Any mechanics / physicians care to comment on the essential differences in performance of a full decat on an OEM exhaust system (and high flow back box) in comparison to a full Milltek/Sports cat/2.5" bore full system.

Ultimately I guess in terms of a "what will give the best" come remap time.

I'm not sure about diesels, but petrols certainly used to require a certain level of back-pressure to idle properly (and still do as far as I know). Assuming this to be the case, the system shouldn't matter as long as this is maintained/compensated for.

Ross is probably the best person to ask.

Edit: That doesn't address your question at all, sorry.

Isnt it different for a turbo? It needs a wide bore to exit the gases as quik aS POS

im not to up on exhausts, but adding large bore exhausts as alot of boy racers do doesnt always help the car. a study a while back showed more than half actually decreased power.

that said, your car isnt standard and the above tends to happen more with small engine cars that werent designed or required to have big bore exhaust.

sorry i cant help with your dilema J but im sure someone will

Jason,

Did your powerflow mod work ok on your pd100?

As you have read I am having problems getting any real power from my elegance estate pd100. People who seem to be in the know on here are suggesting it could be my exhaust, its a july 05 facelift model which is euro 5 compliant and has a different exhaust to 03 and 04 models due to emissions for this euro 5 law.Have checked part numbers and they are different parts.

Michael at Jabba could get no smoke from my car, so we think that this latest particulate filter is cleaning the emmissions up and at the same time causing rather large restrictions which probably wont affect the standard power.

The cheapest option it seems is to go with powerflow, so sorry for the thread hijack but how was yours? I am thinking of straight through pipe to one silencer at the rear.Also do you know if the flange that meets the turbo is the same on the pd130 and the pd100 models, I am thinking maybe I could modiy vrs hatch (maybe blue flame)system to fit my pd100 estate.

Thanks,

Paul.

Can't see there being a whole lot of difference on a diesel really, unless the OEM one is very restrictive (narrow bore?). The Hi-Flow backbox probably just affects the noise so will not have a significant impact

http://www.nsxprime.com/FAQ/Miscellaneous/exhausttheory.htm has a lot of good info, but seems to be focussed on petrols engines.....

Chris

Just a few thoughts......

Its true that some cars/engines do not respond well to overly large bore exhausts........this very much depends on the design and flow capacity of the standard system and the power output of the engine - a 3" bore system on a MINI 1000 is not an advantage!. Given that manufacturers have to comply with noise emission regs most systems are designed to reduce the sound levels the cheapest way, normally by baffled exhaust boxes.

These do inhibit flow, but are used as they are cheaper to manufacture and the sound deadening performance is constant with age unlike most aftermarket sports systems.

Aftermarket systems mainly rely on peforated tube surrounded by steel and fibreglass wools as a means of silencing the exhaust noise, not as effiecient but a straight tube does not impeed the gas flow.

This helps the engine breath better, but there is a point at which too big a bore can cause the gas to 'stall' in the system at low flow rates i.e tickover and waste gases can be sucked back into the cylinders giving a lumpy idle.

My experience with large bore systems is mainly on 205GTi's...I had a custom made stainless steel manifold and 2.5" bore systemon an engine producing over 150BHP (the system was good for around 200BHP) .......ok for around 18 months then the noise levels increased as the sound deadning wools deteriorated.

Anyone into big bikes with sports exhaust will have come across boxes that could be taken appart and 're-stuffed' to reduce the noise levels again.

What should also be thought about is that in general turbo equipped cars generally require less silencing as the turbo itself does a reasonable job of reducing the exhasut noise.

Any mechanics / physicians care to comment on the essential differences in performance of a full decat on an OEM exhaust system (and high flow back box) in comparison to a full Milltek/Sports cat/2.5" bore full system.

Ultimately I guess in terms of a "what will give the best" come remap time.

I presume you mean Physicist or is a Miltek exhaust living tissue? !!! LOL

physicians/quantum mechanics/brain surgeons ya know, the usual ones to know about exhausts.

Striker - In answer to your Q - exhausts never played a role like you say in restriting power - My first remap on my PD100 was 147bhp with little or no mods (no exhaust mods at least) - Then I smashed it up and got new one, fitted exhaust (just decat and powerflow backbox) and filter, and Mike took it up to 154bhp. Then I had a fuelling issue with the ECU, MIke remapped my spare one as I had two, and was running 151bhp up until recently when my conversion took place.

For someone pushing 200 horses I'm wondering if perhaps a bigger bore Milltek would be better than a standard deat and backbox (which works fine really, its just OEM in terms of pipe bore)

A smaller exhaust pipe could lead to a restriction.

Certainly on yours Jason is recommened it.

I was under the impression as well that having a less restrictive air intake & exhaust combined would give the fastest turbo spool-up times?

I was under the impression as well that having a less restrictive air intake & exhaust combined would give the fastest turbo spool-up times?

Yes but you still need some backpressure, or youll lose out on a bit of low end torque.