Lotus Elan and Lotus Elan Plus 2 Forums

Hello everyone. I am a newbie and seeking your expert advice.

My car is fitted with twin Dellortos and a standard airbox with ducting which leads down to the inlet air filter located in the nose. I believe this is a standard arrangement but I would like to change it by fitting an air filter "up-top" adjacent to the air box. Does anyone know of a supplier/type/model number ?

Appreciate any guidance you can give. Thanks

Hi. One option is to stick with the downpipe and airbox and fit a K&N filter assembly in the nose. Cliveboy sells this arrangement:

elan-f15/cliveyboy-breather-and-filter-conversion-t17520.html

It has the advantage of not needing modifications to get clearance, and maintains the protection that the airbox provides against fuel leaks and blowback. This is the route that I adopted. The second is to get some K&N air filters to fit directly to the carbs.

The above thread has more discussion on this.

All the best.

Sean.

ps welcome to the forum

This way you are pulling cold air in to the engine too, rather than warm air.

I haven't fitted one of these, but I intend to do something similar

Does anyone have any comparative performance figures for an Elan / +2 running different induction systems?

I appreciate the desirability of using cold air (greater expansion etc.) but i wonder if the losses of that long Intake System make it all worthwhile?
My older Lotus's ran open Carbs.
The 7 had them pointing out of the Bonnet right at the inside of the front Wheel & the Elite's Webers also had no form of Filter on them, similarly the 23b which being a race Car that runs mostly at full Throttle is another fluid dynamics story & of course an end of Season Engine rebuild (If I'd had it that long )
The idea of taking the whole lot off my Elan & running open trumpets has crossed my mind more than once
After all how much Muck can pentrate that far into the Engine Bay under normal (Elan, not daily driver) Road use?
Most of the incoming Air passes through a sort of Filter, that being the Radiator & the higher pressure under the Bonnet will most likely prevent any unclean Air being sucked up from the Road in the open gaps under & around the Engine
Just the idea of driving through Tunnels with open Weber's on song aaaaah!
(Men grow older but never grow up!)

So apart from the potentially higher wear problem what power losses should we expect from sucking in Engine bay temperature Air as opposed to ambient temperature Air?

Cheers
John

[quote="D.J.Pelly"]Does anyone have any comparative performance figures for an Elan / +2 running different induction systems?

My Dad's Elan ingested a nut under road conditions - even with the standard filter sytem on... No it wasn't missing from anywhere past the filter! No we haven't investigated further than that!

alaric wrote:Hi. One option is to stick with the downpipe and airbox and fit a K&N filter assembly in the nose. Cliveboy sells this arrangement:

elan-f15/cliveyboy-breather-and-filter-conversion-t17520.html

It has the advantage of not needing modifications to get clearance, and maintains the protection that the airbox provides against fuel leaks and blowback. This is the route that I adopted. The second is to get some K&N air filters to fit directly to the carbs.

The above thread has more discussion on this.

All the best.

Sean.

ps welcome to the forum

I'm with Sean , I have the Cliveyboy set up and its great. His duct material is especially good and doesn't come apart and mis-shape like the original
Welcome!
Terry

My dyno testing shows the original aircleaner and duct has no signficant affect on engine output at least up to 150 hp which is max for a typical 1600 cc road application. The original airbox on the carbs however has a small affect ( 2 to 3 bhp in 150 hp engine) due to the taper on the box restricting air to No4 cylinder a little.

Other tests show that if the original open part next to the radiator where the duct went is - is left open and the duct removed - then the air temp to the carbs without the ducting and airbox remains about the same with it present or not.

If looking for absolute performance a couple of possible mods

1. modifiy the airbox to make it deeper ( TTR sells a modified one)
2. put foam socks on the carbs and remove the airbox / filter system -noisier !!!

Replacing the orginal filter with a K&N up front and retaining the orginal duct and airbox may make service easier and cheaper and look better but it will not affect the engine power as far as I can tell

cheers
Rohan

memnon wrote:

D.J.Pelly wrote:Does anyone have any comparative performance figures for an Elan / +2 running different induction systems?

My Dad's Elan ingested a nut under road conditions - even with the standard filter sytem on... No it wasn't missing from anywhere past the filter! No we haven't investigated further than that!

