Launch technique - Ford Mustang Forum
 
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post #1 of 12 (permalink) Old 07-02-2016 Thread Starter
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Launch technique

I have a question about launching my car. First, this is what I've got. It's a 68 coupe 3100 lbs with me in it, 306 with a stock bottom end except a windage tray\girdle a high vol pump and deep pan. The heads are 58cc AFR 185's fully ported and polished with full roller rockers. The cam is an older Comp Cams flat tappet hyd "Thumper"(TONS of overlap) absolutely no one home before 2700RPM although it sounds great. (I know, I know but its getting a new hyd roller cam over the winter!) 5-7 in of Hg. Intake is an Edelbrock Performer RPM with a 650 Holley DP. 10:1 compression. Trans is a TCI Street Fighter with a TCI 3000 stall. Rear is a 9" 4.11:1 and a locker. I run on 26" tall Mickey Thompson ET Streets. Runs high 12's at 104-105.

The way I normally launch it is to do a burnout, stage, then load the converter as much as the brakes will allow (2200 or so) and then hit it on the last yellow.

I've been told recently that I should stage following the burnout, not load the converter and just hit it at the last yellow and that loading the converter just adds heat and does little else. He said the converter will flare to 3000 (it does) regardless. I plan on testing this at the next test and tune but wanted your opinions. It seems to me that adding the 1500 RPM will save a little time. It does add heat but I have a cooler with a fan so it stays below 200. I'm reluctant to believe that this will work. Comments??

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post #2 of 12 (permalink) Old 07-02-2016
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It is better to launch just slightly higher than idle then stab gas on last just before about to turn green.

Launching at lower RPM will flash the converter harder.

Trying to torque up before launching is a waste of energy.

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post #3 of 12 (permalink) Old 07-05-2016
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+1 With your combination it "should" be better to launch at a lower rpm. It will as stang93mustang mentioned, flash higher from the lower rpm than if it is "hard stalled" like you are doing. BUT to work right the carburetor jetting and squirters must be right or it could stumble as it transitions from part to full throttle. This will also affect your reaction time to the tree. To improve the under 2,700 rpm performance , you could advance the cam 2 or 4 degrees. This will help that area and possible the overall performance as well.

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post #4 of 12 (permalink) Old 07-05-2016
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You never mentioned what kind of 60' times your getting?

With a trans brake that will eliminate your stumble if you had one because you foot is all ready to the floor before green.
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post #5 of 12 (permalink) Old 07-05-2016
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I'd also come down on your final gear. Imo......I would use a 3.73.

You are on 26's so little tire, you will gain some MPH using less rpm. That also means you can add more power to gain the torque area up and stay within power band.
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post #6 of 12 (permalink) Old 07-06-2016 Thread Starter
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Quote:
Originally Posted by Gt350HR View Post
+1 With your combination it "should" be better to launch at a lower rpm. It will as stang93mustang mentioned, flash higher from the lower rpm than if it is "hard stalled" like you are doing. BUT to work right the carburetor jetting and squirters must be right or it could stumble as it transitions from part to full throttle. This will also affect your reaction time to the tree. To improve the under 2,700 rpm performance , you could advance the cam 2 or 4 degrees. This will help that area and possible the overall performance as well.
Do you mean ignition timing? If I'm pulling it apart to re-degree the cam, it's coming out. The cam was in the motor already when I got the car. As far as I know, it was installed straight up. I'm already running light springs in the HEI so the curve is pretty short. (Yes, I'm running an high performance GM style HEI for simplicity) total timing is 36 and it's all in by 2000 or so. I upgraded the squirters after an EPIC lean backfire so the power valve got replaced and upgraded as well. Jetting seems fine by color on the plugs.
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post #7 of 12 (permalink) Old 07-06-2016 Thread Starter
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Quote:
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I'd also come down on your final gear. Imo......I would use a 3.73.

You are on 26's so little tire, you will gain some MPH using less rpm. That also means you can add more power to gain the torque area up and stay within power band.
I'm shifting at 6-6.5K and going through the traps at 6-6.5K. It's still pulling hard at 6K. That's supposed to be the power peak for this cam. I went with the smaller tire since the engine seems to really love the high RPM's so I wanted it to unwind faster. Couldn't I go with a taller tire and accomplish the same thing? Setting up gears in a 9" is such a pain.
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post #8 of 12 (permalink) Old 07-06-2016 Thread Starter
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Quote:
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You never mentioned what kind of 60' times your getting?

With a trans brake that will eliminate your stumble if you had one because you foot is all ready to the floor before green.
I looked for the time slip and couldn't find it. That would tell me a lot. It's under 2 seconds but I don't remember how much. Going back next week. I'm going to try the new technique as well as the old to see what happens. I'll let you know.
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post #9 of 12 (permalink) Old 07-06-2016
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Quote:
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Quote:
Originally Posted by stang93mustang View Post
I'd also come down on your final gear. Imo......I would use a 3.73.

You are on 26's so little tire, you will gain some MPH using less rpm. That also means you can add more power to gain the torque area up and stay within power band.
I'm shifting at 6-6.5K and going through the traps at 6-6.5K. It's still pulling hard at 6K. That's supposed to be the power peak for this cam. I went with the smaller tire since the engine seems to really love the high RPM's so I wanted it to unwind faster. Couldn't I go with a taller tire and accomplish the same thing? Setting up gears in a 9" is such a pain.
You could always give it a try. I know about those 9" setups! Lol
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No I was talking about camshaft advance. That would help the torque which would lower the 60' and overall ET. Might even help the MPH. Your engine should rev to 7,000 as it is. You want to be a few hundred past peak power when hitting the finish line. Make sure you advance the new cam , especially if it has more duration at .050 than your current cam.
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What rpm does it trap at? Had it on a dyno to see where you make your peak power at? That will tell you a lot about what gears or tire height you need. I always get the best 60' (and best times) when I floor it off idle. And I have a 3400 stall. With auto's you need it all set up correctly. My 14 GT auto is N/A with a 3.15 gear and my best is a 1.7 60' 11.97 at 117mph on 275 nitto nt05r's. But I also found out my af ratio is 11.1-11.4 at wot all through the rpm. I was expecting a mid 11 and now I'm working with my tuner to lean it back out since that's way too rich.
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post #12 of 12 (permalink) Old 07-10-2016 Thread Starter
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What rpm does it trap at? Had it on a dyno to see where you make your peak power at? That will tell you a lot about what gears or tire height you need. I always get the best 60' (and best times) when I floor it off idle. And I have a 3400 stall. With auto's you need it all set up correctly. My 14 GT auto is N/A with a 3.15 gear and my best is a 1.7 60' 11.97 at 117mph on 275 nitto nt05r's. But I also found out my af ratio is 11.1-11.4 at wot all through the rpm. I was expecting a mid 11 and now I'm working with my tuner to lean it back out since that's way too rich.
I wish I could put it on a dyno. There isn't one close to me. Installing an AF meter into the collector of the long tubes so that should help.
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