Engine mount ala Porsche

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edgedj
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Joined: Sun Oct 31, 2010 4:10 pm

Re: Engine mount ala Porsche

Post by edgedj »

Just one Porsche required as there are two of these mounts in every porker engine bay! I've been up and running again recently with it after a long period in the garage moving the steering column up and into the scuttle instead of between the pedals. It really is like a different car to drive now, far superior in handling and response than before and including when it was a Stiletto (I transferred all my mechanicals from my rusty old stiletto). NVH has 100% been sorted with the engine mounts, throttle response particularly at very low speed is really nice to drive. I can now in retrospect feel the slop in the original imp design, just by its absence.

Engine is Megasquirt v3, nippon denso injectors, davies craig water pump, recon Renault 5 Garrett T2 turbo, air to water heat exchanger in the rear with a small secondary davies craig water pump sending water to a motorbike rad ahead of the rad in the nose.

I've probably done 500 miles in it now with the current configuration and it's so quiet that I'm now chasing down shock absorber top bush squeak and front right brake pad rattle. I can hold a near whisper conversation in the car with a passenger (8 year old daughter who hates round noises with a passion, she says it's now ok for noise).

In the past month I've made some inner wheel arches to stop the gunk flying into the engine bay as I had to cut the old ones out of the rear clam to make it unbolt easily. Again using corematt in the construction results in something hugely strong compared to weight (three strips used in the GRP sandwich each side)
Inner arches
Inner arches
davrian6140
Posts: 181
Joined: Thu Dec 23, 2010 9:32 pm
Location: Stedham,west sussex

Re: Engine mount ala Porsche

Post by davrian6140 »

Hi edgdj sound's like the car is well sorted and looks good to
Hope you can bring it to the September meeting at castle Combe.
I'm in France at the moment at a place named Lignac 36370.
On a Renault car rally driving a 1912 ax. Just a bit different.
If you are quite close give me a call on my mobile 07761300386.
Dave
Dave Cooper
davrian6140

Mk6a DAV 373H
Teddie2003
Posts: 82
Joined: Wed Jul 13, 2011 1:18 pm
Location: Hants

Re: Engine mount ala Porsche

Post by Teddie2003 »

Hi edgdj

1/We were talking about engine mounts at the local Imp club meet the other night and I mentioned your take on it for your car.

Do you think that this could work on an Imp?

I wondered if the engine mounts could be fitted to plates and bolted through the rear chassis legs and the engine hangar plate placed behind the rear panel?

I suppose it would depend on what thickness the hangar plate is and if it would fit between the rear panel and the fanbelt?

2/ The other thing I wondered regarding this arrangement on a Davrian, was if you had a rectangular frame like the one on masermat’s Italian Mk5 but a little bit longer to clear the engine.

Do you think the Porsche mounts could be fitted under that type of frame and then have the hangar plate rocking on them on them from below, rather than above on your arrangement?


Steve
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edgedj
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Re: Engine mount ala Porsche

Post by edgedj »

It would be interesting to take a look inside an imp engine and think about what's best. The setup I'm running is one of the biggest mods I've ever driven in an imp variant. If anyone has driven a Lotus Elise, this is the feeling you get through your seat. It's only when the imp slip is gone you realise what it was doing to upset the handling. The key parts are:

Mounts are the widest possible points in the vehicle for stability and control over engine rock

The engine hangs from the Porsche mounts

Sound and vibrations are not transferred to the structure by the over strong central imp mount but spread in two places with the weaker and softer side mounts. They can be much softer and compliant because they are at such a strong leverage position.

I think you could invert the Porsche design so the flat plate is in a crescent shape going over the engine rather than behind it. Key is to having a flat plate with ribs welded around the perimeter.
Teddie2003
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Location: Hants

Re: Engine mount ala Porsche

Post by Teddie2003 »

It would be interesting to take a look inside an imp engine and think about what's best.

"Yes that makes sense, maybe one of the “professional” engine builders might be able to comment on if the reduced engine movement is of any concern in the long term."

