Cold Air Duct to Engine Fan

We talked about this a few months ago here: www.speedsterowners.com/forum/readmsg.asp?t=1895. Bruce has a 4" cold air duct feeding his fan cool outside air. I am in the process of making this mod. What I am wondering is, where should I run the inlet hose to?

I was going to run it down in front of the rear wheel like Bruce did, but then got to thinking about all the road grunge down there, and am now considering leaving it to draw air from between the firewall and the rear seat. At the speeds we drive there is no 'ram-air' effect to speak of so I don't need to have it exposed under the car for that reason. Having access to a shut off for colder days is needed, but I can use a gate valve with a 6' cable to open/close the inlet. Access to the screen so I can clean it if it gets covered by a leaf or something is valid.

Any other thoughts or ideas?

At first I thought: "Where the hell IS he that it gets that cold to worry about fan inlet temps?" Then I saw your address!

I'm running a pseudo-duct from the fan inlet into the space between the firewall and rear seat (CMC) and it seems to be working ok on my 2110. I now have a thermemoter dip-stick to better tell me what's going on, but it's still a bit chilly to get out there (and the temp gauge would never get off the "cold" peg right now, anyway).

I ran the hell out of it during the hottest part of last Summer and running turnpike speeds (70 - 75 around here) my temp gauge runs just shy of mid-scale and drops to 1/4 scale around town (lots of 3rd gear under 50 MPH, keeping RPM's to around 3K).

I'm pleased with just having a short duct, the size of the fan inlet, from the fan shroud to the firewall cowl.

Gordon

Are you running a screen over the inlet, and if so, what size?

No screen on there yet, but now that you ask I think it might be a darn good idea.

I remember seeing a relatively open scren (similar in look to headlight grills) on some dune buggies a while ago.......it mounted on the fan shroud over the inlet and went on with sheetmetal screws. 'Course, you have to pull the engine to install it, but it's pretty effective and really trick looking.

In my case, I could get something like an 8 inch square piece of 1/4" opening screen and glass it onto the front side of the firewall over the extended inlet opening.

gn

Looks like a easy worthwile modification. Curious from others the best method/tool to use for punching the hole thru the firewall - doesnt look like alot of room to work between it and the body. I would also think the hole w/no piping would work. Any additional engine noise after the process?
Thx

Use a hole saw of the correct size. If you don't want to pull the engine to put the hole in, then pull the alternator and fan and drill through the middle of the shroud.

I like the idea of no hose on the inlet, but that means getting under the car every once in a while to make sure there is nothing blocking the inlet. That's easier if you use a hose that drops down somewhere near the frame/pan, and if you do get a blockage on a long trip and the car starts to heat up, you are going to get very dirty trying to reach up under the car to clear out whatever is blocking the inlet, if you can reach it at all.

So I went with no hose. Just a hole through the firewall, but with a gate valve and screen. I am hoping I can reach the screen if need be, from inside the engine compartment. We'll see once the engine is back in.

Ron,

Are you saying you did not have an air inlet hole in your firewall before? And so this is the first hole in your firewall?

Right, I did not have any air holes in the firewall. Do you?

Ron,

I didn't mean that to be a dumb question, just assumed an air inlet hole in the firewall was a normal part of every build and wanted to make sure I understood what you were describing. If I recall correctly, my CMC build manual instructed cutting a hole in the firewall directly in front of the shroud and the same size opening as the shroud...which is what I did. Apparently this is not standard ops for all builds. I like the gate valve idea, what is the size of the opening and where did you find it?

One mistake that needs to be fixed on my Speedetsr, my external oil cooler is mounted on the shroud in the incoming air. My plan is to move it in between the firewall and the rear seat, add a fan and direct some fresh air to it.

I didn't take it as a dumb question Bruce. None of the IMs have a hole in the firewall, but I didn't know what the other manufacturers were doing. The only air source for an IM, for both the carbs and the fan, is the opening in the engine cover.

The mounting ring and gate valve are RV parts. I got them at the local RV dealer. The screen is plastic screen used to cover gutters to keep leaves out. The hole saw I used was 4", but the smallest diameter is 3". In US$, the mount was $6, the gate valve was $22, and the screen was $4 for about 40 feet of the stuff.

As an aside, I put Henry's newest sound deadening material in the engine compartment. The piece, cut to fit the firewall, weighs about 20 pounds!

Ron, your idea sounds interesting, especially since your motor is out. I've thought of adding a smaller air scoope to my motor grill, to aid in forcing air into the engine compartment. If I'm not mistaken, years ago VW had a clear, plastic scoop over the fresh air intake, just in front of the windshield. I don't know if it would do any good, but I wouldn't mind trying it out.
Ron

Seriously, don't these cars get enough cooling air through the vent/s on the engine lid?

If I recall correctly. my VW Beetle had vents in the engine lid but also a hole in the firewall that was ducted directly to the shroud. That's why I was surprised some Speedsters did not have the opening. I do notice that I will get some dust and an occasional leaf up through this opening and into the engine compartment so an occasional cleaning is in order.

If the opening goes directly into the shroud, wouldn't that exhaust air? The only inlet is in the middle of the fan.

My VS has a hole in the firewall opposite the fan opening.
ed

I plan on placing a NACA duct beneath the side rocker area in front of the rear tires. Then a NACA hose will be route up to the oil cooler and the engine compartment fire wall. I also have a low profile ram air duct that mounts on the belly pan just in front of the trans shifter connection. Fine mesh SS screens will keep the debris out. Future plans are to build aluminum cold boxes around each air cleaner.
Joe

WOW! This tread has been an eye opener!! I just assumed that ALL speedster bodies had a cut-out in the firewall just ahead of the fan inlet as the CMC does. I can understand why Bruce Stumpp was confused.....I was, too!

