Engine Masters - 3" single vs 2.5" dual

[135 Honolulu]

I'm sharing this from harristuning.com

Exhaust, You need to start there because doesn’t matter how much you improve the air going in, if you can’t get it out it will run poorly and the stock exhaust is terrible. Well the KEY issues with the exhaust is the Y pipe and the catalytic converter. GM intentionally made that Y pipe restrictive to increase back pressure and most have paid someone to spread a myth that back pressure in the exhaust is GOOD. Its NOT. Air velocity is good not back pressure. The reason for the back pressure was so that the EGR smog system would work better and the increased pressure would build up a lot of heat to keep the o2 sensor hot. A good free flowing exhaust does typically need a 3 wire heated o2 sensor conversion to maintain its temperature. To fix 90% of the exhaust issues, I recommend a Flowmaster Y250300 collector from your favorite vendor and replace that section of Y pipe where the 2 pipes merge. Dramatic improvement over that stock GM design. As for the cat, I know most say it should fall off and turn a blind eye but I personally don’t like the smell of the exhaust with no cat and want to do my part towards our environment as well. you can search ebay for THUNDERBOLT 3 CATALYTIC and those high flow cats are like $50. As for headers, not really recommended on engines under 300hp and for muffler, you want an aggressive sound that’s fine pick from several. I have been using a FULL BOAR SS muffler off ebay which are stainless and cheap and flow well but not going to be a huge gain in power. the Y pipe will add a noticeable amount though and will help support more modifications.I clipped this picture from my latest Hot Rod magazine on choosing the size of your exhaust pipe.

 

[135 Honolulu]

I decided to try the Flowmaster y250300 that was mentioned above. I got mine from Amazon

 

[PlayingWithTBI]

I recommend a Flowmaster Y250300 collector from your favorite vendor and replace that section of Y pipe where the 2 pipes merge.

I bought the FlowMaster collector and compared it to the JBA Y pipe - not a lot of difference but, the OE Y pipes crimp bends were horrible compared to the JBA mandrel bent so, I returned the FlowMaster. Yes, more expensive but a lot better flow.

 

[L31MaxExpress]

I'm sharing this from harristuning.com

Exhaust, You need to start there because doesn’t matter how much you improve the air going in, if you can’t get it out it will run poorly and the stock exhaust is terrible. Well the KEY issues with the exhaust is the Y pipe and the catalytic converter. GM intentionally made that Y pipe restrictive to increase back pressure and most have paid someone to spread a myth that back pressure in the exhaust is GOOD. Its NOT. Air velocity is good not back pressure. The reason for the back pressure was so that the EGR smog system would work better and the increased pressure would build up a lot of heat to keep the o2 sensor hot. A good free flowing exhaust does typically need a 3 wire heated o2 sensor conversion to maintain its temperature. To fix 90% of the exhaust issues, I recommend a Flowmaster Y250300 collector from your favorite vendor and replace that section of Y pipe where the 2 pipes merge. Dramatic improvement over that stock GM design. As for the cat, I know most say it should fall off and turn a blind eye but I personally don’t like the smell of the exhaust with no cat and want to do my part towards our environment as well. you can search ebay for THUNDERBOLT 3 CATALYTIC and those high flow cats are like $50. As for headers, not really recommended on engines under 300hp and for muffler, you want an aggressive sound that’s fine pick from several. I have been using a FULL BOAR SS muffler off ebay which are stainless and cheap and flow well but not going to be a huge gain in power. the Y pipe will add a noticeable amount though and will help support more modifications.I clipped this picture from my latest Hot Rod magazine on choosing the size of your exhaust pipe.

Harris has some information that is just plain wrong. One of those goodwrench smog 350s was tested on a dyno. A set of 1 5/8" long tubes gained 53 ft/lbs of torque on a stock 350 at one point in the RPM range with torque gains everywhere. Headers and exhaust would be my first change to a small block. 1.6 roller rockers next. Then some induction mods. Alot to be gained even with stock heads and cam. Back in the day a set of thorley tri-ys, dual 2.5" exhaust with a X-pipe and a performer rpm intake gave my stock 305 a much needed shot in the arm. Felt like I added a small shot of nitrous it was so effective. Stock manifolds would make good anchors for a canoe.

 

[OutlawDrifter]

Harris has some information that is just plain wrong. One of those goodwrench smog 350s was tested on a dyno. A set of 1 5/8" long tubes gained 53 ft/lbs of torque on a stock 350 at one point in the RPM range with torque gains everywhere. Headers and exhaust would be my first change to a small block. 1.6 roller rockers next. Then some induction mods. Alot to be gained even with stock heads and cam. Back in the day a set of thorley tri-ys, dual 2.5" exhaust with a X-pipe and a performer rpm intake gave my stock 305 a much needed shot in the arm. Felt like I added a small shot of nitrous it was so effective. Stock manifolds would make good anchors for a canoe.

