Opening up BBK longtube collector

[Grn92LX]

What was his n/a 331 combo? Are you saying he didn't swap to the correct valve spring for his camshaft? Thats a big no-no!

 

[04sleeper]

What was his n/a 331 combo? Are you saying he didn't swap to the correct valve spring for his camshaft? Thats a big no-no!

331 with 10.5-1. AFR 185's, Ported Holley Intake, Accufab 75 MM TB, 42 lb. injectors, Cam Motions Custom Cam, Pro-M 80, Custom power pipe, etc....

He did switch to new springs but the cam was too radical of a profile to run on the street and put a lot of miles on. It was a grind for True Street.

 

[Grn92LX]

Sleeper, do you happen to have access to your friends dyno sheet showing the before and after gains of the 3" collector vs stock collector? I wanna see where the gains were and if it was through out the entire curve. Thanks pal.

Looks like this thread is very informative!

 

[dirtysohc]

I would've guessed 5 to 10 HP, but 15 is even better! And all for just a few minutes of grinding! My headers have been sitting under my hood for years (engine in the garage) and have become rusty. They were chrome not ceramic so they've gotten nasty lookin'. But I'm taking them and the Dr. Gas X-Pipe to a local coating place to have them jet hotted soon.

 

[vristang]

I know I am coming in late, but I have done this with my MAC headers, and wanted to offer a caution.

Do not do this without mocking things up first. My mac headers and prochamber midpipe do not quite match up perfectly. The mid pipe mates up to the header flange at an angle. If I had just started grinding as was done in the pictures that dirtysohc provided, I would have had massive exhaust leaks. If you run the exhaust for a while you will build up some carbon deposits on all the parts of the header flange that does not make contact with the midpipe. You can safely grind all of this material away. If anything in the exhaust changes however you may lose the seal.

Best of luck,
jason

 

[dirtysohc]

Good point vristang. ALWAYS mock it up first to see how much you should actually grind away or you could ruin it or at the very least cause a bad seal. I was lucky in the fact that my Dr. Gas X-Pipe came in pieces and the first length of pipe after the header flange is a straight shot. After mocking it up I then fit the pieces together under the car, tack welded it and then removed it for complete welding. But if the x or h pipe is pre-made you may not be able to grind as much away. Better safe than sorry.

 

[Grn92LX]

When my friend did this his car was N/A. It made 395 RWHP before switching the collectors and 410 RWHP after switching. Now that he has a blower, I'm sure the gains would have been more.

When he swapped to the 3" collector did he swap to a 3" mid pipe too? Im assumming the 15hp was a collector and 3" mid pipe swap from the 2.5" mid pipe?

Do you happen to have access to his before/after dyno sheets after the swap? I know you said he gained 15hp but i'd like to see the gains through out if possible

Mike

 

[04sleeper]

When he swapped to the 3" collector did he swap to a 3" mid pipe too? Im assumming the 15hp was a collector and 3" mid pipe swap from the 2.5" mid pipe?

Do you happen to have access to his before/after dyno sheets after the swap? I know you said he gained 15hp but i'd like to see the gains through out if possible

Mike

Actually he had a 2.5" mid pipe and 2.5" Dynomax Super Turbo mufflers and tails. He probably could have made more power with different mufflers but he wanted to try to keep it quiet.
I will ask him if he can scan his sheets for me.

 

[Grn92LX]

Wow so all he did was swap to a 3" collector and modified the 2.5" H pipe to work? If you can get those dyno sheet's that'd be great!

Hopefully I can see a decent gain by opening up the collector and swapping to a 3" mid pipe.

 

[Vapors]

Is this problem on the shorty BBKs as well? I never knew they necked down so much!

Are there any headers out their that dont neck down so much at the collector?

 

[04sleeper]

Is this problem on the shorty BBKs as well? I never knew they necked down so much!

Are there any headers out their that dont neck down so much at the collector?

Kooks.

Wow so all he did was swap to a 3" collector and modified the 2.5" H pipe to work? If you can get those dyno sheet's that'd be great!

Hopefully I can see a decent gain by opening up the collector and swapping to a 3" mid pipe.

OK. I'll try to get them for you. I called him and left a message.

 

[Grn92LX]

Thanks man for going out of your way to help.

 

[04sleeper]

No Problem Mike.

Sorry for the delay but here it is. He also changed the valve springs but it just extended his RPM due to valve float at around 5580 RPM. You can see the same pattern as the RPM's increase. But you can clearly see the gains throughout the range from the header flange.

Enjoy.
View attachment 499730

 

[Grn92LX]

Thank you, I appriciate the help! Those are nice gains through out! Thats impressive since yopu said he still kept a 2.5" mid pipe and all he did was weld on a 3" 3 bolt style collector and whatever he did to make the 2.5" H pipe work. I can't wait to do mine

 

[04sleeper]

No Problem. This is what he did on the header side.
View attachment 499702

Then he just welded on a 3 bolt flange on his mid-pipe to connect it to.

Good Luck.

 

[N8Miller]

I had a feeling it was you who posted the results, Sleeper. Thank you. I'd like to see near 400rwhp on a dynojet if possible. Regardless, these collectors are restrictions on my combo and most other combo's.

damn, see, this is why i cant talk to you.... you always got me thinking of how to get more power out of my combo! see, you and I have the same headers, similar motor power outputs, and have the same desires. now if i could find out why mine doenst run, id be right with ya

 

[wild_stang04]

That's a gain of 24.1 horsepower. I believe the new springs played a major role in that kind of gain. In the old run, the power drops off at around 5500. The new run, the power starts to drop off at around 6000, the springs allowed him the extra RPM, and horsepower. Opening up the collector may have gotten him 10HP of the 24 he gained. But what the hell, it's a free mod, there's no reason not to do it.