Maximum Horse-Power Without Stress?

[SteveAvery]

I want to increase power only by adding a cold air induction system and a sports exhaust system with a 'Fast 'n' Loud' / Mustang-type switchable opening exhaust valve before the two rear cats. I'm guessing that this could take it close to 350 hp, perhaps. Does anyone have a notion of the maximum horse-power that the SC430 can take without the need to uprate or strengthen anything on the car?

[ColinBarber]

I'd say the engine internals are good for 350-400 bhp but I doubt you would get near 350 bhp with what you are suggesting. The intake, without an ECU mod, will only get you 5 bhp. With a straight through exhaust you will lose low end torque, and again without adding in some way to retune the fuelling you won't get too much benefit.

[SteveAvery]

I'd say the engine internals are good for 350-400 bhp but I doubt you would get near 350 bhp with what you are suggesting. The intake, without an ECU mod, will only get you 5 bhp. With a straight through exhaust you will lose low end torque, and again without adding in some way to retune the fuelling you won't get too much benefit.

That's very disappointing. It's greater acceleration at low speeds that I want. I thought that a sports exhaust system with sports cats would give me that. Or are you referring solely to the switchable opening valve that I mentioned, when you say that I'd lose low-end torque?

[ColinBarber]

If you replace the cats with high-flow ones then you shouldn't lose torque, its it you went straight through that you may. People in the US seem to believe that the main restriction is with the exhaust manifolds, getting some new headers and a more free-flowing exhaust could give you some power gains but you really need to make use of the potential by using a fuel computer to mod the existing programming.

Take a look at the swift racing intake for the SC430, that supposedly gives good gains as it includes an ECU mod.

[SteveAvery]

I think that, thanks to your advice, I've come to a decision.

I'll drop the switchable opening straight-through valve.

I'll fit:

- the SR intake and ECU mod,

- equal-length headers,

- stainless steel sports exhaust system with sports cats.

Thank you.

[Neil E]

Good luck with it.

PPE make the headers in the US to fit to the original cats but I'm informed they haven't produced any for the rhd SC430 yet. Their manifold pipes don't appear to be of equal length so I can see the logic in thinking that they could be improved upon by another specialist manifold builder to attain more power. 350 may be optimistic but from what I've read, significant gains have already been achieved by US owners with similar mods using the PPE headers.

[SteveAvery]

Hello again, Neil. Thanks for that info.

It's taken a while and input from several knowledgeable enthusiasts, but I think that, finally, I'm getting to where I want to be.

[CraigIson]

... Just run a 50hp shot of Nitrous :-D


A well designed exhaust system will be the biggest help to free up power, Equal length headers would be the best bet with decatting. . Remapping or running a different ECU is a must, And tbh i think you would have to change the cams also.

Its hard to get extra power from a NA with out having to spend silly amounts of money. You could always supercharge it. Which gives nearly a 75HP increase with out any supporting mods ... but expect to pay over £8k for the kit with out fitting

Good luck :-)

[SteveAvery]

Thank you for the summary, Craig, and for the note about the cams. What the reasoning behind the necessity for a change of cams, then?

[CraigIson]

Changing the cams will allow a much longer lift duration for the valves. So it allow more air/fuel mix to get into the combustion chamber, giving a bigger bang = more power. If you also change the strength of the valve springs it will help raise the rev limit (As long as the ignition system is adjusted to match) So you have more revs to get power from.

IF you aggressively cam a v8. the Idle does go a bit ... ummm ... well you can see for yourself ...

The idle goes all old school v8 :-P

[SteveAvery]

Oh, dear. The words "slippery slope" spring to mind, and I certainly don't want the problems heard from the car in the video. Perhaps I got the mistaken impression that new cams were necessary when installing sports headers and exhaust. If it's OK to install the exhaust system without changing the cams, I'd much rather just do that. You all probably think that I'm naïve. That's because I am.

[alphacat]

Any extra power on a 430 SC will make it dangerous. Its a great ride but road holding even on the mk 2 isn't up to over 300bhp even with the best tyres fitted. No point in these sort of mods without doing it properly and that means so much money your better off changing cars.

[Stuno1]

Can't help with your question but contact Hayward and Scott as they will build you a very high quality system.

[SteveAvery]

Thanks for the valuable advice. Food for thought, indeed.