"In this Product Series, I document the development, unboxing and installation of the InfinityDesign Long Tube S85 V3 headers.

This entry covers my experiences with merge collector leakage issues, the potential culprits and how we got it fixed."
- Matt

The original install. 

The V3 headers I received in late 2021 were designed with slip-on merge collectors. It had been Infinity's go-to design for the last few years. We also reused the OEM gaskets that were on the original headers as they were deemed in good condition. 

We used high temperature silicone to seal the merge collectors to the runners. In the picture below, the orange is the silicone. 

The leaks. 

The first issues. 

I started running into collector slippage issues causing leaks and a drastic noise change around Spring time. I jokingly said it made my M5 sound like Lambo - some took that literally. 

The first fix. 

My mechanics had not tack welded the flange on the driver side headers that bolts to the section 1. It was initially deemed unnecessary by Infinity as many do without. We decided to tack that flange and a few spot welds to the collectors.  

The second fix. 

I had slippage another time in the Summer and we said screw this, we're welding the collector. For a while, it worked and all was good. The V10 was singing and making power. 

After fitting the CSL carbon plenum and going to AlphaN, I started experiencing idle issues. 

The MSS65 would trigger misfire protections on Bank 2 (driver side) at low engine speeds. It would make some subtle tractor-like noises when lugging the engine next to a concrete wall.

I had to keep the car in Neutral and give it gas at every stop light to avoid triggering misfire protection. The M5 is my daily - I grew aggravated. 

All along, we focused on potential leaks from plenum. 

We went down a rabbit hole. 

After much testing and monitoring, we found it would trigger CEL and misfire protection after long term adaptions on air leaks had settled into its max negative value of -10.00.

I got the car in to my mechanics and we tested for an exhaust leak. We found out Cylinder 4 had a leak at the gasket: it was blackened around the exhaust port.

It had been leaking for a while. Upon removing the headers, we immediately noticed Cylinder 4 had much less heat discolouration. 

The culprit? 

The MSS65 is complex, and proficient at its main job: protecting the S85 from itself [...] and mechanics. I'll never truly know what caused this. 

I can give options: 

1. The header gasket of cylinder 4 wasn't fitted back correctly at initial installation. 
2. The header gasket of cylinder 4 was worn and failed. 
3. The cylinder 4 runner wasn't torqued down correctly considering it's hard to get to.
4. The merge collector slippage issues lead to gasket failure on this specific cylinder. 
5. The merge collectors being welded lead to gasket failure on this specific cylinder. 
6. The cylinder 4 header flange wasn't flat and caused gasket failure. 
7. Heat did it's thing. 

The V2 merge collectors. 

Infinity suggested to re-use a previous merge collector design with 2x bolts to add a reliability net to potential collector slippage. It had been abandoned during design revisions. 

Since January 2023, all headers are shipped using the new collectors with bolts. Should you worry if you got slip-on collectors? InfinityDesign says no.

The bolts are threaded through a welded tunnel on the collectors and 2x runners. 

These are the previous slip-on collectors. The bolts being on runner 8 and 9 make these somewhat accessible during installation. 

The V2 collector fixed leakage issues. 

I could immediately tell the V10 sounded better. At idle and low engine speed acceleration, there weren't any tractor noises. The classic diesel VANOS noise was back, and I liked it. 

The mid range sounded deeper, by 5,000, the raspier tone of the V10 started to wail all the way to 8,500. I've been driving with the backseats folded ever since. 

We reset long term adaptions on air leaks and I for extended drives over the next few days. It didn't trigger any codes. 

I started getting codes for VANOS values on intake and exhaust valve. After testing the high pressure lines, it was fine. The solenoids were out of range, barely hitting 0.4 on ISTA diagnostics. 

I laughed. This is the V10 life. Onwards!

Up next: Spring is around the corner.

I will finally get to final driving impressions and sound clips.

My car has a stock exhaust system otherwise, this will settle the debate whether these headers muddy the signature V10 sound track.