What gear ratio should I go with

I have a 64 galaxie that weighs 3840lbs or so with me in it. I have a 347 stroker in it with AFR185 heads,248/254 at .50 614/621 solid roller,parker funnel web,650dp,hooker comp headers,c-4 trans with a 4500stall(On the trans brake),4:11 gears and 275-50-15 mt drag radials. I ran it today(before my pos milidon water pump started leaking)and I shifted it at 7000, hit drive right about the 1/8th mile piont and went through the traps right at 6000. So I need a new gear should I go to a 4:30 or a 4:56 gear? According to my desk top dyno my peak hp should be at 6500 so do I want to be right at 6500 or should I trap the same RPM as I'm shifting at. I just got this thing back together and since I have been crankin up to 7000,7500 I have lost a altenator and now my water pump went. Would this be from turning them to fast? If so would going to underdrive pulleys help?

Crossing RPM should be just about the time that your "average" HP starts to fall off and not based on the peak. I would be leary of using desktop dyno to determine a rear gear, but I am pretty sure that you are heading in the right direction.

I can give a real life example. All the following info is found on my custom cam card: Basic cam info: .598/.587 lift, 234/248 duration. Peak HP was estimated at 5800rpm. Shift point is 6400rpm and the RPM to cross the traps is 6700rpm.

For this example, a 4.56 would be just about ideal using my 26" tall tire.

For me, reality has to set in too. I am not really interested in running 4.56's on the street and thus I compromise by using the 4.11's and cross at 6200rpm.

What is the height of your rear tires? My uneducated guess would be that either a 4.56 or a 4.88 would maximize your combo better (if your tires were also 26" tall.) Since you are pushing 500lbs more than me, I would lean toward the latter in this example.

Underdrive pulleys will certainly help. I use a 4" alternator pulley and the stock type water pump stuff--but I only max it out to 6700rpm.

If you want to turn the fastest times at the quarter mile track, you should turn the engine 10 too 15 percent over the actual HP peak, EXAMPLE--HP peak 6500, gear for 7150-to 7475. A good RPM to shoot for would be 7300. I run every engine I build on the dyno, so I know exactly where the HP peak is. If you dont have dyno information, a best guess will be pretty close. This is much more important on very heavy cars ( such as yours) I have seen the rear end gears change the ET and MPH by as much as one HALF a second andd as much as NINE MPH, without any changes to the engine.

JOE SHERMAN RACING ENGINES

Sorta what Joe said...

You need all the help you can get... getting that heavy boat moving off the line! Gearing is your friend with that galaxie and a small block!

Having 15% too much gear, like Joe said, can help... especially with a big car like yours. The assistance it gives in the first part of the track FAR outweighs any hinderence there is over-revving at the finish line.

If your car peaks out at 6500 rpm, you might shift at 7000 and go out the back door around 7300... when gearing the car for best et at the track.

The ideal shift point will be one that uses the maximum average power. For example, let's say an engine pulls hard from 5000, peaks at 6500, and and pulls hard to 7000... and the trans drops the rpm 2k rpm per shift... Pulling the handle at 6500 rpm puts the engine in a 'bog' at 4500 rpm, and shifting at 7000, where the engine is still strong, lands you back at 5000, which is in the 'meat' of the powerband.

Shift it where the engine 'wants' shifted, and put as much gear in it as you can stand.

As for pulleys, you DEFINITELY need an underdrive crank pulley. You don't need to worry about the rest of them.... If the crank pulley is made smaller, the rest of them will slow down. (of course, a matched set is 'prettier')

Good Luck!

Thanks for your input guys I had my mind set on 4:56's but I started second guessing myself but I'm back on track and I will go with the 56's. I used to drive the car on the road alot but with gas prices It cost nearly 40 bucks for a short trip town and back,so I won't be driving it on the street much at all. I am going to pick up a set of underdrive pulleys as well.

This table is a great starting point to pick a starting line ratio. Many times a "hook problem' turns out to be more related to startling line ratios. Here is a helpful chart that may help. It was made by Dave Morgan from his Door Slammers Chassis book..

Weight ...........2000 2500 3000 3500
3-0 stroke (In) 11.00 11.25 11.50 11.75
3.25 stroke......10.50 10.75 11.00 11.25
3.5 stroke........10.00 10.25 10.50 10.75
3.75 stroke.......9.50..9.75...10.00 10.25
4 stroke...........9.00..9.25...9.50...9.75

Take the rear gear ration x 1st gear ration= S/L ratio..

I have also hear that a good way to tell if a car is geared right is if it shifts into high gear at the 1/8 mile mark. Not sure if thats accurate or not. I personally run a 4.30 gear in my 69 coupe that weighs 3350 roughly with me in it. My fastest pass is 13.45 at 105. It seemes to work very well.

We run a 4:30 with a 28x10 hoosier. Works great for us.