You have to love to drive it!
 

Ok so I'm an a week away from ordering my chassis. Buying an art morrison GT chassis. I can't decide on the gear ratio though. I think I'm pretty set on tire size I know my transmission. Motor is an ls2. Possible upgrade of a supercharger . 550 a 600 hp goal. What gear ratio does one want though? This isn't the first time I've asked similar questions to this but still don't have the answer.

So I started looking at z06 corvettes to see their stock ratios. This is what I came up with.

Re: You have to love to drive it!
 

Seems like a fairly tall 1st gear and who doesn't like driving a vette. However 6th seems really tall. I want a quick 0-60 and the truck to be very sporty. Maybe an occasional auto crossing on the weekends.

This is what I initially was thinking but now I have some doubts about it all. Tell me what you think.

Re: You have to love to drive it!
 

Comparing Vette to truck might not be appropriate. Vette is more aerodynamic and possibly lighter. What's the truck's expected finished weight? What kind of 0-60 and / or 0 - 1/4 mile time would make you feel happy? What does the engine torque curve look like? Try to match peak torque rpm to highway cruise speed, use online simulators to check desired 0-60 and 1/4 mile times. 3.42 seems low with .57 OD available. 3.9 to 4.1 is direction I'd tend toward.

Oh, yeah, quit fooling with gear ratios and charge your battery!

Re: You have to love to drive it!
 

The bonneville guys have an online calculator that uses weight, drag coefficeint and frontal area to calculate hp required to get to a certain mph. Don't have time to look for it but I used it with the one you have to see what it would take to get my 64 Chevelle to 160+. That takes the Corvette to truck difference out of the equation.

Re: You have to love to drive it!
 

I went with a 3.73:1 with my art morrison chassis. I'm going to be running a 4l65e trans and the tires are 26.1 in. and figured that I should be in the 2200 rpm with this set up at 65mph

Re: You have to love to drive it!
 

Hahaha yeah i spend too much time researching this stuff. Battery was about gone. I am going with an ls2 and a t56 out of a 06 gto. I know it's a hard comparison with an old truck and a vette but unfortunately I can't find anything to compare to. I'd love to be in the 4.5 sec 0-60 range. Thats if I can get it. 12s in the 1/4. Don't know much about the torque curve range but I'll start looking into it. I was leaving towards the 3.7 a 3.89 range for the rear end.

So much to consider.

Re: You have to love to drive it!
 

A lot of the rear axle ratio depends on what is more important, quarter mile times or hitting the long roads and covering ground while still pulling reasonable gas mileage.

Myself, I'd gear it out so that the engine was turning the same rpm at 75 or 80 that it would have in the GTO at the same speed with the gearing and tires it had. That way it will still be pretty dog gone quick and at the same time run down the highway comfortably while pulling close to the same mileage the GTO did. I don't know how close the closest drag strip is to Burley but I'd guess you will have a bit of a drive to get there.

Re: You have to love to drive it!
 

Yeah no drag strip around here. Need to go to Boise area. I've kind of been thinking match the gto. If I super charge it that will get me the extra speed I want with out screwing up drivability. That's the thought anyway...

Re: You have to love to drive it!
 

I was looking up some figures as the build I am working on is only slightly similar and I was wanting to see the possible weight differences for both handling and for fuel mileage as I want to make mine a daily. The stock weight of the 3100 was 3175 lbs curb weight. A 90's model c4 was 3317 lbs curb weight (using the c4 because this is the suspension I am using- like I said, only slightly similar).

This is where it gets fun. The engine that came in the 3100 stock was the 216. Last I looked for the information I think that engine came in at over 675 lbs whereas the LS3 I am wanting to use, seeing that it will be an aluminum block, was in the 400s. You are probably going to go with a transmission with an aluminum case to replace the cast iron one that originally came with the truck and you are dropping the heavy cast front and rear suspension that came with the truck to go with lighter parts there as well.

