I have an 88 IROC with the 350, you can see the mods in my sig, nothing big as you can see.

I have a 9-bolt rear and I getting ready to change out the 2.77 gears, series 2 posi, and rear cover. I have 3.27 gears to put in, series 3, and waiting for TA to finish the girdle.

I am about to put on AS&M LTR siamesed runners, ported plenum to match. Should I go with 3.70 gears? I would really prefer and think that 3.45 gears would complement my setup now and in the future, but I can't find any 3.45 gears for sale, all I can find is the entire rear and usually for too much.

I personally think that the 3.70 would push me out of my power band too quickly and would be a waste, but a friend disagrees and this is where the question came from.

Thanks guys.

 

I'm no expert, but with a TPI setup and an auto, you're probably right about 3.70's being "too high". Is this a daily driver? If so, that would absolutely kill any kind of gas mileage as well. I've got the 3:42 rear (still a 10 bolt) in my 91 Formula T-5 383SR, and would not go over a 3.70 if/when I change mine out (and auto's typically have lower gears than my manual). If this is pretty much a strip only car or sees relatively little driving time, the higher gears might be fun to drive but still probably lose performance on the strip in the 1/4 (probably be real good for an 1/8th strip tho)

Just my , YMMV.

 

I've been running 3.70 rear gears for several years now, and I do not feel that the gear ratio puts me out of the power band too soon.

If fuel mileage is very important to you, go with the 3.27s.

I think that run better ETs with the 3.70s.

 

Any 3 series gears will work fine for you. I have 4.10's in my 95LT1 and they are fine even for daily driving. Gas mileage isnt what it should be for the city but oh well. It's better on the highway. I can cruise at 2000/2200rpms in 6th gear on the highway.

 

Yeah - but he has an auto. The 6 speeds are known for handling a much higher rear ratio - they need it due to their gearing.

But that's just my opinion, Capt.!

 

Correct me if I am wrong..but, your 700r4 has a first gear ratio of 3.06 or 3.08? This is somthing to keep in mind, because the idea is to not have too steep rear gears with a steep 1st gear in the trans. Thats why guys with TH350s are getting away with 4.10s, because I believe their 1st. ratio is, like a , 2.60. The 3.42 is probably the most gear I would install. And this is from experience. You want you gears to keep the engine in its sweet spot. I installed 3.50s in my 9in. because of this....Tom

 

Appearently you want to stay around mid 10s in the calculation (first grear x rear ratio). Since 3.70 would be 11.3, the first gear would be a little challenging for first gear. 3.45s in this calculation is 10.557 which is prefect.

I really want some 3.45 gears, I have seen two rear ends for sale, one for $400 and the other for $900. The one for $400 won't ship from new jersey to Texas and the other lives about 12 miles from me, but I'm not paying $900 for a 9-bolt rear.

 

i asked this question in the DRAG racing section and got the response that if i plan on changing my intake (which i do) then go with 3.70's.

i feel 3.45's are ideal for most all setups with 700r4 except the miniram combos with peak powers above 6000rpms. LOL

those LTR siamesed tubes could allow you to rev to 5500rpms. if thats the case, i would say go with the 3.70's. i plan on doing that myself. i got 3.27's to go in next spring and still considering a 3.70 gearset. LOL mine is a daily driver and gas is a concern. i also got a 2800rpm stall so i feel 3.70's may be a tad big. traction off the line may be limited too and i dont want to lose that.

http://www.speedworldmotorplex.com/calc.htm
according to this, with .7 overdrive and 3.70's, your doing 2000rpms at 60mph. not all that bad, especially with lock up converter. with 3.27's, your doing 66mph at 2000rpms so thats close to 1800rpms for 60mph. not much of a difference. compare that to 2.77's as you and I got now. LOL your doing 60 at 1500rpms. i would do 3.70's

 

Well, since I'm doing an LTR setup and keeping the auto, I need to stay below 3.6 ratio, there are only two there 3.27 and 3.45.

 

You have a 9-bolt rear end, as I do. My stock ratio was 3.27. I do not think that 3.45 gears are available for ther 9-bolt, at least they were not available to me when I research this about 6-7 years ago. Therefore, I think that you are limited to 3.70 or 3.27.

Yes, we have a steep first gear in the 700R4s, as listed above around 3.08,,,, so maybe you have answered your own question, go with the 3.27s.

 

you can buy 3.70's from reider racing for 295.99 and i believe Yukon gear makes them as well. 3:45 gears came in some factory cars and the only way to get them is to find them at swap meets or ebay, but they bring a high price cuz they are so rare and everyone wants them. 3.27's are fairly common on ebay. thats where i got mine. LOL

 

Yeah, I wish somebody that made aftermarket gears would make 3.45 gears.

 

I looked at Randy's Ring and Pinions website today and found 3.45 ratio. I was amazed, then I called them and found out that they don't sell them!! Why list them on your website!

 

no you would be just fine with 3.70s you intown would go down for millage but your etas would be better cause u are getting the power to the ground alot faster with the higher ratio a friend of mine is runnin 4.10s in his 88 iroc and it works great as a daily drive he has the stock 700r4