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Learning how to build Lotus Seven replicas...together!
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 Post subject: Re: Exo Hot Rod
PostPosted: May 15, 2019, 11:42 pm 
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I've now got the runstand integrated into the chassis, in a super-temporary hack-job sort of way, so that I can soon run the engine again. I'd like to do that partly because it's good for the engine and partly because it's good for my psyche.

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Yes, the radiator's in the front, and no, it's not permanent. I actually did a purposefully shoddy job of mounting it so that I wouldn't be tempted to run it that way later. I just used scraps bolted to the bumper and hood ornament mounts to hold it in place for now. It actually doesn't look bad up there, but I need it in back for balance. The suburban expansion reservoir, which I'm not going to use, is also just ziptied in place, just like the gauge/switch panel mount. It's all temporary for while I'm finishing the steel fab work. The real stuff will, hopefully, come in a few months.

The fuel system is also ready to go, I just need to plug the hose into the tank. I'm waiting to get a few tabs welded in first, since the temporary hose routing ends up nearer those spots than makes me comfortable with 10k degrees of plasma going on. So I'll get those floor panel tabs and a few others done then finish setting things up.

I've got some other updates, but I'm too tired tonight. So stay tuned, I guess.

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 Post subject: Re: Exo Hot Rod
PostPosted: May 16, 2019, 9:36 am 
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Unless airflow around the car has been modeled, keep the option open for keeping the radiator up front. Moving it aft will improve balance, but at least check by how much via spreadsheet. I once calculated that moving my fuel cell from the rear to the front only changed balance by something like 0.4%. Moving the radiator aft cleans up the front, but of course necessitates running coolant lines the length of the car, increasing weight and being a bother in the passenger compartment.

Most important is getting sufficient airflow to it. Unless you plan an above-windscreen duct to feed it, it's a bit of an unknown. I ran into this when my side-mounted intercooler proved ineffective, solved by moving to an overhead duct. Side ducts can be a real mixed bag because of the turbulent air coming off the front wheels and suspension. Of course, having an electric fan on it means it can be made to work just about anywhere, but may have to run continuously.

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 Post subject: Re: Exo Hot Rod
PostPosted: May 17, 2019, 6:01 pm 
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Thanks, Kurt, for your words of experience. You are, of course, correct. I have no idea if a rear-mounted radiator will actually work here. Here are the reasons, justifications, and a few tidbits about how and why I'm going to at least try it:

I did the math for front vs. rear radiator awhile back, and it was a larger shift than I would have thought. A coolant-filled, V8-sized radiator with sufficient fan probably weighs 50 pounds (I'm still speculating on that), and that's a lot of weight which could potentially be taken off the frontmost part of a sub-2000 pound vehicle. Could be 2.5% of the curb weight.

Without putting the radiator in the back, I'll probably end up with a nose-heavy car. Maybe only by a percent or two, but still nose-heavy. The engine in the front is about 200 pounds heavier than the transmission and differential in the back, so even though the frame is 50 pounds heavier in the back I still need to make up 150 pounds. The only other heavy stuff is the battery, the fuel tank/load, and the radiator. Seats are not that heavy, and are only slightly rear of the car's center. One of my goals with this build was to have an autocross/track day car that could be under 2000 pounds in race trim while still not being front heavy. I knew it was going to require some special planning, additional complications, and some compromises because it's hard to do with this platform.

My aesthetic design/initial concept for this car, from the first draft, includes an extremely short front overhang. In fact, it might not even be called an overhang. Aesthetically, the radiator is better not in the front.

I've left room to plumb the coolant under the car. So it won't go through the passenger compartment.

I plan to try drawing air from under the car through the radiator, not from the side or top. I have no idea if this will work, and I won't find out until I can actually test it.

I'm okay with a continuously running fan, if that's what it takes.

So, that's what I'm thinking, more or less. It may change, and I'm certainly not going to do anything that will preclude me from putting a radiator in the front (I'm not putting anything else there).

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 Post subject: Re: Exo Hot Rod
PostPosted: May 18, 2019, 6:39 am 
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Omaha Vette Graveyard wrote:
A coolant-filled, V8-sized radiator with sufficient fan probably weighs 50 pounds (I'm still speculating on that), [SNIP] I'm okay with a continuously running fan, if that's what it takes.
Yo, Graveyard-Dude! A gallon of water weighs 8.3 pounds. I'm not sure about the 50 lbs total weight, but all that "stuff" would weigh something, for sure.

