When do headers become restrictive?
#1
When do headers become restrictive?
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.
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.
#2
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.
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.
#3
Scooby Regular
iTrader: (13)
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.
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.
Last edited by joz8968; 29 August 2015 at 12:05 PM.
#5
Scooby Regular
iTrader: (13)
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...)
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...)
Last edited by joz8968; 29 August 2015 at 12:20 PM.
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#9
Scooby Regular
iTrader: (13)
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?
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?
Last edited by joz8968; 29 August 2015 at 02:04 PM.
#11
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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....
#15
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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.
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.
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