Hi Guys, I have a 1988 Trans Am with a 305 TPI setup, the car is completely stock (except Hi-Flow cat installed about 2 months ago). And last week I had a Flowmaster 3" Cat Back System (American Thunder) installed. And I was wondering am I supposed to gain hp or feel some kind of difference in performance? The car sounds pretty nice now, but I'm not experiencing almost any power increase, actually zero to be exact. Does anyone have any suggestions. And one more thing, when i received the whole system, the inlet sticker was misplaced on one of the outlets on the muffler (80 series, 1 inlet & 2 outlet setup). Is there a possibly the muffler was installed improply, is that the reason for no performance increase. (I checked and it looks fine to me, and i checked the design diagrams 20 times over so it should be fine now). Is my timing in the car off, maybe? Thanks for your help guys, in advance.

If your still running factory manifolds + y-pipe it doesn't really matter whats in back of em because they are the main bottleneck in the system. You will feel a hugh difference if you add headers if you don't already have a set.

diffintly what 89RSpower said...... No flow no go! lol gotta ditch the factory Y-pipe and manifold for a decent gain then that will start putting that cat back to use cause the car will flow more!

A couple of years ago I took the exhaust manifolds and exhaust off a third-gen 305 TBI and at the same time my friend took the exhaust off a mid-80's 2.8L S-10 pickup. Side-by-side the S-10 exhaust was clearly superior to the third-gen's. The Y-pipe was clearly better and the intermediate pipe had fewer crimped bends (the pipes were the same size). I thought it was actually sad how pathetic the third-gen's exhaust was. It was cruel that GM would force a V-8 to breathe through that when it wasn't even sufficient for a decent 4-cyl. IIRC the stock TPI exhaust is a little bigger diameter than the stock TBI, but it does give you an idea of how truly useless the manifolds and exhausts were on these cars. I've honestly never seen an exhaust so bad in my life. I can't even begin to figure out why GM did that (they probably wanted to make sure that the F-bodies didn't get too close to the Corvette in output).

So, yeah, the manifolds, Y-pipe and intermediate pipe are HUGE restrictions on these cars. Almost nothing will result in significant power gains until the stock system is taken off and put on a motorcycle or something (and it better be a small motorcycle at that). I was actually embarassed to throw my old exhaust out because I was ashamed to let the garbage man see it.

On the bright side, headers and exhaust will give you a massive, noticeable gain in output ...you've got nowhere to go but up.

I perfer to have no mufflers at all. Just high flow cats and stright pipes all the way back. It sounds nice and scares the crap out of people at full trottle. I had a flowmaster and didnt like it so I cut it off. I felt like I had more power without it. I plan on having a true dual exhaust system soon.

Yeah You aint gonna feel much of a difference from a catback. If anything you gained maybe like 4 or 5 horses. But thats not really enough to feel a difference. A flowmaster catback, a slightly bigger y pipe, and a cat removal made barely any power difference from the stock exhaust. It just made it much louder. It all comes down to the restrictive manifolds.

wow...that has to sound so bad. get a muffler

Thanks for the info. I'm planning on putting headers on my car over the winter as well as a flowmaster :-)

Hey, a Newfie! I'm in St. John's/Carbonear. I've been working on my car (1988 IROC) since '88. I'm in the process of completely rebuilding it now. I've done the headers and rear gears (3.42's), along with almost everything else on the car, so if there's anything I can help you with let me know.

By the way, I got a set of new Flowtech headers in my garage and a VTech muffler for your car, if you're interested. I bought them last year but never used them.

I am not discounting that the manifolds and the y pipe are restrictive, they are just way too small, but what they are saying is not true about the exhaust. When i put the 3" catalytic converter and a 3" catback to a dual outlet Borla muffler, there was definitely an improvement. I dont like Flowmasters very much, but there should be a destinct power improvement over stock. My dad put almost the same exact setup as yours on his Carbed LG4 305 and that car will shred the tries halfway done the block and really fly. What size cat do you have? I would definitely check the timing on your car to make sure its firing correctly. My TPI, if the timing isnt correct, will hesitate when you romp it, because the 305 engines are very timing sensitive. Make sure also that your cat is 3" inlet and outlet and that the muffler INLET is 3" inlet. Are the American thunder series pipes mandrel bent? When i upgraded to the CS144 alternator, and put the exhaust on, i totally spanked my buddies Stealth. Good luck getting that TPI to go fast.

