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Username Post: Straight pipes burn valves?        (Topic#264084)
LukeMI 
Forum Newbie
Posts: 6

Reg: 06-03-11
06-03-11 04:14 PM - Post#2098974    

Hi all, I am new here, I own a 1989 Chevy Silverado with a 350 small block, stock as far as I know, It was given to me by my grandpa this past october before he passed away. I recently straight piped it with no cat. A friend of mine told me that this could cause the valves to burn up because there is no back preassure. Is this true?

I currently have a 2.5" pipe that comes back to just behind the cab. plan on running it back to a Y pipe to duals then come out 3" apart on either side of the Reese hitch.



 
brainwashed2566 
Forum Newbie
Posts: 83
brainwashed2566
Loc: Idaho
Reg: 02-10-10
06-03-11 07:52 PM - Post#2099064    
    In response to LukeMI

I've heard the same thing. I don't know if it is true or not but I drove around with a straight pipe for about a week before I could get my welder running again, and nothing bad happened. That was about 3 years ago and the engine is still running fine. Might just be a myth, or maybe it's more of a long term thing, either way I didn't like the sound or feel of the truck with nothing on the pipe.
-Charlie

If it ain't broken, fix it till it is


 
62chevy427 
"8th Year" Silver Supporting Member
Posts: 1689
62chevy427
Loc: laurens sc
Reg: 04-13-06
06-03-11 08:06 PM - Post#2099071    
    In response to LukeMI

keep on driving. straight pipes do not burn valves. sometimes they burn pocket books or billfolds when paying a fine for excessive noise.
56 bel air ((since 2002)
62 impala ss (since 1965)
65 el camino (since 1969)
66 nova (since 1987)
67 malibu convertible (since 1981)
72 el camino ss454 (since 1985)
83 gmc 4wd (since 1991)
95 impala (new)
14 camaro (new)


 
someotherguy 
Moderator
Posts: 25142
someotherguy
Age: 43
Loc: Texas
Reg: 08-01-03
06-04-11 05:51 AM - Post#2099172    
    In response to 62chevy427

Another certainty is you'll lose a little low-end torque if you go completely straight piped - no cat or muffler. A cat does a pretty good job of being a muffler all on its own, so if you have one or the other you won't be ridiculously loud, and shouldn't notice a performance decrease. If you remove both...counterproductive, other than making a lot of noise.

Richard
94 C2500LD / 94 C1500 / 06 300C SRT8
Check out my truck shop projects


 
Bill K.b 
Senior Member
Posts: 4158

Loc: upstate NY
Reg: 10-24-05
06-06-11 07:12 PM - Post#2100218    
    In response to someotherguy

My van was fine with nothing but manifolds on the test drive and drive home. The '91 came to me with no cat and duals cobbed on it and it was fine, but plus one on the lack of torque, even with a correct Y, cat and muffler on it's still kind of a dog.

One thing I also noticed with the '89 in my sig is when the muffler fell off and I was on the road and couldn't fix it right away, the milage dropped off a bunch too. Well, like from 15 to 11 or so.
Those who can, do. Those who can't, criticize it on the internet.

1991 G20 van 5.7L - swap meet spl.
1993 3500 dually 5.7L NV4500 - tow truck
1991 Suburban 5.7

Plus cars for swap and sale
&yes, I once tried a frame swap on a 51 Chevy.


 
Randy_W 
None
Posts: 27804

Reg: 01-06-02
06-07-11 04:03 AM - Post#2100347    
    In response to Bill K.b

A quick primer; Straight pipes cut off at or near the manifolds can warp valves due to cold air reversion, not as likely on modern engines, but still possible. If you have at least 3 feet of pipe past the manifold you pretty much eliminate that problem.
The back pressure issue gets beaten to death. Back pressure is always bad, period. It's also unavoidable. The reason you often lose torque with straight pipes or dual exhaust is that your system is improperly designed and sized for optimal performance. Welcome to the world, they all pretty much are. The factory isn't interested in your 1/4 mile times in your Silverado.
In most systems when you take out the muffler and cat, your system is too big to maintain exhaust gas velocity so your cylinders don't scavenge well. On a truck like yours a good y pipe to 3" single running through a 3" Magnaflow with a single 2.5-2.75" tailpipe would be nearly ideal. The reason the tailpipe is smaller is because as the gasses travel through the pipe they cool, thus slowing down, so smaller pipe is need to keep the speed of flow up.
Randy

DON'T mess with Old Men, we didn't get old by being, STUPID!!!

"The veneer of civilization is very thin!" (Arlo)


 
355Cheyenne 
Senior Member
Posts: 3762
355Cheyenne
Loc: Northern MN
Reg: 10-27-04
06-07-11 06:43 AM - Post#2100396    
    In response to Randy_W

  • Randy_W Said:
In most systems when you take out the muffler and cat, your system is too big to maintain exhaust gas velocity so your cylinders don't scavenge well.


