Exhaust-modify or not?

[Johnwindwood]

Guys

Now that the suspension rebuild is complete, it's time to get a new exhaust system for our 1984 low compression car. (I've patched it up but it now really is falling apart!)

We have a good local place that builds stainless systems to the car, and we are not worried too much about originality.
Question-is there any benefit to enlarging pipework, deleting boxes etc or are we better keeping it to standard specs? I'm interested in peoples experiences with such things.


Thanks.

[richardw]

Guys

Now that the suspension rebuild is complete, it's time to get a new exhaust system for our 1984 low compression car. (I've patched it up but it now really is falling apart!)

We have a good local place that builds stainless systems to the car, and we are not worried too much about originality.
Question-is there any benefit to enlarging pipework, deleting boxes etc or are we better keeping it to standard specs? I'm interested in peoples experiences with such things.


Thanks.

It depends what you want. I believe the original Lotus design was pretty good in that it offered a good compromise between performance and refinement. You can open it up and delete boxes but you run the risk of making it noisy. If you want to keep the original sound, then follow the original design as far as you can. And if you can, retain the cast iron exhaust manifold - it has excellent sound and vibration damping qualities which you will lose if you go to a stainless fabrication.

SJ Sportscars do a replacement system in stainless if you want something off the shelf!

ATB Richard

[Tanz]

I went for the Lotusbits sports exhaust with branch manifold and larger front pipe. As Richard says above, it is noisy but that is what I like about it most.
Sounds great. I want the Lotus to be different to driving the family car and a great sounding exhaust is one difference. There is a slight performance improvement but I would need to do other work on the engine to get the most out of it.

[Lotus-e-Clan]

I definitely LOST some torque with a bespoke full SS system. Knew it as soon as I left the workshop!

The very expensive SS rear boxes (I wanted the best they had - and I stupidly trusted their self-promoted reputation) plus large bore tailpipe s actually slowed the overall gas flow down! - So be aware that some of these bespoke exhaust centres have no idea about tuning exhausts to specific applications - and certainly they will know nothing about getting the best out of the 912 engine. These guys just lack the necessary FAB-SKI -(fabulous skills knowledge and intelligence) required for exhaust-tuning classics.

Large bore counts for nothing (and can detract) performance-wise unless you have uprated the engine's gas flow.

The tail pipes look and sound FAB mind!

[Hawaiis0]

Removal of my center box seemed to liven up the car no end

[AndyC]

I definitely LOST some torque with a bespoke full SS system. Knew it as soon as I left the workshop!

The very expensive SS rear boxes (I wanted the best they had - and I stupidly trusted their self-promoted reputation) plus large bore tailpipe s actually slowed the overall gas flow down! - So be aware that some of these bespoke exhaust centres have no idea about tuning exhausts to specific applications - and certainly they will know nothing about getting the best out of the 912 engine. These guys just lack the necessary FAB-SKI -(fabulous skills knowledge and intelligence) required for exhaust-tuning classics.

Large bore counts for nothing (and can detract) performance-wise unless you have uprated the engine's gas flow.

The tail pipes look and sound FAB mind!

It's easy to increase gas-flow but so reduce back pressure or cause resonance and end up with less power. I've read about people who actually specify pipes smaller than the aftermarket manufacturer recommends, and end up with more (usable) power/ torque characteristics that way.
Still not great for you, but then our cars are not out and out power monsters, they are designed to handle well and so beat others through twisty roads/ tracks.

[Lotus-e-Clan]

I definitely LOST some torque with a bespoke full SS system. Knew it as soon as I left the workshop!

The very expensive SS rear boxes (I wanted the best they had - and I stupidly trusted their self-promoted reputation) plus large bore tailpipe s actually slowed the overall gas flow down! - So be aware that some of these bespoke exhaust centres have no idea about tuning exhausts to specific applications - and certainly they will know nothing about getting the best out of the 912 engine. These guys just lack the necessary FAB-SKI -(fabulous skills knowledge and intelligence) required for exhaust-tuning classics.

Large bore counts for nothing (and can detract) performance-wise unless you have uprated the engine's gas flow.

The tail pipes look and sound FAB mind!

It's easy to increase gas-flow but so reduce back pressure or cause resonance and end up with less power. I've read about people who actually specify pipes smaller than the aftermarket manufacturer recommends, and end up with more (usable) power/ torque characteristics that way.
Still not great for you, but then our cars are not out and out power monsters, they are designed to handle well and so beat others through twisty roads/ tracks.

Yes that's exactly my point Andy - the smaller bore std SE Lotus system is betterfor the std SE than an aftermarket large bore - unless you are chasing more maximum power at higher revs (rather than usable workaday torque at lower rpm) . Just giving folk a heads-up on fitting large bore just for the sake of large bore without engine mods.

[Johnwindwood]

Removal of my center box seemed to liven up the car no end

Did it significantly increase noise levels?

[shaunw]

A very timely thread as i am in discussion with a custom exhaust place to make a complete system ( from the flexi pipe back ) for my car and they have recommended starting by deleting the centre resonator box and using slightly less restrictive rear silencers. Ive told them i want a nice noise but not too boomy and dont want to loose mid range torque. They are going to order two different types of silencers for the back so that i can choose between them. Ive been reading up about deleting resonators and opinion is split 50 50 as to whether this is a good idea. My car has hotter cams larger idle jets and a lightened flywheel so hopefully the resonator deletion will compliment the set up. We will.see! Ive been in two Excels with the SJS system and to my ears they sound far too quiet in the car. Currenty mine is pretty loud as the exhaust is original and the baffles have rotted away ( I assume )currently its a bit drony on long motorway runs but like Tanz says, i want it to sound like a sports car!

[MrCoolA]

In my experience you should Roling road your car post any major change in exhaust and beware the specific type of baffles in the back boxes from non oem built exhaust can affect the performance in a negative way.

[don.hasi]

I have different experiences. First I had the stock SE exhaust, than SS which brought more noise and a bit of more power and at least the big bore full system of Lotusbits. Maybe it had the same soft spot in midrange, but after that, the growl came in and with it a serious (!) power gain.

My experience with every other car is a power gain through the complete rev range without any engine jobs if you just take a serious manifold as well. With it, you get faster through the revs so you have no time to notice any flat spots. Yes, machining the inlet and outlet ports will help further, but it has an effect from the start even without it.

The diameter of the oem exhaust increased several times. The factory will know why...

[Hawaiis0]

Removal of my center box seemed to liven up the car no end

Did it significantly increase noise levels?

Pardon?

No seems the same.

[fueltheburn]

My experience:

Nothing is perfect:

- SJS standard system is expensive, shockingly bad quality and not a great fit without serious adjustment. Corrodes really quickly. Barely should be classed as stainless.

- Removed the centre box, ever so slightly louder, more likely to go quicker due to less weight.

- Custom made system. No issues, lifetime guarantee. Good value

- Lotusbits big bore system. Quality material used. Fits well with relatively little adjustment. Had to remove high spots and weld splatter inside of the tubular manifold (Friday afternoon job ). Sounds good.
Expensive.

[Bluie]

Mine has the Lotusbits Stainless steel silencer. It has a lovely sound with a nice burble at tickover. It is relatively loud when pulling away but quietens down when cruising. I love it!

[Johnwindwood]

Thanks guys-all very useful comments. It's booked in for a tailor made system on Monday. I'll have a chat with them to see how they feel about a centre box delete.