Exhausts, previous owners , straight through or not?

[jingleycatjaguar]

I have finally got around to removing the stainless exhaust from my series 1 2+2 ( manual ) to repair a cracked weld.
I find that the PO fitted one conventional silencer and one straight through.
That may account for the differing exhaust sound from each pipe at idle.
So I am going to replace the whole system.
Two questions pop up,
Straight through or not?
I have two specially extended front pipes like a non 2+2. Do I use them or the 'correct' 2+2 pipes?

Thanks
Steve

[mgcjag]

Hi Steve...If u are keeping everything on the car fairly standard then the easy option is a standard 2+2 set up......there are a few people talking about exhausts at the moment on here....just do a quick search......Steve

[1954Etype]

Depends what you want the car for. If you want it for long distance work, a straight through would become very wearing because of the noise.

[mystery type]

I find that the PO fitted one conventional silencer and one straight through.

Did this make a difference to the noise?
i have always wanted my 2+2 to sound more like a sports car.
im not to bothered about the noise on long journeys,
and would welcome any suggestions.

[Heuer]

Stick to standard bore (1.75") and get straight through silencers which should give you an extra 6% according to Jaguar tests. The resonators are already straight through. No real increase in noise under light throttle but a throaty roar when you put your foot down.

[Woolfi]

If you change to two thraight through silencers , you have to do a "needle-job", otherwiese the mixture will lean out under full throttle conditions. You are loosing power and pistons or valves can get burned.
Regards Wolfgang Gatza

[Moeregaard]

I did the straight-through thing, per the factory tuning manual. With straight pipes fitted in lieu of the front silencers, the car was fun for about the first 15 minutes. Things weren't too bad if I kept it below 3,000 RPM, but anything above that was really loud. A 300-mile road trip became an ordeal, although blasting through tunnels was fun.

[Heuer]

Yes Moe, but you were presumably running a 3.54 diff? With the higher ratio Euro diffs the cruise noise is not a problem between 50 and 80mph.

[jingleycatjaguar]

Decision made. A full double S system with non 2+2 front pipes. Straight through silencers.
What needle will I need to use with this set and standard inlet filter arrangement?

Thanks
Steve

[Heuer]

Standard needles should be fine.

[Moeregaard]

Yes Moe, but you were presumably running a 3.54 diff? With the higher ratio Euro diffs the cruise noise is not a problem between 50 and 80mph.

Yes, I had the terrible 3.54: gears--3,200 RPM @ 70 MPH. Below 3,000 everything was fine; above that and drivers around me started winding up their windows. Since my E-Type was a 4.2, with the short resonators, I'd be curious if the longer units used on the early 3.8-litre cars would be a little less obnoxious. My original reason for eliminating the forward silencers was to see if this reduced the amount of heat transmitted to the interior.

[malcolm]

The big change for me in replacing the 2+2 system I had with a new SS one was getting rid of the sily 2 into 1 arrangement.
On 2+2s, certainly the series 2 ones at least, the two pipes from the manifolds go into one for just about 9 inches before splitting into two again to enter the front boxes. Couldn't see why, and this obviously restricts the gas flow to a great extent. My new system just carried on with the two pipes straight into the front box. My average cruising mpg went from 22 to the gallon to 27.
Found out why the sily configuration is as it is.
On automatic 2+2s, you need the 2 into 1 to avoid the gearbox sump. You don't need it on a manual, but Jaguar wanted one standard set up for all 2+2s (for reasons of cost) and so had to go with the wackly 2 into 1, with the inboard pipe curving out to meet the outboard one.
My new mpg figures came with no change from silenced to straight through; My system from front boxes to the final tail pipes was already SS, so I just changed the manifolds and front downpipes. So the avoiding the 2 into 1 was the only real change that would have affected consumption (and presumably BHP a little as well)

[rolando38]

Hi all

I'm not sure to fully understand the discussion above (maybe because english is not my mother language)
what is "straight through" ? what is "double straight through" ?

