454 dually header/exhaust question

[cag]

My dually has headers that form into one tube similar to stock, this is a 3" in outlet, question is what are my options for down stream, a single 3" muffler? or do they make a kit where it splits right after the headers? currently has a single inlet and outlet flowmaster, better muffler options?

[THI]

What year is your truck? Trying to figure out why a single exhaust vs dual exhaust.

From a different point of view, a 3" single exhaust flows about the same as a 2-1/4" dual exhaust if the intersection of the two pipes is not sharp. I have a 1979 C3500 Dually with headers and dual exhaust (it came from the factory with dual exhaust and no converter) and it is currently in need of a new system - plan on using a new set of Hedman Elite Heders along with a 2-1/2" dual system, they are available from Flowmaster and Pypes.

[cag]

Originally Posted by THI

What year is your truck? Trying to figure out why a single exhaust vs dual exhaust.

From a different point of view, a 3" single exhaust flows about the same as a 2-1/4" dual exhaust if the intersection of the two pipes is not sharp. I have a 1979 C3500 Dually with headers and dual exhaust (it came from the factory with dual exhaust and no converter) and it is currently in need of a new system - plan on using a new set of Hedman Elite Heders along with a 2-1/2" dual system, they are available from Flowmaster and Pypes.

its a 91 with throttle body injection and an o2 sensor in the pipe, I picked it up this way, the headers are stainless and not looking to replace, thinking changing the down stream setup

[kwmech]

A 91 with throttle body injection will see no noticeable gains by using headers. Going back to the stock manifolds, a free flowing cat convertor an using a heated O2 sensor with the single 3'' pipe will be your best bet unless there were significant changes to the internals of the engine and a new programmed chip

[cag]

Originally Posted by kwmech

a 91 with throttle body injection will see no noticeable gains by using headers. Going back to the stock manifolds, a free flowing cat convertor an using a heated o2 sensor with the single 3'' pipe will be your best bet unless there were significant changes to the internals of the engine and a new programmed chip

i got with the headers on, not changing them, heated o2? There is no cat...

[THI]

If the O2 sensor is anywhere downstream you need a heated O2 sensor to operate properly (with or without a cat). If emission testing is not an issue (you mentioned no cat) I would go with one of the dual exhaust kits and get a collector that has the bung for the O2 sensor and wire in a heated O2 sensor.

The factory 454 TBI exhaust had two choke points, the factory "Y" pipe overlapped inside where the two pipes met, and the stock muffler choked down to 1-7/8" just inside of the 3" inlet. Because of excessive heat the converter was placed after the muffler. The exhaust manifolds themselves were not bad considering they had a 2-1/4" outlet. I mention this because if your system is using the original "Y" pipe cut to fit, you have the issue of the overlap at the connection of the two pipes.

[cag]

Originally Posted by THI

If the O2 sensor is anywhere downstream you need a heated O2 sensor to operate properly (with or without a cat). If emission testing is not an issue (you mentioned no cat) I would go with one of the dual exhaust kits and get a collector that has the bung for the O2 sensor and wire in a heated O2 sensor.

The factory 454 TBI exhaust had two choke points, the factory "Y" pipe overlapped inside where the two pipes met, and the stock muffler choked down to 1-7/8" just inside of the 3" inlet. Because of excessive heat the converter was placed after the muffler. The exhaust manifolds themselves were not bad considering they had a 2-1/4" outlet. I mention this because if your system is using the original "Y" pipe cut to fit, you have the issue of the overlap at the connection of the two pipes.

no testing here, wisconsin, and the o2 is in the header, this is like a tri y set up that the ps comes over and meets with the ds then has a 3" outlet, I guess a y pipe of sorts, thanks for the info all yall!

[SCOTI]

Originally Posted by THI

If the O2 sensor is anywhere downstream you need a heated O2 sensor to operate properly (with or without a cat). If emission testing is not an issue (you mentioned no cat) I would go with one of the dual exhaust kits and get a collector that has the bung for the O2 sensor and wire in a heated O2 sensor.

The factory 454 TBI exhaust had two choke points, the factory "Y" pipe overlapped inside where the two pipes met, and the stock muffler choked down to 1-7/8" just inside of the 3" inlet. Because of excessive heat the converter was placed after the muffler. The exhaust manifolds themselves were not bad considering they had a 2-1/4" outlet. I mention this because if your system is using the original "Y" pipe cut to fit, you have the issue of the overlap at the connection of the two pipes.

This is how mine is done. 1.75 x 3" full length headers into dual 3" head-pipes; though an 'H" pipe; into 3" In/Out mufflers; then reduced down to 2.5" dual tailpipes that discharge @ the rear bed corners.

[cag]

Originally Posted by SCOTI

This is how mine is done. 1.75 x 3" full length headers into dual 3" head-pipes; though an 'H" pipe; into 3" In/Out mufflers; then reduced down to 2.5" dual tailpipes that discharge @ the rear bed corners.

nice, carbed big block?

[SCOTI]

Originally Posted by cag

nice, carbed big block?

TBI. Edelbrock TBI intake w/coolant loop deleted & TBI chip for the ECU. Does ok but the idle hunts (surging @ idle). I don't drive it enough to worry about it but it does fine @ speed.

I've debated swapping to a carb or spending more & switching to a Holley EFI set-up that's NOT TBI based. Most likely it will get a carb because big-blocks in CC duallys aren't exactly efficient so it seems ROI would be nonexistent.

[cag]

Originally Posted by SCOTI

TBI. Edelbrock TBI intake w/coolant loop deleted & TBI chip for the ECU. Does ok but the idle hunts (surging @ idle). I don't drive it enough to worry about it but it does fine @ speed.

I've debated swapping to a carb or spending more & switching to a Holley EFI set-up that's NOT TBI based. Most likely it will get a carb because big-blocks in CC duallys aren't exactly efficient so it seems ROI would be nonexistent.

where did you put to o2? how do you like that intake? did it make a diff?

[SCOTI]

Originally Posted by cag

where did you put to o2? how do you like that intake? did it make a diff?

o2 sensor is near the end of the collector. You have to make sure there's X-amount inches of exhaust tubing post sensor (I don't recall what it was @ the moment).

My truck had the factory GM cast iron QJ carb intake w/the aluminum TBI 'adapter' so it's a better intake (looks & weight). Hard to say performance wise as the cast iron/adapted TBI set-up had 100k on the clock (dished pistons/wear & tear/stock cam etc....) vs. a fresh flat-top piston long block + BBC Melling 'RV/Towing' cam (same OE heads just rebuilt w/the block).

Truck can light up the duals post build vs when I bought it. Definitely feels more responsive but it's hard to say what the largest contributor to that is/was.