a good deal.

side note: at the WRX dealer they asked about my V6 when I was trying to get a price quote (the 3 sites I looked at all said 12K) and they asked me "is it a Shelby or Boss 302?" I considered saying yes.
I'm 6'0 / 175 lbs and for me to fit in my NB miata with a helmet i would have had to bolt my seat to the floor and clearance the trans tunnel a bit. It is a bit of a chore to get a racing seat in a miata...

My buddy has an MK7 GTI, and while i would never spend my own money on one, it is a very nice, and very capable car, i dont think you'd be unhappy.

That WRX is something else though. We have a friend who has one, and i've been in some cars that can handle pretty damn good, but that AWD system is just ridiculous.
Personally i'd never own another FWD "sports car," as im just tired of not having traction and having too much understeer, but really i dont think you'd be unhappy with any of those options.
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Old 09-25-2017, 09:40 PM   #27
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When I had my SM I used a Kirkey racing seat that fit me like a glove. I think it had a 15% layback although I'm not positive. Like Voltwings I was 6' although my frame was little heavier at 225 and getting in and out of the SM was not pretty as the cage was a Spec SCCA with twin door bars. The seat was bolted directly to the floor and it had hardly any padding with the exception of very thin piece of foam under my butt...so after each race getting out of the car quickly was mandatory.
The first time I got into the SM without my helmet and suit was the first time I felt clostrophobic in my life although I learned to become used to it. Without having a removable steering wheel I could have never gotten in the SM. At the end of 2 days of racing the left side of my body was a little black and blue as the cage made contact with my left side on hard right hand turns. I'm not trying to be negative because those 6 years were some of the best racing of my life and much more challenging that going 9.80 in the 1/4 mile...IMHO
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Old 10-04-2017, 06:57 PM   #28
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I transplanted a 2005 Honda S2000 engine and gearbox into a '91 Morgan 4/4. When it got back on the road it had a power to weight ratio of about 8.5 pounds per horsepower. It was an animal, but could it run with a Mustang GT with the same ratio? Probably not. Someone mentioned torque earlier. For acceleration that is a very important factor.
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