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psyolent wrote:yeah me and vlad were talking about it the other day.
i did similar on a vt v6 and lost torque, but, it had twin cats twin muffler and joined before the rear resonator.
i think i will just stick with the Y piece for the meantime.

Shouldn't you be able to retune the timing map a bit to make back some of that torque?

BTW, nice colouring

What we talked about was loss when using a full twin system right to the rear as 2ndary scavenging and velocity is lost in such a system.

V6 dont benefit much for a twin system as they are already even firing and nearly all the gains are made at the primary.

with v8 the primaries dont work correctly due to odd firing and they benefit a lot from twin systems with a cross over.

My theory is twin cats and then merge into a single 2.5 from there. The 2ndary collector can actually do its work when the cats are moved before the collector.

re: tune.............thats something i didn't do in the VT. it had a 'chip' but whatever that means who knows

zactly right vlad.
thinking about the VS, they had that central cat and one muffler setup. which is interesting. actually i think the VT on are the same too?

vlad01 wrote:What we talked about was loss when using a full twin system right to the rear as 2ndary scavenging and velocity is lost in such a system.

V6 dont benefit much for a twin system as they are already even firing and nearly all the gains are made at the primary.

with v8 the primaries dont work correctly due to odd firing and they benefit a lot from twin systems with a cross over.

My theory is twin cats and then merge into a single 2.5 from there. The 2ndary collector can actually do its work when the cats are moved before the collector.

I just put a full twin system (LS exhaust) on our L67 VX (already had twin cats and mufflers into single system) and I don't think there been any noticeable loss in low RPM torque.

I'm still yet to play around with the timing but I'm sure there is more to be had then the factory tune gives us.

Could always start with the XU6 tune. I done one for a bloke once on a VY. Used the XU6 timing and adjusted some fuelling and he was very happy.

My base tune is The1's enhanced tune which is based on the HSV code

In the lower areas the timing maps are identical between Holden and HSV, it's only at higher airflow and rpm areas it has more timing really from what I can see.

Sounds like a good start then.

i have some work to do with tune. need to learn a bit first. roll on next weekend.
in other news dropped in the radiator, picked up some new hoses and pulled the electric fan apart to paint/clean it up.
been going a bit slow this week, not a good week for sleep

Is the motor modified?

dylan, no. its got pacemakers and 65mm TB. no bellmouth. ecotec injectors. so not really.