Adjustments to 1/4 times

[TexasRedLT4]

Adjustments to 1/4 mile times?

Browsing through this forum I've seen some awfully impressive 1/4 mile times run with LT4 Vettes, and have also read an interesting post on the variation of HP output of LT4 engines.

I'm looking for information on the typical adjustments you would see in quarter mile times due to air temperature, elevation etc. I know that the magazines typically adjust their recorded times to sea level and 70 degrees F (?) using a pretty complex formula that also includes atmospheric pressure etc.

When I lived out in West Texas I took my LT4 Vette down to the local drag strip one time for what they called a "test & tune" (basically unlimited runs against whoever was pulled up next to you). I had a lot of people wanting to race me and won most of them (except for the true hot rods - one guy ran a 10 sec qtr against me), but I was a little disappointed in the numbers I ran and have always been curious about the impact of less than ideal conditions. My best run was 14.0867 seconds at 99.62 mph. I know I was hampered by the following conditions:

• elevation - 2700 ft above sea level
• approx. 90 degrees F outside air temperature
• running on Goodyear runflat tires (that were about to be replaced)
• less than ideal track conditions (i.e., West Texas is always dry, dusty, and windy; therefore track surface probably wasn't the best for traction)

I would like to know what the impact or adjustment to the times and ending speed would be due to the elevation and air temperature (i.e., is there a simple formula, any rules of thumb, or just what you've observed from experience, etc.). I'm also curious if any of you have experience with the runflat tires and how they perform in this application. I've know that most people did not order them as an option in 1996, but my wife liked them as a safety feature. Any help, input etc. on these questions would be appreciated!

 

[Fugitive]

Yo where are all you guys who talk about 12 sedond quarter mile runs with simple bolt ons? Come on Trance, and all you Grand Sport nuts how come none of you are hitting this post up? You guys weren't exagerating were you? I know I read a few guys that claimed you were clocked at 181 top speed! I was hopping my car is capable of this! I depend on mine as a daily driver so I'm not so quick to push the limits on mine. But for real I want to know if you guys are comng real or just talking? Lets here! Scott

 

[CKA_Racing]

I have experience running both the runflat and non-runflat GSC at the track. I could run as low as 1.9 60ft times with the regular GSC tires. Running the runflats was pretty bad. The best I could do was 2.3 60ft times. My times were in the 13.5-14.0 in the 1/4 with runflats during mid summer runs. With non-runflats of GSC and other tires I consistently run in the 12.9-13.3 range at 107-110mph. Having the run flats and the LTWS is not worth it in my book. You get a very hard ride with the runflats, the sensors are hard to find and expensive. During tire changes they are almost always broken by the tire installer or not installed correctly. I saw a vette on a dyno have one of the sensors strap break during the dyno run. The wheel starting jumping up and down really bad. Everyone present including the dyno operator was surprise nothing else broke in the suspension due to the pounding it took.
Plus you have allot more tire options running non runflats.

So in short I can't stand run flat tires. Unless you live in some very remote region or are handicapped in a way that does not allow you to change into the spare tire, I would not be worried about having to use runflats.

 

[UB2 SLOW]

Where in West Texas are you from? I am originaly from Big Spring. Anyway, I have a simple Bolt on LT1. Most of my parts are LT4 parts that I bolted on. I ran 13.7 stock at 70 degrees at 1000ft elevation on 275/45/17 GS-C's. That was an LT1 Auto. After bolt ons(Heads, Cam, Exhuast, TC, gears, Headers, injectors) same elevation and 75 degrees, I ran a 12.5. Granted you are at a higher elevation and it is hotter, but you should be running low 13's at my elevation, add the bolt ons that I made to my LT1 to your LT4 and you would be low 12's. I agree wtih CKA, the first thing I would do is lose the runflats. They are heavy and dont give the best traction. Go with 295 or 315's GS-C's or F1's. I turned 1.9 60ft times with the GS-C's and SZ50's. I then changed to NITTO DR 315/35/17's and my 60ft time went to low 1.8's. Keep in mind that when you go to track with street tires, DO NOT GO TO THE PIT. :nono You want to go around the pit, if possible and then just spin them enough to clean them off.

 

[Vettelt193]

How are you shifting, at what RPM? How is the car running? Your numbers seem odd to me, not the time so much as the MPH. That number is equal to about 275 crank HP, which is really low, even for bad conditions. If you can't hook up, you can roll off the line, then get on it. Another trick is to change your shift points... lowering your 1-2, and 2-3 shift RPM can actually increase your track time and speeds if you are having trouble with traction. (this is especially true for LT4's because of the torque curve)

 

[lt4 gs]

When my first set of EMT's were bald .......they really hooked up good. I should have saved them. Sticky to sticky. Of sourse the last time I saw 14 seconds, I was driving a Ford. That was my Mark VII LSC.

 

[Fugitive]

LT4GS, I only seen one GS with your color scheme it looks great! Hell it might have been yours! You get it with those colors? Did you specail order it? Or bought it used? Scott

 

[CKA_Racing]

LT4GS, I only seen one GS with your color scheme it looks great! Hell it might have been yours! You get it with those colors? Did you specail order it? Or bought it used? Scott

:confused :Silly

No such thing as a red with white strip Grand Sport.

