Test pipes vs HFCs and related questions
 

I was wondering if someone could answer these questions for me. As a side note it doesn’t matter what brand of HFC/test pipe and I do understand there will be differences from one brand to the next.

What are the number gain differences between high flow cats and test pipes?

How do I prevent my CEL from light coming on with either installed?

Will it be 100% necessary to get a tune after installing test pipes? As from what I understand any tampering with the computer automatically voids the warranty.

Right now I’m leaning more towards some resonated test pipes but I want to make sure I ask opinions as a part of my due diligence before buying.

Thanks for the help.

Not much. We're talking less than 5hp.

You buy a brand that has a good track record. I have 6k mi on my ERZ HFCs and no CEL.

There is no need to get a tune after adding either test pipes or HFCs. The computer can adjust A/F ratios to keep things in range. The tune becomes necessary when you've done more than three bolt-ons (cbe, hfcs, intakes, headers). Doing all four can lead to lean situations and a tune is highly recommended by the tuning companies sponsoring this site.

Remember that test pipes have some negatives that may not offset the marginal hp gain over HFCs. 1) more rasp: HFCs have some, test pipes have more. 2) smell: your exhaust will wreak after adding test pipes. 3) bumper stains: the uncatalyzed exhaust can leave yellow tinges to your rear bumper that require some additional 'work' to remove when washing the car. 4) noise: test pipes will be louder overall than hfcs. 5) emissions: in states that check computer codes, both should pass as long as there is no CEL. If they use a sniffer, a HFC has a small chance of passing, test pipes don't have a prayer.

Hope that helps.

^^ that does help, ive heard that many HFCs dont usually thow a CEL but your almost gaurnteed to get one with test pipes, if I did purchase test pipes (right now im close to buying some fast intentions test pipes) how do i ensure no CEL comes on?

Best bet is to get some extended bungs for the O2 sensors and perhaps try the steel wool trick (pack steel wool in the bungs to insulate the O2 sensors from the exhaust gases). I've read that the sensors look for a range though, so too little emissions can throw a CEL as well. ie, don't use a ton of steel wool.

By chance do you know if some resonated test pipes will bolt right in with the stock exhaust?

I have yet to throw a cell from my test pipes.. but there is a little rasp and does leave stains on my bumper.. I love my exhaust note and so does most other people though.. with stillen it sounds nice still, test pipes with my buddies greddy is LOUD and very raspy .. so i think it varies on which exhaust system you have.. with OEM exhaust and test pipes it sounded great to me.

thx for the help, after a few days of searching I feel pretty confident about going with fast intentions resonated test pipes.

On my G35, I dynoed with FI resonated test pipes and 3 hrs later dynoed with HFCs. The results...1whp gain only at the very top of the rpms. It actually lost a few hp down low compared to the HFCs.

The 0-to-miniml gains with test pipes, mixed with the rasp and gas smell make me highly discourage others from getting them.