Tedly

I had my C6 to the drags a few times (am not a rookie, have raced off and on for about 30 years, in cars that ran between 11 seconds and 7 seconds). The car has a fresh air box as the only modification. I made two runs and the first was a 12.83 @ 111 MPH, second was a 13.56 @ 107 MPH. I was told by a friend that the computer would "see" the wide open throttle and then make an adjustment and the second run would be slower, then after two runs would again go back to being more consistent. But since I only made two runs that day I don't know, but last year I ran it a few times (without the fresh air box) and it did seem to have a similar pattern. Can anyone shed some light on this for me? Thanks in advance.

rpmextra

stock tune? manual or auto? can you post your 2 time slips? and what tire?

Tedly

Yes, stock tune, Automatic, stock tires, 29 pounds of air, track was prepped and it did not seem to spin the tires the second run, so that was not the cause. did not load the converter, wanted it to flash. I am getting ready to go to work now so can not scan slips but info is as follows. I am leaning towards the computer. 60 foot went from 1.996 to 2.113 330ft from 5.540 to 5.902 1/8 from 8.377 to 8.902 1000ft from 10.811 to 11.449 1/4 from 12.839 to 13.562 and MPH from 111.69 to 107.31 I did stage a little deeper the second run but did not put the top bulb out. Deep staging will slow it down some, but I remember last year it acted the same way when I made 3 or 4 runs, second run was slower, then third and fourth came back but never was very consistent. I know it is not going to be as consistent as my real race cars were, but should be at least within a tenth or tenth and a half I would think.

HOXXOH

I think your friend was stretching to find something you'd believe, however it's the first time I've heard that story. I too have a long history dating back to 1958, so I understand your concerns. Shortly after I semi-retired and bought my C6, I returned to the track after a many year absence. The first time was getting my groove back and had nearly 3 tenths variation in 5 passes. The following week, I made 4 passes within .05 and .26 mph and never looked back on consistency.

What exactly is the "fresh air box" you mention? I ask because heat soak on these cars can cause the computer to pull massive amounts of timing and therefore lots of HP. If the IAT were high on the second pass, the problem is easy to solve.

Joe_G

It's due to your inlet air temperature rising waiting in the staging lanes. The car pulls up to 12 degrees of timing which is about ½ of total commanded timing.

Give this thread a read and see the testing done and table included therein with some potential solutions.

https://www.corvetteforum.com/forums...month-now.html

COSPEED

Correct, and the disparity between high and low octane tables for timing.

There are several racers here that could give instructions for a good "bracket tune" for consistency.

rpmextra

That's exactly what I was thinking too. 2nd pass was always the slower one in your case. Joe remembers I had some timing being pulled and the game changed pick time when that was cleared up. I would suspect its intake air temp. get some ice in the intake between runs and let it cool down. You may also want to use higher octane fuel if you don't already.

Joe_G

Rpmxtra I'm not so sure the ice trick is really necessary for our nylon intakes and air cleaners.

But I am not always correct.

I suspect that the IAT very quickly gets up above ambient when you close the hood and start the car. I have a Vararam that sucks air from in front of the grille and it's about 5-10 above ambient all the time. But if you have an underhood breather, it'll heat up fast. I've scanned a c6Z at 152 IAT after only a couple of minutes in the lanes on a 70 degree day.

If you have time sometime, run a test with and without ice and see how the IAT reacts after say 5 minutes in the lanes (most of us have to wait at least 5 minutes in the lanes, you get the red carpet treatment at your track I think lol).

rpmextra

Yeah I do get the red carpet treatment here, and I'll never take it for granted

I know on a very hot day, I experienced a small amount of Knock retard, we put her on ice, ice was melting fast, waited a bit as to let it cool between runs. when ready closed the hood 2nd gear burnout to keep revs down which keeps heat at bay, and ran (back then PB) 10.57@136.26mph even without a tremendous 60ft which was 1.61....Checked it out, no KR, all timing delivered and have been doing it since. You may be 100% correct Joe, but for 5$ of ice and it keeps my water bottles cold I like to think it works lol.

Joe_G

When you get a few minutes check your IAT with and without ice (if you remember which is which), just for fun.

It might still be a valid trick! Curious minds want to know!

rpmextra

Let me dig through the data logs. Lets see if i can break down the timing. you got me curious too

Joe_G

Just look at IAT. I'm sure your IAT timing table has been reduced from stock settings...most tuners reduce it.

rpmextra

Ok so here is the best example that I have at least logged

August 30th, 4:00pm-5:00pm Dragtimes states 75.2F in my area


4:29pm ice taken off and go IAT 80.6f, launched at 87.8 after burnout, dropped and never passed 80.6f during the run from 2nd gear. but crawled up to 82.4f on the return road.

4:39pm no ice (hot lap) staged IAT hit 98.6 after burnout and launch at 100.4, and only reduced too 95f by the time i hit 2nd. and took all the way till 4th gear to see 80.6 again. and had 1.0kr for about 1 sec at the end of 3rd.

Joe_G

Well, a 10 degree reduction for pretty much the entire run is a pretty good reduction. More than I would have expected! Good test, useful information.

Do you have a cool air intake or does it breathe from the engine compartment like stock?

Hanlon's Law

Almost certainly heat related. At least in the case of my Z, it starts pulling timing if above 214f coolant and something like 90f IAT.

When I took it to the track the first time, I let it sit for about 2 hours before my first run. Trapped 127 mph on that run. Immediately hotlapped it after idling in the lanes (with coolant temp at 220F on the 2nd run, not sure on IAT but definitely hot) and trapped 122mph. Let it cool down again, pushed it through the lanes instead of idling, and it was back to 127.

rpmextra

Halltech mf108 and removed some material so the car grabs air from the z06 vent. Which apparently is a high pressure zone.

Tedly

Joe G. mentioned the Vararam fresh air intake, that is the one I have too. Thanks for all of the responses. Sounds like everyone is going with the temperature changing the timing. That is probably what it is. I was told by another friend who had a C5 that his was not consistent until he had it tuned on a dyno. I am not planning to race much so probably won't go that route. I just like to go make some passes on test n tune days. A street car really doesn't make a good race car and a race car doesn't make a good street car. I get more kicks out of driving on the street than sitting around a race track all day. Been there, done that.

Joe_G

The Vararam really helps keep the IAT's down, but even with that, as you can see from the table going from 85 to 100 in the lanes can cut a lot of timing. A tune will alleviate this and make the car much more consistent.

I found through experience that these cars can be modded to run mid-11's and be very reliable and fun. Below that, the chassis will start breaking.

If you decide to mod, this thread might be helpful to you. If you've got an automatic, a 3600 stall will get you in the mid 11's with no other mods.

https://www.corvetteforum.com/forums...ast-heads.html

Tedly

Thanks a lot Joe G. It might be worth getting it tuned. I'm not getting out to the track anymore this season. But something to give some thought to over the winter. I surely do not want to break anything so I am not looking for super fast times, just have some fun. I do know from my younger years that speed is addictive, and you always want more! Luckily I'm older and hopefully wiser.

Joe_G

I said that when my modded c5 got stolen, I was going to leave my c6 more stock....

Don''t count on it...it's addicting...