[mogeo]

Couple of questions that I need answered.


1. Whic is more a function of power or torque: Speed at the end of the quarter, or trap speed? For example...

Was reading a Hemmings Muscle Machines and noticed a 1970 Dodge Charger R/T ran a 14.9 at 98 MPH (no options, 440/ 727 trans, 3.55 Dana and 3770 #). On its maiden voyage last fall, my HEAVY 68 firebird convertible (with A/C) ran a 14.3 at 97mph. Spec 400WT/ 16x,068 cam, Holley, stock exhaust; TH 400; 2.73; 4090# with me....

2. I would think that the lighter Charger with a slight HP/ Torque and rear gear advantage on paper woud beat my firebird. Could I be putting out more power than i realize?

3. My car FEELS sluggish of the line (2.15 60' time). Thinking of a limited slip and 3.55 in my 8.2" rear. Car really only sees street time and is not raced, but I want it to FEEL faster. What would the gear change do to my time/ trap speed?

Thanks,

Rich

[Jeff V]

4.10 gears would make it feel so much faster,but you're highway crusin days wouldn't be much fun.3.73's are a good all around gear.Even 3.55 would feel much better than what you have now.

Those articles from the past usually don't tell how bad the car spun leaving the line.Most of the time on the old bias ply skinny tires it would lose alot of et off the line but run good on the top end.Strap a set of m&h's on that Charger and it would run low 13's no problem.

[Dragncar]

A few things.
Is there a difference between trap speed and end of the quarter speed. They are the same thing.
Are you sure the 68 convertible weighed 4000+?
Those 70 Chargers were big cars and not exactly light.
I do not think any 4000 pound car with a stock 400 would click off a 14.3 with 2.73 gears.
You would never get it in 3rd gear.
A 13 second car back in the day was a fast street car. The tires sucked.
Even a low 14 car would just about beat anything on the street.

[mogeo]

Yes, I weighed the car myself. With 1/2 tank of fuel,the spare, and a subwoofer in the trunk it weight 3950 without me in it. Figured pull out the spare and speaker, then add 180# driver....
Maybe somewhere my rear gears were changed out. But the code on the tube would be for a 2.73. And yes, it just shifted to 3rd near the end of the quarter.
Lousy 60 foot time.

Does speed at the end of the quarter, or time at the end of the quarter indicate horsepower? Maybe my car is making more horsepower than i think? Hard time spinning the tires off the line unless i power brake it though. Pulls nice otherwise. 3.55 should help.

[goatless]

Yes the trap speed is a pretty good measure of the power being made. The ET is affected by launch much more, so two cars with the same power could be second or more off in ET even if their MPH was the same.

I race my Lemans in F.A.S.T. stock appearing events and I'm often quicker down the tack than my speed would indicate because I can get my car to launch on those skinny tires. Many of the guys that run similar ETs to me are running as much as 4-5 MPH faster but their 60 foot times stink.


A gear change in your car really would wake it up off of the line, but there needs to be a compromise between acceleration and drivability- especially if your car will see little to no track time as you say. For a pure street cruiser I'd probably stay at 3.31 or less.

[Basher 75]

I have run 15.0x at 100.2x with a spin-bog-spin 2.6 short time, and 13.5x at 92 with a 1.9 short time (4.56s and worn out valvesprings= valve float at 1000 ft.). Two completely different cars, but the 100 mph one would get killed by the 92 mph one. My trap speed always seems fairly consistent, no matter how bad my launch is, and I have a hell of a time repeating to within 3 or 4 tenths 60-foot.

[1stGen Brawler]

Originally Posted by mogeo

Couple of questions that I need answered.

3. My car FEELS sluggish of the line (2.15 60' time). Thinking of a limited slip and 3.55 in my 8.2" rear. Car really only sees street time and is not raced, but I want it to FEEL faster. What would the gear change do to my time/ trap speed?

Thanks,

Rich

Rich, your post caught my eye because I have walked your road in the past. If you have any question about your rear gear ratio you can always verify it. I know you said the code specifies a 2.73 but if you suspect it having been changed just take a peak inside your pumpkin and find out. By simply dividing the ring gear tooth count by the pinion gear tooth count, the ratio is determined. For example, if we divide a ring gear with 41 teeth by a pinion gear with 10 teeth we find that the gear ratio is 4.10:1 (41/10 = 4.10). This way you will know for sure. Or if you don't wanna open the pumpkin us Pontiac Dude's calculator at the bottom of this page.
http://www.angelfire.com/fl4/pontiacdude428/Hot.html

My Bird came with a 2.56 when I bought it so I feel your starting line pain. Before you pick a new ratio bear in mind the changes that tire diameter will have on your final drive ratio. I first went to a 3.55 gear but was running a 26in tire. I eventually went to a 28in tire for traction reasons and stepped up to a 3.73 tire. My car is street driven but very rarely highway driven. I have a TH350 tranny. Can you run a steep gear (higher than 3:73) without an overdrive tranny? Sure you can. But you car will be noisy at speed, use more fuel, and your cooling system better be A+.

