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Username Post: Exhaust size        (Topic#366361)
1carguy 
Poster
Posts: 59

Reg: 11-30-08
09-09-21 01:11 PM - Post#2826785    

I'm running a sbc 350 in my '70 El Camino. It was bored .060 over, flat top pistons, 202 heads with a Comp Cam 230-236, Edelbrock 650 carb on a Performer 2120 manifold. It's probably around 300 hp.
Question: the builder put 3" exhaust from the headers back to the mufflers, then went with 2.5" from the muffler out the back. It sounds pretty good but I've read that 3" exhaust on a mild 350 is too big and won't provide enough exhaust pressure for that motor. The exhaust system hangs down too low so I'm going to have a muffler shop redo it. Should I just bite the bullet and redo the entire system with smaller exhaust?



 


Lead sled 
Frequent Contributor
Posts: 2095
Lead sled
Age: 61
Loc: Walton,NY.
Reg: 11-04-09
09-09-21 01:26 PM - Post#2826787    
    In response to 1carguy

Sounds too big to me. I would use a 2 1/2" reducer, about 6"-8" behind the collector(if you have the room for it), then run 2 1/2" mufflers, and tail pipes. Just my 2 cents

Late yr model (Dec. 51 Bel Air/ 52 trim), with a basically stock 68 Camaro SS350/300hp Turbo Fire Edelbrock 1405,Saginaw 4spd/355 geared 55/6 Chevy rear.2,1st places, and 1 top five award trophies so far
http://www.picturetrail.com/bris51deluxe


 
Rick_L 
Member #409
Posts: 27913
Rick_L
Loc: Katy, Tx, USA
Reg: 07-06-00
09-09-21 01:47 PM - Post#2826789    
    In response to Lead sled

No real detriment to having it too big. Engines don't need back pressure. Otherwise race cars would all have mufflers.

Start with where it hangs too low and fix it.



 
rumrumm 
"20th Year" Silver Supporting Member
Posts: 2120
rumrumm
Loc: Macomb, IL
Reg: 10-18-01
09-09-21 07:38 PM - Post#2826820    
    In response to 1carguy

What Rick said. It's bigger than it needs to be, but it won't hurt anything. Keep it.

Lynn

"There's no 12-step program for stupid."


383 sbc, Eagle, AFR, SRP, CompCams, Edelbrock Pro-Flo 4 EFI. Dyno #'s: 450 hp @ 5700, 468 lb. ft. of torque @ 4300.



 
1983G20Van 
Super Senior Member
Posts: 3894

Loc: Bedford, Texas, USA
Reg: 11-13-02
09-09-21 08:10 PM - Post#2826824    
    In response to rumrumm

Won't hurt a thing having dual 3" pipes. My stock 245 net hp 350 came from the factory with 3" pipes to the muffler. Manifold exits were 2.25", but the pipes bumped up to 3" within 6" of the manifolds. Stock setup for a 1997 Express van.

1983 G20 Van, 350 TPI, Ported 906 Vortecs, Edelbrock 3817 Base, ASM oversize runners. Reed Custom Roller cam, 700r4, 12 bolt with 3.08 gears, Doug Thorley Tri-Y headers, true duals


Edited by 1983G20Van on 09-09-21 08:10 PM. Reason for edit: No reason given.

 
japete92 
"7th Year" Silver Supporting Member
Posts: 1777
japete92
Loc: No. Virginia
Reg: 01-18-13
09-10-21 05:35 AM - Post#2826834    
    In response to 1carguy

Performance wise, there's no real reason to change.

But, if you need to reduce the size for ground clearance; one could mimic the OEM GM size 'pipes' (from memory the 'biggest' were 2 1/2" to the muffler; 2" after muffler).

You may 'lose' a little higher RPM performance, but that MAY resolve the clearance problems. Depending on how much 'clearance' you need, you MAY also need to nix the headers. Similar performance 'price'.

The decision depends on your priorities.

Pete





 
beagrizzly 
Frequent Contributor
Posts: 2256
beagrizzly
Age: 71
Loc: south texas
Reg: 08-04-12
09-10-21 09:09 AM - Post#2826839    
    In response to 1carguy

If I can add a couple of pennies here?

