KanzlerBismarck

SO, I am in the process of installing the Hawk's Ram Air Intake , doing the coolant line delete on the throttle body and with the K&N filters in there I feel that will be enough for the intake on my (New to me) 89 IROC.

Next I want to do exhaust. What I have in there right now looks to be mostly 2.5" stock stuff. What I would like is to step up to 3" full exhaust.

I am thinking a Magnaflow 16450 Y Pipe, MAYBE a high flow cat like a Walker 15043 (As I live in an area where my car does not require emissions), a Flowmaster 17234 to finish things up.

Cause what I have noticed on my 89 5.7 is that is really gasps for air at 4500 rpm... it wheezes... like it has trouble blowing past about 115 MPH as that is the power-band I am in at that speed(2.77 Rear End 700r4).

Now I don't want a drag car, I just want something that sounds sweet, keeps it MONSTER TORQUE (seriously, this car is super fun to tear *** around town in), sounds a bit throatier and maybe flows air bit better. But I wonder if the stock Manifolds are so restrictive that, even for my needs, such modifications are just "noise makers"?

Drew

iTrader: (58)

The worst part of the 89 L98 exhaust is pretty easily the factory Y-pipe. It's more like a T pipe, chalk full of crinkle crushed bends. Beyond that, the cat should be the nice 3" cat, with a nice mandrel bent 2.75" or 3" intermediate pipe back to the muffler and 2.25" pipes. That's assuming it's all stock stuff.

The cars that got royally screwed on the exhaust, were the 90-up cars without N10, the LG4 cars, L03s, etc. They all got the smaller outlet exhaust manifolds, 2.25" cat and intermediate pipe, etc.

You'll see more improvement from headers, than a cat-back. But then headers are more expensive and create more headaches too. Flowmasters will sound good, if you like the sound of Flowmasters, but it'll probably flow worse than the stock muffler. The 1/4" increase in diameter won't make that much difference really. It'll just seem impressive because it'll be louder.

The L98 manifolds really aren't that bad. Sure headers are better for performance, but are they worth the trade off? You don't ever hear people complaining about the stock manifolds rusting out, leaking, getting loose bolts, burning plug wires, making it impossible to change spark plugs, rubbing the steering shaft, blah blah blah.

Jacobaxeman

83 Crossfire TA

iTrader: (2)

How restrictive are they? They're not as good as headers but better than a lot of manifolds. If they're the right L98 manifolds then they have 2.25" outlets and they're not the reason that the L98 falls on its face at about 4600rpm, that's the TPI setup. That said, it should pull up to something in the 140's without much problem.

KanzlerBismarck

So maybe a manifold port is in order along with a 3" and a cat delete.

Also, I work this old gas out of the tank she is getting more and more lively. Took her out on the highway today and she had little trouble going deep into the 100s.

I have to say, I have a 2nd gen 78 TA 400 4 Speed, driven tons of 4th Gens.. done a lot of 1st gen stuff with my buddies 69 DZ302. But for whatever reason, I like this IROC-Z the best. Seems to have a streetable powerband, get's off the line fast, zero issues making tire smoke, and really pushes hard out of turns.

And maybe I am crazy, but this is one of the best handling cars I have ever driven.

Dyno Don

iTrader: (7)

If you think they are not that bad, then you should look up inside that 2 1/4" outlet. It's only 1 3/4" inside.

FormulaL98

The exhaust manifolds are terrible on these cars. I installed Dyno Dons on my 88 L98 and picked up 4 mph in 1/4 mile, no other changes on a 90 degree day.

KanzlerBismarck

I keep hearing your name over and over. I am new around here.. but it seems you may be the guy to talk to?

86LG4Bird

iTrader: (1)

TPI (L98/LB9) manifolds are definitely not terrible on these cars.
See my sig for results with factory TPI exhaust, except cat delete and Magnaflow muffler.

