S1 4.2 Rear Exhaust without expansion box

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eddiecross
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#1 S1 4.2 Rear Exhaust without expansion box

Post by eddiecross » Fri May 11, 2018 3:48 pm

I have the standard exhaust ( 1 3/4" bore I think) on my '67 4.2 which is too muffled for my liking.
If I swapped in straight through pipes at the rear in place of the pair with the expansion boxes would it make much difference?

S/S Tubing is only about £30 and I have an excellent mechanic who is a dab hand on fabrication and TIG welding so it looks pretty straight forward. Will it give more bite to the exhaust note?

Thx
Eddie

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Geoff Allam
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#2 Re: S1 4.2 Rear Exhaust without expansion box

Post by Geoff Allam » Fri May 11, 2018 4:24 pm

Have you considered that while you may like the sound of loud engines the vast majority of the people who inhabit the areas you drive through do not. If you are using your car for track purposes I say go for it, but for the average street driven car the quieter the exhaust note the happier the general public will be. There is enough opposition to the old car hobby from the “green” brigade without annoying the general public as well. This may be just the opinion of an old goat and you are free to do as you like but I think it is food for thought.
Geoff Allam
67 series1 ots under restoration
64 series 1 fhc burning lots of oil
53 xk 120 fhc sitting in garage waiting for attention

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chrisfell
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#3 Re: S1 4.2 Rear Exhaust without expansion box

Post by chrisfell » Fri May 11, 2018 6:07 pm

Fit straight sections of stainless steel pipe instead of the main silencers, keep the rear resonators. Fabrication only required to mount the pipes on the silencer hangers.


Easily reversible if the neighbours complain.

Which they wont.
Chris '67 S1 2+2

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Tom W
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#4 Re: S1 4.2 Rear Exhaust without expansion box

Post by Tom W » Sat May 12, 2018 5:42 pm

chrisfell wrote:
Fri May 11, 2018 6:07 pm
Fit straight sections of stainless steel pipe instead of the main silencers, keep the rear resonators. Fabrication only required to mount the pipes on the silencer hangers.


Easily reversible if the neighbours complain.

Which they wont.
I tried this once. Being a cheapskate, I just bought some plain mild steel exhaust pipe from the local motor factors, and cobbled it together with some universal exhaust hanger brackets and u-bolts. Under hard acceleration, it sounded fantastic. Just like the unsilenced race cars at Goodwood, and presumably just as loud to bystanders. At idle, it was slightly louder than the original exhaust, but poke the throttle, and it would really bark.

The problem was, it droned loudly and unpleasantly at cruising speed, and it was impossible to drive through town without everyone turning round to stare. It would pop very loudly on overrun too, like a shot-gun going off, even when steadily approaching junctions. Not great in a built up area. This may have been down to air leaks though, as I never flared the pipes to the correct size. In the end, I reverted back to the sports centre silencer the car came with. That sounds great under load, but could still do with a bit more bark at idle for my taste.

I still have a hankering to try something different again, and make a better go of fabricating a proper centre silencer replacement.
Last edited by Tom W on Sun May 13, 2018 7:36 am, edited 1 time in total.
Tom
1970 S2 FHC

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Series1 Stu
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#5 Re: S1 4.2 Rear Exhaust without expansion box

Post by Series1 Stu » Sat May 12, 2018 9:12 pm

Geoff Allam wrote:
Fri May 11, 2018 4:24 pm
If you are using your car for track purposes I say go for it, but for the average street driven car the quieter the exhaust note the happier the general public will be.
You may be surprised that you're more likely to be black flagged for exhaust noise on a race circuit than you are to get a ticket on the road.

Eddie, why not just move up to a 2 inch system?

Regards
Stuart

If you can't make it work, make it complicated!

'62 FHC - Work In (slow) Progress
'69 Daimler 420 Sovereign
'94 X300 XJR basket case

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Heuer
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#6 Re: S1 4.2 Rear Exhaust without expansion box

Post by Heuer » Sun May 13, 2018 11:12 am

My advice would be to avoid a big bore exhaust (i.e. anything above stock) as it will cause a torque dip between 2,250 and 2,750 rpm and booming at normal road speeds. More noise, lower power but if that floats your boat go ahead. Your best option is to replace the silencers with straight through versions - the resonators are already straight through. This setup will give you more power (approx 6% according to the Factory) and a nice sound during acceleration. At cruise it will be relatively quiet.

As already mentioned race cars are subject to strict noise regulations and tracks have decibel meters for use during scrutineering and dotted around the track during the race.
David Jones
S1 OTS OSB; S1 FHC ODB

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JD-JAG66
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#7 Re: S1 4.2 Rear Exhaust without expansion box

Post by JD-JAG66 » Sun May 13, 2018 2:29 pm

I need some "translation" here. :wink:
A "straight through" silencer is basically just a tube, right? Or would it be a silencer with nothing inside...
I used to have a MG with a straight through exhaust and that was just a tube really.

Reason I am asking is that I am about to bring my car a 4.2 2+2 to a exhaust shop and was considering to keep the centre silencers and just have "some bent tubes" at the end

Given Heuers feedback, I would change it all and follow his advice but would like to know about the "straight through" part.

