I am running a 4.56 ring pinion and I want to know if going from 4.56 to 4.88 will help me at the track .

tires .31 x 16.5 M/T Sportmans Pro
trans. th350

Might improve your 60' time,but might take away from your top end.

Why wind up your 427 that high and cause increased wear? Unless you have heavy car and high compression to utilize-sounds like way to excessive to me! Could you tell us specifics, wt of car, cam, pistons, induction system etc.
:cool:

Definitely post more specs about the entire motor/drivetrain/car combo. Your car just might be desperately crying for more gear and it could benefit. At the sime time, you could already be overgeared and it may pick up with less of a gear. Thats why you can just say yes or no cause it can go either way. Along with that other info, what is your shift point rpm from 1-2 and from 2-3 and what rpm are you running at when crossing the finish line. Plus, how well does the car hook(whether it hooks well or not, that could show some info about your 60 footers and how much more potential there is/isnt there)?

Sorry for the incomplete inf.
1971 GMC SPRINT , complete, no fiberglass
BBC tall deck block 427 @.030 over
6.535 rods ,forged pistons ,
10.1 compression
RPM AIR GAP intake ,
990 heads ,2.3 valves -1.88
Holley 850
1 3/4 headers 2 1/2 mufflers
TH350 trans.
4.56 rear / 31 x 16.5 /15 M/T Sportman PRO TIRES
shift 1-2 7000 rpm, 2-3 6500 rpm
best 60ft.1.78 most of the time 1.82
passing the line(1/4) I am not sure if it is 5800-6000rpm,??? I really can not remember if it is lest than that graemlins/clonk.gif ,I hope this help. graemlins/thumbsup.gif

Javier, just my way of thinking - but I'll bet you would be quicker and faster with 4.10's.

Thomas

since you didn't post cam info, going by your shift points you could use the extra gear so yu go thru the lights at around 6500. Maybe borrow some shorter slicks once and give them a try, if you gain you need more gear.

Still not enough info! You haven't even mentioned what converter stalls at and what rpm leaving at starting line? Not utilizing combo correctly if going thru traps at 6000 with 456 gears! I run 456's and shift at 6500 and thru traps at 6800! Also, do you know for sure rods are 6.535's? Seems like a long rod! How much hp is your engine producing? Something really is puzzling here:::

The converter is a 10" ,3500 ,cam solid XS282S

VALVE ADJUST .016
GROSS VALVE LIFT - 590IN / 598EX.

@.015 282/290

OPEN CLOSE
IN 35 BTDC 67 ABDC
EX 79 BBDC 31 ATDC
AT 106 intake center line
@.050 244/252
LOBE LIFT .3470IN .3520EX
LOBE SEPARATION 110

Bomber thanks for the advise but I improved my 60ft going from 3.90 to 4.56 it may help but what Orange said is a good option ,to try lower tires .
Blazerbob I am using a tall deck block 10.2, the 6.535 rods are needed to bring the normal deck (9.8) pistons to the top .
I footbrake at 3500rpm ,I am running very tall tires 31" tall x 16.5" wide .what tires are you running ??

More gear :D That's an awefully tall tire. Orange has it right on. borrow some tires.

Also, that 1-2 shift is rather high, even for a rect. head motor. That's not avery big cam. Try shifting at 6400-6500 at all shifts.

Trap RPM is TOO low. Just like Bob said 300-800 RPMs above your shift points for trap RPM.

Rob

Before you even swap tires(just to save a little work for yourself), try out shifting lower. Although it might rev allright that high, it sounds from the combo that you shouldnt really gain anything from running it above 6500rpm. If you run the first half of the track faster by shifting a little earlier, you might wind up further through the second half of the track. Just a though. I really dont see any reason to go any bigger on the gear so far. If you were making plenty of power all the way to 7 grand with the 427 as is, Id think you should see more than 104mph...which makes me think that this surely isnt a super "peaky" engine. After you try some differing shift points and see what the results are with everything as is, Id then experiment with different tire heights along with different shiftpoints with the different height tire to see what happens. Although this is a little off topic, how much work have you done with the tuneup? Right now(and maybe even with some experimenting) it may seem that your current gears are off the mark, but, if theres a lot of hidden power in there, some experimenting with the tuneup can help pull through on the big end. All the sudden, it might not look like your gears are all that far off.

