Lordkdog

I have a 1987 Trans am GTA with the 5.7 and the 700r4 i am unsure of the rear end. I had a rebuilt l98 put in that has just under 20,000 miles as of now. It has factory runners and plenum but a bbk 52mm throttle body, also I am running 22# injectors. I am looking to bore out the runners and plenum soon though or replace them with a better option for tpi. I want to find my next step for what to do with this car. I like the way tpi feels so I don't want to switch to HSR or anything like that and I want to be able to drive this daily so I don't need to push 500 hp. I want to get it to be a bit better for now. I was thinking that tuning it might be the next best step but figured I ask if there is something more important I should do first. Any advice for possible moves or steps is appreciated!
Edit : I also have redone headers and exhuast, i have the hooker 2460s going to 3 inch exhuast all the way back.

dmccain

iTrader: (2)

Gears. 3.42s or 3.73s. Shift kit, headers..

formularpm

With an MAF car especially, I don't think that you'll see much in gains from just tuning. The car does have some adaptability built in to account for greater airflow.

With what you've done already, the intake is about the last place to find more power with bolt-ons.

Lower gears will help too, but that's always a tradeoff.

Could also look into a higher-rpm converter.

Lordkdog

I haven't ever done any work on a transmission so that could be fun, a shift kit, and then a higher rpm converter. I'll have to look into both. I don't know if I want to change gears cus I like the mileage I'm capable of while still feeling some power! Thanks. Anything else from anyone will be appreciated!

sofakingdom

iTrader: (1)

Then become sure.

Changed the fluid lately?

I thought not.

Good place to start. Make a point of determining what model of rear it is (probably a 9-bolt, butt LOOK to make sure), and LOOK at the gears to see what they are. Odds are, they SUCK, although who knows, you never do until you LOOK. Which of course the eeeeeeezyest time to do that it while coming to grips with the deferred maintenance.

We won't go into "rebuilt L98" quite yet. I'd be almost willing to bet though, it's a 70s block with dished "rebuilder" pistons such as Silv-O-Lite, a flat tappet cam (probably a 929 replica), and typical 70s smogger heads such as 882, 993, or 624; or TBI ones such as 193. Power killers in ALL cases. Butt, too late for worrying about that now, and too soon to worry about fixing it. Change your rear end grease first and report back.

Lordkdog

The crate motor was from atk it was the ATK 059-DCN7 it had all the cast numbers I'd have to look to make sure of what's what on it. I had the rear dif serviced when the motor went in which is why I haven't been back there yet but it is coming up soon so I'll look when I do it. when i do look how do I know what's a bad gear set. If there's a sticky or page for it I'll gladly look and correct it.

sofakingdom

iTrader: (1)

Count the teeth on the pinion and the ring. One ... two ... three ... not that hard. If it's still the original rear, it'll have either 13 on the pinion and 36 on the ring (36 ÷ 13 = 2.7692307 etc., aka 2.77, or 11 and 36 (36 ÷ 11 = 3.27272727 etc. aka 3.27). It's not that hard.

Not sure about stickies or pages that have LOOKED AT THE PARTS inside YOUR rear axle TODAY. There might be one butt I wouldn't bet on it. People change that stuff all the time, either because the original broke or because they're upgrading or because ... no idea, they're HUMANS, ... butt don't bother to change web pages and whatnot for YOUR PARTICULAR CAR afterwards. They're just [mr_spock]HUMANS[/mr_spock] after all.

As far as whether it's a 9-bolt (the rear that would have come in it) or a 10-bolt (the other rear that came in lots of these cars as well), it's equally hard. Look at the cover bolts. Count them. One ... two ... three ... nothing really technical or hard to figure out here. It's just an antique car.

I wouldn't bother looking at "specs" and "receipts" and stuff like that, to figure out what heads and block and cam you have. LOOK AT THE PARTS. They don't lie. EVER. They ARE what they ARE. Almost as simple as the gears. You just LOOK; that is, place the gaze of your eyeballs on them; and their part #s are cast right into them. LOOK AT THE PARTS. Not sure how many times I can say that. THE PARTS will tell you what you've got. All the rest of that is subject to lying, cheating, changing, "honest mistakes", and so on. THE PARTS won't have any of those things. I can't emphasize enough, LOOK, and IT'S NOT THAT HARD.

Lordkdog

I'm editing my original response cus I didn't like the way it sounded.
I do understand that knowing these will be good info for me to have so now that it's been pointed out I'll look so that I know for future reference. With the motor specifically it's not super important to me because I cant do much about it. I don't have space or tools to build a motor from the ground up which is why I went the route I did with the crate. Hopefully it's solid and everything on it is decent. I'll check over the weekend when I have some time. I do understand how to check my gears in the rear end lol I meant what is considered a bad set. I do know that, based off of tire size transmission and rpm at speed I should have either 3.7 or 3.73. Ill check the bolt count this weekend as well. I havent serviced it becuase i was told 25k to 30k how often to do it and I'm not there yet but I can go ahead and do it soon just to double check everything. This is the first car I've ever done anything other than repairs to so I'm fairly new to the game so please forgive me for not knowing everything like I should lol. I appreciate the um detailed advice on how to find it tho 🤣
anything else I should know or do is appreciated!!

AlkyIROC

Unless it's been swapped to the weaker 7.5" 10 bolt, a 1987 with a 5.7 and 700R4 will have a 3.27 geared 9 bolt diff. Gears are not as easy to find as those for a 10 bolt are and they are not cheap. The common aftermarket option was 3.70 gears but there are a few other options now. 9bolt.com is probably your best choice unless you wanted to swap the entire diff to a direct bolt in 9" or 12 bolt which again, is not cheap.