Exhaust question...

[Midlife]

Hello, I have a standard 130S can anyone tell me what diameter the exhaust pipe should be? My main pipe down the middle of the car seems very small around 1 5/8" OD?

Cheers

Doug

[Dave_Newcastle]

I have same car with an original pattern stainless steel exhaust. have just measured it for you and the diameter on the main long run is also just over 1 5/8" .

[ppnelan]

My main pipe down the middle of the car seems very small around 1 5/8" OD?

Quote from Twin Cam Engine book by Miles Wilkins:
'Lotus went to great lengths to get the pipe diameters & baffling correct. Do not alter the systems.'

i.e. If it is a standard-ish engine, stick with the original sizes. It may not be fashionable today, but it'll probably go better and clear those 'sleeping policemen'

Matthew

[cbguerrajr]

I too read that comment in the twincam book. I was puzzled.
I own a '66 S2 and the stock muffler has a single 1 3/8" OD tailpipe. That's smaller than in some motorcycles with much smaller displacement engines!
Could that really be the optimum? For what, performance of noise reduction?

cg

[mikealdren]

I had a bad backfire when I had a hole in the manifold on my +2. I suspect that the valve timing takes into account the back pressure.

On a different front, the layout of the exhaust has significant issues for noise and vibration although I think Lotus probably paid less attention to this! The exhaust mounts should be positioned at vibration nodes so that they transmit less vibration into the cabin and also so that they are allowed to vibrate freely to minimise vibration failures. Of course the nodes vary with the vibration mode, it's a compromise and the low frequency modes are more important.
regards
Mike

[steveww]

I just fitted large bore headers, mufflers etc. to my S4 and it certainly improved the performance. In the racing community it is generally accepted that the twinc responds well to improved exhaust flow. The David Vizard book "Tuning Twin Cam Fords" also states that improved exhaust flow is a good thing for the twinc. I have no idea why Miles Wilkins does not like exhaust manufactures

[sk178ta]

I have a Sprint engine in my S3 with the standard S3 exhaust and wonder if a larger bore would be beneficial. Steve, how much were the larger bore headers (exhaust manifold in English) and where from? TT ?
Jim

[rgh0]

Steve

I suspect the comment arose becasue given the headers that Lotus used the pipe diameters and baffling for the exhaust downstream were probably Ok and certainly cheap and not warranting changing.

However the original single downpipe cast header was very poor, the SE twin downpipe cast header a little better and the sprint tubular header a little better again but still to small even for a standard engine.

I guess Lotus used these driven by cost and space available and only increased them when chasing more power as the car evolved.

Going to bigger bore headers and matching tail pipe and muffler good for all cars.

Rohan

[steveww]

I have a Sprint engine in my S3 with the standard S3 exhaust and wonder if a larger bore would be beneficial. Steve, how much were the larger bore headers (exhaust manifold in English) and where from? TT ?
Jim

Jim,

The manifold was off ebay and was new old stock, sorry I can't remember who made it originally. I have not measured it but the manifold tubes are at least one inch and the system is 2.25". It is a 4-2-1 design, for more info see my site http://www.steveww.org/

[stuartgb100]

My understanding is that TTR's big-bore system is well thought of.

Tony offers a fast road system for up to 165 bhp, a full race system, and a race system with high ground clearance for S1-S3.

All have large bore handmade 4-2-1 manifolds (tuned lengths), with ss centre pipes and silencers. Several silencer versions/options are available.

Regards,
Stuart.

[stuartgb100]

My understanding is that TTR's big-bore system is well thought of.

Tony offers a fast road system for up to 165 bhp, a full race system, and a race system with high ground clearance for S1-S3.

All have large bore handmade 4-2-1 manifolds (tuned lengths), with ss centre pipes and silencers. Several silencer versions/options are available.

Regards,
Stuart.

[Midlife]

Thanks to all for the feedback, some interesting points. the outlet from my collector is 1 3/4" OD so Im thinking I will follow on from this. I will try differant options over the summer, and will let you all know where I get improvements.

Cheers, Doug.