60-130 MPH: New performance measurement!
12-05-2006, 07:39 PM
#916
Instructor
Join Date: Nov 2004
Posts: 162
Likes: 0
Received 0 Likes
on
0 Posts
Originally Posted by JBL930
My car isn't stock, no aircon, lighter headers, no rear wiper, and even with no fuel in it would weigh at least 1320kg. These are facts, period! The factory figures are clearly wrong.
12-06-2006, 02:24 AM
#917
Not Forgotten
Join Date: Apr 2006
Location: South East, UK
Posts: 1,215
Likes: 0
Received 0 Likes
on
0 Posts
Originally Posted by AZ930
Why in the world is it so heavy?? I weighed my car on our corner balance scales at the shop I work at. My car is stripped down and even with 1/2 tank, roll bar, heavy seats it was 1170kg.
I have no idea? The scales my car was weighed on are the pit lane scales at Brands Hatch, i was there for a track day the other weekend. Apart from the couple of bits i've listed my car is stock weight, electric heated seats, full leather, sunroof etc, also everything under the hood i.e spare wheeel, jack, tool kit. I can only assume that the stock weight figures are for a car with no fuel and no oil?
12-06-2006, 03:59 AM
#918
Addict
Lifetime Rennlist
Member
Lifetime Rennlist
Member
Originally Posted by JBL930
My car isn't stock, no aircon, lighter headers, no rear wiper, and even with no fuel in it would weigh at least 1320kg. These are facts, period! The factory figures are clearly wrong.
I have not debated the weight of your car anywhere? If you say it weighs this much, then it is true!
I was talking about factory specs in general and my estimate of 400HP for a stock factory weighing car as published by them.
12-06-2006, 04:49 AM
#919
Intermediate
Join Date: Apr 2006
Location: Cambridge, UK
Posts: 41
Likes: 0
Received 0 Likes
on
0 Posts
My experience of factory weights is that they are underquoted but I suppose they quote for a basic model and not one that has any extra features. There is a big difference between dry and wet weights as well. AZ930's car is very light for a road going turbo and I am sure it must go well.
It is very difficult and very expensive to reduce the weight of a turbo below 1100kgs and still have all the equipment needed to go racing, yet alone drive on the road.
As for Colins question regarding power, I have no idea! I thought I might have a go at calculating an estimate but there is so much I would have to guess (CdA, gearbox losses etc) I may as well guess the result without any calcs! How about 450 based on nothing but feel? Knowing the Ninemeister there is probably something demon with the car and I am a mile off! Oh well, keep on guessing!!
Cheers, Richard.
It is very difficult and very expensive to reduce the weight of a turbo below 1100kgs and still have all the equipment needed to go racing, yet alone drive on the road.
As for Colins question regarding power, I have no idea! I thought I might have a go at calculating an estimate but there is so much I would have to guess (CdA, gearbox losses etc) I may as well guess the result without any calcs! How about 450 based on nothing but feel? Knowing the Ninemeister there is probably something demon with the car and I am a mile off! Oh well, keep on guessing!!
Cheers, Richard.
12-06-2006, 05:52 AM
#920
Addict
Rennlist
Site Sponsor
Rennlist
Site Sponsor
It's no mystery car Richard, just a well tuned 930 on K-Jet. I'm just using it as an example as to why on the road acceleration data is meaningless unless we can build mathematics into the the results which correct for different vehicle mass, transmission loss and aero properties. In my opinion the best that a 60-130 measure can hope to attain if you know the mass and bodystyle of the car is a guide to the available power (at the tyres) on the day it was tested. Unfortunately nobody seems able to use the current data to do anything other than prove who's car is faster than another, which is a little shy of being able to predict the true engine hp.
