Is the low ratio gearset worth it for a street truck?

I am building a 472" truck engine for my street truck.

Vehicle breaks down as:

1979 F250 Supercab 4x4
Wt: 5300
Engine: Iron headed 472...prob 375-400hp/500ft-lbs
Tires: 35"
Gears: 3.55


I am considering having Broader Performance build me a C6 with his truck valve body and truck convertor.

Not sure if I need to spend the extra coin on the low ratio gearset or not. (aka..will I notice the difference)


Truck usage as:

95% hauling 500lbs or less
4% hauling 500lbs-3000lbs
1% towing up to 10000.

total mileage/yr : about 2500 (aka...not much)


So given the above parameters....would the low-ratio gearset be a noticable upgrade in driveability? Right now with an anemic 351m making 175hp it doesn't feel like it needs more gear in first....

It's about a 12% increase in ratio in first...so those 3.55's would be like 4.00.


Thoughts?

I cut some firewood over the weekend and was out in my slightly rutted field...wishing I had either more rear gear or put it in 4-low.


Anyway...think i will just go "all-in" on this trans and get the low ratio gear set as well.

Let us know how it goes when you get it done. Sounds good for a on-off road truck, lower gearing for off road and a good "highway" gear when you get back on good roads.

somethingclever wrote:I am building a 472" truck engine for my street truck.

Vehicle breaks down as:

1979 F250 Supercab 4x4
Wt: 5300
Engine: Iron headed 472...prob 375-400hp/500ft-lbs
Tires: 35"
Gears: 3.55


I am considering having Broader Performance build me a C6 with his truck valve body and truck convertor.

Not sure if I need to spend the extra coin on the low ratio gearset or not. (aka..will I notice the difference)


Truck usage as:

95% hauling 500lbs or less
4% hauling 500lbs-3000lbs
1% towing up to 10000.

total mileage/yr : about 2500 (aka...not much)


So given the above parameters....would the low-ratio gearset be a noticable upgrade in driveability? Right now with an anemic 351m making 175hp it doesn't feel like it needs more gear in first....

It's about a 12% increase in ratio in first...so those 3.55's would be like 4.00.


Thoughts?

No. If the 351M is working now the 472 will work much better.

PS: Match your torque convertor to your cam and intended usage.

Another thing to consider is that you went from a 31" tire (@stock size) to a 35" tire so you went up @10% so any gear change will help if you do it in the transmission or if you do it in the differentials. The low gear set for the transmission costs less then a set of gears and has a 6 pinion planetary.

For the truck application why not just put in the OD transmission it already has the gears and an OD to boot?

Oh yeah and if you're thinking about changing gears in the differentials don't forget that some diffs may require a new carrier depending on what gear you're planning on using.

http://www.differentials.com/technical-help-2/carrier-breaks/

I am not looking to re-gear the truck diff's....they are both in good condition.

The trans is showing some age so it needs rebuilt.

I am not sure whats involved with converting to an OD transmission in this application.

If it's bolt-on to NP205 and mounts the same as C-6 and only needs a stand-alone controller, I would consider it.

I am not looking to make this a big project....tough enough to find time for engine/trans swap much less build custom stuff while I'm at it.



Anyone know the particulars of swapping in automatic OD in this truck?

Did a little looking online.

Dave McClain was considering this for his 79 2wd...i will have to PM him to see if he went through with the swap.


The short of it is;

Trans is 4" longer
Requires custom/modified cross member
Requires longer front driveshaft
Requires shorter rear driveshaft
Requires shift linkage modifications/fabrication
Requires $600 controller and wiring kit
Requires TPS adapted to carb
May require exhaust modifications (was going to do those anyway)


At the end of the day this is more screwing around than I am looking for at the moment. Plus of course I just rebuilt both driveshafts complete and setup all linkages properly...etc. I am sure the swap mileage improvement would be nice....maybe even 2-3 mpg...sounds like a payback of 4-5 yrs in fuel costs at $3/gal.

I don't have time to do stuff once, much less twice.

somethingclever wrote:Did a little looking online.

Dave McClain was considering this for his 79 2wd...i will have to PM him to see if he went through with the swap.


The short of it is;

Trans is 4" longer
Requires custom/modified cross member
Requires longer front driveshaft
Requires shorter rear driveshaft
Requires shift linkage modifications/fabrication
Requires $600 controller and wiring kit
Requires TPS adapted to carb
May require exhaust modifications (was going to do those anyway)


At the end of the day this is more screwing around than I am looking for at the moment. Plus of course I just rebuilt both driveshafts complete and setup all linkages properly...etc. I am sure the swap mileage improvement would be nice....maybe even  2-3 mpg...sounds like a payback of 4-5 yrs in fuel costs at $3/gal.

I don't have time to do stuff once, much less twice.  

I would rebuild the C6 with good parts and likely a 2,200-2,400 convertor and call it a day. With the 3.55 gears and 35" tires you are close to already having overdrive with a C6 and I doubt you would pick up much gas mileage especially when loaded with a 4 speed OD. If the engine has a RV or mild Performance cam the 4 Spd. OD with your gears and tires size would likely be under it peak cruise speed for optimum gas mileage at legal highway speeds also.

http://www.wallaceracing.com/calc-rpm.php

I come up with 1,670rpm at 70 mph with the OD trans. 2,386rpm with the C6 plus add a little for slippage of the convertor since they don't have lockup. If you like to do a lot of long distance high speed freeway flying, then the OD would be very nice.

I have a 71 f250 4x4 that I just converted over to an e4od and 4407 transfer case and I can tell you that it was more than I originally bargained for. I had just planned to do the c6 and 205 and it fit in there nicely, but the e4od and 4407 case are much longer and larger altogether. I had to cut out crossmembers and have new ones made and had to notch out part of the lower frame rail to fit the case. I have mine down to the frame so it wasn't too bad but it sounds like more than what you're trying to do. I think you'll be in good shape with what you are doing. If it were me I'd put lower gears in it but even with 3.54 it should be ok

You can also put a lower 1st gear in the trans to help out the final gear ratio. E40D gears or Jay at Broader has different gear ratio's for the C-6