Actually it sounds pretty good. Alot of people tell me that they like it too.

With the best possible outcome you won't get more than about an extra 10 hp with a high-flow muffler ...probably less. For a year or so I ran my car with no muffler at all and there really wasn't a noticeable difference. Perhaps there was something a little extra up top, but it certainly wasn't dramatic. It wasn't until I put headers on the car that it started to wake up. Before that, everything was held back. Without changing the exhaust manifolds the only noticeable gains I could get out of the car is when I changed the rear-end gears, posi and installed a shift-kit, poly trans mount and aluminum driveshaft ...and none of that had anything to do with the motor.

I haven't seen the flow numbers for the Flowmaster 80 series but, judging from other mufflers, I'd guess that they flow less than 200 cfm over stock ...good for less than 10 hp on a stockish motor.

Hey guys, thanks to all the helpful info, judging by all the replies I guess the only way to go is headers (the last part i have to upgrade to complete the exhaust system). So what would you guys go with shorty or full length headers, painted or ceranmic, and how is the maintenance on headers i heard its a nightmare with the frequent retighting?????

Lucid, the cat is 3" inlet & outlet and the whole cat back system is 3" aswell, even the outlets of the muffler are 3". The previous cat & catback exhaust on my car wasn't that bad, it was also 3" (intermediate pipe all the way to the muffler inlet) just that it wasn't a high flow cat and it was using a plain stock muffler. So I'm not really disappointed with the no gain (just a bit). But you also mentioned about the timing of the car (i feel my car is little off). How did you found out that your timing was off, was your fuel mileage suffering, how did you tune the timing??? (my car is pretty responsive on the thottle and my mileage is about 18 mpg combing both city & hwy)

All and all, the car is pretty torquey and quick (sometimes), but still after 4000 rpm the hps just go >>>>>>>>>down all the way to 4500 shift point.

Just a few facts about my car, to maybe help troubleshoot (lol) its 4 spd auto, 165,000 km, k&n air filter, new o2sensor and platium plugs about 30,000 km ago (3 years ago). The car feels a little off tune, timing or something, any recommandations for timing or getting it back to tune????

Sorry about the long message guys, and i know i have like 5 questions in this reply. Thanks for all your help and replies.

dont listen to them.

I felt a huge gain from my dynomax catback and !air.

while the manifolds are a big problem, the reason you feel no difference is because flowmasters dont flow good...

but you wont feel a gain by switching the mufflers out now... just get headers and y pipe then when you go into real high hp numbers swap out the muffler

Well TPI motors are known for there high low end torque and they dont make power above 4500 or 5000. You can only flow as good as your smallest part of the exaust. So if anything infront of your 3" catback is less than 3" then you arent helping anything. When you get headers make shure everything is 3".

You might wanna do some research on the headers. There are so many different brands so it may be hard to pick one. Your 88 TPI engine most likely has the small peanut cam in it. It's power band is extremely narrow! Were talkin 1,000 to 4,000 rpm's. Thats why its so torquey but it breaks up at higher rpm's. Even if You installed a bigger cam, the TPI intake is extremely restrictive in the high range and it would prevent the cam from making more power. As for timing, I believe the stock timing is 6 degrees BTDC. And for a tune up... Well You already have decent plugs so You might wanna upgrade Your coil to a high performance one, replace the cap and rotor, and definitely change the fuel filter! Make sure You have no vacuum leaks and that all sensors are operating properly too.

Give it up man.... Flowmasters flow about just as well as any other aftermarket performance muffler. They may flow slightly more or slightly less than other brands. I'm not saying they are the best on the market. But a flowmaster surely flows more than a stock muffler. And they sound good too!

love my flowmaster

Thanks for all the help, guys.

But I just came back from a drive with the car, and if anything the car feels slower with the 3" flowmaster system than the oem muffler. ? I don't understand, the car was driving it's normal average speed and accerlation, and I drove 100km on the new system today, and the car felt slower on acceleration (a bit), less responsive on the throttle, and the gas mileage was lower. Did i get a deficitive muffler or something, i did a visual of system and it looks fine.

