Most of the gain is from getting rid of the cats. I saw 15 hp with the downpipe and 11 more with them open. Having done that and knowing what the exhaust manifolds look like I figured at least 15 hp more from the headers which would jive with what Dyno Comp claims. The cork gaskets have leaked on me before and unless its a real bad leak it's hard to know for sure. I changed my plugs recently and they were black even though at WOT the afr's are lean. That's the only reason I suspect a leak. The car runs strong and the idle isn't horrible which happens with a bad leak. I ordered 2 sets of OEM gaskets so I don't get caught needing some and not having any. The local dealer charges $25 a gasket. I found them for $6.62 online.

Les

 

Any news on this Les?

 

You're still running the resonator and OEM muffler, right?

Based on what you've found, I'm tempted to simply get rid of the rear cats, replace them with an X-pipe, and maybe (mayyyyyybeee) run an aftermarket muffler (but keep the resonator). And then call it a day. I can do all of that for ~$300 installed. Downpipes are a little rich for my blood, unfortunately.

The resonator is fairly free-flowing, the cats are not. And if I'm only removing either the cats or resonator, I'd rather remove weight from the front of the exhaust system than the rear...

I'll retain the primary cats, for emissions friendliness. But those secondaries are just extra bricks in the system.

 

Just playing devils advocate here but I wonder what would happen if you put the cats back on. Not knowing what these headers were designed/intended for (emphasis on intended) for (cats vs no cats, let's assume w/cats) you might just be lacking sufficient back pressure. Maybe MHB went a little overboard with the primaries? On the other hand these headers would most likely rock on a full tilt build, high boost, race gas, ported heads, cams etc.

 

I say we just do something like this:

SLR muffler bypass, Quicksilver - MBWorld.org Forums

 

Damn that must be loud as fack!

 

No news. I ordered gaskets from Cali and they never shipped (or charged me) so I reordered from RM. It took them a few days but today the gaskets shipped. If they arrive soon enough I'll get them on before my track day on Sunday. If not I have a good pair of used ones ready to go with some trusty copper spray. I suspect leaks with the cork gaskets as the AFR's are fluctuating at idle, cruise and generally acting strange except at WOT.

A little recap for you guys. The downpipes and teflon Y pipe gained 15hp. (no cats) With the cutouts open 26hp. (no cats) Headers 4 hp over the open cutouts. (no cats)

Les

 

Thank you for the breakdown... sometimes we all get lost in the posts.

Perhaps it's a no-brainer question, but I'm assuming there's no harm in running the open cutouts once you are tuned for the closed downpipes, right? Also, I recall this being a torque killer so it might be advantageous to keep them closed until you're off the line...

I would need to run 200-cell race cats at the very least. In TN, I can get by with 2 cats, but cat-free isn't an option.

 

Here's the only picture I have.

 

You guys did a great job of figuring out how to piece the system together using portions of your NW's downpipes, trans. bracket connections, o2 J bungs, etc. Your shop must have scratched their heads for at least a little bit?
Is that DEI titanium exhaust wrap I see coming down your headers? Well done Les.

 

Yes, I wrapped the headers with the best. In retrospect, now that I see how they fit in the engine bay, it wasn't necessary. Part of the long wait to get the headers on was lack of stainless, no header wrap in stock etc. When a stainless shipment arrived they got it done quick and professionally. The shop welder is an artist as you can see. I'm still waiting on the gaskets.

Les

 

First time I've seen O2 sensors mounted like that. Seems like they wouldn't get as good a reading vs OEM mounting position.

 

Without the cats the O2 sensors throw a cell. Mounting them this way helps prevent O2 sensor codes.

Les

 

Does it work? I tried the long "spark plug non foulers" at first, but still got codes. They were straight, not the J bends you have.

I went the these:
O2 Simulator Mini Cat Cel Fix best oxygen sensor simulator made.
and they work great. Have not had a code sense.

 

I found a leak! My new gaskets arrived and ..... wrong gaskets so I had to put on some good used ones with copper spray. It looks like installer error to me. Let's see what she does with all the cylinders at full power.

Les

 

Are you going to try and run this weekend?

 

I installed the "new" used gaskets on Saturday and had a track day on Sunday and all I can tell you is I found some missing power. I have a Solo 1 competition on the 21st and 1/2 mile on the 28th. I'm trying to find time to get on the dyno this week. The 1/2 mile event is being held at a different airport (Roosevelt Roads) and will be with a tail wind instead of a head wind so the comparison times won't mean much. Not to mention I'm thinking of slipping on my Code 3 for a little extra boost. I hope to break the 145 barrier .... actually 148 but perhaps I'm dreaming. I need a fast time or Grip will take the record from me in September. The latest drag rentals were rained out and the next date is still pending. The car really ran strong all day at the track. Lot's of questions from the people that know my car about what's different now. Part of that is the race tires. I was able to get the power down real early and exiting the turns higher up in the power band from increased grip. Pleased, excited about what's coming up, happy to be driving up to the cars capability .... at last. I've toyed with changing the suspension, again, but I have the car predictable now. Yes, it still dives a lot under braking and rolls side to side in the corners more than you'd think is acceptable, but it's so darned predictable that when it starts to slide it's so easy to gather up. So I've left it alone. The headers, the headers. Until I get back on the dyno I don't want to say much. The instal is a *****, they're rubbing somewhere because I can feel it in the steering wheel. Not bad, acceptable for me, but perhaps not for a daily driver. Power is up. How much? I hope to find out soon. This instal has been FUBAR and I'm frustrated. I wanted the results to be clear and indisputable and now that's impossible. Too many variables and so much time has passed since the instal. But I'll report.

Les

 

can't wait to read about the results...

 

I'm glad that you've got some power back!