Misuse and Abuse
The most common failure we see in turbo manifolds, not just 6boost but all turbo manifolds is due to misuse and abuse. Understanding the basics of thermal load and material capabilities is essential to helping your turbo system and manifold survive in such a torturous environment.
Turbo manifold materials generally are broken down into 2 types, mild steel and stainless. Most turbo manifolds made in Australia including all 6boost manifolds are made from mild steel. Providing the following basics are understood and applied, you can expect a trouble-free life from your 6boost manifold with some of our customers having manifolds for upwards of 15 years and 100k klm’s these days.
The problem with stainless steel is its expansion rates are more than double that of mild steel. The upside to its material properties is more extensive heat handling capability. What does that mean to the average performance enthusiast?
Due to these expansion rates, cracking is often accelerated in a daily use type environment. Think of your manifold runners like a piece of wire. If you grab the wire and bend it in the middle, then bend it back the other way repeatedly, this is similar to what is happening to your runners over and over again with each heat cycle. With a mild steel manifold think of the runner (piece of wire) bending back and forth very little with each heat cycle.
Now think of the stainless manifold (piece of wire) bending back and forth twice as much with each heat cycle. Obviously, the wire bent more than twice as far each heat cycle will lead to significantly faster failure rates (cracking) than the mild steel manifold. Stainless is also more brittle and does l=not like being bent which is another factory in accelerated cracking and fatigue.
So why do people make manifolds from stainless steel you ask? While in our experience the primary factor is looks, the major upside to stainless is it has superior heat handling capability when being abused before the material breaks down (the base material property becomes crystalline) with well over 500*f difference between the 2 materials. If you place a stainless manifold in a high abuse environment, while it will still crack over time due to expansion and contraction it will likely outlast the mild steel manifold due to handling the heat expended on it (in a high abuse environment).
In most applications when tuned correctly and used appropriately, the mild steel material never sees the kinds of heat cycle abuse that would see premature failure and as such will far outlast a stainless manifold which will crack far sooner due to expansion and contraction, meaning you the customer will see many years or even decades of trouble-free use. It goes without saying that we have repaired and replaced nearly every big-name stainless manifold in the world in our time in business due to this heat cycle cracking. The products have been fantastic quality and built to very high standards, its simply impossible to avoid the effects of heat cycle expansion and failure.
The follow on from this is understanding what constitutes abuse, and what you should be aware of when installing your mild steel manifold with the hopes of years of trouble-free use. The first and most important is tuning. The most common failure we see is heat cycle abuse from poor tuning or a poor understanding about effects of your setup and tuning on the manifold.
Fitting a turbo setup to your stock compression and camshaft non turbo engine then tuning on low octane or petrol fuels is the most common fault. The most common of these combinations are heavy 4wd vehicles with large capacity 6-cylinder engines (1FZ Toyota and TB48 Nissan specifically) with high compression (north of 10:1), stock torque converters and automatic transmissions (high load), often used for towing or off-roading (high continuous load) and tuned for low octane fuels (often 91 octane for extended travel capabilities).
The customer often doesn’t realise that even though they only run 5-7psi of boost, that the engine will only tolerate very low ignition timing number (2-6* total advance under boost) leading to very high exhaust gas temperatures and as such exhaust manifold material temperatures. Further to this problem many of these customers then try to handle the extreme temperatures created by doing things such as heat wrapping the exhaust manifold which only further heightens surface temps and leads to even more accelerated failure.
The other type of use that commonly leads to failure is class limited motorsport where you are dictated a maximum turbo size and maximum 98 octane pump fuel, hill climb, and various circuit style vehicles are the most common. With times under WOT of 12-20min with the maximum boost possible the turbo will make (22-35psi) and maximum backpressure, coupled with low ignition timing numbers due to the highlighted boost and backpressure situation, surface temps again climb to levels not sustainable with mild steel materials.
Now after pointing out all these issues with mild steel, why not just go a stainless manifold? If we head back to our previous point about bending a piece of wire, providing we don’t melt the middle out of it with a blow torch, the mild steel manifold (wire) will last a lifetime. A stainless manifold by comparison will often crack and fail in 3-5 years maximum due to heat cycle expansion. Once the first signs of cracking begin it is often the onset of regular failure until the item is replaced.
After reading through and beginning to understand the exhaust gas temperature (EGT) control and management in the turbo environment, you may ask what exactly then is the limit and deciding factor in material and thus manifold choice for your application? And this is quite often a very simple answer which is fuel, and ignition timing. A mid steel manifold will live literally decades at 2500+hp on an inline 6 cylinder with methanol fuel as it will have significant amounts of ignition timing and good EGT control.
The same applies to most E85 street and race cars, with anywhere up to 50+psi of boost most of these engines still see upwards of 10-12* of ignition timing and still have good EGT control. 98 octane pump fuel engines with 15 to 25psi of boost also have very good longevity, providing the engine is built for boost and not severely timing limited, also providing adequate EGT control.
We have hundreds if not 1000’a of 98 octane customers who well exceed these numbers, and to some extent have setups that would, providing enough abuse destroy their manifold. However, driving the vehicle in such a manner as to be mindful of the heat being generated and not being WOT and thrashing it for minutes or 10’s of minutes on end relentlessly will also lead to a lifetime of trouble-free use. Be aware that it is not just exhaust manifolds that are copping this abuse but also exhaust valves and seats and engine oils and fluids.