this is my theory

[Tyler]

please correct me if im wrong..

all the mods i plan on doing to my car are as follows :

Headers, 3inch in and out high flow cat, 3inch spipe, 3 inch I pipe, and my flowmaster american thunder muffler. Slp or free Cold air intake, and 3.73 with lsd.

a lot of people say i would lose A LOT of back pressure and therefore ruin my acceleration like a mofo. but i put thinking into this.. and wouldnt the 3.73 bring up my torque on the low end and basically cancell that out?

oh ya, forgot to add another mod. 1piece aluminum drive shaft.

am i correct about this? cause thats what im planning on doing

[Tyler]

i really think this question shoulda stayed in GENERAL...because its more of a General question.. not specified towards exhaust...sheesh! that wasnt kool.. now im gonna get crappy answers

[Blue Flame V6]

<blockquote>quote:</font><hr>Originally posted by Tyler:
i really think this question shoulda stayed in GENERAL...because its more of a General question.. not specified towards exhaust...sheesh! that wasnt kool.. now im gonna get crappy answers<hr></blockquote>

Ok number one don't be an ******* to the mods. Number 2 those gears are probably going to hurt you more than they will help you. The reason for this is that in a 1/4 mile you will have to shift into 4th towards the end and loose a bit of momentum. The 3in exhaust won't hurt your low end very bad. I had straight pipe from the manifolds and still could spin going into 2nd. I say go for it but put 3.42 gears in instead.

[John_D.]

Tyler, you may lose a little bit on low-end, but I think probably not much. Back pressure is a little over-rated, especially for efi cars, they're not nearly as sensitive to it as carb cars were.

You have RS in your sig, so you already have the 3.42 gears, right?

I have also seen some other people on here talk about going 3.73 to make up for any low end loss. Wouldn't hurt, but probably not needed.

If anything, I may put in a higher stall torque converter later, so then I won't be as low in the rpm range when I nail WOT on takeoff. It's up to 4k pretty quickly on take off anyway.

Losing a little bit on low end just keeps you from having to go wild with suspension mods for traction... The improvement on top end should more than make up for it.

I still need to get to the track and prove that theory in my own case...

[ June 10, 2002: Message edited by: John_D. ]</p>

[Blue Flame V6]

<blockquote>quote:</font><hr>Originally posted by John_D.:
Tyler, you may lose a little bit on low-end, You have RS in your sig, so you already have the 3.42 gears, right? <hr></blockquote>

He has 3.23 gears. All M5 came with them. RS is just an appearance package any way the gear package on the A4 is Y87.

[Tyler]

ya, all i have is the RS sports appearance package (body kit and 3 piece wing)

but i still dont understand how bigger gears will HURT my take off's. wouldnt you think that bigger gears create more power at the lowend?


and btw: about me being an *******.. the above posts prove my point that this really has nothing to do with exhaust.. its more on a drivetrain/general topic.. but whatever. i wish it were kept in general because more people would look at it and give me opinions/recommendations. so if your a mod, could you please put this back in general or drivetrain?

[John_D.]

<blockquote>quote:</font><hr>Originally posted by Blue Flame V6:
He has 3.23 gears. All M5 came with them. RS is just an appearance package any way the gear package on the A4 is Y87.<hr></blockquote>

Yeh, I sometimes think of mine as the RS equivalent, except there was no RS that year... And since mine has both the y87 and y3f rpo's on it, I sometimes think of the 3.42 gears as part of the old RS option package, even though it is really two distinct options.

p.s., when I used to work for EDS back in the day, I worked on the Chevrolet Engineering account for 3 years, and for the next 3 years was involved with developing systems for the Vehicle Description System, Assembly/Component Tracking System, Mass Analysis System (cool stuff, evaluation of the mass of all components, sprung and unsprung, such as different brake calipers for different options, radiators and condensors for hd vs regular options, with precise x/y/z coordinates on each model of car), the Engineering Work Order System, and several others. So rpo's are kinda familiar...

[ June 10, 2002: Message edited by: John_D. ]</p>

[John_D.]

<blockquote>quote:</font><hr>Originally posted by Tyler:
but i still dont understand how bigger gears will HURT my take off's. wouldnt you think that bigger gears create more power at the lowend?
<hr></blockquote>

You definitely will get more torque to the wheels in the lower gears, quicker 0-60, etc.

