Lotus Elan

New Deep Carb Airbox

PostPost by: William2 » Sun Sep 10, 2017 3:40 pm

I have just fitted a new deeper airbox which was made for me by a gentleman up in Yorkshire called Dave Milner. This is a brand new version he has produced specifically to fit S4 and Sprint Elans with Weber or Dellorto carbs and 3 bolt mounting. I would just like to comment that the box is extremely well made and the grp is a nice thick layup with bonded in mounting washers. Mine has a satin black gel coat but matt black is also possible. It fits perfectly without any fettling necessary. I believe that they can add an extra 2/3 bhp to the engine and make a possible small reduction in induction noise.
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PostPost by: gherlt » Sun Sep 10, 2017 6:27 pm

Looks nice ! May I ask about the price ?
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PostPost by: Mazzini » Sun Sep 10, 2017 9:19 pm

And his contact details? Many thanks.
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PostPost by: William2 » Mon Sep 11, 2017 12:04 pm

You can email Dave at [email protected] and the cost is ?75 + postage.
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PostPost by: Mazzini » Mon Sep 11, 2017 1:18 pm

Thanks.
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PostPost by: 7skypilot » Mon Sep 11, 2017 4:27 pm

I fitted the same airbox to my S4 about a year ago. It is superb in every way, and much better finished than the original!
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PostPost by: Davidb » Tue Sep 12, 2017 5:18 pm

I too bought an airbox from Dave and I am impressed with the quality of it. However, the backplate that I bought for it, here in Vancouver, is obviously wrong-it is several inches longer than the airbox. Is this a Federal S4 airbox back plate/filter? :
p1070427.jpg and
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PostPost by: pharriso » Tue Sep 12, 2017 5:41 pm

Davidb wrote:Is this a Federal S4 airbox back plate/filter? :
The attachment P1070427.JPG is no longer available


Looks homemade... Here's the Weber backing plate you're after

airboxseal_vincehayden_ebay_022015_2.jpg and


airboxseal_vincehayden_ebay_022015_3.jpg and


Federal S4s & Sprints had Strombergs & a totally different airbox.
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PostPost by: Davidb » Tue Sep 12, 2017 8:17 pm

Definately not home made! Very good welding plus spot welding-fits over the Webers on the Elan perfectly. 16.25" long, 5.25 high and the filter arrangement is a snug fit.I bead blasted and painted it in anticipation of using it on my car.
p1070430.jpg and
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PostPost by: 1owner69Elan » Wed Sep 13, 2017 5:56 am

If you are in need of an S4 / Sprint Weber backplate I have a brand new one, never used.

Changing from a Stromberg to a Weber head I was going to use the backplate with the stock S4 / Sprint Weber airbox (which I also have and never used) but when I found out it robbed 7 hp on the dyno, I had a deep custom airbox and plate made. The fabricator didn't use the the stock backplate.

Looks like these deep air boxes that are being made by Dave Milner will do the the trick. Apparently, you just need the stock S4 Weber backplate.

PM me if you are interested in the backplate. I'm in California.
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PostPost by: Grizzly » Wed Sep 13, 2017 10:59 am

1owner69Elan, When you say the stock airbox robs 7hp is that running no filters (open) or with a different air box fitted?

I ask because we only saw 3hp difference between no air box / Filter fitted and with the stock air box / Paper filter fitted in the stock can (on the UK spec twin weber set up) also with stock jets we didn't see any leaning/riching out at high rpm on the back cylinder (i welded 02 sensors into each runner of my old stainless manifold) we put the hp difference down to Filter v's no filter, might be a more pronounced difference if it was tuned but my car is stock and we didn't exactly bounce it off the redline either.
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PostPost by: 1owner69Elan » Thu Sep 14, 2017 4:30 am

We measured 7 hp difference with the stock air box vs no air box.

When we had the air box on, we tried with and without a K&N filter on the end of the trunking. There was no difference noted - the filter had no effect.

Conclusion was that the narrow air box itself was the cause of the 7 hp drop. Solution was to fabricate a deep air box based upon one being used on a 26r. This new air box uses a custom backplate as well.

We did not go back with the new deeper air box and run further dyno tests. The air box is about as big as you can get into the space. (It was a real trick to get it installed with the engine and carbs in place. Sort of 3D puzzle. Had to position it just right and feed it into the space.)

So, no definitive test with the deep air box, but the thought is better to feed colder air than with no air box for a denser charge.

I should further note that the 7 hp drop was evidenced on a high spec motor (181 hp, 143 lb-ft), 1700 cc. A street motor nonetheless with an imposed 7K redline. The 26r from which the air box was copied has 45 dcoe's (not sure of choke size). I have 40 dcoe's and 32mm chokes.
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PostPost by: Grizzly » Thu Sep 14, 2017 9:29 am

Ahh ok and the 7hp was at peak (7K) i take it? you might have just simply been pulling more volume of air. We only ran ours upto 6250 and the 3hp was almost all the way across the range and all four cylinders afr moved slightly which made us think it was air filter (Stock air box can and paper filter, stock ram pipes too) there was some debate if we could get some back adjusting the jets a little better but i was getting charged by the hour :)

I have to go back to the dyno at some point to have the car fine tuned so i'll have a better look, i'd also be interested to see if K&N directly on the carbs would improve or hinder the power? I have seen a number of tests that would suggest a Cold air intake can make as much as 5kw (6hp) peak on a NA car (with the bonnet shut and EFI so afr might be more acurate)
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PostPost by: William2 » Thu Sep 14, 2017 3:39 pm

I am sure that drawing in cool air via the filter is better than warm air through K & N filters bolted directly onto carbs. Also the enclosed air box gives more protection against fire hazards. All in all, 2/3HP power increase on a stock motor using the deeper box all seems quite plausible. I have heard some people drill holes in the side of the metal air filter box to slightly aid air flow.
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PostPost by: prezoom » Thu Sep 14, 2017 4:20 pm

While near impossible to check on a chassis dyno, I found that ram air through a filter, direct to the carburetor was a significant power increase. This was on a 1200cc Nissan A series engine, equipped with a 40 DCNF, using 26mm chokes on a ported standard intake manifold. A 6 inch hose from a headlight opening, to a good sized box, sealed to the top of the carb was configured. We tested with this set up at Willow Springs from turn 9 to the turn 1, down the front straight. When the hose was removed, and the hot air from the engine compartment was the only source, it resulted in a 600 rpm drop at the end of the straight verses the cooler ram air through the headlight opening. The engine compartment was sealed, and the only air that passed into the compartment was through the radiator, or the hose direct to the carb. Oil temperature was controlled with a water to oil Setrab heat exchanger, no cooling air required. The test also included sealing the opening through the headlight opening when the hose was removed.
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