Dragstrip FAQ: (possibly make it a sticky?)

[THe_DeTAiL3R]

Since people ask the same questions often and there is a bit of technique to get a good time in the 1/4 mile I thought I'd start a post for FAQs.

I don't really have any questions except one:

What exactly is the 60 foot time, how is it important?

[god910]

The 60' time is the time it takes the car to travel to the 60' mark. (60 feet from the start) It is quite important when deciding how you launch, tire pressures, wheelspin, etc. Most of the time the car settle's before the 60' mark, so it gives you an idea of how all the launch factors affect your total run. (For the most part anyhow)
EDIT: Cutting .1-.2 seconds off the 60' time can DRAMATICALLY effect the ET. ~.3 - .5 sec. or more. Shows how important a good launch is. :wink:

[BIGBULS]

MY question:

Why is it good to *manually* hold 2nd gear across the line in an LQ1 auto?




Answer:

There are two benefits to holding 2nd gear over the line:

a ) The stock 2-3 shift in "D" is set at 80mph (although the shift normally doesn't actually occur until ~81-82mph/~6200rpm). Since the car will normally trap at around 86.5-87.5mph in stock form, you can lock the gear selector into "2", thus eliminating a time wasting shift.

b ) Benefit #2 is the fact that the engine makes more power at 6200rpm (the top of 2nd gear) than it does at 4400rpm (the rpm you drop to in 3rd gear).............this means that the stock shiftpoint is also less than optimal, meaning you will actually pull harder in 2nd (until ~6600-6700rpm.....the ideal shiftpoint) than you would at the same speed in 3rd.

[Garrett8]

why dont you hold it in first then switch to second though?

[god910]

IIRC, the computer sees you trying to abuse the tranny, and manually shifts it into second, earlier than it would if it were allowed to make the shift itself. Did I get it right?? :D

[BIGBULS]

My question #2:

What are some good shiftpoints for an LQ1 manual (Getrag HM-284 transmission) to use for maximum acceleration?




Answer:

To figure out optimum shiftpoints with a manual transmissioned car you need to know two things; the transmission's gearing, and the engine's powercurve (meaning a dyno chart needs to be available).

First the gearing of the HM-284:

1st 3.46
2nd 2.28
3rd 1.48
4th 1.09
5th 0.72
Axle 3.67 (this one is actually not important where shiftpoints are concerned though)

Next you need a dyno chart:

http://fiero.cc/fiero-tdc/members/mws/intake/dyno.jpg

This chart seems to be fairly representitive of manual LQ1's (even though it was actually DYNOED after going into an 88 Fiero :D)...........

Now, since a shift from the 3.46:1 1st gear into the 2.28:1 2nd drops you to ~65.9% of the rpm you had in 1st (2.28/3.46 = 0.65896), you need to see what rpm the powercurves would intersect (where you'd be making equal power in each gear...thus no loss OR gain off of the shift)............looking at the chart you'll find that at 6600rpm the car is making ~148whp in stock form...........since a shift drops you to ~4350rpm (6600*65.9% = 4349rpm) where you are ALSO making ~148whp, you have a matched shift.

Lets try the same thing for the other gears. From 2nd ( 2.28 ) to 3rd ( 1.48 ), you drop to ~64.9% (1.48/2.28 = 0.64912) of the rpm you had in 2nd (yes that is a slightly LARGER gap/rpm drop than your 1-2 shift). Looking at the chart we see that at 6650rpm you have ~145whp available............a shift drops you to just over 4300rpm (6650*64.9% = 4316rpm), again where you are making ~145whp. The 3-4 shift is much tighter with a 73.6% rpm drop (1.09/1.48 = 0.73649), and a 6200rpm (~156whp) shift drops you to ~4565rpm (also ~156whp), again an ideal shift. Shifting from 4-5, you will again have much wider spacing (0.72/1.09 = 0.66055), with a 66.1% drop (almost EXACTLY the same as the 1-2 shift), thus meaning another 6600rpm shift is in order.

