4.0 header options/information

gt500swim

Well-Known Member
Joined
Dec 11, 2010
Location
Gastonia
as we all know the 4.0's have a terrible design of the exhaust manifold. when my oem manifold cracked i did plenty of research and the one thing that i read the most was that the manifolds with the expansion ports were the cure for the cracking issue. false. i have had mine on my jeep for 2 years now and it has cracked at the expansion port! if they were so good then they would outlast the oem manifolds... which mine went through hell and still lasted about 9 years(po put one in a few years before i bought it) i still have the oem manifold on my 98 xj, 220k miles on it.. no cracks yet. so i just want to put it out there that the whole expansion port thing is a joke.

secondly i am going to be trying a new project and would like everyones input/ opinion on it. what i plan on doing is getting this exhaust manifold...

http://www.ebay.com/itm/1996-97-98-...s=63&clkid=7357406487532700708#ht_1889wt_1037

to me it looks like a good design, very stout mount flange (1/2") (oem is 1/4)and the pipes are the same diameter as the borla(1 5/8")(oem is 1 1/2"). the only thing i do not like is the output flange imo looks like it is the restriction to the whole system. so i have been talking with my local muffler shop and they have agreed to cut the small 2 1/4" flange off and weld on a huge 3" flange, AND mendrel bend me a custom 3" downpipe. all i need to get is the cat from a silverado(3" in/out). the best thing is the price... 65 bucks for the manifold mod, and the downpipe modification and mount. if this works the way i want it too i may try and buy a couple, do the modifications and see how they sell...

the only thing im really contemplating is if i can fit those 3" pipes through the back of the jeep. or if i want too. i also need ur opinions on this. should i just slap a 3"flowmaster on there with a turn down? or try and actually run a tailpipe? or say screw the muffler and turn it down at the cat :p

one thing i will do is run it on the dyno afterwards to see if there is any improvement. i had my yj dyno'd a couple weeks ago and it came up with 136 hp and 184 lb/ft torque at the rear wheels (35's) which from my research is quite good for my highly abused but anally taken care of motor. so we shall see what happens when i get it dynoed if there is any improvement.

let me know what u think of my idea and any feedback is greatly appreciated as usual! thanks guys
 
Do you NEED 3" exhaust? I think 2 1/2" should be plenty, that's what I ran behind a fairly strong 4.6 stroker. Should be easier to fit. Also, especially if you DD this jeep, run the tailpipe all the way to the back. It quietens down the exhaust sound a lot inside.

136/184 on 35s sounds really good, enjoy.
 
i agree the 3" might be a little overkill.. but i just had the idea the other day and it would be at a fraction of the cost of a borla still. and definitely a good point about the tailpipe. i dont want it to resonate like all the ricers around town when i try and take off.lol.

as far as the dyno numbers go the guy that owns it was really impressed... there was a 2011 civic si that got ran just before me and he only pulled out a 115/120. so i think my numbers are good considering the mileage... i also had my FPR disconnected so he said that cost me some hp. i did however just put a fpr in from a 93 chrysler t&c (3.3) so im now running at 40 psi with vaccum and 45 without. definitely made a difference since i was running lean with the hotter coil and newer intake. all i need now is some 24# injectors and i should be good..
 
I think 3" will hurt more than help. I think I would rather have 2 1/4 over 3 with 2 1/2 being ideal. On a side note, under wide open throttle there is no vacuum on the FPR so it is essentially unhooked anyway. Dont see how that cost you any hp.
 
ok so i sent some emails to some of the sellers of the headers... (78 bucks, 99 bucks, and 140 bucks) asking about their guage tubing and what makes their header better than the others on ebay... i got a response from the seller of the 140 buck header and he had this to say about his header " its 14 guage tubing, its made in china. and there is no warranty" if thats what makes their header better than the others i hate to know what the negatives are of it... HAHAHAHAHA
 
i managed to get that exact header... MADE IN USA for 106 bucks. now my question is.. do you guys think there would be any negitives of me modifying it to a 3" collector if i include a 3" cat and put a flowmaster on it??
 
http://www.mk5cortinaestate.co.uk/calculator5.php
The larger tube will hurt your low end power to some extent. 2.25 tube is capable of flowing over 200 hp according to the link above. If all you care about is the dyno number, go for 3". If you would like it to respond at low speeds like it was some kind of offroad vehicle or something, Id stick with 2.25. Although it seems most of the quality headers(thorley,banks,etc) are 2.5"
 
Back
Top