Right on. I would also like to add that the only benefit to some amount of back pressure is for the o2 sensor. From my understanding, if you uncork an exhaust with a non heated o2, the exhaust wont be able to heat that o2 sensor up enough at low rpm so you could see additional costs in reduced fuel economy particularly in stop and go and idling environments.

98 Silverado k1500 4x4 350


 
Randy_W 
None
Posts: 27804

Reg: 01-06-02
06-07-11 06:15 PM - Post#2100704    
    In response to 355Cheyenne

  • 355Cheyenne Said:
  • Randy_W Said:
In most systems when you take out the muffler and cat, your system is too big to maintain exhaust gas velocity so your cylinders don't scavenge well.


Right on. I would also like to add that the only benefit to some amount of back pressure is for the o2 sensor. From my understanding, if you uncork an exhaust with a non heated o2, the exhaust wont be able to heat that o2 sensor up enough at low rpm so you could see additional costs in reduced fuel economy particularly in stop and go and idling environments.




Even that would be fixed with proper sizing and shape.
Randy

DON'T mess with Old Men, we didn't get old by being, STUPID!!!

"The veneer of civilization is very thin!" (Arlo)


 
355Cheyenne 
Senior Member
Posts: 3762
355Cheyenne
Loc: Northern MN
Reg: 10-27-04
06-07-11 09:11 PM - Post#2100767    
    In response to Randy_W

or a 3 wire o2 sensor. Always a solution.
98 Silverado k1500 4x4 350


 
Bill K.b 
Senior Member
Posts: 4158

Loc: upstate NY
Reg: 10-24-05
06-08-11 12:41 AM - Post#2100801    
    In response to 355Cheyenne

Unless someone's changed one for whatever reason, TBI trucks with a non-heated O2 have it in the left manifold outlet. That should pretty well keep it warm as long as some kind of Y-pipe is on the truck.
Those who can, do. Those who can't, criticize it on the internet.

1991 G20 van 5.7L - swap meet spl.
1993 3500 dually 5.7L NV4500 - tow truck
1991 Suburban 5.7

Plus cars for swap and sale
&yes, I once tried a frame swap on a 51 Chevy.


 
Randy_W 
None
Posts: 27804

Reg: 01-06-02
06-08-11 04:14 AM - Post#2100823    
    In response to 355Cheyenne

  • 355Cheyenne Said:
or a 3 wire o2 sensor. Always a solution.


In the manifold usually will keep the heat up but anytime I significantly free up exhaust, I like to use a heated sensor. Not always required, but cheap insurance.
Randy

DON'T mess with Old Men, we didn't get old by being, STUPID!!!

"The veneer of civilization is very thin!" (Arlo)


 
someotherguy 
Moderator
Posts: 25142
someotherguy
Age: 43
Loc: Texas
Reg: 08-01-03
06-08-11 04:21 AM - Post#2100826    
    In response to Randy_W

  • Randy_W Said:
  • 355Cheyenne Said:
or a 3 wire o2 sensor. Always a solution.


In the manifold usually will keep the heat up but anytime I significantly free up exhaust, I like to use a heated sensor. Not always required, but cheap insurance.


I'm thirding it.

Richard
94 C2500LD / 94 C1500 / 06 300C SRT8
Check out my truck shop projects


 
JustRedneckit 
Forum Newbie
Posts: 1

Reg: 12-11-13
12-11-13 12:13 PM - Post#2406733    
    In response to Randy_W

Now i drive a 06 silverado and right behind the headers there is a manifold with 2 bolts and if you undo these bolts its pretty much the same as straight piping it, now I was told not to do it cause it ruins the valves cause now I don't have enough back pressure...... is this correct?

 
Allan In NE 
Frequent Contributor
Posts: 1278

Reg: 12-27-11
12-11-13 02:20 PM - Post#2406764    
    In response to LukeMI

The "Back Pressure" tale is pure uncut BS. Who starts these stories anyway?

"Short" straight pipes could possibly 'warp' a stem by letting cold air in on that hot valve.

Allan
Lifelong GM automatic transmission specialist


 
bowtie44s 
Contributor
Posts: 835
bowtie44s
Age: 31
Loc: wv
Reg: 08-29-12
12-11-13 03:11 PM - Post#2406773    
    In response to JustRedneckit

Manifold behind headers? I have no clue what you're talking about. You'll probably run into a lot of problems with straight pipes on an 06. This is really the wrong forum for an 06 though.

Drag cars, pulling trucks, and a lot of other rigs run open headers and don't burn valves. I've never heard that tale before.
Jeff

'88 chevy k3500 aluminum head 454
NV 4500

'84 chevy short bed dana 60 14bolt ff 383 stroker
44" boggers (rear) 44" tsl (front) hydraulic assist
welded front and rear 5.13 gears
th400 np205 twin stick -SOLD-


 
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