what gear do i need to run

[daves 72 dart]

hello everyone.what gears do you guys think i need to run? it is a 72 dart swinger with a 8 3/4 rear with 4.88, frame connectors,cal tracks with there springs.727 trany with a 4200 stall converter the engine is a 340
Work done: O-ringed, tubed for roller cam, oil gallies enlarged, bored to 4.07
(.030 over) and honed with deck plates by Herb McCandless.

340 steel crank
Prepared by Lunati, stroked .110 to 3.42 stroke and balanced to 8000 rpm's.im planning on shifting at 7200.

340 steel rods
Prepped by Lunati. Hand picked set. All are within .001 of each other in length. Bronze bushed, balanced and lightened.shot peaned

Heads
340 X heads with 2.08 intake valves and 1.60 exhausts. Double springs for
.700 lift cam, Maximum porting on intake and exhaust ports.Ports are 63cc combustion chambers. heads flow a little over 260 cfm.

Pistons
Venolia lightweight forged pistons. Uses dykes top ring, 1/16 2nd ring and standard tension oil rings. Weight is 510 grams.the Compression is 11.3

Intake
Holley Strip Dominator ported to match heads.950 biggs carb

Camshaft
Cam Motion roller 269 275 @ .050 and .631 lift with 1.5 rocker Valves set on .024 .028
RPM range 4500-7500. Cam is degreed in at 104 deg centerline.

Other Parts
High volume Melling oil pump, Comp Cams roller lifters, Crane 1.5 roller rockers(gold), Fluid Balancer, windage tray, Cloyes double roller timing set. SCE copper head gaskets(.060). Tall valve covers for use with roller rockers. Moroso 8 qt deep sump oil pan. Bronze cam gear for use with roller cams
thanks.

[daves 72 dart]

it will have 28'' tires 275/60/15s.

[cudabob496]

http://www.slowgt.com/Calc1.htm

http://www.wallaceracing.com/calcrgr.php

[JVMopar]

Well it all depends on what your engine actually dyno's at and what graph looks like.

A common mistake among drag racers is to shift at the same RPM for every gear. This is fine as long as the RPM drop for each gear is the same. So first we figure out how much RPM drop is between gears. On a 727 or 904 with 2.74, 1.45, and 1.00 gears the drop from 1st to 2nd is 2267 rpm. From 2nd to third is 1791 RPM. And there will be some converter slippage but that should be insignificant. The 727 or 904 comes out alot closer with 2.45, 1.45, and 1.00 gears (only 33rpm difference). SO now you take your dyno graph and find the maximum area under the curve for the amount of RPM change between each gear. When you find the max area then you know the RPM you should shift for each gear. So you may want to shift at 7,600 for one gear and 7,200 for the next.

After you know this stuff then you can determine what gear ratio to run.

We learned and did this stuff in school. We put it to use too. The school had a '99 silverado that we modified for E85 (milled head, supercharger, extra injectors, etc) It was a competition for emissions and performance combined on a national level. We won the hill climb but had problems with the drag race. Spark plug wires kept popping off during the runs. The Accel plug wire boots fit so tight that the air inside would expand with the heat and push the boots off (that's all we could figure out). We poked holes in the boots and they stayed on for the hill climb. Of course having a dyno at our disposal was big benifit.

[daves 72 dart]

jvmopar thanks for the info.but what im looking for is what gear to run so i dont run out of gear before i cross the line.

[toad490]

Dave, go to this site and you can play with all kinds of combinations.
http://www.golenengineservice.com/html/calculators.html
My quess would be 4.11s.

[toad490]

4.11s at 6500rpm would give you 132mph thru the traps. The ? is do you have enough hp for the wieght of your car to get you there. Your ? is hard to answer with out an acurrate hp at what rpm and weight of your car. IMHO

[JVMopar]

Yea I know your wondering what rear end gear to run.

But lets say your peak HP is at 6700 rpm and is flat after that till 7000 then falls off just as fast as it was rising before 6700. So you'll want to run through the traps at about 7600 rpm. So you want to run 10 seconds in the quarter mile at around 130 mph.

So 130 mph, 27.99" tire, 1.00 trans ratio, 7600 rpm, puts it at like 4.88:1 rear end ratio. Which that's a fairly wide tire and it will probably get a little taller with the speed your running. So you may want to go even a little higher like 4.9:1.

That's just an example.

I'm no drag race expert, but like I said this is the stuff the taught us in school. We did simulations on the chassi dyno after calculating road HP at different speeds. So we knew how much HP was going to get eaten up for the particular vehicle we were using.

[daves 72 dart]

thanks for the help guys.i think i will stay with the 4.88s and see how it goes.