LT3D

Hi all, I have an 88 GTA with an L98. I've only had the car for about a year and I'd like to keep adding power over the next few years. So far the car has the following done:

- Cam (installed by one of the PO, unsure of specs - video of cam at idle https://drive.google.com/file/d/1foN...ew?usp=sharing)
- CAI
- airfoil
- Doug's headers (1 5/8" primaries)
- 3" from the y-pipe back exhaust
- Outer SFCs
- tubular panhard bar
- tubular rear control arms
- wonder bar
- BMR strut brace
- KYB adjustable shocks
- Eiback lowering springs
- Proforged center link, idler arm, inner/outer tie rods and sleeves

As is, the car is surprisingly fast. It spins the tires pretty easily if I'm not careful with the throttle. I had an LT1 in the past and it's not even comparable. So I am not sure if there were any other mods done to the car before I bought it. But the heads/intake look stock.
I don't plan on racing the car, but I would like to max it out as a street car. I do NOT want to change the runner length as I don't want to change the power curve. I just want more of what I got. This is where I am looking for opinions.

- Should I invest in a FIRST intake?
- Should I change the heads? If so, which ones? AFR, machined Vortecs, ported L98 heads, other? What accompanying mods do I need? 1.6 rockers? 24lb injectors? AFPR?
- Do I need to change the torque converter (I think I still have the stock one)? How much power can the stock transmission handle?
- Would porting the stock heads and intake result in any appreciable gains?
- Do I need to get the car tuned? Have the PROM changed? It is next to impossible finding shops that can do this to third gens where I live.
- Should I leave the car as is?

Thanks everyone

QwkTrip

iTrader: (22)

Tires that won't spin, and torque converter.

LT3D

So, no engine mods, just a new converter? What stall do you suggest?

Komet

This topic has been covered to death by the thousands of those who came before you doing the same thing. Your TPI setup was maxed out on the stock L98, so you could certainly pick up some power with a FIRST setup, or by porting what you have and adding larger diameter runners. You could also pick up power with better flowing heads, if vortecs are your choice you'll need the vortec TPI lower or the FIRST for vortec heads. There is power to be had by porting the stock equipment, but if you're paying someone else to do it, it's likely not worth the cost. Intake and / or head swap will likely necessitate a new tune.

Rockers depend on the cam, you need larger injectors if you're running out of duty cycle, and an afpr is needed if you decide to run something other than stock fuel pressure, or dial in what you have. I don't recommend it as a tuning device as you're unlikely to want to richen the fuel map everywhere.

89fast5oh

I have done this over and over on different cars. And every time when I was done I wished I had kept it stock or near stock.

I am debating pulling the 383 & Probuilt 700r4 out of my 87 putting the stock 305 TPI back in..

LT3D

Thanks for the response Komet. I'm still unsure if I want to go with vortecs. Having the stock intake and heads ported would cost me about 1k, plus around 400 for bigger runners. One of the big reasons going this route is because fitment is guaranteed. But depending on how much power that makes, it may not be worth it. Regarding the duty cycle of the injectors, is there a way to calculate this? Or do you know if the car is not running right? And with the engine mods, do you recommend any mods to the transmission?

LT3D

This is very interesting. What made you regret it?

Orr89RocZ

iTrader: (20)

The bolt ons make a nice difference. Intake mods plus 1.6 rockers and tune to support, with 2800 stall and built trans, adjust shifts right and 3.23-3.42 gear on a drag radial it will drop half second or more in the 1/4 mile. Def fun to drive

heads and tune will get few more ponies for sure but its a big investment with tpi. First is nice but if cam is any good it would make more power with a short runner intake like a stealth ram mini ram pro flo or single plane efi intake

aliceempire

iTrader: (14)

Car runs good, drives good now? Feels really fast for you? Then yeah, converter and tires. Best bang, lowest buck. Anything else you do to it is going to need something else and it's a rabbit hole that puts the car out of driving time. Troubleshooting, parts finding, problems that creep up, all take away from driving it.

LT3D

Thanks for the suggestions Orr. It's definitely looking like the converter is at least one of the next logical steps.

LT3D

That rabbit hole is something I'm trying to avoid. I got into that this season with all the work I did to it, I only got to enjoy the car August/September. What stall do you think for the converter? 2800 as well? Would I need a tune after installing it? Would I need a trans cooler?

