Machining rover efi plenum to fit stag

[djw113uk]

I am going to replace my Holley carb'd rover engine with a 3.9efi system. I have trial fitted the plenum to the engine in the car tonight and the bonnet fouls the vacuum union on top the plenum. Long term I also want to loose the bonnet bulge. My engine is bolted to the chassis mounts, not to the subframe so dropping the cross member isn't going to help me.

I have a friendly local machine shop, and know that it is the underside of the trumpet base that I need to get reduced. Clearly if too much is removed the then fuel rail and injectors are going to clash, but can anyone tell me how much I can get trimmed off please?

Thanks

[Motorsport Micky]

Every application is different, you may need to remove and shorten the trumpets inside the plenum also. Mock it up with templates in cardboard copying the plenum and try the fits and make measurements.

Micky

[djw113uk]

I thought I would get as much as possible taken off but so that it still goes back together properly. No point taking 6mm off if you can get away with 12mm! It looks to me like I can get about 8mm removed and still miss the fuel rail and injectors

[rasspe]

Hi I have just finished mine and took 12 mm off if you want to see it give me a call 07792703220 I am only in studley

[TR5convalescent]

Won't the reduction in air intake size affect performance? I seem to recall that some experts advise increase the PI air intake box on TRs to get more air in?

Just asking.

[Motorsport Micky]

Won't the reduction in air intake size affect performance? I seem to recall that some experts advise increase the PI air intake box on TRs to get more air in?

Just asking.

David,

If the cars were being used to their full performance extent you'd be correct, that's another reason why when shorten the height of the plenum height you may decide to remove and shorten the height of the trumpets inside to maintain a reasonable space infront of the trumpets and not to restrict them. However for the HP being achieved by road cars (in the main) the shortening and consequent plenum volume reduction will not compromise the performance.

Micky

[V Mad]

My engine is bolted to the chassis mounts, not to the subframe so dropping the cross member isn't going to help me.
Thanks

True but in my experience, the sub-frame is usually lowered about 12mm to allow the engine to be lowered as far as possible. Then trimming of plenum, if any is minimal.

[djw113uk]

Rasspe - I will be in touch - thankyou.

V Mad - I have the exhaust manifolds which both exit forwards. I am keen not to loose any more ground clearance if possible. My 2.5 saloon with rover V8 uses block huggers so the exhausts can sit much higher. I think if I lower the subframe I will change manifolds to raise the exhausts!

[bullstarz]

Drop the cross member 10-25mm then drop the engine down by the same amount, machine the base of the plenum, where it meets the the inlet manifold ( theres load that can come off) and there's no need to shorten the trumpet's.

I had a Twin plenum but it eventually fitted with the bonnet closed with no need for the bulge.

IMAG0611.jpgIMAG0625.jpg

There's loads of room in the engine bay, that is until you put the engine in.

IMAG1432.jpg

[greystag]

hi sorry to but in, i have a Rover v8 with carb and stag radiator but cant cool it ,it boils the petrol in the carb, which rad do you have ,can you give me any advise Im desperate.

[djw113uk]

To be honest the rover stag has never been road worthy or run long enough to establish if there is a problem.

However I also have a MKII PI saloon which is running a rover 3.5 engine, via twin strombergs, and LT77 gearbox. It has a standard shape triumph 2000 rad, but I believe the previous owner had it uprated. To be honest I always thought if the stag rad is man enough for the triumph engine it must be more than enough for a rover engine.

I don't have an issue with fuel vaporisation on the saloon - but then again it runs on LPG 98 % of the time. It generally sits at just over halfway on the gauge when idling and goes up to just shy of 3/4 when travelling on the motorway. When I first saw this I was concerned, but previous owner said temp sender wasn't an exact match, and it never blows out any water, or shows any sign of distress so I assume its happy as it is. Its now clocked up over 25,000miles so must be happy enough.

The saloon and stag both have no mechanical fan. The stag has some pokey little yellow thing that might be from an SD1, but I think it needs to be upgraded. The saloon is running twin electric fans from a Peugeot 406 or something. They run all the time (once engine has reached halfway on the gauge), but only at a low speed. It has never needed anything else and is used most days in all weathers and all traffic conditions.

[TR5convalescent]

David,

If the cars were being used to their full performance extent you'd be correct, that's another reason why when shorten the height of the plenum height you may decide to remove and shorten the height of the trumpets inside to maintain a reasonable space infront of the trumpets and not to restrict them. However for the HP being achieved by road cars (in the main) the shortening and consequent plenum volume reduction will not compromise the performance.

Micky

Thanks, Mickey. I think I understand. If you are racing you would be trying to increase work done and therefore shoving a lot more air and fuel through. In daily use presumably the restriction has no practical effect because you will only occasionally bump up against the air flow limit?

[Motorsport Micky]

Thanks, Mickey. I think I understand. If you are racing you would be trying to increase work done and therefore shoving a lot more air and fuel through. In daily use presumably the restriction has no practical effect because you will only occasionally bump up against the air flow limit?

The engine will normally have enough spare airflow capacity on the standard plenum sizing to almost double the output on a 3.9 Rover engine , the restriction will be in the Air flow meter and the butterfly to the plenum. Both these items can be amended to give more power and all this on the standard plenum.

Micky

[jakesmig]

Most of the airflow restriction problem is in the shape and size of the ports, smoothing them and matching them to the manifolds eases the problems but the ports have and always will be rubbish.

My millstone has 12mm plates between the chasis legs and crossmember but during the current refurb I intend reducing this to gain more groundclearance.

I shaved 10mm off the bottom face of the trumpet assembly / manifold and a further 6mm off the plenum chamber in mine and that gave enough clearance under the bulgless bonnet.
I took a corresponding 6mm off the length of the trumpets.

I did away with the plenum water heater, to allow clearance over the rocker cover, and the vacum pipe on the top of the plenum. Minor filling of the plenum face was needed to repair half ground screw hole for which I used Q-bond.

3.9rv8.jpg

John