performance exaust, mpg increase?

[dkjones96]

Originally Posted by theholycow

Why would they program their automatic to shift after the redline? Somebody must have been asleep at the engineering table.

Not sure why they did that. In the Tracker and the Cressida I used to hold them out past the redline anyways but that was because there was still power to be had. I haven't purchased the programmer that lets me move those shift points yet but it is on the list. I'm thinking 4400 but that 360 does sound sweet close to 5k.

I should also note that at 5800ft it is out of breath by 4200, at sea level it pulled hard all the way to the shift.

[bobc455]

Originally Posted by R.I.D.E.

The lack of the 30 pound cast iron heat sink that was the stock in line 6 cylinder manifold 1970-1983 240-260-280 engines would also dramatically reduce engine compartment heat levels which was especially significant in an engine where the exhaust manifold was directly under the intake manifold.

Gary-

I would think that the in most situations would be the opposite, although I've never done any real measurements / calculations:

1) Headers generally have much more under-hood surface area
2) Headers are generally much thinner (giving higher heat transfer to the engine compartment)
3) heat transfer coefficient of cast iron vs. steel (or stainless steel if you used that for headers) ??

... unless, of course, you wrapped the headers with insulation materials or otherwise shrouded the tubes.

Of course on #1, on the straight 6 manifolds I would think that the exhaust manifold casting must've had a very high surface area because of the engine layout. So I'm probably wrong on that account.

I would also think that casting would be *much* cheaper than making headers, once the forms were manufactured (which could be amortized over the tens of thousands of manifolds produced from the mold). On a low-quantity production run it would be closer, but in high volumes I've seen castings win every time.

[theholycow]

Originally Posted by spotaneagle

ya ya, but less resistance might prove you right even more so cow, like removing some bends?, alot of these people are removing their cats and seeing a 10mpg increase, thats why im saying a hi flow cat might do the trick, especially since i quoted one guy with a car like mine, i would think it might be different for each car

10mpg is a lot for me to believe for anyone, but it's easier to believe in gains when we're talking about people who spend a lot of time at 6000RPM. My thoughts about utilization of the exhaust system apply to hypermiler-style driving only, where the driver rarely requests 1/4 of the available power.

I have to agree with gary, if they got 10mpg, the converter was probably broken.

Originally Posted by R.I.D.E.

I still believe that, considering the benefits of proper exhaust design that would be directly related to better mileage, that any manufacturer would be short sighted to allow the exhaust design to reduce mileage, as long as mileage was their objective. With the cost and penalties of failure to reach CAFE required fleet mileage averages, and especially considering the ease with which the redesign could be accomplished there is no incentive to poorly design any exhaust system, other than cost, which would be practically nothing.

That is the same conclusion I've come to by following my own logic, knowing what I know about car manufacturers. They are in it for the money, and the government influences them by making it expensive to not be efficient. Exhaust is an extremely mature technology and very cheap to do however they want to do it, so it's not like they can't figure out how to produce results that some guy can do in his garage, nor is it like they can't do it cost-effectively.

[theholycow]

LOL, I just realized I'm repeating myself, that I've already said a lot of that in this thread.

There have been some decent arguments for certain types of exhaust construction (not merely shoving any old magnaflow catback on) helping FE for hypermilers, but I remain unconvinced...and either way I'm sure it will never pay for itself with whatever improvement it does manage.

[dkjones96]

It's always been my experience that headers make the engine bay hotter...

Castings do play a big role but where casting technology has gone makes a big difference too. They make stock manifolds now that look like iron headers. Mine looks nothing like that because they were probably still using the same castings they did back in the 50s when the A engine came out!

The new 4.7 being made around the time my 5.9 was got a really nice exhaust manifold that sees little to no increases from a header.

I also agree that if removing the cat gave 10mpg something was up with that cat. The catalytic converter is designed to not be a major restriction, you can see right through the cat if it's in good condition and the exhaust on the other side of the cat is extremely organized.

Not to mention the fact that the cat helps re-heat the exhaust gasses so EGV increases a little.

[R.I.D.E.]

I measured the temp of my headers in my old 240Z powered 49 Plymouth on a Nissan truck frame.

At idle the headers were 165 degrees. That's not a misprint. At higher speeds (no load) they quickly rose to 350+ degrees but they rapidly cooled back to 165 when you let the engine idle. That would never happen with a 30 pound cast iron manifold.

The old Z cars were especially susceptible to heat soak when they were shut off for a few minutes then restarted. I have measured temps at the windshield base of 160 degrees in the summer with the hood open.

