Post Number: 24
|Posted on Wednesday, 21 June, 2006 - 10:32 pm: |
In a previous thread regarding camshaft design, there seems to be a conclusion of sorts that the most potential improvement in power lies with the exhaust system, and that is particularly the case for the single exhaust cars (excepting Continentals).
Improvements to the exhaust are inherently more elegant and by nature improve refinement of the cars because they are removing power losses rather than increasing the BMEP on the piston. Changes to camshafts and carburetors may have adverse effects on fuel economy but exhaust improvements will improve every aspect of performance. Compression ratio changes gain performance by improving the thermal efficiency of the cycle, but as RR discovered, may have unwanted side effects that cancel out cycle efficiency improvements.
Does anyone have specific recommendations on where exhaust improvements can be achieved? For example, changes to the front or rear silencer, and what to expect in power improvements and also what effects to exhaust noise.
What can a Silver Wraith owner do to improve the exhaust without making the components obviously not authentic and without making the exhaust note significantly louder?
Same question for 4 1/4 Mk VI Bentley with the difference being exhaust sound increase is not nearly so much of a concern.
Posted From: 22.214.171.124
|Posted on Friday, 23 June, 2006 - 08:55 pm: |
When I had the stainless system made, I put in 4 mufflers in the original positions, but of the "sports" variety. The twin system sounds awesome! Quite a bit louder than original, but not overbearing. The difference in power was very noticable. I have never had it on a dyno, so no idea of horsepower figures before and after, but the difference in my personal opinion would have been in the vacinity of a 10 - 15 per cent increase in power. And that 4 1/2 litre 6 cylinder twin pipe sound! Better than any jaguar!
(Message approved by david_gore)
Posted From: 126.96.36.199
|Posted on Thursday, 29 June, 2006 - 07:41 am: |
I can tell you for sure that if you fitted a Continental exhaust to say a 4.25ltr Bentley after the H series range, the result is quite good. I specifically mention H series as the early cars had small carbs, which really need changing.The exhaust note is one to which you have to get accustomed. Noise does increase, you cannot have something for nothing! Positioning of the rear resinator box seems to affect the noise/ burble, as does the silencer end plate thickness.
I have not tried taking the inhards out of the rear silencer on a single system, so I cannot comment on that move, I have however taken the insides out of the rear ones of the twin system. Once again the noise increases as you would expect but not too noticable.
Power increase when the Continental exhaust is fitted takes a 4.25 ltr to about the same output as a 4.5 ltr.
For instance about two weeks ago I was following Ashley James driving his 4.25 ltr Bentley with a Continental exhaust, I was in my automatic R type, both cars heavily loaded. Ashleys car has a 3.42:1 axle, mine had a 3.08:1 Continental, I could keep up with him, but not pass him up to say 65 mph. I would say both cars were evenly match or so, until higher speeds are experienced when mine has the edge.
I have driven his car empty and at least two more 4.25 ltr cars with exhaust alterations, they all perfomed much like a 4.5 ltr.
I cannot help in respect of the Silver Wraith, except to suggest similar exhaust modifications. Don't try to fit the Continental MKVI system, the Silver Wraith first silencer is different due to the wheel base!
The Silver Warith and Silver Dawn are certainly quiet in connection with their exhausts, these along with the Bentley Continental were made at Crewe by R-R. The R type / MKVI and later Silver Dawn exhausts were made by Burgess.
R-R went to a lot of trouble with the thickness of the silencer ends and the methods of fold overs in the silencers so no protruding edges would be in the gas streams, if thats any help.
As an aside, any 4.25 ltr Silver Wraith will be dead in the water if it is fitted with an oil bath air cleaner, just in case you have that throttling restriction.
Sorry I cannot be more specific, its more a suck it and see thing.
(Message approved by david_gore)
Post Number: 19
|Posted on Thursday, 29 June, 2006 - 03:15 pm: |
I am not being critical, - each to his own, - but for me one of the big attractions of the Bentleys and Rolls-Royces of the fifties is their totally silent progress. It is more than just being quiet, it is a total lack of any associated vibration.
I remember a road tester once remarking that; "..it is difficult to believe that reciprocating motion plays any part generating the power.." or words to that effect.
It is interesting to watch and listen to cars driving quietly down the street in a quiet country town. Even the latest slushmobiles hum and drum, but a Bentley will glide past with nary a sound.....magnificent.
I find that in my Silver Cloud I have to be very careful when leaving a parking spot as pedestrians only become aware of the movement, not the sound, and it would be very easy to surprise one to their cost.
