Two seperate questions
1)Does anybody feel that replacing the inlet pipe would be of benefit,ie is the OEM restrictive?
2)On the classic Scoob it was worth porting the head as the design was quite bad.Has anybody looked at the Sti7 head to see if its similar?

 

Anybody?

 

Deep,

Think you will be waiting a while on this one. Most of us are enjoying Xmas turkey. Just come on here because I can't get to the telly?

 

Merry Xmas Wacky! I've been escaping from the family(and Turkey) from time to time to get my Scooby fix! Unfortunately none of my family/friends are into cars,prefer discussing interior decorating!

 

There is only one way to find out...

Might be worth measuring some pressure drops in the inlet pipe?

 

Inlet pipe... I'd have to say yes, it's restrictive compared to some aftermarket jobbies, but then they are expensive for what they are & may well not be worth the cash.
Inlet manifold? Um, dunno there

 

A friend fitted a locally designed header/up-pipe - great for track work, but really seems to hamper spool up (I guess this is down to the design, same set-up moved spool point 3-500rpm up on the classics too).

He took it off and we'll try again now we can map around it.

Only way to know for sure is to try it - if you plan on a remap anyway, fit the headers first

Richard

 

Deep,

the inlet pipe, even the after market ones, are restrictive, as was proven quite graphically by ChristianR when his literally collapsed and prevented him from making much over 350 BHP on the rollers. I ditched that item years ago, replacing it not with an aftermarket one but a combination of teo samco pipes... a 70 to 56mm straight reducer, and a 70mm 90 degree bend. The two are attached to eachother with a length of 70mm stainless steel tube (hence no collapsing issues).

On a classic you need to relocate the PS reservoir to allow such a "large" tube to get to the drivers side wing area from under the manifold, but you may not have that problem. There will probably be other things in the way though, like fuel pipes (I chopped all mine out and replaced with larger bore rubber pipe).

With regard to the exhaust headers, they haven't changed fundamentally in design, so it would definitely, beyond a shadow of a doubt, be worth porting them. The stock ones have mounting holes somewhat larger than the bolts (this allows for thermal expansion without shearing off the bolts), which allows the header to be mounted onto the engine "misaligned". The exhaust port and header internal diameters are about the same, but because the header can be fitted offset, you get a "lip" that disrupts gasflow . By porting the headers, there exists a smooth flow for gas regardless of whether they are misaligned or not. It is important not to go too wild though, as there will be a discontinuity in diameters, and anyone who has studied transmission line theory, any such chance will result in a change in characteristic impedance and phase velocity; such step changes cause pressure wave reflections which could reduce cylinder scavenging.

Additionally, there will exist a "lip" between the header and the head after porting, which impede gas flow back into the cylinder (the lip will create turbulence which will extend well into the "open" area"). This is again a step change and will cause pressure wave reflections back down the exhaust system, rather than into the head (where you don't want it).

All in all, there are more positive effects of porting than there are negative ones. I remember when I ported mine (back in Jurassic times ). To the best of my knowledge I was the first to try it, after Pete C and I looked at a set that were off an engine and thought "what a naff design!"... I spent a whole evening porting a set, then fitting them the next day... I think I damaged my lambda sensor while fitting them (this was before moving it to the downpipe, earlier cars have them in the headers), I remeber adding fuel and it not making much difference... I "found" the right AFR eventually without the sensor showing it as rich, the fact that all four wheels were spinning in third was a fair indication

Other than porting standard headers, I also have a set of MRT headers for sale; with these I can genuinely say that they required an additional 25% fuel, and were maxing out 550cc injectors (with a good fuel pump) on an STi IV with an MD195 hybrid turbo (running a conservative 1.5 bar). If you do the maths that's gotta be the best part of 400 BHP. They do look a little odd and feeble, but they work really well

Cheers,

Pat.

 

Pat would the MRT headers fit my car? Would there be any loss of power lower down with these do you think? When you say feeble you d'ont mean looking like they're about to crack do you?
Cheers,Deep.

 

MRT headers are made from pretty thin tubes, from what I remeber. Which is, of course, a good thing
So, Pat, these headers how much?

 

Deep,

To the best of my knowledge, they *should* fit, I would need to do a bit of digging to be sure, but as far as I can remember, the up pipe is the same as the early car (we've fitted stainless up pipes to cars which had normal ones and they fit) so if that's the same then odds are everything else up to the turbo is the same too.

With regard to low down torque, I don't recall any reduction, but then this was on an MD195 which is somewhat large and lacking in low down grunt anyway... difficult to say how your "stock" IHI is gonna react, but we can always regain some torque with altered fuelling and ignition, should there be a noticeable reduction.

When I say feeble, I mean they don't look very impressive, anorexic would be a reasonable description With regard to cracking, they have cracked in the past due to a manufacturing booboo... MRT weld the tubes together where they bend round and then go up; this is to reduce noise (rattles). Over time thermal stress fractures the pipes at this location. Suffice to say that they are no longer welded together at this location, and that the pipes have been repaired by a TIG welder, so they're stronger there now than they were when they left the factory I used the minimum amount of current necessary to get the metal flowing, so as not to create any additional stresses in the base material. The pipes were adjusted such there was a little clearance between them to stop any rattles. Additionally, the slip joints in the cross pipes have been replaced (they MRT design was quite poor and would blow) by Hayward & Scott for a much longer double overlapped design, which has performed flawlessly.

Nom,

The early MRT headers (which these are, the later ones are more of an equal length design) have a tapering mouth; they match the gasket at the head, and then taper down to a smaller tube diameter before they bend. The smooth reduction helps inprove gas speed while not creating undue turbulence and flow restriction.

Price wise I guess I'de be looking at about UKP 600.

Cheers,

Pat.

 

Pat depending on other plans I might be interested.I'd like to have a look first and then start haggling!

 

As am I ... which would mean there would be a nice set of HKS headers freed up

 

Nom,why do you want to change from the HKS ones?

 

Mainly, ahem, I like playing

I have a knack of trying a heap of different products & then going back to the originals... great way of spending money ! (in this case that would be the HKS!)

Also, keeping the 2nd hand market stocked. That's a second hobby that naturally follows the first