4.6 manifolds

[mcc1979ian]

Just wondering if anyone could recommend the best place to get a pair of stainless 4 branch manifolds for my 4.6 landrover 90, cheers

[Chicken Drumstick]

Afraid I can't. All I can say is, you want what our American friends would call Long Tube headers.

Most British 4 branch manifolds for Land Rover V8's are always short tube header style. i.e. the primaries are very short.

These manifolds improve breathing, but unless you are going forced induction, they won't really give you much in the way of gains.

What you want are long primaries, these promote a thing called exhaust scavenging. Which is where you get the most power gains from with an n/a motor. Short primaries do scavenge, but at much higher rpm (probably 8000-9000rpm+), long primaries will scavenge at much more useful revs.

For a 4.6 you'll want at least a 2.5" collector, or maybe 3" if you are planning on lots of upgrades.

[daslandroverman]

Depends how easy you want to make it.

The Double S stainless systems are good enough for the money with a pair of 4 into 1 manifolds and following the original pipe routing under the car.

The P38 type ones are also good, although the engine is offset to the right rather than the left, so the N/S manifold may need a little massaging for clearance.

[FridgeFreezer]

P38 ones foul the clutch slave on manuals, ask me how I know

[mcc1979ian]

Is that the original cast ones that catch?

[daslandroverman]

P38's have 4 into 1 tubular stainless manifolds.

The cast ones were for earlier Range Rovers and Disco 1 and 2, so will fit fine.

[Carloz]

Those late RV8's like the 4.6 have different heads so far I know.. I am not sure, but do the exhaust ports match with manifolds ment for the older type of heads?

I found that those aftermarket stainless systems have even smaller secondairies than the late RRC original systems, which is quite disappointing! :-( It's like 2x 2" for the aftermarket stuff and 2x 2,125" for the original systems

When they go to one pipe it is 2,125 for the aftermarket and 2,5" for the original '95 system.

But of course, the latter one has catalytic inverters with the old cast manifolds in front which spoil the party.

[Bowie69]

Heads are fundamentally identical, everything bolts up.

Just 4 less head bolt holes, different valve guide seals, and a slight skim.

[FridgeFreezer]

Also every P38 one I've seen has cracked where they join, nothing that can't be welded, but they do seem to all crack.

[garrycol]

In have seen them with the concertina sections removed and a piece of pipe welded in as a replacement.

[FridgeFreezer]

I think the concertina sections are there for a reason, I've had a fair few cast manifolds that crack between the two halves as well, I guess the concertinas are there to try and take some stress off. Being thinner tube rather than cast I guess they still crack eventually, but a quick spurt with the welder sorts it out which is handy.

Anyway, bit academical as they don't fit I wanted to update the 109 and the 127 to P38 manifolds and that's now been nixed as both are manual. D2 V8 headers are cast, one might hope they've got the hang of them by then, I'll find out when I try to fit the pair I've just bought

[garrycol]

I totally agree - the P38 headers then do crack elsewhere.

I have heard (no personal experience) that the standard cast exhaust manifolds on the 3.9, 4.0 and US 4.6 D2s are actually quite good. Certainly aftermarket headers do offer a bit of improvement but is not all that cost effective for the improvement achieved and real improvements in the D2 are to be made in the exhaust system after the manifolds so this is where to spend the money.

[Chicken Drumstick]

Unless the RV8 defies physics and doesn't react the same as other engines, then most exhaust gains for an n/a engine are almost always from good set of manifolds.

[Bowie69]

Point is though,the later 3.9-onwards manifolds are all pretty good.

In fact I think JED was selling bored out 3.9 manifolds at one point, and even cast some larger bore manifolds but of the same design.

The P38 ones are not bad really, and the gains from any tubular manifolds are going to be minimal in an application where you don't stay at 6000rpm all the time.

The 3.9 manifolds were 4-2-1 with the 2-1 bit right back under the truck, so pretty good for the application.

[FridgeFreezer]

Bowie - I was going to ask at which end of the rev range the gains are had, so much performance stuff is worked out on racecar principles but that doesn't always tally with what's useful on a 2-ton wheeled brick.

[Bowie69]

Pretty sure the 4-1 long branch manifolds are for top end, the 4-2-1 for lower down.

I could check in a book, but just moved and can't find anything anywhere

But if JED are happy to use 4-2-1 even on their 5.0l variants and bothered to cast their own I doubt 4-1 have many benefits, even higher up the rev range on a relatively lazy, poorly breathing RV8. No point having 'extractors' if the front end of the engine only has two measly valves per cylinder, and ancient cylinder head designs.

All this will depend on valve overlap as well, if you have a gnarly cam in there, some back pressure from the exhaust can raise the low down torque, but of course kill top end power, so you can't have your cake and eat it....

For a RV8 in a LR, a 4-2-1 with a cross pipe has been proven to be best for good torque spread.

So yes, a good set of manifolds is great, but the stock stuff is pretty good anyways.

[Bowie69]

This is one such post, after a 30-second google, pretty safe test with conclusions that 4-2-1 were better than stock, 4-1 moved the power up the band, with some small losses low down.

http://www.superstreetonline.com/how-to/aftermarket-parts/htup-0804-honda-header-tri-y-vs-4-into-1-dyno-test/

Biggest point to note, though, is that while there were gains, even with the 4-2-1 peak gain was 7BHP, or about 3.5%. So on a 4.6 RV8 you *may* see 10BHP difference, lots more noise, and a tendency to crack and rust through. That and a very empty wallet, but you go for it if you want

http://www.v8tuner.co.uk/product.php?id=856

A good guy there, no idea on these manifolds specifically though.

[Carloz]

@ Bowie69: The "the later 3.9 systems" where already on the 3,5 injection RRC's back in the eighties. The cast 4 into 2 manifolds are the same. only the stuff further backwards (from the 2 into 1 part) are better from the later systems

I fitted last week a complete 3.9, 8-4-2-1 system onto my standard '74 3,5V8 CR8,25 with stromberg carbs. I can tell for sure it gives more power than the ancient exhaust stuf from '74 without any drawbacks.

The 4 into 1 part was for a Autobox so I needed to change the crosmember too and.... needed to "adjust" the manual gearbox filter plug and make a small dent in the pipe to stay clear. GREAT, that exchange ability of parts! :-P

[Bowie69]

You may well be right, looks like they swapped once EFI arrived on the 3.5, they also changed in MY92 for the RRC again, similar design though.

[=jon=]

I'm about to make the same swap on my 110 v8 - currently 3.5 carb manifolds and pipes, going to a 3.9 4-2-1 cast setup with a TD5/puma exhaust from the Y pipe back.

If you look at the size of the pipework on the 3.5 carb system it's tiny compared - the main exhaust system is probably the same diameter as the '2' pipe on the headers...

[mcc1979ian]

This is one such post, after a 30-second google, pretty safe test with conclusions that 4-2-1 were better than stock, 4-1 moved the power up the band, with some small losses low down.

http://www.superstreetonline.com/how-to/aftermarket-parts/htup-0804-honda-header-tri-y-vs-4-into-1-dyno-test/

Biggest point to note, though, is that while there were gains, even with the 4-2-1 peak gain was 7BHP, or about 3.5%. So on a 4.6 RV8 you *may* see 10BHP difference, lots more noise, and a tendency to crack and rust through. That and a very empty wallet, but you go for it if you want

http://www.v8tuner.co.uk/product.php?id=856

A good guy there, no idea on these manifolds specifically though.

Wonder if it's possible to get these in stainless