All I am saying is that I do not like snake oil, but if we can get our brains around this there is the possibility that we can produce an accurate mathematical model that can predict the engine hp of any Porsche from the 60-130 acceleration run time. If I remember rightly, the equations governing vehicle motion give the following:
Power to accelerate mass (overcome inertia) Pa = V x M x A
Rolling resistance power Rr = M x g x (R0 + R1V + R2V^2 + R3V^3)V
Aerodynamic power = Af x Cd x V^3 x D/2
where
V = velocity
M = total mass
A = acceleration
g = 9.81 (acceleration due to gravty)
R0,1,2 = rolling resistance coefficients
Af = frontal area
Cd = coefficient of drag
D = air density
If someone knows what proportion of the power is used to overcome inertia, drag and rolling resistance at any given speed it should be possible to predict the effect that a 10% increase in mass would have on the cars acceleration. Similarly for different body shapes, eg 930/965/993tt. Therefore predicting tyre hp should be relatively accurate, as should predicting the improvement in 60-130 time from a reduction in mass. This way we can all make an educated decision whether to re-tune the engine or simply leave the wife at home because she has a "negative effect on the inertial resistance"...
All I am saying is that I do not like snake oil, but if we can get our brains around this there is the possibility that we can produce an accurate mathematical model that can predict the engine hp of any Porsche from the 60-130 acceleration run time. If I remember rightly, the equations governing vehicle motion give the following:
Power to accelerate mass (overcome inertia) Pa = V x M x A
Rolling resistance power Rr = M x g x (R0 + R1V + R2V^2 + R3V^3)V
Aerodynamic power = Af x Cd x V^3 x D/2
where
V = velocity
M = total mass
A = acceleration
g = 9.81 (acceleration due to gravty)
R0,1,2 = rolling resistance coefficients
Af = frontal area
Cd = coefficient of drag
D = air density
If someone knows what proportion of the power is used to overcome inertia, drag and rolling resistance at any given speed it should be possible to predict the effect that a 10% increase in mass would have on the cars acceleration. Similarly for different body shapes, eg 930/965/993tt. Therefore predicting tyre hp should be relatively accurate, as should predicting the improvement in 60-130 time from a reduction in mass. This way we can all make an educated decision whether to re-tune the engine or simply leave the wife at home because she has a "negative effect on the inertial resistance"...
12-06-2006, 06:09 AM
#921
Racer
Join Date: Nov 2005
Location: London
Posts: 310
Likes: 0
Received 0 Likes
on
0 Posts
I agree completely with 965racer. Here are the basic calculations:
Starting with a super lightweight out-and-out racer, Geoffrey's car (na widebody 964) including all fluids: 1,009 kgs
Add weight of turbo engine and plumbing: 93 lbs (964 RS engine wght: 498 lbs, 993 tt wght: 591 lbs)
Add 4wd front diff: 120 lbs
Therefore, total weight for an out-and-out 993 tt racer would be around 1,100 kgs, that certainly would not be street legal or street driveable. Full composite body panels, plastic windows, no bumpers, no cats, no heat, no air, no instruments, no airbag etc etc.
The lightest street 993 tt (with full fluids) would probably be around 1,230 to 1,250 kgs subject 2wd.
Starting with a super lightweight out-and-out racer, Geoffrey's car (na widebody 964) including all fluids: 1,009 kgs
Add weight of turbo engine and plumbing: 93 lbs (964 RS engine wght: 498 lbs, 993 tt wght: 591 lbs)
Add 4wd front diff: 120 lbs
Therefore, total weight for an out-and-out 993 tt racer would be around 1,100 kgs, that certainly would not be street legal or street driveable. Full composite body panels, plastic windows, no bumpers, no cats, no heat, no air, no instruments, no airbag etc etc.
The lightest street 993 tt (with full fluids) would probably be around 1,230 to 1,250 kgs subject 2wd.
12-06-2006, 06:48 AM
#922
Addict
Rennlist Member
RIP
Rennlist Member
RIP
Join Date: Feb 2002
Location: London
Posts: 802
Likes: 0
Received 0 Likes
on
0 Posts
You could use a NN program (approx. to multidimensional regression) that should, with reasonable sample data, be able to accurately predict the HP of a number of modified porsches. Accurate sample data would have to include various examples of different models that we know the true HP. However, from there we could 'interpolate' many variations. One of the nice things of this approach is that you could feed in the total data set from an AX22...