I have a 2+2 AutoBox, and I have this at the moment:



as it is leaky and rusty (at least for downpipes) I would like to change; do I have an other option than fitting the below (belived correct) version ?



thanks for your help

Roland

[Woolfi]

"My average cruising mpg went from 22 to the gallon to 27. "

"So the avoiding the 2 into 1 was the only real change that would have affected consumption (and presumably BHP a little as well)"

Hello Malcolm !

Be carefull. If the consumption went up from 22 to 27 mpg, the reason is, that the motor (mixture) is running leaner than before. For a low consumption at half throttle, lean is a good solution.
The original needles are shaped, that the motor is running fat at full throttle. If the back pressure of the exhaust system is lower now, the motor is running more lean at full throttle.
To "cure" this wrong mixture, you should change the needles or "reshape" your original Stromberg needles. I have measured this with a lmabda gauge from innovate at my car. If you reduce the thickness of the needles from 60% carb opening to 100 % carb opening by roundabout 1/100 to 3/100 mm, the mixture will be fat (roundabout Lambda 0,9) at full throttle again.
If this work should be done perfect, you need a Lambda mesuring system in the car. Also on a dyno with 4gas-tester this work is possible to do.
Drive, mesure, change needle profile, drive, measure again. In a few steps it is possible, to find the perfect needle profile for your motor. I was forced to do this with my EV12 after I have changed to a 6,0l motor , with wider inlet trumpet (58mm instead of 32 mm ) of the airfilters and "open" exhaust system. After I have changed the needle profile, the bigger motor came to life. Now my mixture is nearly perfect, iddle is very good, gas consumption is roundabout 20 mpg and mixture is fat at full throttle for max power and long piston and valve life.
Withouit this change of the needle profile, the hp will be lower than original, because the mixture is too lean (more than Lambda 1,0) for max power.
There is a book from Des Hammill about SU-Carbs. He is descibing the "reshaping" of the needles very exactly, also with drawings. I have done with very fine sanding-paper of 800 und 2000. For Stromberg carbs there are very few needles. For SU-Carbs there are more than 700 needles to buy. Therefore you have to reshape your Stromberg-needles by yourself.
Regards Wolfgang Gatza

[KingRichard]

Hi, this is very interesting. I have the SNG B SS exhaust for my 2+2 fitted, which is good I think, apart from the silencer brackets which are front and rear the same, and originally they were not. So at the rear the don't fit correct. I made the rubber brackets myself. See my website for the pictures of this. Never got an answer back from SNG now I think of it. I did mention it though.

What part you exactly exchanged from the 2+2 system? Is it the complete section from the manifolds to the silencers?

It a modification/upgrade I never thought off before. I have manual so.

Thanks,
Richard

T

The big change for me in replacing the 2+2 system I had with a new SS one was getting rid of the sily 2 into 1 arrangement.
On 2+2s, certainly the series 2 ones at least, the two pipes from the manifolds go into one for just about 9 inches before splitting into two again to enter the front boxes. Couldn't see why, and this obviously restricts the gas flow to a great extent. My new system just carried on with the two pipes straight into the front box. My average cruising mpg went from 22 to the gallon to 27.
Found out why the sily configuration is as it is.
On automatic 2+2s, you need the 2 into 1 to avoid the gearbox sump. You don't need it on a manual, but Jaguar wanted one standard set up for all 2+2s (for reasons of cost) and so had to go with the wackly 2 into 1, with the inboard pipe curving out to meet the outboard one.
My new mpg figures came with no change from silenced to straight through; My system from front boxes to the final tail pipes was already SS, so I just changed the manifolds and front downpipes. So the avoiding the 2 into 1 was the only real change that would have affected consumption (and presumably BHP a little as well)

[malcolm]

