Header size for high hp whipple cobra

[RoadRash]

I've been searching around and can't quite find the answer. I'm currently building a new motor (.030 over, stock rods, crank, ported heads/stock cams, ported lower). My power will probably be 650+ / 600+ range with a whipple 2.3.

I am looking at Kooks and ARH long tube headers. What size primary should I choose? I have been thinking bigger is better and looking at the 1 7/8" into a 3" collector with a 3" xpipe to 2.5" bassani catback.

With the 1 /7/8" primary, how large is the header flange opening? Will I need to have the shop port match the heads to the new header?

 

[Teej281]

Stepped headers would be best i'd say and if youre doing everything 3", why not upgrade to the 3" bassani catback and let another member enjoy the 2.5" catback. lol

 

[cobracide]

Yeah why narrow down from a 3" collector if you want to max it out at that level? 3" all the way back!

 

[RoadRash]

Ok, cool. NOW, I have a bassani 2.5" catback for sale and matching bassani xpipe ..

So stick with the 1 7/8" primary and 3" all the way FTW!

How about this question? >> With the 1 /7/8" primary, how large is the header flange opening? Will I need to have the shop port match the heads to the new header?

 

[cobracide]

Depends on the headers.. I recommend kooks as they should not have any overlap on the exhaust port. You will just have to see or call them but you should be clear without any blockage.

 

[RoadRash]

Stepped headers would be best i'd say ....

By stepped you mean the 1 3/4" to 1 7/8" to 3" collector? Is that the way to go to maintain low end torque? Is this necessary with a PD blower?

 

[RoadRash]

Depends on the headers.. I recommend kooks as they should not have any overlap on the exhaust port. You will just have to see or call them but you should be clear without any blockage.

I've never had headers before and didn't realize that even with larger primaries they shrink the flange end to the stock exhaust port size .. Is that correct?

I was hoping that with larger primaries the flange end would be larger and I could have the heads port matched for even more flow.

 

[Teej281]

Well you can port the flange a little bit to open it up, but yea, stepped headers typically give the best performance, but they are a little bit more expensive due to the fact that they need to be put together from different size tubing. But stepped is definitely the way to go.

 

[Fat-cat]

I have a set of kooks long tubes going in.. on boost applications you can get away with a smaller header.. 3inch is big exhaust and i have ground clearance issues already. im not sure what size the primaries are on the ones that i purchased 1-5/8th i think. And they should flow just fine to my 2.5 inch collector and make good power. I wanted them more for sound then the power gain though.

 

[RoadRash]

I have a set of kooks long tubes going in.. on boost applications you can get away with a smaller header..

I thought that would cause higher boost (more heat) than a larger header. With the stock logs, I hit 21psi with a whipple 2.3 gen2 and a 3" pulley (stock lower). I'm hoping to really bring that boost down with the headers (and pulley it back up) and up the power.

3 inch is big exhaust and i have ground clearance issues already. im not sure what size the primaries are on the ones that i purchased 1-5/8th i think. And they should flow just fine to my 2.5 inch collector and make good power. I wanted them more for sound then the power gain though.

Different goals. Not sure why you would do headers for just the sound .. my 2.5" bassani x to catback sounds great with the stock logs. Thanks for the input. I'd like to hear how your setup ends up. Going to get any before/ after dyno sheets?

I'm hoping for more power under the curve .. Anyone else done a 3" full exhaust with a TS blower??

 

[Posi]

I've ran 22lbs on a 2.3 Whipple with 1 5/8th's Kook's and never once worried nor thought I needed to go larger. These cars make 600hp with factory headers so that's why I never thought to go larger. Plus the ground clearance is not an issue at all.

 

[GodStang]

I have been running 1-3/4" kooks for years at 700+ and no problems. As far as port matching your two options are porting both the header and heads to the same gasket or send them your headers and have them match to that but that may not be worth it.

 

[RoadRash]

I've ran 22lbs on a 2.3 Whipple with 1 5/8th's Kook's and never once worried nor thought I needed to go larger. These cars make 600hp with factory headers so that's why I never thought to go larger. Plus the ground clearance is not an issue at all.

Brian, do your 1 5/8" Kooks have a 2.5" collector with a 2.5" xpipe?

I'm still looking for real results with a 3" exhaust . . . do it or not??

 

[RoadRash]

I have been running 1-3/4" kooks for years at 700+ and no problems.

1 3/4" .. 2.5" or 3" collector / xpipe?

 

[GodStang]

3" collector and the midpipe necks down about 4 inches in to 2.5". My exhaust rubs a lot and I am stock height.

 

[Jimmysidecarr]

A very small step where the exhaust port meets the header flange will reduce exhaust reversion. Port matching, at least on these engines, is over rated IMHO.

The exhaust flange should be slightly larger than the exhaust port.
The intake port on the head should be slightly larger than the port on the intake manifold.

These heads are so beyond the heads of old, a lot of those power finding tricks like port matching, don't do much on ports as big and as nicely shaped as these are.

 

[RoadRash]

3" collector and the midpipe necks down about 4 inches in to 2.5". My exhaust rubs a lot and I am stock height.

Man, stock height and rubbing .. then I am screwed. Should I look at ARH's? I've heard they tuck a bit better...

 

[RoadRash]

A very small step where the exhaust port meets the header flange will reduce exhaust reversion. Port matching, at least on these engines, is over rated IMHO.

The exhaust flange should be slightly larger than the exhaust port.
The intake port on the head should be slightly larger than the port on the intake manifold.

These heads are so beyond the heads of old, a lot of those power finding tricks like port matching, don't do much on ports as big and as nicely shaped as these are.

Jimmy, thanks for the input. That is what I was looking for .. didn't really know what could or should be done to these heads.

 

[GodStang]

Man, stock height and rubbing .. then I am screwed. Should I look at ARH's? I've heard they tuck a bit better...

ARH are great and the newer Kooks tuck better. I have had the Kooks for 5 years so they are the old style.

 

[SlowSVT]

I don't think you will gain much by going to a 3" system. Headers arn't much of an improvement over the stock logs until 600 hp or higher. At your power level expect to see about a 10 hp gain. The big exhaust will drone due to the lower resonance frequency and a small loss of low end response. If you were racing and kept the engine above 6000 rpm then the larger tubes would make more sense.

Personally I won’t run LT's due to scraping, leaking, makes it harder to work on and won't pass emissions :cuss: I have JBA shorties with 1 5/8 primaries which will reduce some of the pumping losses in the engine, can fit many combinations of off-the-shelf exhaust systems and will pass emissions. 2 1/2" front to back will maintain higher exhaust velocity and purge the system better and low to moderate rpm's.