Is my 305 just too small in deplacemnt or not enough powerful (in stock form) to take advantage of the 3" flowmaster system, that the flowmaster system plays a reverse act on my performace and overall efficiency.

Thanks again everyone for your help.

double post

If nothing else has been changed then your VE and spark tables need adjustment on the chip. As it stands now your car is breathing a little better and the stock PROM tables are probably *slightly* off. I'm surprised that you'd notice that with a simple exhaust upgrade, but that's what it seems to be to me.

It will take a while for your ECM to update the tables in the PROM, but it should "learn" within a few days of driving. After that the car will get back to normal with perhaps a little increase. If you really want a dead-on tune you'll have to modify the tables yourself (especially the spark tables) but it really isn't a necessity at this stage ...it'll work itself out.

I honestly dont think that the flowmaster would reduce gas mileage and make Your car slower. It may have possibly killed a little bit of your low rpm power in exchange for top end power. But it shouldnt have been enough to even notice. I would take other things into consideration. Maybe when it was stock and You were nailing it... the engine temp was lower than what it was after the exhaust was installed. Engine temp plays a critical role in Your cars performance. Maybe when You were out driving it last time... the outside temperature and humidity was higher than when You were driving it with the stock exhaust. That factor can also make a big difference. Sometimes too, the computer takes a little time to adjust the spark advance and fuel curves for a new exhaust setup. Maybe it will take a few more miles to compensate for the huge reduction in backpressure that the flowmaster creates. Give it a little more time and see what happens.

does the pipe going into the muffler enter in front of or behind the tail pipe?
do the pipes stick out much past the bumper?

you wont feel a difference unless u have headers.

hey guys,

rik89gta, your right about the temp, my car performs better at 70C than at 100C but i have tookin that into consideration with the new exhaust and it runs bad at 70C and even worst at 100C. Maybe its like you and casey said, it just takes time to adjust the backpressure from the prom.

86TA, you bring up a really good point, I have been thinking the same thing the whole time in the back of my head. When i received the exhaust i looked at the Muffler (80 series 2 outlet, 1 inlet) and there was only one sticker on the muffler, it was on ones of the outlets and it said inlet, to label the inlet opening, however to me and the design schematic it looked like one of the outlets. So i took the label off the outlet and put it on the actual inlet. So maybe i made a mistake, and my best friends uncle (he's my mechanic) put it in wrong. However the way the muffler is in now, makes it fit almost perfectly, and the schematic from flowmaster say it should be this way. The only thing i regard, is not checking to see inside of the muffler and look for the chambers within. I'll paste a pic of my exhaust tomorrow, as right now its too dark to get a good pic.

I don't really know, what is going on, I thought my car was going to be a little quicker but it slower and worser on gas now, man. Is there a possibility my 3" exhaust system, starting at the y-pipe which is 3", 3"cat and now 3" cat back exhaust system is too big in diameter or too free flowing for my stock 305 that its actually more restrictive. Or is this system (3") too restrictive with the stock exhaust manifolds. As opposed with my previous 2.5 oem exhaust which worked better with stock manifolds.

Maybe the exhaust system is completely out of tune or unbalanced. Maybe stock manifolds work better with the smaller 2.5" exhaust. And to see the benefit of the new 3" cat-back i need to syncerize they with matched size headers.

Thanks again guys and i'll post the pic of the exhaust tomorrow or on tuesday the lastest.

Thats why I just cut mine off and ran striaght pipes, I felt that it took away power. Two of my friends said that they lost power with there flowmaster system too. The only thing you can do now is get a set of headers I guess, that should give you some noticable gains.

It isn't any of that. Yes, your stock exhaust manifolds are a huge bottle-neck that prevent the motor from breathing up high, but there isn't a mismatch between your better-flowing cat-back and your stock manifolds that would cause a torque/power/economy loss. Less back pressure is almost always better and that goes for stock 3rd-gens also. The only way the Flowmaster setup would cause a power loss on a properly tuned motor is if it created more back pressure ...which is highly unlikely. Without the headers though, your cat-back can only get you 5-10 hp -- which isn't really noticeable.