 

[lt4 gs]

we're gettin off the threaded course here.....and hi-jacking threads is a no-no.........there is a color thread here:


http://corvetteactioncenter.com/forums/showthread.php?s=&threadid=19630

 

[TexasRedLT4]

The car was and is running fine as far as I know, but I am thinking of having it serviced just to be sure (I have had bad luck taking my Vettes to dealerships and avoid them if at all possible). In hindsight, I know I was shifting too late (i.e., basically at or close to the redline). I was either still in 3rd or had just shifted into 4th at the end of the quarter, and after reviewing the magazine tests I realized that I probably needed to shift earlier, since I could not reach their reported trap speeds in 3rd gear (which tops out at 104 mph). This was in 1999, so the exact details aren't as clear anymore. I did go back a couple of months later, but unfortunately it was much hotter and I didn't improve any (my 60 ft times were also worse). The best 60 ft time I got was 2.1 sec (the first time around).

 

[CKA_Racing]

Well it even makes less now about your 1/4 speed. Here's why.
I also cross the end of the 1/4 at redline in third gear or about a split second into fourth. My highest 1/4 speed recorded was 110mph just shifting into fourth a hair before the line. So i'e have had my in third gear up to 108mph. All of the lower speeds ranged from 105 -108mph all attained by crossing the line at or near redline in third gear. All other stock LT4's i have seen have done the same. My best times were done by shifting a hair before the rev limiter kicked in in each gear. So if you are saying you are crossing the line redlining in third or just shifting into fourth but are only going 99mph, it makes no sense. That is very strange to me. Of course i'm assuming you are running factory gears in the rear since you have not stated otherwise. Are you sure your vette does not have 3.73 or 4.10 gears in the rear? This could explain why you are have a hard time getting traction off the line if you are having this issue.

Does Altitude affect the mph vs which gear that speed is attained?

 

[TexasRedLT4]

My Vette is bone stock, not even a different air cleaner, so I'm running the factory gears. The top speed of 104 mph in 3rd gear that I quoted was taken from a 1996 Car and Driver article (table listing the top speed in each gear). The low end-of-quarter speeds didn't make much sense to me either, which is why I posted the questions inquiring about the effect of elevation and temperature. As mentioned in another thread, I've had my Vette up to 165 mph (at the same elevation) and it was still accelerating, so I don't think that I have a particularly low HP engine (though I probably don't have one of the really high ones either based on the quarter). I'm also not a drag strip regular (I've only done it for the two trips in 1999), so I don't know how much of this is due to my driving skill (or lack thereof). I'm starting to feel the need to find a local drag strip again (at least I'm at sea level now), but my wife wasn't too keen on me doing it the last time. We'll see....

 

[Vettelt193]

Does Altitude affect the mph vs which gear that speed is attained?

The speed is really based upon RPM... at any given RPM, in a certain gear, your tires must be moving a certain speed, regardless of how much horsepower you are making. If you aren't making the horsepower, you simply won't be able to reach higher RPM's.

 

[Vettelt193]

My Vette is bone stock, not even a different air cleaner, so I'm running the factory gears. The top speed of 104 mph in 3rd gear that I quoted was taken from a 1996 Car and Driver article (table listing the top speed in each gear). The low end-of-quarter speeds didn't make much sense to me either, which is why I posted the questions inquiring about the effect of elevation and temperature. As mentioned in another thread, I've had my Vette up to 165 mph (at the same elevation) and it was still accelerating, so I don't think that I have a particularly low HP engine (though I probably don't have one of the really high ones either based on the quarter). I'm also not a drag strip regular (I've only done it for the two trips in 1999), so I don't know how much of this is due to my driving skill (or lack thereof). I'm starting to feel the need to find a local drag strip again (at least I'm at sea level now), but my wife wasn't too keen on me doing it the last time. We'll see....

So you went through the trap in 3rd or 4th? If you were in 4th, one of two things could have happened...

1) you shifted too soon, so you didn't obtain the best speed or times (assuming you shifted too soon in all the other gears as well... this could really kill your 1/4 mile)

2) the track was not calibrated properly... how did the other close to stock corvettes run at the track?

If you were in 3rd: the elevation could have really killed your power

 

[TexasRedLT4]

I don't believe that I was shifting too soon (I remember being concerned that I was shifting too late - i.e., past the power peak, but its hard to say now since its been so long). There were very few "stock" (or even new) cars at this track, most were project cars that were highly modified. I do remember one other Vette, a newer C-5 car, that ran the quarter with a trap speed of around 103 mph (if I remember right) and high 13's. I don't know if it had any modifications or was stock.

 

[CKA_Racing]

The speed is really based upon RPM... at any given RPM, in a certain gear, your tires must be moving a certain speed, regardless of how much horsepower you are making. If you aren't making the horsepower, you simply won't be able to reach higher RPM's.

Yup I am aware of what you are stating. I guess my question was not really what i was trying to ask. Let me try again. Can altitude affect at what max rpm the engine can reach? This has more to do with the engines breathing capability than gearing.
Is it a mute point unless we are talking about some very high altitudes. I think my question is still not clear on what I'm asking.

:J :Silly :bash :gap