I was just reading another thread here about a guy with a crush-bent exhaust and it got me wondering.

Do people not know the differences between crush, compression, and mandrel bending such that they're using the wrong terms, or do shops actually crush bend pipes?

As I understand it, shops use compression bends to custom bend pipes. These bends are nice and smooth, though the pipe is partially distorted so the diameter reduces a bit through the bend. For all intents and purposes, these are perfectly good for a car of our calibre.

Shops with lots of money (or performance companies who sell prefab exhausts) use a mandrel bender. This is the best since the diameter stays the same throughout the bend.

Companies that mass produce stock-replacement exhausts or sections of pipe use crush bends because they can be automated in a factory to be done very quickly. You know these when you see them, since the inside of the bend has been crushed like an accordian baffle.

So my question is this... how do you end up with a custom made exhaust that's crush bent? Are there shops with machines that can crush bend pipes or do they take prefab sections with crush bends in them and just weld them together to fit where they want them?

I know that shops without a mandrel bender do that with prefab mandrel bent pipes.

Just curious...

Yes shops really do use crushed bent. The shop I use did for years, but have moved up to compression bends. Very few shops have mandrel benders.



FU Tuning

There is literanly only 1 shop around here that actually uses mandrel bender. Everyone one else is compression or crushed bent pipe.
Compression is the norm around here but,....
Crushed bent is still very common these days.....at least around where i live.



PRND321 Till I DIE
Old Motor: 160whp & 152ft/lbs, 1/4 Mile 15.4 @88.2
M45 + LD9 + 4T40-E, GO GO GO

they guy i went to used compression...i asked him why he didnt have a mandrel bender....he said cuz it would have cost him $10,000.00. compression bent is good because the cross-sectional area of the pipe is almost the same throughout the bend, while cruch is well....not.


Ill make a sig someday

Few shop around here do compression bent most do crush bends.

I have thought this but no one has commented. That a mandrel bent 2.25" is good but a 2.5" is good if you do compression bend seeing the bends are distorted.


2004 Grand Prix GTP (Competition Group)
SOLD-->1999 Z24 5M-#30 to register on JBO
"You can please some of the people some of the time but you can't please all the people'
all the time

Mylife75 (ajose) wrote:Few shop around here do compression bent most do crush bends.

I have thought this but no one has commented. That a mandrel bent 2.25" is good but a 2.5" is good if you do compression bend seeing the bends are distorted.

For most of our applications a 2.25" compression bent pipe is close enough to a 2.25 mandrel bent pipe. I would say a 2.5-2.75" pipe would be similar if it was Crushed bent.



PRND321 Till I DIE
Old Motor: 160whp & 152ft/lbs, 1/4 Mile 15.4 @88.2
M45 + LD9 + 4T40-E, GO GO GO

But the pipes with distortions on the inside bend are absolutely miserable for flow! The pipe has huge amounts of distortion which really creates turbulence and reduces total flow volume. Better to go small pipe with a reduced radius than larger pipe with high level of distortion.

I've never been to a shop which produces similar bends to what comes from the auto parts store. Although "crush bent" is the term that I've always heard applied to what the exhaust shops produce. "compression" and "crush" are almost the same thing, so I dunno.

-->Slow

I have NEVER seen a shop do crush bends around here, all coompression and rarely manderal

my dad has a crush bender the main reason he has it is the cost of a mandrel bender ( for those who ask for it) due to the high flow and some dragster cars he works on, and the compression is practicly the same as crush. So why upgrade to do the same thing? Most exhaust shops that redue STOCK tubing have people who could care less if there was any restriction, turbulance, etc...

compression is not the same thing as crush, no where near it... smoother flow and less distorsion to pipe size using compression..

the two terms are ALWAYS mixed up here on JBO from what i've been reading... There are alot of shops that do crush bend pipes. these are normally the "smaller" guy on the block type of shops. Around here the standard is compression, no shop has a mandrel bender as they cost more than they're worth new (compression for a top of the line is $16,000 and for a mandrel entry level is 22,000.. if you want to play in the big boy legue doing truck exhaust or anything from 3" up you can spend upwards to 32,000 for a bender...




_______________________
** Flat Broke Racing Inc.**

See the attachment to see what a crush bent pipe looks like. This is the sort of stuff that comes pre-bent from China to replace rusted out OEM exhausts.

A compression bend looks nice and smooth. It's just not uniform in diameter throughout the bend. That's what makes the mandrel bent pipe better.

Attachments

closecrush.jpg (14k)

That attachment says it all. That's a true "crush" bend, see the ripples on the inside of the turn? Around here it's all compression bend with 1 shop having a mandrel bender. That shop is always loaded with people's hot-rods, old Camaro's, Chevelles, Mustangs..etc. Just about all the high performance people go there, and it's higher in price too. They have to charge more 'cause the mandrel bender is like $20K for an entry level machine. Compression bending is much better than crush bending, smooth radius does not produce "areas of turbulant flow". (I'm an engineer, and that's the engineering term for that).
Don

that is what i had long time ago now i compression bent


2004 Grand Prix GTP (Competition Group)
SOLD-->1999 Z24 5M-#30 to register on JBO
"You can please some of the people some of the time but you can't please all the people'
all the time

I had my exhaust done on a 96 about 2 years ago. I knew about mandrel but no shops around me had it. So i went ahead and got the 2.25 inch and of course ive got those ripples. At the time I had a header, downpipe put on and from there is where the 2.25 starts. The converter is stock but from a silverado cause it has the same size piping. Only difference I could tell was top end and the exhuast was louder at low rpms. Should I go to mandrel instead? just curious