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120 Exhaust System

120 Exhaust System

Do you know if any later 120's left the factory with two holes, even if fitted with single exhaust? The hole doesn't look to be a modification. Does anybody else have two? - Scott Allard

Scott: I would not regard the twin exhaust with 2 holes in the chassis as factory fitted. I agree that the SEs went under the chassis. Anyone have any further comments? Also, not all SEs had dual exhausts - later FHC for example had single (too noisy?). Regards, John Elmgreen

Scott, Your other question, is it about the 2 holes in the chassis cross member? I'm pretty sure all the XK chassis' have them. I assume them to be a strengthing member. Box sections are strong, but when a cross section is added as they are, they become stronger. - George Badger

My question was about the two holes - I was under the mistaken impression that not all XK's have them. Why wouldn't the SE's dual exhaust run through those? - Scott Allard

671187 has one 4" diameter hole through the chassis cross member. - Mike Eck

I'm going to take a look at the two holes in mine to hopefully determine if they were factory jobs. Has anyone heard of these holes being drilled out as a modification after the factory? - Scott Allard

I used to know of a car that was modified to have the two holes in the frame. It was a 53 XK120 FHC. I know the machine shop that did the work. It was owned by an astronaunt (now deceased) and the car went to Holland. I think it was bought by a Dutch astronaunt. Lost track of it after that. Navy blue with biscuit is what I remember. - Cleo Bay

Mine is 53 120FHC in holland and from the states, but I am not an astronaut. There is only one dutch astronaut. I will try to find out. As far as I knew?: The fhc's started with double exhausts but went single early 53. - Duco Avis

Hi Scott, John Elmgreen, & all -- my '54 XK12SE OTS, S674619 (sold in '89 after 13 years of restoration & FUN!), had the twin pipes under the chassis. - hope this helps -- Larry Martz

I recently replaced the single exhaust on our 120 with a dual system obtained from Bill Bassett. It goes under the frame. It sounds terrific. Resonates at about 1,600 and 3,200 rpm. I believe for the best sound, the two exhaust paths need to be very close to the same length. The exhaust system is similar to a musical instrument - which is why it resonates at certain frequencies. What we have with the 120 is two three cylinder instruments playing in concert with some interaction inside the silencer. The individual sound pulses for each instrument are at a frequency of 1/4 the rpm of the engine with the pulses alternating between the two pipes. If the pipes are of unequal length, the alternating pulses will not be evenly spaced and the tonal quality will be diminished. If you listen closely to the sound of the system, you will be able to hear a low frequency which is the note produced by each pipe. One octave above that, you will hear another note produced by the alternating pulses between the pipes. These are in perfect harmony. At the second resonance, there are again two basic frequencies an octave apart plus an undertone at half the first resonance. (Try humming with the differents notes - it makes them easier to identify.) The quality of all this harmony starts to fall apart with inequality of path length in the pipes so it is important in a dual system to keep the lengths the same. The loudness will be about the same with unequal lengths, but the system won't "sing" as well. - Bruce Cunningham - 53 OTS

Since restoring my 1953 XK 120 a few years back I have been driving with a single exhaust system. It has a very long (36") straight through muffler and sounds fine BUT it is not the REALLY great sound I associate with the 120s of my youth. Given that most of those had dual exhaust systems, I have decided to add a second exhaust. Also, given that those 50s cars didn't have stainless systems, I've decided to stay with mild steel. Does anyone out there have any suggestions regarding the type/size muffler, etc. that might bring that original sound? I know the original system had a single muffler with two inlets and outlets. Is it necessary for me to duplicate that or can I simply add another straight-through muffler along side the existing one? Any and all advice is appreciated. - Earl Huff XK 120, XJS

Earl:

I looked for a while before finding a mild steel dual exhaust for my 120 - finally found what I was looking for from David Laughton at Coventry Classic Cars. David's price was typically reasonable - I think around $115 complete, picked up at Carlisle flea market this past spring. It was all new but I wire brushed it down and gave it a couple of coats of stainless exhaust paint, which I've used with excellent results on my E-type manifolds. Can't tell you what it sounds like, 'though - haven't fired the car up yet. Incidentally, I have a Falcon stainless exhaust on my E-type and it sounds great. - Nick Saltarelli 1954 XK120SE OTS, 1968 E-type OTS

