scott tomcat

ok almost stock uk car, has slp lid,ramair air element and magnex cat back and 3.73fd and suspension mods.
Cars quick and launchs really well but feels a bit breathless coming up to the 6k change rpm.

Cat back exhaust looks really good flow, but the stock front y pipe section to me looks very restrictive and small.

I was thinking of getting this section remade in 2 1/2" with magnaflow universal high flow cats, but retaining the std manifolds as these came out fairly well in tests I've seen.

Anybody done this and what sort of power gains and did it pick up?


thanks
Scott

RPM WS6

iTrader: (3)

Not sure what tests you've seen, but the stock exhaust manifolds aren't good at all compared to LT headers; in fact they are the biggest restriction in the stock system. You won't gain much with aftermarket cats and Y-pipe attached to stock manifolds, the cost likely won't justify the marginal gains. If anything, you'd at least want to go to an ORY to gain a bit more power.

By ~6,000rpm, the stock cam is running out of steam so a bigger exhaust isn't what you need to gain real power in that range and above - you'd want a more aggressive cam, stronger valve train and headers/intake to improve flow.

scott tomcat

Thanks Yeah I realise headers would be an improvement but -pretty expensive over here with shipping and guessing not nice to fit without lift.

From what I've read people seam to gain 25bhp with lt headers - however surely a fair lump of this maybe 10bhp must come from the replacement y pipe/high flow/no cats as these are always replaced at the same time?

I need to get mine on a ramp as front section looks very small, not sure if uk cars are same as us cars as they were quoted at less hp?

It also looks a bit rusty.

I have a good exhaust fabricator close by who could custom make this section for probably less than ordering/shipping from usa..

Yeah cams would be nice out the question at the moment but if I can get it to be a bit quicker to the change rpm it will help

had it dynoed at 325bhp but power was dropping over 5300rpm
have since added slp lid and going to do free cold air mod and port throttle body and smooth bore pipe hopefully this might add another 10bhp


Scott

murphinator

iTrader: (2)

assuming this is an automatic car your best bang for the buck mod that totally transforms the way the car pulls is a quality convertor in the 3600-4000 range - car will be night and day different

RPM WS6

iTrader: (3)

The Y-pipe/cats get replaced or deleted during a header swap due to the fact that they don't bolt up to the headers, so replacement pieces either come with the headers or are fabricated. Yes, once LT headers are added the size of the factory Y-pipe and cats would become a restriction, but prior to headers there is no significant power to be gained by swapping them. Any gain from a cat/Y-pipe swap on a stock manifold car is marginal at best, not even 10rwhp would be likely. But, that's on a US-spec car. You might be right about the UK-spec - I'm not sure what might have been changed regarding the exhaust system, so perhaps your results would be different than what's typical for US cars.

Other than internal engine mods or some sort of forced induction, headers would be the most helpful thing you could do to increase horsepower at this point. But the stock cam will still become a limiting factor at high rpm ranges.

scott tomcat

ok thanks

I'll finish the free mods first then see how it is , try a 1/4" run and go from there

I don't really fancy the torque convertor don't want to ruin it for the road and fuel bit dearer over here!

Also my local 1/4" is concrete runway so I doubt it will grip going off at tickover

cheers
Scott

JD_AMG

If you are after 1/4 mile times then you would be silly not to do long tube headers, they will make a significant, noticeable difference.
Also not all converters ruin the way the car drives, they will make a huge difference in the way the car accelerates and launches. Dont bother with a cam if you have the stock converter, you will be leaving a lot on the table.

farmington

iTrader: (14)

If I had a stock car and wanted to do an exhaust on it today I would do the Hooker Blackheart system hands down. If you get their 1 7/8 mid length headers, they go on way easier than longtubes. The whole system is the way to go. A friend has this on his car and I'm jealous of the nice sound.

thatoneguybriz

iTrader: (2)

^This