weight versus power

[nicolas]

i was thinking what power was needed to propel a heavy streetcar (or in my case a fastback) as quick off the line as a light bug. i think torque is very important in this equation, but i was thinking there has to be a relation between the two... so HP could be impressive, but would not get my car off the line fast enough, so a torquey engine would be better i guess

but to what extend? what is the ratio between hp and torque considering the weight off the car?

(just thinking out loud after seeing the Bentley report in topgear.)

[tikimadness]

I think there is a 3rd important item the gearbox.
I see a lot of cars with less horsepower then me who are quicker because of the better ratios in their gearboxes.

What is the weight difference? 150 kg?

Michael

[nicolas]

the fastback brochure says the car weighs aroun 1000kg

[Sarge]

I feel that there is a problem with "Look" versus function.  The "Look" dictates big tires on the rear of our cars.  Not all of us are going to benefit from big diameter tires out back (especially those with smaller displacement engines).  After driving around with big tires, try bolting on some 23"-24" tall tires (as opposed to 25"-26") and feel the difference.  Just the change from 195/65X15 to 205/65X15 is noticeable.  The Cal Look Fashion Police won't approve but who cares.... you'll be kicking some ass at the track for a change.  As for light versus heavy, light ALWAYS wins.  My $.02.

[Diederick/DVK]

nicolas already runs 185/70 tyres...

[Jon]

HP is the most important, because it cant be changed with the gearbox... torque however CAN be changed with the gearbox.

Just something I read last week...

[j-f]

That's why I keep my 165/15 on my bug   I prefer train myself to launch the car properly.

Take a look how race cars were build in the 70's and 80's. As light as possible. Body acid treated, cut heater channel and the rest is so simple.  

[Jim Ratto]

I feel that there is a problem with "Look" versus function.  The "Look" dictates big tires on the rear of our cars.  Not all of us are going to benefit from big diameter tires out back (especially those with smaller displacement engines).  After driving around with big tires, try bolting on some 23"-24" tall tires (as opposed to 25"-26") and feel the difference.  Just the change from 195/65X15 to 205/65X15 is noticeable.  The Cal Look Fashion Police won't approve but who cares.... you'll be kicking some ass at the track for a change.  As for light versus heavy, light ALWAYS wins.  My $.02.

So true.

I remember back before the trend of high aspect tires came around, I ran 60-series 195 Yokohamas, and my car accelerated REAL well, even with smaller motor (1641, 2054). And before that I ran 195/50 BF Goodrich TA's in the late 1980's, yes on the rear. This was with my supertuned 1641 and it would literally pin you in the seat, and would nudge 6000 in 4th, willingly. Wouldn't have been able to do that with big tall 70 series.
Reason why slicks and tall gears don't work.

Weight issue... I agree again. The focus on hp is fine, but then to hang a bunch of stuff on the car that isn't necessary.... not such a good thing. A lot of top notch "world beater" cal look cars are too focused on gadgets and looks, and not getting the job done.
If it doesn't make the car run better, you don't need it.

I think a Type 3 with 150-160hp should open your eyes plenty wide.

[Mike Lawless]

I feel that there is a problem with "Look" versus function.  The "Look" dictates big tires on the rear of our cars.  Not all of us are going to benefit from big diameter tires out back (especially those with smaller displacement engines).  After driving around with big tires, try bolting on some 23"-24" tall tires (as opposed to 25"-26") and feel the difference.  Just the change from 195/65X15 to 205/65X15 is noticeable.  The Cal Look Fashion Police won't approve but who cares.... you'll be kicking some ass at the track for a change.  As for light versus heavy, light ALWAYS wins.  My $.02.

Right on the money Sarge.

I remember recommending some 22" tall slicks to someone who wanted both worlds. Tall gears for the street, and good track performance.

It wasn't even to be considered because "It would look funny!"

Just for info's sake, our 1900 lb Ghia is at 7.3 lbs per horsepower. Equals 11.40s

But anything under 10 or 12 pounds per hp on the street would be a really fun ride!

[dirk zeyen]

my opinion sarge!!!

i have not that big engine:
78X90.5
sock valve heads poted and polished
120 cam
9.1/1 compression
45 dells

stock ratio gear box 0.93 4th and 4.375r/p

with 195/65-15 fun on the street
with 195/50-15 fun on the track (long time ago)- sorry cal-look police

tire size ( or gearbox) and weight are so important

dirk zeyen

[lawrence]

I dont have a ton of experience but it would be beneficial for a heavy car to have the peak torque at a low rpm and peak horsepower at a higher rpm. Stock gears and R/P would be best because there is more torque to spin those shorter gears.

I guess it all boils down to whether the car is for street or race. Any lightening of the car would help acceleration.

[Sam K]

I've heard that every 100 lbs is worth a tenth of a second in drag race application. Even more if it's unsprung weight. A ligher car is lso easier on drivetrain parts as well.

[Bruce]

I've heard that every 100 lbs is worth a tenth of a second in drag race application.

There is no such rule of thumb.  If you took 100 lbs out of an Impala, you probably couldn't measure the difference.  But if you were able to take 100 lbs out of the SSB, it would have a HUGE effect, much more than only a tenth.  A faster lighter car will react much more than a heavier slower car.

The best way to look at it is like Mike said above.  His car is 7.3lbs/hp.  That means that for every 7.3 lbs he takes out of it, it is equal to adding 1hp.  100lbs for Mike is like adding almost 14hp.

