anybody have 3.73s in a tpi car? ive been told on other sites that they wont work due to the low rpm powerband on a tpi car. the low gears will take you outta powerband too quickly and actually hurt you.. anybody have any experience?

 

There's guys running 3.73's with TPI. It's true that you'll wind past the high peak of the TPI powerband really quick with them. 3.23's or 3.42's are the gears most commonly recommended as working good with TPI motors. You'd have insane low end take off capability, and be able to do incredible burnouts, but yeah, your motor would wind out of the powerbrand pretty quick with them. If you were running a 4th gen T56 trans, 3.73's would be a good starting point, with 4.10's probably being even better. But with a 700r4 or a T5, the 3.73's are a bit much.

 

Do you go to the drag strip? 3.73's are fine, as you'll shift before you get out of the powerband. However at the drag strip you might run out of RPM before you get to the finish line.

 

I've done it. and it's not just TPI they sucked on. they felt equally as bad with TPI as they did with TBI .... I recently changed to 3.08 gears and while off the line theres no comparison the 3.08's offer a much better powerband through all the gears and nicer acceleration, where as 3.73's the car performed better skipping gears.

1st felt like a granny low in a pickup truck but yea like the others said it could if I wanted to do insane burn outs at will. and out of the hole performance was awsome. but aside from that they sucked. Don't go over 342's with a 305 and I'de say stay with 323 since the 350 has more torque anyways.

 

I ran 3.73's in my 89 tbi 305 rs and it ran great. It even smoked my iroc when I had my slightly modded tpi 305 in it. In my iroc with tpi I run 3.42's and have had no complaints. They do well in every area where as 3.73's will give you an insane launch and high rpms at highway speeds. They will work fine in a tpi car. They peak at 4500rpm and will still pull to 5000rpm. My tpi 355 pulls to 6000 in first 5500 in second and 5000 in third and pulls down mid to high 13's. and the tpi is stock.

 

Hey Jproz, I can totally relate to skipping gears. My 69 Camaro has 3.73's with a Muncie M20 4-speed, and sometimes I skip from 1st right into 4th if I'm just cruising nice and mellow. In fact, I can shift it into 4th @ 30 mph.

 

I put 3.73's in my bone stock 88 Formula when it was an auto and it made a huge difference over the 3.23's.
I went from a 15.7 @ 87mph to a 15.2 @ 90mph with only the gear change.

 

not trying to jack your thread but i have also thought about putting 3.73's in. i basicly want it for 1/4 and a possible street race here and there. what would be a good medium one?

 

As long as you only drive on the freeway occasionally, 3.73's would be very well suited for what you stated. Ah, for that matter, 3.73's aren't even that bad on the freeway with the overdrive in a 700r4. I take my 69 Camaro for short freeway trips periodically with no overdrive and 3.73's, and it's wound up between 3600-3800 to keep pace with the other cars. If I had an OD trans, it'd be considerably less than that.

 

I have 3.73's with a 700r4 and a 350 TPI. I drive it on the highway all the time. I went from 2.73's to the 3.73's and it was a huge difference. I love it. I still get about 18 mpg highway. Its way more fun to drive and takes off like crazy. I wouldn't race anyone on the highway tho because you will max out the power band quickly. I got SLP siamesed runners and did some plenum porting and extend the power band so I get more pull up top with the gears.

 

I notice the majority here have good things to say but notice they are the ones with automatics as well. I think the problem area lies with 5 speeds TPI and 3.73's .... I can tell you with this combination motor either runs out of breath real fast or jumps out of it's torque band to make use of port injections qualities. 1st gear is completely useless for anything but getting moving.

I honestly don't think the electronics and mechanical stuff made the old 305 h.o. perform like they did. In my opinion it was the 373's and that motors ability to wind to 6K rpm is all. Now I think if TPI could breathe that high you'de have a winning combination. But say like this in 1st gear with 373 your barely going 20 and it's tached out and it goes there so fast.

So yea, with a automatic it probably wouln't be affected as much by 373's as the T-5's low first gear and the drivers inability to shift it fast enough and keep tpi in it's great power/torque band.

 

i have 373 gears and they work well with my combo

 

Keep in mind that if you have a TPI 350 and a T5 the owner should be contemplating a T-56 swap shortly. 3.73 gears are just about perfect for the taller overall gearing of the T-56.

 

well i have a 305tpi ( i feel like an idiot now) what would you say the best gear for getting out of the hole and still getting up there ?

 

3.42's are a great all around gear both in accel. and highway and top speed. With 3.42's in my iroc with my 700R4 which has the same gearing for OD I run 150 MPH at 4500 rpms at half throttle. The 3.73's aren't that bad but your top speed will drop to around 130 MPH. Unless you work on getting the tpi to breathe better at higher rpms.

