ooops I logged on with the wrong screen name. My post is the one above (BADBLUESS) is my bro...

<img src="graemlins/fluffy.gif" border="0" alt="[Fluffy]" />

 

Hmmm, I don't know who to agree with here... I too have a TH350 with a 2.52 1st gear. I have 4.33's in the rear, and 28" tires. My car goes through the traps at ~6600rpm or so. Would a 2.75 1st help me? I usually 60' in the 1.45 range if the track's good. I can see how in theory the 2.75 1st would help launch the car better, but then the car would have more "spread" on the 1-2 and 2-3 shifts, since the gear ratios become less closely matched with the 2.75 planetary (albeit a small amount). With my rear gear and converter that I run, I don't believe I'd benefit any from the 2.75 1st gear.

Also, I don't have a tranny-brake. Foot brake only.

 

[quote]Originally posted by steve:
<strong>are we going to get into the strength issue too?
i know what a 2.75 planetary set is used for.
i also know thats its not as strong as the 2.52.

heck, for the t400, you can get em as high as 3.00 these days.

the question remains, why would albert need the 2.75. its going to cost about 400 or so dollars just for the parts right?

stephen, are you saying that you had wished you had gotten the 4.10/4.11 ratio in your 12 bolt?

whats your rpm going through the lights?

steve frank</strong><hr></blockquote>

I agree, a 2.75 1st gear isn't as strong as a 2.52 1st gear. But, I REALLY don't think that's an issue for Albert or even for me. If it is I'll find out in my quest for 8s.

Albert only needs a 2.75 IF he wants to maximize his performance. He'll of course need adequate traction take full advantage of a harder launch. If the launch that he gets from a 2.52 1st gear is satisfactory to him then he obviously doesn't need a 2.75 1st. Much in the same way of saying that one who is satisfied with their launch with 3.73s doesn't need 4.10s.

As I said earlier in this thread, I have 4.10 gears. I do not have 3.73 gears. For me to get the kind of TQ multiplication that I have off the line with a 2.52 1st I would need a theoretical 4.47 rearend gear. With a 4.47 rearend gear I would have to be turning about 7480 RPM across the line at my current trap speed. That is NOT an option.

So, in my case, not only are 2.75s not a waste of money but they are absolutely mandantory for me to run the times that I'm running with the car as it is. If I were satified with low 10s instead of high 9s then a 2.52 1st gear would be fine.

My RPMs are about 6860 across the line which is exactly where I want to be.

[ December 03, 2001: Message edited by: Colonel ]</p>

 

Let's just say your running 10.60's in the 1/4 off the th350 and a 1st 252. w/411's in the rear. What would be your gains if you added the 275 1st in the th350???

Anyone?

I know it takes alot more when you in this catagory....(10's that is)

 

if you see a .1 gain in the 60' which would REALLY bring your tires into play, you would see about a .1 in the big end. hard to say. whats done to the motor, whats redline, what do you cross at?

 

[quote]Originally posted by Colonel:
<strong>


As I said earlier in this thread, I have 4.10 gears. I do not have 3.73 gears. For me to get the kind of TQ multiplication that I have off the line with a 2.52 1st I would need a theoretical 4.47 rearend gear. With a 4.47 rearend gear I would have to be turning about 7480 RPM across the line at my current trap speed. That is NOT an option.


[ December 03, 2001: Message edited by: Colonel ]</strong><hr></blockquote>


Colonel,
Could you please explain how exactly to figure out RPM's based on gears in the rear end and tranny, I know it also involves tire height?

 

There are ways to calculate it by hand but I'm the lazy sort so I just use a calculator like this one...

http://www.richmondgear.com/streetcalculators.html

I add 3 MPH to the measured trap speed to account for the difference in actual trap speed (what you're really doing when you cross the line) and what your timeslip says (an average of the last 60ft of your run.) This would vary from car to car depending on how fast you are accelerating at that time. It might be that you only add 1 or 2 mph for you car.

I add about .25" to the measured height of the tire to account for tire growth (often times the measured height of the tire will be more or less than what is designated on the sidewall.) This growth varies between tires. Radial tires will have almost no growth.

Enter the transmission ratio in the box designated "Overdrive Ratio".

For an automatic car you must account for converter slippage. I take the rpm given by the calculator and divide that number by the efficiency of the converter (in my case this is about .955.) This step is not necessary for a manual transmission car since you shouldn't have any slippage taking place.

So, in my case I have...

4.10 gears

A MPH of 139 (my timeslip reads about 136.)

29.25" tires

I enter 1 for the tranny ratio since my third gear is a 1:1 ratio and is the gear I cross the line in. If I were seeing my RPM at a given speed in 1st gear I would enter 2.75 since that's what ratio my 1st gear is.

This gives me 6547. I divide that by .955 and get 6855. <img src="images/icons/smile.gif" border="0">

[ December 04, 2001: Message edited by: Colonel ]

[ December 04, 2001: Message edited by: Colonel ]</p>

 

[quote]i dont see the need in the 2.75 planetary either.its a waste of money in my opinion <hr></blockquote>

I don't understand how you reached that conclusion either? <img src="images/icons/rolleyes.gif" border="0">

I have the 3.06 first gear set from Yank. It is NOT a waste of $!

 

[quote]Originally posted by Colonel:
<strong>This gives me 6547. I divide that by .955 and get 6855. <img src="images/icons/smile.gif" border="0"> </strong><hr></blockquote>

Umm, yeah.. very nice <img src="gr_images/icons/wink.gif" border="0">

 

Can I buy a TH350 that will bolt in, use a lockup LS1 torque converter, have a 3.06 1st gear ratio, and use the stock driveshaft from YANK?

 

yes, you can get a t350, not sure of the gear set tho.
i know they make t350 sets up to about 2.75:1.

lockup converter? get with chuck at flp about that.

use a 9 inch tail shaft and the stock driveshaft will work.

and me and albert have spoke via mail on numerous occasions before this post was made, i know what he is after and what i think would benifit him and what would not. the point is, he is going to need other parts for his car long before he would need that gear set.

steve frank

 

I am doing a th400

should I do the 275 1st gear?

moser 12 bolt 3.73's good traction.
mti stage 2 heads/c2 cam/ tnt 100 shot