hi would i be able to fit equal length headers to my98 impreza without getting a remap as it works out very expensive, bloody 98's!!!!!!!!!!!

 

You've just inadvertently told us that you're running a more or less standard 98MY Impreza Turbo 2000. As such, the short answer is not to bother, for a couple of reasons.

Firstly, correct, you will need a remap to get the best out of aftermarket exhaust manifolds.

Secondly, most aftermarket manifolds are designed for larger turbos making more power than the TD04 on your car and as such, even with a remap, you may well find that your car runs better on the standard bits than what you want to buy.

Given where you're at at the moment, fitting an aftermarket exhaust manifold would be a waste of money.

 

sorry should ov said its got an open decat and straight through pipe an did have a vf28 which i removed 4 odvious reasons and a green panel filter i will get it remaped (apexi fc) but just gettin it up to scratch at the min so just wondering if this will end up blowing it up in the mean time its not used very often as i work away in the week?

 

A few seconds on full chat and you run the risk of damage. Causing serious engine damage is quite easy, it does not matter how infrequently you use the car, just it takes a little longer for the damage to occur if you do not use it often. It is not dependant on what day of the week you drive the car so working away during the week only helps to delay the potential for damage.

To be serious, if you change headers to tubular, injectors, turbo or intercooler and do not remap you run the risk of picking up a piston in the bore or worse. Drive off boost until remapped. There will be exceptions but is it worth the risk?
As a minimum, ask some competant person with WBO equipment to check out your car in road conditions.

 

OT I know, but what does the phrase "picking up" actually mean and/or imply?

 

Does this apply for a straight through exhaust aswell?

 

Usually means the outside diameter of the piston beginning to melt and starting to gall against the bore - a process that quickly becomes a vicious circle, as aluminium deposited on the bore creates even more friction and heat as it rubs against the piston, which encourages even more melting...

However in practice, and especially with cast pistons, the other common failure mode is cracking of the ring lands, which will immediately reduce compression and will themselves eventually start to gall if left to their own devices.

Changes to the exhaust are usually less critical to stability than making alterations "nearer" to the engine but there are always exceptions. It's also often the case that older engines are already carrying little niggles here and there, so that a modification you could have got away with when the car was brand new might now interact with an existing (sub-critical) problem to create a more significant one.

The only way to be certain is, as Harvey has already suggested, to get someone with some data acquisition kit to check your car over.

 

Exactly as above. Generally you can change an exhaust system and a remap can be avoided although you will not get the best out of your mods until your remap.
Fitting tubular headers and not remapping and you have the possibility of picking up a piston in the bore. On WOT there is a lot of heat so the aluminium piston expands more than the steel cylinder to the point that the piston is tight in the bore and the thrust face is in contact with the bore which in turn creates more heat. Catch it in time and the bore is covered in aluminium from the piston and if you are lucky you can get away with a new piston and honing the bore. Usually however you will need a rebore.