What are you plans for the car? Is it slowly morphing into a race machine? They tend to do that, trust me, I know. Everything is a compromise. The seat of the pants feel you want is going to cost you to some degree in street manners. Maybe a little, maybe more.

If you are going to switch gears consider this. That 8.2 is not known for its strength. On street tires probably okay. You will not apply enough torque to matter. But if you plan on going to a race/dot tire of any sort and banging out some hard starts at the track I would give real thought to putting in an 8.5. That is what we did on my Bird.

Hope some of this helps.

[NYH1]

I haven't been to the track with my Camaro yet. I rebuilt the drive train this past summer (engine, trans. and rear end). My car came with 2.41 gears with an open differential (one wheel peel). My engine was built for low end torque and mid range power. Basically off idle to 56/5800 RPM or so.

My new engine actually pulled better then I thought with the 2.41 gears. I was surprised. However, once I had my rear end rebuilt and drove it with the new Yukon Duragrip Posi Unit and 3.42 gears, I was amazed at the difference it made.

I'm have a TH350, a 27 inch tall tires and turn 2800 RPM at 65 MPH. Most of my driving is just around town though. I think 3.42/3.55 gears are just right for non-overdrive cars with mildly built engines. I think you'll be happy with either 3.55's in your 8.2, or 3.42's in a 8.5" if you change rear ends as another member mentioned.

I've heard that the BOP 8.2" 10 bolt is a little stronger then the Chevy 8.2" 10 bolt. I know a bunch of guys that have gone pretty fast with 8.5" 10 bolt rear ends with really good luck. I went 12.50's with my last '78 Camaro with a stock 8.5" 10 bolt with 4.10's and street slicks.

Good luck, NYH1!

[lust4speed]

I don't believe that anyone made the direct statement that to determine HP, you need both weight and quarter mile speed of the car. A fair example of this is a friend with street tires that doesn't hook up that often. His ET's will vary between 12.6 and 13.4 at the track on the same day depending on wheel spin, but his MPH remain constant at 105 plus or minus a tenth. All you need then is an accurate weight and the horsepower is easy to compute. If you want to be really lazy, just use the calculators at Wallace Racing.

The horsepower produced on that day also is dependent on all the weather, and you can't compare a run on a cold day with exceptional air to a run months later on a hot, humid day with bad air. While there are conversion tables to equalize things, it's easier to compare cars on the same day or at least similar days.

When my son in the 2+2 runs 6 MPH faster in a barge that weighs 450 pounds more than my 400 GTO at the track the same day, there's no question who has the most horsepower - and with the calculators, we can compute what the actual horsepower is for each car on that day.

[Half-Inch Stud]

3.23:1 (or 3.31:1) rear and an ATI 10" 2800-3200 Converter will make that car strong off-idle, and highway friendly.


With some time you could hit 12.0 ETs too; see 12.0 ET signature. HIS

[Brent Flynn]

Originally Posted by mogeo

Couple of questions that I need answered.


1. Whic is more a function of power or torque: Speed at the end of the quarter, or trap speed? For example...

Was reading a Hemmings Muscle Machines and noticed a 1970 Dodge Charger R/T ran a 14.9 at 98 MPH (no options, 440/ 727 trans, 3.55 Dana and 3770 #). On its maiden voyage last fall, my HEAVY 68 firebird convertible (with A/C) ran a 14.3 at 97mph. Spec 400WT/ 16x,068 cam, Holley, stock exhaust; TH 400; 2.73; 4090# with me....

2. I would think that the lighter Charger with a slight HP/ Torque and rear gear advantage on paper woud beat my firebird. Could I be putting out more power than i realize?

3. My car FEELS sluggish of the line (2.15 60' time). Thinking of a limited slip and 3.55 in my 8.2" rear. Car really only sees street time and is not raced, but I want it to FEEL faster. What would the gear change do to my time/ trap speed?

Thanks,

Rich

I believe that with a gear change....no more than 3.55, you will pick up some ET, but your MPH wont change much because of your combo... also, it will want to spin more unless you have good tires... MPH is what indicates HP, your 60ft times will affect ET more than anything as long as the car runs well down track. Id say 3.31 gears with your combo... maybe as much as 3.73 if you runnin 28'' tires. Your combo is a torque combo...wont need nuch gear to get the max out of it in my opinion.

[lust4speed]

Another example with my same friend with his car. Years ago he was running a larger engine than his current one, and his car had even more trouble hooking up. I was running 12.33 and 109 MPH with my street car and he was running 13.34 at 110 MPH. It was taking him a second longer to run the quarter but the MPH showed that his combo was either making more horsepower or weighed less than my car. His car with him in it weighed in about 100 pounds less so we were probably making really close to the same horsepower.

Another example is if you plug in different rear end ratios and traction coefficients into Dyno 2003 without changing engine parameters -- results for the ET change, but MPH stays within a hundredth.