davrian.net

In an attempt to reduce NVH in my dav I'm fabbing up a rear crossmember structure to replace the single dangling pivot. I googled a few porsche pics and noticed they have a very different approach to engine suspension to that on imps and davrians. It's bascically a wide bracket solidly mounted to the engine which meets engine mounts inline with the inside face of the rear wheels.

Stage 1 complete - purchase of 2 x porsche Carreras 2 engine mounts
Stage 2 in planning - making a buck for the rear crossmember.

I've been posting pictures on Facebook but in case people here aren't on FB...

So the frame that goes round the engine in Pic 1 is that a f/glass box construction?

yes it's a GRP construction with lots of corematt and weighs in at around 6KG. The arms extend inside the cabin and are glassed in and around the rear spring turrets. If I put enough weight on them I can lift the nose of the car in the air off the axle stands which are about 6" ahead of the rear wheels.

So is that something that you made to fit around the engine?

Or have you modified the original frame support so that you could then fit the Porsche type mount?

and now complete! I've only driven it a mile or so but it's really nice to drive, the most startling difference I've noticed so far is the low speed control and setting off, none of the standard imp bite and bounce (which I never noticed until it wasn't there). When you lift the clutch it really steadily applies the power and smoothly heads off. Need to get my windscreen back in next before a bigger test. Seems nice and solid and the engine is way more accessible than ever before with the A frame.
This is a completely custom from the ground up build of an engine frame using Porsche mounts, but the frame (GRP) and the engine hanger (steel) are custom made to achieve this.

Now I've re-fitted my windscreen, heading out onto the road tomorrow for a better test.

Dave

update on NVH - after about 20 miles it looks like the harmonic vibrations are gone. I don't know if the A frame or engine mount location was responsible but aside from volume and pitch changes, the painful bass vibrations are gone.

Before the work on the engine frame I used a decibel meter app on my iPhone to record noise in the cabin and with the windows shut I was getting high 60s (67-68) at low running speed and 70-75 when revving over 3krpm

I drove to work yesterday with a decibel meter app running on my iPhone and here are the results, post new engine mount:

Idle : 48-50 dB
normal running: 55-60 dB
high rpm: 60-63 dB
engine running at speed with heater fan: 63-65 dB

In short an amazing difference, the Porsche mounts and their location make a huge difference to transferred noise to the cabin. Idle noise is less than half what it was and running is something like an 80% drop. I can now hear the fuel pump (mounted under the floor) as a whine when driving it's getting that quiet.

Handling is also massively impacted, it corners much more predictably then before and low speed driving is vastly improved with clutch bite point being firm and easy to handle. I always noticed before how an imp novice would struggle to handle set off and more often than not stall the engine, with the wide engine mounts and lack of slop the car sets off really predictably and smoothly. Very hard to define or describe the difference but if you drive a modern car in traffic you'll notice you can just move the clutch up or down smoothly with zero throttle and the car behaves nicely, well an imp engine with wide engine mounts will also do that...

Very impressive I must say!

However, if as you say you had to buy two Carreras just for some bits, can I have the leftovers please?

Sorry nopt to have been keeping up on the build, but what have you done to the engine, is it now fuel injected? Which system?

Looks like you've been mighty busy on it!