I just installed a set of dyno don headers, magnaflow dual cats and a magnaflow cat back exhaust on my 89 gta with a tpi 350. I feel like I got no power gain. my car was struggling to break the tries free. Also the sound is to close to stock. I expected a louder more aggressive tone. I am kind of disappointed. Has anybody gone thru something similar or have any opitions on this?

 

what size is your catback?

 

Exhaust, by itself, will do little for performance.

Rather, it is THE FOUNDATION FOR EVERYTHING ELSE. That is, NOTHING ELSE will do anything either, until AFTER the exhaust is improved.

Now you're ready to start doing stuff that will make the car faster... which IMO should start with replacing TPI with some other EFI system that doesn't choke the motor to death.

 

were the O2's hooked back up? leave a spark plug wire off? something small like that can make a huge difference in the cars performance.

 

is it faster or slower than before? or did u just feel no change? the sound comes from the muffler.

 

the cat back is a 3". I checked everything. The car idles perfect, it does not sound like there is a miss. just a little exhaust leak the needs to be welded up. Before the exhaust work, i was able to lite up the tires, no problem.
ninetyone I feel like there is no change. I wish it was louder
sofakingdom I would love to do a procharger!

 

You wanted a more agressive sound so you went with a magnaflow? Do you know ANYTHING about cars? magnaflow has the most mild exhaust out there.

 

A 350 TPI 700r4 with what you say is a stock rear end (3.27) with or without Posi (LSD) and you are having a hard time breaking the tires loose. What tires are you running ? If there street tires than you have a problem some were. I bumped my timing advanced 4* and that alone helped with throttle response off the line. Thats on my TBI.

 

dakota, I do know something about cars and I heard nice sounding magnaflow exhausts before. You should be a little nicer to people you don't know

 

I ordered Mufflex exhaust, which was ordered to fit the car. Unfortunately my 85 firebird did not have room for true duals unless I wanted to lose it crossing the railroad tracks that run thru my driveway, but I ran 3" from headers ("y" pipe) to 4" all the way back to cat back muffler which has two 3" pipes coming out the back. It sounds great! I have a built 350 with a Holley 650 double pumper. I do not have a converter, but do have collector plates, which cuts me some slack from the local police in MN. I do have a bigger cam and the exhaust I ordered complements the cam as it does soud extremely lumpy and is only loud when I get on the gas. It is louder than any stock firebird in the same years. Look up Mufflex exhaust and let me know what you think. I spent approximately $800.00 on the Mufflex set up, which did not include the headers and "Y" pipe. The nice thing is it was prebent to fit right in and around the axel. The biggest issue was making the flange to tie in the 3" to the 4", not many shops in the north country that have benders and dies for 4". It was as good as gets without having true dual exhaust, the motor breathes great with the rumble comparable to duals. You can roder this exhaust to fit any F body and model, duals or single depending on the car.

 

where exactly is the leak? u probably had more low end with the smaller exhaust,what happened is u may have just moved the powerband up higher,thus making more hp. u can try richening up the mixture by increasing fuel pressure by a pound or two,but i would fix the exhaust leak first.It will sound deeper too with increased fuel pressure

 

sounds good ninetyone,I wanted to do a fuel pressure regulator anyway

 

Did you have stock manifolds on before? You should be able to tell a difference. I went 14.8@93 stock. Then 14.4@96 with Hooker 2055's and Y pipe. Then I went 14.0@98 with the hooker 2055's, y pipe, 3" catback with a powerstick muffler.

 

Yeah I had stock manifolds before. I should have gotten a base line before I did the work.

 

get rid of the cats an you'll feel an notice a difference . just do it in a way you can put them back for inspection . with a auto you won't get alot of babble when decelerating .but it will free up the flkow some an sound better .

 

If your cats are still on, it will be mellow. I'd leave them on at this point in your build and unless they are plugged they aren't holding you back.
Start looking at a good trans rebuild with a smaller torque converter and have the trans built as well or better than your budget can handle! (http://www.700r4l60e.com/ can help you out)
*this advice is for a stock chip only* Check your timming and bump it up a few degs, get a adjst fuel psi reg and bump it until car slows down a bit then drop it back. (check these at the track)
Look for a SLP cold air box.
Street underdrive pulleys
There is more you can do.

 

Check your base timing. It should be *6-*8. Gut your airbox. You should have gain more power across the board like I did when my car was stock. Make sure the O2 sensor is connected and no vacumn leaks. Ask Kevin91z to send you the same chip he did for a 89 GTA 350 that made 251whp with the exact same set up you have. You may have to pay him for the chip. He's Dyno Dons son.

Stand outside your car and have someone to drive down the street and check out the sound. It gets loud when you hammer it but have a smooth sound at cruise. It's louder with a modded engine.