Scavaging and expansion of gases isn't going to have any significant effects after the Y-pipe on your motor. Your problem is most likely the stock PROM tune. Your timing and fuel tables probably need a little tweaking (and maybe the accel enrich tables also), but with such a small modification, the ECM should be able to compensate adequately (though it won't advance the timing by itself). Give it some time and see what happens. If things don't improve in a few days (or weeks, depending on how much you drive) then it'll be time to look into it more seriously.

Patgta,

I'm not going to say that Flowmasters aren't good, i just dont like the sound. My Borla is also stainless steel, it purs like a kitten at idle and when you rev it, then it really sounds mean. The muffler installer had to bend my heat shield to get the muffler in, it was a beefy muffler.
Theres something not right with the way your engine is running for some reason. My car would barely even run with the 2.5" exhaust this muffler guy tried to put on my car, i drove down the street and the muffler shop i trust cut it off and mandrel bent some 3" tubing for me. Do you know what the lift numbers are for your Cam? My stock LB9 cam had great takeoff but would fall short because it only made like 190HP stock. The other thing i did was the throttle body bypass and put K&N's that helped the way the engine responded. Check your TP sensor volts at idle, and make sure your Coolant Temp Sensor is working properly. Is your car speed density or MAF? My car is a MAF so when i put in a more peppy cam it automatically adjusted and it runs well. If your car is SD then you are going to have to get a tweaked PROM. The 4 to 5 horsepower gain sounds pretty conservative.
Also are we talking about an Auto or 5 Speed car?
Do a search about adjusting the timing. What i do is i ground the diagnostic connector, which makes the ECM set the base timing (static timing). Make sure that your car is warmed up before changing anything. Then you can loosen the distributor and turn it to adjust the timing, of course you need a timing light. After you set the static timing ( different cars have different settings that work optimally for them, my car runs well at 12-13 degrees base timing, whereas i have heard others get good results 6-8 degrees). Tighten the distributor bolt, and turn off the car, unground the diag terminal. Then restart the engine and now set your dynamic timing, again by turning the distributor cap by hand. I'm not sure how much advance in terms of numbers, maybe someone can help out here, but usually if you snap the throttle and it hesitates and bogs, its retarded....if it responds well but you hear drivetrain clack then its too advanced.
BTW you know your car best, i believe you when you say its not running right. When something isnt right with my TPI, my fuel mileage suffers, shes like a woman, if its not just right she lets me know. I do want to mention about those platinum plugs.... I used to run those AC Delco, regular plain jane stock suckers, and i would change them about every 3 months. I ran the Bosch Platinums, the single prong type, they lasted much longer, but i would always get some deposits stuck between the electrode and the body of the spark plug. It would usually be just one near the back of the engine, it wouldnt be enough to make a dead cylinder, but just enough to make it run like crap. I am running the 4 prong Bosch Platinums right now, they seem to be doing the trick. From 70mph + this sucker seems to hit a sweet spot, and i dont have a high output coil yet.
Hope this helps some.

Hey man; wait a second.

When you have a problem, always go back to the last work right before the problem showed up. Keep it simple...

It ran fine, you swapped the cat-back system, and now it's slower? What was that you said about the pipes being labeled wrong? You sure about that?

I've never had a Flowmaster muffler that slowed me down; I LOVE THEM! Even my V6 car perked up noticably after I put a used Flowmaster cat-back on from a wrecked 86 T/A...

Check that "mislabeled" pipe again...

If you are feeding the exhaust into the tailpipe outlet, then you will slow down. The way that Flowmasters are made with the chambers and "V" shaped baffles would definitely slow you down if it were hooked up wrong...

Good luck!

P.S. If you take it off because you think the Flowmaster is bad, I'll take it!!

