Reaching out to the community for information, guidance, and advice.
So here's the back ground of where I am now and what I would like to do possibly:
Start point 1974 FJ40 F.5 J30, 4.11 diff, 31.10.5R15 tires
- Upsized tires to 235/85R16
- Replaced J30 with 81 FJ60 H42/34MM split transfer case
- Mark A carb, seems to run on the rich side by the smell but it is a great improvement over the stock Chinese carbs or a Weber. Plus the secondary circuit is very noticeable, big difference on how the truck runs
- Dobinsons 2" lift, 2 degree caster shim
My COVID project is now mostly done (if there is such a thing), I now drive it to work when time permits and plan to eventually use on mild trails. This is my first build and don't really have a point of reference on what is considered sound or right. It does get loud above 2.5k rpm, I have sound deadening in the hard top cap and raptor lined floors that has made it easier to converse at a mild yell level. I will be pulling the headers and adding a 3FE exhaust manifold with a new exhaust over the winter. I dont want to add any more sound deadening stuff, its a rolling tin can shaped in the form of a brick and I know this. I am more focused on fine tuning the drive line.
Overall the truck runs great, just seems like its running hard to go above 55. It will do 70 with a good run up without an issue but over 3k rpms seems like I am pushing it hard. Its right about 3k at 65 now. I drove diesel trucks for most of my life and I am more accustomed to the lower rpm band. Here are the ideas I have running through my head:
Option #1 (5spd) - I really don't see the need to install a 5 spd, the first gear is lower than what I have now and would be a waste unless I either add an overdrive gear to the split case (38mm case) or swap out the diffs for 3.73s, the overdrive is less than a 9-10% diff (.85) from 4th gear (1.0)
Option #2 (taller tires) - I have the wheel well space for 255/85r16s tires, staying with my current H42 and 4.11 diffs I am guessing this will drop my ratio enough to almost equate either the transfer case OD or re-gearing of the diffs. Will this affect my take off in 1st gear enough to be similar to the J30 first gear ratio (not a fan of the 1st gear ratio in the J30)
Option #3 (split case OD) - also contemplating keeping my H42 and replacing my 34mm case with a 38mm case and adding the 10% overdrive gear while keeping the 4.11s
Option #4 (Diff re-gear) - re-gear both diffs to 3.73 and keep 235/85r16s. Basically same ration as a FJ60. Guessing this may hurt me on trails.
Option #5 (Good enough) - Stop tinkering and trying to fine tune this truck.
know there are many ways to tackle this. It could also be a combination the options available. I do not want to add an additional overdrive transmission. Feel free to add your thoughts and advice on what was tried and what I should avoid.
So here's the back ground of where I am now and what I would like to do possibly:
Start point 1974 FJ40 F.5 J30, 4.11 diff, 31.10.5R15 tires
- Upsized tires to 235/85R16
- Replaced J30 with 81 FJ60 H42/34MM split transfer case
- Mark A carb, seems to run on the rich side by the smell but it is a great improvement over the stock Chinese carbs or a Weber. Plus the secondary circuit is very noticeable, big difference on how the truck runs
- Dobinsons 2" lift, 2 degree caster shim
My COVID project is now mostly done (if there is such a thing), I now drive it to work when time permits and plan to eventually use on mild trails. This is my first build and don't really have a point of reference on what is considered sound or right. It does get loud above 2.5k rpm, I have sound deadening in the hard top cap and raptor lined floors that has made it easier to converse at a mild yell level. I will be pulling the headers and adding a 3FE exhaust manifold with a new exhaust over the winter. I dont want to add any more sound deadening stuff, its a rolling tin can shaped in the form of a brick and I know this. I am more focused on fine tuning the drive line.
Overall the truck runs great, just seems like its running hard to go above 55. It will do 70 with a good run up without an issue but over 3k rpms seems like I am pushing it hard. Its right about 3k at 65 now. I drove diesel trucks for most of my life and I am more accustomed to the lower rpm band. Here are the ideas I have running through my head:
Option #1 (5spd) - I really don't see the need to install a 5 spd, the first gear is lower than what I have now and would be a waste unless I either add an overdrive gear to the split case (38mm case) or swap out the diffs for 3.73s, the overdrive is less than a 9-10% diff (.85) from 4th gear (1.0)
Option #2 (taller tires) - I have the wheel well space for 255/85r16s tires, staying with my current H42 and 4.11 diffs I am guessing this will drop my ratio enough to almost equate either the transfer case OD or re-gearing of the diffs. Will this affect my take off in 1st gear enough to be similar to the J30 first gear ratio (not a fan of the 1st gear ratio in the J30)
Option #3 (split case OD) - also contemplating keeping my H42 and replacing my 34mm case with a 38mm case and adding the 10% overdrive gear while keeping the 4.11s
Option #4 (Diff re-gear) - re-gear both diffs to 3.73 and keep 235/85r16s. Basically same ration as a FJ60. Guessing this may hurt me on trails.
Option #5 (Good enough) - Stop tinkering and trying to fine tune this truck.
know there are many ways to tackle this. It could also be a combination the options available. I do not want to add an additional overdrive transmission. Feel free to add your thoughts and advice on what was tried and what I should avoid.
