Is there a lap time calculator?
 

What I am looking for is a calculator or some type of Butt dyno calculator that can estimate the decrease in lap time based on HP increase and or weight reduction etc. I thought I ran across one on this forum once but I can't find it.

I know this is not going to be real accurate but it is winter and I just received the dyno numbers on my new motor and I am in the process of a major weight reduction campaign on the car/driver weight (emphasis on the driver) and I want to estimate what my lap times might be assuming all other factors are the same tires, suspension setup, etc.

Any help would be appreciated.

Bosch Lapsim, bottom of the page:

Bosch Motorsport - Software

that's gonna be a really hard calculation...it'd also have to depend on the track and how tight it is.

Lapsim takes that into account- if you follow the link and load it you'll see it has a number of pre-loaded track maps. Unfortunately over the years they have taken some functionality out of the free version, so you can't tune all the variables. It's still very good for relative predictions, however.

Petevb,
I tried running the lapsim and either I didn't download it right or I just can't figure it out. I plan to retry when I have some time to figure it out. Other wise I thought there might be a simple calculator that might estimate your improved lap time based on an increase in HP and the length of the track assuming all other things being the same.
Meaning if my average lap time at Miller motorsports park is a 3:06 when I was running 290 rwhp then with all other factors the same (suspension setup, weight, weather, driver, etc), in theory I should run XXX faster per mile or per 10th of a mile with 390 rwhp.

When you fire up the "start lapsim" launcher do you get to the Lapsim window, or doesn't it launch? If you don't get there you probably need to install the matlab engine. If I remember correctly there are instructions for this in the "read me" someplace... It's worth figuring out as it will answer you question fairly exactly once you get it set up, though it doesn't have Miller as one of the standard tracks...

I don't believe you can generalize whp vs laptime without more data. For example on some cars (ie something heavy car with sticky tires) 390 whp might not be near the traction limit, so the extra 100 hp might be easy to deploy and make a large difference. On a car already close to the traction limit, on the other hand, you'd see very little improvement from the same power.

With those caveats I might guess on your 911 you'd find 3-5 seconds assuming you're not on the traction limit and you can drive it.

hmm trying it now.

Ive seen rule of thumb thrown around that every 100lb reduction in weight is equivalent to 10hp gain.
That being said assuming your cornering speeds cannot increase from hp improvments because youre assuming your cornering at maximum limits already. the only benefits will be decreasing time to run the straights with the increase in accelerative force from the hp increase. of course the accuracy would depend upon how many assumptions you want to make to simplify the calculations. You would need to account for increased stopping distance as well from the higher top speeds attained on the straights with more power, still an involved calculation.
I think your better off just trying it out next season and seeing then. I found i am always disappointed between what i think i should gain from what i do in reality once i run on track....but that is my ego always doing the estimating, and i am an optomist.
I have been told i could loose 20 lbs of dead weight by cutting off my head......more than once.

fredmeister,
I agree there is no easy way to do this. The only real answer and the most fun is to get it on the track.
I think the lapsim by Bosch posted by Petevb would be fairly accurate but I don't have most of the data readily available that it requests to get an answer. If I get some free time I will try to gather all the info and try to get the sim to work.

Hopefully you are just doing this for diet motivation...

What all are you changing?

Shape of horsepower curve, location of peak and size of area under curve
Suspension and/or alignment
Tires
Reduction of vehicle weight (which kind, sprung or unsprung, rotational or not) (where.. front back high low)
Reduction of driver weight
What about those cogs in the tranny

If you provide some of these data, perhaps folks can share experiences that may be at least partially relevant.

Mike,
The initial thought with this thread was to just get a quick and dirty estimate of how much time would be shaved just due to the increased HP all other factors remaining the same. I am aware that the other changes will also have a significant effect on lap times but I was curious if there was any way to estimate the time savings based on a HP increase alone per mile or 1oth of a mile.

