Stock VS Aftermarket exhaust manifolds.. Waste of money?

[Mekkahfire]

In the MR2 community, a heated debate is going on right now about aftermarket exhaust manifolds (equal length, tubular, etc) are a waste of money.

The argument is the length of an aftermarket manifold acts as a small radiator, cooling off the exhaust gasses (whereas hotter gasses move faster, translating into more power, etc).

The counter-argument is that tubular, equal length manifolds pump exhaust gasses in a more equal, evened out pattern resulting in noticable advances in spool time.



What do you guys think?

[KiwiBacon]

Why not lag an aftermarket manifold?

Then you'll get the pulse advantage of equal length pipes without the greater heat loss.

[Mekkahfire]

...Lag an aftermarket manifold?

[Schister66]

they must be making a shitload of power on those cars if they're worried about losing a little heat in an EQ manifold....also, hasn't anyone heard of heatwrap or is that just in my area of the country?

flow of an EQ tubular is worth the minimal loss of heat....due to the design of the log manifold, the exhaust gas inside is turbulent and is therefore less efficient

EQ ramhorn or topmount FTW

[Mekkahfire]

Heres some pretty gruesome facts about heat wrap...


THE FACTS:

*Header wraps are designed to keep the heat in the header to improve scavenging of the cylinders. Keeping the heat in the header allows the exhaust speed to remain high. (the right idea)

*There are no header manufacturers that I know of that will warranty their headers if any header wraps are installed on their products.
In most cases the header wrap damages the headers beyond repair. (I will explain below)

*If you run a lean mixture, you "may" see a slim performance gain using header wraps. A rich mixture may show slim to absolutely NO gain in performance.

*If you do not mind replacing your headers and header gaskets regularly, and you like that ugly look of a wrapped header, go ahead and use the heat wrap.


BACKGROUND INFORMATION:

In the past, almost all NASCAR and other racing engine builders used the header wraps for the added power gains. But, after having to replace the headers after each race due to the wrap being about the only thing holding the header together, they do not promote the practice any longer! They now utilize the thermal coatings that are chemically and electrically applied to the headers. Those include Airborn, Jet Hot, HPC, and others.

Imagine having to replace a $1200.00 plus set of headers after each race weekend! Few but the most financially well-off race teams can afford to do this. But, it is also in the downtime for remaking a custom set of headers. Most custom header makers do not have copies readily available.

*I believe that the wraps are good to protect various items from heat, but not to hold the heat in the header. For example: you can use the wrapping for the protection of fuel and oil lines, wiring, etc.

*Cool air needs to be around the header, and insulating it with a wrap to hold exhaust heat in makes the header material temperatures near molten. When you wrap the header you trap the heat in the header, but also in the material that needs to breathe to dissipate heat for it's own survival.

*Engineers, Metallurgists, and other experts out there will state that there is no way that the material can fail because it can withstand, and it was designed to withstand, the internal temperatures of exhaust gases. TRUE! But, when the header is not allowed to cool so as to dissipate those extreme temperatures that the wrap is controlling, you have now developed a heat absorption that compares to thermal friction which will will continue to gain in temperature beyond the normal exhaust gas temperatures (EGT's). This is the same as with most any insulation.

Try this experiment ... launder a load of bath towels and then dry them. Immediately pull them out of the dryer and just toss them in a snug pile on your bed. Now leave them there for a day and then open them. You will find that there is still a considerable amount of heat left in the center towels. This heat, even though the outer towels and bed are normal room temperature have been able to contain their heat. This is a simple thermal insulation test, but with your headers you have an internal heat supply coming from the engine. The heat on the outside portion of the header material is trapped between the warp and the header and will continue to fatigue the header. This build of heat is amplified by the wrap. Towels do not need to breathe, header material does.

The EGTs stay the same but the properties of the header material changes in a way of amplifying the temperatures because of the insulation. This action goes against normal laws of thermal dynamics, but this effect is fact, and you have to pull the ears off most engineers before they believe you. This is the trouble with plenty of education, but NO "common sense"!

Something else that few Racers and Car Owners realize:
Headers Oxidize!

Under normal use and even more with higher EGTs and header surface temperatures, headers will oxidize and material is actually removed from the headers. This means they get lighter and weaker.

Try these actual test numbers:
Mild Steel (1010) uncoated header exposed to 1200º F. in normal air will have a weight loss percentage of roughly 25% with only 10 hours use at this temperature.

Stainless Steel (410) uncoated header will have roughly 8% weight loss in the same 10 hour period.

A coated mild steel header will have NO weight loss at temperatures up to 1200º F. In fact it will actually gain a bit of weight! Between 1300º F. and 1600º F. the coating will begin to show signs of mud cracking or like the look of lacquer checking. However, limited diffusion takes place between the coating and the substrate, producing a very thin film of iron aluminide, which continues to inhibit oxidation.

On A Side Note:

Do you understand the physics of exhaust flow in regards to step-headers?

Step headers are designed to allow controlled and efficient exhaust gas expansion at a selected engine RPM. What does this mean? As exhaust gases are exiting the engine into the header they are still burning and rapidly expanding down the primary tubes. If you design the header to take advantage of the pulse expansions of the exhaust gases you WILL gain horsepower. But, you'd better do it right, or that $1200.00 or more for a set of headers is a waste of money. When you set up a step header, you'd better know where you want the maximum power at, since steps are RPM specific to each engine combination.