Orr89RocZ

iTrader: (20)

Imo trans cooler is always a good thing. Factory style thru the rad aint bad if the thermostat and fan is tuned to run much cooler than stock like say 170-180 deg. I like trans temps no higher than that

dont need to tune for it but could play with converter tcc lockup speeds to suit your driving preferences

Abubaca

iTrader: (3)

I'm another "been there, done that" guy. If I ever had another L98 car, that does NOT need to stay all original, but I'm not gonna LS swap, I'd leave the engine alone, except for headers/exhaust. Then do gears and a converter. Well....ultimately I'd go gears and a manual transmission, but assuming that level project isn't in the cards, gears and a converter. I had a zz4 cam/headers on an otherwise stock L98. Made a difference, but you know, nothing crazy. swapped out the 2.77 rear for a 3.27 rear, and added a 2300 converter, and it was absolutely night and day. And MORE than enough to be fun for sure! ...that manual though is the ticket. I'd rather be stock with a manual than really anything with an automatic. Just me though.

LT3D

Thank you for your input Abubaca. The "been there, done that" experiences is exactly what I'm looking for. I have considered shorter gears, and it seems a bigger stall TC is a good bang for the buck. I will need to figure out, if the TC and gears are stock on the car. I wouldn't want to swap out something if it's already been done from a PO.

Abubaca

iTrader: (3)

Yeah, I had a few people tell me I needed a TC, but I just couldn't imagine it making a big difference, assuming I went with one small enough to be streetable. Ended up blowing up the stock 700r4, and picked one up from a buddy, which had a B&M holeshot TC, either 22 or 2300, can't quite remember. Here's a good way to describe the difference. My dad has a '12 C6 Corvette. LS3/automatic. Now obviously it's quick, but the car feels so watered down. Doesn't FEEL like 400 HP, or whatever it has. Throttle response is ok, and it's a pleasure to drive. -It's not exactly FUN. I had a 92 Celica GT when I was about 20, and this car was a blast. Instant throttle response, as the weak suspension struggled to control a launch which channeled every bit of 160 HP through the front wheels. Line those two cars up and the Vette would crush the Celica, but dang, I'm here to tell you that Celica would've been my choice to just jump in the car and go. THAT is what the TC did for my car. Made it more fun to drive. -and every one of friends who had seat time BEFORE the TC, agreed, and was just as surprised how big a difference it made.

LT3D

And that's ultimately what I'm looking for in this car. A fun street car. So I guess it's official, come spring next year, I'll upgrade the TC and rear diff. Any preferences on who makes the best TCs for these transmissions? And for rear diff gears for the 9 bolt?

Abubaca

iTrader: (3)

I've been out of the automatic game for awhile. I'd probably just post up in the transmission forum and ask what people are using. For your power levels, I don't think you need to break the bank with a top of the line part. ......as for gears, easy/cheap option would be to find a 3.27 geared 9 bolt, or a 3.23 10 bolt. The 9 bolt is nominally better, but I wouldn't put work into one. Either find the whole thing, or look into a 10 bolt. ....and if you're gonna PUT gears into a rear, I'd opt for a 3.45/3.42. My opinion is that it's an ideal gear for a TPI. You're just not likely to find one already set up since so very few thirdgens came with those gears.

Don't know where you are, but found a 3.27 in Ohio. 4th result on a facebook search. Price is a little steep, but every day that goes by they become harder and harder to find, so I can't say that's not a fair price. Anyhow, there's also a 3.73 10 bolt for $500, and I haven't even scrolled yet! ....they're out there.....just be patient. ....and another 3.27 in KY.

IROCThe5.7L

I put a HSR intake on my L98. AFR 195 heads. And a comp cam XR276HR. Full exhaust. That thing was pretty zippy for what it was. It absolutely needed a torque convertor. I never had a chance to install one as I built a new motor.

LT3D

thanks for the links! Unfortunately, I'm in Canada, so it's very difficult finding them here and finding them at a reasonable price. I think like you said, I'll just have to be patient and keep an eye out.

LT3D

just out of curiosity, how different did it feel from the stock engine?

Thirdgen89GTA

iTrader: (5)

It would feel significantly different from the stock engine completely different power-band. If you like an L98's powerband (all torque), then a HSR and bigger cam is not what you want.

LT3D

I figure so. I really like the stock powerband. I drive mostly around the city, so high rpm and top speed aren't really something I'm after. I just want more of what that powerband lol.

Thirdgen89GTA

iTrader: (5)

Super ram + mild cam similar to a lt4 hot cam.

Komet

This will illustrate all your TPI options:

Reddragon88gta

I was researching TCs too and what I seemed to hear a lot of was Vigilante was the best, or Circle D but those are considerably more money and really geared for racing but the quality is top notch. What I was thinking for my lightly modded L98 was Edge converters, they seem like a strong mid level option, same as Yank, that ppl on here have had success with and the price is reasonable IMO, around $400-$600ish. Stick with a 9.5 inch diameter converter from one of these reputable companies and avoid TCI or B&M, a lot of guys on here have reported problems with those. I was going to try Edge out but I will likely wait until my trans needs an overhaul before adding one, that way it can get a performance oriented rebuild to complement the new TC.