Those cars just sort of arrive and leave, without a sound.
Yet to post message
Post Number: 1
|Posted on Friday, 30 June, 2006 - 07:40 pm: |
I have a Mk6 4.25L with a reconditioned engine,but with an oil bath air cleaner. Noting Norm's comment of the restriction. Is there any modification to ease the restriction???, and does this really enhance the performance. (It goes really well already) Kit
Post Number: 1034
|Posted on Friday, 30 June, 2006 - 11:01 pm: |
My two bob's worth.
The rear mufflers on my R-Type (dual exhaust system of course) used to rust out in about two years before I went to a thick-gauge austenitic/stainless system. Removing and welding or replacing rear mufflers was decidely boring, whereas stainless systems last forever. I ran it for a while with blanking pipes in place of the rear mufflers, but quickly did my research and had a new stainless system made up when my brother pointed out that it sounded as crappy as something between a Monaro and a Kingswood 202 with an irritatingly noisy exhaust.
To address the noise and flow issues as a package, I had the replica stainless system made up. It looks authentic, the sound boxes are the right size and shape, and it is quieter than the original system. I even used the original muffler lagging and aluminium covers for the front mufflers. The only visible change is the inclusion of flexible bellows just before the front mufflers to eliminate all stresses, particularly on the manifolds: despite the downpipe clamps, some movement and stress is always present without the bellows.
Now the trick. Originally, the front two mufflers were restrictive reflex types, and the smaller rears were straight-throughs. The new stainless front ones, made to order in Lithgow of all places, are straight-through high-flow types. To negate any noise increase, the new rears are a special high-flow semi-reflex type.
Whilst there may be better solutions for exhaust flow, I feel that this arrangement is probably near to the best solution. This is particularly so if you don't want a rorty Bentley which probably looks wrong, and especially if you don't want to go for tuned extractors in place of the manifolds.
Post Number: 2
|Posted on Thursday, 06 July, 2006 - 07:04 pm: |
I am still interested to know if the original style oil bath air cleaner on the 4.25L is un-necesssarily restrictive for induction air, and if so, can it be modified without altering the appearance by installing a modern paper filter insert?????Thank you
Post Number: 1041
|Posted on Thursday, 06 July, 2006 - 07:39 pm: |
Why do you want to modify the air filter on a car over half a century old ?
Once set up, there is no difference in behaviour between motors with the various types of air filter until the throttle is over 80% open at RPM above 3900. Above that, there is a very slight power increase with the AC type filter, but combustion and economy are unaffected provided that you rejet the carburettors correctly. A modified filter will be somewhere in between in terms of peak power.
Be aware that any change in filter type whatsoever requires that the carburettors be rejetted. For example, on a 4 1/4, an oil bath filter requires an SU carburettor needle type SF (0.086" min diameter at the tip), an AC requires an SC (0.074") and a paper type about a TK (0.080"). For any change, the correct jets may only be determined properly on a dynamometer over the full power and speed range with a gas analyser. I can assure you first hand that it an expensive and time consuming exercise.
Given that your oil bath air cleaner does an excellent job when kept clean and properly oiled, why fool around with it ? There is a slightly better case for messing around with the AC type, but please show me just one Crewe car which has suffered in any way from the original air cleaner.
Posted From: 188.8.131.52
|Posted on Thursday, 06 July, 2006 - 10:03 pm: |
Hello Kit Maxwell
There is currently an interesting topic on www.rrbew.co.uk http://rrbew.mywowbb.com/forum2/308.html under Engines – Paper Air Filters for R-Type/Mk.VI which may be of interest to you given your question relative to Oil Bath Air Cleaners and Paper Filters.
It has been suggested there are no Paper Air Filters suitable for Mk.VIR-type. However, RYCO A50 and WESFIL A505 Paper Air Filters have been used for the last 12 years on R-Types originally fitted with the Mesh Type Air Silencers. Additionally FRAM CA146 and FLEETGUARD AF308 appear to also fit these Air Silencers. I do not know where anyone who uses these Paper Filters has altered the Carburettor Needles,or found Performance Adversely Affected.
Additionally, with regard to Aftermarket Re-Usable Air Filters for Mk.VI/R-Type, note Ashley James states ITG FILTERS are available from FLEXOLITE LTD in the UK and Derek from Flexolite advises Mail Order to Australia is available. Derek also advises suitable Oil to service the Filter should be available in Australia. Neither Ashley or Derek at FLEXOLITE have advised of any need to change Carburettor Needles.
