ACT Twin Throttle Carbon Fibre Plenum - Writeup

[MPoxon]

Afternoon chaps, as some of you may know I recently had the ACT twin throttle carbon fibre plenum fitted. There does not seem to be a massive amount on information about the product on the web so I thought I would share my thoughts in the form of a write up.

My Griffth has a standard Land Rover plenum chamber fitted which when originally designed was optimised for low speed torque which is great for heavy 4x4s but perhaps not optimal for a sports car. I have already changed the trumpets inside the plenum for the ACT flared carbon fibre versions which improve mid-range torque, top end power and I already have the ACT smooth bore induction hose. In addition to the larger capacity air box and smooth airflow characteristics the plenum kit also features twin Jenvey throttle bodies which improve throttle response.



After speaking with a fellow Griff owner in Holland he had fitted an upgraded throttle linkage to his ACT plenum which looked improved over the original design. I spoke to Tim Lamont at ACT products about the possibility of supplying a plenum kit with an upgraded linkage. Tim had previously been working with Jenvey on an upgraded linkage option for the plenum kits and already had some test units in the workshop. I ordered the plenum with the upgraded linkage, once the new throttle bodies where received from Jenvey and the plenum built, Tim sucessfuly tested the fit and clearance of the new linkage the plenum on a car at Austec. Below you can see the difference between the existing linkage design and the new upgraded version:

Existing Linkage


Jenvey Linkage




I had the plenum fitted to the car by my TVR specialist David Batty who did absolutely fantastic job of fitting it. It took a little bit longer than expected to fit as the car has power steering and is running and the original coil, both of which bolted to the old plenum so the mounts needed modification. I bought an old pair of Rover SD1 rockers from eBay and had them powder coated in a black crinkle finish which David also fitted. The flame trap is one of Clive Letherby's CNC master pieces (Point CNC).

New rocker covers


New plenum and rockers fitted




I have only had the plenum fitted for a couple of weeks but I must say I am very impressed. This is so far the most noticeable modification I have completed performance wise. The car feels like it has gained top end power but I cannot quantify this until I get it on the dyno. The main difference however is the throttle response which is now unbelievable, any input on the throttle pedal is now instant. I asked David Batty to use the for a couple of days to give it a shakedown before I picked it up and to let me know his thoughts. David said he was very impressed with the way the car drove which is big praise from an experienced specialist. I am also very pleased with the throttle pedal weight which is much lighter than the old setup which was very heavy and become tiresome on long motorway journeys but not too light that is lacks feel.

The only minor downside with the plenum is the chatter from the valve train is noticeably louder, I assume the original plenum being thicker deadened the sound. This isn't really an issue as I have only noticed the difference when on idle and with the roof off.

Tim did mention when I purchased the plenum that he fitted the product to a RV8 race car for testing and the car lapped significantly quicker with the plenum than without. Although the plenum does provide a little extra power the increased lap times were mainly due to the driving being able to get back on the power quicker with the increased throttle response. Having now done a track day with the plenum I can certainly believe that claim.

[carsy]

Very nice Matthew.

Mapped ignition next ? to make full use of the new plenum.

[jimed]

Looks a very nice and neat job with well engineered throttle linkage.
Jim

[MPoxon]

carsy said:

Very nice Matthew.

Mapped ignition next ? to make full use of the new plenum.

Thanks Ian, yes that is next on the list. I am thinking possibly an Omex 200 unit mapped up by Mark Adams to complement the Tornado setup, leaving the 14CUX to control the fuelling and the OMEX to control the ignition.

[BigGriff540]

Hi Mathew

Great write up!

I have a twin ACT plenum on my Griff which I have just purchased. Whats the difference between the standard throttle linkage and the Jenvey ones?

Thanks

Adam

[griffdude]

Good writeup. Will be very interesting to see before & after rolling road printouts.

[MPoxon]

BigGriff540 said:

Hi Mathew

Great write up!

I have a twin ACT plenum on my Griff which I have just purchased. Whats the difference between the standard throttle linkage and the Jenvey ones?

Thanks

Adam

Thanks Adam. I am not entirely sure what the actual benefit is Tim at ACT would be able to give you a better answer than me but I assume they give a better weight and feel to the throttle pedal. I have never driven one with the standard linkage so not able to give a direct comparison. I know Tim is selling these as a retro fit option.