Check that the muffler's on right then go buy a timing light, a new fuel filter, a die grinder, porting and polishing bits (carbide cutters work great), and a fuel pressure regulator. Pull off the plenum and port out the walls behind the throttle body, and smooth or remove the walls between the runner tubes (there's write ups on how to do this just search for them). Install your fuel filter and adjustable regulator, turn the fuel pressure up to around 45psi at idle and adjust the timing up to around 10 degrees, if it doesn't like that go down to 8, doesn't like that go back to 6. What your no gains from the exhaust is showing you is that you have an issue with the timing, fuel, or air coming into the engine. When you got more exhaust out it made it show worse. The free mods will DEFINETLY wake up your car, and alot of the times the fuel filters on our cars have been ignored until over 100,000, it's easily overlooked. Good luck on the car, hopefully you get it tracked down and it's faster than before.

does anyone have track experience with flowmaster 80s and other mufflers

i do.

and i didnt see much of a gain from 3inch 80 series to a 20inch long chambered tube muffler that is straight thru with mild baffles in side. i might have picked up .5mph. et was about the same. the weather was abit warmer on the one of the chambered test days, but still didnt pick up like i thought it would. i was expecting 1mph at least.

and i still have factory cat but hooker headers and y pipe.

some flowmasters can flow more than u think. that chambered tube outflows that flowmaster more than likely..but the added gain doesnt really benefit mild stock motors. maybe someday if i compare it on a hot 383 combo, i'll know for sure

hey guys thanks for all the replies again,

when i got the exhaust last week, i also reset the ecm (by unpluging the ecm connector by the battery, this blanks the ecm along with any trouble codes) that same morning (last week), but i thought it would reprogram the fuel maps and everything else quicker (like in 30mins of driving), but i guess thats not the case it takes about a week or so of normal driving like Casey and rik89gta said. And if that doesn't work, its time to do some retarding or advancing.

So i guess, i just have to wait it out for a week or so. Also Lucid that is a good point about knowing that something is wrong with your car, when your gas mileage is off or lower, thats the exact same rule i go by. Thats how i knew right away that something was off, when i drove the car for about 100kms and more than 1 / 3 of my fuel was gone (normal driving).

here, i'll list my car maintenance and tune history, and if you guys can make any recommandations that would be great:

1988 trans am 305 tpi auto (basically fully loaded with suspension, everything) it currently has 165,000 km

1988: my dad bought the car new.
2000: i received the car as a gift from my dad. (he's into vettes now, anyways)

2002 june (car mileage 138,000 km at this time): platium spark plugs (bosch single tip), k&n air filter, new o2 sensor (bosch), new fuel filter, new pcv.
at this time i took the car to the dyno and it produced 161 hp at 4000 and 256 lbs at 3300.
2002 aug (140,000 km) tranny fluid change and gaskets, new brakes installed.
2006 july (162,500 km) high flow cat installed
2006 sept (165,000 km) flowmaster cat back installed

I'll probably go to the dyno within a few weeks for some updated numbers and they can checked the a/f ratio at the whole rpm range,

again thanks for the support guys, and sticking with me.
please give any recommandations, thanks again

pat

and one more thing for the tuning part in april 2006 i put on a set of z rated tires and had a complete alignment done (which it needed badly) and my fuel mileage at june 2006 before the cat and cat back system installation was about: 17.5 mpg in city and bit of hwy, and 22 mpg hwy (is that good? i guess its ok)

pat

17.5/22 isnt bad. my l98 does about that if not abit better...but i drive it alot harder than most probly. i dont really drive "city" but i do have some stop and goes but mostly highway where i'm cruisin but sometimes just open it up.

Pat, the reason I suspect your PROM is now a little "inadequate" for your new flow is because your problems started when you installed the cat-back. If the performance decrease started when you didn't do any modifications then I'd suspect you have a timing/plugs/distributor cap/rotor problem ...essentially a basic tune.

If the muffler is on right, then the car will either come around in a few days, or you probably do have a tuning problem. I never had a good experience with Bosch platinum plugs on my '88 IROC, so you might want to take a look at them. Also, if you haven't had a new distributor cap and rotor in the last 50k or so then I can practically guarantee that the time is coming. In any case, take the distributor cap off and take a look at the posts. These cars will run with terribly worn rotors and posts -- the car will run, but it will be sluggish and "feel" like it needs a tune. I ran the stock distributor cap and rotor from 1988 to 2003 and, believe me, there was nothing left inside it, but the car still ran (that was when I got serious about restoring and modifying the car).

After you visually inspect those parts and give the car a few days for the PROM to update (if it even has to on a MAF-based car such as your's) then you'll know whether you've got a timing problem or something else going on.