Also with regard to Aftermarket Re-Usable Air Filters, K & N FILTERS Australian Agent advises the K & N Type KNE1000 is Cross referenced to the RYCO A50. However, these Filters are Not Readily available in Australia and delivery has been quoted as 8 weeks after Order Placement. Oil suitable to service the Filter appears available in Australia.
I have found R-Types fitted with Oil Bath Air Filters Perform Most Acceptably. However, in the event I wished to change from an Oil Bath to a Paper Element Filter, instead of locating a Suitable Paper or Re-Usable Filter to fit the Oil Bath Bowl, I would obtain and fit an Original Mesh Type Air Silencer and then simply install either a Paper Element or Re-Usable Filter of my choice, which will simply fit where the Original Mesh Filter does. In the event Carburettor Needles need to be changed, this does not appear to be difficult, given that these Fine Cars could be delivered with either Filter Type. Furthermore, fitment of a Mesh Type Air Silencer may well obviate the Fault where the Bracket fitted to the Elbow joining the Air Silencer to the Oil Bath Assembly sometimes cracks and requires Repair/Welding.
Doubtless you will weigh all comments to determine your action.
(Message approved by david_gore)
Post Number: 1044
|Posted on Friday, 07 July, 2006 - 05:20 pm: |
As you state, SU needles are very easily replaced.
I must make a warning here. If someone converts from an AC mesh filter to an aftermarket type, especially to the more restrictive K&N, the motor will run rich on heavy load. No problem, there will just be a little more fuel consumption, a bit of black smoke, and soot will be generated, all without any real damage. However, if converting from an oil bath without changing from SF needles, then there is a problem as the motor will run dangerously lean. Crewe fitted SF needles to oil bath-equipped motors, but SC needles (early cars with SU type H4 carburettors) or SJ (later 4 1/4 with H6 and 4 1/2s) to AC equipped motors for obvious reasons. The SF has a minimum diameter of 0.084" and the SJ 0.069". Thus, at the danger point, the SF needles are up to as much as 22% smaller in diameter, or a massive 49% smaller in cross-sectional area, than the SJ.
This means that an SF needle in an AC-filtered motor will run massively lean on heavy loads. The exhaust valves will burn to bits if an oil bath is simply swapped without changing the SU needles from SF to SJ.
Crewe did not make such a large change in needle types for fun I can assure you. SF and SJ needles are at the opposite ends of the spectrum of SU needle types.
To be safe, I have even swapped from SF needles to SN (0.073" minimum diameter) on my R-Type with an oil bath air cleaner as I was a little concerned that the SFs are a little lean even with the oil bath air cleaner.
Post Number: 3
|Posted on Friday, 07 July, 2006 - 06:13 pm: |
Thank you for your guidance. I will leave well alone. It is a KM series MK6 car with oilbath air filter and new SF needles and new jets and goes well. I will go back to fiddling with the 1909 wolseley which is also original specification, but always responds to fiddling.
Posted From: 184.108.40.206
|Posted on Monday, 10 July, 2006 - 09:55 pm: |
Thank you for the information in your post. Sorry for the delay in getting back to you, but with playing host to 7 extra people staying for extended weekends during the school holidays here, my days are not long enough.
Not being a mechanic, I am confused by the latter portion of paragraph 1 in your last post, where you state, “The SF has a minimum diameter of 0.084" and the SJ 0.069". Thus, at the danger point, the SF needles are up to as much as 22% smaller in diameter, or a massive 49% smaller in cross-sectional area, than the SJ.” I thought the “SJ” Needles were the Smaller Needles but have never been able to remember how this lettering system works.
When I had the Mesh Air Filters fitted to some of my R–Types replaced with Paper Air Filters 12 years ago, I did so after consultation with specialist mechanics in Adelaide and Melbourne. The Carburettor Needles were left in situ as it was found the Performance of the cars was within Acceptable Parameters. There were No discernable Changes to Fuel Consumption, Absolutely No Black Smoke and No Soot generated. When in Adelaide, I like to run the R-Types & Shadow from Adelaide to Strathalbyn and back, as the run up the fairly steep Adelaide Hills can sort out whether a car has problems and the road to Strathalbyn is sometimes used for various car events. Absolutely No Smoke/Soot from these Fine Crewe conveyances whatsoever. Similarly, other R-Types I know of that use Paper Air Filters Also Do Not have Any Problems with Black Smoke, Soot or Fuel Consumption.
