View Full Version : OBX and KOOKS questions along with primary size pros/cons???


NeverSatisfied02
07-27-2012, 12:27 PM
Alright fellas,
I'm curious about a couple of things. The OBX header are supposed to be an exact replica of the kooks headers correct? I just heard recently that the OBX collector on their 1-7/8 header (only option they have) is 2.5" while the kooks come with a 3" collector on both their 1-3/4 and 1-7/8 headers. Is that true?

I suppose thats not too big of a deal to have a 2.5" collector if you are running 2.5" exhaust but if you're running 3", that complicates things a little.

At what point (power wise) do you actually benefit from the 1-7/8 primaries over the 1-3/4? I've been dealing with a clearance issue with my OBX 1-7/8 headers and my steering shaft and i have about had it! I dont want to cave in the primary to make it clear although i have been very tempted to do so. Instead, I ground on the steering shaft a bit and it seems to have helped a bunch but its still not 100% yet.

Do the kooks 1-7/8's have this same issue with clearing the steering shaft as well due to the size in general or is it OBX specific??

The reason im asking is because I'm getting tempted to pull these off and sell them and just go with a set of 1-3/4 kooks headers. I had the 1-3/4 on my old V with no problems at all. I just don't know if i'd be working in reverse to go from a 1-7/8 primary to a 1-3/4 primary on the headers. If the kooks 1-7/8 clear with no issues, i'd be tempted to go that route as well. Anything to get me away from having to clearance the primary on the header!!

I am unsure of how accurate this information is but I was initially told that the 1-3/4 primaries would be plenty on this car when N/A and 1-7/8 were beneficial on FI applications. Does FI include nitrous???? I wouldn't think so because its not boost like with a turbo or blower but in my case since i spray the car, i really don't know which size primary i'd be better to run.

So... Pros and cons when comparing 1-3/4 to 1-7/8?

BudRacing
07-27-2012, 12:36 PM
I think your spray would benefit from 1 7/8 headers.

I found a solution to the steering shaft problem.
I used a dremel with a sanding wheel and moved the groove that the bolt goes through back so that the shaft can be mounted just slightly farther up the stub. (if that makes any sense.)

Basically, the goal is to back the steering shaft off the stub slightly. I've had no troubles with angles or anything afterward.

NeverSatisfied02
07-27-2012, 01:12 PM
Ok. I was unsure how nitrous would effect the exhaust flow or if it would even make a difference between 1-3/4 and 1-7/8 on a nitrous car. Are the primaries in fact 2.5" as opposed to 3" though? I know I can take the header apart measure myself but trying to avoid the work if someone here can confirm it.

I may have to try your steering shaft solution. If that works for me, I'd be happy.

garrettg
07-27-2012, 01:41 PM
1 7/8 kooks no issues with steering shaft rub
cs motor/trans mounts installed prior

NeverSatisfied02
07-27-2012, 01:59 PM
Good to hear. I hope all kooks 1-7/8 don't have issues and you're not just a lucky candidate. Lol my obx issues got worse when I put the UMI solid mounts in because they are slightly shorter than stock.

DACTARI
07-27-2012, 02:03 PM
Good to hear. I hope all kooks 1-7/8 don't have issues and you're not just a lucky candidate. Lol my obx issues got worse when I put the UMI solid mounts in because they are slightly shorter than stock.

My mechanic is installing OBX 1-7/8 and UMI mounts next week. What should I warn him about, besides saying that a small dent in the headers may be neccessary for steering shaft clearance? I guess I'm asking, how much more compressed is in in there with UMI mounts?

Thanks yo.

NeverSatisfied02
07-27-2012, 02:22 PM
The UMI mounts aren't that much shorter than stock but enough to make the clearance a little tighter. If u plan to dent the header, ur fine. I'm just trying to get around having to do that if I can. I did some grinding on my steering shaft but I've taken off as much as I feel safe removing so now it's time to dent the header if anything unless I decide to swap to kooks.

garrettg
07-27-2012, 02:26 PM
My mechanic is installing OBX 1-7/8 and UMI mounts next week. What should I warn him about, besides saying that a small dent in the headers may be neccessary for steering shaft clearance? I guess I'm asking, how much more compressed is in in there with UMI mounts?

