3.55 or 3.73 Gear Change Effects

Reply Subscribe

Thread Tools

Search this Thread

01-16-2017, 09:27 AM

#41

fishslayer143

Drifting

Member Since: Aug 2009

Location: new iberia la

Posts: 1,346

Likes: 4

Received 156 Likes on 143 Posts

Quote:

Originally Posted by jb78L-82

Wow...sounds great!

I think with an auto, the 3.70 is probably spot on. With 525 HP with a 5/6 speed, if it was me, I would aim for 1,800-2,200 RPM @ 80 mph and some on the forum have achieved 25+ MPG.....

I love it.. with my big cam, the 3.73 gear works great.. I can go 40mph in OD without issue and I have exceeded 160mph too. I m happy with the mpg, if I m going out of state I ll drive my C5 .. 29mpg!

Reply Like

01-16-2017, 01:05 PM

#42

Kacyc3

Drifting

Member Since: Jun 2012

Location: Port St. Lucie Fl

Posts: 1,988

Likes: 16

Received 184 Likes on 158 Posts

I didn't see anyone suggest keeping his 308s and going to the richmond 5spd non OD that has the gears to work with his 308s

Reply Like

01-16-2017, 01:32 PM

#43

Cool bean

Racer

Member Since: Jan 2015

Location: Woodbury NJ

Posts: 314

Likes: 150

Received 48 Likes on 44 Posts

I was happy to see this post come back to life like Lazarus. I read it back when doing research for the 700r4 swap and find it helpful to have the progression of upgrades in one post.

Way back in post #17, Fast81 listed a setup much like what mine is has evolved to. To answer the question, here's all the variables that went into my decision:

74 Coupe, L48 / TH400 / stock converter (2000 stall) / 3.08 is now:
355 with about 400hp/400tq at the crank. Aluminum heads, 64cc chamber, 195 runners, 10:1, 1.75 headers, 2.5 exhaust out the back. 700r4, 2800 stall converter with electric lockup.
Cam is CompCams 12-601-4 (2200-6100, 107 lsa, 287/305, 235/249 @0.050,) installed straight up.

The rear is still a 3.08, but the spare core I sent to Mike in Galveston is currently being reborn as a HD-3.73. 'Can't wait...even more so now after reading this thread.

I wanted the cruising speed at approx 70 to be right where the cam comes alive. We'll see if the plan is successful.

Everyone that shared their knowledge over the years helped me make this decision. Thank you! I'm looking forward to reporting back about what kind of scores I got on the seat-of-the-pants charts.

Last edited by Cool bean; 01-16-2017 at 01:33 PM.

Reply Like

01-16-2017, 09:25 PM

#44

fishslayer143

Drifting

Member Since: Aug 2009

Location: new iberia la

Posts: 1,346

Likes: 4

Received 156 Likes on 143 Posts

Quote:

Originally Posted by Kacyc3

I didn't see anyone suggest keeping his 308s and going to the richmond 5spd non OD that has the gears to work with his 308s

I did that in the 80s.. 3.08 s with a Doug Nash 5spd with a low 1st and 1:1 for 5th gear .. its worked but the early Doug Nash 5spds were difficult to shift at WOT .. they are better now , If he wants a manual trans for fun.... an Automatic will always be faster

Reply Like

01-16-2017, 10:46 PM

#45

Alwyn678

Team Owner

Member Since: Jun 2001

Location: Thomson Georgia

Posts: 43,095

Likes: 365

Received 143 Likes on 126 Posts

Quote:

Originally Posted by fishslayer143

If your goal is to eventually go to OD trans, I would go 3.73... My 81 started with factory 2.87... a joke with 185HP .. I went to 3.31 and it helped somewhat.. I then went to 525HP and 700r4 .. 3.31 was just too low in OD .. I yanked it out, went to 3.73 and it was perfect.. very strong, and with a 26 inch tire, I m only turning 2550 RPM at 80 MILES PER HOUR ..and I get 18-19 mpg hiway

I also have the 3:73 gears. What a fantastic change. I switched from a Th-400 w/3:08 to a 700R4 w/3:73.

Best two changes I did for my 74.....along w/ New Heads and Cam...Demon carb also does Not hurt, while we are at it.