Performance question??

[Oldschool]

I have a question about the effect rear gearing has on the performance of a vehicle in the 1/4 mile.  I have tried to snoop around on the net and find out, and have asked a few folks, but I can't get an answer with any certainty.

Example:

You have a car that will run 10.50 @ 130 in the 1/4.  This combo is a BB Dart that weighs 3450 with driver.  It is running a 31" tall tire and a 4:10 gear. Traction is not an issue up to this point. It is turning about 6400 rpm through the traps.
What will the numbers be if a 4:56 was put in the rear, leaving everything else the same?  I understand the trap rpm will be higher, but what will the ET and MPH do?  Let me know what you think please.   My Dart buddy is wanting to know if it will be worth spending the money on the change.....      

[Chryco Psycho]

My experience was interesting , my Duster 3440 lbs with driver & 440 4 spd ran 12.0 with 3.23 gears & 11.7 with 4.30 , the torque really worked with either gear , I think a small block would see more benefit , fi the engine is not that light internally allowing it to rev faster may make no difference as the engine will still slow the rise time , personally I would not do the swap from 4.10 to 4.3 or 4.56 , I doubt he would see much if any gain

[Moparal]

You can try this

http://www.moparts.org/Tech/tech/index.html

or maybe this

http://www.wallaceracing.com/Calculators.htm

[Oldschool]

I appreciate you responses.     I have looked at those calculators before, but there is nothing there will allow you to get the info I am seeking. They can tell what gear you need to turn a certain rpm etc.  None will say if you change from this gear to a different gear, your ET and or MPH will do this.  I am too stupid to figure out a formula....        

[Moparal]

Morroso ha a slide chart that comes with the info you want. I have one somewhere. I will see if I can find it. It comes in real handy. If not summit carries them or I will go up to the speed shop and buy you one. They have them over by Bullitt99's house. Is your friend running an 8 3/4  if so 742 housing?  I got some almost new 456 gears I will let go

If his car keeps pulling to 6700  then a 456 gear would give him around a tenth and a half et and maybe 5-7 mph

[71chally416]

Drag type cars will ET best when they trap a few hundred RPM past their engine dyno peak RPM. If you don't know where that is you can just change ratios until you find it.  With a typical BB I would think he's already pretty close unless he has some great heads and a radical roller cam. Even if he's a little off he won't see a gain worth the expense of gearing differently. Probably a few 100th's and not tenths, unless he's overgeared and the motor is laying down at the 1,000ft mark. In that case LESS gear might help quite a bit. 

[jims challenger]

I went from 4.56 to 4.10 in my 440/727  Scamp...I gained or lost nothing, my numbers where pretty well identical, car always ran 11.50's @ 117mph

[moparniac]

converter 

[Chryco Psycho]

There are better places to put the $$ to improve performance

[71chally416]

   The typical Mopar big block runs out of head at 6K or even before unless you have some good B-1 or Indy heads. No need to gear it to trap over 6,400.

[ntstlgl1970]

What kind of 60 foot times does the car run? Is it a leaf spring car? How much of a gain is he looking for?
Maybe he could pick up some there with a converter (like stroker mentioned) and chassis tuning as opposed to a numerically small gear change?
If I remember right the rule of thumb is 1 tenth gain in 60 foot time = 2 tenths on the top end.
If it has an 8 3/4 then borrowing a 4.56 pumpkin would be the easy way to find out.

[Moparal]

well seeing a 10.50 # 130 mph already says he has some chassis tuning to do. He should be closer to a 10.0  with that mph

[moparniac]

well seeing a 10.50 # 130 mph already says he has some chassis tuning to do. He should be closer to a 10.0  with that mph

I was gonna say the same thing alan... but I didnt know if that was just a vague comment or actual numbers.. 

[the_engineers]

Closer...
http://www.nationaldrivetrain.com/calcs/dragcalc.html

[moparniac]

Closer...
http://www.nationaldrivetrain.com/calcs/dragcalc.html

I hope thats close.... its got me running pretty good into the 9's on all motor