 

I had 4.10's with my T5 last year. 1st gear was totally useless but the rest of the gears were really good (3rd and 4th were the best), pulled nice in 5th gear but topped out at about 125.
When I broke that rear, I bought a stock 01 SS 3.42 rear and I had a hard time getting used to it over the 4.10's since I'd bog like crazy and the car felt a bit slower, but it ran the exact time in the 1/4 mile, 15.2@93mph.

 

3.42's are an excellent choice with a tpi car for all around performance. When it comes to choosing rearend gears, it largely depends on what the main purpose of your car is going to be. If it's mostly going to be street driven, with only occasional trips to the track, you really can't go wrong with 3.42's. Of course the one exception to that is what Fast355 said. If you plan on running a T56, 3.73's should be considered the starting point.

 

i guess im still torn as i have a T-5, i have condidered the T56 swap but dont have the funds right now so i guess ill wait.

 

T-5's had several different first gear ratio's, commonly either 3.50, or 2.95, with a few other options. The 700R4's first gear is a 3.06. I can see a 3.73 rear with a 3.50 first gear being quite a handful. With a 2.95 it would be pretty nice. So, I guess recommending a gear ratio for a T-5 owner would depend on which tranny they had. Lots of tranny ratios here: https://www.thirdgen.org/calculations

Automatic TPI cars should love 3.73's, even with a stock converter they should leave hard. Trap speed of 95mph should be about 4800rpm, just about right for a stock TPI motor. As you mod up, you'll trap faster, with more RPM, but likely you'll have increased your breathing and top-end, so 3.73's should continue to work good.

With my 305, 700r4, and 3.73's I shift at 5500rpm at 35mph into second, 5300rpm at 67mph into third, which can goes to about 107mph at 5500rpm. I don't have the tranny converted to go into 4th at WOT, so I've not verified a top speed. Don't really need to go that fast anyways...

 

Mine shifted about the same with the 3.73's and my auto,
I did a 70-130 run one night on the way home and would've gone faster but my exit was coming up,
http://www.youtube.com/watch?v=BZIeHa-LwaE

 

I have them in my nearly stock 91', I trap 97+ MPH, and the car noses over before I reach the stripe. For me, they're too much. I average around 20 MPG, but have gotten as low as 18. On the highway I am around 2700-2800 on the tach running with traffic. (around 80 MPH)

My 86' had an 87' L98 swap, small cam, tune, pullies, ported plenum & base, roller rockers, tri-y headers, no cat, borla CB, 3K stall, susp, DR's. I slowed down .1 - .15 on average vs. the stock 3.23's. The 60' times were within .02 between both gear sets. They might have worked well if I had swapped to a 28" tall tire.

Just my $0.10 worth...

 

What RPM where you at the strip at? More specifics on the cam?

 

In my 91' - I am sitting around 5100-ish when I cross the stripe. My 86' had a comp 218/224 .485/.502 114LSA cam. I was around 5400-5500 RPM in the lights with the 3.73's and 4600-4700 with my stock 3.23's. I consistently picked up at least a tenth and MPH with the 3.23's vs. my 3.73's and the 60's were nearly identical.

 

i have a 1987 sport coupe camaro with a 305 4bbl with the 700r4 transmission, i blew the tranny and im gona replace it with a tci sizzler 700r4 tranny with sizzler torque converter which brings my stall speed to about 1000rpm. it has a 2.73 ring and pinion gear and i fidgured id go for the home run and get that changed to either a 3.73 or a 3.42 with posi- im a 17 yr old kid that is allways street racing and "driving the wheels of my car" what do you recomend for the best street perforance? which would allow me to run a faster quarter mile time the 373 or the 342. some one please break this down for me and give a me some good advise.

 

This thread pretty well has broken down the pros and cons to each of those ratios already. As you can see by 86 Iroc's reply, sometimes the lower gears can actually slow you down a bit in the quarter, especially if you're exceeding your engine's top rpm capability before crossing the finish line. If you're more concerned about being the king of light to light racing in town though, then yeah, the 3.73's would work the best. In fact, if that's your main goal you could always throw 4.10's in it.

 

with the 273 my car tops out at about 135 and runs a 14.2 in the quarter. if i put the 342 in what will my top speed and quarter time drop to? {estimate} and the same for 373?[estimate again]. thanks

 

I'm not sure how you top out at 135mph, unless you're refering to your top speed in third gear. In overdrive, my Camaro will do 135 or better, and I'm running a 3.73 rear.

Here is a neat calculator - http://www.f-body.org/gears/

I put your top speed at 98 mph (based on you're indicating 135 is your top speed) with a 3.73, 107 mph with 3.42.