Now you can say that was due to solar heat, but it's not a factor in the shade. You learn the hard way how long you need to wait to work on a customers care when they are waiting and have limited time.

Believe me when I speak from experience, when you lean over that fender on the drivers side of a cast iron manifolded Z car you experience heat that makes headers seem like a cool breeze.

Now that is one specific example, but you can bet it takes a long time for the heat to radiate out of 30 pounds of cast iron, even with the engine off.

Heat radiation is a function of surface area for sure, but the duration of that heat radiation is a function of the weight of the manifold as well as the surface area. In fact less surface area means the heat will be radiated longer.

I am not sure which is more expensive to produce, my assumption was based on sand casting of exhaust manifolds which is very heat intensive. I could certainly be wrong there.

We once pulled a transmission on a 300, and took the flywheel 8 miles to the machine shop. It was still too hot to put on the flywheel surfacing machine. Maybe not really relevant but you get the idea about heat retention in heavy iron and steel parts.

Most manufacturers now use stainless steel in exhaust systems, so cost may be a factor but that contradicts the use of stainless. Longevity of stock exhaust systems has increased dramatically with stainless components.

Don't think I have ever seen a BSFC comparison as the basis of the need for any aftermarket exhaust system, just something else to consider. It would add considerable credibility to the sales pitch.

On the other hand, if I had to replace my exhaust system, because it was worn out. I might consider aftermarket, if I could find evidence of a efficiency improvement. Most if not all of the systems claim more power. I haven't seen any that claim better economy, much less any vehicle owner claim better economy, unless there was a restriction due to collapsed baffles or other problems with the stock system.

That's from someone who made money installing exhaust systems, so my financial incentive would have been to sell, sell, sell. I always found honesty to be the best sales pitch.

This post represents my perspective based on 60k hours and 30 years experience working on cars for 30 years. It is not meant to be confrontational and or critical of any other perspective of any other board member, just my best recollection from my own personal observation.

regards
gary

[theholycow]

Originally Posted by R.I.D.E.

Most manufacturers now use stainless steel in exhaust systems, so cost may be a factor but that contradicts the use of stainless. Longevity of stock exhaust systems has increased dramatically with stainless components.

It seems to me that cars used to almost all need exhaust repairs during their normal service life; everyone had to go the muffler shop occasionally. With the proliferance of stainless steel (and better quality materials even when not stainless), it's now quite rare to repair exhaust. Most modern cars seem to go to the junkyard with their original stainless steel exhaust.

On the other hand, if I had to replace my exhaust system, because it was worn out. I might consider aftermarket

It's a whole other ballgame when you need to replace it anyway. The cost difference between the exhaust your car already has and a new system is huge. The difference between a new OEM system and a new aftermarket system, not quite so huge...

I haven't seen any that claim better economy, much less any vehicle owner claim better economy, unless there was a restriction due to collapsed baffles or other problems with the stock system.

I found that to be an interesting statement, so I checked the first exhaust brand name I could think of. Magnaflow makes no such claim, which is very interesting since they have every reason to toot their own horn. If it could even be slightly true you can be sure they'd include it in their marketing, right on their website. Any advantage is worth touting, but they did not.

Then I checked Corsa and they suggest it but stop short of entirely promising it:
http://www.corsaperf.com/corsaProductRollOver.aspx

Potential For Better Fuel Economy

Less back pressure and more power means your engine functions more efficiently and that translates into better fuel economy (if you can keep your foot out of it).

They title it "Potential" but state "translates into better fuel economy".

[Jay2TheRescue]

Over the years I think I've put 2 or 3 exhaust systems in the Hooptie. The most recent one has been in there at least 10 years. The pipe has some flaky rust on it, but its not leaking yet. I can remember we had my old 1980 Bonneville wagon over 180,000 miles on the stock exhaust, but that took taking it apart and working on the exhaust every year at inspection time. I really wish dad had just replaced it when he started having problems with it. What he had me do was if the pipe was rusted through in a section he'd have me take it apart and slide a 6 inch long section of flexible exhaust pipe over the hole, and clamp it down. That was hard work. I guess since he was just supervising, and not doing the work himself he decided to go the cheap route.

[theholycow]

It never occured to me to hack my exhaust like that. Considering my budget, I might just try that on Christine...

[BumblingB]

I did a freer flowing exhaust on one of my 2 smarts. Along with the exhaust I put on a freer flowing air filter (that I keep oiled regularly for all the haters). Those two mods consistently get me 2-3 mpg more than the stock car.