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.

[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.

[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.

[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.

[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.

[MPoxon]

panic said:

I have the triple carbn plenum plus rebored intake base and carbn trumpets since a few years now, ACT sent me then a remapped (by Mark Adams) tornado chip to match with it but I've always thought this juicy piece of hardware deserved a better box then the CUX14...what would be the best choice to give this intake the best electronic companion?

The 14CUX is a very accurate ECU when it comes to fuelling and can happily work with high output motors if you fit the larger bosch airflow meter and high flow rate injectors. Where the 14CUX is let down is the mechanical ignition timing via the dizzy vacuum. The ideal solution is GEMS as others has said however not easy to retrofit especially if you have an earlier block without the bosses for the knock sensors.

I am planning to get the car back to Mark Adams at some point this year to map up the plenum properly. I have already had the car mapped by Mark before and although mine will never win any BHP competitions the car drives very nicely indeed, pulls strong in every gear and is very well behaved in traffic and cold start etc which is exactly the result I want. I am not convinced that a lot of these aftermarket systems are capable of matching the accuracy of the 14CUX with an airflow meter for fuelling and general road manners. Headline BHP figures are one thing but getting the car to behave well and idle correctly are very difficult. I am considering going for an OMEX 200 ECU to control the spark and keep the 14CUX for fuelling. Mark reckons this will beef up the mid range torque and further improve the manners once mapped correctly. Interestingly enough Mark said that he had the 14CUX and OMEX200 system running on a customers car and he swapped it for an OMEX710 ECU to take over 14CUX and OMEX200 and there was no difference in the peak BHP figure.

[MPoxon]

TV8 said:

Hoover. said:

MPoxon said:

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.

may be worth swapping the AFM for a larger one....just a thought as the 5AM is now a major bottle neck in your induction system... 20AM ??? best chat with MA as he will advise best, he steered me away from the Bosch for my car

I would have a word with Jules (spitfire4v8) he has started remapping the Lucas system. I was his first customer and I am very pleased with the results. I went with the 20am and larger injectors and he set the lot up. He is well known for mapping Tuscans and Cerberas and has lots of recommendations on here.

Cheers Hoover good to catch up today and I hope you get your Griff sorted soon. If my plenum ever mysteriously goes missing I'll know who to ask!

I already have the larger Bosch AFM, red top spray pattern Bosch injectors all mapped using the Tornado software. I wasn't aware Jules had branched out to 14CUX, I am familiar with his work with the Cerb MBE systems. Thanks for the recommendation but I will be sticking with Mark Adams for the time being. I have used Mark Adams for many years now, he fully understands my expectations and is familiar with the car having mapped it a number of times for various mods.

[MPoxon]

griffdude said:

Nice feature in Sprint Matthew. Got it on a rolling road yet to give any idea of power delivery?

Thank you very much Howard, glad you enjoyed it. The team at the TVRCC have done a really good job with the article, it looks great.

Not as yet, I am booked in at TVR Power on the 24th June with Mark Adams. It will be interesting to see how the shape of the graphs have changed from last year. Mark reckons he may be able to get it to perform even better with a few tweaks to the fuelling to make use of the increased airflow.

[MPoxon]

ThePrisoner said:

Matthew

Just got this months Sprint, great article and pictures. Always looks good in print, you must be proud with that.

Hi Brian, hope you are well. Yes very pleased with it, I never appreciated how much work goes into the articles until I wrote that. All I supplied was the text and few photos, they have managed to make it look absolutely fantastic. The track photographer at Bedford very kindly let us use a couple of his pics for which I am very grateful.

SILICONEKID345HP said:

Did you dyno it before and after ?

Not as yet Daz, I am booked in at TVR Power on the 24th June with Mark Adams.

[MPoxon]

As Eric and Howard have pointed out if you are going for a larger AFM you should look at changing the injectors for upgraded items at the same time.

I had the large Bosch meter, Bosch red top spray pattern injectors and 3bar fuel reg fitted to mine last year and mapped up by Mark Adams. I did a write up on that at the time:
http://www.pistonheads.com/gassing/topic.asp?t=127...

The 20am and vectra injectors I am lead to believe will do the same job and will be cheaper.

[MPoxon]

No problems whatsoever on the thread hi-jack it is all relevant and related so crack on.

You are correct the original ECU chip cannot be re-programmed. There are two ways the tackle this, either buy a Tornado chip which replaces the EPROM in the original 14CUX, and get Mark Adams to remap it as per the link the that tread in my previous post. Or you can go for an aftermarket ECU.

[MPoxon]

Hi Anthony, thanks and glad you liked the article. I did look at the Vitesse twin plenums for I bought the ACT one and they are going for silly money now, a good piece of kit and has a nice OEM look to it. I did see one sell on eBay for not far off £1000!!!!

I remember speaking to you about your car before, is has a cracking engine in it 4.5BV very rare and has all the free revving nature of the 400 / 430s but with more power than a 500. Good to hear it is running right as well, getting big numbers is fairly easy but getting it to idle correctly, drive smoothly at low speed and cold start are a challenge but essential for a road car.