If you're not racing, the exhaust you use makes NO difference in just driving a car.

You will never notice any difference in the stop light grand prix. At the strip you probably could not make .2 difference in E.T. by doing anything with the exhaust on a small block.

Again, my two pennies.

Griff

if you're gonna be a bear..................

1960 Biscayne (the 6T)
2005 Yukon XL
2007 GMC Sierra Classic 8.1
2009 Silverado
2011 Escalade ESV


 
japete92 
"7th Year" Silver Supporting Member
Posts: 1777
japete92
Loc: No. Virginia
Reg: 01-18-13
09-11-21 05:14 AM - Post#2826875    
    In response to beagrizzly

  • beagrizzly Said:
If I can add a couple of pennies here?

If you're not racing, the exhaust you use makes NO difference in just driving a car.

You will never notice any difference in the stop light grand prix. At the strip you probably could not make .2 difference in E.T. by doing anything with the exhaust on a small block.

Again, my two pennies.

Griff



Conceptually, I agree. Not racing? No headers/exotic exhaust.

And, there's no info on the car's drive train (which is a significant factor). A 4 speed with a low ratio rear will max out the engine's high rpm performance (if performance is high on your priority list). A 2 speed power glide with a 3.08 rear will 'suck up' whatever 'performance' the headers/exhaust might add.

More pennies

Pete






 
bobb 
Super Senior Member
Posts: 5899

Loc: paradise
Reg: 09-05-03
09-11-21 09:07 AM - Post#2826883    
    In response to 1carguy

you dont have a max motor so performance should not be noticeable. bigger pipes make your motor sound bigger. most people think i have a bligblock. 3" pipes with 3.5" tailpipes, flowblasters and resonators.

70 L camino, grampa engine, g-force 5 spd, road rage suspension. Pray first before all else fails.


 
1carguy 
Poster
Posts: 59

Reg: 11-30-08
09-12-21 02:45 PM - Post#2826947    
    In response to bobb

Ok, sorry I didn't offer more info. It's got headman headers, mufflers are Borla. Tranny is a 700R4, Diff is a 3.73 posi. With this exhaust it roars like a lion, but is a fairly tame performer. For me it's a cruiser but I like to tromp on it occasionally.



 
grumpyvette 
Senior Chevytalk Moderator -- Performance Subject Matter Expert --
Posts: 17663
grumpyvette
Age: 73
Loc: FLORIDA USA
Reg: 03-16-01
09-12-21 05:34 PM - Post#2826959    
    In response to 1carguy

http://garage.grumpysperformance.com/index.php?thr...

http://garage.grumpysperformance.com/index.php?thr...

http://garage.grumpysperformance.com/index.php?thr...

use the math the links and sub links provide, you don't need to guess, or wonder at the correct answers, you have the ability to find the right answers

IF YOU CAN,T SMOKE THE TIRES AT WILL,FROM A 60 MPH ROLLING START YOUR ENGINE NEEDS MORE WORK!!"!
IF YOU CAN , YOU NEED BETTER TIRES AND YOUR SUSPENSION NEEDS MORE WORK!!


 
Mercedes 
Contributor
Posts: 352

Reg: 07-09-18
09-13-21 01:43 AM - Post#2826978    
    In response to 1carguy

My view here is that way too much money is wasted on exhaust systems. There are organizations out there that make record profits convincing people that their magic pipes will transform your vehicle into a race car. The fact is that the exhaust ports on the head are a certain size. No matter how big the pipes are that exist the head, it won't make much difference.

Noise is not horsepower.



 
grumpyvette 
Senior Chevytalk Moderator -- Performance Subject Matter Expert --
Posts: 17663
grumpyvette
Age: 73
Loc: FLORIDA USA
Reg: 03-16-01
09-13-21 05:20 AM - Post#2826987    
    In response to Mercedes

back pressure kills hp, exhaust pipes must be large enough to not be restrictive , once that point is reached larger pipes don't help and might hurt power in some cases, stock exhaust systems are designed to match stock engine hp & air flow rates, if you significantly increase power exhaust flow has increased, but it may or may not require a larger exhaust.
this is not guess work the math is known and
predicted values, and expected results well tested.
http://garage.grumpysperformance.com/index.php?thr...

