Gear ratios, and how low is too low?

[Ziegelsteinfaust]

I am putting my 383 reverse cooled engine in my 83 stepside as free time allows, and I am dreaming of muscle truck glory.

The engine is something like a 475hp/475tq 383 built to smog legal standards, and is backed by a TH700. It came out of a 92 Vette with the best of everything 94 build, and with a dyno sheet of 460hp/450tq. I only had the paperwork long enough to quickly look it over. To which I added proper long tube headers, and the gmpp 4 barrel intake.

So now with a smog legal cam, and a manifold that works better. Hp/tq should be up quite a bit under the curve, and hold out up top. Due to the better exhaust I am running for power.

The tire sizes I will run will will either be 33/12.50/15's or 285/75/16's. Depending on if I keep it a C10 or C20. The suspension will be optimized for bombing dirt roads in a rally cross fashion.

So for the guys who have had deep gearing, and or still do. Would I have a burn out machine unable to hook up. Or would it potentially make the truck faster in the 1/4?

Or would I be better off with 5.13's if I built a revvy 302, or 327 which would make less torque down low?

Thoughts opinions...

[Getter-Done]

Here is a link to calc for alot of option of the Answer you are looking for.

Link: http://www.wallaceracing.com/Calculators.htm







.

[mongocanfly]

thats a good list getterd...havnt seen that one before

if your making 475hp and riding a dirt road..i think youll be making roostertails no matter the gear
with a 31-33in tire and 5.13s and od trans youll be around 23-2500rpm at 65mph

[Ziegelsteinfaust]

Originally Posted by Getter-Done

Here is a link to calc for alot of option of the Answer you are looking for.

Link: http://www.wallaceracing.com/Calculators.htm







.

I have used the Richmond gear version, but it assumes your going for 1/4 times on a prepared track. Or just decent traction. Where off road tires throw a interesting monkey wrench in there.

According to Richmond with a 33" tire, 475 hp, 4500 pound curb weight, and a 6000 rpm through the lights. It gives me a technical 11.60 eith a 5.32 gear.

Personally I think a 12.50 would be more realistic based on past experiences, but that maybe a technical limit. If I had everything 100% for a 1/4 time.

[Getter-Done]

The 5:13 sounds like it would be a great gear.

With the ratios of the 700 , And that much HP






......

[Ziegelsteinfaust]

Originally Posted by mongocanfly

thats a good list getterd...havnt seen that one before

if your making 475hp and riding a dirt road..i think youll be making roostertails no matter the gear
with a 31-33in tire and 5.13s and od trans youll be around 23-2500rpm at 65mph

It is the engine I had when I accidentally killed the original 350 I got it with. Plus it has a built 4L60 that I built for the car I pulled it out of.

The paperwork I have seen for the engine, the AFR heads I can see, and the way it sounded before I pulled it out of the wrecked Vette. It is a legit engine built by a local speed shop like I said in 94-95. So this truck will hustle. As I have had these trucks before with a solid 350hp, and was happy before. I may have a smile a mortician couldn't remove when I pass.

Since the truck needs no work besides a engine I had to do it.

When I calculated rpm I used 75mph as that's where I like to cruise, and it was easily livable for me. I love the sound of a engine at 2500 rpm.

I could go to 4.33's for the highest gear ratio, and 4.11's maybe ok. That is based on my non lock up 2500 rpm converter. So I have to be close to that rpm at cruising to not just beat the fluid to death. Or I would have to swap in a 4L80E for the lock up function. I am not a TH700 fan with the big 1-2 gear drop, but it fit the car so there I went.

The truck has 12 bolt with 3.42's in it now which was fine with a th350 for me going 75. It maybe fine with the new engine, but I have to find out first. Depending on how much rubber it burns with the current ratio. I may end up swapping in a built TH350 or TH400 with a 2500-3000 rpm converter. As I want that passing power.

[Ziegelsteinfaust]

Originally Posted by Getter-Done

The 5:13 sounds like it would be a great gear.

With the ratios of the 700 , And that much HP






......

That is the allure. I have seen the Roadkill muscle truck with the original 5.13s pass me a couple of times. Let's just say I was jealous.

[Richard]

In my experience you should add 200 rpm to those calculators when using an auto trans. With the 5.13's at 75 mph in OD you will be over 3k rpm.

I am going to use 5.13's (6l90) with my 37's. Expecting 2200-2400 rpm at 70. Should roast the tires at will.

[kwmech]

I'm running 4.56 gears with a 285/75-16s---good off the line and decent cruising although I am not running a high horsepower engine. Basically a stock 350 TBI with a couple of minor mods to it at the moment. What do you plan on doing with this truck?

[Richard]

A little more info on gear change experience. Had a pinion failure. Just installed 3.73's in my 94 DD coming from 3.42's. RPM at 70 is about 2200-2300 on the tach with a 31.8 spec tire. Barks the tires again in second sometimes. This is a stock motor C1500 rated at 190 hp with 180,000 miles.

[burnin oil]

02 jeep with 4.88s sitting on 32s with a 5spd manual. It rarely is driven past 60 MPH but sees that speed alot. I always say I should have went 5.14.

I have a similar but wilder motor in my k20 sitting in 32s. Current gears are 4.10 and I am going to 5.14s when I get around to it. Parts are sitting there but other things trumped the priority list. Anyways it has a nv4500 and I only use 5th gear for coasting on semi flat grades unless going over 65mph. It just needs the higher engine speeds to get into the power band. Bombing the back country thourofare is 4th gear and let the ponies run.

[Ziegelsteinfaust]

Originally Posted by kwmech

I'm running 4.56 gears with a 285/75-16s---good off the line and decent cruising although I am not running a high horsepower engine. Basically a stock 350 TBI with a couple of minor mods to it at the moment. What do you plan on doing with this truck?

Driving it around mostly, and bombing dirt roads when I can. There is a ton of dirt roads in the high desert around where some of my family lives.

If you watch Roadkill. They took the muscle truck to Glamis, and then to Pismo

So I want a realistic version of that truck. One that can bombing the dunes or dirt roads. Yet still runs hard on the street. Yet with full fenders.

I am not sure where it will end up as I am trying to avoid spending money twice. So I am asking questions to find a balance where it is just good enough at everything I need a truck to do. My original plans were for a 400hp 327 backed by a 6L80E, but that is out the window for quite a few years.

[Ziegelsteinfaust]

Originally Posted by Richard

A little more info on gear change experience. Had a pinion failure. Just installed 3.73's in my 94 DD coming from 3.42's. RPM at 70 is about 2200-2300 on the tach with a 31.8 spec tire. Barks the tires again in second sometimes. This is a stock motor C1500 rated at 190 hp with 180,000 miles.

What trans are you running?

[Richard]

Originally Posted by Ziegelsteinfaust

What trans are you running?

4l60e in the 94. I rebuilt myself about 100k ago due to snapping the output shaft. Was lowered and running a 285/40/17 tire at the time (reason I purchased new with 3.42's). Has a shift kit in it, other than that all stock. Made the shift a bit tamer when I rebuilt it. With the new gearing I almost went with 4.10's for a bit more performance but most of my driving is highway. Happy with my choice.

Net gearing will be just a bit lower in my 72 with 5.13. Should be great as it will have more than 3 times the HP and torque and it is FI.