Thanks Wolfgang, although I have SUs and not Strombergs. The point about mixture is taken though. However, I have checked the mixture (I use a colortune system, air volume meter and normal other checks) and believe the mixture is fine. i think the improvement comes from 2 things:
1) The bigger bore pipes alow a better flow of gases
2) Avoiding the 2 into 1 back to 2, and instead having 2 pipes straight from the manifold to the first box, avoids restricting the flow and unnecessary back pressure

Richard, the part I replaced was the whole section from the manifold to the first box. Each manifold has 3 pipes going into 1, and each goes directly to that first silencer box. Therefore, there is no place on my system where there is only one pipe handling all the exhaust gases. As I said earlier, on the standard 2+2 set up, there is a short section (as can be seen in the parts diagram shown in the earlier post) where all the gases get squeezed into one pipe, just so that pipe can be curved to avoid the larger automatic gearbox. If you have a manual gearbox, you don't need this curve into one pipe.

[mgcjag]

Hi Malcolm....did u have this made up for u or was it something straight off the shelf that others could buy and use. If so details would be great....Steve

[Woolfi]

Hello Malcolm !
"Thanks Wolfgang, although I have SUs and not Strombergs. The point about mixture is taken though. However, I have checked the mixture (I use a colortune system, air volume meter and normal other checks) and believe the mixture is fine."

With colortunes you CAN'T check the mixture at half or full throttle. If you change the original exhaust system to a big-bore system, the mixture will be exactly the same at idle, but with (maybe big) difference at high load.
You need a measuring system, which tells you the exact mixture at higher loads. A on board wide-band lambda system like innovate is able to do this.
I have checked this on my car over month very exactly. Since I am using a Lambda-gauge, I realised that the "ass-meter" often gives you wrong information. It is like driving in thick fog.

"I think the improvement comes from 2 things"

You believe, but you don't know exactly. Most people believe because of "more" sound the car has more ponies. This often is wrong.

Regards Wolfgang Gatza

[christopher storey]

Your hypothesis , Wolfgang, is not necessarily correct . With less back pressure, it is likely that there is better cylinder filling at full throttle, and the effective mixture is probably unchanged. Given that on a road car, full throttle is probably used for no more than 10 seconds at a time , the difference is minimal. In any event, the plain fact is that neither Jaguar ( nor SU ) thought that there was any need for a needle change , UM being the standard needle for all the 6 cylinder cars irrespective of exhaust system

[Woolfi]

Hello Christopher !
A plain fact is, that grandmaster of tuning David Vizzard wrote, "if you change the exhaust system to a big bore system, the carb sees another world".
A plain fact is also, that 35 years ago I have tuned my Honda Monkey. Big carb and big bore exhaust. After I have changed to the original small exhaust, the mixture was much too fat.
Plain fact is also, that I have changed the exhaust and air filter of my EV12. Aftert this the REAL mixture was MUCH too lean from half to full throttle. After I have grinded the 4 needles very carefully thinner, the mixture was correct again.
It is a plain fact, that open exhaust systems for motorcycles with carbs, are often sold with another carb needles or jets. Otherwise the mixture would be too lean.
It is a plain fact, that Roger Bywater is offering a reprogramming of the injection computer, if he is selling a more open exhaust system for the V12 cars. He is wiring on his site, that the car "came to life", after the reprogramming.
Maybe all e-type 6-cyl exhaust-systems have a similar back pressure and therefore there is only minor need for another needle. Maybe some e-type owners in this forum have changed to big-bore exhaust systems. Have they also changed the needles ?
There is a book from Des Hammill about SU-carbs. He is decribing very exactly, why and how to change the needle profile, if the motor is rebuilt to more power. Why, if not necessary ?
If I remeber correct, "Heuer" wrote in this forum, that the needles of the 3 SU should be changed, if the air filter-system is changed.
A jag owner I know in Germany, has got 2 thaight through cherry bombs on his EV12. Now the motor runs much too lean and he is very unsatiesfied with the result.
In my posting before, I wrote about reality not theory.
Regards Wolfgang Gatza