[Rennsurfer]

After watching my race fanatic fellow P.C.A. friends remove everything that wasn't useful in their 911 cars, I'm a strong believer that if you want to fast, you do just that. Strip the car. The more stuff that you can rid of, the faster you'll go. Plain and simple economics and sound logic. Looking at my
'67, it's painfully obvious and rather clear that I'm not interested in going fast.

 

[nicolas]

hmm weight is a big issue, but i think i am not talking about thenths but more seconds... 

i talked to the guy who build the engine and he had similar engines (same concept ranging from 1776's to 1914's) all same heads 40IDF's and the same webcam)

they ran times between high 14's and mid to high 15's. i on the other hand have had a best off 16.79. so we are talking a full two seconds that i am slower; and i refuse to take blame myself for that 

but thanks allready for helping out as there is indeed much to be gained with weighlosing and lowprofile tyres.

[BeetleBug]

hmm weight is a big issue, but i think i am not talking about thenths but more seconds... 

they ran times between high 14's and mid to high 15's. i on the other hand have had a best off 16.79. so we are talking a full two seconds that i am slower; and i refuse to take blame myself for that 

Well... if you stop during your run to connect your throttle cable you will be loosing some valuable seconds.   

[nicolas]

hmm weight is a big issue, but i think i am not talking about thenths but more seconds... 

they ran times between high 14's and mid to high 15's. i on the other hand have had a best off 16.79. so we are talking a full two seconds that i am slower; and i refuse to take blame myself for that 

Well... if you stop during your run to connect your throttle cable you will be loosing some valuable seconds.   

 

thanks for reminding me that!

i have been working on that and bought some runningshoes to get out and in the car quicker.

[Hotrodvw]

I have also heard that 1oz of rotating mass, is equal to 16oz. of non-rotating mass.  Not sure how true that is though.

[j-f]

Well... if you stop during your run to connect your throttle cable you will be loosing some valuable seconds.   

  Ouch, that's a good one.

There is maybe a difference of driving . You race your car in the way to go back home safely. If you look how some guys cross their gears always full throttle, you can go faster, but maybe can not go home. 

[nicolas]

Well... if you stop during your run to connect your throttle cable you will be loosing some valuable seconds.   

  Ouch, that's a good one.

There is maybe a difference of driving . You race your car in the way to go back home safely. If you look how some guys cross their gears always full throttle, you can go faster, but maybe can not go home. 

actually i did that at SCC...  i didn't get off the trottle and shifted. that was after Roland told me he was going to do the same to get more out off it, but he has MSD and it cuts out and i don't... so me being a barbarian is allready good enough, i do need some practice and get better, but there are 2 seconds to win here, or at least 1 second.

[j-f]

You can simply add a rev limiting rotor to help prevent over revving   

[Bruce]

I have also heard that 1oz of rotating mass, is equal to 16oz. of non-rotating mass. 

The distance from the axis of rotation is very significant, not just the mass.  1 oz at the axle shaft means almost nothing compared to 1 oz at the tire tread, when you are talking about rotational inertia.

[Hotrodvw]

I used this forumla on smaller 1/10th scale hobby stuff....in a 1:1 situation, I'm not 100% sure it's going to apply.

[Lee.C]

hmm weight is a big issue, but i think i am not talking about thenths but more seconds... 

they ran times between high 14's and mid to high 15's. i on the other hand have had a best off 16.79. so we are talking a full two seconds that i am slower; and i refuse to take blame myself for that 

Well... if you stop during your run to connect your throttle cable you will be loosing some valuable seconds.   

Or refit the airfilters  Looks like I am already beating you then dude as I have had a 16.02 at Santa pod 

I can't wait for next season - should be fun 

[holmsen]

Ran a 15.94 this year with a t4 engine,2,6L 188hp. in a 75 crew cab,,will upgrade the engine to a 3L next year and use it in a bus,also a late bay, hoping to get close to 240hp in it. any suggestion on what times to expect ?
Jan.

[BeetleBug]

Ran a 15.94 this year with a t4 engine,2,6L 188hp. in a 75 crew cab,,will upgrade the engine to a 3L next year and use it in a bus,also a late bay, hoping to get close to 240hp in it. any suggestion on what times to expect ?
Jan.

Welcome to The Lounge Holmsen.

First off.. why settle for only 240hp in a 3 liter engine?

Then it will help to know your vehicle total weight incl. you. Let say you manage 240hp to the wheels and your bus weigh in at around 1200kg. My calculation say you will manage 13.21 and 162 km/h. If you drop your weight to 1000kg it says 12.54 and 168 km/h. Just to play with the numbers and still keep the weight of around 1000 kg but tune your engine to 275hp you you will manage 11.99 and 176 km/h.... Now we`re talking 

Please also consider that your car bus has the same aerodynamics as a parachute... that does not help your ET. 

[louisb]

One area most of us can lose some weight is in the driver's seat. That is what Judy Kawell recommended to me one time anyway. 

--louis

[Bewitched666]

Its a combination between the engine hp and the gearbox

[BeetleBug]

Its a combination between the engine hp and the gearbox

Indeed, you can`t have one without the other.

 

[louisb]

Its a combination between the engine hp and the gearbox

Indeed, you can`t have one without the other.

 

Actually, the trans is not really required, but you wouldn't get far without an engine. 

--louis