[TVR Beaver]

That looks great!!! can't wait to see the RR results

[MPoxon]

Yes I would be very interested to see the RR results. I am planning to get a session booked in with Mark Adams at TVR power to adjust the map to make the most of the plenum so I will keep you posted.

[BarnFind]

Thanks for that,i have the original linkage which is a little agricultural by modern standards and i originally had a few issues with the trottle getting stuck open at times,will definitely get the upgrade.

[db484bhpv8]

Excellent work Matthew.
You should bring it along to Shakey a week on Sat/Sun to show us

[BigGriff540]

BarnFind said:

Thanks for that,i have the original linkage which is a little agricultural by modern standards and i originally had a few issues with the trottle getting stuck open at times,will definitely get the upgrade.

...So it not just me who has had issues with the throttle sticking open on the ACT plenum.

[simonwedge]

Really like those crackle black rocker covers. They look especially good with the carbon plenum. Excellent.

[pjac67]

MPoxon said:

BigGriff540 said:

Hi Mathew

Great write up!

I have a twin ACT plenum on my Griff which I have just purchased. Whats the difference between the standard throttle linkage and the Jenvey ones?

Thanks

Adam

Thanks Adam. I am not entirely sure what the actual benefit is Tim at ACT would be able to give you a better answer than me but I assume they give a better weight and feel to the throttle pedal. I have never driven one with the standard linkage so not able to give a direct comparison. I know Tim is selling these as a retro fit option.

Great write up Matt - looks lovely too...

Adam - you DO NOT need quicker throttle response on your car (you may have Jenveys or similar already fitted...?).

Hopefully see you guys at GG. Paul.

[rigga]

I wonder if one of these would work well with my jools blended base .

[neutral 3]

The sloooooow throttle response is something I'm very unhappy with as well.

What's the cost of the new set up ?

[gifdy]

I had the ACT twin plenum on my 5L V8S and noticed the same thing - faster throttle response. It felt more powerful as well but that may be imagination/wishful thinking.

I blew a couple to smithereens when I had a problem with a Meqasquirt installation so I went back to the standard metal plenum. The fuelling was setup with the ACT plenum and with the std plenum the car seems to run rich which suggests the intake is now more restricted.

My memories of exploding CF has faded and the MS issue seems to have been solved so I'll be going back to a ACT plenum this summer. If I can find a good MS tuner and RR I could do a proper before and after comparison.......

[BarnFind]

Just ordered my new linkage this morning.All in all a great piece of kit,definitely more power and throttle response.Tim as always a pleasure to deal with,recommended upgrade,well worth the money.I also have the carbon trumpets and smooth bore induction kit,particularliy recommended over the TVR Ele's trunk.

Edited by BarnFind on Friday 16th May 11:00

[MPoxon]

gifdy said:

I had the ACT twin plenum on my 5L V8S and noticed the same thing - faster throttle response. It felt more powerful as well but that may be imagination/wishful thinking.

I blew a couple to smithereens when I had a problem with a Meqasquirt installation so I went back to the standard metal plenum. The fuelling was setup with the ACT plenum and with the std plenum the car seems to run rich which suggests the intake is now more restricted.

My memories of exploding CF has faded and the MS issue seems to have been solved so I'll be going back to a ACT plenum this summer. If I can find a good MS tuner and RR I could do a proper before and after comparison.......

I cannot get my head around it, my car goes like a rocket now but I refuse to believe the plenum has added a large amount of power. Maybe it is a perception thing but is certainly drives better now, I also find myself hitting the rev limiter more often now as the power used to fade around 5k but now it seems to pull strong all the way up to the limiter.

[gifdy]

MPoxon said:

I cannot get my head around it, my car goes like a rocket now but I refuse to believe the plenum has added a large amount of power. Maybe it is a perception thing but is certainly drives better now, I also find myself hitting the rev limiter more often now as the power used to fade around 5k but now it seems to pull strong all the way up to the limiter.

To be honest, if I found out it added 0 bhp I would still get another, because it looks cooool !

I've come to terms with being shallow