IF YOU CAN,T SMOKE THE TIRES AT WILL,FROM A 60 MPH ROLLING START YOUR ENGINE NEEDS MORE WORK!!"!
IF YOU CAN , YOU NEED BETTER TIRES AND YOUR SUSPENSION NEEDS MORE WORK!!


 
japete92 
"7th Year" Silver Supporting Member
Posts: 1777
japete92
Loc: No. Virginia
Reg: 01-18-13
09-13-21 05:49 AM - Post#2826994    
    In response to Mercedes

  • Mercedes Said:
My view here is that way too much money is wasted on exhaust systems. There are organizations out there that make record profits convincing people that their magic pipes will transform your vehicle into a race car. The fact is that the exhaust ports on the head are a certain size. No matter how big the pipes are that exist the head, it won't make much difference.

Noise is not horsepower.




Donkey doo.

See Grumpyvette's post for correct info.

Pete




 
japete92 
"7th Year" Silver Supporting Member
Posts: 1777
japete92
Loc: No. Virginia
Reg: 01-18-13
09-13-21 06:02 AM - Post#2826998    
    In response to 1carguy

  • 1carguy Said:
Ok, sorry I didn't offer more info. It's got headman headers, mufflers are Borla. Tranny is a 700R4, Diff is a 3.73 posi. With this exhaust it roars like a lion, but is a fairly tame performer. For me it's a cruiser but I like to tromp on it occasionally.



Original question:

'Should I just bite the bullet and redo the entire system with smaller exhaust?'

My opinion:

ONLY to resolve ground clearance problem. If I could simply reduce tail pipe diameter and/or re-route the tail pipes (to behind the rear wheels?) to resolve clearance issues, I'd likely do that.

My 63 Impala would not get in/out of my sloped driveway with your 'type' exhaust system. I would HAVE to change it.

Pete



 
paulo57509 
Senior Member
Posts: 531

Loc: CA
Reg: 07-18-00
09-13-21 04:41 PM - Post#2827039    
    In response to japete92

Video - Stop saying car exhausts need back pressure

Probably not a big deal in this case but it explains the downside of too large a diameter exhaust pipe.

1987 IROC-Z 5.0L
1992 Lumina Euro 3.1L
2003 GMC Safari


 
1983G20Van 
Super Senior Member
Posts: 3894

Loc: Bedford, Texas, USA
Reg: 11-13-02
09-13-21 07:42 PM - Post#2827052    
    In response to beagrizzly

  • beagrizzly Said:
If I can add a couple of pennies here?

If you're not racing, the exhaust you use makes NO difference in just driving a car.

You will never notice any difference in the stop light grand prix. At the strip you probably could not make .2 difference in E.T. by doing anything with the exhaust on a small block.

Again, my two pennies.

Griff



I went from stock manifolds to shorties on a stock 5.7L, noticeable difference in power everywhere. Then I went from shorties to tri-ys and it was even more of a shot in the arm than manifolds to shorties was. The MAF registered close to 45 gms/sec more airflow with the tri-ys than the stock manifolds and around 25 more than the shorties. Torque and hp gain from both changes was instantly noticeable.

1983 G20 Van, 350 TPI, Ported 906 Vortecs, Edelbrock 3817 Base, ASM oversize runners. Reed Custom Roller cam, 700r4, 12 bolt with 3.08 gears, Doug Thorley Tri-Y headers, true duals


Edited by 1983G20Van on 09-13-21 08:03 PM. Reason for edit: No reason given.

 
1983G20Van 
Super Senior Member
Posts: 3894

Loc: Bedford, Texas, USA
Reg: 11-13-02
09-13-21 07:54 PM - Post#2827053    
    In response to 1983G20Van

Shorty headers on this run, shifting at 5,200.

https://youtu.be/m1LuNdCcG_c

Tri-Y headers shifting at ~4,800.


https://youtu.be/-6DZhPN7VHQ

Way more get up and go with the added torque of the tri-ys. Was also very noticeable towing, the extra torque kept it in 3rd gear on many grades that had previously forced a 3-2 downshift. Same van, same gears, same trailer, same weight.