Mounts are the widest possible points in the vehicle for stability and control over engine rock.

"So between the rear chassis on an Imp that might work"

The engine hangs from the Porsche mounts Sound and vibrations are not transferred to the structure by the over strong central imp mount but spread in two places with the weaker and softer side mounts. They can be much softer and compliant because they are at such a strong leverage position.

"That makes a lot of sense"

I think you could invert the Porsche design so the flat plate is in a crescent shape going over the engine rather than behind it. Key is to having a flat plate with ribs welded around the perimeter.

"Sounds like the CAD(Carboard Aided Design) needs to be used to check if that’s practical in an Imp and if the Davrian "A" frame is removed and replaced with a rectangular arrangement then the mounts could be positioned on a wider top mount bar."

So on the picture of your hangar you have the conventional Imp centre mount position. Plus to the lower left it looks like you have a rose joint that picks up on the block where the water pump would mount to help reduce rock? Does the lower right one connect to anything?
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edgedj
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Re: Engine mount ala Porsche

Post by edgedj »

The left and right hand sides are rose jointed to the block to prevent any rocking so the plate stays exactly in the same place WRT the engine. The right hand rose joint you can see dropping vertically is an unrelated one holding the silencer up whilst allowing the pipes to grow with turbo heat.

I think it's sensible to place the mounts in an imp somewhere higher in the wings or on a frame yes. I'd just pick a place where they are easy to get to on either side and go from there, perhaps off the inner arches? You could chop all the box sectioning away about 6" behind the rear arches and weld up small platforms here for the two mounts. Following this you could replace the normal rear panel with a thin grp light skin as this now only serves the purpose of keeping the outer wings the same distance apart. I think you could shed 5 kgs at least. The new engine frame then goes aft of the alternator, over the block somewhere in line with pluglead #2.
Teddie2003
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Re: Engine mount ala Porsche

Post by Teddie2003 »

Hi,

yes I guessed that the RH might have gone to the block to steady up that side as well.

And moving it back along the engine if it was in an Imp makes more sense than trying to fit it into between the pulleys and the rear panel.
Plus if you used a rectangular frame on a Davrian instead of the A frame that would be a better position to aim for on that arrangement.

Is your hangar plate alloy and what thickeness is it?


Steve
robfromsomerset
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Re: Engine mount ala Porsche

Post by robfromsomerset »

I am glad that this works as well as you say, since it goes against much of the traditional engine mount design theory, but so do many other configurations used in more recent configurations.
The theory says that the engine and gearbox unit mounts should be placed with their primary degree of freedom (flex direction) aligned on a tangent to the axis of least enertia of the whole powertrain, and torque generated by the powertrain can then be constrained within that mount arrangement or by use of an additional torque restraint.
This is why most front engine rear drive cars have angled mounts low at the front and a single mount at the rear with the A.L.E passing through the front top of the cam cover and exiting through the underside of the gearbox towards the back (normall where the GB mount is).

This application is using a mount designed for a heavier flat six (perfect balance) on an imp engine with very low enertial and powertrain loads (short stroke, light weight, no real power)...

The rule of thumb was that any engine mount bracket should be super stiff (4 times stiffer than the mount IIRC), and I think that it is in this aspect that the design performs compared to the scaffold tubes running into the cabin of the original design. The isolation element utilised clearly works and hasnt read the automotive design books, but the decoupling of the mount system from the roll cage, shortening the cantilever would all help, probably to a degree that the was noticable in NVH to the occupant

Thanks for sharing.

Rob
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edgedj
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Re: Engine mount ala Porsche

Post by edgedj »

robfromsomerset wrote: Wed Aug 16, 2017 12:55 pm mounts should be placed with their primary degree of freedom (flex direction) aligned on a tangent to the axis of least enertia of the whole powertrain
Where would this theoretically be with an imp setup then? I've tried to replay the description in my head but failed on three occasions!
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