Another new engine

We’re reconsidering the engine in the Mini- it’s great, but it doesn’t suit the way we actually use the car.

The current engine was built to be fairly powerful to suit a fun car, something to thrash about, maybe the odd track day or autocross. Unfortunately we seem to have installed it in something with leather seats, wilton carpet, and immaculate bodywork. It’s way too shiny for the mud, and too expensive for a close encounter with the tyre wall. Blasting down the motorway is fun for about half an hour, and then 3900rpm becomes tiring despite inches of Dynamat under the carpet.

So we’ve bought a new engine. I plan to fit a 2.9:1 diff (cruising at 3200rpm instead of 3800rpm might be nice), a more sensibly weighted flywheel for smoothness, and a cam that will make lots of lovely torque rather than outright power. We’ll see how it goes- we can always put the old engine back if it’s not right.

Or put the old engine into something a bit less precious.

Exhaust Mounts

As part of driving a Mini with a solid mounted subframe, sporty cam, and lightweight flywheel, I’ve naturally become interested in the art of vehicle refinement, and specifically the isolation of engine noise and harmonics from the passenger compartment.

It turns out to be an exceedingly complex science when done properly, and effective solutions tend to be extremely specific, but there are a few broad principles to start with. Like this one concerning rubber mounts on vibrating components: the brackets supporting the rubber mount should be as rigid as possible, and the rubber as soft as possible.

So, the exact opposite of standard 1960’s Mini exhaust mounts then. Right. Where’s my welder. Let’s start with the rear mount:

RearBracketOld

Those rubber cotton reel mounts are rock solid. Modern exhaust mounts are little more than a couple of rubber straps, designed to stretch and move. So that’s what I’ll use, and make up a couple of brackets to bolt it to the existing mount holes. (Minis from around 1990 used this style of hanger, but with welded-on brackets.)

RearBracket

RearBracket2

Interestingly, the exhaust gets about 8mm longer when it’s hot. I’m going to need to align this mount carefully so it doesn’t hit anything.

RearBracketInstalled3

RearBracketInstalled2

RearBracketInstalled1

And now the middle mount. Same deal:

FrontBracket3

FrontBracket2

That’s the standard mount in the front- just a big block of solid rubber. It really doesn’t move much.

FrontBracketPartInstalled1

FrontBracketInstalled2

FrontBracketInstalled1

And there we go! All fixed. The loud booming from the rear cabin has completely gone, and the exhaust is free to expand and move about a bit without stressing the mountings. We’ll see how long it lasts…