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 Post subject: Gear change
 Post Posted: Thu Dec 02, 2010 5:31 pm 
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Just trying to figure out if I changed rear end ratio if there is any benefit.Is there a program I can use to figure that out?Thinking of going to 4.88's from 5.13's in a Dana 60.
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 Post subject: Re: Gear change
 Post Posted: Thu Dec 02, 2010 5:35 pm 
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small block??

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 Post subject: Re: Gear change
 Post Posted: Thu Dec 02, 2010 9:56 pm 
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Yes Barry,small block.Here are some particulars.
67 Camaro 2640 lbs. 358 cu.in. 14.5-1 compression,Brodix Track 1 aluminum heads,roller 670 lift/310 camshaft,750 Barry Grant carb,(going to Terminator alcohol injection)powerglide with brake,5700 tci converter,Dana 60 5.13 gears,14x31-15 slicks.................Best time 10.50@126.89mph@3800ft.
Hope this helps.
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 Post subject: Re: Gear change
 Post Posted: Fri Dec 03, 2010 6:09 am 
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I did a change like that when I first got my Vega as it had 4.88s in it and went to a 4.56 gear. I was trying to get rid of some rpm at the finish line and turned out to have a better short time and et and mile per hour..A plus all around..
Your not making a big change but your converter slip factor will increase some.

There is a program that can figure that out but I can't find it #-o ..Maybe some else can post it.... ;-)

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 Post subject: Re: Gear change
 Post Posted: Fri Dec 03, 2010 10:26 am 
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What RPM range do you operate this engine in now?

Studebaker @ 3500 lbs was 10.0s @ 135 and was turning around 7700 at the stripe w/5:13 and a 33" tire. That engine was on methanol and was a 23* engine w/Brodix Track 1s. Compression was low enough to run pump gas though and the car was driven on the street a fair amount. That gear was too low for a quarter mile though and I probably should have had a 4:88 in it because of the finish line RPM. I ran a 5:13 though because I wanted to run both eight and quarter mile tracks and that gear was somewhere in between the two.

Logic would tell you that the lower gear will get it moving quicker, ie, quicker short times which will "usually" translate to quicker overall ET unless you're running out of engine on the top end.

I've got a link to some race calculators somewhere on one of these 4 computers I use. Will have to look to see if I can find it and post it here. Wait, I do think it's been posted here before? I'll search to see if it turns up under my username.

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 Post subject: Re: Gear change
 Post Posted: Fri Dec 03, 2010 11:02 am 
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Knew I had it somewhere :- ...

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

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 Post subject: Re: Gear change
 Post Posted: Fri Dec 03, 2010 11:19 am 
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Ken,shift rpm is 7500 and trap rpm through the 1/4 is 7600 with the 5.13'
I will check out that link Barry....................Thanks guys


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 Post subject: Re: Gear change
 Post Posted: Fri Dec 03, 2010 11:36 am 
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I don't think I would change anything...7600 for a SB is very safe IMO...

Did you check your converter slip??? You don't want it tight..

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 Post subject: Re: Gear change
 Post Posted: Fri Dec 03, 2010 12:23 pm 
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I'll have to agree with Barry to a point but not because of the "safe" part but more that you're probably at max RPM now for that particular head configuration. On my 23* engine it started to lay over around 7200 so with your smaller CID it's probably close to max now.

About the only way you'd really benefit from the lower gear is if you could run a larger tire to cancel it out up top. Larger tire "might" give you more hook and maybe lower short times, which "might" give you a lower ET on the other end.

And on another note, methanol tends to increase torque at lower RPM.

Since you've got more than one change you want to make, I'd change to the methanol setup FIRST and get a baseline on what THAT change does to your combo before you mess with anything else.

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 Post subject: Re: Gear change
 Post Posted: Fri Dec 03, 2010 12:34 pm 
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Ken,I can agree with one change at a time but I am concerned that with the change to the alcohol setup that the engine may buzz a little higher on the top end.Am I right on that or worrying about nothing?
Thanks,Paul


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 Post subject: Re: Gear change
 Post Posted: Fri Dec 03, 2010 12:37 pm 
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Barry,converter slippage seems to be ok.Just had it freshened and it's better than it was before.
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 Post subject: Re: Gear change
 Post Posted: Fri Dec 03, 2010 1:45 pm 
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In most cases where traction is not an issue, more gear will ET better than less gear, especially with a small engine like a 355ci. Geared to run an engine well past ideal shift point at the stripe in 1/4 is normally quickest.

There will always be a point where you can have too much gear for the car/engine combo.

In general
Things that will want more gear for lowest ET ... (the inverse will then be true as well)

a heavier car
smaller engine
less power in same rpm range
same power at higher rpm range
lighter rotating parts in engine, trans, driveshaft

A 5.13 sounds like it would be pretty close and would most likely be quicker than a 4.88. Switching to methanol may give enough more torque to offset it. Im with Ken on waiting to see what the methanol does.

Rick


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 Post subject: Re: Gear change
 Post Posted: Fri Dec 03, 2010 11:14 pm 
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Thanks for the input guys.I will have to wait another 6 months as our racing season is done for now with all the snow we have. =P~
That gives me lots of time to get the alcohol injection installed and running. :-
Barry,I used the calculator link you posted and it gave me a choice of staying with the ratio I have or 4.79 which would be close enough to 4.88's.
Paul


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