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Old 12-13-2011, 10:12 AM
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3.73 Gears with Turbo 350 drivability?

I have a '70 Monte with a 400sb, all the bolt-ons, jegs 282/292 465/488 hydraulic flat tapped cam with 1.6 rockers and +.100 pushrods, and freedom series 210 aluminum heads. It's 224/234 duration at .050" lift and LSA 112 (max lift with his 1.6 rockers is more than he stated above) Jegs #200105. right now It has the factory 2.73 gears and no posi with street tires. I'm looking to maximize my usable torque curve without ruining regular driving streetability. I've been told my power curve is from 2500 to 6200rpms but I'm not reaching that with the current setup. It has a factory 12 bolt rear end and I'm looking maximize the power I have. I figured the best way to do this would be 3.73 gears and posi. Jegs has a 3.73 gear and posi kit you can buy from them for about $750. I'm going to school about 400 miles away from home and it is not my daily driver anymore. I don't do alot of in town driving in it, but then agian i don't do alot of driving in it much period. It's been an ongoing project since I was 15. I just want to know will I loose highway and country backroad drivability by adding posi and the 3.73 gears? And if I do go through with this will it be unhealthy for the engine to cruse at 60mph with the 3.73 gears? Will it be worth the money? All help is appreciated, thanks!

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Old 12-13-2011, 11:14 AM
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It won't kill your "drivability" it will kill your gas mileage! lol
You'll have a big jump on the cruise RPM tho. If your engine is healthy then cruising at 3500 is not a problem. BUT...
lets make sure we're trying to fix the right thing here..
if you are trying to get out of the hole quicker, or get better 60' or 1/8 mile times, yea a gear will help you. but if you are trying this because you are not reaching 6200 RPMs... that is, the trans is shifting too early, say at 4500, then that will not change! What you need is to change your GOVERNOR configuration. To get higher RPM max throttle shifts, you need lighter secondary weights and springs. If you need a high output governor i can get you one, or get you a weight and spring kit that will get you there.

Dean

Quote:
Originally Posted by 70montecarlo400
right now It has the factory 2.73 gears and no posi with street tires. I'm looking to maximize my usable torque curve without ruining regular driving streetability. I've been told my power curve is from 2500 to 6200rpms but I'm not reaching that with the current setup. It has a factory 12 bolt rear end and I'm looking maximize the power I have. I figured the best way to do this would be 3.73 gears and posi.
I just want to know will I loose highway and country backroad drivability by adding posi and the 3.73 gears? And if I do go through with this will it be unhealthy for the engine to cruse at 60mph with the 3.73 gears? Will it be worth the money? All help is appreciated, thanks!
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Old 12-13-2011, 11:36 AM
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Shift kit? Adjustable?

I bought the car from a transmission mechanic and I know it has some kind of shift kit in it. I assume this is what is making it shift early. It shifts hard but rairly do the rpm climb to 4000 when even when I get on it. This is a problem my and my mechanic are working on via timing and cam retard. I have never heard of the spring kit your talking about; could the trans be adjusted without adding or replacing any parts? is the spring kit affordable? easy to install? will it always wait till that high of rpm's to shift or only under heavy acceleration? Also if i were to go the direction of the posh and gears. Do you know what the average labor time/cost is for such an installation? I don't have the tools to do it at my house. I have also heard of welding something in the rear to create "posi" while that may be cheaper, the basic idea doesn't sit well in my head. is that something that is more of a low budget "bubba" hotrod fix?
Thanks
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Old 12-13-2011, 03:50 PM
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before you can do any gear ratio and RPM calculations
we will need to know what size rear tire you are running
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Old 12-13-2011, 03:56 PM
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calculations are not necessary. its handled.
The trans is shifting too early.


Quote:
Originally Posted by matts37chev
before you can do any gear ratio and RPM calculations
we will need to know what size rear tire you are running
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Old 12-13-2011, 03:57 PM
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Quote:
Originally Posted by 70montecarlo400
I bought the car from a transmission mechanic and I know it has some kind of shift kit in it. I assume this is what is making it shift early. It shifts hard but rairly do the rpm climb to 4000 when even when I get on it. This is a problem my and my mechanic are working on via timing and cam retard. I have never heard of the spring kit your talking about; could the trans be adjusted without adding or replacing any parts? is the spring kit affordable? easy to install? will it always wait till that high of rpm's to shift or only under heavy acceleration? Also if i were to go the direction of the posh and gears. Do you know what the average labor time/cost is for such an installation? I don't have the tools to do it at my house. I have also heard of welding something in the rear to create "posi" while that may be cheaper, the basic idea doesn't sit well in my head. is that something that is more of a low budget "bubba" hotrod fix?
Thanks
What Trans does the Monte have, TH350, TH400?
The Governor Recalibration Kit will allow you to tune the WOT/WideOpenThrottle shift points. It will still shift at a normal rpm at Part Throttle. If you plan on changing the Rear Gear I'd wait to tune the Gov.
Gov Recal Kit >> http://www.summitracing.com/parts/BMM-20248/
You don't want to Weld the Spider Gears for use on Pavement or Street use. A Eaton, Yukon DuraGrip or Eaton/Detroit TrueTrac Posi Carrier would work well. Shop around for prices on Diff, Gears & Master Install Kit. Quick Performance has a Package Deal for about $575.
http://www.ebay.com/itm/GM-12-Bolt-C...item5646f1afb2