Thanks yo.

Breaking spark plug wires, most replace them and the plugs during the install as they need need to be removed anyway.

NeverSatisfied02
07-27-2012, 02:29 PM
Oh yeah... My stock wires ripped during install. I have MSD's now. If u have MSD's, u should be fine. Just tell them to grab low on the boot when removing them.

DMM
07-27-2012, 02:34 PM
I was under the impression that the OBX were 1 7/8" with 3" collectors, just like the Kooks. The Kooks neck down to 2 1/2" at the converters (or tuning pipes) anyhow, so not really any difference.

1 7/8" primaries will make power everywhere when compared to 1 3/4" tests were done on an LS1 with varying mods, the bigger headers made more power everywhere, not just up top as with typical SBC results. This has been found true for smaller displacement 5.3 motors as well.

I installed Kooks 1 7/8" and had to beat the shit out of one drivers primary b/c it contacted the steering shaft. I wrapped mine about 3/4 of the way down, have not had any problems with them at all.

NeverSatisfied02
07-27-2012, 02:40 PM
I assumed the OBX were 3" as well but since I've been told they are 2.5", it made me curious which is why I posted here. I know the kooks connector pipes neck down to 2.5 where it connects to the exhaust but at least on those having the 3" collector, u can cut and re-weld the connector pipe to make it 3" all the way. Nothing you can do with the collector size to change it if it's only 2.5".

So are the OBX in fact 2.5" at the collector? If so, is there any performance advantage to having 3" collectors with a 2.5" exhaust? Any benefit to having the 3" collectors with a 3" exhaust?

I know back pressure plays a role somewhere. I was going to run a 3" B&ab catback but it the OBX collector is 2.5", i might as well stay 2.5" because the exhaust will only flow as much as the smallest point will allow it to. Is there even an advantage to going full 3" on these cars?

And it makes me feel a little better that u had clearance issues with your kooks 1-7/8. If 1-7/8 make better power, I'll just pull my drivers side header off and dent the primary enough to clear. Guess that's the only way to get around this issue. I just hate denting my headers if I don't have to.

vmapper
07-27-2012, 02:47 PM
Ill get a picture for you of the OBX header collector size after work.
As DMM mentioned, there are no CONS (power wise) other than having to beat on the one primary for clearance.

NeverSatisfied02
07-27-2012, 02:49 PM
Perfect! Thanks!! I just didn't wanna go yanking mine all apart just to get a measurement.

I wish there was a side by side comparison of the Kooks and OBX. I'm just hoping the OBX collector is indeed 3". And if it's not, I'm hoping there is no performance loss from that considering the rest of the exhaust is 2.5" anyway unless you go with the 3" B&B setup.

garrettg
07-27-2012, 02:53 PM
Stainless works and B&B headers are both 1 3/4 with 3inch collectors. Nobody seems to make the all around big pipe like a 1 7/8 or 2 inch primary to a 3 inch collector.

NeverSatisfied02
07-27-2012, 03:02 PM
Kooks headers are 1-7/8 with 3" collectors but you're right about those other two coming in only 1-3/4. Kooks and OBX are the only two making 1-7/8 primaries that I know about. And if what I've been told is true about the OBX collector being 2.5", then kooks is the only one making the 1-7/8 with 3" collector.

DACTARI
07-27-2012, 03:31 PM
Oh yeah... My stock wires ripped during install. I have MSD's now. If u have MSD's, u should be fine. Just tell them to grab low on the boot when removing them.

No, still on stock wires. Are MSDs really that much better? What is it about them that's so special?