In May 2005, when after research I decided to Fit Extractors and a Complete New Stainless Exhaust System to B.20.RT, the Carburettors were reconditioned. Standard Needles were fitted and B.20.RT was Dyno Tuned with a Paper Air Filter through the Full Range of Idle, Cruise and Full Load, with Power and Air/Fuel graphs confirming all was within Acceptable Operating Parameters and there was no need to select other Needles.
As I comprehend it, SU Needle Specifications determined by the Factory when the car/engine was new are predicated upon all other engine characteristics/components being of original specification in terms of working/running tolerance. Thus over time (Some 50 plus years), as well as often unknown mileages, with or without any form of engine repair, rebuild or modification etc, there are other engine specs/parameters which affect overall engine tuning that enter the equation to determine Needle Selection, such as Coke/Carbon build-up, Camshaft wear (Lobes and/or Bearings) which will affect volumetric efficiency, as does any wear upon the Carburettor Main Jet in which the Needle operates.
I understand that when Tuning Mk.VI/R-Types the workshop I used conducts Individual Testing via its Dynomometer on a case by case basis in order to identify the Needles and Other Tuning Settings which provide the Optimum Overall Performance in terms of Power and Economy from a given engine, where the actual preferred outcomes will, for a variety of reasons, vary from car to car, engine to engine etc.
One Pertinent Question is whether Owners have an Option to replace Oil Bath Air Filter with a Paper Air Filter and the answer appears to be Yes, As you point out, “For any change, the correct jets may only be determined properly on a dynamometer over the full power and speed range with a gas analyser.” My experiences are that Dyno Tuning to Determine or Confirm Needle Selection/Fitment s not overly expensive, time consuming or prohibitive. I would expect to pay approx A$80 for an hour of Dyno time.
I never changed the Oil Bath Air Filter fitted to B.191.UL as I have found them to be a Good Filter which does not “sap power” and I have only one Spare Mesh Type Air Silencer in my Parts Inventory compared to three Spare Oil Bath Type Air Silencers. However, given the Facts that Flexolite has had ITG produce a Re-usable Filter for Mk.VI/R-Type, a K & N Re-usable Filter appears available and the Proven use of Paper Air Filters for over a decade, if I were to swap from an Oil Bath Air Filter to a Paper/Re-usable Air Filter, I would do so by packing the Oil Bath Filter and Air Silencer away in my Parts Inventory, installing a Standard Mesh Type Air Silencer fitted with my choice of Paper/Re-usable Filter coupled with a Carburettor Needles selected by Dyno Tuning to suit the car, where the Mesh Air Filter Standard Needles you refer to would be used as a Starting Point to see if Other Factors required different Needles. As stated I believe the replacement of the Oil Bath Type Air Silencer with the Mesh Type Air Silencer would also obviate the Fault with the cracking of the Bracket on the Oil Bath Type Air Silencer to Air Bath Filter Elbow.
With regard to you stating the K & N filters are More Restrictive, I understand K & N Air filters are so-called Hi-Flo/ High Performance Filters, often used on Carburettor fitted cars where frequently Jets have to be changed to Richer due to the increase AIR flow provided by the K & N Air Filters.
With regard to concerns Paper Air Filters are More Restrictive than AC Wire Mesh types, I am not aware of any official tests which confirm concerns/that to be the case. The advice I was given some 12 years ago was that the Paper Filters were More Efficient, as well as Superior to the Mesh Type and would Not in any way Degrade Performance. Is there any Comparative Study available ?
Exposition by way of these posts, as well as those on the RRBEW Forum, should assist any Individual contemplating replacing Mesh/Oil Bath Air Filters with Paper or Re-usable Air Filters.
(Message approved by david_gore)
Post Number: 1047
|Posted on Wednesday, 12 July, 2006 - 12:21 am: |
Your notes echo my theme. However, when my father first bought my R-Type in 1969, it had SH needles (0.066" minimum diameter: see the data sheets in an earlier post) and the oil bath air cleaner. It went fine, but on kickdown at 55mph there was always a quaint and arrogant puff of black smoke. On reading the literature, we changed it to the original SF.
Years later, armed with a selection of needles, some dollars, a gas analyser and a dyno (Dave's Dyno in Newtown, Sydney), I changed to SN (0.073") to optimise combustion. That was ideal with the particular compression ratio, fuel type and valve timing. It all shows that, even if it's running nicely, the whole setup may be far from ideal unless you do the hard work.
Posted From: 220.127.116.11
|Posted on Friday, 06 January, 2017 - 08:34 pm: |
Hello out there,
Has any one changed the brass nuts that connect the manifolds to the down pipes of the exhaust, mine are constantly coming loose
(Message approved by david_gore)