BMW M5 Forum and M6 Forums banner

1 - 13 of 13 Posts

·
Registered
Joined
·
109 Posts
Discussion Starter · #1 · (Edited)
Hayward and Scott have just done some work for my Subaru, and i was thinking of asking them to do a catback for the M5.

Anyone interested in a group buy? I should be able to wrangle a discount from them :)
 

·
Registered
Joined
·
1,618 Posts
Who??
 

·
Registered
Joined
·
1,618 Posts

·
Registered
Joined
·
109 Posts
Discussion Starter · #5 ·
Not sure, never dealt with them.

As for the price, i would need an idea of numbers before approaching Ian at H&S
 

·
Registered
Joined
·
1,832 Posts
My 3.8 came with a H&S CAT back and it was shockingly bad.

Very poorly built, created numerous flat spots in the rev range and different loads (these went away when I went back to standard) and it was horrible under cruising speeds.

I've seen some Jap stuff recently and the internal and external finishing is pretty poor to say the least.

It's not anywhere near as good as the Supersprint or Eisenmann stuff.

Just my experience mind you, I'm sure others may have had better but going by what I've seen I cannot recommend them.

Sal
 

·
Moderator Emeritus
Joined
·
4,273 Posts
Sal is absolutely correct here.
This manufacturer cannot produce a good n/a system as witnessed on several
n/a vehicles over the last 7 years.
They make them fit & they make them noisy.
(Those with engine transplants & rare cars have little choice here)
The FI systems work but that is not difficult.

Naturally aspirated exhaust design & manufacture actually requires some
Science.
Nil atmospheric back pressure is actually a disadvantage for most vehicles.
Our vehicles require a specific Kpa figure to work properly & allow the manifolds
equal length headers to use the engines firing order to scavenge exhaust
gas from each other.
The Length & diameter of the exhaust & the position of the cats are no accident.
Pulse separation of the exhaust gas is tuned & back pressure figures
calculated & measured.
There are basic first engineering principles to designing an exhaust.


In deference to this, the Forced induction vehicle is operating on a different
extraction technique & is using Heated exhuast gas energy to spin a in-stream
turbine wheel.
Therefore, its generally accepted that for fixed turbine geometry FI vehicles,
that once MAP exceeds atmospheric, any excess pack pressure will create
a heat energy drag on the exhaust turbine wheel & restrict power & throttle
response.

It's much easier for the aftermarket to produce a large intermediate pipe
with a oil drum sized rear absorption baffled muffler, that produces more
noise, heat & resonance, knowing that they cannot fail in making more power,
if as is often the case, the engine will be running more MAP with a resulting
increase in exhaust gas temp & flow.

It's clear is that those making these aftermarket parts love an uninformed & ignorant public.
Even better, the public don't appear to want the knowledge, even when it's
given to them on a cyclic basis.

Farrell
 

·
Registered
Joined
·
1,063 Posts
Interesting post Farrel thanks!

OT: So in your opinion does an Eisenmann Race back muffler do more harm than good?
 

·
Moderator Emeritus
Joined
·
4,273 Posts
Hello.
The muffler you mention will have no negative effect in my view, assumimg that
the rest of the system is present & working.

Due to this mufflers different internal baffle arrangement & material, it will be louder,
but little else, & that is what some owners want.

Farrell
 

·
Registered
Joined
·
1,289 Posts
If you want a recent, real world example, a friend recently bought an Accord Type R and fitted an aftermarket exhaust (with a cat replacement).

The car felt terrible - went on the dyno and produced about 160BHP at the flywheel.

My tuner told him to go get his original Honda exhaust and come back.

The car then gained 50BHP and returned roughly factory figures!

All because the aftermarket exhaust was so compromised, even though "it looked great".

That's serious, serious figures!
 

·
Registered
Joined
·
109 Posts
Discussion Starter · #11 ·
Very Interesting, have to say i've never had a problem with the F/I stuff they have done for me, but they have never done any N/A stuff for me.

Considering the Eisenmann system is only slightly more expensive, that might be the way to go, but i'm not convinced by the exhaust tips, really want some that look completely standard.
 

·
Registered
Joined
·
1,832 Posts
Hello.
The muffler you mention will have no negative effect in my view, assumimg that
the rest of the system is present & working.

Due to this mufflers different internal baffle arrangement & material, it will be louder,
but little else, & that is what some owners want.

Farrell
I wish I could confirm this but on 'other' M power cars I have lost upto 10 bhp on a dyno (rear wheel figure) with Eisenmann. I am not the only one who has seen this on M power cars.

With Supersprint we nearly always get an increase in power and never a loss.

Unfortunately the tail pipes on the Supersprints are not to everyone's taste but this can easily be rectified to make them look like stock. This is where H&S could be very useful.

Sal
 

·
Registered
Joined
·
1,832 Posts
Very Interesting, have to say i've never had a problem with the F/I stuff they have done for me, but they have never done any N/A stuff for me.

Considering the Eisenmann system is only slightly more expensive, that might be the way to go, but i'm not convinced by the exhaust tips, really want some that look completely standard.
The F/I stuff I have tested on the same cars from them and other manufacturers gives around the same gains. H&S is far from anything special.

I recently had a system in for an Mitsubishi Evo6 and the quality was appauling. Fitted well.

When you see aftermarket exhausts from the likes of Supersprint you understand what quality actually is.

Sal
 
1 - 13 of 13 Posts
Top