Just received my new "Double S" twin exhaust system for my 120. Can someone please tell me what holds the rear twin pipes to the body bracket at the very rear where they exit the car? I have the bracket that bolts to the spare tire floor and the rubber mount bushing, but shouldn't there be a bracket welded to the pipes that attaches to these items? My two pipes are nice and polished but no bracket there. Is there some type of clamping bracket that goes over the pipes and attaches to the mount bushing/rubber? Thanks for any help. - Jamie

Jamie: There should be a half to 5/8" wide strap welded across the top of the pipes with a hole in the center of it to receive a bolt from your bracket. - Dick Cavicke

Thanks Dick for your reply, That is what I thought there should be. If you get a chance could you tell me what the center to center spacing of the two rear pipes should be, and also a placement measurment for the bracket that bolts to the floor? Distance from the left boot edge and distance in from the rear edge in lets say would work great for me to drill the two mounting holes for the bracket. Thanks very much. Good luck with this weekends concours! I know some of the 120's up here are going to caravan down. I am trying to get mine back together but this bracket problem and also a leaking freeze plug are trying to make it difficult for me to take the car down off the jack stands. Hopefully I can get it zipped back together on Saturday to make the ride down to your show. Regards - Jamie

Since restoring my 1953 XK 120 a few years back I have been driving with a single exhaust system. It has a very long (36") straight through muffler and sounds fine BUT it is not the REALLY great sound I associate with the 120s of my youth.Given that most of those had dual exhaust systems, I have decided to add a second exhaust. Also, given that those 50s cars didn't have stainless systems, I've decided to stay with mild steel. Does anyone out there have any suggestionregarding the type/size muffler, etc. that might bring that original sound? I know the original system had a single muffler with two inlets and outlets. Is it necessary for me to duplicate that or can I simply add another straight-through muffler along side the existing one? Any and all advice is appreciated. - Earl Huff

Earl, Generically it is recommended to do a "balance tube" between the pipes on V-8 dual exhaust systems, just in front of the mufflers. This improves the sound by giving more small pulses through each pipe rather than the higher amplitude further spaced pulses that would occur with the pipes being separate through the entire length. My 140 does though have separate pipes for the entire length, but since it isn't running yet I can't speak to the sound. At this point I'm looking forward to any sound at all. ;-) The balance tube may give a similar sound to the two in, two out muffler you refer to. $0.02 - Ken Boetzer

Earl, if you have a British Auto XK catalog, (1-800-4jagpts) they have a single muffler, with dual input and exhaust. - Neil Skipper

Best sounds out of Jags I have owned were: 1. XK 150 FHC with single exhaust, one long muffler with a couple holes (looked like someone shot the thing with a .45 !) [quite possible as I was living in the 'boonies ' of Oklahoma at the time]. The car had a really long legged final drive as it had no accelleration to speak of but seemed to want to rev forever. Due to the condition of the tires, brakes (round, really shiny pads) etc. I never did find out what the top end was, but Oh the wonderful sounds!! My kids, small at the time would do whatever it would take for them to be able to ride in the jump seats, hold their hands over their ears and scream at the top of their lungs! They called that one 'Funny, Funny Car' It sounded so good, I never did replace the muffler and either did the next owner! 2. 64 E type FHC. Mufflers and resonators all went out at the same time and it was safety inspection time. I couldnt afford the whole deal so I bought new resonators from JC Whitney ($19.50 Each) and got a muffler shop to cut 2 plain exhaust pipes the length of the mufflers thinking that I would replace the mufflers next payday. It passed inspection ( "Whut kind of Danged Cur is Thet?" A JigWar? Whull I be Danged") to quote the inspector, but it sounded so good I owned the car another for another 6 years and never did get around to 'fixing' it. At the time I worked downtown where the cars were parked in a nine story parking garage, all concrete, and it was worth the 30 mile round trip just to go down there on Sundayas when the place was empty and blast round and round from bottom to top and round to the exit again......What FUN!!! So based on all the above, My question to you is What the hell do you need with a Mufller???????( I know someone will answer back with, "Horrors, it wont be original, they original were 9 and 37/64 english inches in diameter and 21 and 74/96 english inches in length and made of 'Unobtainium' etc etc etc" or " You must have 2.4 Inches of Mercury back Pressure as designed by Wallace L. Pecksniff, Sir WM Lyons engineer extraordinaire, etc.etc.etc." But I for one, dont care it was GREAT FUN! , in fact I think Im going to take the mufflers off my 150S....of the floor that is, as they are not ready to go back on yet any way! (Boy have you noticed how some people can really get themselves wound up about this stuff?) - Dave Drenzek

If you have any questions or comments send e-mail to: ted@jag-lovers.org
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