What's new
CK5
Register an account today to become a member! Once signed in, you'll be able to participate on this site by adding your own topics and posts, as well as connect with other members.

Gearvendors length

Well just under 2000 should be fine, the thing that you don't want is the engine to lug around 1200-1500 would be like it was idleing
 
Thats the one I use, but it doesn't account for tire size in the final drive equation they use. It is not the effective final drive ratio. Anyway I don't think I'll have any issues. My cruise rpm is 30 less than a 700/3.73/31 inch tire combo.
 
Let us assume you complete the project and install the Cad 500/465/205/GV OD and 35" tires. You accelerate and move through the gears smoothly. You feel the massive torque of this engine trying to yank your b***s off from behind you. As you quickly reach 70 mph you engage OD, as you step on the gas you notice ------------------------nothing. No power, no acceleration, no response except the slight pinging of the bearings (spark knock) as the vehicle - ever so slowly- looses speed. Your shock and frustration is equally suprised when you take it out of OD and all the engine power and acceleration has returned. You return home, pissed off and angry at the time, effort, and cost of somethine that is totally useless. After smacking yourself a few times you ponder the situation. In desperation you swap the 35" tires for the 31". You repeat the test drive, this time,however, after engaging OD the engine responds correctly, acceleration is slow but responsive. You are a happy camper now.
This is the senario that will occur. And you can take that to the bank!
 
Okay so would 35s and 4.10 be a better setup? The rpms are very similar between 3.73 with 31 and 4.10 and 35.
 
Mike, you said the minimum final drive required to move a vehicle on level highway is 2.70:1. Unqualified, this statement is easily shown false, whether by math or by personal experience. I have a 1983 Chev C10 with a 350/700R4/3.08 rear gears. The 700R4 has a .73:1 overdrive, combined with 3.08 rear gears gives me a final drive of 2.24:1 in OD. With 29" tires, I still have plenty of acceleration, and with light throttle use can maintain speed/accelerate slowly from 40MPH without kicking down a gear.

Mathematically, you need to know some other rather relevant information before you can make statements about the effectiveness of final drive ratio. Assuming 300lb/ft of torque from the engine, an overdrive of .78:1 and axle gears of 3.73:1 gives you 872.82lb/ft of torque at the wheel. A 36" wheel gives you a 1-1/2 foot radius, so divide 872.82lb/ft by 1.5= 581.88lbs.

Of course, torque is more relevant to acceleration, whereas horsepower is a measure of work. Vehicle speed, aerodynamic efficiency, vehicle weight, road grade, etc., are all factors, but that is WAAAAAY beyond what is required to push your average 7-8000lb vehicle down a level road at 70MPH.
 
Yeah, I can't see any basis in saying you won't be able to use your overdrive, especially behind a 465.

Heck, I'm still planning to put a GV unit behind my NV4500/205 combo in my diesel, staying with the 235/85/R16 tires (31.8") of course. Double overdrive should put me right in the 18-1900RPM powerband of the 6.5 for empty cruising, and obviously I wouldn't use the double OD for towing . . .
 
Mike D said:
You feel the massive torque of this engine trying to yank your b***s off from behind you. As you quickly reach 70 mph you engage OD, as you step on the gas you notice ------------------------nothing. No power, no acceleration, no response except the slight pinging of the bearings (spark knock) as the vehicle - ever so slowly- looses speed. Your shock and frustration is equally suprised when you take it out of OD and all the engine power and acceleration has returned.
Click to expand...

I believe this is why we don't have 1 speed transmissions, and even two speed automatics that are 40 years old have an automatic downshifting mechanism. :)
 
The 700 R4 had different ratios OD available. 0.86:1 was used also. Therefore 3.08 x 0.86 = 2.65 effective axle ratio. With 29" tires the factory probably expected acceptable customer satisfaction.
15 years ago I read in some OEM technical journal that a 2.70:1 axle ratio is the lowest neumeric ratio that that a V8 engine would pull. Please bear in mind a smaller (lighter) more aerodinamic body powered by a V6 ( torque range 1200 - 1800rpm ) probably could handle a lower 2.54:1 ratio.
A Suburban or Blazer is heavy, not aerodinamic, and is designed to haul loads. GM would not risk its reputation on a less than adequate truck.
The ideal truck for highway use should have a 3.08 - 3.23 axle. This truck should get resonable fuel economy and still haul the freight. This is my opinion.
 
GM never changed the ratio of OD on the 700R4 AFAIK. No idea where you got that info.

3.08 is a decent freeway gear. It sucks for towing and wheeling. If you can get 4.88's to a final drive of 2.56 for instance (just a random ratio) and cruise comfortably, you are actually doing better than starting with a numerically low axle ratio, which is why OD is the standard now.
 