Orr89RocZ

iTrader: (20)

I remember feeling a seat of the pants improvement with shorty headers over my stock exhaust. Mainly it sounded better.

I did not get track times with it bone stock i dont think. It had the headers on with full catback upgrade and a converter and it went 13.63 at 97 on bias ply drag tires. I thought that was pretty good.

chazman

iTrader: (4)

As has been mentioned, your 4500 RPM restriction isn't the fault of exhaust manifolds, it's more likely due to the TPI system designed for 5.0 liter displacement. With that said, maybe your cat is clogged?

Ibazzabar92

This issue is on the intake side with these cars. Ditch the TPI intake manifold for a Holley Stealth Ram.

KanzlerBismarck

Well, actually since I have filled her with new gas she is running a lot better. Took her out on the highway and she had little trouble getting deeper into the hundreds. My goals would be something like 300-350 HP at the crank.. but still keeping that instant torque curve our cars possess. Is this possible with the stock manifolds?

Drew

iTrader: (58)

With the work that'll go into adding another 100hp naturally aspirated, why wouldn't you go to headers?

86LG4Bird

iTrader: (1)

absolutely

KanzlerBismarck

Well.. cause headers are such a monster pain in the *** in every other way. LOL Cant get to the plugs, gotta practically pull the motor to get them in/out.

At least the ones I have dealt with. Granted I have not seen these "Dyno Don" headers. They seem to be custom for our cars.

Ty92Z

iTrader: (11)

SLP 1 3/4’s up top, Dyno Don’s below. I don’t think you could get too much worse than changing plugs with the factory manifolds.

Fast355

iTrader: (2)

My mildly cammed 9:1 vortec 350 pulled strong to well past 5,000 rpm with stock TPI runners and plenum. Peak HP happened in the 5,500 rpm range. Power flattened out and HP was practically table top flat from 5,000-6,000 but it certainly did not fall on its face. Same cam and heads on a 383 with SLP runners that were siamessed to a ported plenum hit peak HP at about 5,600 rpm and kept pulling to 6,200. The 10.5:1 383 was stronger across the whole rpm range.

To me headers make the plug changes easier on these cars if anything.

86LG4Bird

iTrader: (1)

You can't be serious ??
I can't imagine an easier plug change than with stock manifolds. I've never seen ANY header on any of the 50-odd vehicles I've changed plugs in being any easier!
It doesn't get any easier! Seriously, if changing plugs with TPI manifolds is hard for you, you need to get another hobby!

dmccain

iTrader: (2)

I tried to run TPI manifolds on my last build just for making plugs easier to get to and simplicity. Wound up changing to headers and then my starter wouldn't act right and yes burnt wires and headache changing plugs but I know it made way more power. My next build I haven't decided yet. Its going to be a mild 350 and I have the TPI manifolds and some Hooker Headers I just haven't made up my mind yet. Drawbacks to either one.

Ty92Z

iTrader: (11)

Never said it was hard. One compared to the other on this particular car isn’t much of a difference difficulty wise. If he can change the plugs with manifolds, he can change them with headers. Since my hobby choice bothers you so much and you’re such an authority, I’ll get right on changing hobbies. Have any more useful info?

Fast355

iTrader: (2)

TPI manifolds are a pain to change the plugs. I personally find headers easier. Also on my 5.7 in the Express van there is more room to change the plugs with the Thorley Tri-Y headers than the OEM manifolds.

brianlibby791

I was talking to one of the guys at my local car show, he has a mildly built tpi. He says that going to headers sucks and that stock manifolds are perfectly fine.

chazman

iTrader: (4)

Just talking off the top of my head, but I remember reading some flow numbers on the N10 exhaust. The N10 roughly added as much flow to the single cat 2.25" manifold exhaust as taking a non N10 and adding headers.

I realize we are talking about stock flow demands and that YMMV.

86LG4Bird

iTrader: (1)

Well damn,...my bad!
Just the way I interpreted your statement: "I don’t think you could get too much worse than changing plugs with the factory manifolds."
So sorry I've upset you.

