Long tubes and economy?

[custm2500]

Everyone says that long tubes make noticeable power and better fuel economy then the stock manifolds. My question is does anyone have hard numbers before and after headers for gas millage? I have the pace setters for my project truck but unless I hit the lottery it won't be getting finished this year again. One more tax return and she will finial be done. I have the headers sitting here and think I am going to throw then on the Tahoe. I would probably keep most of the stock system and probably add a muffler along with the headers. I want it to stay fairly quiet because I am always hauling the family.

The other question how much have you guys had invested in adapting the long tubes to the stock exhaust at some point? The truck is a 2006 Tahoe for those who don't know.

[stunna p]

Amazing!.. nobody answered your question? Id like to know this too!

[Outlawz2004]

I dont think you would really gain much as far as fuel economy, but you shouldnt lose any either. The power is worth it though.You may gain 1mpg, but most people arent adding headers for gas mileage.

[Doober]

LS manifolds are far better than Gen 1 SBC manifolds, I don't think there is much to be gained on a stock engine. The heat retained by the manifolds also helps keep exhaust velocity up.

[stunna p]

i am hoping with lonetubes i can improve mpg somewhat....

[jamesphilo30]

they will help more on freeway driving then in the city. most people don't see much because they start sticking there foot in the gas more. so if you drive the same and not like a high school kid with his first car then it will help.

[phoebeisis]

ZERO chance that the aftermarket can beat OEM engineers for part throttle FE.
OEM engineers fight for every .01 mpg-and they have the extremely expensive gadgets to actually measure these improvement.
The aftermarket MIGHT beat the OEMs in respect to PEAK HP- by compromising FE or noise or HP/TORQUE under curve/or throttle response
But they will never beat them in respect part throttle FE- not a modern engine- probably not since 1996 or so and maybe not since they switched to EFI-mid 1980's.
In the old days-carbs with lots of vacuum lines heavy crude cast iron intakes(exhaust and intake)-aftermarket could beat OEM
No way they can now-OEMs got semi serious about FE in about 1979 during the second fuel crunch-and once EFI was developed with the Throttle bodies and attendant computer controls (mid 1980's and later)- the OEMs had too much of an advantage.

GM makes these engines very efficient-
Modifications that might improve FE
1) Pulse and glide-driver modification-worth 15% in city
2)Weight loss especially wheel tire weight- tiny but real city improvement
3)Lower rolling resistance tires-can be quite a bit if you have all terrain type tires vs all season tires(but if you need all terrain you need all terrain)
Don't buy headers for part throttle FE
Charlie

[Doober]

I'll agree to a point... while they're working to get better efficiency. They also have to deal with bean counters and packaging requirements/serviceability. You can bet the OE could come up with a header designed for max efficiency in a specific rpm range, but that would possibly negate a sound level requirement, and would almost definitely be outside the packaging/cost envelope. I'm not saying modern manifolds aren't way ahead of '80s-'90s technology, but there is always a little more to be coaxed out somewhere... you just have to remember your goal and not the idea that "bigger is always better". I believe a smallish tube header tuned for the proper firing sequences of an LS would make excellent low end torque compared to manifolds (scavenging + exhaust velocity), with little to no top end loss.

[phoebeisis]

Doober
Right-there is a little volumetric efficiency (hp torque) intentionally left on the table by the OEM engineers-either because of cost/packaging/noise-
but at part throttle-which is where we actually run these engines-low loads- there just isn't much efficiency lost to having to "push" the small burnt charge out of the CC
Yeah it is hard to beat the OEM guys in the one area they really really focus on-FE
These SBC 2 valve pushrods used to seem kinda crude old fashioned to me-the 4 valve heads OHC seemed much high tech more modern- but GM has been perfecting them improving efficiency for 50 years-
they are a compact package- not as wide as the OHC- inexpensive to build-and at lower RPMs probably have less internal friction than the more expensive 4 valve OHC motors.
Simple-refined-inexpensive-efficient-compact package-easy to work on- no valve adj-
Really hard to beat- owner proof/driver proof to some extent!

Now I know most folks here aren't into hypermiling- but in its simplest form-15% better FE- it just means gliding instead of gas/brake/gas/brake- GMs 1/2 ton transmissions are MADE for pulse and glide!
You get midsized crossover city FE from a Suburban-in 2008 with gas up many many folks practically gave away/traded 4-5 year old Suburbans to get midsized crossover FE(AND A $30,000 note)!!
Next time gas spikes(depending on my finances)-I'm going to buy a 2004 Suburban for $6000-upgrade my 1998-just because someone will dump his Suburban because of its FE.Makes more sense to just change driving style-keep all the full sized utility!
Charlie

[jamesphilo30]

what is "pulse and drive"?

[phoebeisis]

You pulse(accelerate normally, not slowly, up to the speed limit, take your foot completely off the gas and glide losing about 9 mph)
for example-Sitting at redlight-accelerate normally to 35mph-lift off gas at 35mph- your speed will actually peak at about 37 mph-glide down to 28 mph-all total you'll cover about 1/4 mile per 37>28mph cycle. This is typical of what you might do in a 35 mph zone.
This is strictly for city driving-when you know your routes-know the lights stops etc.
It will get you about 2-3 mpg better in pure city driving- it is maybe 1-1.5 mpg better than the old "accelerate like you have an egg between your foot and the pedal"

GM truck transmissions act like they are DESIGNED for P&G- if you lift completely off the gas at speeds under 40 mph or so-they have ZERO engine braking if they are in D. THye act in D as if they are in N-just glide- no engine braking.
Other manufacturers do it also- but GM did it early- my 1998 Suburban glides anf glides-37>28 mph will cover 1/4 mile in maybe 30 seconds
Just repeat repeat Pulse up to 37 glide down to 28>37>28>37
Charlie

[phoebeisis]

You pulse(accelerate normally, not slowly, up to the speed limit, take your foot completely off the gas and glide losing about 9 mph)
for example-Sitting at redlight-accelerate normally to 35mph-lift off gas at 35mph- your speed will actually peak at about 37 mph-glide down to 28 mph-all total you'll cover about 1/4 mile per 37>28mph cycle. This is typical of what you might do in a 35 mph zone.
This is strictly for city driving-when you know your routes-know the lights stops etc.
It will get you about 2-3 mpg better in pure city driving- it is maybe 1-1.5 mpg better than the old "accelerate like you have an egg between your foot and the pedal"

GM truck transmissions act like they are DESIGNED for P&G- if you lift completely off the gas at speeds under 40 mph or so-they have ZERO engine braking if they are in D. THye act in D as if they are in N-just glide- no engine braking.
Other manufacturers do it also- but GM did it early- my 1998 Suburban glides anf glides-37>28 mph will cover 1/4 mile in maybe 30 seconds
Just repeat repeat Pulse up to 37 glide down to 28>37>28>37
Charlie