Sorry for the threadjack. I will try to keep my head down.

vmapper
07-27-2012, 03:51 PM
I prefer stock wires... why?
Long needlenose pliers around the metal jacket indent, squeeze hard so no slip... use long screwdriver and pry against side of head and the pliers (just push the screwdriver towards engine (so pushing pliers outward away from plug)... pop... next plug... pop. Takes 30 seconds to pull all plugs, and you will never rip or pull apart. This works well because there is no side angle when using your hand or just pliers.

vmapper
07-27-2012, 03:52 PM
Ill have your pic in less than 2 hours NeverSatisfied02

NeverSatisfied02
07-27-2012, 04:37 PM
That is a good way to remove wires. I always use my hands or pliers but I'll try that next time.

And thanks bud! I appreciate it! :cheers:

vmapper
07-27-2012, 06:30 PM
Enjoy

NeverSatisfied02
07-27-2012, 06:51 PM
Ahh ha!! So it is a 3" collector on the OBX!! I thought so but when I heard it was 2.5", I had to look into it myself. Lol that makes me feel a lot better! Pretty headers BTW and thanks for posting the pics bud!!

I'll be staying OBX after all since they are indeed indentical to the kooks anyway and both have clearance issues with the steering shaft on the 1-7/8 headers. I'll just put a minor dent in my primary and be done with it.

NeverSatisfied02
07-27-2012, 11:48 PM
So now that I know the collectors are 3", is there an advantage to full 3" exhaust over the 2.5"?

Fuzzy_Wuzzy
07-28-2012, 11:22 AM
It looks like it does neck down to 2.5" right where the pipes merge then flares back up to 3" for the connector.

I think it is down to a cost per HP if you want to compare OBX vs Kooks, if comparing kooks to kooks it is probably worth going bigger for the smaller cost increase.

DMM
07-28-2012, 03:53 PM
So now that I know the collectors are 3", is there an advantage to full 3" exhaust over the 2.5"?

Not unless you're shooting for over 1200 hp.

vmapper
07-28-2012, 05:14 PM
Sorry, should have done this in the first place.
3" on smallest O.D. portion of the collector.
1 7/8 primaries, however, the I.D. near the head is 1.75" for some and others are 1.9" .. f*%k Looks like someone forgot to grind... (1st pic vs last pic)

NeverSatisfied02
07-28-2012, 06:33 PM
Thanks for the pics again bud!! Either way, the OBX look nice. I'd bet you'd find some minor flaws on the kooks if you looked that close as well. Im sure its hard to get them 100% perfect and flawless. And even if they do vary between 1-3/4 - 1-7/8 on the primaries, i can't see that hurting anymore than denting the primary for steering shaft clearance so i'm sure they are just fine. Still a major power upgrade over factory manifolds.

I was asking about the 2.5" vs. 3" because I just bought a cut up B&B catback. I have the 3" X pipe, 3" mufflers/tips and the 3" kooks connector pipes for the headers but everything in between was previously fabbed to fit the headers and around a 9" rear on another car so it was all useless from being formed differently than id need it so we cut it all apart. Debating on whether id be better off paying to have the exhaust shop put the 3" all back together on my car and run the B&B or just throw on the 2.5" magnaflow catback i have in the garage. Only reason im hesitant to use the magnaflow is because it has yet to be cut on yet and its perfect. Almost thinking since the B&B has been cut and i need to cut for headers anyway, maybe i should just have the exhaust shop fit it to my car and be done. Maybe throw some cutouts in later.

Fuzzy_Wuzzy
07-28-2012, 09:01 PM
one other thing to consider is that there is a difference in a very short neck down to 2.5" with a 3" exhaust behind it, and a 2.5" exhaust the entire way. (blow through a short section of straw then one much longer)

NeverSatisfied02
07-28-2012, 09:04 PM
If I go 3", it would all be 3" from the 3" collector back.

I get what youre saying though so which would be more beneficial?

vmapper
07-28-2012, 11:03 PM
FYI

Kooks connector AND the OBX resonator connector are 3" down to 2.5". The 3" side mate up to the header collector and the outlet back is 2.5"

NeverSatisfied02
07-28-2012, 11:10 PM
I know that but the looks connectors have been cut and made 100% 3" for the B&B. My obx is still the way it came but if I got B&B, I'll use the custom made kooks solid 3" connectors and if I run the magnaflow, I'll keep my obx 2.5" reducer connectors.