12-06-2006, 09:11 AM
#923
Addict
Lifetime Rennlist
Member
Lifetime Rennlist
Member
Originally Posted by NineMeister
It's no mystery car Richard, just a well tuned 930 on K-Jet. I'm just using it as an example as to why on the road acceleration data is meaningless unless we can build mathematics into the the results which correct for different vehicle mass, transmission loss and aero properties. In my opinion the best that a 60-130 measure can hope to attain if you know the mass and bodystyle of the car is a guide to the available power (at the tyres) on the day it was tested. Unfortunately nobody seems able to use the current data to do anything other than prove who's car is faster than another, which is a little shy of being able to predict the true engine hp.
All I am saying is that I do not like snake oil, but if we can get our brains around this there is the possibility that we can produce an accurate mathematical model that can predict the engine hp of any Porsche from the 60-130 acceleration run time. If I remember rightly, the equations governing vehicle motion give the following:
Power to accelerate mass (overcome inertia) Pa = V x M x A
Rolling resistance power Rr = M x g x (R0 + R1V + R2V^2 + R3V^3)V
Aerodynamic power = Af x Cd x V^3 x D/2
where
V = velocity
M = total mass
A = acceleration
g = 9.81 (acceleration due to gravty)
R0,1,2 = rolling resistance coefficients
Af = frontal area
Cd = coefficient of drag
D = air density
If someone knows what proportion of the power is used to overcome inertia, drag and rolling resistance at any given speed it should be possible to predict the effect that a 10% increase in mass would have on the cars acceleration. Similarly for different body shapes, eg 930/965/993tt. Therefore predicting tyre hp should be relatively accurate, as should predicting the improvement in 60-130 time from a reduction in mass. This way we can all make an educated decision whether to re-tune the engine or simply leave the wife at home because she has a "negative effect on the inertial resistance"...
All I am saying is that I do not like snake oil, but if we can get our brains around this there is the possibility that we can produce an accurate mathematical model that can predict the engine hp of any Porsche from the 60-130 acceleration run time. If I remember rightly, the equations governing vehicle motion give the following:
Power to accelerate mass (overcome inertia) Pa = V x M x A
Rolling resistance power Rr = M x g x (R0 + R1V + R2V^2 + R3V^3)V
Aerodynamic power = Af x Cd x V^3 x D/2
where
V = velocity
M = total mass
A = acceleration
g = 9.81 (acceleration due to gravty)
R0,1,2 = rolling resistance coefficients
Af = frontal area
Cd = coefficient of drag
D = air density
If someone knows what proportion of the power is used to overcome inertia, drag and rolling resistance at any given speed it should be possible to predict the effect that a 10% increase in mass would have on the cars acceleration. Similarly for different body shapes, eg 930/965/993tt. Therefore predicting tyre hp should be relatively accurate, as should predicting the improvement in 60-130 time from a reduction in mass. This way we can all make an educated decision whether to re-tune the engine or simply leave the wife at home because she has a "negative effect on the inertial resistance"...
Not everyone is interested in hearing the mumbo jumbo that you, I or some other guys are talking about. In fact, this same thread has died as soon as it moved into "the dark side", I know because of the multiple PMs I have recieved in this respect.
I will not dig deeper into this, or at least not on this thread. I have done all the calculations and simulations that you mention above, I have mentioned it before I believe. I have worked closely with an engineer in Australia to develop a model that would use the data from long Gs from the datalogger and take them all the way back to an engine dyno torque curve. It also uses all the parameters you mentioned above such as rolling resistence, aerodynamics, gearboxes, tire sizes etc.. I can list many formulas here but it would get boring. Also, this is a hobby for me and I only do it for personal learning, so my time is limited for this sort of things.
In the absence of that elaborate work, taking a bench of similar cars (996,993,964 etc) with similar gearing, one can quite accurately make an estimate of where that car stands as far as power is concerned. Not very scientific, but big variances can be spotted. In fact I also have a database showing all these ratios and how they relate to performance on a wide universe of Porsche cars. Some patterns can be spotted.