An 2004R, or 700R4 OD Trans would give you the best of both worlds combined with the 3.73 gear. Better accelleration and retain your cruising rpm.

Trans---------1st------2nd-------3rd-------4th Gear---
TH350--------2.52-----1.52------1.00------------------
TH400--------2.48-----1.48------1.00------------------
TH200-4R-----2.74-----1.57------1.00------0.67--------
TH700-R4-----3.06-----1.62------1.00------0.70 --------

3.73 X .67 = 2.50
3.73 X .70 = 2.61
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Old 12-13-2011, 04:53 PM
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Tires and such. T350!

I'm not familiar with the 1st 2nd and 3rd equation you've laid out for me could you elaborate on what that means? I have a t350 trans. The tires are 70r15 radial ta's but I all be moving down to 60's to better match my current gear ratio. Thanks for the links I will check them out. Also a good note is that I have a 1900 stall (at least one back wheel begins to turn with a brake stand at 1900). A 700r4 will probably eventually be added if i go the route of the 3.73 gears. Thanks again fellas.
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Old 12-13-2011, 05:04 PM
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I don't know how I missed the TH350 in the Subject line.
Those are the Gear ratios of the 4 different Trans, 1st gear, 2nd gear, 3rd gear etc..
The .67 & .70 is the 4th/OD gear ratio of the 2004R & 700R4 Trans.

The 2004R is the same length as the TH350, so you could use the same Driveshaft, you would need a TH400 A-Body Crosmember tho' as the 2004R & TH400 rear mount is in the same location.
The 700R4 is 3" longer than the TH350.
Trans ID & Specs:
http://www.maliburacing.com/auto_tranny_id.htm

Calculators for MPH & RPM etc.:
http://www.f-body.org/gears/
2nd one here >> http://hotrodworks.net/hotrodmath/quarter.html
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Old 12-13-2011, 07:30 PM
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uh.. excuse me. i'm handling this. what is not needed is confusing information. We're working on a 350. Data for 400, 700, and 2004R is irrelevant. As for your statement...
"The Governor Recalibration Kit will allow you to tune the WOT shift points. It will still shift at a normal rpm at Part Throttle." This is incorrect and misleading. ANY change to the governor will change the shift timing AT EVERY THROTTLE OPENING. The part throttle, closed throttle, or mid-throttle shift timing will be moved proportionally, relative to the the change made.
But misinformation confuses the situation. Now, please let me guide this gentleman to the correct procedure.

As for the B&M kit, i have it cheaper and better. AND i will provide the tech support to get it fixed to his satisfaction.

Quote:
Originally Posted by SSedan64
What Trans does the Monte have, TH350, TH400?
The Governor Recalibration Kit will allow you to tune the WOT/WideOpenThrottle shift points. It will still shift at a normal rpm at Part Throttle. If you plan on changing the Rear Gear I'd wait to tune the Gov.
Gov Recal Kit >> http://www.summitracing.com/parts/BMM-20248/
You don't want to Weld the Spider Gears for use on Pavement or Street use. A Eaton, Yukon DuraGrip or Eaton/Detroit TrueTrac Posi Carrier would work well. Shop around for prices on Diff, Gears & Master Install Kit. Quick Performance has a Package Deal for about $575.
http://www.ebay.com/itm/GM-12-Bolt-C...item5646f1afb2

An 2004R, or 700R4 OD Trans would give you the best of both worlds combined with the 3.73 gear. Better accelleration and retain your cruising rpm.

Trans---------1st------2nd-------3rd-------4th Gear---
TH350--------2.52-----1.52------1.00------------------
TH400--------2.48-----1.48------1.00------------------
TH200-4R-----2.74-----1.57------1.00------0.67--------
TH700-R4-----3.06-----1.62------1.00------0.70 --------

3.73 X .67 = 2.50
3.73 X .70 = 2.61
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Old 12-13-2011, 08:18 PM
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Quote:
Originally Posted by 70montecarlo400
Will it always wait till that high of rpm's to shift or only under heavy acceleration? Thanks
I was referring to this part of th OP's question.