My car has the radiator in the front, leaning forward a good bit. In it's first life, the (electric) fan was on the front side, mounted directly on the radiator, blowing air thru the rad. It worked OK... Moved some air... Can't say overheating was a problem, but the temp got pretty warm when I ran the car a few times around a track.

At some point, I decided to move the fan to the back (outlet) side of the radiator and enclose it in a "box" type fan shroud. It is amazing how much more air it moves that way. I think the shroud enclosure is a lot of it and it just seems to work better pulling air through the rad than it did pushing it. Don't know why, but it does. Temps now seem to stay under 200 even when I run it hard thru an autocross course on a warm day. Much more better-er! :mrgreen:

The fan has a manual switch on the dash. I don't turn it on when I'm warming up the engine. When the car is staged the first time, about to get the green light, I turn it on. After that, it goes on every time I start the car. Can't hear it over those damn loud pipes anyway! :mrgreen:

And that's the nickle tour on the cooling fan placement on the Slotus. Iffen you already knew all that stuff, sorry to preach to the choir. If not, I hope it helps!

Enjoying your build in general, can't wait to see that beastie on the track somewhere soon!
:cheers:
JDK

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Quinn the Slotus:Ford 302 Powered, Mallock-Inspired, Tube Frame, Hillclimb Special
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 Post subject: Re: Exo Hot Rod
PostPosted: May 18, 2019, 1:40 pm 
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Hey JD,

Thanks for the fact check. My estimate of 50 pounds is probably a little high.

-A big aluminum radiator, maybe 19" x 32" x 3", seems to weigh anywhere from 15 to maybe 20 pounds dry. (I wish the weights were published more frequently.) Let's say 18 pounds on this.

-If that radiator holds lots of coolant, say, with large tanks and two rows of core, how much does it hold? A gallon? That seems high, but I've never measured one, and I've never seen the capacity of the radiator itself published. Let's say it's a big one, and holds a gallon, so that's another 8.3 pounds.

-A larger radiator fan generally weighs 5-8 pounds (the motor is heavy), and I'm planning on having 2, so let's say another 12 pounds for fans.

-An aluminum shroud will weigh very little, so I won't even include that.

-The mounting brackets and hardware could be made very solid with 5 pounds worth of steel in the front, maybe a little less in the back since the mounting points are more abundant and nearer to the radiator's corners. So, let's say 3.5 pounds for that stuff.

-I suppose one could count the weight of the hoses (plus fluid inside) as well, but you could really only count half of those or maybe a third. I'm figuring it's negligible. Same with the radiator cap and any sensors/switches or wiring.

Adding it up:

18 for the radiator
8.3 for the coolant
12 for the fans
3.5 for the mounting stuff

= 41.8 pounds. Well, that's better than 50, but still more than 2% of the vehicle's curb weight.

Maybe that's still high. I could imagine being delighted in the future when I find a setup that works well and weighs only 32 pounds. Maybe a well-shrouded single fan, and the radiator only holds 1/2 a gallon of coolant.

Even at a super-light 30 pounds (which seems unlikely), I think it might be worth trying to take that weight off the most weight-sensitive part of the car and put it where it will help. It's like a much more complicated and problematic version of moving the battery to the trunk.

That's enough math for one day. Time for some grinding!

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 Post subject: Re: Exo Hot Rod
PostPosted: May 20, 2019, 12:13 pm 
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I'll question if you've done the homework on picking up cooling air from below. Typically that is a low pressure area. Depending on your aero at the air exit area, you could be having reverse airflow thru a rear mounted radiator. Or worse, it could flip flop at different speeds. You need a differential in air pressures in order to get air flow. Usually with the rad at the front, that is done with forward movement of the vehicle. IF the rad is at the rear AND the air is reverse of what you expect, the fans will be very inefficient.

Then consider that the air under the car, next to the asphalt and downstream of the heat from the engine and exhaust may be quite a bit warmer than outside air thus reducing the cooling capability that much more.

My 2nd point is related to overall weight. Assuming a 1-1/2 inch dia coolant pipes feeding the engine at 100 inches long x 2 would add ~20# of coolant ignoring the weight of the tube itself. If you are good with that, then ignore this part.

