Classic exhaust manifolds

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dkl1971

Active Member
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306
Looks like my engine is coming out so it seems to make sense to change the manifolds if I'm going to.
The question seems to be is there really any advantage to a "performance" tubular stainless manifold on a brick and if so which one. Janspeed do one as do rimmers etc. Is it the same part for a 4.2 as a 3.9?
Any suggestions?
 
It wont matter if they improve the performance or not, as you say its brick like shape far outweighs any advantage you will gain
 
The generally accepted wisdom is that such modifications are best considered as part of an overall performance package & it's unlikely to produce much in the way of 'bangs for your buck' on it's own - but I would imagine enough for your insurer to be interested :oops:
 
Its having a rebuild back to OEM spec and output, I resisted the 4.8 option. It would undoubtedly be easier to fit the manifolds as part of this rather than afterwards. I'd plan to replace the whole system in due course but mainly for slightly freer breathing, longevity of the system and a bit more noise.
 
Looks like my engine is coming out so it seems to make sense to change the manifolds if I'm going to.
The question seems to be is there really any advantage to a "performance" tubular stainless manifold on a brick and if so which one. Janspeed do one as do rimmers etc. Is it the same part for a 4.2 as a 3.9?
Any suggestions?
A basic understanding of engine tuning and exhaust dynamics will help loads in this regard.

Afraid I don't know what spec engine you have, or what you are planning.

The main aim in exhaust tuning is:

-more flow
-scavenging

Flow rate is important, but only to an extent. Forced induction setups will generally want the most flow rate possible.

Scavenging however is very important on n/a engines and can release a lot of performance potential. Essentially what this aims to do, is the exhaust pressure wave from one cylinder, helps 'suck' or pull in air to the cylinder with the inlet valve open. This means you get more air into the combustion chamber, and essentially a bigger bang and more power.

A good exhaust will be part of entire setup, so the rest of the exhaust, the induction and the engine spec can all play a part. But good exhaust manifolds can and will yield good gains.

I don't know what is available. But you want something that has long primary pipes, this will promote scavenging at lower rpm. Short primary pipes look cool and will out flow factory log style manifolds. But yield little to no gains in power unless you are running forced induction (turbo or super charger). Short primary pipes do scavenge, but only at high rpm, maybe 8000rpm or higher. Hence their limited appeal on a OHV V8.

Long primaries come with the downside of costing and packaging. Which is why they are normally rarer.


Engine displacement doesn't really have a bearing on exhaust manifolds. Not at this level anyhow.

A good set of manifold will result in the car needing to be tuned however, as the fuelling will be out. And don't believe anyone that tells you that you need back pressure on a petrol engine.
 
Why is my comment so wrong
Common sense and failing that logic and physics. ;)

If extra power makes no difference, how come a 3.9 V8 goes a lot quicker than a carb 3.5 V8, which goes better than a Tdi. If power makes no odds because it's brick shaped, why not shoehorn in a 2.25 n/a diesel from a series, obviously it will still perform the same....
 
I think maybe we are talking across purposes a little.
I have no doubt all you say is correct but will only make a difference as part of a bigger package which I'm not planning. There is no point spending £500 on a fancy set of headers if it makes a 2% improvement in power or requires another £5000 worth of engine mods to make the best of it. The rebuild is only aiming to restore the original 200bhp, as I said I declined the 4.8 rebore, lovely though it might be.
If a couple of hundred pounds on a known set of manifolds would make a reasonable difference then it would be worthwhile and save the labour of doing it afterwards.
If the above is true then it probably isn't worth it, possibly hence Mr tarphenry's comments.
 
What engine do you have? If it's a 3.9 they make 182bhp at factory spec. A 4.2 should be about 200hp.

Personally I can't really see the point rebuilding an engine to factory spec, when you can get so many gains for little or no extra effort or cost during the build.

A mild cam, a good induction setup, some nice manifolds and free flow exhaust will make a MASSIVE difference. On paper the numbers might not be massive, but it'll drive and feel like you gained a 100hp most likely. The engine will be much more free reving and it's the under the curve or mid range performance that will see the biggest gains.

Yes manifolds need to be part of an entire system. But if you are putting a new exhaust on anyhow and having the engine apart, then something like a stump pullet cam and then a nice induction setup. It'll make a world of difference to how it goes.

As an example of what mods can do. I have a TR7 V8, when I originally fitted the engine it was a stock 3.5 from an SD1 (had just been rebuilt, but not by me) and twin SU carbs. In theory these make 155hp. The car went ok.

The final spec on that engine was a mildish cam from RealSteel, a 4 barrel Edlebrock/Weber carb, free flow exhaust and long tube exhaust headers. On the rollers it was making an estimated 230hp fly and 219ft lb.

