| Author | Message | ||
     John Richardson Unregistered guest Posted From: 203.61.193.9 |
REF:R-type Exhaust Manifold/Downpipes - Whether Originals or Modern Substitutes are Best? My experience is that when R-type Exhaust Manfolds are removed for gasket/front side cover gasket replacement etc, warping occurs so the Manifold/s require machining etc. They also appear to become brittle. The absence of a Generous Flexible Section in each Manifold Downpipe appears curious. I do not mind practical, acceptable modifications, whereby vehicle Originality can be recovered by the simple wielding of appropriate spanners/screwdrivers etc. It has been suggested to me, that in the 21st Century it is far more Efficient/Sensible to use modern Headers/ Downpipes etc, which also obviates the Factory fastening arrangement. Has anyone fitted such a modification to an R-type/Mk.VI and has it proven Beneficial ? Any problems with backpressure etc ? I visit your forum on an occasional basis and seem to recollect some brief discussion relating to this type of modification. However, I have been unable to readily locate any such discussion as I cannot remember where I saw it. Assistance to locate any such Forum postings/discussion will be appreciated, as will any comments pro or con. Thank you in anticipation, Johnny } (Message approved by admin) | ||
| Richard Treacy Grand Master Username: richard_treacy Post Number: 545 Registered: 4-2003 |
Johhny, Your experience with these manifolds is typical. I know of a few cars, at least two MkVI and one R-Type, with custom headers, and I expect the owners will post the benefits. On my own R-Type, I replaced both manifolds with new genuine ones in the 1980s. They were very expensive back then, but are relatively cheaper nowadays at around A$600 each. Having invested so, I didn't opt for custom headers although I am assured that a properly designed header will make very real improvements in all aspects of economy and performance. It is noteworthy that improved exhaust breathing was the main contributor to the power increase in the early 4.5L R-Type Continental over the standard vehicles. I did, however, have a flexible bellows fitted on each downpipe just before its front silencer. It is a beautul job in stainless steel along with the entire exhaust system, done by Powatone in Canberra around 1994. The aim is, as you imply, to ensure that the manifolds are not stressed as the engine mounts give and take, and more importantly to protect if something strikes the exhaust from beneath. The latter destroyed one of my manifolds on a friend's farm once. The bellows are useful despite the downpipes being tied to the block by brackets before bending towards the front silencers. The brackets were the rationale behind not using bellows in the first place, but any loosness, give or breakage in the brackets leaves the manifolds very prone to damage. I can highly recommend fitting the flexible bellows with standard manifolds. With fabricated steel headers, bellows may I admit be overkill, but would certainly be a good thing anyhow. | ||
| Laurie Fox Experienced User Username: laurie_fox Post Number: 9 Registered: 6-2004 |
My MK VI (B420EY) has the single exhaust system and there have been no problems. Is the twin exhaust system more vulnerable? I have always taken care to fit things up properly so that there is no undue stress caused by misanlignment etc. when fitting the two manifolds to the block and to the single exhaust pipe. To that end the bolt holes in the manifolds have been slightly enlarged so as to allow some repositioning and the various bolts tightened progressively, making sure that the bottom end of the downpipe does go through the middle of the hole in the chassis member. I also take care that the various exhaust syspension straps are straight and seem to be carrying their own proper share of the load although I have removed the suspension strap immediately aft of the rear silencer for two reasons. One is that it is difficult to get at anyway and the second is that without this strap the whole exhaust system is more free to rotate as the engine rocks. The support bracket from the crankcase to the middle of the downpipe needs to be properly set up and tight so as to avoid strain on the manifolds. Given these precautions the result has been a robust system which survived some self inflicted damage when (in France) I backed into a traffic sign pole which made contact with the back end of the exhaust pipe and pushed it in several inches. The bends in the pipe aft of the rear silencer were substantially distorted as was the aftmost rubber support bracket but there was no other damage although the load on the manifolds must have been substantial. | ||
| Richard Treacy Grand Master Username: richard_treacy Post Number: 547 Registered: 4-2003 |
To respond to your comments, Laurie: I totally agree that the exhausts on all these cars are not exactly high on the improvements totem pole. The dual exhausts are more vulnerable than yours as you imply. The rear manifold is completely different from the single exhaust variety and is more fragile to start. Once machined flat after warping, they usually crack to compensate soon afterwards. I once asked how many manifolds R-R sold as spares, and was shocked at the high count for R-Types, very few for single exhaust Dawns and MkVIs, and for S1s practically none. Your single system 6 into 2 into 1 is inherently easy on the manifolds as just one pipe (with the 2 into 1 section at the top) is attached to both manifolds with six bolts and nuts. Using the square law, it is probably 4 times more robust than a dual system with the two separate pipes each with three nuts and bolts. However, if correctly secured as you describe, neither type is really at risk. That clamp you mention on the pipe below the manifold is vital but fallible, and a bump from beneath will defeat it. The trouble with exhausts is that the fasteners seize up quickly and fail without prior visible warning and go unnoticed for days. The damage is done. If the manifolds are expensive like these, it is cheap and effective to spend a few dollars to fit a bellows when replacing the downpipes. It is also cheap insurance in incidents as the one you describe or when an engine mount becomes soft. |