I realize that aerodynamics are going to come into play in a pretty major way but I'll be really excited to see what the truck weighs when it's finished. I think that will be the first thing I do when I get the build I'm working on finished is take it to the local scrap yard and use their scale. Surly the weight difference could help to make up for the deficits in aerodynamics.

I don't know though, I'm not an engineer so I'm only going off estimations in my head. Maybe someone else with a better knowledge could make up for any faulty thinking.

Re: You have to love to drive it!
 

via Summit's calculator I plugged the bottom three values to arrive at a rear end ratio:
Solve For
Gear Ratio (ex. 4.56) @ 2.74

RPM (ex. 5000) @ 2300

Tire Diameter (in.) @ 28"

MPH (ex. 45) @ 70mph

Would I be able to pull away from a stop sign with that tall a ratio?:lol:
Will my mild 350 with a T350 be able to pull a 2.74 at 50mph? Right now I am in third by 40mph.
Daily driver and don't care if I can smoke the tires.

http://www.summitracing.com/expertad...tio-calculator

Re: You have to love to drive it!
 

I have a brand new crate 350/290 with a mildly worked TH350 and stock 3.90 rear. If I mash the pedal from a stop tires will smoke. Chirps second easily and at less than half throttle. 2600 rpm at 60 mph.

Re: You have to love to drive it!
 

Based on the donor being a '75 C20, I'd guess a 3:73 for mine.
It's only rated at 165 hp, via engine numbers.

Re: You have to love to drive it!
 

Too much analysis here.You can't go wrong with 4.10s and an OD transmission.It's the way Chevy has done it on late model LS engine trucks for years.3.73 on diesels that have lots more torque.

That's a 12 second truck...if you can hook it up.Like always, tires and tuning the suspension is everything to hook power up.

Re: You have to love to drive it!
 

I have a 3.90 in one truck and a 4.10 in another. Both are 4L80s. I like them both a lot. If I had to do it over I think it would be 4.10s for both. If you plan on actually using that 6th gear you will need a pretty steep gear of at least a 4.10 in my opinion.

Jeff

Re: You have to love to drive it!
 

You also have to take into account that I have a t56 transmission.
That's a different of a is 2.48 and 2.97 first gear. The 4l65 or 4l80 compared to a T56 would respond very different to a 3.90 and 4.10 rear end. About 3mph difference at 2000rpm. 6mph at 4000rpm. Ect... I would need a 3.42 rear end to make a t56 comparable to a 4.10 with a 4l80e.

Re: You have to love to drive it!
 

OK,T-56,I didnt pick up on that.Yeah that 6th gear is a challenge,.5 to 1 OD,depending on your rear you may not see it until 75mph,and super low rpms aint real compatible with a s/c. I see you short-shifting 1st or not utilizing 6th all that much.Or with 4.10s you could probably drive it well enough taking off in 2nd for getting groceries and using 1st for a hard launch.Just ideas.

Re: You have to love to drive it!
 

The 2nd ratio I posted is fairly short. That is the 3.89. That might be along the lines you are talking. I am interested to see how anyone else likes that short first gear. With that said the 1st ratio is the vette and it's a taller gear but if I can get a truck to perform like the vette, who wouldn't be happy with that?

Re: You have to love to drive it!
 

How steep of a first do most guys want?

Re: You have to love to drive it!
 

my daily has a 2.73 camaro rear with mild roller cam 350 with th350 tran it runs 9.90s @ 74-77 mph in 1/8 so it will still leave the lights fine and 2200 rpm's is 61-62 mph.

Re: You have to love to drive it!
 

Thanks, bear. Gives me something to consider.

Re: You have to love to drive it!
 

Chances are you'd end up skipping second gear and possibly third during light to moderate acceleration. Research CAGS in the C4 or the previous gen Camaro. 4X4 Toyota turbo pickups from the '80s w/ manual trans (R151F) had a gear ratio swing of 4.31 first, 2.31 second, 1.44 first combined with 4.10 rear gear. Fun for crawling but it's a wide range for light cruise. You learn to live with it though.

