Ducted/vented hoods, any DIY?

[Clifton]

I found that front mount radiators don't work with the stock outlet and need to vent it out the top. First time I have driven it near 90 degree temps and cruising got a little warm, Without the hood on I can beat on it and it will not budge over t stat opening temp.

 I know Banks sells one and the one Foose did looks real good. Anyone else with a front mount radiator do their own that opens it up that much? I thought about using abs sheet as a form and fiberglass it on the back then remove the sheet but the hood has a left to right radius and will make that hard to do. I also hate to chop up a good hood.

[JR73]

Can give you some dimensions off the Banks one if you want?

You could always make the lower part as a separate piece that the bonnet sits onto (with the corresponding bit cut out of course!) - works Esprit V8 racer had something like that at one point.

[Clifton]

I appreciate the offer. Could you measure the opening inside I'll post a pic of Mecky's, it looks to be about 6 or 7" top to bottom?  There is a guy on the Superlite SL-C board that hired and ex F1 areo guy. Supposedly the outlet should be 14% greater than the inlet. He did a bunch of modeling.

I have the hood off and the opening marked to what will work. I'm just hesitant on cutting that hole on a newly painted hood. It would be easier to build an aluminum duct and just have a hole in the hood. Some kind of grill on it would look ok but not great. I may call Banks and see what shipping is.

How was the fit on your hood?

[JR73]

The pics I have to hand atm (not near the car until maybe tomorrow) are the ones I took for Mecky on his thread in Paddock, the tape across the radiator core should give you an idea of the approximate dimensions at the bottom of the duct as it sits against my radiator.
Which measurement do you want?! - height of the duct from the face of the bonnet down to the bottom of the duct? If it’s that one then worth bearing in mind that the bonnet comes untrimmed and the duct would be slightly longer than mine is now and the position of your rad could alter this.

Apart from trimming the bottom of the duct to fit against the rad there was very little, if any, fitting required. - shell had never had any repairs.

[Clifton]

Did you remove the hinge pivot holes or do they not come with them? I could only find one ducted hood on Banks site for the 62. I assume it's the only one. I'm curious on what these measurements are.

[JR73]

Mine doesn’t pivot like the original, two forward facing pins fixed on the front edge of the bonnet locate through two holes in the vertical lip and there are two dzus fasteners on the rear corners - can see the two simple holes in the 3rd pic, undo the dzus 1/4 turns and lift out. You might be able to pivot like the original but it depends on clearance to the duct...

https://www.lotus-supplies.com/parts/bodywork/panels-bodywork/bonnet-ducted-isophthalic-47r-62s/
That’s the bonnet.

Will get the measurements ASAP, not near the car atm.

[JR73]

Measurements on pics, hopefully they make enough sense.

The duct starts slightly ahead of the front edge of the bonnet, I think the intention is not only to allow for trimming to fit each application but also to give the option of it hooking under the shell at the front of the bonnet aperture if needed.

The front to rear arrow that you drew is a little awkward to measure, the duct shape ends 18” back from the leading edge as shown. It is not a simple ‘letter box’ type cut out from the face of the original bonnet, the side view shows the shape of the duct.

[Clifton]

Thanks for the measurements. I have tape all over my hood and taped up the hood opening. I came up with close to what you have. I have not called Banks yet. I think I'm going to cut mine up.

[RonPNW]

A question to those who have driven a ducted Lotus.
Did it help with front end stability. My 70 S2 (with a low nose) would always get twitchy at highway speeds All the indications where that there was a bit of lift in the front. This also made winding mountain roads more exciting than they needed to be.
So, did having a duct help?
I would also expect that the duct would reduce air drag and allow a slightly higher top speed and higher high speed acceleration.
I have an 807 engine with an oil cooler and electric water pump. I've never had any cooling issues. OK, I did shoot myself in the foot a few times but once properly configured and serviced the stock radiator and location seemed to work fine. Additional road stability would be nice.

Thanx

[JR73]

I think it has been reported often enough (starting from original press reports) that the S1 and S2 tended to experience a bit of front end lift at higher speeds, I think that is why the TC’s had the front spoiler added.

There where also a number of companies that offered aftermarket front spoilers along with their other tuning items when the cars where still in production to combat this.

It’s quite some time since I’ve driven anything back to back but I do remember that there was a noticeable difference between a car fitted with a front spoiler vs one without at motorway speeds. The ducted bonnet cars that I have driven (other than my own that has always had the Banks front spoiler along with the ducted bonnet) where exclusively Banks chassis cars that had at least the TC spoiler fitted and they sit and ride quite differently to the originals anyway. - I can’t remember encountering an original car with a revised radiator and a ducted bonnet without a front spoiler.

I did have wind tunnel data that quantified some different front spoiler designs, ducted front bonnet and revised radiator placement, floor and diffusers and even rear wings but unfortunately I can’t find it and my memory isn’t good enough to remember all of the figures to accurately list them here to be useful.

A long winded way around but I think you might notice a difference in the front end lift that you have encountered if you considered a front spoiler first.

[Kendo]

Richard (Hill?) had built and described a splitter that he said worked better than the spoiler. Of course it isn't stock.

[Kendo]

Since I couldn't figure out how to attach two items at once...

[Clifton]

Ducting out the top is for front mount radiators. Isn't going to help much for down force.  The fronts are just very light. It doesn't take much wheel movement to get a result. When I first got mine on the road driving at 70 mph was two hands with fear and no chance of going faster than 75 mph. I re aligned and all is good. I have stupid power (400hp+) and have been over 100 way too many times to remember as it's a quick blip in third. My car is dead stable with one hand and cruising at 90 on the freeway is nothing. I haven't been over 130 but it was stable up to that too. I drove without the hood to check temps. Didn't make any difference in feel, just ran cooler. If yours is darty at speed, it's too much or too little front toe and not enough rear toe. Maybe high tire psi? I used what the Elise's use and it's perfect. They run more caster than you can easily get on a Europa. You can get more caster though. Europa's spec front toe in is way too much IMO. Close to zero or just under feels much better.

[BDA]

... You can get more caster though. Europa's spec front toe in is way too much IMO. Close to zero or just under feels much better.

I'm curious how you got more caster. I have one side that does not have enough and I haven't been able to make much of a difference by adding washers (I almost positive I added them behind the lower shock mount - between the A-arm and shock - and behind the lower A-arm at the pivot - between the frame and A-arm - but sadly, I'm too lazy to check that right now! Sorry.)

I'm surprised you suggest less front toe in for stability. Within reason or specs, I've always thought that stability was enhanced with greater toe in. Can you help explain?

[jbcollier]

With the stock set-up, castor (and camber) are not adjustable.  Camber you can adjust by fitting adjustable upper arms.  Castor is more complicated because the trunnion is fixed in one plane by its screw thread.  Trying to “shim” it sideways will just adversely load the trunnion causing it to wear (more) quickly.  You would have to replace the trunnion with a spherical joint as they did with later Caterhams.

Before going that way, 99.9% of the time, if the castor or camber are off at the front, something is bent.  Both the stock upright and stock a-arms are designed to fold first to help protect the chassis.  I first made adjustable arms before I realized that my fine-looking uprights were bent.  Fit new uprights and stock arms, and everything was back in spec.