LT3D

Hey Komet, thanks for the video. I've gone through his videos before and this one is a great one. The only issue I have with it is that he's using a hopped up 383. So the power gains he is getting with the different intakes are really taking advantage of the upgrades on that engine. Still, it is impressive how much power was gained with the ported stock intake. I'm just not sure how it would translate to a stock motor with a hot cam.

LT3D

This is very helpful information brother. I also read that TCI wasn't well reviewed. I have heard good things about Yank, but I need to look into Edge. It seems we have the same car actually, just mine is white, but looks like the same year, same engine, same trans, same rear diff lol.

Komet

The curves will be the same, just lower.

Abubaca

iTrader: (3)

One of the things that "we" all eventually learn, is to be able to seperate a peak horsepower dyno chart from the seat of the pants feel of actually driving the car. One of the best illustrations of that was my personal experience with my 89 around 15 years ago. The LS1 4th gens were the big guns back then, and we had an active club full of 'em. I had a mostly stock L98, zz4 cam, 24# injectors, PCMforless mail order tune and full exhaust. Had a T5 trans and 3.27 gears. I could hang with the bolt on LS cars on the street (under 65mph), but I don't think I ever came even close to winning a race down the 1/8 mile. On more than one occasion we'd be bench racing and discuss how they couldn't understand how I could hang on the street, but performed so badly at the track! -and it's because when you're recording quantifiable metrics, you realize just how much better the LS1 was compared to my bolt on L98. On the street, among friends, with burnouts and no real "start" and no real "end", where a half a car doesn't even matter, it was good enough, right!? . ....which begs the question, what's more important? The way it drives and feels, or what the dyno says?

dmccain

iTrader: (2)

A good shift kit, gears (3.42-3.73s) and a lil torque converter maybe 2400 stall makes a huge seat of pants difference in these cars. Even when I had an L03 engine it made a big difference and now with the mild 350... feels very strong out of the hole. Fun lil car stoplight to stoplight.

Arctic White 91 RS

New sticky tires for hooking up the power the car already has would be the biggest reward for the least expense. Next a nice quality stall converter.

Personally, I'd stick with well known highly reputable like Circle D, Precision Industries Vigilante or Yank that has lots of customers and feedback. I have a nice tight Yank 3,200 in my 72 vette's TH400 and it drives practically stock until one gets on the the throttle. Definitely makes for a more fun driving car.

After those two mod's maybe time for a FIRST etc if you want more.

LT3D

Makes sense, I guess the question is how much lower lol. But I do need to change the injectors (they're on their way out) so I can also swap out the intake for a heavily ported stock intake. I'll do the work myself so it's not a big investment.

LT3D

That is a big question. And for this car, it's all about the butt dyno lol. If I got the car on an actual dyno it would be for curiosity only. So how the car feels is paramount to me vs the actual numbers.

LT3D

Gears and TC are definitely what I'm leaning to now. And stickier tires. I was originally leaning towards 3.73s but not sure if I should go a bit taller.

LT3D

Yeah, next season I'm definitely getting some new tires. Do you think 3,200 is necessary for a mild TPI though?

SbFormula

YES!

The tunes are bad from factory. I am in the process of retuning a complete stock '89 Camaro IROC-Z LB9 M5. It's amazing how badly tuned they are from factory. And yes, it's hard to find people that really know how to tune them. The datalogging is a pain in the b***. That was my biggest challenge when I swapped my LB9 in my '91 Formula for a 383 stroker with FIRST TPI. Took countless hours of tuning and a dyno session at the end to dial in Spark Advance and AFR at WOT. Knowing what I know about early GM EFI systems, I would go with after market 100% and would not bother with the ancient technology.

First and foremost, it's impossible to tune without an AFR gauge and a dyno session is paramount. To use an AFR gauge you have to disable AIR system and install a sensor in the Y pipe. This "BLM 128" stuff you read everywhere is completely inaccurate and useless. BLM cells division makes no sense from factory and they cover a wide area that can be extremally rich and lean at same time giving you an average that looks ok.

Your set-up is a MAF system and they max out at 255g/s of air flow. Also the Spark Advance is inaccurate from factory due to bad latency tuning (user input does not equal same at balancer). Your 22lbs injectors will max out at around 300hp @ 85% duty cycle. On my Camaro, the factory tune (APYS) was so bad that at WOT the injectors were working at 95%DC giving me a super rich AFR. GM had these car running way too rich. And so on so forth.

What I am saying here is, if you are going to increase power and invest in new intake, heads, etc.. Get yourself a nice aftermarket speed density (SD) EFI system (FAST, Mega Squirt, to name a few). SOoooo much easier to tune with fast refresh rate and WB sensor. Night and day. No ALDL cable, ECM on floor and burning chip. We use Mega Squirt on our race car and it's a charm to use. Got tuned on the dyno by a shop in less than 3 hours. With modern after market EFI system, it's easier to find expertise.

