Crazyquik

For the best ET in the 1/4 mile, which combo would work the best?

Horsepower/Torque
380/420
400/400
420/380

J.

Nickn20

I think vehicle weight, and where the horsepower and TQ occur would be a factor, and I think peak TQ numbers occur before 5200 rpm, and peak HP after, I would go with the 420/380 since it will be more time in your power band for racing IE 5000-6500 or so

[ January 31, 2002: Message edited by: Nickn20 ]</p>

LS1derfull

420 ft. lbs.=tire smoke, 420 HP = accelleration, so my vote is for 420/380 <img src="graemlins/burnout.gif" border="0" alt="[Burnout]" />

Colonel

420/380 and the right converter and gearing to go with it.

ChrisB

It depends on the total average horsepower you put down at the track (area under the curve). 420 but peaky, with an average of 380 would loose to a flat 400 curve. On the other hand if it's not peaky but normal it would be better.

You need to look at the entire setup though.

Chris

Crazyquik

When I posted this I was thinking 400/400, kinda undecided how I stood though. I really think in a manual the 400/400 would do better than the 420/380 since you typically have a larger rpm band that you race in, and you dont have the torque multiplcation of the converter.

J.

LS1derfull

That may be true but m6 has very little drop in rpm between gear so peakiness would be more acceptable and unless car is on slicks i still think 420/380 would be more usefull overall.

WeatherGuy

I'm not quite sure I understand how really definitive answers can be given to the number selections above.

The best ET is going to come from the car that maximizes the average applied horsepower (per fixed weight). Usually, people say that is given by area under the curve, but that is only true to the extent that a single pass through the entire curve holds. The area under the curve approximates the answer if the areal calculation is restricted to the powerband that you are going to use. The real best answer is to do a path dependent line integral - but that is overkill here (and I am not sure I could do it).

This entire problem gets much worse once gearing and torque converters are factored in - and then there is the traction issue!

Having said all of the above, giving only the peak power/torque levels tells you little about the overall shape and slope of the respective curves. That overall shape AND the values are where the real information is - peak power/torque numbers only tell you what the peak engine output is (and if you are clever, you can guess where in the RPM the peak HP and torque values are occurring since HP = torque*RPM/5250).

joe blow

hi, i think this is my first post on this forum. just thought i'd share something.

check this out....

interesting info....

Colonel

"I'm not quite sure I understand how really definitive answers can be given to the number selections above."

Because there is more potential for work with the engine that is making 420 RWHP. Now, assuming that the power range isn't extremely narrow (and it shouldn't be with an LS1 making that power) you can utilize this power through proper gearing and converter. It's the average HP to the ground over the course of the 1/4 that counts and this will be highest with 420 RWHP engine IF it's geared properly (a numerically higher gear than with the others, presumably, which provides more TQ multiplication) and the proper converter is used (a higher stalling converter, presumably.)

WeatherGuy

[quote]Originally posted by Colonel:
<strong>"I'm not quite sure I understand how really definitive answers can be given to the number selections above."

. . . Because there is more potential for work with the engine that is making 420 RWHP. Now, assuming that the power range isn't extremely narrow (and it shouldn't be with an LS1 making that power) you can utilize this power through proper gearing and converter. . . . </strong><hr></blockquote>

Yeah Colonel, I agree, but the key phrase here is assuming that the power range isn't extremely narrow. I guess a common sense read that this is an LS1 is in order (this is after all an LS1 board), which directly implies a power range that is not narrow. However, one reason I wrote what I did is that too many people are focusing only on those peak numbers and not looking at the overall shape/area/work potential of the curve. This is especially the case with some of the recent debates on this and other boards of extreme RWHP values achieved by some Supras and other cars.

Crazyquik

Yup, definently LS1 oriented. Trust me, I am far from wrapped up in peak numbers (I would have got an M6 if I were <img src="gr_images/icons/wink.gif" border="0"> )

J.

Colonel

Generally, having wide power ranges with lots of power under the curve gets more and more important the wider the gap in tranny gears there is, the numerically lower the rearend gearing is, and the tighter the converter that is used...among other things.

In in this thread I'm speaking of LS1s that are setup properly for maximum 1/4 mile performance.

If we want to talk about other cars (which would seem a bit out of place here) then we will surely need alot more details to make good guesses.

[ January 31, 2002: Message edited by: Colonel ]</p>

LS1derfull

This post didnt indicate m6 or a4 so heres my m6 answer: Bring revs to 5500, engage clutch properly
shift at 6000, rpm drops to 5000, right back up to
6000 shift,and repeat one more time. There you go 420/380 wins, no problems with fat torque curves,etc., etc. Torque is for steady state work,
HP is for fast accelleration. <img src="gr_stretch.gif" border="0">

Plan B

The Only Thing You Really Need to Know
Repeat after me. "It is better to make torque at high rpm than at low rpm, because you can take advantage of *gearing*." <img src="gr_stretch.gif" border="0">
Thanks for your time.

Good one joe blow <img src="gr_stretch.gif" border="0">

Patrick G

iTrader: (14)

A quote from Warren Johnson: "He who makes the most explosions over the 1/4 mile wins the race". What he was saying is, take a 346 ci LS1 making 440hp/385tq with peak power at 6500 rpms vs. a 400 ci LS1 making 440/420tq at 6000 rpms...gear them both to use the most of their powerband and the smaller LS1 would win. Why? Because it made more explosions over the quarter mile than the larger LS1. Remember, we're talking identical horsepower here. In a race car, hp is everything and torque is nothing.

Again, these are all Warrne Johnson's theories and they are not exclusive to Pro Stockers. They are sound principles that apply to LS1s too.

Colonel

Plan B, I agree. I can't emphasize enough how important it is to grasp the concept of HP being work and gearing being the way that we channel this work.

"Torque is for steady state work"

This one is kinda like "TQ gets you going but HP keeps you there" or other similar sayings. They are incorrect. Torque in itself performs no work. I don't care if you have 1,000,000 lbs of TQ...with no HP, NO WORK has taken place. Torque combined with movement is work (and this is called HP!) <img src="graemlins/burnout.gif" border="0" alt="[Burnout]" />

Colonel

Lemme expound a little on what Patrick said to help some...

Now remember, we're talking about race cars where the tranny ratios, gearing, clutch slippage or converters are matched almost perfectly to the engines.

With the HP being made at a higher RPM you will be using a numerically higher ratio rearend gear (as in using 4.56s instead of 4.10s) than you would be with an engine making the same HP at a lower RPM. This extra gearing (we could say, this extra TQ multiplication) equals more average HP to the ground over the course of the 1/4 mile and that means a quicker car.

Once you stop looking at power from the crank and start focusing on power to the ground (this means taking into consideration all forms of TQ mulitplication), it becomes much easier to understand. <img src="graemlins/burnout.gif" border="0" alt="[Burnout]" />

[ February 01, 2002: Message edited by: Colonel ]</p>

ChrisB

The fact is though, as WeatherGuy pointed out, you have to assume properties given the above peak numbers if you want to determine the winner.

Once you start assuming/guessing numbers then you have gone from physics to intuition. From the numbers given above you can only make a determination if we are told the power/torque curve is distributed evenly around each peak point - or that the above values are average hp/torque numbers as observed down the strip.


Chris

LS1derfull

Not to over simplify things but the reason 420/380 makes 420 hp is because it makes 380 tqe. at higher rpm than other choices mentioned, this is what you really need to get out of all that info above my post here. So with that said i still think im right , and i believe a back to back test on the same vehicle would prove it! <img src="gr_tounge.gif" border="0">