What's the deal with the Y manifold design?

[B19GRR]

Hey all!

So home come the exhaust manifold on the Rover engine is designed with that big Y thing as opposed to keeping the two sides separate as per Cerbie and most other V8s?

Only reason I can think of is that you'd only need one lambda sensor (don't shoot me if there's two, still not got my bible yet )

Is it a pulse timing scavenging thing or just easier? Has anyone tried different manifold designs with the the Rover engined TVRs?

Cheers,
Curious Rob!

[mongoose]

the big 'y' peice houses the main cat.there is one lambda sensor in each manifod(visible from above)-mv

[HarryW]

The layout for the RV8 Tivs went to the big dustbin cat arrangement in 94. Prior to that the V8S and precat Griffs had a nice blended Y piece roughly tuned to the engine. The dustbin is large so that the flow is not compromised, it should, without a cat be around 2.5" dia and be shaped to allow the exhaust to escape quickly from the heads. Earlier cars ie the big wedges had seperate secondaries going back to the first box, the blending was done here, it then exited as a single pipe. Either arrangement sounds glorious btw.
Tim at ACT spent some time developing a improved pre-cat arrangement for the griff and has an improved set-up for the V8S as well , both of these would mean a new set of manifolds and Y piece for a catted car btw.
The only problem is the car will need to chipped to take the pre-cat arrangement and the tune resistor changed. If you already have a MA chip this is not a major issue, but it will need to re-mapped. To be strictly correct the MA chip can have two maps which are selected by the tune resistor, so again once its done it's relatively easy to cahnge between the two.
If you are considering anything like this go in with your eyes open, but there are benefits IMHO .
All assuming this is not an idle question .


Harry

[joospeed]

makes no odds on these rover v8 thingies, the firing order means you can't take advantage of proper exhaust scavenging, pulse tuning may come into it on more radical cams, but to remain emmissions compliant you have to run minimal lift on overlap so individual chamber scavenging doesn't take place to any noticeable degree. And it's easier than routing two pipes.

[B19GRR]

And there endeth the lesson, thanks Joolz

Harry, yes it's a bit of an idle question as I currently don't have such an engine but I thought quite interesting anyway. One possible advantage I could see to re-designing the manifold - if no performance gains are to be made - would be to shift the CAT(s) somewhere else, perhaps under the chassis like the Cerbera which would aid cooling them and help keep under bonnet temperatures down. I seems a little silly to me to have a ruddy great CAT just a few inches from the radiator. That theory could easily be confirmed if pre-cat cars under bonnet temps differ much from the 5L engines.

Cheers,
Rob

[HarryW]

B19GRR said:

And there endeth the lesson, thanks Joolz Harry, yes it's a bit of an idle question as I currently don't have such an engine but I thought quite interesting anyway. ..... Cheers, Rob

Whilst I don't disagree totally with Joolz here and he knows more about Tivs than I ever will. But as he has left the door slightly open in his post here goes .

There are gains to be had, the standard Tiv system is not the best designed, it is overbore in the first instant. The standard V8S 'Y' piece is a also very bad design being effectively a 'T' piece not 'Y'.

I'll give you a theoretical set of figures here , exchanging a full cat system on a 4ltr to a 'tuned' set of pre-cat manifolds and Y piece can release 18bhp peak and 7/8bhp across the entire rev range and a max of 30lb torque with an average 10/15lb across the whole range. These figures may be before its had the fueling fully mapped to suit it, so there may be a little bit more to come.

A recent V8S has just changed the Y piece as a stand alone bit and gained 6bhp/lb, caution here, but it needs to be mapped to exploit it as it has shown up possible fueling issues lower down. It has also spread the power and torque to extend further up the rev range so it doesn't run out of puff so easily.

Like any impprovement to Tivs nothing is cheap, always go in with your eyes open, if you ever do go down the road.
All IMHO and no garantee's are given..........


Harry

[icamm]

B19GRR said:

One possible advantage I could see to re-designing the manifold - if no performance gains are to be made - would be to shift the CAT(s) somewhere else, perhaps under the chassis like the Cerbera which would aid cooling them and help keep under bonnet temperatures down. I seems a little silly to me to have a ruddy great CAT just a few inches from the radiator. That theory could easily be confirmed if pre-cat cars under bonnet temps differ much from the 5L engines. Cheers, Rob

Not sure about this as CAT's need to be pretty damn hot to actually be effective. If they are not hot enough (and in most UK cars on most journeys they don't really get hot enough IIRC) then they don't actually cut emissions. So having them were they can get hot quickly would actually make them more effective.

