Let me start of by saying that this not the typical 1 3/4 vs 1 7/8 argument, since there's a lot more to a header than primaries diameter.

I'm starting to notice why some headers perform better than others and why some people fail to see one of the main differences in them. I have some 1 3/4 JBA headers, which come with a v-band collector and I was able to use a Kooks o/r x pipe with them, after an easy mod since the jBAs come with an additional flange for the mid pipe.

Anyways, I feel that my vette lacks some torque in the lower rpms, and the cam does't help either. Well only after 3k rpms. I've been reading everything I can about headers and noticed that the most overlooked area is the tube length. I see that kooks headers seems to have lower torque numbers compared to the LGs, SWs, ARHs, even the OBXs. What do those have in common? The tube lengths are somewhere between 27"- 32". The Kooks? Somewhere between 21"-23" according to another member who measured them. Now if you have not seen the JBAs for the LS2/3, the part number is 6819s. Take a look, and you will see why Im bringing this up. Their primaries are as short if not shorter than kooks. So, this is why I believe that mine feels somewhat lazy. I took a ride on dev1360 vette and even thought he has 1 7/8 OBX headers, he could easily cruise at slow speeds and higher gears with no noticeable vibration due to lack of low end grunt. Before anyone says, his mods are almost exactly as mine and the cam specs are strikingly similar too. The one thing is that I have a full 3" exhaust with '11 zr1 mufflers and his neck down to 2.5" with a corsa exhaust. Also at the track he has 4-6 mph at the 1/8 mile even with the same 60ft!! And with the same drag configuration.

Another area where I am not liking the JBAs is that the v-band clamp pretty much is a one time use. jBa already sent me a new pair once but the second pair looks like I would not be able to reuse it again either. The bolt and nuts of those clamps look like they are aluminum and get stripped at only 13ft-pounds of torque.

With that...I'm seriously considering switching to a longer tube header. Do you think that I'm leaving a lot on the table with the shorter header? Is the full 3" exhaust helping or affecting? I know gears will take care of that deficit, but at this point I decided that for my goal they are not necessary.

Discuss please. Thanks!

 

If that little bit of power is important, but I think you are wasting your money.

 

While far from being an authority on exhaust systems, I had a great interest back in the '60's when more serious intake and exhaust design was first being developed. Theoretically, an ideal V8 exhaust system would have 4 tubes coming from each head that would start at the port diameter, then taper to join into 2 tubes that would taper to join into 1 tube that would taper into atmosphere. The length and diameter of each portion would change according to RPM and VE and the would be no bends in the tubes. However, by the time we have created the force field technology to do that, piston powered transportation will be a minor footnote in history.

Now back to reality and the C6. Unlike a shoebox Chevy, header design is limited to the tiny space available. Within those confines, you have only a couple of variables you can control. Length of the primaries and diameters need to fit the RPM range and the VE you have.

The thing to remember is the volume of the exhaust gas changes as it cools and therefore the space to maintain the velocity must get smaller as the length gets longer.

In your system, the most glaring issue is the full 3" from the collector to the exit that has slowed the flow.

 

Well in reality what I am thinking of doing was to swap to a longer tube, most likely OBX and go back to the stock 2 1/2 axle back. I purchased the zr1 axle back at a spectacular price, so if I was to sell my current headers, mid pipe and zr1 axle back, that will cover the cost of the new headers with mid pipe and still make money on top of it.

 

Ahh I was hoping I'll get a reply like yours. If I dont do the headers, I am going back to the base axle back. My main concern is the low to mid range torque. I've seen several post in which SpinMonster talks about how he replaced the kooks 1 3/4 for LGs 1 3/4 and gained 30+ foot pounds of torque down low. He always point to the length of the primaries as to why some people claim that 1 7/8 don't lose anything to the 1 3/4, but for example they are replacing a set of kooks which are like 23" with some arh which have a longer pipe, 27" iirc. Like I said, after being in another vette with longer primaries and even when they were 1 7/8, the extra torque down low was noticeable.

I may just wait and give the oem axle back a try. I am also running a stock air intake bridge, but have a halltech mf103 waiting to be installed.

 

The base OEM mufflers will be too much restriction, but the NPP/Z06/ZR1 mufflers and some aftermarket ones will work well. Neck down the 3" pipe to 2.5" about halfway between the header collectors and the muffler inlet. At the back end of the X pipe will work fine. Since the muffler inlet is already 2.5" on the above mufflers, the flow rate was maintained well before the inlet. You'll never attain the ideal system, so the best you can get is a happy medium to match the performance range you desire.

Getting cold air to the engine is every bit as important as getting the exhaust out. I prefer the Vararam, because it acquires air from the front rather than the bottom where road surface heat can be a factor and affect your 60' time.

 

Also bear in mind that intake temps and DA can factor in quite a bit. I was hot lapping my car, which kept intake temps down. DA was also -100'.

Our cams are pretty similar, but crunching the numbers there is a difference of 3* overlap at .050. (10*/7*).

It's hard to say where the difference is. A lot of things can play into it.

 

Let me see if I understand this....you're saying one header (any header) gained 30 lb ft of tq over another? If that's what you're saying, someone has their info completely out of wack.

 

The kooks mid pipe I have can easily be converted back to 2.5. I may have to use the axle tubes from the base mufflers.

I didnt realize that I was missing the intake part of the equation. If I want to hit 10s and be there solidly, I think intake is a must.

 

I didnt think that it was possible to get that type of DA at Gateway lol. As for the intake temps, that's why I decided to give the halltech another try. Guess I never tried it with the cam installed.

You are right! The cams are not the same, but I never expected that little overlap to make a big difference if that is the case.

Are you still loving that clutch? Later man...

 

Not any header. SpinMonster swapped kooks for lg when he was NA, on the same diameter, but they are obviously different lengths. He did the test and the claim. Where is Spin when you need him?!

 

I'm hitting 10's in 2000' DA with a stock cam, so you should have no problem if you get the intake/exhaust sorted out. Vararam is the best for performance. Also, don't use a full length x-pipe at 2.5". Keep it at 3" initially and then drop the size to 2'5" just before it attaches to the over-the-axle pipe.

 

My kooks mid is a two piece design and it reduces to 2.5 about half way past the x. So it sounds about right what you are saying. I like the idea behind the vararam, I just dont want one in my car.

Thank you for the info!

 

I switched from Kooks 1 3/4 to LG 1 3/4 and it gained 29rwtq under the curve at 3800rpm. At peak it gained 17.

Under the curve does not mean at peak nor do peak numbers tell the whole story.

The race merge collector on the LG pro's are the reason. Kooks later upgraded the garbage collectors on the headers they sold me when the C6 first came out so I doubt its indicative of their current product. I saw the newer Kooks merge collector in 2008 and it was upgraded. My post went up in 2006.

I dont feel like getting into an old time header debate. LG put up plenty of dyno sheets showing the differences with header swaps. If you dont credit them then leave it be. I duplicated the results myself and was happy. I later went to AR 1 7/8 to not have slip fits and it made little (no) difference on my FI car.

 

I honestly dont think its worth it but that is my thought, I am sure a retune will be needed in order to TRY and pick up any additional HP. Seems like a waste of $$$ to try and gain some more power. If you want more power throw a shot of NOS on it call it a day.