Skyline Owners Forum banner

1 - 5 of 5 Posts

·
M's Factory
Joined
·
5,240 Posts
Discussion Starter #1
Consider this a continuation of yesterdays thread on exhausts. If there are mistakes i apologise, but I thought it best to continue on some of the points raised.

I hope to give a clearer answer to the question raised about the catalytic converter also and how on an off road situation on a track it can give benefits of more power and free flow to the engine.

Exhaust ( Tip 1 )

The first step should be the exhaust. In order that the cat gets heated quickly enough, pipes in front of the cat tend to be small (reducing their surface area and so conveying heat more quickly to the cat on start-up) and so restrictive.

Just to clear up this doesnt matter whether it's a turbo or naturally aspirated engine, the first section of exhaust is usually too small for best power.

Then there's the cat itself - usually the single most restrictive element in the exhaust. This can be replaced with a "high-flow" design (the term's meaningless without comparative data but if you go up in pipe size you'll pretty well always go up in flow capability as well), although emission performance will be altered.

Before you ask, no i dont have any data to prove this, but there are plenty of companies out there who have, ie people who provide Sports Cats Etc.

Behind the cat you'll find a muffler, or a resonator.

These days, it's pretty well only the size that differentiates them - many mufflers are built just like resonators!

A good straight-through muffler causes nearly no restriction and gives a sound quality that's usually pretty pleasing, and running two of them in series will give even less noise and usually stop resonances.

This is because the flow of a well-designed straight-thru is so good, there's no power penalty in fitting multiple units.

Stainless steel? ( I hear you ask )

It's touted as a huge upgrade but in reality it just makes the exhaust look prettier and last longer. But both terms are relative - if it's under the car getting covered in grime does it matter much whether it's polished (unless it's a show car of course), and even a mild steel system will last for years - 10 years isn't uncommon if the car is not driven for short trips all the time.

Mandrel bends are another thing that people get their rocks off over, but the flow variation in mandrel and press bends is relatively mild, until the bends become sharper than about 45 degrees or there abouts.

If the exhaust can be made with just shallow-angle bends, mandrel (this could be pricey!) ain't worth it.

The bendier the exhaust route, the more important mandrel bends become.

On an atmo car extractors - individual tuned-length pipes coming from each cylinder - can give some gains, but it's in this area that many OE manufacturers have made major gains with their cast iron designs.

Check under a range of modern bonnets and you'll see some great shapes - all in original cast iron.

The first step should be an exhaust from the turbo or factory manifolds back ( resulting tip ).

A good exhaust will release more power in pretty well all cars, and in turbo cars will have the additional benefit of bringing up boost faster. Additionally watch out when you have changed these components as you shoudl notice your boost will be slightly higher than previously measured before the change of exhaust component, this is due to the fact is is easier for the turbo to flow resulting in a higher boost level, be sure it is still within safe limits at this point.


Intake ( Tip 2 ) ( H&M is for a leading brand of air conical filter )

The days of people ripping out the airbox and sticking a great big exposed conical H&M under the bonnet are now thankfully pretty well past - nothing much wrong with the H&M but plenty wrong with sucking hot air from around the engine ( Cough Cough Nova ).

If you want to use a new filter, best to box it up so that air can only be drawn from outside of the engine bay - good for power (both because of the different air density and lessened likelihood of hot air causing knock retard) and good for engine health (that knocking again).

However, unless the standard airbox is a godawful squashed design, it might be better sticking with the standard box and factory filter and simply whacking a bloody big cold air feed to it. It's simple, cheap, almost always very effective, and doesn't degrade the factory filtering. Of course, the filter will tend to get dirty quicker, so should be inspected more frequently.

Also you wont get your wonderful woosh woosh and spin up noises which is after all , what you all want.

Nearly all cars already have a factory cold air intake, but it's usually too small for best results.

Typically a 3 or 4-inch pipe should be used if the pressure drop through it is to be minimal.

A Cold Air Intake will give better throttle response as well as top-end power, and will make a noticeable change especially in hot conditions.

Im off for a coffee now.
 

·
Registered
Joined
·
2,433 Posts
Very nice thread! I love this stuff. Communally, we all know a HELL of a lot about cars, maybe without realising it. Good to see some thought provoking stuff rearing its head.

PS Where did you dig up this stuff?
 

·
Registered
Joined
·
469 Posts
Great tips but I disagree about keep the OEM filter - a well made aftermarket panel filter will flow a lot more air than the OEM filter for most cars (no direct experiences of skylines though).

And ... a well designed oiled filter will do so whilst filtering the air more effectively than a dry paper filter - though obviously they're more hassle to maintain.

Is exhaust back pressure an issue with skylines ? I know that a lot of tuners think that Evo's need some back pressure for best performance - does the same apply here ?
 

·
Registered
Joined
·
7 Posts
with the exhaust. I've got a 3" HKS Priest from the turbo back, but with compliance they've dumped a 2" cat in.

How much difference do you think swapping that to a Hi Flow 3" will make?
 

·
M's Factory
Joined
·
5,240 Posts
Discussion Starter #5
your car will just feel smoother, but will flow more, so you will make more power at the turbo as in boost, and get there slightly easier on the engine. Engine should make more power, torque. Not much , slightly.
 
1 - 5 of 5 Posts
Top