89formula350b2l

iTrader: (11)

i was wondering if anybody had dyno'ed their car with 3" exhaust and then switched to dual 2.5 pipes OR 3.5 inch and then re dyno'ed. What was your improvement?
thanks
ed

89formula350b2l

iTrader: (11)

or maybe 1/4 mile time difference? anybody?

xpndbl3

iTrader: (5)

65hp

onfire

xpndbl3,

Please elaborate.

Rabi C.

84TranzAm

iTrader: (2)

Well when I was setting up my car, this time around I went with 1 3/4 inch slp headers and a borla cat back. I had duals on the car before and driving on the streets up here is real hard with duals. They do not like speed bumps and curbs. I knocked them off several times. No one up here can do mandrel bends and the bends were not nice and you know they were restricted. I asked alot of people different opinions and the biggest thing was how much horsepower are you going to be pushing. I pretty near recieved the same answer from everyone. You will not see a significant gain if you are pushing under 350 horspower. They only need to move so much exhaust to get all the performace you will get. Going more pipes and bigger pipes is not going to work for every set up. If you are pushing 500 yes definateley. It will need it. But dual 2.5 put on correctley to run on the street with lots of ground clearance and ugly bends will not see much change vrs 3 inch with 350 horspower . This is just some info I was told and read . With my plates out of my Borla exhaust it flows pretty damn free. Too free or loud I think, maybe I am getting to old

TheScaryOne

iTrader: (3)

The less power your engine is making, the less an exhaust mod will help. In fact, if I'm not mistaken, cars need a certain length and diameter exhaust to flow properly, and going too large can actually reduce performance.

But if you plan on modding the engine soon, why not prepare? Although if you plan about making power, there's other things more important for you to worry about. Subframe Connectors (I hear the Spohn and Alston can be used at the same time), the entire suspension could use poly bushings and replacement of worn parts, transmission, driveshaft, rear axle assy. All of that will need replacement or upgrades before I'd even touch the engine. Even with a few bolt ons. These cars were built to run the low-output engines GM put in them. Change too much there, and you have to change a lot.

Edit: Just read you sig, and saw that you make power. So you've probably done a lot of that all ready. Well, I can't see how the typical 2.5" dual setup would hurt. I'd recommend checking out Willie's ride for a good layout of how to make a ground clearanced dual setup. Lotsa bends, all mandrel.

xpndbl3

iTrader: (5)

on a buddies built SBC which is pretty radical to be driven on the street we picked up 65hp from a 3" catback to 2.5" true duals all mandrel bent. This wasn't a stock 350 tpi so results may vary if you see any gain at all on a smaller motor with less HP, but if the flow is needed it will hold you back.

ZONES89RS

iTrader: (2)

I have installed a LT header setup with 2.5 into a 23 inch y, i have dual cutouts on the 2.5s. I have not taken it to the track, but with the cutouts open it feels allot harder on the topend. I know he sound itself can make you think it is stronger, but it spins conciderably more, not just a little, this does have allot less back pressure.

jerrod75110

Im glad people are talking about this! Not just saying do a search or it's not worth it ground clearance. I have shortys and a single 3inch and im debating puting long tubes and duals on my car. My motor should have a least 400hp!
I would like to see more people post their resluts on here!

nelapse

iTrader: (17)

I highly doubt this.

wgripp

iTrader: (1)

If/When you need to upgrade your exhaust, I'd consider going to a single 3.5 inch or 4 inch system. It's cheaper, easier to route, and will give you more than enough air flow.

89formula350b2l

iTrader: (11)

ok anybody got dyno sheets or slips to prove this? and would this be worth my time/money to go to two 2.5 inch intermediate pipes?
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[quote=nelapse;3394423]

KrisW

iTrader: (5)

I read an article that was close;

In Custom Rodder they were dyno-ing the difference between those two setups, the 3 inch single and the dual 2 and half. This test was done on a 65 Buick Skylark (like a chevelle)

The single 3 inch was superior or equal in all of the tests. Even after an x pipe on the duals. Their key was actually in the y-pipe. They used a flowmaster 2 into 1 transition off of the engine and then the single 3 inch all the way back with a 3" muffler and tailpipe.

The dual 2 1/2 system was louder with 2 1/4 tailpipes with a small gain in torque and drop in HP, with 2 1/2 tailpipes it was only slightly less (no driveable difference as I recall) on torque and HP, with 3 inch tailpipes it gained HP slightly and lost torque...

Hope this helps. I have a nice pic of a y-pipe on this forum where it was homemade with that same flowmaster transition. It was the Buick 455 powered 87 Trans Am that ran 11's... I'll see if I can find the pic

KrisW

iTrader: (5)

Here is the y-pipe

He had to run off of the manifolds because there is just no room for headers - even shortys - with the Buick 455!

xpndbl3

iTrader: (5)

do you just follow me around the boards trying to call me a liar? First the seat belt thing and now this. Only swap he did was the exhaust, sprayed the same shot through the motor 65hp difference. What do you want me to say?

nelapse

iTrader: (17)

I see an article that suggest Y-pipe 3" exhaust out performs Dual, so where does this "Magical" 65 HP come from?

Hmm... I would like to use a life line...

Let's call Mr. BS Flag

xpndbl3

iTrader: (5)

You're right, a 3" catback outperforms a dual 2.5" even though there is more cross sectional area for exhaust to flow. Guess all those idiots who run duals or 4" mufflex exhaust are doing it for no gain at all.

nelapse

iTrader: (17)

If you truly believe your Magical 65 HP is real then you are misinformed not a liar.