I'd better say this now ... a step is an increase in tube diameter.

Here is an example:

A basic Chevrolet 350 cubic inch engine ... 3.48 stroke, 5.7" connecting rod length, 4.0" bore, 10.5:1 compression ratio, standard 2.02 / 1.60 valves ... designed for 6500 RPM operation. Cam specs are: .500" lift, 235º duration @ .050" lift, 112º lobe centerline.

For the average Joe Bracket Racer this would be a standard 1-5/8" or 1-3/4" primary header primary tube size, depending on vehicle weight and where you want your power. Here is the "exact" header size for a racing engine operating at 6500 RPM. Note: This is for max power at 6500 RPM!


BASIC KNOWLEDGE:

As you may or may not know from any education of standard thermal expansion physics, if you heat donut does it shrink or expand the hole? Of course since we live in a 3-dimensional world, it is a 3-dimensional reaction and it shrinks the hole! If any engineers want to argue this, start with your professors, not with me. I already know the facts and I have had engineering "students" argue this fact with me on numerous occasions.

Because of the expanding gases, if you have had the experience (as I have) to see first hand where a header with a wrap fails, it is typically where a step would be. I have had headers in my hand where literally the only thing keeping the header in one piece was the wrap. Whole chunks of the header material was gone, melted away. Talk to most "engineers" (I use that title with caution) and they will probably tell you that aliens stole the metal as the car was racing around the track! They say this because the wrap is causing problems that are not part of normal metallurgy and thermal dynamics theory <key word>. The header warp allows temperatures between the wrap and the header to turn the material molten.

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IN CLOSING:

We know that header manufacturers will NOT WARRANTY a header which has had a wrap installed on it. We know that I have personally seen, tested and inspected headers that have been destroyed after running wrapped headers on a perfectly tuned engine.

Just because an item or product is advertised for a specific use does not mean it does not do what it is promoted as, but it also does not mean it is the best choice either. We have all seen the recent TV commercials on all of these "medical miracles" that do such feats as fast weight loss and re-grow your hair. How often have we laughed at the side affects, like the most common being penile failure. Oh sure, I want to take some drug if my hair starts falling out (yes, it is currently all here) that makes my sex life go to hell. NOT !!! Those pharmaceutical companies can pucker up and kiss my "bald" backside! I'd rather have function than hair.

The same can hold true with other products. Heat wraps are great, just do not use them ON the header. Use them on a device or component on your vehicle that you are trying to protect from header heat.

If you want a true thermal barrier that will reduce thermal loss in the header, reduce under hood temperatures, and make a few horsepower in the process, have your headers coated by one of the many companies available (links to a few are above). Most all of the coating companies offer inside and outside complete coating as standard. DO NOT allow your headers to only be coated on the outside, this is not a complete or quality process.

Some other considerations about the coatings. Once the header is coated, it's permanent. That means that if you screw up your header, it is not an ease job to repair and most header companies do not want to even attempt a repair. The coating permeates into the header material which makes welding processes on a coated material less than adequate. This is why you always coat the headers last, after all modifications to the header are made, and you are 100% sure the header will fit your vehicle.






>>Source: http://www.centuryperformance.com/heatwraps.asp

[Moppie]

Hmm, that article has all the logic of a good wifes tale.

[Mekkahfire]

How do you figure?

[Moppie]

It makes a really big effort to say that thermal wrap will destroy your headers, but never actualy explains how.
It sites examples of thermal wrapped headers breaking down, but provides no evidence it was the thermal wrap that caused it, and there is some waffel in there about Nascar not useing it anymore, with only speculation as to the reasons.

Its a whole lot of waffel, and lacks any rational or well reasoned agruments.

[KiwiBacon]

Originally Posted by Mekkahfire

Heres some pretty gruesome facts about heat wrap...


>>Source: http://www.centuryperformance.com/heatwraps.asp

Sorry man, but that article is a load of BS.
It has been written by someone with absolutely no idea of how heat transfer works. The mechansim of "thermal friction" does not exist.

It is impossible for an exhaust header to get hotter than the exhaust gas heating it.

[Schister66]

i still say EQ manifold over logs anyday...

[Mekkahfire]

Log manifolds suck. The gas pounds into the rear, i dont understand how anyone could think thats logical.

[KiwiBacon]

Originally Posted by Schister66

i still say EQ manifold over logs anyday...

Logs sure suck. But a lot of factory 4-2-1 manifolds aren't that bad.

[Schister66]

hey....i have a log on my GSR...i take offence to that comment

logs might suck, but they still get you boosted

[Moppie]

Originally Posted by Mekkahfire

Log manifolds suck.

I thought that was the point of a good exhaust manifold, to suck out the waste gas.

[UncleBob]

not all log manifolds are teh same. I've seen some very well thought out log's that where QUITE effective.

As for the original question: many after market EQ's are very heavy tube. They will retain the heat very effectively. Heat retention though, is also effected by length. If its a short header, its not as important.

I agree though, the gains are very tiny. You'll gain a lot more IMO, paying attention to whats AFTER the turbo than you will with whats before it as far as pure HP gain. Assuming you have a tiny bit of fabrication ability, its quite cheap....depending on what you do anyway.