Alfa Romeo Forum banner

1 - 15 of 15 Posts

·
Registered
Joined
·
47 Posts
Discussion Starter #1
Hi Guys , i've briefly skimmed through a couple of threads and seen a few youtube vids about equal length down pipes ,
can anyone advise on the real benefits / downside of fitting them (156 2.5v6) and who sells them / price , i'm pretty sold on getting some but would like to do a bit more research before choosing who to get them from

My Car has a MIJ full sport exhaust with sports cat , Alfatune eprom change and autodelta filter , so it's getting there just looking for ways to get it finished off and get as much extra power/noise without going into engine upgrades ,
cheers
Dave
 

·
Registered
Joined
·
9,912 Posts
equal length down pipes let pulses of burnt gases line up in exhaust and help extraction and excavation of cylinder..imagine a pin pong ball as combusted gases going down a tube .then next cylinder fires then next .you want them to line up going down tube so to speak.... on standard system they bounce into each other like snooker balls and affect flow and excavation of cylinder...if you where able to have access to temperature gun and car was at full chat you would see heat build up at restriction ..this is the point of gases bouncing off each other



ps gus is guy to speak to ..he done your map
 
M

·
Guest
Joined
·
0 Posts
The real benefit is improved exhaust flow and better scavenging (as long as bore of pipe is correct for application). the reason it is better is due to the pulse of exhaust gas coming from each cyl arriving and combining in exhaust pipe one after the other. unequal lengths mean timing between different cyl's exhaust gas is not equally spaced apart.

Having correct bore on manifold and exhaust is very important as well, the velocity of gas leaving exhaust scavenges (helps pull the exhaust gasses out of the cylinders leaving less combusted gas in them so more room for air and fuel). too big and flow of gases is too slow to assist dragging gases out. too small and it can't flow enough for power. Different on a tubby car but in NA cars you need to get correct bore for engine power as both too small and too big will reduce power. Just right can give you nice gains over a little wrong.
 

·
Vendor
Joined
·
45,756 Posts
Unicorse equal length front pipes made a big difference at low revs on my old 2.5, I don't think they make as much difference on the GTA tho.

It's a shame that the primaries are all unequal length.
 

·
Vendor
Joined
·
45,756 Posts
What year is your car and is it auto or manual? It's matters as they use different FPs..
 

·
Registered
Joined
·
2,627 Posts
For this scavenging theory to work wouldn't the lengths from the exhaust port have to be equal? That's not going to happen without equal length primary's. Or have I missed something?
 
M

·
Guest
Joined
·
0 Posts
No, scavenging always works it's mostly down to pipe bore to get correct velocity of gas. loss of scavenging is why crap boy racer saxo's loose power getting a big bore system... it's just better with equal length as there is removal of congestion caused by gases arriving at different times. I would want an equal length pipe to take into account of the other pipes not being equal though, surely that should be a given. if not what's the point? Or can you buy equal length on primary as well?

Probs reduces congestion a lot as would have thought the unequal lengths on manifold are not as severe and piston firing order probe means there isn't two bursts of exhaust gar arriving together for ultimate you'd want equal length header/manifold as well. best guess is downpipe will make more difference than manifold.
 
M

·
Guest
Joined
·
0 Posts
Had a look at std manifolds there isn't anywhere near as big a difference as downpipes. Plus with firing order manifold will only make a small difference in timing but shouldn't cause gases to arrive together.
 

·
Registered
Joined
·
47 Posts
Discussion Starter #9
Cheers chaps ,
starting to make a bit more sense now :thumbs:

My car is an S Reg , manual , it has the factory fitted body kit and lowered suspension so really looks the part , i'm trying to make the performance match it's looks :)

I'd post a picture if i knew how to.

What about exhaust note , will they change that and if so how ?

Ta
Dave:thumbs:
 

·
Registered
Joined
·
47 Posts
Discussion Starter #10
Has anyone got any pics/links of them from the different manufacturers ?
the unicorse one i take you can't get from the UK ? is that right ?
 

Attachments

·
Vendor
Joined
·
45,756 Posts
Equal length front pipes tend to smoothen the exhaust note and make it a bit higher pitched.. I really like the sound :thumbs:
 

·
Registered
Joined
·
47 Posts
Discussion Starter #14
Here's my old 3 litre with Unicorse equal length front pipes and backbox:

Dan's genuine Unicorse system.mp4 - YouTube
Oh that was you was it , i've watched that video time and time again , the best sounding 156 on you tube i think:thumbs:

Mine sounds a bit deeper than that at the moment , loud but pretty spectacular though ,
i'll try and get a video uploaded.
 

·
Vendor
Joined
·
45,756 Posts
You should put a video up, there's nothing you can do to a V6 to stop it sounding epic, best sounding six ever built I reckon :thumbs:
 
1 - 15 of 15 Posts
Top