tubular manifolds
- Thread starter thinkpad
- Start date
Before I had the 4.6 litre Rover V8 installed, I did as much research as I could on the subject of tubular manifolds, or "extractors" as they are called here in Australia.
What I did learn was that they would be more beneficial on a car with a manual gearbox as opposed to an automatic, where engine revs would be higher for a far greater percentage of the time.
The performance improvement would only be seen once engine revs exceeded approx 3500rpm.
There would be a substantial increase in under bonnet temperatures as the thin walls of the manifold do not "hold" the heat in the same way as the original cast iron manifolds do.
Wrapping tubular manifolds with special heat cladding does reduce the amount of heat radiation, but the downside in this process is that the life of the manifolds are significantly reduced. Less than two years being common place so I am informed.
Ceramic coating of the manifolds is a much better and much more expensive alternative than wrapping. Various finishes are available, including a polished chrome look.
Tubular manifolds have a bad habit of cracking, especially when mounted onto an aluminium alloy head, due to the different rates of expansion between the two metals. To minimise the possibility of cracking, all four pipes ideally should be joined by a common backing plate made which then bolts directly to the head.
They can, depending on the design, make spark plug removal much more difficult.
The biggest downside though for me is the cost. The sets from RPI are over 500 Pounds. To obtain some locally would require a custom made to fit set, so I would still be looking at close to $2000 when all is said and done.
Ron.
What I did learn was that they would be more beneficial on a car with a manual gearbox as opposed to an automatic, where engine revs would be higher for a far greater percentage of the time.
The performance improvement would only be seen once engine revs exceeded approx 3500rpm.
There would be a substantial increase in under bonnet temperatures as the thin walls of the manifold do not "hold" the heat in the same way as the original cast iron manifolds do.
Wrapping tubular manifolds with special heat cladding does reduce the amount of heat radiation, but the downside in this process is that the life of the manifolds are significantly reduced. Less than two years being common place so I am informed.
Ceramic coating of the manifolds is a much better and much more expensive alternative than wrapping. Various finishes are available, including a polished chrome look.
Tubular manifolds have a bad habit of cracking, especially when mounted onto an aluminium alloy head, due to the different rates of expansion between the two metals. To minimise the possibility of cracking, all four pipes ideally should be joined by a common backing plate made which then bolts directly to the head.
They can, depending on the design, make spark plug removal much more difficult.
The biggest downside though for me is the cost. The sets from RPI are over 500 Pounds. To obtain some locally would require a custom made to fit set, so I would still be looking at close to $2000 when all is said and done.
Ron.
Hello Demetris,
The tubing, either mild or stainless steel that is used in the construction of tubular manifolds is quite thin, that is to say..the wall thickness. As such the surface temperature of the tubular manifolds in comparison to the cast iron manifolds is considerably greater. To prevent the possibility of severe burns, should unintentional contact be made with the hot tubes, not to mention reducing the significant increase in under bonnet temperatures, wrapping the tubes with an exhaust manifold cladding is sometimes used.
The use of such helps to prevent possible heat damage to the plastic fuel lines and rubber hoses along with electronic ignition components etc. By retaining so much of the heat, the tubular manifolds also work more efficiently in that the exhaust gases maintain a higher velocity, thus exiting the system more efficiently. Cooler exhaust gases by comparison travel with reduced velocity, and the system then works less efficiently.
Whether a person driving a P6B fitted with bare tubular manifolds then wrapped tubular manifiolds would be able to pick the difference from a power perspective would remain to be seen.
Typically stainless steel tubular manifolds have a 10 year manufacturers warranty, while mild steel tubular manifolds have a 3 year manufacturers warranty. These periods are "typical" and don't represent all such warranties.
Now the downside......wrapping tubular manifolds with the appropriate material designed for such whether they be stainless or mild steel will result in a significant reduction in the useable life of the manifold. It is my understanding that the degredation is both a combination of moisture retention by the wrapping which expediates the corrosion process, combined with the heat generated within the tubes being unable to escape. The corrosive effects of the trapped heat attack the very structure of the tubes, eroding them from the inside out.
By wrapping tubular manifolds you will also void the manufacturers warranty. When I was investigating the pros and cons of using extractors on my 4.6, this was one area that all manufacturers had in common. A void warranty. :shock: Once wrapped, removal will leave definitive evidence which the manufacturers will be able to see, so should the manifold crack or display holes where the metal has corroded away, no reponsibilty for repairs or replacement will be offered. The warranties typically state that the use of "heat wrap" products will void the warranty.