RE: the early VW bodies, my '57 never had a hole in the firewall for fresh air into the engine compartment. ALL air to the engine came through the louvers above the engine cover - that's why so many people added those spacers to their hood hinges to lift the forward edge of the hood and let in more air, or ran convertible hoods with built in louvers (or both!). I think the Super-Beetles had a grill above the hood as well as another grill across the hood, but not quite sure.

ON CMC bodies, just ahead of the fan inlet is a mini-collar glassed into the firewall (and covered over when delivered) which is meant to guide air from the open area between the rear seat and the firewall into the fan inlet. Page IV-18 in the 1984 CMC manual shows you where to cut out the cover in the fiberglass firewall and then make an apron to enhance the "tunnel" effect toward the fan inlet (see it in the on-line library).

Once this is done, ALL air for cooling is drawn in from the "void" space through that opening. If the rest of the engine compartment is properly sealed, then only the carbs get air through the grill on the engine cover.

I used a Saber-Saw to cut mine out, followed by a rotary rasp in a hand-drill to clean up the hole, but that was done from the engine-side of the firewall w/no engine. If I were to try it from inside the "void" between rear seat and firewall, I would be tempted to try a "roto-saw" (after covering the engine shroud with something to avoid dust). Any way you do it with the engine in there, it's gonna get dusty.

Gordon

Bob, I really don't know...but I'd like to (know more on air flow)).
Ron

Attached is a photo of the opening in the CMC engine compartment.Is this what you are talking about?

Yup, that's the one, only I don't have those BIG holes at the top of my firewall......Isn't that where the hood hinges are supposed to go??

I have a piece of 3/8 thick rubber material (like dense soundproofing material) lining my firewall, and a piece of similar, although stiffer rubber around the little tunnel lip, kind-of like flashing, to extend the tunnel closer to the fan inlet.

That's about it. Works fine, lasts a long time...........

Gordon

Oh, BTW: Noticed your ducting in the other picture.......thought about it but decided to try what I explained above without the ducting and see how it worked (because the ducting was a pita to install). So far it has been working OK without the ducting.........

gn

Gordon,

Interesting discussion, helps me understand a couple of previous threads. Some of the past confusion for me was the about how/where to mount a remote cooler. Mine is currently mounted on the shroud between it and the firewall and I plan to move it and add a fan. Refresh my memory, how did you handle your remote cooler?

Gordon,
The hole at the top are for the mounts for the rear deck hinges. I removed the two pieces of wood that were between the firewall and back seat. I also have an internal crash/roll bar that is mounted behind the firewall. I have brackets mounted to the crash bar for the remote oil cooler. One on the NACA duct system is dedicated for the remote oil cooling system. I have fabricated aluminum sheet metal panels that will line the engine compartment which will cover the holes that you see in the picture.It's been a slow going profect. I had to install a electric motor on my sheet metal bead roller to make it a one man process. I'll have some pictures of the belly ram air system later.

Joe S

Easiest insatllation of a remote oil cooler uses a MOCAL thermostat adapter that fits between the oil filter adapter and the oil filter. Art Thraen sells them; he also sells Setrab oil coolers. He's at acevw@aol.com.

Shoot....I don't even have ROOM in my garage/shop to keep a sheet metal bead roller!!

Bruce: Been thinking about a remote oil cooler, but that's as far as I've gotten (although I have a 9-pass DeVale in the shop). I want to keep the stock cooling I have on there and see what the temps really are first (just got a dip-stick temp gauge) and then make my decision. I may have two problems to overcome:

(1.) I have a Melling high volume oil pump that looks much deeper than any others I've seen, so much so that the cover is almost touching the crank pulley (In fact, I had to grind off the tops of the mounting bolts a bit for pulley clearance), so forget about using a top-of-the-pump take-off for cooling or filter lines unless I go to a different pump (yes, that means I'm not running an external filter).

(2.) is getting enough air flow through the remote cooler and for that I've decided that a front mounted cooler, at an angle between the front bumper mounts with some sort of shallow, under-nose scoop is in order. Then I would have to run oil lines through the central tunnel with an in-line thermostat (already have one of those, too). This is all speculation and, if my running temps with stock cooling and fresh air to the fan from the void in front of the firewall are reasonable, then I'll leave it at that and not do a remote cooler.

Gordon

I'd be interested in the before and after effects of this mod to be sure it's working. Seems like a good idea, what do the original 356 guys do?

Also in my experiance the Kendal 20-50 oil cools better than the Mobile one 10-30 by about ten deg. This might be due to the viscosity though.

I also had the idea for using boat hull fans (two thermo controlled units) to drive air into the engine bay towards the fan.
Just an idea.


J-P

A screened hole in the firewall with or without ducting is quite common with the VW performance crowd. Probably a good idea on any car putting out over 100 BHP - the standard vent worked fine for up through Porsche Super 90's and early Carreras (about 100 BHP) but note that later Carreras had the louvered rear decklids and relieved deck lid rainguard "humps".

Definitely a good idea if your engine makes over 100 BHP and you drive in ambient temperatures above 80 F.

George: Do you know if the 356 performance and racing crowd ever opened up a hole through the firewall as we're talking about?

Or was the louvered deck lid considered to be enough?