14 replies to this topic

[funkpolice]

My 3.73 getrag is making a lot of clicking noises and also has a leak at the axle seal.  I want to replace it before the racing season starts, but I'm unsure what I should do.  With the 3.73, 28" slicks, and w/o n20 I was trapping 111mph and going into 4th annoying close to the finish line.  This year I'm planning on hitting it with a DP 150 shot.  The car dynoed 560ish at the wheel on the nitrous.  Initially I was set on a 3.23 with the upgraded clutches.  Since then they 3.23 is harder to find and I'm not sure that I'll be able to hold 3rd with that setup anyway. I don't know what I can expect my mph to be with the nitrous, but I was thinking maybe 120?   So, should I go 3.06 which is cheaper and available,  or hunt for a 3.23?  I was thinking that the 3.06 with a 26" drag radial might be a good setup providing I can get it to stick at the line.  With my 3.73 and a 26" tire traction was hit or miss, thus I bought the slicks.  Either way I'm going to have BFNY put the clutches in it and also go with a set of DSS axles and maybe a new drive shaft.   Any thoughts? Also if anyone has a set of axles the are willing to sell please let me know.

 

bill

oh, and if you are interested in my 3.73, it'll be available at some point in the future.  I don't know if it's better to sell it as is really cheap, or maybe send it to BFNY and have them address whatever is going on with it, maybe upgrade the clutches, and sell it as a built, working unit.

 

bill

[Goehner]

I liked the 3.73 gears, but I drive the shit out of my car when it runs.

I say send it or the car to Erik.

[rdrdr90]

^^^^^this

[funkpolice]

I am going to send a diff to eric.  My question is whether to go with a 3.06 or try to find a 3.23.  I already have a 3.73 and it's not what I need at the track.  Too many kids and traffic violations have put me in a place that I don't care how the car performs on the street anymore.   in the 1/4 mile, 560 rwhp, 120 mph, is a 3.06 a good choice?

 

bill

[cnister]

3.23 wasn't a factory option. You can buy a set of those or 3.55.

Imo I would just buy whatever gears you decide to go with and send the whole thing to BFNY to be refreshed and new gears installed.

[Goehner]

Well I am confident the 3.73 would perform better at the track than the 3.06, but if you don't care about that, I would go 3.06 cause they are a dime a dozen

[rdrdr90]

So are 3.91's. The difference between it and the 3.73 is minimal in every way except cost.

[funkpolice]

hmm.  I was under the impression that 3.73 was a poor choice for most builds in the 1/4 mile.  It would be easier for me to decide if I had an idea what the car will do with n2o functioning properly, but as of now it's only worked on the dyno.  so, with a guess at 120 mph and my 28" tires the 3.06 would put me around 6200 in 3rd gear, the 3.73 is 5400 in 4th gear, and a 3.91 would be 5600 in 4th.  I don't know whether winding out 3rd would do more for me than staying with the shorter gear and having better 60's.  Somehow I got it in my head that most over 500 hp were seeing better results with the 3.06, 3.23, or 4.10 rear.  Goehner, what were your ets, hp, mph when you had a 3.73?  Maybe I'll buy a 3.06, have the 3.73 overhauled, and do a comparison for myself.

[Goehner]

I went from 11.30 to 11.06 changing from 3.06 to 3.73. I had P1 at 9 psi on the factory 392.

[chief455]

3.23 wasn't a factory option. You can buy a set of those or 3.55.

Imo I would just buy whatever gears you decide to go with and send the whole thing to BFNY to be refreshed and new gears installed.

just the LSD refresh will be a grand (parts/labor), plus cost of ring and pinion.

Erik has stated recently, that it could be cheaper/easier to buy a new Getrag LSD unit - he thinks they are also ~ a grand.

I have yet to hear back from where these are sold.

 

I'd keep doing the math as you are, and chose a gear best suited for the rpm/mph you'd like to be at. And decide if that choice is for street OR strip. Can't really have one ratio be best at both.

[El Diablo]

You may end up limited to factory ratio's, US Gear stopped making the gears for the Getrag. Only other company that I know of that made gears for them was Richmond and there was a lot of people complaining about them not holding up and being noisey even when set up properly.

[rdrdr90]

hmm. I was under the impression that 3.73 was a poor choice for most builds in the 1/4 mile. It would be easier for me to decide if I had an idea what the car will do with n2o functioning properly, but as of now it's only worked on the dyno. so, with a guess at 120 mph and my 28" tires the 3.06 would put me around 6200 in 3rd gear, the 3.73 is 5400 in 4th gear, and a 3.91 would be 5600 in 4th. I don't know whether winding out 3rd would do more for me than staying with the shorter gear and having better 60's. Somehow I got it in my head that most over 500 hp were seeing better results with the 3.06, 3.23, or 4.10 rear. Goehner, what were your ets, hp, mph when you had a 3.73? Maybe I'll buy a 3.06, have the 3.73 overhauled, and do a comparison for myself.

You are correct with your assumptions. I'm at 118mph and I'm right about 5400 in 4th with the 3.91. I was at the very top of 3rd with the 3.06. If I go to a 26" DR I should be able to get to the top of 4th.

I want to cross the line in the top of whatever gear I am in.

[funkpolice]

 I spent some time playing around with the Wallace racing calculator.  I don't know how accurate it is, but it sure calls for a lot of inputs.  I put in all my torque values from the dyno graph, and as much of the info as I could find about my car, and it spit out a 11.11 @ 118mph with the 3.73.  3.06 was a 11.16 @ 121mph.  3.23, 11.14 @ 119 mph.  3.92, 11.11 @ 117 mph.  I don't think my car will run an 11.1x, as the projected 60's were awefully low in the 1.5 to high 1.4s, and I'm fairly certain something is amiss there.  Looks like I'll stick with the 3.73 and have it built a bit stronger with new clutches.   Where I really saw some crazy numbers was messing with the weight of the car.  Makes me want to go outside and start gutting it now.

 

I still need something to put in my car while the 3.73 is being serviced.  The seller I was speaking with on lx has either sold the part, or decided he wants to hold onto it, as he stopped replying to my pms, and has refunded another guys money that had sent payment.  If anyone has a used getrag they will sell to me I'd appreciate it.  I'll only use it for a month or two, so the cheaper the better.

 

bill

[chief455]

Bill

I've been using the Wallace calulators for years. They are close for a guesstimate. Yes, shedding 100lbs is better than any tire or gear change

Convertor slip and rear suspension ability to launch seems the main variance factors from dead on calculations.

I think if you are leaning toward E.T. reduction than street rpm vs mph, 3.73 - 3.92 will make you happy. Can always run a bit taller tire to compensate if needed.

I think we are lucky to not have bought that 3.06 w/ 30k miles from a buddy with no proof.

Good luck on your saearch, I'm on mine!

kbr577 has a sweet 3.73 w/ heavy clutches in NY on th lx forum...

[funkpolice]

I'll look him up, thanks.

 

bill