After the failure with the ITB's I had gone back to the original setup and used that over the Summer of 2006. I knew I still had to get more air into the intake but wasn't sure which way to go with it until I had to fit a MegaSquirt ECU to Rob's (V8Developments) 5.5L engine that he had fitted in a TVR. This had an ACT triple plenum carbon intake on it and it was as responsive as I could imagine any engine. In fact it was so responsive off load we couldn't get the acceleration enrichment tuned to Robs liking using MAP, we had to go over to TPS as the load scale of the fueling map. The only problem with this setup was that it was too responsive at low rpm's and is very hard to drive in the city, as all 3 throttles open up together at the same time, but I was certain a plenum could be made to be more drivable and allow enough air in to feed my engine.

Triple plenum on V8Developments TVR

I couldn't afford to get the ACT setup, its around £1500 and hard to justify at that cost, so I decided to look into using the original setup and improve on that.

Many people, including TVR Power, had improved the trumpet base by removing the tubes and blending the material into the holes to form a sort of trumpet. Jooles at www.track-car-solutions.co.uk recorded an 8BHP increase in his old 4.0L by blending his base and fitting a Jag throttle to his plenum. Crude it may be, but even if you look at the after market trumpets for the RV8 they are all cut and bent to fit, so these are far from ideal. I wouldn't think the overall power gain from a perfect trumpet base would be that great anyhow, maybe 5BHP, so any improvents I could make here would need to be cheap as 5BHP is not worth the sort of money carbon trumpets cost. The main concern with this though is that there are 2 levels at which the trumpets should sit so that they are all the same overall length, but blending them in would mean 4 were longer than the other 4, which is not ideal, but I think I may have cured that, or at least helped a little. Basically the original tubes are all the same length and they sat on a lip inside the base, this lip is what regulated the height they sat out of the base at. So when I blended it all I kept this lip but simply rounded it into the larger part of the tube, so this has kept the length that is 45mm all the same. Also the inner 6 holes don't have enough meat around them to blend them to the height of the base, so I cut away at the metal that was there so the top of the 45mm lip was at the point where the metal ran out. This I hope would mean the length of the trumpet would all be the same for those 6 as as soon as the air meets the area with no metal it will no longer act as a tube. Even if it doesn't, the lengths are only a little bit out anyhow.

Trumpet base mods

The next thing to concider was the plenum/throttle. I really disliked the way the RV8 EFI setup's intake is on one side as it looks lop sided and not particually pretty. I'd seen on the net that 2 plenums were cut in half and welded down the middle so there was an intake on both sides, this was also a suggestion my Son made, so after a lot of thought about other idea's I decided this may be the easiest option. I got hold of a pair of old plenums and set to work cutting them, I didn't cut them in half as theres a flat area on the back of them for the idle valve, so I decided to cut it just to the side of that so the front and rear still looked the same as it was.

Siamese plenum

As I'd already fitted 2 throttle cables to the pedal for the ITB's I decided to use these for the twin intake setup too. It didn't need balancing like the ITB's either, so it was vertually a plug and play mod, especially as I'm running an MS, this setup isn't possible with a Lucas setup without some serious mods to the system. The main problem with the ACT setup was drivability at low rpm, I decided to over come this by staging the throttle openings a little, this is very easy to do as I had 2 cables, I simply set one so it was a little slack. This means the cable wont start pulling the throttle opening untill the first throttle was around 10% open. I have the original side intake as the main throttle control and the other side is the one that comes in later.

Throttle linkage and installed pictures

The throttle linkage on the new side needed to be altered, as the original linkage was obstructed by the oil catcher out of the rocker cover. This was acheived by simply cutting some of it out and drilling a new fixing hole for the throttle cable.

The first thing that struck me, once I started to drive it, was how responsive the engine feels now. I know it should be as I now have 2 throttles opening, but it feels faster due to being more responsive. I can't really notice any more power at the top end, in fact a few people even say it should lose power in the mid range, but what power increase would it need to be to feel it? If I've gained 10BHP would I feel it? I doubt it. The only real issue I have is that the engine will not idle any lower than 1000RPM due to the 2 intakes. I just can't get either one of them to completely shut, so both let air in at idle!! Theres nothing I can do really without boring out the throttle and making new throttle plates for them so they seal. For now I have to live with it.

I've hit 6150 RPM whilst datalogging and I had a loss of around 2KPa, so the theory has worked in that the twin setup is letting enough air in to feed the 5.0L, where as the original intake started to become restrictive at 3000 RPM.

I've replaced the TVR rocker covers with Ford small block "COBRA" rocker covers. I've also bought a metal polishing kit and some flapper wheels, after a few evenings work on the plenum, alternator and brackets this is what it looks like:

Polished plenum pictures with a pair of Ford Cobra Rocker Covers

Sequential Fuel and Spark