Cheers
Jan
Jan Deurinck
Series 1 - 1966 - 2+2 - LHD - American Import
Si vales, bene est, ego valeo

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#8 Re: S1 4.2 Rear Exhaust without expansion box

Post by Heuer » Sun May 13, 2018 3:45 pm

Jan

A straight through silencer is a single perforated tube surrounded by sound deadening material in the casing. It goes 'straight through' the silencer from front pipe to rear pipe. A normal silencer uses baffles or walls to deflect the sound into the sound deadening material - a sort of simple maze. It is these baffles which reduce the gas flow which compromises performance slightly but makes the car pleasant to drive, especially in the case of a FHC. Most big bore exhausts are straight through but they bring other problems. In terms of sound, from quietest to loudest:

Standard 1.75" mild steel with baffled silencers
Standard 1.75" mild steel with straight through silencers
Big bore 2" mild steel with baffled silencers
Big bore 2" mild steel with straight through silencers
1.75" mild steel with no silencers or resonators (probably illegal in most countries!)

Stainless steel changes the timbre of the sound moving it up a couple of octaves. Sounds sharper and harsher. A good compromise is to use stainless pipes and silencers with mild steel resonators. Using tubular manifolds rather than cast iron increases cabin noise still further and bring about rtheir own set of compromises. Best avoided for a road car.
David Jones
S1 OTS OSB; S1 FHC ODB

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JD-JAG66
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#9 Re: S1 4.2 Rear Exhaust without expansion box

Post by JD-JAG66 » Sun May 13, 2018 9:11 pm

Thanks David,

Will take this up with my exhaust shop and see what they can fabricate.
Again, thanks, most useful!

Have a great day
Jan
Jan Deurinck
Series 1 - 1966 - 2+2 - LHD - American Import
Si vales, bene est, ego valeo

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eddiecross
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#10 Re: S1 4.2 Rear Exhaust without expansion box

Post by eddiecross » Mon May 14, 2018 12:41 pm

Many thanks for everyones input. Some really useful information. I guess I'm sticking with rear extg pipes.

I may try cherry bombs to replace the main silencers if I can find some 1 3/4" for a decent price.

Thx
Eddie

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rfs1957
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#11 Re: S1 4.2 Rear Exhaust without expansion box

Post by rfs1957 » Thu May 17, 2018 9:08 pm

I've forgotten what my E-Type looks like, as the workshop is full of many more pressing and needy 2-wheeled projects.

At this rate, indeed, I'll never remember how to put it all (engine, and complete front end) back together again ........... at least without recourse to printing out the 50 pictures I shot over the winter, as I dismantled it, and making my own "E-Types For Dummies" book.

HOWEVER I can perhaps add something useful about the exhaust system - before I forget this as well !

I too wanted something a little more sonorous than my bog-standard (but stainless) system, and so tried the No-Centre-Boxes set-up, making a pair of perfect straight-through centre sections that hung off the original rubbers.

The result was great to listen to, briefly, but undriveable ; it was unpleasantly noisy IN the cabin, and as the vibration characteristics of the centre pipes are (obviously) completely different, the rubber hangers transmitted a lot of drumming through into the body.

It was like driving a 205 GTi - great for 5 minutes, and afterwards a rather wearing PITA - and nothing like the E-Type I loved. It was stressful and felt (was) ostentatious.

BUT, I did find a compromise - and wrote about it here at the time, maybe 6 or so years ago.

To my great surprise, by modifying a Bosch hole-saw (adding a stem to essentially be able to drive it further down a tube) of a suitable just-fits diameter, I was able to go down the entry pipes of each centre box and go through the first - and, amazingly, only - baffle.

All of a sudden I could see right through the centre boxes, from start to finish.

The sound produced is in no way a nuisance for bystanders, and when the car is driven sedately it's the purring cat, but when you cane it a bit you get the howl you're after.

The noise inside the car is not an issue, I can't remember noticing the change in fact, but there is an edge to the sound that is exactly what I had been looking for.

It probably took me 10 minutes to make the tool, and 10 minutes to drill through the baffles.
Rory
3.8 OTS Cream 877393 Built May 28th 1962
1978 Mini Van
(plus bevel and belt single-cylinder Ducatis)

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#12 Re: S1 4.2 Rear Exhaust without expansion box

Post by Moeregaard » Fri May 18, 2018 4:41 am

I've weighed in on this subject before, so apologies for the repeat. When I got my '65 FHC back on the road in 1993, I "conveniently" substituted straight-through pipes for the under-floor silencers, while leaving the rear resonators in place. This is listed as an approved modification in the factory tuning manual. On road trips, it was tolerable for the first 30 minutes, although tunnels were great fun. Fortunately, I never had a run-in with the law, since excessive noise in California results in points on the licence. Previously, I'd kept the forward silencers in place, while getting rid of the rear resonators. The sound had a nice bark, but it wasn't so loud as to attract unwanted (and expensive) attention.
Mark (Moe) Shipley
Former owner '66FHC, #1E32208
Former owner '65FHC, #1E30036

Planning on getting E-Type No. 3 as soon as possible....

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marc
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#13 Re: S1 4.2 Rear Exhaust without expansion box

Post by marc » Fri May 18, 2018 9:06 am

Hi everybody,
i find the stainless steel wide bore exhaust line I have on the car too noisy: where should I best (quality/price) order one in mild steel for a 1963 FHC? I'd like to get the long resonators. I already have the original manifolds.
thank you for your advice, best regards
Marc 1963 3.8 FHC

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#14 Re: S1 4.2 Rear Exhaust without expansion box

Post by Heuer » Fri May 18, 2018 10:16 am

You can buy the complete mild steel system including chromed resonators from Jaguar Classic. You could have a system made for you for about £600 but then you would need to have the resonators plated which will cost you about £300.

People chose stainless because the resonators can be polished. Mild steel sounds better and is the way an E Type sounded in period and as Jaguar intended. Buy the Jaguar Classic system - if we support them they will produce more pattern correct parts.
David Jones
S1 OTS OSB; S1 FHC ODB

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