street use but some track time

vettestr · #1 (**permalink**) 10-06-2007, 10:28 AM

This car is used on the street for the most part but want to do a little autocross and maybe some of the shorter tracks. The street time is not the issue but will adding about 52 pounds of weight to the front end (front bias weight) really make that much difference? I can move other weights around to try and offset the weight gain but I question how big a deal 52 pounds added to the front end will really affect the performance of this car. At a lower drivers skill level to even a skilled driver is a front end weight bias of less than a 2% change really affect the cars performance? I am not a pro or have the advanced skills as a driver to realize how big a deal this is.

What do you Pro's think about this question. I know the cars set up as well as shifting things around can help to absorb this gain but there are no free lunches here. ????

I got into a long bench racing session with a couple other guys over this question and had to listen for the most part but started to take the side that it was just not that big a deal at most peoples skill levels and the limited amount of track time car was being used on.

The entire argument is about how much the added weight (105 pounds gross) a big block engine makes over the lighter small block. The gross weight is only 105 pounds before considerations of where the increase % on the front end and to cars total etc... I left the big / small block engine out of the first part of thread because the argument was not about the virtues of each but about true weight and set up implications. What do you racers think about this from a set up point of view?

vettestr · #2 (**permalink**) 10-06-2007, 11:18 AM

The short question is could you tell the difference? If you climbed into 4 cars, 1 after the other all set up to the same optimized settings for that car at a local track. !st car had an all cast iron engine, 2nd had same goodies but was a lighter full aluminum engine, 3rd was a cast iron BB and Th the lighter full aluminum BB engine. In this case the all alum. versions were 100 pounds lighter than is cast iron brother.

patrickt · #3 (**permalink**) 10-06-2007, 11:25 AM

Quote:

Originally Posted by vettestr

The short question is could you tell the difference?

When you're really familiar with your car, you can tell a difference. I can tell whether my gas tank is low or full simply by driving it hard and paying attention to the feedback it gives me (and that's roughly an 85 pound difference or so).

RACER X #99 · #4 (**permalink**) 10-06-2007, 11:32 AM

Unless you are gung ho and have to be that fastest of the fast a street Cobra will offer you plenty of fun time on any race track. Serious racers are no longer driving Cobras except for the Vintage racing series ad those guys are not turning lap times as fast as todays supercars.

To answer you question, Will a proper set up Cobra with great front to rear balance outperform a strictly stock Cobra? Probably . The question is just how much money do you want to spend so that you can still see the tailights of the Zo6's and turbo Porsches?

BTW I am not a pro but I do get to see their tailghts on a regular basis.

patrickt · #5 (**permalink**) 10-06-2007, 11:50 AM

Quote:

Originally Posted by RACER X #99

Will a proper set up Cobra with great front to rear balance outperform a strictly stock Cobra?

Click here http://www.capitalareacobraclub.com/...c,5722.45.html for a chart of the weights and balances from the "weigh day" we had this Summer at the Capital Area Cobra Club. Note that the FFRs were the clear winners on total weight, with my ERA coming in at 2653 49/51 -- our one attending Shelby came in last

. RACER X is right about having a Cobra's suspension set up right. Having your car tuned in properly is much more important than just shaving weight (although lighter is better).

Tommy · #6 (**permalink**) 10-06-2007, 12:29 PM

Speaking for myself, an occasional amatuer track guy, I doubt my lap times would vary much between a 400 HP small block and a 500 HP big block. In both cases, the driver (me) is a much greater limiting factor than the car.

Having said that, I'll mention that adding weight affects acceleration, deceleration, body roll, cornering G's, and many other performance dynamics. I wouldn't discount the importance of 100 extra pounds on a car driven by a skilled driver.

Jerry Clayton · #7 (**permalink**) 10-06-2007, 03:09 PM

I have driven several of my customers cars---the small blocks were all kind of more nimble/quicker reacting to quick steering imputs. Out of a few various( RU, Shell Valley) with cast iron Fe engines,they seemed to vary more from the steering feed back from probably the castor settings. The Superformance big block cars felt just more heavy steering in the front than the lighter small block cars---probably the best as for driver feedback was Got Snakes small block BDR.

A point that needs to be considered is individual driver comfort levels---for an example I'll use Shifter karts, a common toy of F1 and Champ car drivers as they have a very high reaction factor to accel/decel turn inputs---One of our customers was very fast at Daytona, passing two drafting faster team karts on the back straight , but running lap times that were not up to par---upon examining data from the differentkarts, we discovered that no matter what track he was on, he always slowed down to aprox 60mph in the turns, as that was the g loading he was comfortable with----

However, to return to the Cobras, I think one very important thing that is being over looked is driver seating---does your seat fit and support your body so that you can feel the car????Are your pedals and steering wheel where they need to be for max performance driving or are they just comfy???

