Vetterman Exhaust Cowl Clearance

[Nev]

Spoke with Clint today. He has offered to pay shipping via courier if I send the exhaust back, and he will tighten it up to provide clearance. (Normal freight to NZ takes months at present). This is what I’ll do and hopefully it’ll be back in a few weeks.

He said that until about 2-3 years ago there were very few issues. Then a few exhausts didn’t fit as they had previously. I wondered if it had something to do with the change to the Bravo model, given the timeframe. I think also any variation in the firewall position between builders could have an effect too. Just a few thoughts. Clint was going to phone Mark and discuss.

As frustrating as the issue is I can’t complain with the service.

[Bcone1381]

We get to choose which nose bowl we want when ordering a kit. I wonder if one gives more clearance for the exhaust than the the other.

[22LD]

Clint is a good guy and took care of mine for me. I have probably one of the older kits - definitely not a Bravo model. So I'm not sure where the difference has come in.

[Nev]

An update.

I sent my exhausts back to Clint. It cost a reasonable amount obviously, but I didn’t want to be performing “work arounds” on my new aircraft. The upside is that 6 weeks later I received my exhausts back, and at this point they look to have tons of clearance. Clint has re-made them from scratch.

Clint has come up trumps with the service.

The shape of the new pipes is very different and they flow straight backwards to where they join. The original ones had a number of curves forward which is where the clearance issues arose. I’m not sure of the performance differences. I’ve sent a note to Clint and if he uses this design for new 4-place pipes then I wouldn’t think there should be any issues.

[Battson]

Pictures would be great!

[Nev]

Here you go. One change appears to be that the heat muffs are a little further rearward. I was already having to get creative with clearance on the oil cooler, now a little more so.

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D6D8B678-BC0F-4C43-BE63-7E4631520E41.jpeg

[schu]

Did Mark and Clint speak? Did the firewall change on the B-model kits? I have an A model and need exhaust, but I'd rather have equal length headers.

schu

[zkelley2]

Clint's exhaust bolted right up to my plane with no issues at all.

[Nev]

This was the issue. Some did, and some didn’t. The new design has a ton of clearance.

[Nev]

Schu, I didn’t ever find out what the issue was. My new exhausts fit well, but I think the trade-off is uneven lengths. That said, I needed to keep moving forward and I’m happy with the result albeit at significant extra cost.

[schu]

I just talked to Clint. He said that there wasn't any noticeable issue with the uneven lengths due to it being a 6 cyl and the firing order. That's the same exhaust that they use on the harmon rocket.


I'm just going to have him build me one like yours, so that I can be sure not to screw with it.

[Nev]

Good idea, I would recommend this to anyone getting an exhaust for the 4-place 540 from this point onwards.

[schu]

Nev,

Can you tell me the size of the tubes? 2"? Also, is the bottom tube that everything flows into bigger?

schu

[schu]

I bet this has something to do with long vs short engine mount. It seems to me that the short mount would give you a tiny bit more clearance, and that is what Zach has. The pictures above appear to be long mount.

One thing I'm concerned with is CHT. Bearhawks already run hot, and I've read that the more efficient your exhaust system is, the better the heat gets out, thus less CHT.

schu

[jaredyates]

My first system from Clint didn't clear the cowl, so he made one for me thst fit tighter to the engine. I have a theory though about pipes being closer to the sump, transferring energy to the oil. Especially with the 4-cylinder crossover pipes.

[schu]

The 4 cyl is a totally different thing. From what I understand you need the crossover for any efficiency because of how the firing order is.

[Nev]

I bet this has something to do with long vs short engine mount. It seems to me that the short mount would give you a tiny bit more clearance

This is quite possibly the issue, it hadn’t occurred to me. Plus some guys have extended their prop mounts which would naturally give then more clearance on the front pipes.

[zkelley2]

I bet this has something to do with long vs short engine mount. It seems to me that the short mount would give you a tiny bit more clearance, and that is what Zach has. The pictures above appear to be long mount.

One thing I'm concerned with is CHT. Bearhawks already run hot, and I've read that the more efficient your exhaust system is, the better the heat gets out, thus less CHT.

schu

I bet it is, since the further from the firewall you go the more narrow the cowl becomes. Not by much, but there is a taper. Just kind of thinking out loud here. On the other hand, the nosebowl width is as narrow as it'll go regardless of distance from the firewall. There are a couple styles of nosebowls out there if I remember correctly. Maybe one is slightly more narrow than the other?

I've thought about at some point swapping for the longer mount. It'd be a pita. Cables, wires, cowl, etc all would have to be re-made, but if it gets my CG enough further forward so I can haul more stuff in the far back, it'd be worth it long term.

[Nev]

That’d be a big job. Is the CG an issue yet ?

[zkelley2]

It's kind of an issue for me. With my 2 blade carbon prop and the short engine mount, my empty CG is such that it's hard to put 4 adults and any bags in the airplane. I don't actually do that much(4 people anyways), but I very commonly have enough mass in the back to get it to the limit.
I've also put the aft limit at 20.0, further limiting the envelope, because of neutral and eventually negative longitudinal dynamic stability aft of that.

I'm doing a pretty heavy mod right now that might fix it well enough to not worry about it. I'll post in a few days when I'm done.

[Nev]

Look forward to hearing your results and hope it goes well. I was also thinking of limiting the CG envelope myself, and at least starting with a clean sheet for the test flying and W&B.

[Nev]

schu

Can you tell me the size of the tubes? 2"? Also, is the bottom tube that everything flows into bigger?

The 6 pipes are 1.75” diameter and they all flow into a 2” diameter main pipe.

[schu]

Thanks for that. It sounds like it will work fine. I was looking at this article trying to understand the performance differences: https://www.kitplanes.com/headlong-for-headers/

[Bissetg]

I ordered a Vetterman exhaust with my original kit, like Nev’s it didn’t fit. I modified mine locally but ended up having to change it again after my first engine had to be replaced. Long story short, I’d gone with 4 straight pipes and it wasn’t pleasant from a noise or appearance perspective. Whees description of “obnoxious” was flattering I think. It was truly awful.

I’ve just had a completely new exhaust, heat muff, and muffler fabricated by the local aviation slash motor racing gurus.

The 4 into 1 tuned exhaust with muffler and better heat muff has made for a much quieter aircraft that is more comfortable in sub zero temps in all respects.

It’s been an expensive way to the finish line but I’m happy with where it’s landed.

I totally agree with Jared that we all have a responsibility to mitigate our noise foot print as much as we can and would strongly recommend builders consider this important issue in their planning.