Optimum exhaust diameter

[Hellraiser]

Hey guys,

I am unsure which exhaust diameter is ideal for our little D14 engines. From what I've gathered so far, it seems as the majority of people with aftermarket exhaust tend to use 50 mms/2 inches or 55 mms.
Has anyone done back-to-back testing which of the two is better in terms of peak power and/or the overall power curve of the engine?
In the future, I am going to fit a custom exhaust to my Civic. So before buying the silencers, tubes etc. I'd like to have some information.

Regards

[saxophonias]

Ι have used 50mm and 55mm. If you go for extended mods you could go for 55mm tube without fear.
These days my exhaust set up is 4-1 dc header, 55mm tube, ek9jdm cat, open mid pipe and dc2 back box. Quite happy with it, torquy from low revs and almost stock sound (no problem with MOT and police etc.) I couldn't imagine how much of an improvement in mid and low revs the dc2 back box could be over an open aftermarket one. As for high end power maybe there are some losses there but nothing major comparing to the low and mid gains.

[hondaNickx]

I've used several different types 50mm , 55mm and 60mm .To be honest 50 or 55mm would be the best .
60mm if you're going to turbocharge the D14,For D14 N/A form 50mm is more then enough.
EK9 and ITR exhaust is 57mm outside and they are around 185-190hp with 1.6 to 1.8L .
So a 1.4L that is going to get 130-140hp with a vtec head and some tuning would work fine with a 50mm exhaust.
That is ,if the exhaust is made without any bottle necks or restrictions.

[Hellraiser]

Thanks for the input so far! But have you found any particular difference when comparing the 50mm to the 55mm exhaust system?
I'm generally learning towards a 55mm exhaust system. BUT, as far as I know, must headers for the D series engines have a 50mm collector. Hence my following train of thought: if the exhaust gases flow through the aforementioned 50mm collector; wouldn't a larger diameter than the collector size of the header reduce the velocity, therefore reducing power?
As I am not an engineer or automotive technician I might overlook some important factors here. Can anyone chime in on this?

[hondaNickx]

Thanks for the input so far! But have you found any particular difference when comparing the 50mm to the 55mm exhaust system?
I'm generally learning towards a 55mm exhaust system. BUT, as far as I know, must headers for the D series engines have a 50mm collector. Hence my following train of thought: if the exhaust gases flow through the aforementioned 50mm collector; wouldn't a larger diameter than the collector size of the header reduce the velocity, therefore reducing power?
As I am not an engineer or automotive technician I might overlook some important factors here. Can anyone chime in on this?

I haven't found any big differences in hp , but i do think the torque is better with a smaller pipe.Although i don't have a dyno comparison of the 2 exhaust sizes.
And you're right ,All oem systems taper down in diameter the more they go to the back of the car.This is because the exhaust gasses cool down and take in less place.
Mostly honda krimps down the size where the rear muffler is connected to the mid pipe.EK9 and ITR exhaust systems are 57mm outside diameter and 55mm inside diameter.
At the rear muffler they taper down to aprox 50mm inside diameter.An exhaust that tapers gradually from the front to the back would be perfect but very difficult to build.
All the D-series exhaust manifolds i ever had all had a 50mm exhaust diameter.

[MR.D]

Hey guys.
Im building my ej9 with a d14a4. 1st Ill do a d16Y8 4-2-1 headders, K&N airfiltermatt and a full exhaust systhem.
In the future Ill might do cams, lift the redline or maybe do a minime. Goal is to get somewhere over 105bhp at around 7000 rpm without spending too much money.
Unfortunatly Im verry restricted by the german TÜV so my only options are OEM parts of other hondas that they cant tell apart of the original parts or parts with an ABE or a E number. Thats why the only affordable exhaustsysthems I know are the SRS R60 with a diameter of 60mm or an FOX exhaust with 50mm.
Questions:
1. Any other cat back systhems with an diameter of 55mm because I think thatll be best for 100-130bhp.
2.Any honda oem exhaust parts that will fit my ej9 pre fl and will have a better exhaustflow and have a diameter of atleast 50mm (55mm would be ideal for me).

Thank you and have a nice day!
Mr.D

[Cedi347]

Yo Mr. D, sadly I don't have any recommendations for you, as I am also very new to the whole scene. But I'm also from Germany and just wanted to say something because I'm glad to have finally found someone with the same struggles as me lol