Problem is whenever a theory is shared, some people look for the flaws, or speculate about hidden agendas and how to destroy its validity rather than having a larger spirit and contribute within the possibilities of an internet forum. For this same reason a lot of data is not shared, or very selectively, in private.
The best example is that now we are saying the AX22 is cr@p because of a few bad runs that can be counted with one hand, and that most likely the users did something wrong, not the tool, but possibly discrediting it (or any other similar tool), is easier than accepting a poor engine investment, in some cases..I still have to have an issue with one run alone and I could bet that I am one of the heaviest users.
A few months back, we were still using stop watches and video and thought we had great tools. This has evolved so extensively, however we are still not satisfied with the progress, and now we are talking about wind direction and the likes, or the inaccuracy of the analysis resulting from the numbers seen..
12-06-2006, 10:06 AM
#924
Racer
Join Date: Nov 2005
Location: London
Posts: 310
Likes: 0
Received 0 Likes
on
0 Posts
Sorry Jean, I respect you greatly as you know, but I think you are being a little un-generous to Colin. Lets return to the question:
Your figures show a "stock" 993 TT, weight 1,505 kgs, 408 hp at a 60-130 time of 12.2 secs (see your earlier post)
Colin asks you for to estimate power for a turbo with 1,450 kgs weight, 60-130 at 10.18, and you reply: 400 hp.
How is that possible?
Similar weight, but 2 full seconds faster and yet it generates less power? This simply doesn't compute. Others have assumed around 450hp, my figures imply 440-480 hp.
You need to recheck your numbers, I think.
Your figures show a "stock" 993 TT, weight 1,505 kgs, 408 hp at a 60-130 time of 12.2 secs (see your earlier post)
Colin asks you for to estimate power for a turbo with 1,450 kgs weight, 60-130 at 10.18, and you reply: 400 hp.
How is that possible?
Similar weight, but 2 full seconds faster and yet it generates less power? This simply doesn't compute. Others have assumed around 450hp, my figures imply 440-480 hp.
You need to recheck your numbers, I think.
12-06-2006, 10:12 AM
#925
Addict
Rennlist Member
Rennlist Member
Originally Posted by AVoyvoda
Sorry Jean, I respect you greatly as you know, but I think you are being a little un-generous to Colin. Lets return to the question:
Your figures show a "stock" 993 TT, weight 1,505 kgs, 408 hp at a 60-130 time of 12.2 secs (see your earlier post)
Colin asks you for to estimate power for a turbo with 1,450 kgs weight, 60-130 at 10.18, and you reply: 400 hp.
How is that possible?
Similar weight, but 2 full seconds faster and yet it generates less power? This simply doesn't compute. Others have assumed around 450hp, my figures imply 440-480 hp.
You need to recheck your numbers, I think.
Your figures show a "stock" 993 TT, weight 1,505 kgs, 408 hp at a 60-130 time of 12.2 secs (see your earlier post)
Colin asks you for to estimate power for a turbo with 1,450 kgs weight, 60-130 at 10.18, and you reply: 400 hp.
How is that possible?
Similar weight, but 2 full seconds faster and yet it generates less power? This simply doesn't compute. Others have assumed around 450hp, my figures imply 440-480 hp.
You need to recheck your numbers, I think.
You have to use a similarly configured car - my example of the 965 Turbo S is closest.
12-06-2006, 10:35 AM
#926
Racer
Join Date: Nov 2005
Location: London
Posts: 310
Likes: 0
Received 0 Likes
on
0 Posts
I completely agree with you, TB993TT, that they are dis-similar cars.
As a rule of thumb however, 1 sec faster speed is equivalent to approx. 45 extra hp (everything else remaining equal) or 140 kgs less weight (again, everything else remaining equal).