Orr89RocZ

iTrader: (20)

If you are gonna throw a converter in it, id rebuild refresh beef up the trans while you are at it

Thirdgen89GTA

iTrader: (5)

A good 3200 stall 9.5" Vig is perfectly streetable. Won't affect mileage at all, won't be lazy around town, and really make response to throttle input snappy.

Arctic White 91 RS

Enjoy hurting feelings at stop lights while driving around town with a near stock driving experience?



Had an acquitance slap a similar stall in a bolt on L98 B4C RS Camaro plus a few mod's and weight reduction run high 12's. Basic and drove nice.

Engine doesn't have to high hp & big rpm to really benefit from a quality stall, a tight feeling converter in the 2,800 to 3,200 is probably the ticket. I'd talk to Dave at Yank, he can help figure out what's ideal for your car and will custom build accordingly.

Precision Industries Vigilante are also sweet and can be built to order. Local high performance transmission expert likes Vigilante best says lock up clutch is stronger & more robust. Vigilante's have had a reputation for a 2,800 being closer to 3,200 in many cases so if going Vigilante, I'd carefully explain you want a nice driving tight feel because PI can and will build accordingly if requested to do so.

FWIW ^^^ been looking for a new stall for my bolt on 02 Z28 etc, have direct experience with Yank in 72 vette & friends Camaro, familiar with another friends 2,800 Precision Industries Vigilante.

Best wishes with car and mod's.

LT3D

I have been thinking about installing a WB. I already have a full exhaust with the AIR system gone, so installing the WB won't be a problem. I'm not sure how much power I am making now, but the injectors are on their way out anyways, so I'm contemplating replacing them with 24lb injectors.

I'll have to look into the aftermarket EFI system, but it does sound like a decent amount of work/money to set it up and it may require to change the stock look of the car's interior, which I am not a fan of for this car. Even the WB I was planning to only hook up when tuning and removing it afterwards.

LT3D

I am considering this as well.

LT3D

This is good to know! City driving is 90% of what I do with this car so I don't want that to be affected.

LT3D

A high 12s street car is pretty impressive no matter how you slice it, at least to me it is. Especially for minimal work done to it. Although, I'm not sure how much weight reduction I can do since I want to keep the car as stock looking as possible (I am contemplating deleting the AC since it doesn't work).

I guess I'll have to speak to Yank or PI and get their input for a TC next. The only thing I worry about is if the car already has an aftermarket TC in it lol.

BadSS

Easy enough to test.

LT3D

Simple enough. Thanks brother!

Bill Chase

Not to disagree with you, or nitpick, but gm tuned them that way so they would last 100,000 miles or more, and they had to operate in the rocky mountains, as well as death valley below sea level, survive warranty etc. given the ecu, and hardware they had at the time they accomplished all those goals very well. its hard to know unless you lived through the late 80.s, early 90's and grew up driving used 70's cars, but the ford 5.0, and gm 5.0/5.7 Tpi were kings at one time, when most cars were economical 4 bangers. Tpi made good power, was very reliable! the fact the op has a stock one and it runs as strong as it does 35 years later is a testament to that! sure they can be made faster, but that almost always comes at the expense of economy or reliability! as many above said, mild stall converter, sticky tires, maybe a 3.27-3.45 gear set will really wake it up, probably knock half a second or more off 1/4 mile times, and still be very reliable! and given his questions those are the logical mods to start with. he isnt asking to set the world on fire, just wants a little more ooomph! after personally spending 10 + grand building a 383 afr Miniram, Holley efi blah blah blah blah blah, i can honestly say for a street car gears, a converter, good tires, and maybe a 100-150 hp nitrous kit would've satisfied, cost 2500-3000 tops while still getting 19 mpg or better, plus kept the car original with mods that are easily reversible. just a different way of approaching his goal(s) no offence intended Brother.

SbFormula

In the end after all this opiniated statement on behalf of OP… Fact of the matter is OP still needs a tune! That was one of the PO's original questions.

SbFormula

Sure!

That's what I do with my AFR gauge! It’s portable, plugs in lighter and the bung is plugged after use. Works great and leave the interior stock. Only problem is, it can't be data logged with stock set-up unless you modify tune and wiring.

Arctic White 91 RS

That's very true 👍 Grew up in that era driving a $hit Box AMC Hornet and k-car lol. The fuel injected TPI Camaro, TPI Corvette or 5.0 Mustang were cool and nearly exotic compared to the cars of the mid 1970's and 1980's with few exceptions.

One of the key issues always hold performance cars back in that era was emissions. So in some cases the tuning is probably compromised due to emissions or durability of emissions systems warranty (8 years). Tuning wise, I don't think there was too much concern for engine or transmission longevity with the crappy 1 year 12,000 mile warranties of the era.

SbFormula