Duh! My bad, didn't notice the tall deck---Right on! I'm running 29x12's! Think shifting from 6200-6500 may work better and size of tires are way to big! 28-29's max! What psi in slicks, and what does vehicle weigh?! Anyways-need to tune your application going thru lights at 6500rpm at least! :cool:

There are so many ways this combo could be bad, likely that several things are working against each other.

The part that really sticks out to me is the mph - seems very low for what is known about your car.

Have you gone over the fuel and ignition systems? Something or several things are bottlenecking your power and acceleration. By chance do you still have a 5/16" fuel line from the tank to the pump? Even if you have a good size fuel line, did you pull the fuel tank sending unit and replace the nylon mesh in tank sock? Very common for an old tank sock to be kinda melted and very flow restictive. What is your ignition system and complete advance curve?

Thomas

Hi Thomas ,I did change the tank pickup line to 1/2" and went -8an all the way to the carb with a moroso -8an fuel filter 3ft.from tank ,still using the 120gph CARTER fuel pump .

The distributor is a HEI GM lock ,no advance set with a CRANE FIREBALL ,timing set at 42 (lock ),I try it at 36 ,38 ,40 ,and works best there :confused: .
I recived a foto via mail from the guy who take pictures at the track and noticed something bad .the burnout is got a lot of smoke coming fron the passenger tire and not many from the driver side .
I took the car out and did a burnout with my brother looking.
The driver side tire stops spinning at the burnout ,I think this is causing my problem not getting the same 60ft. all the time ,I got a new posi to intall 8.5 RICHMOND LOCK RIGHT.

The 1/2" line is good. But did you replace the fuel tank sock?

For sure the bad posi is holding your launches back. Still, that does not explain your mph, you should be in the low 11x mph range.

Thomas

"The sock "is the old filter that is connected to the old pick up line ??

I replace the old pickup line in the tank and weld a 1/2" pickup line with no filter in the tank ,the filter is outside .Or there is another "sock" in the tank around the pickup line .SORRY but My english is like my combo we both need some tunning :D .,"but more important we keep on trying "
:eek: Do I really got a 11 sec. combo ? I better install the posi and put my BATMAN BELT full of jets,timing light ,spark plugs ,valves lash wrenches ,ect... :D

If you no longer have a filter/nylon strainer inside your tank then there can't possibly be any restriction there.

Don't worry about your english, I work in a melting pot and would say that you are doing quite well.

Of course fixing your posi can only lead to better results.

The one downside to your large tires is that the same thing that helps you get off the line quickly, ends up as a power drag for the rest of the 1/4 mile. Those tires have considerable rolling resistance.

Still, I think something else is to blame for the slow times - relative to what you have.

Have you done both of the following to verify general engine condition:
1) Compression test, and were all cylinders very close in psi.
2) Leakdown test to see if your rings and valves are up to the task.

Another potential problem is a transmission or torque converter that is not very efficient, causing it to waste a lot of hp. Something to think about - 105 mph with your tire diameter would equate to ~ 5,200 rpm if you had a lock up torque converter. The ~ 6,000 rpm that you actually see going through the lights means that ~ 800 rpm is lost to slippage of the trans or torque converter or both. Either way, that is not good, you are losing ~ 13% to something. A good non-lock up converter and trans would be ~ 3% loss, with ~ 8% on the loose end. You would appear to be way beyond an acceptable slippage %.

Get your Batman belt out, your going to need it.

Thomas