Exhaust Upgrades

After the last run, it was clear I need to put some effort to quietening things down a bit around marinas and so forth. My initial plan was to just downrate the camshaft slightly – sacrifice a few mph top end and be able to run a wet exhaust – however rmbuilder was reluctant to spec me an alternative camshaft and instead recommended mufflers. So a fair bit of hunting round, eventually I found that Gil mufflers can run dry, so I set about making some new tailpipes that would fit the gil mufflers, plus also let me adjust how much water goes in to them.

At the same time, also wanted to reduce reversion. Original plan was to have a large crossover pipe between the banks – since the major point of reversion is due to the uneven firing cycle between banks. Originally planned to have a full 3.5″ inner bore pipe mounted immediately after the collectors, but eventually I realised this was impractical.

Also wanted to have a flange between the collector/manifold and the tailpipes – to give me a better mount point for the O2 sensors and also to have a EGR check valve in – this is another idea, to have an EGR type check valve in so that at idle, rather than suck exhaust (water) back in, fresh air is pulled in via the check valve. Don’t need a huge amount of flow here, just enough so that at idle there’s a little less reversion.

The flange idea also means that as I try different packaging/ideas out – I just need to make a new flange, not a whole new tailpipe each time!

Exhaust Flange

Part 1 was to make the flanges and see if this plan was viable. I needed an aluminium flange, 50mm thick,

Unfortunately, nobody wanted to make me one of these, so had to make it myself.

Started off with a couple of bits of 50mm thick aluminium:

And then slowly using the biggest holesaw I could get to work, cut a hole in the middle:

That was enough to then get it into the lathe with a boring bar:

I think they came out OK:

Tailpipes

Next it was time to build new tailpipes to fit both the flanges and the mufflers. I had new stainless 316 flanges laser cut from fractory, so the first steps were easy to mock up the inner tubes:

However, if you’eve ever looked at a dry tail pipe boat, often the exhausts look asymettrical coming out the back of the boat through the transom – because the exhaust manifolds are offset slight (one bank of cylinders is about 3/4″ forwards than the other, which messes up the angles). This meant that while I could have one bank with a straight tailpipe, the other bank would need to be adjusted to make sure the exhausts are symmetrical on the transom). This took a lot of backwards and forwards for what appeared like a small cut. in the pipe You can see in the below pic that I’ve already welded the inner & outer to the flange, along with the water dump pipes fabricated and welded on, along with half the outer.

It was also necessary to have the flanges bolted to something pretty sturdy to stop them distorting when they were being welded:

And I’m still a beginner at tig welding, but I think it came out OK:

Next it was time to weld on the last bit of the outers (which then means I also need to remove the manifolds to install & remove the tailpipes – aggro!)

Then needed to make some clamp water dumps for out the back. The “idea” is that the mufflers get cooled externally from the outside to avoid burning them up too much – pics below will show:

Final install. I think they came out OK. Hope it works! this pic is with the flaps closed.

Oil Leak

Also noticed a small oil leak from the sump last time I ran it. A bit of googling tells me that the “modern” single piece oil pan gaskets are notorious for leaking as they’ve a bit thick & rigid, so yet again, engine out:

And then when I drained the oil, I found a couple of drops (literally) in the oil. That’s not right! So I pulled the intake manifold off as the most likely culprit. I hope I found it:

So a bunch more work redoing that:

29th July Update

Finally got a chance to test all the work out. Everything seemed to work well, oil leak is fixed and with the mufflers closed, it’s quite a lot quieter. No high-speed footage unfortunately, but you can hear the idle is now tolerable, similar to a wet silenced engine. Not quiet, but acceptable. It currently has a 3mm water hole into the mufflers, primarly to let the tips drain down, but it also helps muffling. Once everything settles down and all the efi map is tweaked, I’ll add another one that’ll help silencing (water is the best silencer) and then review it from there.