[bonestock]

I had these installed, I plan on doing a cam, was told you'll need longtubes, so I got a set.
Car has a p1 stage 2 kit..car sounds crazy. They did say I probably wouldn't pick up that much. First dyno was a winter an this time 100 degrees.

Car has a full exhaust, catless headers x pipe to my mbrp exhaust and a blower with a tial bov. I love how the car sounds, but thought ide get at least 5 hp. I don't know. Car makes 570 on 6.5-7lbs. Fun car though.

[oldman]

I have swapped back and forth the stock headers with various ported cats and cat delete pipes vs LT, I would say SOP stock headers and CA cat deletes are down 15 HP vs LT at my power level. Stock headers and ported front cats are down 20 to 25 HP, stock headers and 4 stock cats 25 to 35 HP... My final build (till I get bored) stock headers, ported factory cats ( I section the pipe and expand portions and reweld) yields good results. I think on a less radical build I can see LT yield 10 to 15 LESS HP. I'll keep my LT just in-case I decide on some crazy build in a few years.

[laynlo15]

Honestly GM built a pretty good exhaust manifold and cat system.

[Umbriel]

Comparing a dyno in the winter to one in 100 degree heat isn't the greatest way to judge something. Did they retune it after the headers? Did you lose any boost?

[KingLT1]

I think you should of gained more then that but honestly the Factory headers flow pretty good with cat deletes. Catless LT's are typically worth 15-20whp over this setup on cars in the 700whp range.

Originally Posted by Umbriel

Comparing a dyno in the winter to one in 100 degree heat isn't the greatest way to judge something. Did they retune it after the headers? Did you lose any boost?

Boost is just a measure of restriction, so a Loss of boost won't effect power if air flow is increased...air flow is what makes power not pressure.

[Tim M]

Apologies on the side track, but can you elaborate on porting of the OEM manifolds/cats? Thanks.

[oldman]

I port the inlet and the 02 bung, I space out the 02 so they are only 1/2 as far into the exhaust flow. I smooth out the transition from cast piece to pipe (really bad here) and then on the driver's side only I cut the pipe at the crush bend and make it round again. This is a pic before I grind away the 02 bung, internal to the pipe, the pipe is rounded out already when picture is snapped.

[Jbanta1983]

Are you still on the lt1 fuel system?

[Tim M]

oldman: Thanks for the info and image. I will start a new thread.

[bonestock]

Originally Posted by Jbanta1983

Are you still on the lt1 fuel system?

Yes. I also had high flow cats already. The shop told me to get a cam I would need headers. And maybe a fuel pump. How much is a lt4 fuel system.?

Car is stock except blower, longtubes and headers..I guess 571 is good for what I paid. I installed it myself. Plus I'm disabled vet. I want 650rwhp. What else would I need to get their

[oldman]

Where in Texas? I can help you install a LT4 fuel system (even the intank), anything for a Vet.

[laynlo15]

Thinking back I didn't run headers till my 1st short block we built after the ring lands broke on the stock lt1. I ran 10.00@139 on the stock exhaust including the stock manifolds and stock cats, so I can see why you didn't really show much increase. I don't know if headers and no cats would have gotten me into the 9s on the stock motor, we were pushing it really hard. Guess I'll never know.

[KingLT1]

I bet it would have. Your EGT's were likely through the roof with the stock cats @ 14psi. Likely might of lived longer had you deleted them before turning the boost up. Toohighpsi made a good post about it in another thread not to long ago.

[laynlo15]

Yep, I agree. I was stupid to think those aftermarket cats would live. The factory cats took a lot more abuse with no issues. Probably had at least 180 something runs and 12000 miles on the stock exhaust system.