 

yep with cats and magnaflow it should be pretty quiet at idle and mellow at cruise but at WOT it should be louder than stock. IF you want louder, gut cats but if you need them for emissions, disregard that. Try taking muffler off and running open pipe for a second to see if you get a noticeable improvement in volume. If it does, then likely could change mufflers and gain the sound you want

My L98 picked up a decent bit from headers/catback exhaust and timing bump to 8 deg. Your probably only gaining 20whp overall since the heads/cam/intake side is more restricted but it still helps make a faster car.

 

my obx 3" cat back sounds like a magnaflo only louder but still no drone on the highway an thats catless

 

When i had just the 350 tbi with 2055s and hooker aerochamber it helped alot throughout with and without the cat. And my 2500 has a magnaflow 3" dual in dual out muffler and its anything but quiet but it to has no cats.

 

With 2 cats on your car of course there will be no power or sound gain.

 

i will say i noticed the same thing with my dads 89 iroc tpi 305 going from manifolds to headers and some how it didnt gain anything even with a brand new cat
and not to mention it already had a 3 inch catback
yet on my 91 Rs that was then a tpi 305 i used the same headers and catback and could feel a major change in power hence the reason i was able to talk dad into getting headers

yet the iroc sounded better and my rs sounded like crap

only real differance in the cars at that time was one was maf on sd

 

WRONG!

 

That exhaust leak you speak of might be more problematic than you think, if it's before the o2 sensor it will throw off the mixture and you loose power, what gaskets did you use?

 

I have some joints in the ypipe that need to be welded

 

Dyno Don's headers are similar to the SLP ones, which in tri-y configuration will give a 12hp increase on an L98. See linked article on the third gen blog I posted a while back.

http://thirdgenfbody.wordpress.com/2...ft-april-1989/

 

Dyno Dons aren't based on those, thats SLPs 1 5/8s tri-Ys.
His are based off of the "1 3/4" shorty headers.
I have both SLP header designs and they used the same size primary header pipe but were advertised as 2 different sizes.

 

no,the N10 dual cat ypipe option is supposed to be worth a 13% power gain.Without a cat u may even lose some low end torque.

 

I realized that right after I posted the link... My bad!

Regardless, the shortys have to add 10 or more hp to a stock TPI as just a redesigned y-pipe adds about 5hp by itself.

 

In 1990 or 91 I added a zz4 cam, factory dual cat exhaust with edelbrock headers, hypertech chip and 160 stat and I could kill LT1 cars. This in a 89 350 tpi iroc with 2.77 gears. The car was incredible to 4600rpm and would kill the rear tires if you stepped on the go pedal to quick. Had that set-up for 12 years or so and it was GREAT for 99% stock and still getting 24mpg. A set-up that is matched well really does make all the difference since what I had was bearly above stock and was very impressive.

 

I did the same magnaflow setup except for the headers on my 1989 Camaro with the L98. After about 5000 miles on the magnaflow dual cats and muffler, the exhaust sounded better and more aggressive. The only problem I had with the set up is that I was using 93 octane, and after awhile my car was running so rich that it wouldn't perform right. So I switched to 89 octane and the car performs better than it did before the magnaflow set up. Also, When I get on the throttle, the full magnaflow exhaut sounds really nice after it was fully broken in.

 

If you were looking for sound and flow you should have gone with GMMG. Its a good flowing exhaust, and sounds aggressive too. Or if you want a price range close to magnaflow there many other exhaust setups that easily improves the sound level. my car has a full 2 1/2 flowmaster catback and it sounds better than most 3in ive heard. Unless your really doing an engine swap, or swaping out EFI systems for a big build, honestly 2 1/2 is all you really need if your keeping TPI. The 3in exhaust on our cars are more prone to popping and whining down when decelerating. the bigger size on the magnaflow 3in may flow a great deal but when it comes down to becoming noticed the sound is not there if you keep the tpi. Now if you keep the exhaust might i suggest a electric cutout, you can open and close it when you chose to, but it will be bit louder than you have now.

 

WRONG! 3in catback improves performance across the board. The smaller 2 1/2 catback chokes the performance and still runs like stock. It's aslo louder because of the smaller pipe(s). It doesn't matter if it's TPI or TBI. The engine still needs to breathe.

 

You only need 3in if you are exceeding over a certain HP mark for the car breathe. But with tpi he is not breathing to well anyway. Come on... he is not even putting out 240HP. Your honestly only making maybe 200 or 210 HP at the rear wheels with tpi. 2 1/2 in is a good exhaust to run if your only using headers. MOST exhaust specialist i talk to say 2 1/2 is a good setup, because Even with tpi exhaust mods they dont gain you anything accept to help breathe a little better. Now if it was a built 350 with a high flow tpi intake i can understand where 3in actually helps you if you ditch the stock heads. but he is virtually running a 350 stock accept headers. 3in is not helping you accept for sound. And your WRONG 2 1/2 actually did a very nice gain over the stock 2 1/4 to 2in exhaust. My car has no emissions, so with the dual cats gone i get a nice flowing exhaust and actually picked up better torque up top.

