ls1 custom exhaust sizing questions for best overall flow.
11-02-2013, 06:21 PM
#1
ls1 custom exhaust sizing questions for best overall flow. Im making plans for an e46 ls1 swap.
goals are 450whp. N/A when swap is done and possible 550whp in the future so it has to flow if I decide I want more power.
from my search it looks like ill be making this header/design (see pic)
sizing however isnt mentioned. and to meet my goals I been crunching some numbers and so please let me know what you think.
what what Ive read 1 3/4" is best.
then merge two into a 2 1/4" pipe.
then merge those two pipes into a 3" pipe
from both headers will be merge into a single collector (see second pic)
then out into a SINGLE 3.5" exhaust/cat back.
what do you guys think?
also could use some input on other sizes that i have considered.
will there be gains to be had from 3.5" vs 4" single cat back?
also since I might be limited on room so would this perform just as well?
1 3/4" start
then merge two into a 2 " pipe.
then merge those two pipes into a 2.5" pipe
from there Y collector into a full 3" or 3.5" exhaust
please advise. I dont want to go bigger than I have to for my goals.
thanks
goals are 450whp. N/A when swap is done and possible 550whp in the future so it has to flow if I decide I want more power.
from my search it looks like ill be making this header/design (see pic)
sizing however isnt mentioned. and to meet my goals I been crunching some numbers and so please let me know what you think.
what what Ive read 1 3/4" is best.
then merge two into a 2 1/4" pipe.
then merge those two pipes into a 3" pipe
from both headers will be merge into a single collector (see second pic)
then out into a SINGLE 3.5" exhaust/cat back.
what do you guys think?
also could use some input on other sizes that i have considered.
will there be gains to be had from 3.5" vs 4" single cat back?
also since I might be limited on room so would this perform just as well?
1 3/4" start
then merge two into a 2 " pipe.
then merge those two pipes into a 2.5" pipe
from there Y collector into a full 3" or 3.5" exhaust
please advise. I dont want to go bigger than I have to for my goals.
thanks
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Homer_Simpson (12-26-2021)
11-03-2013, 06:18 AM
#2
Looks like a solid plan to me, essentially making your own Tri-Y headers. Props for thinking of scavenging. I'd definitely study the design of the Phadt Tri-Y to ensure you're matching the correct two primaries together to promote the scavenging effect.
For your goals I think 3.5" will be plenty.
Only two things to consider would possibly be stepping the primaries from 1 3/4" to 1 7/8" before the 2 1/4" tri-y merge, and possibly a 4" I-pipe with a cutout. Place a transition after the I-pipe to go 3" or 3.5" over the axle if it saves you room at that point. Open the cutout when you want the bit of additional HP.
Either way, looks good. For less of a hassle I think you'll be good with the 3.5" pipe.
For your goals I think 3.5" will be plenty.
Only two things to consider would possibly be stepping the primaries from 1 3/4" to 1 7/8" before the 2 1/4" tri-y merge, and possibly a 4" I-pipe with a cutout. Place a transition after the I-pipe to go 3" or 3.5" over the axle if it saves you room at that point. Open the cutout when you want the bit of additional HP.
Either way, looks good. For less of a hassle I think you'll be good with the 3.5" pipe.
11-03-2013, 02:59 PM
#3
Looks like a solid plan to me, essentially making your own Tri-Y headers. Props for thinking of scavenging. I'd definitely study the design of the Phadt Tri-Y to ensure you're matching the correct two primaries together to promote the scavenging effect.
For your goals I think 3.5" will be plenty.
Only two things to consider would possibly be stepping the primaries from 1 3/4" to 1 7/8" before the 2 1/4" tri-y merge, and possibly a 4" I-pipe with a cutout. Place a transition after the I-pipe to go 3" or 3.5" over the axle if it saves you room at that point. Open the cutout when you want the bit of additional HP.
Either way, looks good. For less of a hassle I think you'll be good with the 3.5" pipe.
For your goals I think 3.5" will be plenty.
Only two things to consider would possibly be stepping the primaries from 1 3/4" to 1 7/8" before the 2 1/4" tri-y merge, and possibly a 4" I-pipe with a cutout. Place a transition after the I-pipe to go 3" or 3.5" over the axle if it saves you room at that point. Open the cutout when you want the bit of additional HP.
Either way, looks good. For less of a hassle I think you'll be good with the 3.5" pipe.
from what ive read online headers with 1 7/8 loose torque all through out and gain very little peak hp. It seems that it isnt worth it unless your after big power or have big cubes.
as far as cutout.
im trying to avoid using it if I dont need it.
ive had them on all my turbo cars and it takes 10 sec to open then another 10 sec to close. and I had the wireless controller so its just one click. I think i just prefer not having it.
since I dont have any axle to go over my only main concern is ground clearance. I guess I will try to see if I can fit 4" first.
thanks
11-03-2013, 03:15 PM
#4
from what ive read online headers with 1 7/8 loose torque all through out and gain very little peak hp. It seems that it isnt worth it unless your after big power or have big cubes. as far as cutout. im trying to avoid using it if I dont need it. ive had them on all my turbo cars and it takes 10 sec to open then another 10 sec to close. and I had the wireless controller so its just one click. I think i just prefer not having it. since I dont have any axle to go over my only main concern is ground clearance. I guess I will try to see if I can fit 4" first. thanks
I'm with you on the cutout. I wouldn't want to run one either. Just something else to fail or break.