I personally ditch the stock manifolds because they are performance robbing, crack prone garbage! They hold heat in the heads as well.

Swapping from shorties to tri-ys knocked nearly a second off the 0-40 and more than that off the 0-80.

1983 G20 Van, 350 TPI, Ported 906 Vortecs, Edelbrock 3817 Base, ASM oversize runners. Reed Custom Roller cam, 700r4, 12 bolt with 3.08 gears, Doug Thorley Tri-Y headers, true duals


Edited by 1983G20Van on 09-13-21 08:04 PM. Reason for edit: No reason given.

 
Mel Foye 
*VIP* Original Founding Member Group
Posts: 5275
Mel Foye
Reg: 09-29-00
09-14-21 09:16 PM - Post#2827105    
    In response to grumpyvette

Read your links and saw the best looking "dump tube" I have ever seen. I was running a 62 Vette at Lions and even though it was my DD I still ran 2-3 times a month with 4-8 passes each time.
My mph were pretty close time after time. Was a 327/250, bone stock and really quiet even on the top end. Had dual dump tubes installed just as the head pipes started to turn under. First pass like always. Un corked her and from then on a little lower ET but 4 mph faster.














































 
Mel Foye 
*VIP* Original Founding Member Group
Posts: 5275
Mel Foye
Reg: 09-29-00
09-14-21 09:48 PM - Post#2827106    
    In response to 1983G20Van

62 Vette with a 400sbc and 69 Suburban with a 400sbc. 62 went from 4 with side pipes to tri ys under body. 69 went from stock to tri ys. Both ran much better. Both when ran hard made me a happy boy.



 
Mel Foye 
*VIP* Original Founding Member Group
Posts: 5275
Mel Foye
Reg: 09-29-00
09-14-21 10:04 PM - Post#2827107    
    In response to Mercedes

I understand at least part of what you say. I look at 3 things why people go with headers: better performance--- looks--- brag. To me all three are valid reasons. As far as wasted money it is their
$$$ and I don't have to eat soup for two months to cover their purchase.
Take care. Mel



 
1983G20Van 
Super Senior Member
Posts: 3894

Loc: Bedford, Texas, USA
Reg: 11-13-02
09-20-21 08:44 PM - Post#2827576    
    In response to Mel Foye

  • Mel Foye Said:
I understand at least part of what you say. I look at 3 things why people go with headers: better performance--- looks--- brag. To me all three are valid reasons. As far as wasted money it is their
$$$ and I don't have to eat soup for two months to cover their purchase.
Take care. Mel



Manifolds were both cracked on my 83 G20 van when I got it. The manifolds on my 97 Express both cracked before 70K. I did not feel like getting CO poisoned. Junk manifolds got thrown in the scrap bin. Both vans had better performance and got better mileage with headers. Went with US built Thorley headers rather than chinese made Dorman junk manifolds. So what if I ate ramen and sandwhiches for a week or two rather than eating out.

1983 G20 Van, 350 TPI, Ported 906 Vortecs, Edelbrock 3817 Base, ASM oversize runners. Reed Custom Roller cam, 700r4, 12 bolt with 3.08 gears, Doug Thorley Tri-Y headers, true duals


Edited by 1983G20Van on 09-20-21 08:45 PM. Reason for edit: No reason given.

 
Murphdog 
Newbie
Posts: 13

Age: 63
Loc: Mid Missouri
Reg: 05-15-21
09-22-21 07:58 AM - Post#2827683    
    In response to 1983G20Van

Food for thought. I work mainly in the antique tractor pull world which is different than automotive, but some principal should still apply. In my world the exhaust port of a "good" head, will flow 85% of the intake port. On the bad heads that number will be 95% or more. On an automotive head that is not the case. Typically a stock 1960's/70's automotive head will be 60 something %. Back pressure are ugly words to me. The exhaust system needs to work with the cam and flow characteristics of the head to correctly scavenge the cylinder. Under scavenge, performance loss. Over scavenge and you suck intake charge thru the engine during valve overlap and waste it. I have had more than 1 person remove their straight pipe and install a muffler and make more power.
Just something to think about.