It's a well known fact that y-pipe from the factory is garbage on TBI engines. Any 350 you pull the stock manifolds off of and add a long tube header in place of, will pick up HP & TQ. TBI O2 sensors were of the non-heated variety...and when you actually freed up the exhaust flow, they ran like poo, cause they O2 never was up to temp...so everyone though an engine needed BACK PRESSURE....creating the greatest myth in exhaust theory ever! Exhaust needs to be correctly sized to create a scavenging effect, it definitely does not need to create BACK PRESSURE!!!!!

What induction mods?...flip the air cleaner lid over? "Cold Air Intake"...?

No argument on stock heads and cam...they were good for mileage and low rpm motivation, not much else. But for a stock daily driver, they did their job.

 

[sync]

I went with the JBA, nice smooth bends, bolted right up, a lot better transition at the Y than the OE.
https://www.summitracing.com/parts/jba-2831sy

Here's a picture of it with the high flow Thunderbolt 3 cat...

I'm assuming TBI Y pipes will bolt up to a Vortec? Just gotta add some O2 sensor ports?

 

[PlayingWithTBI]

I'm assuming TBI Y pipes will bolt up to a Vortec? Just gotta add some O2 sensor ports?

Yes, they'll bolt up but, the Vortec Y pipes have HO2 sensors before the cats which are all part of the Y pipe assy - different animals.

 

[sync]

Yes, they'll bolt up but, the Vortec Y pipes have HO2 sensors before the cats which are all part of the Y pipe assy - different animals.

Good to know. Second question. Anyone know if the JBA pipe fits 4wd? Is there a difference between 2 and 4 wd?

 

[Dirty Bird]

I'm assuming TBI Y pipes will bolt up to a Vortec? Just gotta add some O2 sensor ports?

I have a 96 Vortec 5.7 that uses dual exhaust into the muffler then single all the way out exiting right rear. Was looking at a magnaflo replacement for mine.

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[Dirty Bird]

I'm sharing this from harristuning.com

Exhaust, You need to start there because doesn’t matter how much you improve the air going in, if you can’t get it out it will run poorly and the stock exhaust is terrible. Well the KEY issues with the exhaust is the Y pipe and the catalytic converter. GM intentionally made that Y pipe restrictive to increase back pressure and most have paid someone to spread a myth that back pressure in the exhaust is GOOD. Its NOT. Air velocity is good not back pressure. The reason for the back pressure was so that the EGR smog system would work better and the increased pressure would build up a lot of heat to keep the o2 sensor hot. A good free flowing exhaust does typically need a 3 wire heated o2 sensor conversion to maintain its temperature. To fix 90% of the exhaust issues, I recommend a Flowmaster Y250300 collector from your favorite vendor and replace that section of Y pipe where the 2 pipes merge. Dramatic improvement over that stock GM design. As for the cat, I know most say it should fall off and turn a blind eye but I personally don’t like the smell of the exhaust with no cat and want to do my part towards our environment as well. you can search ebay for THUNDERBOLT 3 CATALYTIC and those high flow cats are like $50. As for headers, not really recommended on engines under 300hp and for muffler, you want an aggressive sound that’s fine pick from several. I have been using a FULL BOAR SS muffler off ebay which are stainless and cheap and flow well but not going to be a huge gain in power. the Y pipe will add a noticeable amount though and will help support more modifications.I clipped this picture from my latest Hot Rod magazine on choosing the size of your exhaust pipe.

Not looking to stir the pot but depending on what you're doing a little back pressure is good. I have Captain's Choice in an old Firebird with a Chevy small block built up. Steel rods/steel crank, sealed power 11.5>1 Pistons, Dart 2 220cc runner heads, Manley pro-flow undercut/swirl finish valves, big lift cam, balanced/blue printed... dont get me started on the tranny, the list goes on and on. I'm running long tube headers "H over pipe" Kindig exhaust cutouts with Flowmasters and exhaust pipes going all the way out to stock trans am tail tips . I have better acceleration with exhaust valves closed but lose on top end. With valve open I lose torq on low but I gain HP. It's is loud as hell! The look on people's faces who want to race when I open up those cutouts is priceless! I think that's why it got the nickname Dirty Bird ...or maybe because it's constantly covered from dust sitting in the garage.

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