exhaust under gas tank

[my56chevytruck]

OK, I'm close to driving my truck and need to have my exhaust put in. we have a great exhaust shop close by, but I'm wondering about running 2 1/2" pipes right under my gas tank. I can run the pipes within the frame up to the tank but to avoid the gas tank I'd have to go outside my frame rails to go out the back end. My 31 gallon tank is out of a suburban and is mounted in the rear end of the frame and is hanging partway below the frame. I've read a lot about the pros and cons of doing this, but wanted the forum's opinion.

[dsraven]

you could run a heat shield if there is no other way.

[dsraven]

throw a couple of pics up so we can see the scenario

[mr48chev]

I'd agree with the heat shield.

[bobdavis2010]

Post some pictures

[roger55]

If you give about an inch of clearance, do it and don't worry about it.

[DransportGarage]

Originally Posted by roger55

If you give about an inch of clearance, do it and don't worry about it.

I agree.

[HUSSEY]

I wouldn't worry to much though a heat wouldn't hurt or wrapping it with header wrap in that area.

[my56chevytruck]

I've asked about putting exhaust under the gas tank. I talked to 2 exhaust companies in my area and BOTH highly recommended not to, and one said he wouldn't even do it. so, I may end up going between the frame to the tank then go outside for the last 3-4ft. Here's the pictures of my tank within the frame.

[MiraclePieCo]

Turn-downs ahead of the rear axle?

[Coupeguy2001]

looks like you are between a rock and a hard place.
There is no real good place to run your exhaust.
what about just run them in the frame rail at the back.
That tank is BIG.

I see you have spacers over the springs, and you took out leaves. you relocated the spring perches. you can't afford to run the pipes under the tank.
I would worry about the shackle pin rubbing the tank and the strength at the shackle end with the crossmember removed. if the frame bows, the tank eats it.
Doesn't look that strong.
good luck with the exhaust

[roger55]

For those that say don't run them under the tank, I'd like to hear why.
With an inch of clearance, I couldn't even see the gas in the tank warming up 1 degree from that.

[Coupeguy2001]

If the truck is too low, hitting a bump just right will smash the pipes into the tank, and possibly crack the tank. Besides, it is gas on exhaust.
In the event of an accident like I had, it would have been catastrophic.
That guy's front end was shoved under the back of my truck almost to the axle.

[roger55]

Originally Posted by Coupeguy2001

If the truck is too low, hitting a bump just right will smash the pipes into the tank, and possibly crack the tank. Besides, it is gas on exhaust.
In the event of an accident like I had, it would have been catastrophic.
That guy's front end was shoved under the back of my truck almost to the axle.

Bumps won't cause a relationship change between the exhaust and the tank.

The pipes impacting the ground might but a steel tank would just dent.
It's one reason I don't care for aluminum tanks and don't own any.

Gas on exhaust doesn't cause ignition. Sparks do that.

[my56chevytruck]

I opted to run the exhaust along the inside of the frame rails and over the rear axle, then it went outside the frame to the back end. I was going to put down draft pipes but a good friend has those and he's constantly kicking up the dust, so that's out. It's very sound and strong, so I'm not concerned about the strength or bottoming out. thanks for all the input and suggestions.

[my56chevytruck]

Originally Posted by Coupeguy2001

If the truck is too low, hitting a bump just right will smash the pipes into the tank, and possibly crack the tank. Besides, it is gas on exhaust.
In the event of an accident like I had, it would have been catastrophic.
That guy's front end was shoved under the back of my truck almost to the axle.

coupeguy, I totaly agree with you and I certainly don't want to take the chance of allowing a catastrophic situation to happen. thanks

[DransportGarage]

If you need to protect against fire in the event of a rear-end collision, better get a rubber fuel cell with a kevlar blanket. If any of our trucks get a car under them to the rear axle, it'll be time to break out the marshmallows anyway. Just sayin'...

[Coupeguy2001]

Roger, what I awas alluding to was:
If you go over a big bump or dip, and the pipes were shoved up into the tank, the hot pipes might scrape, cause sparks, rupture the tank, then it's all over.
I am sure others got it, but I guess my post might have been a little vague.

I have seen steel tanks leak from age and vibration, and his tank is certainly not new.

[MiraclePieCo]

A few ways to avoid running exhaust back by your gas tank:

[my56chevytruck]

All those options of running the exhaust out the side are great. I've had mine run out back and am enjoying the hell out of it. thanks for the opinions and tips.

[DransportGarage]

IIRC, the law in Ohio says the exhaust has to exit behind the rear axle. I just made these out of a Pypes kit and mounted the brackets to the stock frame:



Sorry for not posting this earlier but it's been a little crazy around here.

[Speedbumpauto]

I ran mine inside the frame to the diff and outside the frame beside the tank. I have coil overs, but that probably makes the bend over the diff harder for me than you. It appears you're doing a pro street sort of look so the exit outside the frame on a lowered vehicle looks good, I think. The hardest bend was the tail pipe over the diff. Used a 180 degree bend and two 90's, Tacked it together the first time, it looked good and fit but absolutely could not get the tail pipe out of the vehicle in one piece. Solved the problem by splitting the 180 at the top of the bend and installing two header flanges so it bolts together with a gasket. You can see, sort of, how it works in the pics. You can ignore the other pipes as they are for the electronic cut outs. Mine is within an inch or so to the poly tank in a couple of places but it doesn't appear to be a problem. Had the whole thing coated for what ever help that might be. sorry I don't have a complete installed pic but you can see how it works. You should be able to make yours work.

[joedoh]

if you poke your head under just about any production car build in the last 20 years you will see the exhaust running right under a plastic fuel tank (with a heat shield) mounted under the rear seat area.

[my56chevytruck]

Originally Posted by Speedbumpauto

I ran mine inside the frame to the diff and outside the frame beside the tank. I have coil overs, but that probably makes the bend over the diff harder for me than you. It appears you're doing a pro street sort of look so the exit outside the frame on a lowered vehicle looks good, I think. The hardest bend was the tail pipe over the diff. Used a 180 degree bend and two 90's, Tacked it together the first time, it looked good and fit but absolutely could not get the tail pipe out of the vehicle in one piece. Solved the problem by splitting the 180 at the top of the bend and installing two header flanges so it bolts together with a gasket. You can see, sort of, how it works in the pics. You can ignore the other pipes as they are for the electronic cut outs. Mine is within an inch or so to the poly tank in a couple of places but it doesn't appear to be a problem. Had the whole thing coated for what ever help that might be. sorry I don't have a complete installed pic but you can see how it works. You should be able to make yours work.

Nice exhaust work as well as the complete underside. I really like your exhaust tips. thanks.

[Speedbumpauto]

Thanks. They are Chevelle SS re-pops from Pypes.