If you know that you are spreading BS then if the shoe fits.

All I want is some sort of evidence. Let's be rational about this.

Take a beefy 350 Hp TPI setup.

Take the stock catback off and put on 3" setup, maybe a 20-40 HP increase?

However, you are saying that he took off an already performance exhaust, and put true dual and gained an additional 65 HP

So you remove stock exhaust, put duals on and hope for 100Hp?

Please tell me you are joking.

xpndbl3

iTrader: (5)

I said the motor was much more radical than a 350tpi, it's a carb based bigger cimotor, I was merely stating that for the typical thirdgenner they won't see that big of a gain. Furthermore, take a look on the ls1 sites, people who replace their stock catback with a 3" flowmaster catback actually lose HP on the dyno, he replaced a flowmaster catback with a full mandrel bend with race muffler 2.5" exhaust. I'm sure he sprays more than most people make on motor on this site.

nelapse

iTrader: (17)

I still disagree with you on the seat belts. I have found no evidence to support your theory or mine.

However, if it makes you feel better, your compassion on the matter had made me think about my pregnant wife, so I bought a new set of OEM set belts and I plan on getting rid of the harnesses.
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If this guy has that kind of power why would he waste his time with Dual 2 1/2" setup and not a dual 3"? Or 3 1/2" - 4" Y-Pipe?

You are right about the typical thirdgener, It is sad to say but 95% of people on this forum will probably never see more than 300WHP

4playta

I cant give you any HP #'s but I can give you drag slip times...Last year my TA running a 350 dynod 375 at the crank we got the motor installed and took it to Martin dragway in Michigan and I ran a best 13.23 a 13.30 and a13.39 this was with the long tube headers that came with the car with two 2 1/2" straight pipes with some turbo mufflers and turndowns dumped right before the axle. a few months ago I installed hooker 2055hkr's that came with a 3" Y pipe and ran a 3' pipe all the way back (mandrel bends stock location) with no cat into a dynomax 3" in dual 2 1/2" outs and I took my car back to Martin and ran a 13.25 I was going to try my 150 shot nos system but never got the chance because a fitting for my trans cooler started leaking and I was black flaged off the track but the 13.25 was with no nitrous...I would have to say the temp and track conditions was real close to what they was last fall. Do I think I lost any HP going to a 3"? NO! but that is 375hp...I have activated the nos going down the street and it does pull alot harder but I might be choking it with the 3" now and might be able to free up some HP with duals when I run the Nitrous because it dont feel like a 150 shot it feels more like a 75 shot...I have been told that a good 3" system will flow over 400hp (Not a 3" catback) I am talking about 3" from the y pipe all the way back. But if you are making 450 or 500hp I believe you could free up alot more HP running true duals only I have no basis for comparison and I am happy with the way my car is setup now. I do not plan to upgrade to duals to see if I can gain another 30 40 or even 50hp...The only good dual setups I seen on our cars costed realy big bucks for the exhaust shop to fabricate.

xpndbl3

iTrader: (5)

His motor lost power N/A with dual 3" pipes, since that is a huge flow increase compared to the 2.5" pipes. enlarging both pipes by .5 is basically increasing the exhaust size by 3" overall in area. We didn't want the heavy mufflex 4" system, nor could any of us justify the price $1300-ish, when we're making true duals for under $300 for the 2.5" and $330 for the 3" pipes.

It is weird just like how my motor made more HP with 1 5/8" headmann headers than it did with the hooker 1 3/4" super comps on the dyno. It also made more TQ with the true duals on there than open pipes.

FlippindaBird

iTrader: (10)

i guess we have at home dynos that help us figure out the performance gains we acheive ????

wgripp

iTrader: (1)

Allright... can we agree that dual 2.5s and a single three are ABOUT equal, but that a single 3.5 is better than dual 2.5s?

titchener

Go to www.dynomax.com and download their catalog (the online one sucks). They have a pretty interesting table where they show the optimal single and dual exhaust pipes sizes for different HP ranges.

Going too big hurts you because there is an optimal velocity for the flow through the pipe for best overall flow, if you are too small your velocity is too high, too big and your velocity is too low.

As your HP increases you are flowing more exhaust gas through the pipes, so that's why you need a bigger size to get the optimal velocity.

For your car, which is putting out around 400HP at the flywheel they claim a 3-1/2" single or 2-1/2" dual exhaust would be best. They claim a 3" single exhaust is good for engines in the 300HP range.

I don't think there's necessarily any advantage of a single exhaust versus and dual exhaust as long as both are sized correctly and have free flowing cats and muffers. One issue that comes up however on single exhausts is getting a muffler with enough flow to handle your HP level. Dynomax rates their mufflers for a maximum recommended HP level, and the single mufflers start maxing out at a little over 300 HP, so for high horsepower engines like yours that's probably going to mean the dual system is preferable since you add the HP rating of the 2 dual mufflers.

Paul T.

cheppibear

I am pleased with the performance of my y pipe and single 3" setup. Engine has approx 350 HP at flywheel, TPI Edelbrock headers (headers only), independent y pipes converge into a flowmaster 2 x 2.5" to 3" reducer cone, then all the way back with a 3" pipe into the flowmaster single 3" outlet muffler.

Car ran a best of 13.79 @101 at Englishtown, NJ with street tires. Best part is that it sounds "humble" when cruising and like a drag car when you get on it.

For longevity reasons I will probably upgrade to the 2055 (Jet-Hotted) and keep my single 3" setup.