1989GTA
07-28-2012, 11:17 PM
Does the OBX headers have the "spike" in them? How about the Kooks?

wcryan
07-29-2012, 12:06 AM
I had a very bad experience with OBX. But if I would have done what I tried the second time, it would have been easier (used a different shop the second time)

They had to cute one of the primaries and re-weld it.

It was bending my steering shaft...... That's how bad it was

NeverSatisfied02
07-29-2012, 02:52 PM
Damn... That sucks. I'd imagine that's pretty common if u just install the headers without clearancing for them by denting the primary or grinding on the steering shaft.

So is 2.5" or full 3" exhaust more beneficial on this car?

vmapper
07-29-2012, 03:41 PM
Does the OBX headers have the "spike" in them? How about the Kooks?

OBX does.

NeverSatisfied02
07-29-2012, 03:46 PM
Wtf is a spike? Lol

vmapper
07-29-2012, 03:53 PM
Its deceiving in the picture, but its a few inches in height. Part of the collector.


Here is a better illustration.
http://www.coneeng.com/ (bottom center of page)


Here is an article on it. Supposedly helps with velocity and air turbulence
http://www.carcraft.com/techarticles/116_0304_cams_carbs/index.html

Here is OBX

NeverSatisfied02
07-29-2012, 04:11 PM
Oh ok. Makes sense now! I remember seeing that on mine. I think my kooks had it too on my old car. Thanks for answering all my questions btw. The pics are def helpful! :cheers:

itsslow98
07-29-2012, 05:30 PM
I highly doubt you would see anything gained by going full 3". I would imagine you could find similar gains just by going with a less restrictive set of mufflers on 2.5" exhaust.

NeverSatisfied02
07-29-2012, 05:38 PM
That's what I'm trying to figure out. I sold the corsa mufflers so I need to go early tomorrow to cut them off the car and either install the magnaflow or the B&B. Magnaflow is complete just like u would buy it. B&B is just mufflers/tips, 3" x-pipe and 3" connector pipes but the rest would need to be fabbed together. Not a big deal but it'll prob cost a little more. Just don't know which i'd rather run.

The corsa sounds great at idle but it's got a higher pitched scream than I like at WOT and it still has a little bit of that pingy raspy sound my car had when I had no mufflers because I'm running catless. I think the B&B and magnaflow will both sound deeper and more the way I want it to. Just gotta decide tonight which route to go. Main difference is 2.5" or 3". My main attraction to the B&B is the nice 4.25" tips! I'll prob add cutouts later regardless which one I decide to run.

Big Bu Bu
07-29-2012, 06:22 PM
Back to your original question, this debate rages on daily on forums everywhere. Like this one (http://ls1tech.com/forums/generation-iv-external-engine/1498337-1-3-4-headers-vs-1-7-8-headers-my-experience.html) Same dyno, same brand, same vendor 1 3/4 vs 1 7/8. After reading countless threads, there is no real credible empirical evidence that one size is better than the other on a 346. That's a decision you need to make on your own from what you hear and read. I say do whatever you feel like without the worry you made a bad decision.

NeverSatisfied02
07-29-2012, 06:25 PM
Appreciate the info bud. Only benefit to the 1-3/4 is clearance IMO. Otherwise, I'd think the 1-7/8 would be better for having more room to grow. I'm going to stick with what I have. They are already on the car. Minor dent in the primary to clear the steering shaft and I'll be golden.

scatillac
07-29-2012, 07:25 PM
1 7/8 kooks no issues with steering shaft rub

This. The steering shaft to primary clearance is a bit more than 3/8" with stock motor mounts.

Disclaimer: This could be a product of mine having been special ordered with the D-port flanges, so the headers were more of a custom build as opposed to the standard build.