I'll keep watching. :cheers:

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 Post subject: Re: Exo Hot Rod
PostPosted: May 20, 2019, 12:55 pm 
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Hey Chuck,

I've done some homework on the low-pressure/high-pressure stuff, but I decided there was no way to know until I test it. Usually, it's lower pressure under the car, but this car is so aerodynamically idiosyncratic that I have no idea of that will be true on this car. Exo cars are an aerodynamic mess. Testing will be required.

The exhaust is going to be completely out of the way of the incoming air, as I'm planning side pipes.

The run from the proposed radiator position to the engine will add 65-70 inches of coolant piping (each way), and it will probably be 1.25" aluminum rather than 1.5". I only say that because that's the size I've seen on the mid-engine cars pluming the exact same thing in reverse (engine in back, radiator in front). That said, yes, I do expect 10-20 pounds of added weight due to this particular complication. I have a kind of pipe dream that I can make up some of that weight with a smaller radiator because the aluminum coolant tubing will be exposed to the air under the car, providing some additional cooling, and the wind from the front will be blowing unrestricted across the aluminum block engine. Is this possible? I have no idea.

Thanks for reading, I've got a few updates coming when I get some pictures.

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 Post subject: Re: Exo Hot Rod
PostPosted: June 8, 2019, 7:12 pm 
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My work has slowed down in the last month, partly because of a nagging tendon issue in my elbow that came from scooping after a really heavy snowfall, and partly because I had my dad's Corvair in my garage for a couple of weeks and I decided to replace his rusted-out section of the floor with some fresh steel. I will say that tig butt welding 22 ga. steel took some figuring out, but I had it sorted by the end. Not my prettiest work, but it's under the carpet so whatever.

I have the beginnings of a tunnel now, so I thought I'd post some of the pictures. These won't bring it up to date, but I haven't yet taken pictures of the newer stuff. Hopefully I'll get to that over the weekend while I continue letting my arm heal.

This first piece is what I consider the most important bit of the tunnel, because it is my most solid connection between the left and right sides of the floor, and it is the point where it will link to the cowl, and will be the lifting point for taking the frame off the drivetrain. I probably over-built it.
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I'll also throw in this picture of my 'hood clearance'. I'm not really a big fan of this type of filter, but it will do until I get to making something custom. It is extremely light. As you can see, I could make a triangular 'hood' with a fairly modest bulge and clear everything. I don't know if I'll decide to do that down the road, but it was one of those design elements I considered from the beginning. I think it could really complete the look of the front if I do it just right. I guess I'll have lots of time to think about it.

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More pictures of the tunnel to come.

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 Post subject: Re: Exo Hot Rod
PostPosted: June 10, 2019, 12:29 pm 
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A couple updates and the revelation of a aesthetic problem today.

First, some current pictures of my tunnel.

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Now, with the proposed location of my parking brake:

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As you can see, the in the central and rear portions is to to allow space for the shifter and the parking brake lever. More structure is needed, but first I need to figure out a little better exactly how I want to mount the parking brake, and how I want to route the cable. Mostly what complicates this is the need to panel the tunnel. I think I need to panel it anyway, though I'm reconsidering. It sure would be handy, and kind of cool looking, to keep that central portion between the two bridges open--keeping with the exo aesthetic.

I also tacked in the floor mounting tabs on the passenger side. Not much to it, though I'll likely want additional tabs for the underfoot panels. The plan is to use .100" aluminum sheet. I'm still pretty unsure about this whole method of paneling. I probably need to make at least some of the panels before I paint the frame.

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Since the floors, firewalls, and the side panels will all be mounted via tabs like these, lots of tabs are still to be make. Something like another 80. It's daunting, but I'm able to knock them out pretty quickly when I get into it. I just need my arm to heal so I can get back to work.

The other thing I'm thinking about a lot while unable to work, is the current look of the car from the back. It's funky.

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I knew it would look kind of tall and narrow, but I didn't expect it to look so bottom heavy. Part of the problem is that it's sitting 3/4" lower than I want right now (Stock bolts are 6", I picked up some 8", it needs 7"), but even when I get it back up the look isn't going to be right. I've been toying with different ideas of ways to address it. My first thought was painting the rear subframe flat black, but I'm not sure that will be enough. I can probably also change the shape and visual weight with the rear bumper and lights. I'm just not sure how to do it.

Lots to think about, for now, and then lots to do.

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