3:08 to 3:70 Gears?
Thread Starter
Racer
Joined: Nov 2006
Posts: 435
Likes: 7
From: Wake Forest NC
3:08 to 3:70 Gears?
I'm pretty sure this is the route I'm going. TH400, stock converter, and a mild upgrade to an L48. If anyone has made this change, how drastic of an improvement in acceleration (highway windup is irrelevent)? With stock 3:08s, my F350 will probably kill me in acceleration.
Le Mans Master
Joined: Oct 2001
Posts: 6,798
Likes: 25
From: Pine Bluff Arkansas
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15-'16-'17-'18-‘19-'20-'21
I have 3:55's(or 3:50's?) with a 700r4, which with its first gear is about the limit.
Larry
Race Director
Joined: Nov 2000
Posts: 11,872
Likes: 12
From: Waterloo ontario Canada
You'll notice alot more acceleration but also alot more noise, higher fuel consumption, heat but again better off the line acceleration.
Your top end and highway cruising will suck.
You really need the 700R instead.
Your top end and highway cruising will suck.
You really need the 700R instead.
Melting Slicks
Joined: Jun 2002
Posts: 2,844
Likes: 99
From: Orrtanna Pa.
I made that change ten years ago and with the 355 averaged 17 mpg commuting 400 miles weekly. As posted the highway cruise sucks,taching 3000 at 65 mph. I stay closer to 60 anyway due to the 55 mph speed limit,plus the "hotrod" look my car has draws a lot of Police attention anyway.
For what it's worth I ran a Comp 268H cam with my 355 and it was a fairly spunky combination for a 355.(At the time also was running a B&M th350/2000 Holeshot converter,which isn't much stronger off the line than a stock converter)
For what it's worth I ran a Comp 268H cam with my 355 and it was a fairly spunky combination for a 355.(At the time also was running a B&M th350/2000 Holeshot converter,which isn't much stronger off the line than a stock converter)
Team Owner
Joined: Apr 1999
Posts: 21,953
Likes: 1,445
From: Reno Nevada
2024 C3 of the Year Finalist- Modified
more TQ and HP is what you really need to address
Last edited by gkull; Apr 9, 2007 at 01:10 PM.
Le Mans Master
Joined: Jan 2004
Posts: 8,295
Likes: 30
From: one night in Bangkok you are never lonely
I changed from 3.70 to 3.08. With my 4 speed manual cruising at 85-90 the engine was tacking 4,000 and for long trips it was too much fuel and heat now it is still good light to light and decent on the high ways. 
Over here if your not going 85 cement trucks pass you up.
Over here if your not going 85 cement trucks pass you up.
Le Mans Master
Joined: May 2002
Posts: 5,086
Likes: 787
From: Lebanon Township New Jersey
Changing from 3.08 to 3.73 gears in my car lowered my quarter mile times by half a second.
Like gkull said though, gearing is most critical for standing start acceleration. From a rolling start you might be able to downshift to low gear with 3.08 rear, while with 3.73 gears you might only get down to second.
Like gkull said though, gearing is most critical for standing start acceleration. From a rolling start you might be able to downshift to low gear with 3.08 rear, while with 3.73 gears you might only get down to second.
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Safety Car
Joined: Oct 1999
Posts: 4,101
Likes: 10
From: NorCal
My favorite..
3.73's are great for all-around fun. Yes, the mileage is worse, and hiway cruising is just OK, but for a good launch and great middle speed response, they're hard to beat on a street car. Gear multiplication is one of the easiest performance upgrades there is, and if you ad an OD trans, you get the best of both worlds.
I ran them in my old '64 GTO with a 12 bolt and a THM 400 auto. Good for 12.8 on cheater slicks, and my GF drove it to college during the week. Lots of fun!
Hans
I ran them in my old '64 GTO with a 12 bolt and a THM 400 auto. Good for 12.8 on cheater slicks, and my GF drove it to college during the week. Lots of fun!
Hans
Team Owner
Joined: Apr 1999
Posts: 21,953
Likes: 1,445
From: Reno Nevada
2024 C3 of the Year Finalist- Modified
My 79 came with 3.55 gearing. IMO without an OD tranny it has good exceleration and exceptable rpm going down the road. I have a 4.11 in my Vette and it would drive me nuts without an OD tranny. In fact some times even wish that I had one more gear to get down to a 2.40 overall gearing.
Melting Slicks
Joined: Sep 2004
Posts: 2,655
Likes: 19
Followup question, my 4 speed manual car had a 3.08 rear end put in it somewhere in its life. I actually like it on the highway, where I do most of my driving.
But is there any lower 1st gears ratios available for the 4 speed, to increase my off line acceleration?
But is there any lower 1st gears ratios available for the 4 speed, to increase my off line acceleration?
Safety Car
Joined: Oct 1999
Posts: 4,101
Likes: 10
From: NorCal
Don't see why not (been a while since I did a T-10), but it would be pricey since you also need the cluster gear to match the new first gear. With the money you spend you could be half way to a modern OD trans.
Hans
Hans