So........ideal LQ1 manual shiftpoints (at least for THIS particular car) are as follows:

1-2 @6600rpm
2-3 @6650rpm
3-4 @6200rpm
4-5 @6600rpm




In reality, the only way to get THAT exact on shiftpoints is to have YOUR car dynoed and figure it out from there, but these shiftpoints should be some good guidlines for the manual trannied guys to start with...................

[BIGBULS]

Question:


why dont you hold it in first then switch to second though?

Answer:


IIRC, the computer sees you trying to abuse the tranny, and manually shifts it into second, earlier than it would if it were allowed to make the shift itself. Did I get it right??:D




That is correct (almost :wink: ). In stock form, the PCM does NOT allow you to manually hold 1st gear to an optimum shift (which would be right around 6800-7000rpm with the 4T60-E's gearing and TC lockup strategy), meaning you are stuck with the stock ~6300rpm 1-2 shift.

A chip CAN change this shift (FFP/Vegeta program the best ones), but since the trans is only rated to 6500rpm for the 1-2 shift by GM (as per the old GMpowertrain webpage), you are pushing your luck with an optimum (performance-wise) shiftpoint.

Some FYI..........I believe the automatic upshift if left in "1" is the SAME as it is in "D"...........thus meaning that it isn't actually BAD to leave it in "1", but it IS of NO benefit.

[BIGBULS]

My question #3 ( :roll: ).

What is the best method of launching the LQ1 automatic?



Answer:

Since the LQ1 (the 3.4L DOHC V6 for those of you who aren't familiar with the GM nomenclature) doesn't really open up until nearly 4000rpm (there is a LARGE torque spike starting at ~3500rpm), you actually want as MUCH whelspin as possible with street tires to get the engine into it's powerband sooner. This is accomplished by powerbraking/brake-torqueing/stalling the car to a higher rpm than idle to preload the engine against the torque convertor.

(Brake-torqueing BTW, is holding the car in place with the brake, while simultaneously giving the car gas to raise your rpm............. :wink:)

Most people seem to have best results stalling/brake-torqueing the car to 1800-2000rpm, generally spinning the tires to 2500-3000rpm, netting you a nice jump out of the hole :D

[Garrett8]

thanks i was just wondering

[Garrett8]

thanks i was just wondering

[BIGBULS]

I should have re-arranged my posts and done this last one first (since it's about launching)............

Oops :(

[BIGBULS]

My question #4 (and this one is actually a bit of a question :) ):

What launch method has resulted in the best 60ft times for you LQ1/284 guys (manual tranied cars)?




When *I* owned my 5 speed 3.4L DOHC Grand Prix (now sold to Canada), I got out of the hole best on the street with a ~2700rpm clutch drop, which done *just* right (at least done on the right surface/pavement), would yield wheelspin up to ~4000rpm (right where the engine opens up fully). Unfotunately my one time at the track resulted in only 3 runs, getting too much wheelspin on the first (it spun to 5500+rpm), and a bog to just off idle on the other two runs (and getting me a string of crappy times......15.79, 15.77 and a crapola 16.04).

So what has worked best for those of you who HAVE gotten a fair number of runs in at the track with your manual trannied cars?

[dsgrntld187]

Question: I've never been to the strip in my Cutty 3100. What would the best technique be (launch, tire pressure, shifting, etc) to get hte best time possible? (Auto tranny)

[TurboSedan]

someone is gonna have to clean up this thread lol.

here's my question:

what's the best way to launch a W-body with a TGP engine/Getrag 282 5-speed combo....and what RPM do you shift?

[SigEpCutlass]

My question #3 ( :roll: ).

What is the best method of launching the LQ1 automatic?

do you happen to know what the best method of launching a L82 aka 3100 :wink:

[BIGBULS]

Question: I've never been to the strip in my Cutty 3100. What would the best technique be (launch, tire pressure, shifting, etc) to get hte best time possible? (Auto tranny)


do you happen to know what the best method of launching a L82 aka 3100

For launching these, I have no *direct* experience with what stall speeds work best, but the 3100's in L-Body's (which I DO have experience with) like a ~1200rpm stall to get the most wheelspin possible (they normally only *barely* roll the tires over off the line). Tire pressure likely won't matter much as long as you DO get a little wheelspin off the line (so lowering the pressure may actually be counterproductive).