A far better alternative to wrapping is ceramic coatings. Such coatings help to reduce the level of heat radiation while slowing the corrosive process. As an example...a bare tubular manifold up to normal temperature will measure in the region of 400 degress C, measured 1" away from the tube where it curves away from the cylinder head. The same tube with a ceramic coating will typically measure half that figure.
Warranties typically do not make mention of ceramic coatings, and in some cases the manufacturers themselves will provide such coatings as an option before purchasing.
Ron.
Demetris said:
The tubing, either mild or stainless steel that is used in the construction of tubular manifolds is quite thin, that is to say..the wall thickness. As such the surface temperature of the tubular manifolds in comparison to the cast iron manifolds is considerably greater. To prevent the possibility of severe burns, should unintentional contact be made with the hot tubes, not to mention reducing the significant increase in under bonnet temperatures, wrapping the tubes with an exhaust manifold cladding is sometimes used.
The use of such helps to prevent possible heat damage to the plastic fuel lines and rubber hoses along with electronic ignition components etc. By retaining so much of the heat, the tubular manifolds also work more efficiently in that the exhaust gases maintain a higher velocity, thus exiting the system more efficiently. Cooler exhaust gases by comparison travel with reduced velocity, and the system then works less efficiently.
Whether a person driving a P6B fitted with bare tubular manifolds then wrapped tubular manifiolds would be able to pick the difference from a power perspective would remain to be seen.
Typically stainless steel tubular manifolds have a 10 year manufacturers warranty, while mild steel tubular manifolds have a 3 year manufacturers warranty. These periods are "typical" and don't represent all such warranties.
Now the downside......wrapping tubular manifolds with the appropriate material designed for such whether they be stainless or mild steel will result in a significant reduction in the useable life of the manifold. It is my understanding that the degredation is both a combination of moisture retention by the wrapping which expediates the corrosion process, combined with the heat generated within the tubes being unable to escape. The corrosive effects of the trapped heat attack the very structure of the tubes, eroding them from the inside out.
By wrapping tubular manifolds you will also void the manufacturers warranty. When I was investigating the pros and cons of using extractors on my 4.6, this was one area that all manufacturers had in common. A void warranty. :shock: Once wrapped, removal will leave definitive evidence which the manufacturers will be able to see, so should the manifold crack or display holes where the metal has corroded away, no reponsibilty for repairs or replacement will be offered. The warranties typically state that the use of "heat wrap" products will void the warranty.
A far better alternative to wrapping is ceramic coatings. Such coatings help to reduce the level of heat radiation while slowing the corrosive process. As an example...a bare tubular manifold up to normal temperature will measure in the region of 400 degress C, measured 1" away from the tube where it curves away from the cylinder head. The same tube with a ceramic coating will typically measure half that figure.
Warranties typically do not make mention of ceramic coatings, and in some cases the manufacturers themselves will provide such coatings as an option before purchasing.
Ron.
Demetris
Well-Known Member
Thanks for this Ron,
along with the replacement engine in my TC, came a new exhaust manifold. I thought it was good to wrap it up and give it a a coat of temperature resistant paint before instalation.
So far, i had no problems, and becides the lower underbonnet temperatures (important in the Greek summer) there is also some noise reduction.
In my case, the chances of getting the manifold wet are rather thin, so hopefully it won't suffer from trapped moisture.
Demetris
along with the replacement engine in my TC, came a new exhaust manifold. I thought it was good to wrap it up and give it a a coat of temperature resistant paint before instalation.
So far, i had no problems, and becides the lower underbonnet temperatures (important in the Greek summer) there is also some noise reduction.
In my case, the chances of getting the manifold wet are rather thin, so hopefully it won't suffer from trapped moisture.
Demetris
The RPi manifolds were developed for my "Thai" car which is a 4.6 and the tube sizes were selected to suit the gas flows involved. BUT it is a 4 into 1 type manifold which produces best results at high revs. I would have liked to have a 4 into 2 into 1 which give good results at low rpm (hence the "extractor " name commonly appllied) but we decided there just wasn't enough space in the P6 engine bay to do this with anything approaching the correct length ratios in the "2" section - you finish up with both pipes trying to occupy the same single pipe sized space. Alan at Classeparts at Leighton Buzzard now does do a 4 into 2 into 1 but I haven't seen it installed in a car or had a long chat with him about tube sizes or lengths. He reckons it is possible by assembling the manifolds in situ, threading the components around the key obstacles before coupling them up. I have to say it sounds too compromised to me. One dodge that does improve things is to use one of the high rpm small diameter starters that are available from a number of people aimed at the racing / TVR fraternity.
