Weight vs. Horsepower ratio????

[03CobraVertGrey]

So, how much horsepower/torque does it take to overcome a 115 lbs. curb weight difference? I have an 03 Cobra Vert and a friend an 03 Cobra Coupe. When I was stock and had just an FIPK and he had full exhaust with hi-flow cats, he pulled on me pretty good. Now I have a 2.93 with a tune and a magnaflow catback and my friend is the same as above. I pull on him now but not significantly. I maybe weigh 15 lbs more than he does so the overall difference is only 130 total pounds including the car weight. I would estimate my friend is putting down about 390 rwhp where I should be around 440 rwhp easy. So, if I have 50 more hp & probably 50 more torque, then why am I not pulling hard on him? Does 130 lbs make that much difference?

thanks guys! Definitely not complaining . . . Terminators are amazing!

 

[TrickStang37]

if you got a tune, how do you not know how much power your making?

 

[C55AMG]

u should kill him

 

[03CobraVertGrey]

if you got a tune, how do you not know how much power your making?

Mail order tune to my mods.

 

[IronTerp]

VERY loose estimate is: 100 lbs = 10 RWHP = .10 in 1/4 mile = 1 MPH in 1/4 mile..........

 

[Steeda30]

Just figure it like this

You - 3780 lbs / 440 RWHP = 8.59

Him - 3665 / 390 RWHP = 9.39


I'd say you'll pull him by about 2 cars in a race from say 45-130.

 

[03CobraVertGrey]

Just figure it like this

You - 3780 lbs / 440 RWHP = 8.59

Him - 3665 / 390 RWHP = 9.39


I'd say you'll pull him by about 2 cars in a race from say 45-130.

Ok, I understand the math but what is the significance of the answer? Is there a chart that outlines the horsepower weight ratio with say 1/4 times?

I just don't understand how you got from the ratio to the "2 car" lead in a 45-130 run.

thanks!

 

[Steeda30]

Heh, it's just a guess.

It's hard to say because, for example, my friends C6 Z and I had a .23 difference in w/p. He'd pull me 1.5 cars consistently from 50-140 and it'd be dead even if he had a 170 lb passenger and I didn't.

I was 3665/516 - 7.10

Him - 3130/455 - 6.87

However, cars with a higher numerical weight to power won't see as big of difference in pull with a given difference in w/p. For example, cars with a 10.0 w/p an a 10.5 won't be nearly as far apart as a 5.0 and 5.5. Can't think of a good way to effectively explain the math behind it.

.8 is a pretty big difference, but it won't make as much of a difference as a .8 difference in say me and the Vette. A .8 would make a ~4.5 car pull in the same length race. .26 = 1.5 car difference in this case so .26 x 3.1 = .8 difference and 1.5 cars x 3.1 = 4.5 car pull.

It's kind of like differences in weight affect the acceleration of lighter cars much more than heavier cars, because a given change in weight makes a greater percentage of difference in the overall weight - or something,

 

[TrickStang37]

Mail order tune to my mods.

so you havent checked to make sure the mail order tune is really working correctly for you then?

 

[TrickStang37]

So, how much horsepower/torque does it take to overcome a 115 lbs. curb weight difference? I have an 03 Cobra Vert and a friend an 03 Cobra Coupe. When I was stock and had just an FIPK and he had full exhaust with hi-flow cats, he pulled on me pretty good. Now I have a 2.93 with a tune and a magnaflow catback and my friend is the same as above. I pull on him now but not significantly. I maybe weigh 15 lbs more than he does so the overall difference is only 130 total pounds including the car weight. I would estimate my friend is putting down about 390 rwhp where I should be around 440 rwhp easy. So, if I have 50 more hp & probably 50 more torque, then why am I not pulling hard on him? Does 130 lbs make that much difference?

thanks guys! Definitely not complaining . . . Terminators are amazing!

your rwhp can be as low as 435 and his can be as high as 410. the difference may be closer to 30 hp, you never know. with your 130 more lbs, your advantage may drop to closer to 20hp on him. its a decent size buffer but it doesnt leave an incredible amount of room for error.

 

[Lethalchem]

Also, your estimate of his 390rwhp is probably a bit low as well. Most Cobras seem to hit the 400rwhp mark with just a CAI and exhaust. So if he has a FULL (which I take to mean headers too) exhaust, then he may only be about 30rwhp off where you are. Subtract the 130lbs difference (which would equal 13hp), you're now down to a lead of only 17rwhp. Just tossing out possibilities.

 

[03CobraVertGrey]

Also, your estimate of his 390rwhp is probably a bit low as well. Most Cobras seem to hit the 400rwhp mark with just a CAI and exhaust. So if he has a FULL (which I take to mean headers too) exhaust, then he may only be about 30rwhp off where you are. Subtract the 130lbs difference (which would equal 13hp), you're now down to a lead of only 17rwhp. Just tossing out possibilities.

You brought up a point I need to clarify. By full exhaust I meant magnaflow hi-flow cat mid pipe and catback (no headers & no CAI). That should only be a 30 hp gain at the most, hence the 390 rwhp from 360 stock at the rear wheels.

 

[03CobraVertGrey]

so you havent checked to make sure the mail order tune is really working correctly for you then?

I actually am working with a tuner and I have datalogged and we are really close to right on with the tune. The last step is to get on a dyno and check the a/f at WOT. I am probably slightly rich but my low maf counts are right on the money.

 

[zinc03svt]

My mail order tune gave me 435/435 with 2.80, cai, catback. After dyno tune we jumped to 460/472 with stock midpipe. Proper tuning makes a big difference. fyi

 

[hawaiiancobra]

i did alot of suspension work and frame work on my vert after my friends coupe smoked me, got a switch chip from kenne bell, on the regular tune i smoke him by .5 seconds in the 1/4, on the shoot-out tune i smoke him big time by 1.2 seconds easy. we basically have the same set-up, though i did slip a 4#crank pulley on. i have 2.90 w/ 4#crank pulley, he has 2.76 blower pulley. that gives him a 2.75 ratio and me a 2.96 ratio, thats about 1.5 lb.s of boost more. the stock suspension set-up and all the twisting and flexing is your worst enemy in running against a coupe. he's using a predator tune

 

[TrickStang37]

also, a dyno graph would help to figure your shift points. that may be something there too. in my old 5.0 i used a gtech to figure out the shift points, and gained 1.5 mph in the 1/4 by changing it by 200rpm. that could be 1 1/2 cars in the 1/4 based on loose generalities. what RPM do you shift at? and him?

 

[03CobraVertGrey]

Thanks guys for all your input . . . all very helpful. I guess I need to get on the dyno and determine where I am at and if any adjustments are needed. Also determining when the best place to shift. Thanks again!

 

[ShelbyGuy]

You have a convertible so a certain amount of your power is lost in your wet noodle of a chassis.