[Mark Adams]

As Joolz rightly pointed out, pulse tuning is impossible on a Rover v8 due to the odd firing sequence.

However the Cerbie V8 uses a flat plane crankshaft, which effectively makes it two four cylinders bolted together. Therefore it is very beneficial to separate the two banks so that they CAN be pulse tuned.

Rover lumps rely much more on inertia than pulse tuning. This is the reason why the Cerby V8 revs so much better (incidentatlly so do Rover V8s with flat-plane crankshafts).

I had a new Cerbie 450 on the dyno the other day, and although the peak torque was about the same magnitude as a Griff 500, it stayed flat at that level for another 2500RPM!

[joospeed]

Mark Adams said:

As Joolz rightly pointed out, pulse tuning is impossible on a Rover v8 due to the odd firing sequence. However the Cerbie V8 uses a flat plane crankshaft, which effectively makes it two four cylinders bolted together. Therefore it is very beneficial to separate the two banks so that they CAN be pulse tuned. Rover lumps rely much more on inertia than pulse tuning. This is the reason why the Cerby V8 revs so much better (incidentatlly so do Rover V8s with flat-plane crankshafts). I had a new Cerbie 450 on the dyno the other day, and although the peak torque was about the same magnitude as a Griff 500, it stayed flat at that level for another 2500RPM!

You've hit many nails on many heads there mark ..
The cerbie does indeed run as two four cylinder engines, but the exhaust is fundamentally flawed in that the primary pipes are too short and of unequal lengths.

Added to that, there's a step in the system from the head face to the exhaust manifold flange, I've heard it said that it's put there deliberately to minimise pulse tuning and create a neutral exhaust, well I say fobble to that.

If there's any torque gains to be has on a performance motor you take them, deliberately introducing a step against the natural flow of gas can only be for cost reasons, in that the loaf shape port makes the manifold harder to make and therefore more expensive. By doing this step in the manifold TVR have singularly managed to nullify the ONLY reason for having this engine design in the first place, namely to take advantage of the exhaust design.

Incidently mark, do you have any power info for us? .. and why were you running a cerbie .. anything you'd care to share with us??????? teehee ..

[Mark Adams]

Joolz - sounds like a cue for a Joospeed exhaust sytem if ever I heard one!

The story about the step in the exhaust does have a familiar smell to it. In fact it reminds me of when a scutter (unknown small furry animal) died underneath the floorboards draped over the central heating pipes.....

As for the Cerbie, I was only in the building at the time - honest Guv! However I couldn't help noticing some yawning holes in the mapping from where I was standing.....

[joospeed]

yawning holes .. JR only maps about every 3000th load site from what I can see .. there's massive areas of rich running, and at this level you're talking 7-8bhp per degree of advance,so there's an easy 25lbs torque if the owners run them on decent fuel .. stay tuned ..

[HarryW]

Hey the odd firing order of the RV8 is what gives it the loverly burble we all love . Mark you know me, I do my research before I go into anything, eyes wide open so to speak .
There is exhaust theory and exhaust practice as you well know . I'll stand by my words though, there is plenty of scope to improve upon the current standard RV8 Tiv system, albeit with an odd firing order that cannot be fully pulsed tuned, the Y does help to balance some of that out AFAIK.
The change in exhaust note alone as a by product of trying different 'systems' is worth the effort alone IMHO, even if the power remains unchanged, which would have been disappointing .

harry

[joospeed]

Harry, you are very correct on the "changing the exhaust for something of better design" - the V8S Y section can be dreadful as std as you rightly point out, and the proper Y shapes rather than T shapes or worse still the reverse y shape are the way to go.

[Tam Lin]

joospeed said:

However the Cerbie V8 uses a flat plane crankshaft..TVR have singularly managed to nullify the ONLY reason for having this engine design in the first place, namely to take advantage of the exhaust design. ..

Doesn't the flat plane crank in theory also allow an engine design with a lighter crankshaft, since the counterweights required on a cross-plane crank are not required?

I thought one of the big advantages of the AJP V8 against the SP6 and even the RV8 is the weight saving, even if it does have a weedy manifold/exhaust system.

Thanks for the Season's greetings, BTW, a nice surprise at work.

