What rear gear
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On The Tree
Joined: Jan 2017
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What rear gear I'm in the middle of my build and I'd like to know what everyone is running for gears so I can make a good educated guess on what will work best for me. 72 nova 5.3 LM7, little Johns turbo cam, twin 61mm ON3 turbos, th400 and a 9" out back with a 28" tall tire. It will see the track a lot but I also want to drive the crap out of it on the street. Is 3.50 gear to low or should I be in the 3.20 or 3.08 range?
I run a 3.23 gear with a 1.76 powerglide and 275 pro tires.at full steel /interior weight. run the best of 9.90 so far at 13.5 psi boost. shifting at 6000. leaving at 1-2 psi it goes 1.50 60'.
I haven't run it at the track yet. Maybe some 1/8 mile stuff as the car has no cage. I'm thinking I could sneak through the 1/8 in second gear. That'd put me 110-115 ish depending on how tight I wind it.
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Thread Starter
On The Tree
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Like I said. It will see a lot of time at the track. Maybe I'll do a 3.20s for the happy medium. I'd just hate to be wrong. I'm a baller on a budget and I already know the 4.56s in the car won't work so I only want to change them once
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Need to figure out how much power you’ll likely make and factor in weight. Then decide if ET or cruising is more important… can’t have both with a TH400.
I went with a 3.10, then a 3.25 on a 30” tire. Great for cruising… but I really think it’s hurting my ET a ton. Also harder on the motor (rods) being closer to peak torque most of the time. I’m only at 6200ish thru the traps at 160ish. Around 1000crank HP near as I can figure. If I was closer to 7k I think I’d pick up a lot.
Also need to figure in that TH400 has a short 1st gear, so without some sort of power management you’ll likely be very traction limited if you install the gear for the best ET. And better off traction wise with a super tall cruising gear.
I went with a 3.10, then a 3.25 on a 30” tire. Great for cruising… but I really think it’s hurting my ET a ton. Also harder on the motor (rods) being closer to peak torque most of the time. I’m only at 6200ish thru the traps at 160ish. Around 1000crank HP near as I can figure. If I was closer to 7k I think I’d pick up a lot.
Also need to figure in that TH400 has a short 1st gear, so without some sort of power management you’ll likely be very traction limited if you install the gear for the best ET. And better off traction wise with a super tall cruising gear.
^^^Right! That's why I'd only string it out 'til the 1/8. I can sing it in first and let it run up in second. If I was running the quarter, I'd probably go closer to a 3.50 and leave in second gear.
Thread Starter
On The Tree
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Originally Posted by Forcefed86
Need to figure out how much power you’ll likely make and factor in weight. Then decide if ET or cruising is more important… can’t have both with a TH400.
I went with a 3.10, then a 3.25 on a 30” tire. Great for cruising… but I really think it’s hurting my ET a ton. Also harder on the motor (rods) being closer to peak torque most of the time. I’m only at 6200ish thru the traps at 160ish. Around 1000crank HP near as I can figure. If I was closer to 7k I think I’d pick up a lot.
Also need to figure in that TH400 has a short 1st gear, so without some sort of power management you’ll likely be very traction limited if you install the gear for the best ET. And better off traction wise with a super tall cruising gear.
I went with a 3.10, then a 3.25 on a 30” tire. Great for cruising… but I really think it’s hurting my ET a ton. Also harder on the motor (rods) being closer to peak torque most of the time. I’m only at 6200ish thru the traps at 160ish. Around 1000crank HP near as I can figure. If I was closer to 7k I think I’d pick up a lot.
Also need to figure in that TH400 has a short 1st gear, so without some sort of power management you’ll likely be very traction limited if you install the gear for the best ET. And better off traction wise with a super tall cruising gear.
Without knowing the rest of the combo 15psi doesn’t tell us much power wise. You’ll about double the NA hp at 15-16lbs.
Figure out what speed/rpm you consider comfortable cruising at and gear it as short as possible IMO. You’ll need it at low boost levels. A 3.50 with a 28” tire will put you around 150ish at 6500 rpm. (155 assuming zero converter slip.) Figure out your vehicle weight and we can tell you about how much power you need to go 150ish.
Figure out what speed/rpm you consider comfortable cruising at and gear it as short as possible IMO. You’ll need it at low boost levels. A 3.50 with a 28” tire will put you around 150ish at 6500 rpm. (155 assuming zero converter slip.) Figure out your vehicle weight and we can tell you about how much power you need to go 150ish.
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On The Tree
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With the aluminum headed big block, me, and 12 gallons of fuel I was 3220 last time across the scales. It's a LM7 stock bottom end, china head studs, little Johns stage 2 twin turbo 225/235 cam, air to air intercooler, 3000rpm converter(might change that) and twin 61mm turbos. TH400 with a transbreak. I don't know what it will make for power. I'm about a month maybe two from getting it running and tuned
Thats light for a Big Block Nova. Even with aluminum heads. Might be close with the turbos, intercooler, etc. I'd consider a good/decent turbo converter. Even a tight cheap one can/will get driven through. These turbo setups make a lot of torque.
I run a 3.90 gear with a th400 right now. 1.3 60' on old mt 275s and I've ran 9.17 @ 147 mph at 7200 rpm but I'm out of gear. I'm going to a 3.40 gear soon but if I only ran 1/8 I would not change. Guys with 3.08s dont realize how much they are leaving on the table and how much heat / slip they add to the converter by low rpm at the finish line. You either pick lower cruising rpm or a more efficient track car.
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I run a 3.90 gear with a th400 right now. 1.3 60' on old mt 275s and I've ran 9.17 @ 147 mph at 7200 rpm but I'm out of gear. I'm going to a 3.40 gear soon but if I only ran 1/8 I would not change. Guys with 3.08s dont realize how much they are leaving on the table and how much heat / slip they add to the converter by low rpm at the finish line. You either pick lower cruising rpm or a more efficient track car.
Yup made 830 on 15 psi and I launch in 1st gear. 1% slip 28" tall tire 3600 lbs. Best 1/8th was 5.866 @ 119.5 mph but being out of gear it wont go over 147 in the 1/4.
Last edited by Nitroused383; Feb 24, 2017 at 08:14 PM.
Running a tight PTC 9.5" and it doesn't slip much over 4% thru the traps at 6200. But back before my PTC days I'd see 16% or more at that kind of RPM. Fluids at a solid 210 or so after a run though. Definitely making some heat.