The way I see it is that from the factory you could get either 29 or 31 inch tire. Lets use the the 29 inch tire as a constant to take the effective final drive out of the equation. From the factory you could get the common ratios of 3.08, 3.42, 3.73, 4.10, all with the TH700 and with a 29 inch tire. By your reasoning you are esentially saying that if your truck came with 4.10 and you put 3.08 in, it would no longer be able to cruise in overdrive and propel itself down the road at a steady rate. That makes no sense at all when you would just be going to a different stock gear option. At cruise you are maintaing speed not accelerating, picture driving 70 with the cruise control on. In an auto to accelerate to maintain the set cruise speed, the trans would downshift out of overdrive, reach set speed and return to OD, i.e. driving over an overpass. Essentially the same thing happens in a manual trans configuration, the engine accelerates to maintain speed, with the understanding that yes it is sometimes required to downshift. The downshift really depends on the power band of the engine.
By using the GV overdrive, it would be mimicking the factory auto OD setup, granted with slightly less overdrive reduction. Now the change of the tire size is like changing the gear set itself. It will lower slightly the final drive ratio yet still be very capable of driving down the highway with no problems. I guess all those trucks with the 305/700/3.08 combos that are running 33 inch tires instead of the stock 29s are just magic.
 
The 700 came with a .70 od. I have done many 700 swaps from throughout the GM lineup into truck, midsize, fullsize, f-body etc. they are interchangeable when going from SBC to SBC. Now what you might be thinking of is the 700s that were used behind the 4 cy, and 60degree v6s, I have never messed with them so I don't know. At least for the SBC applications, I have never seen anything other than .70.

I still don't see that it would matter much since a very mild CAD 500 can produce 300+ ftlbs at the 1800 rpm mark and that power is just begining at that mark. Cruising there should be no problem.
 
I am sorry if I opened a can of worms, that was not my intent. 8 years ago I converted my 81 Chevy 3/4 ton with 350 cu.in / SM465/205 33" tires to an automatic. In my research to decide which automatic tranny to use my choises were TH350, 400,700 R4, or 4L60(?). In reading the literature ( this is where I learned about the different OD ratios - did not think about their use on 4 & 6 cyl engines )and asking GM mechanics of the pros and cons of each based on their durability and repair experience. The concensus was either the TH400 or the 4L60(?). At the time the 4L60(?) was about $3000 plus I would need to purchase a stand alone computer to run it. Also I was getting conflicting information about the availability of an adaptor for the NP205. The TH400 was from a 91 wrecker and was completely rebuilt for my use for $300. It does not have OD but has performed flawlessly for 8 years whether empty or hauling 2 tons of gravel for my driveway.
I plan to put a GV OD in my truck next year IF the OD will not wear out ( cause excessive slip ) my torque converter ( Jet Engineering 2400 stall ).
If anyone in CK5 could chime in I would appreciate it.
 
http://books.google.com/books?id=NN...&hl=en&sa=X&oi=book_result&resnum=4&ct=result

This is the best site I found that included everything in one place. This shows how to determine the effective final drive after a tire size change, and how to determine what axle gear ratio is needed to return to the same power level as stock. Using the two burbs I have as comparison with the "zero tire size" at 31 inches, Burb 1: 700/3.42/31 tire, final drive with the 700's .70 OD is 2.39. Burb 2: 465/GV/3.73/35 tire, final drive with eht GV's .78 OD is 2.58.

In this case I still come out ahead with a little more grunt than the 3.42 I have in my DD burb. Not to mention the massive amount of more power from the CAD 500 versus my worn old 350, I am way ahead. Could I upgrade to 4.10s sure but I don't see the need really. I don't really have any issues with my daily driver as far as power, so if I can build another chasis with much more power, less drivetrain loss (manual vs. auto), a little more gear both from take off and while cruising then I am worlds ahead.
 
My dad's truck is a 454/465/205/GV/4.10/33's.

At cruise the GV unit just doesn't give enough drop in RPM's when the speed limit is 70. RPM's with that setup at 70: 2191. That equates to 3.08's BTW.

There is absolutely no doubt that his 454 would pull that 6000lb truck with ease if the RPM's were another 300 less or so. Not to mention that would change the gear splitting points when he needed it, trailering.

We had contemplated swapping in a 3.73 rear just to see how cruise would be, but ended up doing disk brakes on his 4.10 rear instead.
 
Any chance you know or could measure the actual length from the back of the 205 case to where the yoke is on the GV?
 
Using the above mention calculator site, that combo comes out to 2279 rpm at 70. Going with 3.73 would drop it to 2074, that plus 35 tires would be 1955. Of course these numbers all assume that the tires are the actual listed size which they are usually a little smaller which would raise the rpm slightly.
 
How soon do you need the measurement? :)

It's easy enough to take, but I'd have to go over to his house and I'm leaving for over a week tomorrow, so it would be difficult (at best) to accomplish shortly. I can't be crawling under vehicles in my work clothes unfortunately.
 
You must log in or register to reply here.

Latest Posts

Top Bottom