Jerry

Jerry Clayton · #8 (**permalink**) 10-06-2007, 04:43 PM

When I was typing about the seats, I forgot to mention also that GotSnake Sid's BDR has the tightest fitting seat around the hip area---on me at least

Jerry

Morris · #9 (**permalink**) 10-06-2007, 08:10 PM

100#lbs equals a second on a race track.......

vettestr · #10 (**permalink**) 10-07-2007, 12:00 AM

Morris,
Help me understand in more detail what you meant by "1oo lbs = 1 second" I understand that is a general statement but is that directed at 100 lbs out of balance, 100 lbs added to gross car weight, etc.

Is that 100 lbs as important on a longer or faster track as on a slower track? Do various locations of the added weight carry the same time penalty? Is all of this still true if you can or have the adjustments to compensate or accept this change?
Thanks Jeff C

jmarsey · #11 (**permalink**) 10-07-2007, 12:42 AM

Jeff,

You will get far greater results by focusing on:

1. Driving the line consistently and smoothly.
2. Steering, brake, shifting, and throttle control.
3. Seat time, seat time, and more seat time.
4. While practicing the above three, get your spring rates, dampers, castor / camber, tires, and alignment understood and dialed in.
5. Don’t drive over your head. Proper seat, harness, fire suppression, and a roll bar that is at least 3” above the driver’s helmet ( I can go on and on)

If this is a street car, you will have to make considerable compromises in chassis setup. If you don’t mind the hassle, have a set of coil-overs and tires for the track, and a set for the street. If you really want to play, get one cobra for the track and another for the street. 50 or 100 pounds won’t make a hill of beans difference as compared to the driver’s ability and a reasonable chassis setup.

To answer your question in a nutshell, adding weight to the front will change the dynamics / weight transfer of the car under, braking, turn-in, entering thru exiting a turn, but if there is no real basis or baseline, of this hypothetical car / question, to compare to, who knows, it may even help how the car handles. It’s all just lip service until you see how your car behaves on the track with you at the wheel.

Be safe and have fun!

John

Morris · #12 (**permalink**) 10-07-2007, 07:55 AM

Understanding all of the things John just mentioned......and you have a worked out car......

The standard in SCCA GT-1 and GT-2.......

100# lbs added to the weight of the car will slow it down 1 second.....

This is standard procedure ......and it doesn't matter where you put the weight...... most of the time we were adding lead to the bottom of the chassis in the rear...... but you can add it anywhere and slow the car down......

However if it's an Aerodynamic advantage ...then you will gain the second back.....such as KMP 259 has the flat bottom plates and diffuser and wing......and still weighs in at 2630 and is faster with the Aero package and 100 #lbs then without......

Morris

trctrdrvr · #13 (**permalink**) 10-07-2007, 09:22 AM

Quote:

Jeff,

You will get far greater results by focusing on:

1. Driving the line consistently and smoothly.
2. Steering, brake, shifting, and throttle control.
3. Seat time, seat time, and more seat time.
4. While practicing the above three, get your spring rates, dampers, castor / camber, tires, and alignment understood and dialed in.
5. Don’t drive over your head. Proper seat, harness, fire suppression, and a roll bar that is at least 3” above the driver’s helmet ( I can go on and on)

If this is a street car, you will have to make considerable compromises in chassis setup. If you don’t mind the hassle, have a set of coil-overs and tires for the track, and a set for the street. If you really want to play, get one cobra for the track and another for the street. 50 or 100 pounds won’t make a hill of beans difference as compared to the driver’s ability and a reasonable chassis setup.

To answer your question in a nutshell, adding weight to the front will change the dynamics / weight transfer of the car under, braking, turn-in, entering thru exiting a turn, but if there is no real basis or baseline, of this hypothetical car / question, to compare to, who knows, it may even help how the car handles. It’s all just lip service until you see how your car behaves on the track with you at the wheel.

Be safe and have fun!

Jeff
the first thing I would do is take the car to the track and drive it, and if you're really interested, go to a driving school, the more seat time you get the better, as you learn what the car is doing you can adjust you're driving style to compensate, and or , change the setup, springs , shocks, tires, even different tire pressure adjustments will make a difference, but for any change you make to the car to work the first 1st is to be smooth, I learned that years ago racing karts,if you hopped the kart going into the corner or slid sideways it took a long time to make up the time you lost

vettestr · #14 (**permalink**) 10-07-2007, 10:31 PM

You all have given great advise and direction, thank you. The car is very capable and I just need seat time. I have our track suspension package on the car and the added wheelbase length and width provide a very stable car. I do want the torque of the big block though.

Building our Hot Rod version of the Cobra rather than a period correct car of the 60's also allows todays suspension technology. The car is based on a Corvette suspension but then includes all of the track proven modification available for a C3. These updates were refined to complement Cobray's new reduced weight, it is over a 1000 pounds lighter than a stock C3 vette. I have a lot to learn before I outgrow the cars ability.