I once had a new BMW 323i that had a rattle & took it back to complain. They found a bolt in the exhaust pipe..
Even the experts make mistakes.

rgh0 wrote:My dyno testing shows the original aircleaner and duct has no signficant affect on engine output at least up to 150 hp which is max for a typical 1600 cc road application. The original airbox on the carbs however has a small affect ( 2 to 3 bhp in 150 hp engine) due to the taper on the box restricting air to No4 cylinder a little.

Other tests show that if the original open part next to the radiator where the duct went is - is left open and the duct removed - then the air temp to the carbs without the ducting and airbox remains about the same with it present or not.

If looking for absolute performance a couple of possible mods

1. modifiy the airbox to make it deeper ( TTR sells a modified one)
2. put foam socks on the carbs and remove the airbox / filter system -noisier !!!

Replacing the orginal filter with a K&N up front and retaining the orginal duct and airbox may make service easier and cheaper and look better but it will not affect the engine power as far as I can tell

cheers
Rohan

Thanks for that Rohan.

By leaving the opening where the Ducting was next to the Radiator open will cause an air leak & reduce the effectiveness of the radiator theoretically.
Did that show up on your measurements?

My Zetec Elan has the TTR intake system on it but I did have a small problem finding a bit more room for it above the driver's footwell.
The tapering original Airbox & Air starvation on Cyl.4 has been discussed before & I have in my own mind questioned the theory.
I'm surprised that you found such a difference
There is no Ram Air effect due to the Ducting & air Filter but my sort of logic says Cyl.1 takes a part of the delivered volume, Cyl.2 another part & Cyl.3 yet anothr part, subsequently the required cross sectional area of the Airbox could also be reduced proportionally without negative affect?
Just being inquisitive rather tham argumentative

Cheers
John

The airbox is a plenum. For identical airflow, all parts of the plenum should be equal. As Rohan says, there is a small power increase when increasing the depth of cyl 4 plenum.

The size of the plenum is a different question. One article I saw started with a plenum volume of 10X swept volume. There was a small but noticable power increase as the plenum volume increased to 13X or 15X.

Of course, our plenum is not even close to 10X. Enterprising owners of LHD cars could experiment with increased plenum sizes.

David
1968 36/7988

The problem is not the cross sectional area of the box but the proximity of the face of the trumpet to the out cover of the air box face. This restrict the flow into the trumpet itself a little. - nominally you 1.5 diameter above the trumpet to not restrict is flow.

I plug the other 3 radiator corners that lotus leaves open with suitable size blocks of foam rubber and have no cooling problem, when the duct is removed and the space left open in the top rh corner. You certainly will get more air flowing through this gap than originally and that ensures the carbs get cold air. Plugging the other gaps reduces the radiator bypass areeas back to less than it was originally.

cheers
Rohan

rgh0 wrote:The problem is not the cross sectional area of the box but the proximity of the face of the trumpet to the out cover of the air box face. This restrict the flow into the trumpet itself a little. - nominally you 1.5 diameter above the trumpet to not restrict is flow.

I plug the other 3 radiator corners that lotus leaves open with suitable size blocks of foam rubber and have no cooling problem, when the duct is removed and the space left open in the top rh corner. You certainly will get more air flowing through this gap than originally and that ensures the carbs get cold air. Plugging the other gaps reduces the radiator bypass areeas back to less than it was originally.

cheers
Rohan

Thanks,

I forgot about the Air Trumpet protrusion into the Airbox. The Penny's dropped now

Have a good Weekend
John

I'm currently using a pipercross foam box on my S4, and originally had all sides around the radiator blocked off to improve radiator efficiency. I have recently removed the side by the carbs, as Rohan suggests, in order to improve airflow for the carbs and the coil, which was getting hot and causing misfires. To further improve airflow, I'm considering cutting holes in the wheel well and covering with screen similar to the other side. Dan

Does anyone have a phone number for Cliveyboy? I am afraid I am not getting any response to my emails. Thanks

This may be a daft question, but if you are running the +2 with kn?s directly at the carbs either dellortos or webers, you have to remove both the original airbox, and the airbox backplate. This leaves the problem of the return spring, and the breather pipe from the engine block. What do you do?