But you should think about what top speed you will trap at, and what gear can you cross the finish line in. If you have to catch another gear, then that could cancel out any advantage on take-off.

I haven't worked through the gear ratios and speeds, but you should be able to find the information to do that here somewhere. Based on the top speed you plan on hitting, based on the other mods you eventually plan to install.

[Tyler]

the mods i listed above are ALL i want to do. nothing more. its gotta be a quick car yet not a gas hog. cause i gotta take it up to college with me when i go. you know how poor kids are when they are in college.. [img]graemlins/crybaby.gif[/img]

edit: but you say it as if i shift like grandma with a broken wrist. when i race i dont even take my foot off the gas, and barely tap the clutch in. its pretty quick..i impress myself sometimes

[ June 10, 2002: Message edited by: Tyler ]</p>

[John_D.]

<blockquote>quote:</font><hr>Originally posted by Tyler:
but you say it as if i shift like grandma with a broken wrist. when i race i dont even take my foot off the gas, and barely tap the clutch in. its pretty quick..i impress myself sometimes<hr></blockquote>

Oh, hey, I'm not commenting on your shift time.

If you have to catch another higher gear at the end, then you lose torque in the home stretch, that you could have kept if you could have kept it in the lower gear...

Imagine this highly over-simplified example, with three gears to keep it simpler.

First gear 2:1
Second gear 1:1
Third gear .5:1

Rear end 3.23

Effective combined ratio, if you could cross the finish line in 2nd, shifting halfway down the line, would be 6.46 for the first half, and 3.23 for the second half, for an average ratio for the whole run of 4.845

Read end 3.73

Effective combined ratio, crossing the finish line in 3rd, shifting 1-2 a third of the way down the line, shifting 2-3 another third of the way. 7.46 for the first third, 3.73 for the middle third, and 1.865 for the final third. An average ratio of 4.352

So with the 3.23 gears, in this way too simple example, you had an average gear ratio of 4.8, instead of the 4.4 with the 3.73's...

Hopefully that makes some sense?!

[ June 10, 2002: Message edited by: John_D. ]</p>

[Tyler]

you lost me from the very beginning.. lol.

i dont know..i want to hear what wicked v6 says about it.

[John_D.]

<blockquote>quote:</font><hr>Originally posted by Tyler:
you lost me from the very beginning.. lol.<hr></blockquote>

Yeh, it did get too involved.

Basically, yes will get better takeoff, but if you have to get another gear, you won't be pulling as hard at the end of your run. Not as much as you would with your original setup.

So do you get enough gain on the takeoff, to make up for not pulling as hard at the end?

That is the big question. Hard to say...

where is that wicked v6 anyway?

[RacerJ]

Ok, here's the deal - You don't have to moan about your topic not being left in General Tech. I won't venture as to why it was moved, but the fact of the matter is that the replies you're getting here are knowledgeable and accurate.

Yes, you CAN put on the exhaust mods you listed, no problem, they're very popular mods.

Yes, you COULD put on 3.73:1 gears, and it WOULD improve your low end grunt and takeoff, BUT you ARE going to hurt your top speed and gas mileage by doing so. I would also recommend you stick to putting in 3.42 gears. All you have to do is swap in a stock Z28 axle. This would also provide your limited slip differential, as well as upgrade you to rear disc brakes.

Yes, you CAN put in an aluminum DS. That should give you a little quicker acceleration by reducing your drivetrain's rotating mass.

Does that clear everything up nicely?

[Tyler]

uhh... you didnt have to explain what the mods do to my car... i kinda knew that..


my question was, would the gears cancell out the loss of torque with the exhaust mods that im doing....

yes, they may be knowlegable in your book..but they still havent quite answered mine

edit: ill have to give john_D credit caues he actually did answer my question or at least tried. thx for actually reading it

[ June 11, 2002: Message edited by: Tyler ]</p>

[DominusEtDeusNatus]

Back when I had mods like intake, 3.42s, and catback. In that order. 3.42s were a huge difference. Catback was a huge difference above 4K. Intake by itself wasn't as noticable because exhaust was still restrictive.