Abubaca

iTrader: (3)

My SLP headers make it super easy to change plugs. Definitely easier than manifolds, although....no AIR either. -and I'm a lot more experienced now. Haven't had manifolds in awhile, lol.

My feeling is that if you're not planning on keeping it stock, headers and a catback are pretty much a given. IMO anyway.

86LG4Bird

iTrader: (1)

OK. thought we were talking about 3rd Gens here.

Personally I consider changing plugs on a 3rd Gen with TPI manifolds about as difficult as falling out of bed. I wish all my vehicles were so easy!

Fast355

iTrader: (2)

Sorry, you are the one that referenced it being easier on 50 odd vehicle. I was only stating my experience.

86LG4Bird

iTrader: (1)

yes, of about 50 vehicles, I cannot for the life of me remember it being easier on any of them than it is with stock TPI manifolds on the 3rd Gen.

Fast355

iTrader: (2)

Just personal opinon here, but I would have to say your GMT400 truck would be about 10x easier and quicker than any third gen, especially with the truck manifolds. I can change the plugs in my 1999 Tahoe in less than 10 minutes. After I lift the Express van and pull both front wheels, the plugs are remarkably easy to access. I change the first 3 on each bank from the wheel well and the rear plugs in both banks from underneath. With stock manifolds the rear 2 plugs were practically impossible to get to which is why I ran it with single cat type LT1 manifolds for several years. Wish GM engineers had thought to use the LT1 manifolds on the Express chassis from the factory. Made spark plug access so much easier. Engine also ran much better with the LT1 manifolds than it did with the truck style log manifolds.

86LG4Bird

iTrader: (1)

yeah, that truck is a contender for the easiest, when it had stock manifolds.

We're arguing here about what's easiest: drinking a beer or a glass of water. both pretty damn easy!

Fast355

iTrader: (2)

Maybe my hands are just too damn big but I always hated changing the plugs on any small block with those manifolds. B, F or G body always sucked to me.

Ty92Z

iTrader: (11)

The OP mentioned difficult plug changes with headers, he also spoke of Dyno Dons headers. I offered a pic of two sets of quality headers to aid in his decision. My statement was relative to that. I don’t think plug changes with a set of quality headers on this vehicle is going to be any more difficult than with factory manifolds. He can go whatever direction he chooses, but at least he has some type of visual reference.

Orr89RocZ

iTrader: (20)

Dont buy an lt1 4th gen car with headers if you hate plug changes

KanzlerBismarck

Well! Looks like I got some decisions to make. I think I will enjoy her a bit more as she sits and decide what I want.

I may suck it up and do the Dyno Dons.. then just do my tune up at the same time. I probably put about 5000 miles a year on this car so it will be awhile before I go back into it.

83 Crossfire TA

iTrader: (2)

Maybe just really good at posting to any thread mentioning manifolds/headers?

No idea how good they actually are, they're probably the only header/exhaust that I haven't seen on one of these cars in person

Headers really do make these cars sound better, it's a smoother exhaust note. I don't know how much I believe any shorty header really helps on a near stockish engine. I managed to run a 13.48 with a stock '87 L98 formula that only had an SLP cold air and cat back on it (in other words through the stock manifolds. I've always documented better gains with a cat back and ditching the converter on a single converter car.

The breathing issue is on the intake side, and the Holley SR is one way of changing how it breaths, but the fact is that the stock intake setup will breathe enough air to feed nearly 400bhp as long as you don't try to force it to make power where it doesn't want to make power. It gets to be more finesse then the traditional "just make it turn more rpm" answer.

Yes, to run the time that I ran with a stock L98 it had to be making close to 290bhp, a little bit of porting, a well-selected cam and some other tinkering/tuning will get you over 300hp easy. OTOH, bang for the buck, especially WRT to feel and possibly ET would be swapping a quality torque converter.

