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Discussion Starter #1
i was reading through this and i saw that the comptech header performed quite well in the midst of all those headers with bigger collectors. comptech header has a collector that's only 2" OD. can anyone explain this to me???
 

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Comptech header collector = 2"

Which makes its results even more impressive w/ the heavy breathing C5 when pitted against all the other headers w/ much longer primaries and 2.5" collectors.
 

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actually its 2.14" at the flange according to the admin at the comptech forums ;)

The collector pipe itself is 2-1/4" but it does step down a bit to 2.14" at the flange. This is needed so that the correct gasket can be used. The effect on power is negligible.
=)
 

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Discussion Starter #4
there. i changed it to 2". i don't know what i was thinking.

i'm torn here - comptech vs. dc sports. same 4-2-1 design. same 2" collector.

comptech has the stepped up design which helps anti-reversion effect but on the other hand, its primaries start out smaller than the dc sports. according to the great header test, the choice is clear but i'm trying to understand why it would perform the way it did on the test... am i missing something here?
 

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please put the comptech header run in context for that test:

the test was done with a straightpipe and 2.5 in. exhaust on the Comptech runs and a 2.5 in. Carsound cat/2.5 in. exhaust for all the other aftermarket headers in the test, all of which had a 2.5 in. collector. So there was a stepped larger exhaust system after the comptech. keep that in mind when you modify your system.
 

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Discussion Starter #6
so a couple of whp because of the straight pipe and then a few more for the stepped up exhaust setup... i see.

how i'm thinking maybe i should go with a 60mm exhaust instead of a 2.25" exhaust... so confusing...
 

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MD:
It is commonly debated on whether the 2.25" exhausts are best for a bolt-on only (that will end up w/ 140-150whp peak whp; N/A; focusing on a powerband from 4500-6500 rpm) B1 or 60mm exhaust.

Your article says the 2.25" will be more than sufficient for a non-vtec thats gunning for 145ish whp

Your thoughts on a 2" collector-->2.25" cat-->> either 2.25" or 60mm exhaust on a N/A B1?
 

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dragontegz!!!newbie alert!!!...there's no difference between the straightpipe and a properly sized cat for a system...and once again, lose the creative hp accounting by parts mentality please. this part adds this much, this other part adds that much, add the two together and you get the total hp gain? WRoNG!! I thought you would know better by now man...you've been here longer than most. If you put a wrong sized part in the system, your hp accounting by parts falls apart. The entire system extracts the flow not one part by itself. screw up the system and you screw up the flow and therefore hp gain amount. once again, what I tell the beginners: good exhaust systems release power that's already been made by the engine but that power was stiffled by a corked exhaust system. More of the exhaust gas stayed in the cylinder and affected the next combustion cycle.

aftermarket exhausts release power, not make power...

what, did everyone take an amnesia pill and forgot everything they learned here? LOL
 

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I hear you dragontegz, Im going with DC 4-2-1 ss though, because of the slightly greater flow, and the fact that Im mating it to a 60mm exhaust so I dont 'need' the extra reversion from the header. A little extra flow will probably help me out more than extra reversion resistance since I use nitrous. Someone posted a thread about that header test that kinda threw some doubt on it though...
 

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Discussion Starter #10
lol... i KNEW you would jump right on that, MD.


i guess i worded things wrong. i was just saying that the stepped design of the exhaust system comptensated for the smaller collector of the comptech header.

for some bizzarre reason, i was thinking that, within a given exhaust system, a straight pipe outperforms a properly sized cat however miniscule the difference is. on the other hand, chassis dyno runs are not going to be totally accurate anyway, and given that, a difference of 1 or 2 whp is really negligable.


i'd like to know your take on the 2.25" vs. 60mm for a bolt-on-only non-vtecs myself....
 

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dragontegz on Sep/13/02 said:
i guess i worded things wrong. i was just saying that the stepped design of the exhaust system comptensated for the smaller collector of the comptech header.
DC header = 2" collector
Comptech = approx. 2" collector

The collector's are the same. Were you talking about the smaller primaries of the Comptech vs. the slightly larger DC primaries?
 

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The only cat used inthe header test was a 2-1/4" Carsound used with the stock C5 header and cat back. The Comptech header used a 2-1/4"x 2-1/2" stepped test pipe with a 2-1/2" cat back and the other JDM headers used a 2-1/2" test pipe.
 

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thanks for clearing that up Dave. My memory of which header had what cat in that test failed me. So essentially all headers ran on a testpipe except stock baseline. Was that an intentional decision due to possible fitment problems due to jumping from one header to the other (i.e. different collector layout)? To confirm: Did all headers dyno with a 2.5 in. exhaust?
 

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the top 3 with the most area under the hp vs rpm curve in the test [ that was done on an itr with only an intake, testpipe, and 2.5 in. exhaust ]were: the Toda, Spoon, and SMSP...all have 2.5 in. collectors and so you would need the proper cat and exhaust size for them to work properly. The Hytech header was not tested there. None had the engine tuned after installation which is one criticism of the test.

I suspect the SMSP's extra length would result in bigger gains below peak torque over the other 2 with tuning and a mild bump in static CR (like from a 2 layer head gasket). This is only speculation on my part though based on header design theory.on big engine packages with aftermarket cams, bigger CR, bigger IM, and headwork, the difference or gap between the longer hybrid headers like the SMSP and Hytech grows compared to the shorter headers.

the best one depends on your engine package and where you prefer the powerband gains to be. You can't lose if you choose any of these 5 headers as long as you have the right sized cat and exhaust to go with them.
 

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i want to go with some top end power for drag racing.

i have a B18B and i want to do the following

4-1 header (2.5" collector)
Nitrous system
2.5" carsound cat
2.5" exhaust

now, will the 4-1 headers (dc,JDM,spoon,SMSP)fit a B18B head? or are there other obstructions?recommendations on the header portion for my setup would be appreciated
 

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they'll fit at the flange bolted to the head. The JDM ITR and DC JDM would clear your oil pan and I think (but not sure) the Spoon should as well since it sits much lower than most of the headers. The SMSP (made for the GSR or ITR) may not clear the oil pan, since Dave sizes them precisely and fits them for the GSR and ITR, not the B18B. You can certainly call him and he'll make the needed changes for fitment...he is a custom header builder after all and custom means special fitting can be done. The length should not be a problem since the ITR exhaust system and the B18B exhaust system are compatible.

Since you are running nitrous, any of those will work well for you "on the button" but the concern is how will you run off the nitrous. That part I cannot answer. Are you upgrading your cams later?
 

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Are you upgrading your cams later?
i was thinking of doing cams aswell, but not alot out there for a B18B. with 4-1 headers and a drag applicaton, i'm assuming this would help. thats is one article i havent read yet, so i will do so.
 
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