Gear Vendors

[Blue Ox]

He's not running TBI. He's got what you might call a mechanical multiport system.

And yes, I'm being a wise@$$.

 

[Blue Ox]

Yeah, it's a big block!

Maybe PIG Block would be more accurate.

 

[glockholiday]

Looking at the best case scenario going from 10 MPG to 12 is a 20% improvement. What was he expecting?

20% is way better than any mod for any vehicle ever but not for the $2500 he had in it with brand new parts and install back in the 90's.

I would compare pricing to regear front and rear diffs.

 

[roundhouse]

Just get some taller tires
Lot cheaper
Accomplishes the same thing

 

[bucket]

20% is way better than any mod for any vehicle ever but not for the $2500 he had in it with brand new parts and install back in the 90's.

I would compare pricing to regear front and rear diffs.

But then you lose grunt at lower speeds. Which often reduces economy, depending on driving style and terrain.

 

[Blue Ox]

This. ^^^^

Gearing is only equivalent at higher speeds. Gearing high compromises acceleration, pulling power and may increase engine loading which will lower fuel economy.

 

[78C10BigTen]

So while were talking gears.... my c10 is runnin a bone stock 350/th350 and a broken 3.08 gov bomb. It chugs gas on the highway turnin about 2900rm at maybe 75..??? (Speedo dont work) so my question is how would it affect my mileage if i switch to a 3.73 posi? Ive also looked at gear vendors but coming in a $3k thats not a viable option.

 

[Blue Ox]

Let's see, a 21% reduction in gearing, 21% increase in RPM 2900 * 1.21= 3509.

Rough math, but how do you think your mileage will go at 3500 RPM?

I looked at the power curves for a LD 350 in 1978 and that's getting near peak HP. Not that you will be at WOT, but rule of thumb is engines tend to be most efficient around peak torque which is 2400. That is probably near where that engine would be with your 3.08s at the 1978 national speed limit of 55 MPH.

 

[78C10BigTen]

Let's see, a 21% reduction in gearing, 21% increase in RPM 2900 * 1.21= 3509.

Rough math, but how do you think your mileage will go at 3500 RPM?

I looked at the power curves for a LD 350 in 1978 and that's getting near peak HP. Not that you will be at WOT, but rule of thumb is engines tend to be most efficient around peak torque which is 2400. That is probably near where that engine would be with your 3.08s at the 1978 national speed limit of 55 MPH.

Problem there is i dont do anywhere near 55 lol plus im running 31x10.50x15s ive never had a truck with this low of a rear gear so. My last truck had a carb'd 350 with 700r4 and a 3.73 and seemed good( yes i know the 700 is an od) many people bitch about the 700R but i liked it.

 

[Blue Ox]

700R4s, they were wonderful when they worked.

But you see the advantages of the OD. Nice low gearing for pulling and acceleration, but the OD allows economical cruise at higher speeds. Best of both worlds.

 

[78C10BigTen]

700R4s, they were wonderful when they worked.

But you see the advantages of the OD. Nice low gearing for pulling and acceleration, but the OD allows economical cruise at higher speeds. Best of both worlds.

Ill have to ask it in the right thread but how much hassle is it to replace the th350 with the 700R? Sucks because i have a good 700R but its attached to a Tcase.

 

[84 M1008]

I'm going to bite the bullet and go for a new GV unit instead of a transmission swap. A 700R4 is out of the question as I had one in my M1031, and would have to find a 27 spline transfer case and the elusive trans valve cable bracket. Bottom line is, even though I never had any problems with the 700R4, in the back of my mind I never trusted it. The 4l80 is an option but again, it's just too labor intensive and electronic transmissions are really not my thing. I'm sticking with the bullet proof TH400 with a GV behind it.

 

[78C10BigTen]

I'm going to bite the bullet and go for a new GV unit instead of a transmission swap. A 700R4 is out of the question as I had one in my M1031, and would have to find a 27 spline transfer case and the elusive trans valve cable bracket. Bottom line is, even though I never had any problems with the 700R4, in the back of my mind I never trusted it. The 4l80 is an option but again, it's just too labor intensive and electronic transmissions are really not my thing. I'm sticking with the bullet proof TH400 with a GV behind it.

Any idea what transfer cases are 27 spline?

 

[84 M1008]

27 spline transfer cases were used behind the TH350 transmissions. TH400 has a 32 spline output shaft.

 

[84 M1008]

Also, a 32 spline 208 input shaft can be swapped out for the 27 spline input shaft. The case must be split to do this.