Re: You have to love to drive it!
 

I have had a few daily 6 spd cars and I always end up skipping, 1-2-4-6. The idea behind more speeds in a trans is to keep the engine in its peak power longer, always having the right gear.

that .5 overdrive of the vette will not work the same on your truck. vette guys can get high 20s even low 30s on long highway cruises because of the small frontal area and titan amount of torque of their engines. Your truck will have all the slipperiness of a sandpaper condom. As your speed goes up, drag goes up exponentially owing to the velocity squared value of the drag equation. You will be amazed when you convert to tq how much extra you will need to go even 1mph faster. The term is torque limited, meaning a cars top speed is not rpm*gear ratio etc, it is actually limited by aerodynamic drag long before the engine runs out of rpm. Yes, even a corvette.

The best way to figure cruising speed efficiency is to figure out the cruising speed you want and work BACKWARDS to the overdrive gear to put the engine just right below its torque peak rpm. That means that peppy 4 cylinders usually turn 3-4k rpm and some v8 turn happily at 2k and even the corvette with its great plain flatness torque curve can burble along at 1200 rpm. 4 cylinder guys though, see that 3-4k rpm and say "man, my mpg would be so much better if it was turning 1-2k rpm". So they swap gears and find out that their 4 cylinder doesnt have much torque running 75mph at 1200rpm and their mileage actually got worse because it takes a stone age and a couple gallons of gas to even get to 75. Turns out that automotive engineers arent as stupid as we give them credit for and actually knew what they were doing in the first place.

set your most likely cruising speed, figure tires, rear end, and then overdrive backwards to put the engine right at its torque peak. If burnouts are your goal, go with a high numeric rear end gear and get tail happy with it.

Re: You have to love to drive it!
 

I'm am having a hard time trying to find what the ideal rpm range is for that motor. I'm guessing 1800-2000? I'd love a 4 sec 0-60 but I'd also like to see about the ideal range for fuel economy. I'm not looking fastest drag car or a Prius. This will be a daily driver but I was hoping through others experience to find out what they have done and maybe help make a decision of what to do with this truck.

Re: You have to love to drive it!
 

i run: 350hp, 700r4 and 3.27 rearend gear in truk.
i also resurface my asphalt driveway in rubber daily and get 20 mpg highway, 15 mpg in town
i set truk up for highway cruising and have run three 2700 mile plus power tours.

if you only want quick then stay near 3.90 and above
if you want quick and fast then look closer to 3.30 or lower

i never had a time slip for truk, i need to get one someday :D

Re: You have to love to drive it!
 

In order to compare apples to apples from a standing start, you have to throw out all the auto trans stuff due to the torque multiplication of the converter on the launch. IMO, you're going to need the 2.6 1st gear AND the 3.89(Ford ratio) rear to get the truck to step out smartly. My non apples comparison is a 500 cid bbc with 31x16.50 tires, a th-400 and a 30% OD attached. I chose a 4.11 gear and it cruises at about 2550 rpm at 70 mph. To me this is not a fun cruising rpm. I now wish I had chosen the 3.89 gear or maybe even a 3.70.(all ford ratios) I also have to consider some converter slip at cruise, which is annoying, due to the larger frontal area of the truck at speed. I'm now considering ditching the whole drive train in favor of a modified 4L80 and changing to a 3.89 gear. I'll loose 5% on the OD gear but gain the lock up in cruise mode. To sum up. Work backwards like suggested and find where you can get 75mph at 2200 rpm with only slight tweeking and the rest wil take care of itself especially if you supercharge. Then, like me at 500cid, you'll have the torque instantly available to accelerate when needed. I can fry the tires in most any gear but discovered the "love it" part comes in more, for me, in a sweet cruising speed on the highway with possibly a slight dip in stoplight performance. Good luck and remember, the guy who spins the tires is usually the looser. ;)