Edited to remove crappified spelling

>> Edited by Tam Lin on Wednesday 17th December 16:22

[2 sheds]

In my experience, with the Rover engine, exhaust systems that don't have a balance pipe (join together as a single pipe at some point) tend to loose torque, this isn't really a big issue as all the rover engined TVRs have a balance pipe anyway,
As Harry said the reason the Wedge V8 sounds best is that it has smaller bore manifolds with longer secondaries that meet behind the gear box (the "Y"piece), this meeting point is where that lovely howl is produced, in the Griff / Chimaera they howl into a "bucket" in front of the engine, which explains the different noise, they still sound good though, i'm working on a system with separate cats in front of the engine with the "Y" piece beside the engine, something for next year.
Tim

[shpub]

HarryW said:

There are gains to be had, the standard Tiv system is not the best designed, it is overbore in the first instant. The standard V8S 'Y' piece is a also very bad design being effectively a 'T' piece not 'Y'. BIG Cut.... All IMHO and no garantee's are given.......... Harry

The problem is that to get these type of gains, the car had to be remapped. That always raises eyebrows with me because it introduces another set of variables. Having had plenty of cars remapped in my time, I have achieved similar and better gains that those simply by remapping which then means that the comparison with the new exhaust is difficult to make. What is making the difference? The remapping or the exhaust? With decatting you can get the same problem. If the cat is below par or blocked and then effectively removed, there will be power gains but it is difficult to see where exactly the responsible item actually is.

[z_chromozone]

shpub said:

HarryW said: There are gains to be had, the standard Tiv system is not the best designed, it is overbore in the first instant. The standard V8S 'Y' piece is a also very bad design being effectively a 'T' piece not 'Y'. BIG Cut.... All IMHO and no garantee's are given.......... Harry The problem is that to get these type of gains, the car had to be remapped. That always raises eyebrows with me because it introduces another set of variables. Having had plenty of cars remapped in my time, I have achieved similar and better gains that those simply by remapping which then means that the comparison with the new exhaust is difficult to make. What is making the difference? The remapping or the exhaust? With decatting you can get the same problem. If the cat is below par or blocked and then effectively removed, there will be power gains but it is difficult to see where exactly the responsible item actually is.

With that in mind would it not be best to do a remap before and one after to give a good comparison. Sure the cost would be loads more, but someone must have a car already remaped that they want a new y-piece for.

Z

[2 sheds]

shpub said:

HarryW said: There are gains to be had, the standard Tiv system is not the best designed, it is overbore in the first instant. The standard V8S 'Y' piece is a also very bad design being effectively a 'T' piece not 'Y'. BIG Cut.... All IMHO and no garantee's are given.......... Harry The problem is that to get these type of gains, the car had to be remapped. That always raises eyebrows with me because it introduces another set of variables. Having had plenty of cars remapped in my time, I have achieved similar and better gains that those simply by remapping which then means that the comparison with the new exhaust is difficult to make. What is making the difference? The remapping or the exhaust? With decatting you can get the same problem. If the cat is below par or blocked and then effectively removed, there will be power gains but it is difficult to see where exactly the responsible item actually is.

Actually Harrys car made these gains without any remapping he has yet to do that.
Tim

[Pies]

New V8S "Y" piece shows 6bhp over old without any remaping.

The graphs indicate that once remapping has taken place there is a strong likelyhood of better fuel econonmy,as the restriction in the "Y" has been removed.
During remapping i expect there is likely to be more gains although it wont be possible to say weather this is the "Y" or the remapping.Although i suspect it will be a combination of both.

[HarryW]

shpub said:

HarryW said: There are gains to be had, the standard Tiv system is not the best designed, it is overbore in the first instant. The standard V8S 'Y' piece is a also very bad design being effectively a 'T' piece not 'Y'. BIG Cut.... All IMHO and no garantee's are given.......... Harry The problem is that to get these type of gains, the car had to be remapped. That always raises eyebrows with me because it introduces another set of variables. Having had plenty of cars remapped in my time, I have achieved similar and better gains that those simply by remapping which then means that the comparison with the new exhaust is difficult to make. What is making the difference? The remapping or the exhaust? With decatting you can get the same problem. If the cat is below par or blocked and then effectively removed, there will be power gains but it is difficult to see where exactly the responsible item actually is.

Assume the figures quoted are back to back on the same day nothing different except an exhaust change (so could be an iffy cat though ).
Agree mapping may extract more, but mapping may have in this case, been previously done , so it was already optimised so to speak . It now needs to be done again to see if there is more to extract from the improved exhaust, apparently .

To be fair, I believe that once you have done the usual routes in the quest for more oompth from Tivs, bar changing the whole lump for £10K+ for a much better set up . There is scope in exploring one of the few areas that seemed to overlooked, namely .........the exhaust. I feel that perhaps its time that people did this more often .

btw I have no axe to grind on this issue and have no interest in the production or selling of fkall and AIMHO obviously.

Harry