But.

Since the 3100 W-Body's have a 3.33 axle ratio (vs 2.97 for L Body's.......although this is mostly offset by the taller tires) and a more agressive torque convertor, I would think it IS quite possible to spin the tires a little out of the hole (maybe try going full stall: ~2000rpm or so IIRC)..................if possible get enough wheelspin for the tires to HOOK UP at 2800-3000rpm (by which point the 3100 is starting to pull in earnest).



As for shifting, again there is NO way to manually hold 1st gear (4T60-E). Just figure out what selector position gives the highest rpm shift ("D" should snap off 1-2 at ~5600rpm). Then you DO want to lock the gear selector back into 2nd ("2"), and hold this over the line.

For any runs that are LONGER than 1/4 mile, and ideal 2-3 shift is ~5700rpm for a stock-near stock 3100 (vs the 5450-5500rpm shift in "D"), and 3rd ("3") will easily take you to the governor (some cars shortshift to 4th just prior to the governor cut, which is why I recomend holding "3").



Remember.............this advice is for 3100's............NOT 3.1L MFI's. They DO like to be shortshifted :wink:

[Aaron]

The best times and laucnhes in my car come with a 3400rpm drop, they will spin ahrdocre till about 4500, but then it is all fun :lol:

For a TGP 5-speed, I'd probly drop the clutch at about 2000, which is about where they spool up.

[god910]

For a TGP 5-speed, I'd probly drop the clutch at about 2000, which is about where they spool up.
Hey, fucktard, they won't spool SHIT, it's a 5 speed. :lol: J/K Aaron, I love ya man. Either way, if you want to do a clutch drop at 2K, it had better be a good clutch, also, make sure the tranny is GREAT. :x 2K is where my spider gears turned into spider chunks. Here's what I did:
1) Get the tires good and hot (555R's)
2) at my particular dragway I had to hurry my ass upto the line, because I couldn't get the damn thing to keep from rolling
3) Tack it upto about 2K, last yellow, dump the clutch and roll the throttle on.
4) Stop because you just blew a hole in your tranny. :roll:

That mutherfuker hooked like a Backstreet Boy at the gay end of Bourbon Street. For about 5 feet that is, it was an EASY 14.5-14.6 (had my boost kept up anyhow)

[Aaron]

[quote="god910J/K Aaron, I love ya man. [/quote]

Ewwwww that's gross.









Anyways, I was assuming street tires and avoiding the water pit :wink:

[slick]

MY question:

Why is it good to *manually* hold 2nd gear across the line in an LQ1 auto?




Answer:

There are two benefits to holding 2nd gear over the line:

a ) The stock 2-3 shift in "D" is set at 80mph (although the shift normally doesn't actually occur until ~81-82mph/~6200rpm). Since the car will normally trap at around 86.5-87.5mph in stock form, you can lock the gear selector into "2", thus eliminating a time wasting shift.

b ) Benefit #2 is the fact that the engine makes more power at 6200rpm (the top of 2nd gear) than it does at 4400rpm (the rpm you drop to in 3rd gear).............this means that the stock shiftpoint is also less than optimal, meaning you will actually pull harder in 2nd (until ~6600-6700rpm.....the ideal shiftpoint) than you would at the same speed in 3rd.

Not exactly good for me though :wink:

[god910]

J/K Aaron, I love ya man.

Ewwwww that's gross.









Anyways, I was assuming street tires and avoiding the water pit :wink:
well, actually that was without the pit :shock: You're not allowed to take a FWD through the pit at Muncie Dragway. Just a good burnout pre-stage. Then there's that whole Nitto 555R 245/45/17 thing. Damn those tires are sick. A quote from my girlfried: "What's wrong w/ the tires? Why is there gravel all over them?" :lol: :cheers: