SirRobyn0
Full Access Member
- Joined
- Dec 6, 2019
- Posts
- 6,755
- Reaction score
- 11,402
- Location
- In the woods in Western Washington
- First Name
- Rob
- Truck Year
- 1984
- Truck Model
- C20
- Engine Size
- 305
Some of you probably remember that I've been looking to re-gear or possibly swap to a lower geared full floater as I currently have the 14B semi-float. For those that missed the earlier conversations or want a refresher I'll go over that then give some numbers to think about.
The truck 1984 C-20, what was thought to be a 350 turns out to be a 305 after looking at the block numbers. Truck has the 700R4 with temp gauge and cooler and it is in good health, automatically locks converter in OD or has manual switch to engage lockup in 3rd. Current axle ratio is 3.41, stock 31" tires.
The trailer, 18' open car hauler type, but rarely used for cars. Most common loads are, my small tractor gross trailer weight about 5,000Lbs, or feed hauls where the trailer gross is around 6K.
Terrain, hills, lots of them when there isn't hills there's mountain passes that's just the way it is here. Some secondary roads, some freeway use.
Look I know a 305 isn't going to break any land speed records especially with the trailer loaded, but with the current 3.41 gears it will haul it, just not very well. I'm looking to go to either 4.10 or 4.56, I keep looking at the numbers but can't seem to decide so I'm hopeful that someone will look at the numbers or have some personal experience and say something that will get me to make a damn decision and move forward one way or another.
Numbers:
305 makes peak torque 245 @ 2,400RPM, peak horsepower 145 @ 3,800RPM so at the very least we want to keep the RPM within those ranges when towing, but also best if not right up against either end. I tend to like to keep it right around 60MPH on the highway with trailer, both because that's the law and where it feels comfortable, control wise.
current RPM with 3.41
65 MPH 3rd gear 2,400 (at peak torque, not ideal and above preferred cruse speed)
60 MPH 3rd gear 2,200 (below peak torque this is terrible, preferred cruse speed)
55 MPH 3rd gear 2,000 (below peak torque even worse)
If re-geared to 4.10
65 MPH 3rd gear 2,900 RPM (between peak torque and HP this is great)
60 MPH 3rd gear 2,650 RPM (great)
55 MPH 3rd gear 2,450 RPM (at peak torque not great) my biggest concern with this is for example I'm going up a hill or on the pass, I'm maintaining 60 MPH and have to slow down a bit for whatever reason to 55 or 50 I'm going to get under peak torque which may end in down shifting to 2nd and having to stay at or below 50 MPH for the duration of the hill.
If re-geared to 4.56
65 MPH 3,200 RPM (great within torque to horse power range, but my concern is a little high if for some reason I had to drive 65 for extended period.)
60 MPH 2,900 RPM (great within ranges)
55 MPH 2,700 RPM (great within ranges)
50 MPH 2,500 RPM (a little low but still with in ranges and now we are slow enough to reduce wind drag so if I'm pulling a hill at this speed I feel I'd be likely to be able to maintain it).
I understand it's 305 not a 454 and no I will not throw away a perfectly good 305, just because it is under powered, when the 305 is worn out I may consider BB or may go to 350, I'll cross that bridge when I get there, for now I want to get the most out of what I have. Will I modify the 305 slightly maybe, it's currently stock except for the carburetor, for right now I just need to make a gearing choice.
So with the 4.10 my main concern is if I'm on a hill and end up in the 50 -55 MPH range, I maybe forced to slow down more in order to downshift to 2nd and then would have to maintain a lower speed. End of the world no, concern yes.
4.56 would be better for maintaining various hill climbing speeds as outlined in my chart, and also for getting the load moving, my biggest concern with the 4.56: Towing in Washington the speed limit is 60MPH on freeways, while for cars it's 70, sometimes it is simply necessary to go a bit over 60 to keep up with traffic, at least for short periods, will I feel comfortable turning 3,200 RPM or possibly a little more for "a while" on the freeway if necessary? I know GM put 4.56's in 1 tons with 3 speed auto trannys and manuals, so that gives me some comfort but that was also in the day of 55 MPH speed limits for all.
With the 700R4 overdrive makes the high RPMs of the 4.56 a non-issue when I'm not hauling and running unloaded driving 70+ should not be a problem.
4.10 or 4.56 your thoughts?
The truck 1984 C-20, what was thought to be a 350 turns out to be a 305 after looking at the block numbers. Truck has the 700R4 with temp gauge and cooler and it is in good health, automatically locks converter in OD or has manual switch to engage lockup in 3rd. Current axle ratio is 3.41, stock 31" tires.
The trailer, 18' open car hauler type, but rarely used for cars. Most common loads are, my small tractor gross trailer weight about 5,000Lbs, or feed hauls where the trailer gross is around 6K.
Terrain, hills, lots of them when there isn't hills there's mountain passes that's just the way it is here. Some secondary roads, some freeway use.
Look I know a 305 isn't going to break any land speed records especially with the trailer loaded, but with the current 3.41 gears it will haul it, just not very well. I'm looking to go to either 4.10 or 4.56, I keep looking at the numbers but can't seem to decide so I'm hopeful that someone will look at the numbers or have some personal experience and say something that will get me to make a damn decision and move forward one way or another.
Numbers:
305 makes peak torque 245 @ 2,400RPM, peak horsepower 145 @ 3,800RPM so at the very least we want to keep the RPM within those ranges when towing, but also best if not right up against either end. I tend to like to keep it right around 60MPH on the highway with trailer, both because that's the law and where it feels comfortable, control wise.
current RPM with 3.41
65 MPH 3rd gear 2,400 (at peak torque, not ideal and above preferred cruse speed)
60 MPH 3rd gear 2,200 (below peak torque this is terrible, preferred cruse speed)
55 MPH 3rd gear 2,000 (below peak torque even worse)
If re-geared to 4.10
65 MPH 3rd gear 2,900 RPM (between peak torque and HP this is great)
60 MPH 3rd gear 2,650 RPM (great)
55 MPH 3rd gear 2,450 RPM (at peak torque not great) my biggest concern with this is for example I'm going up a hill or on the pass, I'm maintaining 60 MPH and have to slow down a bit for whatever reason to 55 or 50 I'm going to get under peak torque which may end in down shifting to 2nd and having to stay at or below 50 MPH for the duration of the hill.
If re-geared to 4.56
65 MPH 3,200 RPM (great within torque to horse power range, but my concern is a little high if for some reason I had to drive 65 for extended period.)
60 MPH 2,900 RPM (great within ranges)
55 MPH 2,700 RPM (great within ranges)
50 MPH 2,500 RPM (a little low but still with in ranges and now we are slow enough to reduce wind drag so if I'm pulling a hill at this speed I feel I'd be likely to be able to maintain it).
I understand it's 305 not a 454 and no I will not throw away a perfectly good 305, just because it is under powered, when the 305 is worn out I may consider BB or may go to 350, I'll cross that bridge when I get there, for now I want to get the most out of what I have. Will I modify the 305 slightly maybe, it's currently stock except for the carburetor, for right now I just need to make a gearing choice.
So with the 4.10 my main concern is if I'm on a hill and end up in the 50 -55 MPH range, I maybe forced to slow down more in order to downshift to 2nd and then would have to maintain a lower speed. End of the world no, concern yes.
4.56 would be better for maintaining various hill climbing speeds as outlined in my chart, and also for getting the load moving, my biggest concern with the 4.56: Towing in Washington the speed limit is 60MPH on freeways, while for cars it's 70, sometimes it is simply necessary to go a bit over 60 to keep up with traffic, at least for short periods, will I feel comfortable turning 3,200 RPM or possibly a little more for "a while" on the freeway if necessary? I know GM put 4.56's in 1 tons with 3 speed auto trannys and manuals, so that gives me some comfort but that was also in the day of 55 MPH speed limits for all.
With the 700R4 overdrive makes the high RPMs of the 4.56 a non-issue when I'm not hauling and running unloaded driving 70+ should not be a problem.
4.10 or 4.56 your thoughts?
