4.2 Exhaust Manifold Upgrades, Revisited

[redneck truck]

I've just purchased some exhaust manifolds from an early 4.2. They are the style with the (supposedly) larger collector and individual primaries that run all the way to the collector.

I realized that I've made an assumption: 4 primaries to the collector rather than 3, and a bigger collector mean better power output. However, I've never seen empirical evidence to that effect. Has anyone actually bothered to do the swap and can they comment?

[A62TURBO]

Would a header style setup be an option?

[mithril]

Would a header style setup be an option?

Not really. JHM looked at producing headers for the C5 4.2L but needed 10 people to buy in to get it started and couldn't raise the interest. Basically no market means no real non-custom performance upgrades for the 4.2L. The early 4.2's had the same pre-catless system that the S6 got.

[redneck truck]

These are the exhaust manifold part numbers I've been able to find.

077 253 033/034J: early 40v 4.2 non-S. Fits down pipes without precats. 4 visible primaries in collector, free studs (i bought a pair today)
077 253 033/034T: later 40v 4.2, non-S. Fits down pipes with precats. 3 visible primaries in collector, screw-in studs (in my car from the factory)
077 253 033/034Q: all of 40v 4.2 S6/S8. Fits down pipes without precats. 3 visible primaries in collector, free studs

As for down pipes, it seems the only difference I can find is whether or not there are precats; can't find anything on a larger or smaller inlet.

4b3 254 500/550 GX = has precats
4b3 254 500/550 CX = has no precats

[Vinnie981]

i have a 2000 Audi A6 4.2L came stock with
077 253 033/034J: early 40v 4.2 non-S. Fits down pipes without precats. 4 visible primaries in collector, free studs
4b3 254 500/550 CX = has no precats.........cats are located under car which equals less engine bay heat soak.

Also JHM's Audi S4 B6 headers fit the Audi A6 C5 series with the belt driven v8. ......from what i have been told from a couple people. There are very minor mods needed for them to fit.

[alterdcreations]

Totally in for this

[ddillenger]

I'd think the difference would be negligible. Curious to see though.

[A62TURBO]

Totally in for this

That's what everyone said last time too lol

[redneck truck]

I just want to get the best parts in there that I can while the subframe and oil cooler housing are off. Don't really have time to reinvent the wheel or wait for a new parts offering...

[Castor Troy]

That's what everyone said last time too lol

Yup, right up until you figure out they are $1500 and you have to remove the engine to install them, they sound like a great plan.

[NuGGet_PuFFer]

Not to threadjack, but there are a few 4.2 gurus in here, so I figured I'd mention I'm parting out a 4.2 engine that I just pulled out of a 2000 A6 with 100k on it, motor ran fine, timing belt looks new, trans died, obviously. Let me know if you guys need anything.

[mithril]

Yup, right up until you figure out they are $1500 and you have to remove the engine to install them, they sound like a great plan.

ding ding ding!! This is largely why they never took off last time. Installing headers make lots of sense as a "since I'm in there already" type of mod when you already have the engine pulled for something else. To pull the engine just to install headers? The power gains aren't nearly enough to justify it.

[Vinnie981]

^Long tube headers for a v8 that actually are designed correct and create a shotgun effect in the collector are deff worth it. Great increase in bottom end power. now when a set of headers cost 2,700 dollars than yes i agree it may not be worth it especially if you paying to have them installed!

[mithril]

^Long tube headers for a v8 that actually are designed correct and create a shotgun effect in the collector are deff worth it. Great increase in bottom end power. now when a set of headers cost 2,700 dollars than yes i agree it may not be worth it especially if you paying to have them installed!

The JHM headers that fizzled and died on the vine were also long tube and designed specifically for this engine...

I'd have to see dyno charts to prove exactly what the gains are before I could agree whether it's worth it or not. What are you expecting to see in the way of gains? 20hp? 30? Even if these headers show unexpectedly phenomenal gains, once the cost of purchase and installation is factored you're still getting a pretty low power increase/dollar spent ratio and that's why no one has really pursued products stuff like this for the 4.2. $0.02.

[redneck truck]

Exactly my point. This is a "while I'm in there" occasion, as I (think I) can wiggle the motor around and access everything I need to in order to make the installation happen. But my budget is about $100 for 15-25hp, not $1500 for 40hp.

Are the manifolds with 4-1 collectors better the later manifolds with 4-3-1 collectors, or am I better off just staying with what I have?

[aysix]

Exactly my point. This is a "while I'm in there" occasion, as I (think I) can wiggle the motor around and access everything I need to in order to make the installation happen. But my budget is about $100 for 15-25hp, not $1500 for 40hp.

Are the manifolds with 4-1 collectors better the later manifolds with 4-3-1 collectors, or am I better off just staying with what I have?

[redneck truck]

Hmm, that engine seems to be missing a couple cylinders, but it's awfully heavy!

[aysix]

Hmm, that engine seems to be missing a couple cylinders, but it's awfully heavy!

It can also double it's output using spinny things to create power out of nothing.

[redneck truck]

As can the 4.2, if only someone made a set of pistons to handle it!

[Widebody4.2]

Does anyone think there room for a short style header? Something that'll allow more flow but not more constructive.

[Scotty@Advanced]

As can the 4.2, if only someone made a set of pistons to handle it!

THe pistons aren't the weak parts, it's the rods.

[redneck truck]

Well, but the compression is awfully high to be making boost.

[Widebody4.2]

Well, but the compression is awfully high to be making boost.

It'll take 7 psi all day

[Vinnie981]

sure will.....

and as scotty said it the rods and wrist pins to worry about

[Vinnie981]

Does anyone think there room for a short style header? Something that'll allow more flow but not more constructive.

im sure it can be done....but V8's prove best with the long tube header over shorties.