Short induction experiment for the Speed Six Cerbera

You may be reading my blog thinking he just polishes it, drives it and takes photos; and while I do enjoy all of that – I do have a naturally curious mind.
If you know your Cerberas, you will know that the v8 from the factory was not well mapped, in fact it goes further than that, it left the factory with long induction hoses that choke the power.
Many years ago Joolz addressed this and developed a short induction kit; essentially a set of shorter hoses, that when combined with a remap, unleashed a little more power.

But what about the Speed Six Cerbera?

Joolz has also had some success with other Speed Six TVRs, namely the T-cars, and currently produces airboxes with short induction that have proven to give 10-15 BHP on the top-end without sacrificing any power losses lower down the range.
So why isn’t something similar available for the Speed Six Cerbera, was it a case that TVR got it right, or is it a case of no one knows?
What I do know, is that there’s nothing on the market today, and when I asked Joolz why not, he said it’s something he hasn’t investigated, mainly because he hadn’t access to a Speed Six Cerbera to experiment on. And remember, unlike the v8 where the induction hoses are accessible and relatively “simple” to adjust hose length, the Speed Six Cerbera doesn’t have hoses. The airbox sits directly on the throttle bodies, so the induction wizardry takes place inside the airbox.

Cue the experiment

I’ve been to see Joolz a couple of times, he is one of the nicest people you will ever meet, and is a fountain of knowledge on safely squeezing extra power out of TVRs. So when he agreed to conduct an experiment of the S6 Cerbera, I jumped at the chance!
We agreed that if I provide the car and the airbox, he will carve up the airbox, play with the induction, remap & dyno, and see if there are hidden gains.

Step 1 – Find an airbox

airbox for short induction experiment - ebayThese are not easy to come by and rarely come up for sale – but after some patience, one popped up on Ebay, so I grabbed it. I feel bad about destroying one of these, they are afterall limited in numbers – but it was done in the name of science & curiosity. Once received, I immediately shipped it off to Joolz.

Step 2 – Cut it open

inside of old airbox
Joolz enlisted the help of Plasticman (Dave Hillis, the legend of fibreglass) to modify it.
What was found inside was interesting. Notice trumpet 6, how much larger that is than the others.
Was this by design, or a TVR foible? Is it just this airbox?
Drop a comment on this post if you ever get a chance to look inside another.

Step 3 – Shorten the trumpets

inside of modified airbox
Plasticman under direction from Joolz shortened the trumpets by around 2.5 inches, this models the logic of the short induction airbox Joolz has running on his Tuscan racer.

Step 4 – Dyno & Mapping

modified airbox dyno resultI then took the car to Joolz and we did a number of back to back dyno runs and Joolz spent a few hours remapping.
The result was interesting.
At peak power, there was a gain in Horse Power; this was what we were hoping to see.
The % gain was also consistent with other short inductions.
But unlike other short inductions, it came with a trade-off loss of power in the mid-range.


The plan had been to use the access panel cut into the airbox, to easily swap the trumpets with different lengths, and continue experimenting until max power had been dialled in.
Had the first experiment resulted in only changing the peak power (in either direction by any %), then it was deemed it would be worth continuing experimenting with different trumpet lengths. But when the results showed it immediately negatively impacted elsewhere in the range, it was decided not to continue.

It seems TVR got it right straight from the factory

I wouldn’t call this a failure, because I now know the answer to something that has long eluded me; and besides, I got to play with 2 legends in our space.

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