Excuse me for trying to offer other ideas TrannyLab. I'm sorry I didn't understand that only your Info should be Heeded.

SSe


Reminds me of another member of recent days.
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Old 12-13-2011, 09:19 PM
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Quote:
Originally Posted by TransLab
calculations are not necessary. its handled.
The trans is shifting too early.
so you are not going to address his questions about the gear ratio change and posi install also?


Quote:
Originally Posted by TransLab
uh.. excuse me. i'm handling this. what is not needed is confusing information. We're working on a 350. Data for 400, 700, and 2004R is irrelevant. As for your statement...
"The Governor Recalibration Kit will allow you to tune the WOT shift points. It will still shift at a normal rpm at Part Throttle." This is incorrect and misleading. ANY change to the governor will change the shift timing AT EVERY THROTTLE OPENING. The part throttle, closed throttle, or mid-throttle shift timing will be moved proportionally, relative to the the change made.
But misinformation confuses the situation. Now, please let me guide this gentleman to the correct procedure.

As for the B&M kit, i have it cheaper and better. AND i will provide the tech support to get it fixed to his satisfaction.
are you for real?


just because the trans isn't working the way it should be
doesn't mean he wont also gain some performance from a gear change and added posi
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Old 12-13-2011, 10:42 PM
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If you change your 273 gears to a 373 ratio you will be pleased with the performance. You might look at the RPM calculators with your tire height to make sure your ok with the cruise RPM's.
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Old 12-13-2011, 10:56 PM
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At 65 with a 28" tire 3.73 rear gears and lock up 350C trans, my truck is at 2850. Performer cam, 9/1 with 305 vortec 906 heads. The truck came with a 1800 stall as part of the tow package. Hold the brake to wind it up and let her go. My shift and gov kit are from TCI. Gov set at yellow and blue springs with 2 and 5 wts. Shifts at about 5k. 16 mg cruise control on. Ride 65 in the slowlane all day.

Along with a gov setting, PTAC has a TV downshift corrector. It is a spring in front of the TV carb connector that allows for earlier downshifts. Increasing the spirited driving effects of a fine ride.

http://www.400raptor.com/Spring1.jpg
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Old 12-14-2011, 08:29 AM
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Now ladies I promise I appreciate all of your attention equally . Thanks Spinn for the example that helps a lot. Right now I'm cursing at about 2300-2500 on the highway maybe a little hight at 70-75mph, but now its not going to see as much highway use as it used to. I can drive 55 has become its modo as of recent. I think I'm going to go with the WOT governor kit because my engine has close to 80k on it. I'd like to keep it running under as little stress as possible. As for the tires I'm not sure how tall they are all I know is they are 70r on 15's. Would I be better of with 65's or 60's with the stock gears sell in it? Ive been told that helps. Just a side note this is mostly a street car, with limited strip use.
Thanks guys,
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Old 12-14-2011, 10:45 AM
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i DID address his question. I told him the ratio change would get him out of the hole faster, and improve his 60 foot or 1/8th mile time if THAT WAS HIS OBJECTIVE, but his concern was he was not able to REV as high as he wants, and a diff change will NOT correct that. IT IS A TRANS SHIFT TIMING PROBLEM.
I am helping him correct his REAL concern FIRST.

and btw, i have no problem with other suggestions, but if there is misinformation, or misdiagnosis, that is a different issue. It is a HUGE problem in this industry. Shops all over the place sell the customer the wrong stuff because they do not identify the issue correctly. I have spent over 30 years helping transmission shops and professional rebuilders fix it right after a misdiagnosis or failed attempt at correcting a condition.

The key statement was that he was not able to utilize the available engine power curve! the engine is capable of 6200 but he can't shift above 4000.
hello!
Now if this guy brought the car to my shop inquiring about a diff change (and errantly thinking this would get his engine RPMS up) i would fix the shift timing problem FIRST, then roadtest the car with him, and when he feels the power increase cause the engine can revv out a little more, he may decide he's happy with that and forget the diff change idea, BECAUSE HIS COMPLAINT IS FIXED.

And yes you are correct that "just because the trans isn't working the way it should be doesn't mean he wont also gain some performance from a gear change", BUT thats beating around the bush and side stepping the real issue.
But thank you for your contribution.

Dean

Quote:
Originally Posted by matts37chev
so you are not going to address his questions about the gear ratio change and posi install also?

are you for real?

just because the trans isn't working the way it should be
doesn't mean he wont also gain some performance from a gear change and added posi
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