I think a lot of this depends on the size of your hands, the headers you're comparing to and the tools you have.

Someone with small hands should be able to do all the plugs with the stock manifolds easy, but it can get challenging for someone with big hands, ESPECIALLY if the air tubes are still connected. I have a combination of extensions that I can fish out under the master cylinder and through the hood hinge area to get the rearmost plugs with stock manifolds. I have big hands and there's almost no chance of me touching a few of them. With the air tubes plulled it gets a lot easier, then the only really bad part is the back plugs on the driver's side and getting around the brake lines.

Some headers get in the way of the rearmost plugs on some setups, but the typical 3/4 length Headman or Hooker header you can even see all the plugs from up top without even looking hard. Getting them out is cake if you have a good selection of tools, but I could see someone with just a socket set thinking they were impossible. I use a combination of pass through sockets and a regular plug socket and can do all 8 in about 10 minutes.

Again, big vs little hands. If you have big hands the stock manifolds are literally impossible. When I first bought my '97 I got it in the garage the first day, opened the hood and went "where the heck are the plugs?" reached down between the fender and the exhaust manifold on the passenger side and promptly got stuck. Luckily a neighbor of mine drove by and stopped wanting to see my new car and ended up prying me out with a broom handle. Later when I put N2O on that car a friend of mine helped me swap the plugs, we worked out a system where I was under the car and he was over it and for half the plugs we could turn the wrench a fraction of a turn and pass it to the other one. It took us all night to swap the spark plugs and we both looked like we lost a fight with a whole herd of rabid cats, cut up everywhere.

Orr89RocZ

iTrader: (20)

Apparently you never worked on that 97 with headers. Doesnt matter what size hands you have its a several hr job. Repair shop tech book even calls for 3-4 hrs

Thats about what my stock ls1 auto car ran. I have my doubts a stock L98 will do that. Especially at my track

Fast355

iTrader: (2)

I witnessed a 305 TPI G-92 5spd car run 13.9s multiple times at Dallas Dragway when it was still open. STOCK save for timing/fuel pressure tweaks, K&N drop-ins, and some stickier rubber. It was in practically ZERO DA but it did it none the less. I ran in -800 DA one night there in my Ram and I am sure that car would have run even better in those conditions. The Houston guys in winter have even better air than we do at HRP.

chazman

iTrader: (4)

The N10, G92, 5 speed cars are faster than most people think, especially with bumped up timing and other minor tweaks.

Orr89RocZ

iTrader: (20)

Well driven 5 spd in the south low da is one thing... but a stock auto converter 1.95-2.1 60 ft type stuff running 13.48 is a stretch imo. I had to run 1.75 60 ft in a 2800 stall to go 13.63 with headers catback timing mods in a full weight high option L98 but we are alittle higher in DA, 2000 ft or so

I raced my trans am in texas in winter, ran 12.11 at 112, gutted. 12.27-12.31 at 110 i think with interior. Best it did up here in pa in winter was 12.52 at 108 and thats with some extra tuning

KanzlerBismarck

This is a great site! Thank you for all the advice!

SirReveller

iTrader: (4)

I spent a looot of time reading before pulling the trigger and came down to Dyno Dons or Hooker 2055s, both were so universally acclaimed on here. Ultimately went with the 2055s as they came with the Y-pipe. After ordering the ceramics I actually found a ceramic thermal displacement coating place across town so maybe I'd get the cheaper 2055s(+an errand on delivery) to save a bit of $ if I could do it over again. But at the time just confirmed fitment with the 93441 Magnaflow 3" hi-flo cat and Magnaflow 62866 street series catback exhaust with 3.5" tips and that was that. (Obv if you're in no rush you could just keep an eye out for w/e used or NIB etc as I'm sure there are other combos that would work great.)

There's plenty of threads on copper gaskets and locking bolts if you're worried about the headers-loosening issue. Same goes for insulation jackets or better spark plug wires and perhaps the three-wire heated O2 sensor.

