pettrix

1972 Olds 442 Convertible - 3,900 LBS
455 Olds making around 460 HP (crank)
2004R transmission with a 2,400 stall
3.73 Chevy 12 Bolt with HD axles

Car an 12.10 @ 110MPH with 3.73 gears

Looking to put 4.10 gears. With OD transmission, street/highway driving shouldn't be a problem as the 2004R has a 0.67 overdrive ratio, In addition, the 1st gear ratio in a 2004R is 2.74 vs a TH-400 which has a 2.48

How many 10ths can the vehicle gain from 4.10 gears? I was estimating around 2/10th to 4/10th so it would run a 11.70 to 11.90. Sound about right?

Lonnies Performance

It all depends on how far off the original combination is...I'm assuming you already have the 200-4R with 3.73's
It already runs pretty good for a heavy convertible.

The lower first in the 200-4r plus the 4.10's give you a pretty steep first gear.
If you have traction you could see the .2-.4 sec improvement you are asking about.
Picking up .2 in the 60ft times, you can often gain .3 in the 1/4 mi.

The thing to consider is how high do you rev it?
What height tire?
What RPM do you current come through the 1/4 at?

If you start to wind it too tight through the lights (too far above power peak) , too much gear can hurt you.
With a 28" tire, you will be over 5500rpm.

69455

[QUOTE=Lonnies Performance;1167374]It all depends on how far off the original combination is...I'm assuming you already have the 200-4R with 3.73's


What RPM do you current come through the 1/4 at?
#1 question

pettrix

Yes, the 2004R and 3.73 gears are already in and ran the 12.10 @ 110mph

RPM through the traps are around 5500RPM.

One option is to put it into Overdrive if I run out of RPM

Fun71

At what ET does your track require a roll bar?

Lonnies Performance

Hitting OD in the 1/4 will hurt your times. You typically want to cross the finish line at or approx 10% above your peak power RPM.

What is your MAX RPM you will rev the engine to?

If you are seeing 5500 now, you must have a pretty loose converter & may see 6K with 4.10's.

You MPH should stay roughly the same with new gears, so calculate the tires/gears you can get away with.

pettrix

IHRA track. 11.99 or quicker

Lonnies Performance

Current IHRA & NHRA rules state any convertible below 13.49 requires a roll bar.

Hard top cars require a 6pt bar below 11.49

Any hard top vehicle 2008 or newer with an unmodified body/interior is good to 10.0 without a roll bar.

69455

Any hard top vehicle 2008 or newer with an unmodified body/interior is good to 10.0 without a roll bar.[/QUOTE]


Why 2008 ? what changed at that point ?

Lonnies Performance

Basically NHRA/IHRA amended the rules as there are many new performance cars capable of running in the 11's. ZR1 Vettes, ZL1 Camaro's, CTSV Cadillacs, GT500 Mustangs etc. Even my friends new Challenger went 11's with nothing more than a cold air kit & sticky tires.
Being that newer cars have significantly increased protection over older generations with front & side curtain air bags etc., plus numerous other safety improvements, they made a judgement call.... why 2008, I have no idea.
I wish it included vehicles closer to the 2000 model year myself.

It sucks to get booted off the track because your daily driver is too fast.

You don't see much in the way of track accidents with these cars & it helps keep the sport alive.
Keep in mind, tracks originally opened as a safe way to keep people from racing on the streets.

69455

I have been going round and round with myself to bar / cage or not .
Want to for safety
Don't want due to keeping stock look, in and out ease.

I have been wondering how the late model guys don't use in Camaro's, CTSV Cadillacs, GT500 Mustangs etc.
My car has complete aftermarket suspension / brakes runs low 11's pump gas, low 10's with NOS shot. Handles great.
Never been kicked off track however I don't go often and usually on off days. Do not bracket race.

Would not want to wreck in any of them.
Sorry this was not about gears but I run 3:73

pettrix

As long as traction isn't an issue. Going from 3.73 to 4.10 will provide quicker 0-60 acceleration, correct? As the 4.10 gear provides "free" torque multiplication.

coppercutlass

Looking for 4 tenths from that gear swap wont happen. I went right in the middle. from a 3.73 to a 3.90. and saw no change in 60 ft. the biggest gain in 60 ft. I made was going to a 3500 stall from the 2800 stall .

For reference with my last small block I started at 13.3. I made a bunch of little changes and shaved 100 lbs and car eventually went 12.29 @ 109 with a basic bread and butter 350 olds.
one of the biggest improvements was taking the sway bar off at the track in the front. Going from a vacuum secondary carb to a double pumper ( same CFM ) netted a drop in e/t, Running less lifter preload like .010 helped a lot on the upper RPM range not to mention really smoothed out the idle , I also run an x pipe with bolt on mufflers. Most mufflers weight almost 50 lbs together and opening up the exhaust alone is 2 tenths and dropping 50 lbs also helps.

IN the past when I had a slower car I went from running a 14.0 with open headers to running 13.86 with just adding an Xpipe and that was running it through the mufflers.

also driving has lots to do will getting the e/t's down. I played a lot with shift points and figuring out exactly what the car likes goes a long way. do you manually shift the car ? does your trans allow you to have full manual control outside of drive ? Does it have a shift light ?

Just for what its worth. Hope you get some ideas you can try out. to work around the gear swap.

72442conv

I would be amazed if you got anything over a tenth from the gear swap, you may not even get that. Previous poster is probably correct in stating that there is a ton of things that can be done that will probably get you in the 11's with little to no money involved. If you took 100 pounds off that car you will probably touch the 11's. When I used to drag race I was always amazed at the people that ran their cars as they ran them on the street. Floor mats, spare tire, jack, tools and a ton of junk in the car. Front sway bar on the car (at the minimum it should be disconnected), rear seats are easy to take off, passenger seat not so much but it is doable (remove everything from the car that can be removed easily and is not need to go down the 1/4). Disconnect power steering and AC. If you are running your street tires, in the front inflate them to 45-50 psi at the track to lower rolling resistance. Use a cool can on the gas line, cool the intake manifold with ice (wrapped in bags and towels so you do not get water all over the place). Rig up a ram air system, or at least cold air system, we used to get a dual snorkel air cleaner and dryer hose etc... Getting that car into the elevens from where it is right now should be quite easy. Hell, on the right day with the right atmospheric conditions it with will probably do it without touching anything :-)

pettrix

I found this article which explains on how gear ratio helps with acceleration with torque multiplication. Traction of course being important as the higher numerical gear ratio increase torque multiplication.

http://zr1specialist.com/HAT%20Web/a...celeration.pdf