That said there will be changes and adjustments to the car; JRZ's revalved, to better match the much higher spring rates, Ride height and roll centers recalculated, softer rear sway bar, Rebuild and regear the transmission, install new lighter weight body work, rear wing, and front splitter to SCCA GT2 rules, and repaint the car. I am also switching to the Michelin sx slicks from the Pirelli slicks. The car should be around 65-75 lbs lighter and I am trying to loose around 80-100 lbs (I am a fat ass, started at 335 lbs now 305 6'3" tall)

Does anyone have experience with the OS Giken Limited Slip? G-box is recommending it due to a higher number of friction plates over the Guard LSD for longer service life and better performance?
I assume Guard gears are still the best way to go?

Hmmm, well I have never used the simulator... hopefully you will get it working and get some idea.

This type of thing can be really tricky. We have two GT2 cars that are within 1-2 seconds on fresh tires. Both have similar 3.8 liter engines. Both transmissions are nearly optimized 915s. One car is let's say 1900 pounds with say a 160 pound driver. The other car weighs at least 40 pounds more (heavy passenger seat, headlights and a few other differences). The driver of #2 weighs probably 230-250 (just a SWAG). Both drivers are excellent. So that 100-150 pound difference is not more than a second or so, everything else being (nearly) equal.

We have a 3.4 liter GT3 car that weighs about 2000 pounds without driver. I speculate that there would be less than 0.5 seconds of additional time with 100 pounds of well-placed ballast.

The 911/3.6 car that won at the 25 hours of Thunderhill a few years ago had drivers weighing let's say 110, 170, 170, and 230 (something like that) and they were all excellent and all lapped on the same second I believe.

Its just hard to know.

Now what you are doing to your car looks to be pretty drastic and hopefully you will enjoy the result.

I hear you about driver weight, but I am not sure how much it can contribute to going faster. I do believe that it can help drivers feel better before, during and after a race weekend, and likely live a longer and healthier life. I have lost two friends to cardiac issues at racetracks through the years and too much weight can contribute to that type of thing. I also know that getting weight in the right ballpark can help stave off things like diabetes, which can be a very untoward disease later in life.

Don't know what to say about the OS Giken. I think that there are plenty of proven-good diffs for G50's and I would go with something from Guard if I had a G50. For my 915, I have a Torsen style unit-- not sure I am giving anything meaningful up compared to a standard lsd the way my car is set up.

I always like Guard gears, unless I can find a good factory gear in the ratio I want.

How about the GTech Pro SS or RR ?

I have used both and they at least give a good comparison ...

I do a lot of work on MINIs the unit puugs into the cig lighter and will do a run with a customer before and after installs

The run for 0 to 60 and HP is actually a different "style" but the comparison can be made

In My MINI race car the GTech said I had 260 HP the Maverick Dyno read it at 262.

the RR is $299 and the SS only $199 .
it takes some set up (weight, pitch, roll, and for the tach some setting prociedures )
Can be moved easily from car to car

I do run it now in the 911 ... used mainly for its shift light function

Brian, The Gtech may be a good way to giove you an idea of what HP you have when the car is running but I was just trying to get an idea of the increased performance potential of my new motor before I have it in the car. I should have the motor back in a few weeks and once I have it in the car I will tune it for Colorado's altitude and at that point have the actual RWHP.

I've used LapSim, and it seems to work pretty well. It would give you an excellent A-B comparison - just pick a track with 'representative' straights. You can just drag your torque/RPM curve around and re-run a lap and see the difference.

The free version does not include tire camber effects, so the front / rear roll stiffness balance is all that matters for their calculations. Point being, you could have some useful fun even without knowing wheel rates & stab bar rates ...

I too have been using Lapsim (the free version), both for my 924 and for the new car coming (a DSR)... I've had pretty good luck working with the 924 data; having baseline data from my AIM system makes a big difference in developing accuracy of the model.

Unfortunately, the DSR is far enough on the extreme side of motorsports to not simulate well with the free version - have to upgrade to be able to turn the knobs far enough for that car. Prime examples are rev range - need a redline at 14000rpm - and weight - won't allow me to go below 500kg.

Sorry, don't have any 911 models.