I had my exhaust done when the K8 was in a long time ago. It was apparently a mandrel bent 2.25 inch system. Installed my wideband bung today and upon taking apart the exhaust, I see it looks very small and press bent....

My question - I have a test pipe at the moment but would a hi flow cat on proper 2.5 inch piping with mandrel bends be worth spending the money on?

This is for a KL31 cammed KLZE with headers.

Pics -

I had a 2.25 on my first ZE and it seemed fine, now I have a 2.5 mandrel bent with a high flow cat, Vibrant reasonator and dual tip muffler and it's so loud it almost ruins the cruising experience. Just thought you'd like to know this. Between 80-90 kms the drone is not pleasant. For the engine and hp rating 2.25 is suppose to be the proper size for the ZE. http://www.magnaflow.com/wideopen/performdata.asp

Well dont know about the size but on my last k8 I had 2.25" Cat Back to an HKS Hi Power muffler...thing it was 175mm can and 4" tip...had a great sound...ppl thought it sounded like a Camaro...just my two cents on that.

Now on the madrel thing...I can tell u for a fact that those bends or crush bend...but dont worry about it...unless you FI and trying to break the 500HP plus mark the crush bemds wont hurt you in the least...and even if it is may only be 1-3 hp or torque.

For optimum flow the general rule is 1" per liter. But that is just a general guideline. I have full straight through 2.5" crush bent exhaust now with no cat or resonator to the 2" MazdaSpeed muffler. http://www.youtube.com/watch?v=EmwUgKSTNvg&list=UUqnK9d2dM1uUfWxuP_w6_zA&feature=share

Prior to that I had a Cat and Resonator to a magnaflow muffler all 2.5" and it was loud loud with the dronning in the cabin http://youtu.be/eQM69EolsEw?t=25s. With what I have now, the droning is gone. Though I will be upgrading this summer.

I plan on upgrading my downpipes from 1.5" to 2" into a 2.75" mid section then to a 2.5" rear section and a modify my MS muffler to 2.5". All will be done in Stainless and mandrell bent.

For a fact? Can you post a link to where your factual information is coming from. Now if you said in your opinion then that's different.
The size of exhaust mentioned at 2.25" would definitely impair the performance of a 400hp engine much less a 500hp engine IMO and IAW the above posted Magnflow exhaust/HP chart.

Actually I did some reading today and found posey92 is probably on the money with some of his comments. Even properly done mandrels are only marginally better than crush bends and it applies mostly to sharp bends. I don't think we have anything more than a 90 degree bend on our cars.

Other thing is that some places that do "mandrel" sometimes don't have the proper equipment and simply weld the mandrel bends to the straight sections, which unless somehow done perfectly will have internal lips and mis matches, which negates the whole idea of using mandrel.

For now I think I'll stick to my current exhaust until I finish my ECU tuning project and dyno it etc. My main concern were the crush bends and internal overlaps in the pictures making it look more like a 2 inch exhaust. I should have got the tape measure out too, just to see if it was actually 2 1/4 since it may have been 2 inch

I have built way too many exhaust systems now agree with this statement. Even the highest levels of performance and race shops build their mandrel bent systems this way. A mandrel bender is an expensive piece of machinery. If done properly your welds are minimal and only on the outside, not hurting the flow on the inside. I would take a JDM welded bent pieced together bend over a crimp bent pipe any day.

Example:


Your pieces should never overlap if you are doing it correctly. And a reputable place will always grind down any "internal lips" that you mention.

That being said. This exhaust system is definitely crimp bent. Often times you will get really bad bends like this when the shop is too lazy or just does not have all the proper sizes for their bender. The ultimate in pipe bending will always be a hydro bender IMO, but that is a bit unrealistic.

Either way, I agree that the crimp bends will take you from say a 2.5" pipe to a 2" or 2.25" in some bends. My 2.5" crimp bent right now does not have nearly the steps in it as these to. There are more than enough dyno results out there showing some impressive gains by going from crimp bent to "A pieced together" mandrel bent system. You can always buy generic full systems on like Jeggs and Summit racing then that would reduce the amount of your welds.

I am curious just what the purpose of and the price of titanium intercooler piping like that is lol...every dyno stuff ive seen as far as mandrels are concerned have shown good gains for intakes as u want less turbulent air where as exhaust properly sized for its application doesnt show much for mandrel...the few ive seen in person was two of the same cars stock and got a full exhaust done...they wernt mine and it was like 7 yrs ago but they were both 4g eclipses gs 2.4..I had an exhaust done 2.25" cat bak to a hks ti carbon (discobered credit cards as a young Airmen ...the other guy friend of mine was a little smarter in the sense he saved and used cash...he had the shop do a custom mandrel exhaust...not sure if he paid for the curves pre made and the pieced it together or one piece done with mandrels...anyways price difference was bout 300 bux I thnk...we brought our own mufflers so we basically paid for exhaust and weld on hangers and muffler...anyways to make a long story longer we dynoed the next weekend both stock other then exhaust showed a 7hp difference remeber cuz it was 07...plus the car was an 07:)...needless to say he was a lil upset it wasnt more...

So bak to the point...I guess if you wanna phrase it that way...my opinion is money it cost for madrel doesnt make cents <<see what I did there:) until ur pushing 400hp range cuz at that point youve already spent a good chunk of change so ur trying to squeeze every hp you can so a mandrel exhaust makes cents....again LOL bored:(

I always suspect it's the dual-tip mufflers that are the issue for sound. Usually those that test my theory and plug one of the tips with a tennis ball or the such confirm it.

I ran a 2.5" crush bent with headers, no resonator and a magnaflow 4" skewed tip. With no cat the thing was loud as hell, sounded literally like a race car with a straight pipe. It was loud even when I was trying to be quiet and I could be heard dozens of blocks away. Threw in a Magnaflow hi-flow cat and it quieted right down, awesome sound and no resonance.