Let's take a look at the factory exhaust parts first. Below is the original V6 downpipe set - N/A cars were first off the production line. Problem with a transverse Vee engine is the pipework from the rear cylinders. With the 2GR rotated downwards/rearwards, that downpipe runs under the engine/transmission unit and then has to do a 180deg turn to merge with the front downpipe. You really need the front and rear cylinders to have the same pipework lengths/back-pressure to deal with. BUT, this early set had a difference of 9" (228mm) between rear and front downpipe lengths. Not good.
Lotus/Janspeed soon wised up though and they managed to pick up some extra mm's on the front downpipe so that both cylinder banks had the same exhaust back-pressure to deal with.
At 51mm diameter (2") it's not ideal for a 3.5Ltr N/A V6 putting out some 240bhp. Look at that disaster of a "merge" collector. Hold the two downpipes together, fill in the gap with some squirt-gun welding (MIG), then use a cheap pressing to cover up your crimes. I've seen leaks from there several times.
If you're looking for more power, you replace that mess with the 2bular 54mm diameter design below. I took the time to build a little cutting guide for the 2-1 merge - below.
For a SUPERCHARGED 3.5Ltr V6 you need a 57mm bore for your downpipe set. Like the one below! Only 2bular offer these diameters . Only 2bular differentiate between N/A exhausts and supercharged exhausts.
Again, I took the time to build a cutting guide for the bigger 2-1 merge for the supercharged installs. Moving up two bore sizes on the factory pipe needs superior pipe-bending and tooling. You need a nice round, smooth radius to keep the gas-speed high and turbulence free. No other manufacturer in the Lotus market builds anything like this. I see squashed bits of tin for merges, wrong bores. I see tight, welded bends giving a different back-pressure front-to-rear - not good.
I was intrigued to see the latest Exige 380/Evora 400 downpipe design.
Bore increased from 51mm to 60mm! The final bend into the system and the system itself (when the exhaust valve is "open") up to 76mm. Why? Each new V6 model that appears apparently has a power increase to accompany the nomenclature. Thus an Evora 400 has a claimed 400bhp and the Exige GT430 a claimed 430bhp. Those nasty little UTC's in the factory log-manifolds are under more and more stress. But Lotus can't remove them. Solution? Reduce the "back-pressure" in the previous smaller-bore downpipes and 63.5mm system. Unfortunately, you lose a lot of boost when you go up several sizes in exhaust bore - hence a power loss when the 76mm exhaust valve is opened. Consequences - there's always consequences. When I tested my 70mm bore Track system against the 76mm factory system, the gain was 5bhp. Not much but it proved that the smaller-bore increased the boost and didn't lose power. More gains would have been realised once the ECU adjusted for that increased boost but it was just a snap-shot test.
If you're looking for maximum power from the supercharged V6 2GR motor, you need the combination of 2bular 3-1, 48mm stepped manifolds (headers!), into 57mm downpipes then into a 70mm exhaust system. Anything else is wasting your hard-earned cash!
It absolutely baffles me why an owner would spend (say) 5000GBP on an aftermarket tune giving (say) 50bhp. That's (10bhp per 1000GBP spent), then fits a restrictive(quiet) exhaust system which drops that power by at least 12bhp! That's 1200GBP thrown down the drain!! Or this -
I know UK track noise-limits are strict but strangling your motor to help meet them is just insane.
Having mentioned manifolds (headers!) let's take a look at the factory offerings.
Not the best for performance - despite a TLF moderator's claims. Lotus HAVE to fit these manifolds but I bet they'd rather not. Never listen to a forum moderator - they know nothing about everything. Especially when they preface a statement with "the factory told me" - then you KNOW they're an imbecile.