19dabeast85

I know the B20z manifold is essentially sheetmetal stamped together with horrible flow characteristics. With the rtawd it is difficult to find a bolt-on quality product.

Does anyone know if the GSR UPPER manifold will bolt to the crv LOWER (downpipe section) to make it a straight swap? If I use the complete GSR exhaust manifold it will have to modified around the rtawd output casing and I hope to avoid that.

IF the B20z and GSR upper manifolds are a direct swap is the B20z lower section going to be a huge bottleneck?

Eventually I'd like to get a 4-2-1 but it'll have to be somewhat custom to get around the rtawd and no $$$ for that anytime soon.

Thanks for the help.

19dabeast85

87 views and nobody knows?

Guess I may be testing this one myself. I'm not a fan of DCSports but their 4-2-1 for the Integra looks like it could pretty easily be modified to go around the rtawd transfer case. DC would be better than the crap it has now and maybe a step better than OBX?? ehh.

qwrty

i doubt that it will be a better step up than obx... obx copied the comptech headers, only
comptech made an aftermarket headers for gen1 crvs, so either you modify the whole dc
headers(w/c somebody did it already), keep it stock or get the obx one... other than mixing
it up coz youre already wasting time and effort.. not unless you have all the stuff to do this
then good luck.. keep us posted!!

j3wman

im suprised bisi doesnt make **** for this setup

19dabeast85

I've seen good reports on the longevity of the OBX header but it has EXTREMELY short merge collectors.....I know I'm not pushing huge horsepower but that's my main thing against the obx ones....too abrupt of a merge just makes no sense to me.

MonkeyMagic

you are minorly increasing efficiency to something that will only add up to tiny % of the engine's total efficiency which is in it's self, ultimately, tiny. not to mention the exhaust behind that header which is designed 1st as noise reducer, 2nd to take up only available chassis space, and 3rd as an efficient waste-gas relocation device.

as for trying to create a gsr/b20 combo header from the stock pieces.. you'll get 10X the output from simply using some good quality gasoline. ****, gap your spark plugs and change the air filter and adjust the valves and it'll probably run night and day from what you are used to.

but at least you are trying to look at the designs with some reasoning and looking at results with a bit of realism. alas, damn near every header on the market below 1500 bucks is, to one degree or another, essentially an aesthetic mod. so if all it's going to do is look good, save your money up and buy one that looks cool as ****.

19dabeast85

Within the first week of owning the crv I replaced the plugs (Denso), wires (Honda), dizzy cap&rotor (Honda), dropped in a K&N filter, replaced pcv, adjusted the valves. I run Lucas injector clean through every oil change and always use good quality fuel.

I'm looking for the best efficiency between 3500 and 5000. I highly doubt the stock sheet metal is efficient across that rpm band. The oem gsr manifold is probably closer to what I'm looking for from what I've seen.

Here's a pic of the crv manifold, right at 1" or less at its thinnest part:

MonkeyMagic

Ok..

19dabeast85

A 1973cc 4 cylinder with peak torque at 4,500 rpms needs primary pipe diameter of 1.4". The stock one is nowhere close. This 1.4" will have the exhaust gasses at 4,500 rpm flowing at roughly 240mph which is the standard for optimum efficiency. If I were racing this engine it would need a header with primaries 1.4" I.D. Because it's a street machine and I'm looking for optimum efficiency a little lower (around 3,500rpms) primary diameter of 1.23" is optimum there. The GSR, OBX, DCsports are very likely in that range.

MonkeyMagic

just curious, do you know the math behind this? not talking ****. i'm impressed. considering most people wanting to essentially rig-up factory pieces are just junkyard scavengers.. they don't understand and don't want to understand the actual thought process behind what they are trying to accomplish, but i was wrong to assume you were one of them.

if the gsr manifold does play out to your specs, the thought that it is a trememndous lump of cast iron (im assuming it's cast like b16 manifolds and the like) and will hold a substantial amount of heat will also affect the nature of flow. something to consider

i think you should try the entire gsr assembly if it is what you are looking for as far as design goes. iirc it'll be much shorter than the crv unit, so probably a simple cut and insert of slightly bent pipe to fill the space between flanges would be the ticket.

19dabeast85

I understand the theory and can plug numbers into the simple formula all over the net. It's not a perfect calculation because it doesn't consider bends, material quality, etc but it's close:

Primary pipe area = peak-torque rpm / 88,200 x displacement of one cylinder(cubic inches)
1973cc = 120.4 cu.in.

pi * radius^2 = 4,500 / 88,200 * (120.4 / 4)
pi * radius^2 = 4,500 / 88,200 * 30.1
pi * radius^2 = 1.5357143
radius^2 = 1.5357143 / pi
radius^2 = 0.488833
squareroot(radius^2) = squareroot(0.488833)
radius = 0.6991659
diameter = 0.6991659 * 2 = 1.3983318" primary inside diameter

I found some more threads on the subject on hondasuv forums and they're saying the sheetmetal is VERY thick and the welds along the seam actually protrude into the tube in places.....definitely not best environment for smooth flow.

As far as the manifold material (cast vs tubular). I'm pretty sure the GSR is tubular. The cast ones do hold in more heat. When the exhaust gasses remain hot longer they can flow faster through a given pipe size. So a ceramic coated/cast/wrapped header promotes higher exhaust velocity....in most cases a good thing.

Reading around a bit more I think I'm just going to get the OBX header made for the rtawd. Reading the posts over on hondasuv forums it looks like OBX's quality has improved over the years and the early fitment issues are gone. OBX's catback for the CRV gets rave reviews over there also, they've compared it to a greddy and apexi as far as sound goes and fitment was good. It's also possible OBX gets good reviews over there because they're the only one that makes stuff for the crv....I'm hopeing I end up with a good choice.