The system that goes with the RPi manifolds is 2 1/4" with a single rear box of the maximum size to suit the available space and it sounds absolutely wonderful!
Chris
The system that goes with the RPi manifolds is 2 1/4" with a single rear box of the maximum size to suit the available space and it sounds absolutely wonderful!
Chris
TwinPlenum3500S
New Member
Tubular manifolds can be made bespoke at FlowTech exhausts on 0208 586 1717. These guys make all the exhausts for the London Chop Shop on Discovery Channel. Much better than RPi as you will get large primaries and collectors so engine will actually breath better.
They are made to original P6 V8 manifolds so will fit, far better than block huggers supplied by RPi, Pop Browns etc. They are identical to P6 V8 as they are made from my original P6 manifolds, used to make up headers for my Twin Plenum SD1 lump in my P6.
Ask for Paul or Terry.
They are made to original P6 V8 manifolds so will fit, far better than block huggers supplied by RPi, Pop Browns etc. They are identical to P6 V8 as they are made from my original P6 manifolds, used to make up headers for my Twin Plenum SD1 lump in my P6.
Ask for Paul or Terry.
TwinPlenum3500S said:
It is my understanding that should the diameter of the primary pipes be larger than the specification of the engine warrants, then rather than improving engine breathing and performance, the opposite in fact happens.
The factory sized exhaust ports on Rover V8 heads require for best engine performance, primary pipes with an outside diameter of 1.5" to 1.625". The diameter of such pipes has a direct bearing on the positioning of the peak torque delivered by the engine. Smaller diameter pipes position the torque peak lower in the rev range, while larger diameter pipes move it further up the rev range.
If the diameter of the primary pipes is too large for the sizing of the exhaust ports and state of tune of the engine, then the peak will move too far up the rev range with the result that the engine will be less than responsive for everyday driving.
On the other hand, if you are zooming up and down a race track keeping engine revs above 4000rpm, then larger would be better.
The velocity of the exiting exhaust gases is higher with smaller diameter pipes, while it is slower with larger diameter pipes, and this speed has a direct relationship as to the positioning of the torque peak of the engine.
As with all forms of engineering design, compromise is the key and on that score for a P6B road car, with either a 3.5 or a 4.6 Rover V8 under the bonnet, 1.625" primary pipes is the largest that you would require.
Ron.
TwinPlenum3500S
New Member
Flowtech in Romford make all types of custom exhausts. They have been in the motor business for 25 years ..... they are also European Top Fuel Dragster champions 2008, in a car built themselves. Bigger primaries and collectors assist breathing and increase bhp. If you are serious about performance enhancement, they will assist. They can build bespoke custom exhausts, manifolds (all stainless), cam change etc etc.
TwinPlenum3500S
New Member
Similarly if you are really serios about perdormance enhancement, any work on an existing P6 lump to increase bhp will be expensive, as the Rover V8 is by its nature costly to enhance. A late, low mileage range rover 3.9 with hotwire injection, uprated cam, custom manifolds and exhaust would make any P6 a superb, reliable, modernised daily driving car, that whilst by no stretch of the imagination would be a flying machine, still would not hang about.
Or, if you speak to Terry at Flowteh, he is a small block fan ...... small block Chevy in a 1979 Opel Kadett coupe with nitrous ... a street car pushing out 400+ bhp ... thats a powerful motor. Small blocking a P6 is possible.
Or, if you speak to Terry at Flowteh, he is a small block fan ...... small block Chevy in a 1979 Opel Kadett coupe with nitrous ... a street car pushing out 400+ bhp ... thats a powerful motor. Small blocking a P6 is possible.
Mad_Dan_Eccles
Member
quattro said:
I don't think a modern aluminium/aluminum small block weighs so very much great deal more than a Rover V8 - a 6 litre LS2 (as used in the Corvette, GTO/Monaro among others) is about 450lbs for a net increase of about 100lbs. Obviouly you'd want to consider the additional weight of a bigger radiator, stronger transmission and final drive (hopefully one with an limited slip diff)when planning the installation, but the power to weight ratio would get a big boost.
I doubt that the cornering would be too badly affected by the added weight alone , though with 400hp on tap, improvements to springs, shocks and brakes seem advisable
Aidrian