I'm curious to know at what power level do standard headers become an issue?

I've seen people run 400ish on completely stock headers yet other people saying you have to buy aftermarket/harvey etc. I've also seen people talking about porting standard headers but what does this gain?

If anyone has real world figures and not just guesstimates I'd be interested to see what difference, if any there is.

 

Don't know if it's relevant, 353bhp 346lbft with original catted up-pipe (cat removed) and std headers.

 

Until someone posts some kind of meaningful comparison test, then I believe it's 'common conjecture' to move to tubular style (whether single- or twin-scroll) from about 380bhp. This was certainly the advice the late, great Harvey Smith (RIP) passed on to me, when I needed some new ones (and was aiming for 380+). So I bought, IIRC, a slightly second hand set of S.S. 2-bolt GT Spec I jobbies, plus his latest design trick uppipe, off him.

That doesn't mean to say you won't make beyond that on std cast jobbies(?); just that the tubulars are allegedly less restrictive from that kind of power level...

Just don't be tempted to buy eBay cheapo specials... Stick to GT Spec (I think they now do v.II, and which might be 3-bolt - can't remember).

Or even better, splash out on the RCM 3-bolters - considered as some of the best out there.

 

If i'm going to splash out I'd like to see comparisons, mainly between stock and aftermarket but also between ebay cheapys and reputable brands.

 

Sure.

But I'm not certain there is any such concrete info out there, as such(?)

Harvey, himself, used to conduct lots of scientific tests on components...and may well have done so for std verses various brands of tubulars. If you search for his archived threads, you may discover the info you're looking for (enter 'harvey' in the member box...)

 

Cheers mate, i've done some digging around but a lot of info is hearsay. Ideally like to see some people running over 400 on standard headers and their take on it or some mappers advice.

 

Speak to the guys at API.

Send Olly at RCM, and Paul at Zen an email.

Could do a lot worse.

 

My car Was on 427bhp with stock headers and sti top mount.

 

Yeah, New Age STi's are good for c.430-450bhp on std TMIC and manifolds.

The New Age's SS design is basically the same as the Classic GC8's manifolds, so why is there seemingly a difference in their restrictive qualities?.... Or ISN'T there?!

Is it because the New Ages cylinder heads are far more efficient?

 

427 was at 2 bar

Fitted RCM headers and up pipe, also fmic remapped and got 443bhp at 1.7 bar. Much more efficient..

 

As a noob here I'm slightly confused - the question is, at what HP do you need to upgrade your headers? ...Wouldn't a good set of headers be the starting point? Sorry if I seem to be simplifying things....

 

so a 16bhp gain from a fmic and rcm headers/up pipe?

Be interested to know which accounted more for the gain

 

Yes but out of alot less boost!!

 

The only people with the figures to back up the claims are Killer B who have tested their manifolds against alot of other brands....

 

Harvey's ported headers are OEM standard headers re-ported. Mine managed 425bhp with a 2-1/2" decat exhaust before cracking and being replaced with GT2 Spec tubulars.

As the same car on the same rollers can register different power results from day to day or even hour to hour it must be very difficult to quantify exactly what part change does what, especially if the change is relatively small.