 

Anyone who tells you that all you need is a single 2.5" exhaust is thinking about airflow through a 4 or 6 cylinder, a 305 can't breathe through a single 2.5". A 3" is necessary to release the backpressure to allow max power and efficiency.

I personally picked up 35hp by going from a stock 2.25" LG4 exhaust to a 3" y-pipe (no headers), 3" cat, and a 3" banks cat back - in 1990.

 

you knew that you were going to get 1000000000 different opinions right??? if you have a tpi it runs out of steam above 4500rpm. it is going to sound good but it is not going to be loud as you were expecting. you are now getting flow out the exhaust. good thing. there are a couple a questions that i have. is the engine running perfect? are there any other mods? you took away SOME!!!!!!!!!!!!!!!!!! backpressure. backpressure is so misunderstood!!!!!! exhaust exits the engine in pulses. not a stream. when you had a stock exhaust the pulses were short--( hint ) torque. now your pulses are long (hint) horespower and less torque. what you are experiencing is the engines ability to exit more air. but everything else is the same. DRIVE IT!!!! anotherthing to remember is this. ALL ADVERTISED HORSEPOWER CLAIMS ARE AT A CERTAIN RPM!!!! period. what i have done over the years: im 43 and been modding since i was around 14. im not an expert. but i do this. if they claim 40 i expect 20 to 25. I HAVE NEVER BEEN DISAPPOINTED.!!!! drive it some more and see if it improves. and remember BIGGER is not always bigger. your cats are NOT hurting your performance one bit. you have allowed the engine to exit air quicker than it intakes it. another very very very important thing to remember: NO TWO ENGINES PERFORM THE SAME NO MATTER WHERE, WHEN, OR HOW THEY WERE BUILT. best of luck buddy.

 

From my experience with my own car and what I've seen on the Dyno, my car stock is a L98 g92 N10. Just installing SLP 1 3/4in headers and 3in catback the HP went from 209whp to 255whp. 13.4@104mph. That's a big difference on a all stock engine with a tune and gutted air box and K&N filters. Your theory and others is bull crap. This is the best route to go but not too many people have tried it. They did it their own way and had gotten poor results. Oh and by the way, all the smog stuff and A/C in working order. And one more thing, My car is 1990 IROC 5.7 rated at 245hp.

 

C'mon guys, the stock exhaust on a performance car with TPI from the factory is 3" in front and 2 3/4 intermediate pipe to the rear.
The cars with 2.73 axle only had 2 1/2" and it really wakes them up going to 3".

 

I'm guessing your refuring to the single cat Ypipe? the dual cat has 2 pipes maybe 2"? I havent measured them.. yet

 

From the cat(s) back, on performance cars is 3in. Dual cats cars up to the 3in pipe is 2 1/4in.

Dual cat cars made the most HP at 245hp. Single cat cars made the max at 235hp.

 

I'm fairly sure my factory dual cat cars don't have any 3" pipe on them at all.. I'll go measure.
I think the single cat cars also have a smaller pipe inside the 3". They arent a true 3" ( I don't think)
I just measured the pipe after my dual cats on my 89 and 92 cars. All 3 of the cars are only 2 3/4"s .. room 4 improvement there..

The HP ratings for the 350 birds with dual cats were 235hp up to 89 then went to 240 I think in 90 with the SD setups.
Didn't just the vette get 245hp??
I know we are just spliting hairs here tho..

 

take the magna flow back and get flowmaster if its sound you want

 

90-92 G92 5.7 F-Bodies are rated 245HP with the N10 code for dual cats. A G92 F-Body 1989 rated 240 with N10 code for dual cats. There were no dual cat cars before 1989. Look it up!
https://www.thirdgen.org/1990-chevy-camaro

 

I know the N10 started in 89, it was rated at 235hp in the birds.
The power was bumped to 240hp for the SD birds.
Thats what the 89-92 dealer info/brochurs that I have says.

Camaros were different in ratings but really had the same power.
What does the dealer stuff say about the camaro ratings? ( I don't know)

 

Just got my exhaust leaks fixed. Don't know if it was that or something else but I lit up both tires. The did feel more peppy. I might try installing my single cat ypipe and no cat. What difference do u think it will make.

 

No cat? maybe 2hp more?

 

13.4 at 104mph in a 3500 lb car with driver is a lot more like 350hp, not 250hp. Off top of my head probably around 325hp. That is definitely not stock L98 with exhaust kind of power numbers.

 

I am going to be doing a header back exhaust and I knew what headers and cat I was going to run but the cat-back was a different situation. It came down to the Magnaflow and the Borla. In the end I bought the Borla. You Tube helped a little in that decision but I have always wanted the Borla. I am excited as my set up will be going on Saturday

 

You'll probably set off a check engine light from no cats, I know my car did. My car actually performed better with the dual magnaflow cats than without, because I was able to get more accurate fuel mixture readings for the computer.

 

WRONG! There is no after cat O2 sensor on obd1 cars