Carb Air box bolts

[Steve G]

Maybe the hotter engine area air messes with the mix?

Definitely not in my opinion, a lot of poppycock out there with regards to 'heat soaking'. All the boy racer forums pleb on about it because they seem to like fabricating two miles of cold air hosing and having intakes in place of one of their headlights or an intake sticking out four inches from their radiator grille. Maybe a Vectra V6 engined Corsa needs it but with the Elan it is certainly not an issue. When I bought my car it had air horn socks and the airbox removed so I looked into what possible detrimental effects this might have (apart from the higher risk of engine fire) and found this very useful research done by an Elan enthusiast (Steve WW);

The standard air filter set up on the Elan is pretty poor and that is being polite. You have a couple of options to improve matters: you can replace the air filter housing with a universal type performance filter; you can replace the whole airbox, pipe and filter with a back plate and performance filter bolted directly to the carburetors. Performance filters from K&N, Pipercross etc. are all suitable. There is some debate over which is the best solution. Some say that filters mounted directly on the carburetors will draw hot air in from the engine bay and lose power (The colder the air, the denser the charge, the more power produced) and that having a pipe feed cold air from the front is better. I decided to test if there was any truth in this. I fixed a thermometer probe inside the air box and one on the front grill to measure ambient temperature. The air filter arrangement was then swapped over to a directly mounted air filter with the probe in a similar position inside the filter. Readings were taken at a steady 50mph, the difference in temperature between ambient and inside the airbox or filter were identical.

Here's the link;

http://www.steveww.org/lotus/page80.html

Of course it is just someone's personal findings. Some owners will find the idea of removing the original, factory fitted, airbox completely abhorrent, or may disagree with this finding completely. I know that removing the lid of the airbox from my Integra Type-R definitely affected engine power but then it was a very finely balanced system with a fairly restricted route to the airbox from the grille, the Elan engine bay is relatively vacuous.

[StoatWithToast]

Hmmm, very interesting.

I thought the setup was quite antiquated, but then it is a 50 year old design. I think the carbs definitely need more air than they are currently getting, but given my wife's desire to keep the car looking right (i.e. original) I may have a fight on my hands and will end up compromising with a cone filter in front of the rad; I have seen pics of another owner using a cone K&N filter on the ducting in the grill mouth space. And given that I've just bought a new airbox, ducting and filter housing I think this is probably the best way to feel like I'm not wasting cash.

On the other hand, given how messy that space is in front of the rad on my Elan, I was thinking that getting a long K&N or foam ITG filter over the carbs would be an idea, but was worried about the heat (I run a similar setup on the DCOE45 on the XI, but that has a much more open engine bay than the Elan has). That would also (hopefully) solve the rattling free bolt problem Keep the new air bits for shows and selling it - if the buyer cares about the look of it.

[Gray]

Hi

Personally I think the Cliveboy cone filter connected to the original airbox is the best option, looking original in the engine bay and having a cold air source, but with a less restrictive filter.

I think the threads on the bolts holding the fibreglass air box to the backplate have UNF, not UNC threads. It will pay to check first before trying to screw them in.

Gray

[Galwaylotus]

I think the threads on the bolts holding the fibreglass air box to the backplate have UNF, not UNC threads. It will pay to check first before trying to screw them in.

I think you're right. I've just locked up the Lotus for the night but if you want me to check mine tomorrow I can post the results. Just ask!

[StoatWithToast]

Well, like a lot of the car, looks like mine have been re-tapped to M6 - which is actually lucky as I had enough of those to replace the missing ones.

I think I am going to get a length of M6 threaded dowl, cut it to length, lock-tight the studs into the back plate and then use a fibre washer, a regular washer and 2 nuts on each one to hold the air box in place. Make it a bugger to get on and off, but hopefully not impossible.

My wife drove it Saturday (I was a little worse for wear after celbrating quitting work on Friday) and she complained about the way it was driving with the bolts missing. After a bit of tape over the holes and a bit more trying to keep the airbox in place she could tell it was a lot better... weird!

Still - we need to sort out the fuel line to to carbs (remove mechanical pump from line, replace hydraulic pipe with fuel pipe ( ) stick a filter & regulator) and re-fit the carbs to the manifold and those two jobs may make the car drive a lot better.