I am asking: Are a 135 kgs difference (1,585 vis 1,450 kgs), 4 wd, different gearing and aero, likely to account for the 2 full seconds time improvement, just by themselves, with an engine that's 10 hp down on power? Sounds unlikely.
As a rule of thumb however, 1 sec faster speed is equivalent to approx. 45 extra hp (everything else remaining equal) or 140 kgs less weight (again, everything else remaining equal).
I am asking: Are a 135 kgs difference (1,585 vis 1,450 kgs), 4 wd, different gearing and aero, likely to account for the 2 full seconds time improvement, just by themselves, with an engine that's 10 hp down on power? Sounds unlikely.
12-06-2006, 11:34 AM
#927
Addict
Lifetime Rennlist
Member
Lifetime Rennlist
Member
Originally Posted by AVoyvoda
Sorry Jean, I respect you greatly as you know, but I think you are being a little un-generous to Colin. Lets return to the question:
Your figures show a "stock" 993 TT, weight 1,505 kgs, 408 hp at a 60-130 time of 12.2 secs (see your earlier post)
Colin asks you for to estimate power for a turbo with 1,450 kgs weight, 60-130 at 10.18, and you reply: 400 hp.
How is that possible?
Similar weight, but 2 full seconds faster and yet it generates less power? This simply doesn't compute. Others have assumed around 450hp, my figures imply 440-480 hp.
You need to recheck your numbers, I think.
Your figures show a "stock" 993 TT, weight 1,505 kgs, 408 hp at a 60-130 time of 12.2 secs (see your earlier post)
Colin asks you for to estimate power for a turbo with 1,450 kgs weight, 60-130 at 10.18, and you reply: 400 hp.
How is that possible?
Similar weight, but 2 full seconds faster and yet it generates less power? This simply doesn't compute. Others have assumed around 450hp, my figures imply 440-480 hp.
You need to recheck your numbers, I think.
It is ok to disagree, it is healthy.
However let me get the facts right.
Both you and Colin seem to forget that there is a driver in the other car you are comparing to.
I mentioned (again!) that the 400HP would be my estimate for a 930 with stock factory quoted weight of 1,280Kgs or so. So let us forget about the driver for a second or weighed car since it cannot be verified anyway.
The 993TT has a quoted weight of about 1505Kgs or so. The difference is 225Kgs (about 500lbs) between stock 930 and stock 993TT. They said the weight of that car is more than factory, ok, but that is not what I can compare, I can compare both stock cars without driver, per factory specs, which of course could be wrong, agreed.
Based on stock facotry weight, NO DRIVER:
930: 2800lbs/400BHP = 7.04
993TT: 3,311lbs/408BHP= 8.11
Difference: 8.11/7.04= +15% or so
60-130mph
930: 10.18
993TT: 12.2
Difference: 13%
You can see that the difference between both is not far, right? (15% better ratio vs. 13% better acceleration?)
Over and above, factor the 4WD vs 2WD, and the fact that the 930 runs in lower gears for such a run, hence better acceleration (for this particular run)
Even if you add the weight by 30Kgs or so over stock for the 930 you are still not far off. I got 12.2 seconds 60-130mph with a stock 993TT in 36 degrees C, whereas I doubt nowadays you guys are seeing over 10?
I accept to be wrong with my calculations, which is why I rechecked based on your data, but I am not biased (just a little maybe, but then again who is bound to be more biased vis a vis Colin, you or I ?
).
12-06-2006, 12:06 PM
#928
Addict
Lifetime Rennlist
Member
Lifetime Rennlist
Member
Originally Posted by AVoyvoda
I completely agree with you, TB993TT, that they are dis-similar cars.
As a rule of thumb however, 1 sec faster speed is equivalent to approx. 45 extra hp (everything else remaining equal) or 140 kgs less weight (again, everything else remaining equal).
As a rule of thumb however, 1 sec faster speed is equivalent to approx. 45 extra hp (everything else remaining equal) or 140 kgs less weight (again, everything else remaining equal).
Thanks
Last edited by Jean; 12-06-2006 at 01:14 PM. Reason: Irrelevant info.
