isosceles

I'll be installing a new diff in 2 weeks. I currently have a 3.70 with a TH350. When I go to the track it is 100 miles away, mostly highway speed of at least 70 mph. My ultimate plan is to get a 2004r maybe within a year, then a 383 crate motor when finances permit. Think a 383 with a 200r4 and a 3.08 is capable of low 13's?
The lower RPM's of a 3.08 sure look appealing, but how badly will it hurt my acceleration? Does a 383 have enough low end torque to overcome a 3.08? The 200r4 as a little higher gearing in 1st and 2nd than the TH350. I've posted some speed/gears below based on 255/60/15 tires.
I'd really appreciate the opinion of the forum.
3.70 with TH350
Gear 1 2 3
1000 8 14 21
1500 13 21 32
2000 17 28 43
2500 21 35 53
3000 25 42 64
3500 30 49 74
4000 34 56 85
4500 38 63 96
5000 42 70 106
5500 46 77 117

3.08 TH350
Gear 1 2 3
1000 10 17 26
1500 15 25 38
2000 20 34 51
2500 25 42 64
3000 30 50 77
3500 35 59 89
4000 41 67 102
4500 46 76 115
5000 51 84 128
5500 56 92 141

3.70 200R4
Gear 1 2 3 4
1000 8 14 21 32
1500 12 20 32 48
2000 16 27 43 64
2500 19 34 53 79
3000 23 41 64 95
3500 27 47 74 111
4000 31 54 85 127
4500 35 61 96 143
5000 39 68 106 159
5500 43 75 117 175


3.08 200R4
Gear 1 2 3 4
1000 9 16 26 38
1500 14 24 38 57
2000 19 33 51 76
2500 23 41 64 95
3000 28 49 77 114
3500 33 57 89 134
4000 37 65 102 153
4500 42 73 115 172
5000 47 81 128 191
5500 51 90 141 210

Fevre

200r4 with your current 3.70, don't go with the 3.08, maybe 3.55

Jack71

I'd go 336 or 355. I have the 336 with a 700r4 and it VERY highway friendly.

Glensgages

isosceles:
I don't know that particulars of your 383" SBC, but I can offer some info...

#1: A buddy had a 406 w/ CompCams' 268H cam, 'junk' heads, Victor Jr., 750 Holley, etc., backed with a THM400, 'on-sale' 11" converter, 3.08 gears, & 'sticky-streets' in his '71 Camaro.
He'd drive it ( on REAL tires!!! ) 200+ miles to go drag racing, run 13-flats, and drive it back home again, on pump gas...
The 'long-arm' makes GOBS of torque; gearing won't be NEARLY as critical.

#2: I put 3.73s in my other-wise stock '82 Cross-Fire last year, with the 700R4 AOD/4.
With 255/60R15 (approx 27" tall), in OD w/ lock-up, my RPM at 75 MPH is close to 2500, not TOO bad.
I'm not sure what the 200-4r ratio is in 1st Gear, but the 700R4 is 3.06:1, which, combined with 3.73s (or even 3.55s), might multiply the torque TOO much for street tires...

Hope this helps!!!
:thumbs:


[Modified by Glensgages, 8:52 PM 3/2/2004]

American Boy

:withstupid: I have 3,07 rear gear with a lot of low end torque from a roller cam vortec headed 350 and I want more gear. It's not that bad since I ran around 13.50 through stock manifold and 2-1-2 exhaust but my 3.54 rear end will really wake the car up. With a 383 and a mildy cam, I would go with 3.36. With the overdrive it would be awesome. That will be my next move after the exhaust and gear.

Stephan

LT1driver

I would go with 3.36 or 3.55 myself :cheers:

comp

the 200r4 has a lower over-drive than the 700, if you use to high of a rear
gear you will kill it in OD,go 3.70's :thumbs:

aharte

I have 3.08 gears with a 700r4, and 4th gear is gutless. I never use it. If you're going to get an overdrive, stick with the deaper ratio.

GrandSportC3

I voted 3.70's even though there are no 3.70's available for Vettes..

There are only 3.73's :p:

redwingvette

I changed from the 3.08 to 3.55 about 7 years ago. Now that I have the 200R4 I wish I had 3.70. She runs great from 0-130 but it isn't a race car. The 383 should be :cool: 0-60 is still slow 7-8 sec.

Eddie 70

I am not a drag racer, so I can't really comment on the drag race part. But I do have .68 OD and 3:36 gears. On the highway, 80 MPH is approx 2000 RPM. My rear tires are 255/60/15 BFGs. I do like the cruise mode of this car. :thumbs:

Fevre

Factory came with a 3.70 and you can Richmond 3.70's so I guess I have to throw up the :bs flag, sorry. :(

" Ring Gear and Pinion, 1963-79 Corvette, 3.70:1 Ratio"


http://store.summitracing.com/partde...=RMG%2D4900231

allancook5

I'm runin 2.72's its a little slouchy off the line but man does that thing perform on the highway

isosceles

Must be a typo in the Spring Eckler's Catalog. :eek: If Van Steel has one in stock, I'll buy it there, if not Ecklers. Since they're both in FL, I'll save a ton on shipping.

isosceles

hmm, maybe no typo after all....I know they list a 3.73 for 80-81.
I dunno, with 93 octane gas approaching $2.00 per gal, I'm those 3.08's are looking good. With a previous post showing it's possible to get low 13's on street tires with that rear end, I'd be happy. Might take an average and get 3.55's or 3.36's. Some of it is going to depend on supply.
This would temporarily alleviate the tendency my motor has for running 220 on the highway above 3K rpm.