If you're doing Hawks ram air and filters up front the »full« exhaust is a no-brainer IMO. Just my two pfennigs. We have the same car BTW

83 Crossfire TA

iTrader: (2)

While we do get some mineshaft days here in the fall in MD (the ****** Militia meet where I ran the 13.6 in in the 305/5 speed powered TA was one), this was just a good November day, I believe it would correct a little faster, I haven't checked, from my records:
Date November 16, 2001
Track Capitol Raceway, Friday Night TnT
Temperature 70
Pressure 30.09
Humidity 59
Gas 1/4 Tank
Notes Weird for November, spent the whole night outside in a T-shirt and was comfortable. Ran Greg W's BFG DR 275 50 15's at 32 till I spun them. Also had Firebird 15x7's on the front with stock size tires (10# or so lighter). New radio, CD's make the car go faster ;-) no 1/8 mph today
Pass 9
Lane 1
Reaction 1.2019
60ft. 1.8969
330ft. 5.5631
1/8 Mile ET 8.6595
1/8 Mile Speed
1000ft. 11.3356
1/4 Mile ET 13.4775
1/4 Mile Speed 99.9989
Notes: Converter clutch jumpered ALDL still locked. Tires 22psi. Cooled off for about 10 minutes, my seat adjuster let go when I hit the brakes coming to the staging lights and accidently lit up the lights. Didn't go till I pulled the seat back.

dmccain

iTrader: (2)

Ive never seen a stock L98 break into 13s myself. I mean headers, gear change .. that gets you there easy but then its not stock is it. Sure never seen a stock 305 break 13s but I'm sure a 5spd TPI could get close..

Fast355

iTrader: (2)

The stick makes a huge difference. The stock L98/6 speed Corvettes ran in the 13.5-13.7s range at 100-102 mph. The 700r4 Vettes ran in the low14/high 13 range with a 2.59 rear gear. Not exactly a F-car but shows a L98 is no slouch either.

dmccain

iTrader: (2)

Those aluminum head L98s weren't the same. But an iron head L98 F car with a 6spd would have turned 13 sec timeslips I imagine. They should have went with the prototype in 92.

Fast355

iTrader: (2)

The L98 aluminum head motors were not that different. They don't really flow any better but did increase the compression ratio about 1/2 point. IIRC they were rated around 245-250 HP. I can say from experience though, 1.6 roller rockers, long tube headers and a full exhaust makes them run very well though.

83 Crossfire TA

iTrader: (2)

The early aluminum head motors had slightly better intake port flow, significantly worse exhaust ports but had some cute little 1.5" tubular headers which actually worked ok and a decent exhaust. I'm not sure if they actually made more power or just were rated higher. The later C4's had EXACTLY the same LT1 that the F-bodies had the HP ratings climbed from the standard f-body, SS/WS6 and then Corvette (GM claimed better exhaust and air filter assembly) but there didn't seem to be any real difference on a dyno.

KanzlerBismarck

Sounds awesome.. Do you have any images of your car with these headers installed? Also.. do you have video with sound of the exhaust note? Cause, maybe I will just ape your system. Also, did you install yourself or have it done at a shop?

The other thing I was thinking of was maybe just... tossing a electric exhaust by-pass. Would this be the better option? Maybe fixing the shitty y-pipe and tossing in an exhaust by-pass between it and the cat?

Then I get my relatively light exhaust note for the neighborhood, and then can open it up at will for "monster mode".

Street Lethal

iTrader: (16)

Wow, it's 2018, I can't believe you can still find an L98 with stock manifolds, let alone have a whole entire thread with members still arguing about them lol. I'm only kidding. Dyno Don for the win, order them and be done with it. With how fast luxury cars are today, I suspect you will be moddng your L98 faster than you think, so make the right choice now and be ahead of the game for when the engine mods come. I give it a few weeks after being beat by a new Honda Civic...

- Rob