The addition of the cam and carb and getting it setup, made more difference than when I originally fitted the V8 from the 4 pot 2.0 litre.

I clocked the car at 144mph and it would do 0-100mph in under 16 seconds. Not bad for a 1970's British sports car.
 
It's a 4.2 so 200bhp.
This is why I'm asking. The stock 4.2 cams are NLA from LR anyway so yes the cam will be different and I need to choose what goes in. This sort of bolt on mod I would go with but I'm not looking at big cc or turbos/superchargers etc
Out of interest what did you use from RS range?
Did you have the exhaust fabricated or is it a "stock" free flow system? If the latter which one?

Thanks
 
I maintain that my comment is justified, unless you read something in the O/P s question. as a stand alone fitment,even with a tuned exhaust system.janspeed or other manifold system would bring minimal hp gains and would probably go unnoticed.
 
I maintain that my comment is justified, unless you read something in the O/P s question. as a stand alone fitment,even with a tuned exhaust system.janspeed or other manifold system would bring minimal hp gains and would probably go unnoticed.
If you think it would be unnoticed, then I can only assume you've not fitted such things.
 
I maintain that my comment is justified, unless you read something in the O/P s question. as a stand alone fitment,even with a tuned exhaust system.janspeed or other manifold system would bring minimal hp gains and would probably go unnoticed.
Afraid I disagree too. I took a 3.9 rrc and fitted janspeed manifolds and y piece initially, it provided an immediate gain. The claim is 15-20bhp iirc. I can't back these figures up but the difference was noticeable. Eventually I could hit 60 in under 7 seconds, but there were a few more mods to achieve that.
I realise the op wishes to keep original but that needn't go beyond engine no.
My recipe would be a piper 285 cam (same duration as original, a bit more lift, very slightly lumpy idle, smooth from 1000rpm), a nice shiny new pair of built up ported heads / standard valves (stage 1), ported inlet manifold, plenum chamber bored for 71mm throttle. PORT MATCH EVERYTHING to the gaskets. You will have a much more efficient rover v8.
Real steel have very reasonably priced headman headers BTW.
 
It's a 4.2 so 200bhp.
This is why I'm asking. The stock 4.2 cams are NLA from LR anyway so yes the cam will be different and I need to choose what goes in. This sort of bolt on mod I would go with but I'm not looking at big cc or turbos/superchargers etc
Out of interest what did you use from RS range?
Did you have the exhaust fabricated or is it a "stock" free flow system? If the latter which one?

Thanks
You don't need bigger cc or turbos to get a noticeable difference in performance. Bolt on mods, well set up will make it a different animal entirely.

The exhaust on the TR7 (note a car, not a Land Rover ;) ), is a copy of the system the works rally cars used. The manifolds are also of that nature and came from a company called Triumph Tune. Although they wouldn't fit a Land Rover, due to their shape, but the same principle would apply.


If you are planning on an exhaust, and a new cam. Then a good set of manifolds and a tune will make a difference. If you don't feel it would be worth it, then that is fine. But there is plenty of documented evidence on the internet that says it will, and does work.

I've driven and owned a number of stock and modified vehicles over they years. And as a rule the modified vehicles easily and noticeably outperform the standard ones.
 
I think you should read the O/P original post.Rambling on about tuning and cams and various other tuning aids are not asked about. he asked if tubular manifolds were worth putting on a rebuilt stock motor. I would presume if he wanted to know about tuning he would have asked
 
Gents, We're all on the same side here!
I did ask about the manifolds mainly because with the engine out there is a cost saving in just bolting a new pair on. On their own no they don't seem to make much difference.
However I am having a new cam so it may make sense to match these bits together. I'm not sure if I would do the machine work on the inlet and head but maybe. It rather depends on cost andthis and the rest that is being done. There is no doubt that without major fettling an RRC will never be fast and its brick like
Off to look at headman headers.
Thanks all, this is the info I need.
 
Ported heads would be good, but add £££ to the build. A performance cam will only cost marginally more than a stock one, so worth doing IMO. And if you are doing the exhaust anyhow, then it all makes sense.

The other mods would be good, but to be honest, anything induction side is easy to do after the engine is in the vehicle and running. So no need to spend out now on it.

I honestly think you'd be amazed at how much better it will run.

I'd stick with RealSteel or V8Developments for parts. Maybe have a word with them and let them know what you are planning, I'm sure they'll be able to help.
 
As above, induction can be done later, but you are already getting your wallet out and head porting would make such a difference and realise the full potential of better manifolds. If a job is worth doing.....

If you saw a pair side by side with the stock version, you could only conclude from the lack of basic fettling that land rover had no pride in the quality of their product.
 
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