illtres50

I recently gutted the primary cats on my isf with secondary cat, and muffler delete and the power increase is definitely noticeable throughout the rev range. So far I am happy with the outcome and I'm not so sure if its worth going the headers route in the future.

For those of you who have made the jump from gutted manifolds to headers, did you notice much of a increase in power?
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Rossi

iTrader: (5)

Well, the stock manifold design is pretty pathetic. Bummer you destroyed the primary cats, I sold mine for $600 which made my Sikky V2 headers installation FREE. See for yourself......

rmillsISF

My main thought is with all the stock headers I've seen cracked on here there's no reason to keep them around.

Vervish

iTrader: (4)

IMO - if you gutted already - get the RR tune - setup has been dynod at ~400whp with an aftermarket exhaust.

I have gutted stock manifolds with X-force exhaust and RR tune. I ran exhaust and tune before gutting...the tune felt like a bigger bump in HP than the gutting to me. I did not feel a dramatic increase after pulling cats...other than how bad it smelled (I have since added high flow cats to exhaust) just a slight bump.

Leander311

iTrader: (2)

^^^^THIS. From all kinds of research, it seems headers are worth ~10whp over and above gutted cats, at which point the RR Racing intake finally offers minor gains as well. If the added $250/hp is worth it to you (headers), then by all means. For my money, as Vervish stated, exhaust/gutted cats/tune is the smarter approach (~$25/hp). Take the $2.5k you'd spend on headers, and instead add some better brake pads, lightweight wheels, and coilovers. My wheels reduced my rotating mass by 40lbs (while increasing contact patch/traction substantially) for 30% the installed cost of headers and just as much if not more dynamic effect.

2013FSport

iTrader: (2)

The thing is unless the cats are bad, the flow through a gutted cat is far less than ideal.

Think of pouring fluid into a funnel. A large volume into small hole and it all backs up. In terms of exhaust and hot gasses, the gasses expand in the larger volume of the gutted cat and loose heat AND velocity. Now those same gasses must be shoe horned back into that funnel to exit whereby they have lost forward moment and any port scavange effect they had...

Compliance aside, a test pipe near equal to the collector diameter would be best in place of the expansion chamber that was once a CAT.

JM2C...

Leander311

iTrader: (2)

I'd also read this opinion back when researching my decision on this same issue... Has anyone done this without removing the stock manifolds? Dyno results before/after? If aftermarket headers are only achieving another ~10whp over gutted stock manifolds, it would stand to reason your suggestion would also represent a lot of work for minimal gains.

MileHIFcar

Regardless of how much someone spends on headers which are $1,500 for the UEL PPE, and gets more expense as you go up for Sikky V2 $1,899 and then up to EL which are $2,500-2,700, headers regardless of configuration outflow the stock manifolds by a large margin!

I speak from experience as I am FBO (look at sig) and my friend who lives 1 mile away have raced each other about 50 pulls (at least) over the last 18 months, and the outcome is always the same I put about 2 car lengths+ on him every single time by about 100mph. We usually do 40 rolls starting in 2nd gear and my car pulls significantly harder than his. He has the exact same mods as me as the only difference is he has gutted stock manifolds vs headers.

The increase in power from the headers is quite obvious, even so that we really don't race each other anymore because the results are always the same. Needless to say he's started a header fund to let the 2UR-GSE breathe to it's full potential

Leander311

iTrader: (2)

Two car lengths sounds about right... but you're taking advantage of the tuned intake since you've headers, whereas your friend is getting nil from it, according to RR Racing. Regardless, smarter money is in making her lighter. You'll see the same effect for a third the dough for lighter wheels, plus "adding lightness" does wonders on all points of the traction circle. No wonder it's one of EE's very first videos... because it matters! Headers will benefit one vector, but lightness improves all four:
Or as Mike Kojima wisely stated to open his series on race car dynamics, "Horsepower is sexy and chicks dig it, at least a lot of meatheads think that way."

MileHIFcar

Your correct on that fact that his Tuned Intake is probably not giving him the results that I'm getting because of the choke point on stock manifolds... but right can't go wrong with lightening your car either. The best result is to lighten and get headers

Speaking of weight I need to weigh my car..? it's definitely lighter than stock, but by how much I don't know yet

eyzz21

+1. I have had both stock headers gutted and PPE headers. Both w/ RRs tuned intake, tune, and stock exhaust with secondary high flow cats and magnaflow mufflers. With gutted headers i didn't feel as much power increase in the lows and mids, but definitely noticed it on top. With PPE headers, i felt it all around improved. As many have mentioned it has a lot to do with the hallow space when the cats are gutted. I would love to see a side by side of someone running PPE or Sikky headers vs someone with stock headers with a welded pipe in place of the primary cats.

Leander311

iTrader: (2)

Haha, fair enough! I need to weigh mine as well. According to the little spreadsheet I put together, I should be just under 3600 lbs w/half full tank.

My pending weight loss plans are mostly centered around vegan/sober/fit January.

illtres50

I appreciate everyone's input, I think at this point I'm going to invest in a exhaust system and tune and see what hp gains that will yield. I would be more than happy if I were to reach the 400 whp mark.

Also, I found this video on YouTube today of a isf with
Gutted primary cats, secondary cat, and muffler delete vs a isf with PPE Headers & PPE Exhaust Takeda intake. The isf with gutted cats held up pretty well, I'm impressed.

2013FSport

iTrader: (2)

For those who do not have a full name brand exhaust, how many of you kept some form of resonator either as part of the muffler or solo near the oem location?

It does serve a purpose allowing gasses to scavange regardless of the muffler system downstream. But is it helping or hurting its breathing is the question?

Anyone monitoring the MAF flow and see changes?

lobuxracer

iTrader: (2)

You don't need to cut the cat shell out, just stuff a tube inside to prevent the volume change. As much as I am a big fan of properly designed headers for ultimate power, I'd bet the OEM manifolds with a proper diameter tube stuffed in them would be painfully close to header performance for very little money.