FE Fords, Big Block Chevy's & 409's forever!


Edited by Murphdog on 09-22-21 01:33 PM. Reason for edit: No reason given.

 
1carguy 
Poster
Posts: 59

Reg: 11-30-08
10-03-21 02:55 PM - Post#2828443    
    In response to Murphdog

Thanks for all the input. It goes to the muffler shop in a couple weeks and I think he's going to tell me that there isn't enough room to raise the system up very much with the 3" exhaust. I think he'll want to re-do most of it with 2.5" or less. From what I'm reading it probably won't make much difference in performance.



 
TAT_2 
Site Ambassador - Member #26 - "20th Year" Silver Supporting Member
Posts: 37394
TAT_2
Age: 68
Loc: "UNDER THE BOARDWALK"
Reg: 10-29-00
10-05-21 04:21 PM - Post#2828578    
    In response to 1carguy

TOOL ME A WHILE TO PIECE IT TOGETHER BUT WENT WITH 2 1/4 HOOKER COMPLETE DUAL BOLT ON MY SMOG L82 VETTE.
NO MUFFLERS BUT USED TWIN RESONATORS OUT THE BACK.


Attachment: hoohers_on_78.jpg (37.82 KB) 3 View(s)




09 PONTIAC- VIBE
08 PONTIAC- G6
93 VETTE - 40TH ANNIV- RUBY RED- LT1/6-SPD/RAG TOP

PREVIOUS VETTE'S 58,68,70,76,78,85,90


QUOTE FROM HELEN
"WHY YOU LOOKING AT THAT? YA KNOW YA WANT ANOTHER VETTE"












 
Mel Foye 
*VIP* Original Founding Member Group
Posts: 5275
Mel Foye
Reg: 09-29-00
10-06-21 10:59 AM - Post#2828632    
    In response to TAT_2

Friend with an 89 Vette removed the mufflers but left the rest. I was surprised how much better it sounded, a little louder at idle and real nice sound when on it. 65-75mph not too loud.



 
TAT_2 
Site Ambassador - Member #26 - "20th Year" Silver Supporting Member
Posts: 37394
TAT_2
Age: 68
Loc: "UNDER THE BOARDWALK"
Reg: 10-29-00
10-06-21 02:17 PM - Post#2828639    
    In response to Mel Foye

DID THE SAME ON MY 85,JUST BOUGHT THE CAT BACK PIPE,DELETED THE MUFFLERS & USED TWIN TIP RESONATORS ON IT ALSO.
DID THE THRUSH SIDE PIPES ON THE 70


Attachment: 70_VETTE.jpg (10.2 KB) 4 View(s)




09 PONTIAC- VIBE
08 PONTIAC- G6
93 VETTE - 40TH ANNIV- RUBY RED- LT1/6-SPD/RAG TOP

PREVIOUS VETTE'S 58,68,70,76,78,85,90


QUOTE FROM HELEN
"WHY YOU LOOKING AT THAT? YA KNOW YA WANT ANOTHER VETTE"












 
enigma57 
Senior Member
Posts: 9836

Age: 73
Loc: Texas
Reg: 10-28-00
10-11-21 07:30 PM - Post#2829001    
    In response to 1carguy

For full length muffled exhaust systems, I have found this guide to be a good rule of thumb.



2-1/2" dual pipes will support your engine just fine. Just replace the existing 3" from collectors to mufflers with 2-1/2" pipe and retain your present Borla mufflers and 2-1/2" tailpipes. If you need additional ground clearance, consider adding a short length of 'squash pipe' (oval pipe) in the problem area(s).

And if you don't have one at present, consider adding a full sized (2-1/2") H-type crossover (balance) pipe connecting both banks. Its worth the effort. And if ground clearance is an issue, you can use oval pipe or even square or rectangular tubing having same cross sectional area as your 2-1/2" head pipes.

Should be fine,

Harry

"Dark and difficult times lie ahead, Harry. Soon we must all face the choice between what is right...... And what is easy."
Albus Dumbledore


 


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