Patgta,
You had your plugs in your car for 4 years and they still work?
Yeah the other guys have a point, keep it simple, start off with the basics and
get that car tuned, at least pull a couple plugs and look at them. It will tell you if its running rich, or lean, or if it has deposits on them. The distributor cap also gets desposits inside on the terminals, and then the rotor will cut a groove through them eventually. Take a picture of the muffler and post it, somehow i think its engine related this time.

BTW The 88 Trans AM LB9 engine in the automatic developed 195HP @4000 RPM and 295 ft/lbs @2800 RPM in stock trim, according to thirdgen.org.

thanks for the tip about the distributor cap guys, i'll check it out tonight and take a few pics of the exhaust aswell.

about the stats Lucid, are those numbers (195hp / 295lbs) at the wheels or at the engine? the ones i had (161hp / 256lbs) were at the wheels.

thanks again, i'll post soon

Those numbers are most likely an engine dyno. I would assume about 18-20% drivetrain loss in your calculations. So your 161 RWHP is actually pretty good for that engine.

He could have inadequate backpressure. Sounds like you compromised your performance with just that one move.

Installing a highflow catbaclk system won't do you any good unless you have the goods to go up front. Port the intake and add a CAI along with headers. Of course, if you have the time, money, and know-how port the intake plenum and add high-flow runners and an upper intake manifold.

What comes in must go out, and if much ain't comming in, you ain't gonna get much more out.

Ive got question I have 92 camaro 305 tBI I want to change exhuast should I go true dual w/2 high flow cat ,Also I might gut my cat out because they dont test emisssion here, is that bad idea?
It got K&N air clean other than that bone stock(not for long though)

It'll take some fabrication and will be costly. But I wouldn't bother, not with what you've got.

Adrenilineadict, true duals won't be necessary. Gut your cat and put on a mandrel bent 3" system, with a good Y-pipe after the headers.

ok cool now about the headers, stock ones need replacing ? or they are sufficent

The stock exhaust manifolds are the worst exhaust manifolds ever attached to a gasoline engine. Aftermarket headers are a necessity for making power with these cars. Good headers and exhaust is an easy 30 hp on these cars.

I put the issue in bold for ya. No matter what muffler you have if it's not getting to it the power isn't gonna change by going to a better flowing muffler. If the bottle-kneck is before the muffler, a higher flow muffler means nothing. - I've seen the hp difference between good mufflers and flowmasters on a dyno, same car, same piping even, just swapping mufflers to check the difference power and decible wise. They are better than factory, but they're not too good either.

- If you had a traffic jam everyday in town, would you four lane the road ouside of town or would you improve the section that bottles up? - get headers and a good y-pipe. - also, duals will gain you no power, unless you have something that is a bottle-kneck in your single system. Believe me, I know from experience.....

Ok, I'm really trying not to sound like a **** here but...

Are you sure you know which opening is the inlet, and which are the outlets? Is it in the stock location? On the 80 series mufflers, which are designed to be run transversely behind the rear axle, the inlet and one of the outlets are on the same side. If you switched the stickers, and whoever put your muffler on installed it with the "outlets" on the same side, parallell to the car, it's on wrong (which is bad). I've attached a picture to illustrate. Also, as far as I can tell, flowmaster doesn't make an 80 series with all 3" openings. They sell 3" inlet, 2.5" outlet, and 2.5" inlet/outlet sizes. If the openings in your muffler are all the same size, perhaps you have the 2.5" all around version.


42583.jpg

Yes, they do.

Flowmaster American Thunder Exhaust Systems: FLO-17233 - summitracing.com

i have a flowmaster with 3inch openings all the way around...its definately an 80 series.

and yoru correct on the inlet and outlets

Ok, well then I stand corrected. I looked at the 80 series flowmaster mufflers (by themselves, not part of a kit) on summit and on flowmaster's website, and they do not show any with all 3" openings. But if you guys say you definately have them, then I beleive you. Maybe they're just discontinued or something, I dunno.

I got my 80 series with the full 3" cat-back also. But, like you, I can't seem to find that muffler for sale separately anywhere. That doesn't really make sense though, that Flowmaster would make the full system (including 3" stainless steel tips) and not sell the muffler separately ...but who knows?