2.25 or 2.5" CAT



#1
Just ordered my Kiddracing RMF header. It is damn near impossible to find a real one, so yeah...
Anyway.

Should I get a 2.25" high flow Magnaflow CAT or 2.5" for the best performance for now.
My engine is 100% stock for now, but I do know I'm going with 2.25" custom piping from the CAT to the exhaust.

So it would be...
2.25" Narrow header pipe > 2.5" collector > 2.25 or 2.5" CAT > 2.25" piping > 2.5" exhaust
The bolded lettering would eventually turn to 2.5" for sure, once I build the head and bump compression. :)

I have a B18C1.
 


#4
I thought that header was 2.5 collector?
It is, but the shop can fabricate it to fit.
Pretty much what I'm asking is if the 2.5" will cause me to lose too much backpressure for my stock GSR or if it will matter since the piping after that will be 2.25"
 
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#8
ok. I went with an Oval Magnaflow 2.5"

Now I have another dilemma that seems logical...

The reason why I had originally considered 2.25" Piping from CAT to the exhaust was because if the diameter of the piping might be too wide and the exhaust gases would actually begin to slow down and not push out the exhaust gases fast enough "Thus" resulting in power loss unless I rev it up very high. "Due to my research and reading"

(The bolded shows smaller piping and the stuff not in bold is 2.5")

This was my original plan (revised)...
RMF Header 2" Narrow pipe > 2.5" CAT (DECIDED) > 2.25" piping > 2.5" Exhaust

Now that I think about it, this makes more sense...
RMF Header Narrow 2" > 2.5" CAT > 2.5" Piping > 2.5" Exhaust


I don't think I'm making enough power (YET) to properly run this setup, or am I?
I would run this 2.5" setup for about a year or two before I need a rebuild and start to build my longblock.

So should I do the 2.25" from the CAT to Exhaust until I build my longblock?
Would the headers narrow pipe be enough to speed up the exhaust coming through a complete 2.5" piping setup instead of going back down to 2.25" piping?

Or just go for the second complete 2.5" setup after the narrow pipe?
 
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#9
Get the 2.5in header, you will not lose power. You will prob gain some at higher rpms.

Edit: just noticed you have a gsr. In that caseyou should def go with 2.5 all the way.
 
#12
We will see how she does. Ill go with 2.5 all of the way. Hopefully It does feel like crap low end. Lmao

Hopefully Ill be feeling a good 160whp.
Im also heat wrapping the header :)
 
#13
Get the 2.5in header, you will not lose power. You will prob gain some at higher rpms.

Edit: just noticed you have a gsr. In that caseyou should def go with 2.5 all the way.
Sorry if it wasnt clear. The RMF header goes down to a narrow pipe and opens up to a 2.5" collector.
I was referring to 2.5" piping from the CAT to the exhaust.
 

Jay Jay

Administrator
Staff member
#14
I agree with everyone else to go 2.5" header back.I see no point in getting a header with a 2.5" collector and you don't continue 2.5" the rest of the way. I ran a DC Race header with 2.5" collector and exhaust on my almost stock GSR motor years ago and it was fine.
 
#15
I agree with everyone else to go 2.5" header back.I see no point in getting a header with a 2.5" collector and you don't continue 2.5" the rest of the way. I ran a DC Race header with 2.5" collector and exhaust on my almost stock GSR motor years ago and it was fine.
Going with 2.5"
My whole dilemma was the narrow piping making it confusing. Never deal with something like that. :p
 




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