98CayenneT/A

Wondering if it would be foolish for me to switch from my current 3.73's to 3.08's ?

Car: 1998 Pontiac Trans Am
Mods: 3.73's Lt's, Yank ss3600/4l60e
1/4 Mile: 12.2@111 mph
Tire: 26 in. radial

Reasons for considering this change:

As the car is now I run out of gear around 118-120 mph

Plan on spraying 100-150 shot next season which would put me around 120-125 mph trap

I go to a road course event with a long straight away where you can roll race others and I run out of gear pretty quick and would run out even quicker spraying with the 3.73's

For random highway encounters where the speed limit is 60mph I am at a very poor spot for it will not hit second at that speed unless I drop it down in which second runs out to 74 mph.

I just think for what I use the car for and my plans the 3.73's may be to steep.

Any opinions? Am I missing something or should I go for it?

FirstYrLS1Z

iTrader: (4)

Couple questions on the cars' history. Did it have 2.73s'(GU2) or 3.23s'(GU5) originally ? Those two gearsets from the factory required the use of different series carriers. 3.73s'(thick set) are available for a 2.73/3.08 carrier. If you have the 2 series carrier(2.73/3.08),you can use 2.73s' and/or 3.08s'. 3.23s'(thick variety) are not available for the 2 series carrier. If you have a 3 series carrier(for 3.23s'/3.42s'),you CANNOT use 2.73s'/3.08s'.

98CayenneT/A

Sorry. Should of added that in my post. It was originally a 2.73 car series 2 carrier and the first thing I did was change gears.

RPM WS6

iTrader: (3)

I'm not really a fan of 3.73s for an application that already has or will have an optimized stall speed. The downsides of the swap (cost, risk of install issues, need for re-tune), IMO, are bigger than the performance benefits. In fact, with that 3600 stall speed already in place, you could drop down to a 2.73 gear and not lose more than about ~0.10-0.20 seconds of ET. Going to a 3.23 would cost you no more than about one tenth. So I just can't see much value in a 3.73 swap for an application that will have, or already has, an optimized stall. You'd need a much bigger (numeric) gear to really make a worthwhile ET difference for the cost/hassles/risk of the swap. This is, of course, assuming that you're not one of the folks who's extremely sensitive to higher stall speed "looseness" at part throttle.

Having said all that, you already have the 3.73s so now you'd be looking at all those same hassles (cost, risk of install issues, need for a re-tune) to go in the other direction with your existing rear. If not for the fact that you have concerns about running out of gear, I would say to just keep what you have since there really isn't any gain for going back (other than MPG and a shift in what speeds you'll see upshifts/downshifts at.)

If you are worried about running out of gear at the end of a 1/4 mile, and if it's going to be close, perhaps you could increase rear tire diameter? Not sure if that would give you enough, you'd have to use a calculator for that.

Overall, it's my opinion that 3.23 is an ideal ratio with an optimized stall speed for an LS1/4L60E combo. Great street manners, excellent track performance, stock MPG on the highway. If you were going to do the swap, I would recommend this gear, or perhaps a 3.42. The nice thing about going to a 3.23 or 3.42 is that you might be able to find a complete used rear out of a stock GU5/GU6 car that wants to upgrade, and then just bolt that in without the need for swap labor on your gear set - then you could sell your rear or set it aside in case you ever want to go back.

98CayenneT/A

As posted in my above post, gears are the first mod I did. I am now realizing with a nice converter in place the gears become less of a factor threw different post from you and others on here. And seeing my buddies 60' with a similar setup as me but with 3.23.

As far as the gears being set up/cost, tuning/cost ect. that is a non issue in my dilemma.

Converter loosness is not a concern either and would not bother me. If I knew now what I knew back then I would of just rolled with the 2.73's

I would prefer to keep running a 26 in. tire.
At 7% converter slip a 28 in. tire would gain me 5-7 mph so running out of gear around 125 mph

98CayenneT/A

Also for what I use the car for and plans of nitrous I'm more than fine if I lose a tenth or two n/a if it means more fun on the street. The tenth or two I don't see being a issue at the track because I will be more then making up for it with spray, also when needed on the street.

jhshnh

What are your shift points set at?

98CayenneT/A

1-2 is at 6150 and 2-3 is at 6100

RPM WS6

iTrader: (3)

I don't think you'll trap over 125mph, even with the 150 shot, unless you plan other mods in addition. But it may be close.

However if you'd rather keep the 26" tire, and cost/hassles/risks/tuning of the gear swap is a non-issue for you, then you might as well move back to a 3.23/3.42 - whichever gives you enough room to be comfortable. However, as FirstYrLS1Z pointed out above, there may be issues with finding certain ratios for your carrier. Obviously that's a non-issue if you're willing to just swap the whole rear with a stock GU5/GU6 unit, but you haven't mentioned if that's a possible part of the plan or not. Otherwise you may have to go with the 3.08 as mentioned above (unless there is a "thick" 3.42 - I don't know off hand.) Even with a 2.73 you wouldn't lose more than 1-2 tenths NA, maybe not even that much. So a 3.08 certainly wouldn't be any worse.

You mentioned a shift point of 6150/6100. You could bump the 3-4 shift a bit if you just need a touch more rpm to avoid an upshift to 4th for whatever the combo ends up being. The '98 rod bolts are a bit weaker than later years but, especially if you'll be running a window switch, you should still be OK revving to 63-6400 with a 6500 rev limit if that would prevent a shift to 4th.

SteenH

Earlier rod bolts were shittier, but they are absolutely a non issue under 6500 RPM. At that rpm stock valve springs are going to be where the issue lies.
I think you're nuts for wanting go through the trouble of changing your rear gear again. Bump up the shift points and don't worry about the gear in my opinion. And if it still isn't enough move to a 28" tire. You will be surprised how much farther your gear will take you by simply changing the shift points. Best of luck

FirstYrLS1Z

iTrader: (4)

Aftermarket 'thick' 3.42s' are available.

RPM WS6

iTrader: (3)

I agree. I would recommend a valve spring upgrade if you're going to rev into those ranges. With a stock LS1 cam, going with a stock LS6 spring would be a good choice for this purpose.

98CayenneT/A

Thanks for the ideas and opinions.

I would not go to 3.43's but do like the idea of just swapping rear ends around with the purchase of a 3 channel 3.23 10 bolt. That absolutely would be a option.

I think my biggest thing is just wanting more gear for power cruise which is a road course event once a year and with that said I think I'm leaning towards a longer gear so maybe it would be a good idea to try and track down a 2.73 10 bolt.

I do love me 3.73's from a dig on the street. Just trying to get the best of both worlds in 1/4 trapping and roll racing in certain events. But like I said, I am willing to lose a tit in the quarter if any by going to a longer gear if that means more fun during other events.

RPM WS6

iTrader: (3)

A complete 2.73 or 3.23 rear would obviously be the simplest option then, but if you're looking for the best of both worlds between these two then a 3.08 would be a good middle ground/blend.

98CayenneT/A

In your opinion would it be foolish to attempt a gear swap myself? I'm absolutely mechanically inclined just lack experience but not afraid to dive in head first. Rebuilt my 4l60e this past spring for the first time with a flawless victory if that helps with mechanical ability.

Figured I would ask ya since I see you in the gears section often.

kinglt-1

iTrader: (26)

if you can rebuild a transmission then you can rebuild a rear end.