Engine Compartment Air Intake (Manometer test)

Nice report, Bruce. Any chance you could stick the business end of that manometer thru the blocked off six inch hole and take a reading at various speeds of the cavity between the firewall and the rear of the back seat above the transmission ?

I have my heater ( water cooled engine ) mounted in there and there appears to be a fair bit of pressure in that cavity since even with the heater fan turned off, I still get plenty of heat forced thru the heater and into the cabin.

Thanks...David Stroud

That's a great tech tip, Bruce! You did an awesome job putting your car together! 

Great info Bruce! At what speed was the 8 mile test driven at? And how many sq. in. is/are the opening(s) in the engine lid for air intake? I ask that because mine (an older Intermeccanica) has 2 slots in the inner panel of the engine lid- 1 on each side below the grille, and I don't think they add up to more than 12 sq. in. of air intake into the engine compartment. For comparison, the air intake grilles below the rear window in a beetle provide about 60 sq. in. (figure given by someone on the Samba) of air intake and about 30 sq. in. for the factory louvered engine lid. This was deemed adequate by the factory for a single carbed 1600. And a 2180 that revs to 6500 with 48's will need the engine lid propped open when run hard...

And I'm convinced that these cars are definitely not built the same! You have your data, which is great, and then there was Wildbill's pool noodle experiment where he found that even when toodling around at low speeds at the beach, a pool noodle holding the engine lid open dropped oil temps noticeably. I'm not disputing your findings; I'm just pointing out that at least some of these cars need more air intake.

I think some cars can use the firewall hole to take advantage of the under the car higher pressure zone at speed, and not just for feeding the fan and carbs. You know how in some cars the shroud and dipstick get almost too hot to touch? If we could create more airflow through the engine compartment we could cool down all those heat-soaked metal surfaces. The fan and carbs would both be drawing denser, cooler air; the engine would make more hp at operating temps and the cooling system would be more efficient, starting with air that was as much as 40 or even 50' cooler.

Look at the size of the tube feeding air to the firewall of the vintage Speedster race car below; there's no way that engine is using all that air for the fan and carbs. I think they're also removing excess heat with airflow through the engine compartment. In our Speedsters, we just have to figure how to get air out of the engine compartment as well.

Bruce, on my 2013 VS, the side panels of the engine compartment don't extend all the way back. They stop about eight inches short at the back (near the taillights), leaving sizable openings into the wheel wells.

Did yours have these and did you seal them off, too?

There's also an intentional gap at the front of the engine compartment, over the tranny, but well forward of the heads and headers.

I'm assuming VS purposely left all three of these openings to help airflow through the compartment.

I'm doubting the usefulness of the hole through the firewall IF an external oil cooler is installed in the compartment ahead of the engine compartment. The oil cooler heat has nowhere to go and that space gets very hot. My hunch is VS started making those firewall holes for engines without external oil coolers but now just installs them on all of their builds.

One thing I tried was installing a fan in front of the hole (in the oil cooler compartment) to force more air from there into the engine compartment. Because of the heat from the oil cooler, the engine actually runs hotter when I turn that extra fan on.

I'm now thinking of moving the oil cooler from where it is into the driver's side rear wheel well.

I forgot to mention that my temp gauges are Dakota Digital. I checked their accuracy against a gauge I know to be right on the money for accuracy. They are within 5 F degrees plus to minus depending on going up or down in temp.

David...It would be very easy to attach the tube to that area thru the 6" hole. It would give you an indication of whether there is negative or positive pressure in that area. It's a good idea and easy to do so at some point I think I will check it. I have read on here that there is suspicion of atmospheric changes going on at different road speeds in this area.

Al....The 8 mile was at 68mph (I forgot to mention that) I didn't go over that because I'm still in "break-in stage" at this time. Later I will go up to...100?

I haven't measured the square inch area. My thinking was that if I saw negative pressure readings then I would have a base from which to start. Then incrementally start opening up these areas after taking the measurements. I think your comment about "heat soaking" is interesting and have made a note to keep that in mind for future investigation and a possible way to reduce it. Getting cooler denser air in there would be a plus. Too much though, could cause carb. icing which I have experienced on a VW. Also I have done this run twice now but at different times of the day (morning/afternoon) A 20 F degree ambient air temp difference showed up on the gauges as a 11 F. degree difference. I'm thinking of installing a thermocouple wire into the engine compartment to get some value readings of just what is going on in there. Thanks for your input Al

Mitch..  My car had those same huge gaps in the rear of the engine compartment as well. It was very disturbing to me because, to me, it looked like a huge air scoop for the hot air from the engine to be recycled. It's an easy fix though. I don't know how to forward one of my previous posts to you but the Topic was "Engine Compartment Heat Barrier" dated May 21 at 2:30pm. The photos will explain a lot.

The firewall gaps were another issue. It doesn't index with the front engine sheet metal barrier at all. In order to position it correctly I had to layer it with two layers of 3/8" Baltic birch plywood. (3/4" more toward the rear now)The rearmost layer extends 3/8" lower than the other to give me the cross-sectional profile needed to properly install that foam rubber strip VS provides as an engine compartment seal. First though, I installed the bare engine block with that rear tin piece in order to provide a template to draw the correct profile on the new wood firewall.

I think you are right about that oil cooler just pre-heating the air entering the fan hole. By the way these bodies come from Mexico and already have that hole in them when they are delivered to VS. I was there when a truck-load was being dropped off. I must say that I'm not banging on VS. They're in the business to turn out these cars and have, obviously found an expedient/inexpensive way to avoid problems in this area. However, if we want to put bigger motors, etc. we have to find better ways to solve problems created by doing so.

Whew....thats enough for now.........Bruce

Isn't the grille for letting hot air out and not cool air in?

Bruce, thanks for doing these tests...very informative.

Al asked how big the air opening under your grill is.  Did I miss that answer?  Like Al, I have an older IM grill with two small openings on the sides.  Is your opening the same?

I can tell you that getting more air into the engine compartment really cools down the temperature of the engine components (alternator, carbs, shroud, etc.)

I drove my IM on a hot, summer day with the engine lid closed and propped open 4 inches.  After stopping I opened the hood and did a 'feel' test.  With the lid closed I couldn't rest my hand on any of the engine parts.  With the lid open 4 inches I could rest my hand on the shroud, carbs, etc.  They were quite warm (no surprise), but not really hot.

To try to answer some more questions....

Bill.... I'm of the belief that the Grill was to pull air in not exhaust it.  It is certainly possible that some cars out there are doing the opposite though

Ron ....I just went out and measured the Grill in my VS. It has an effective open area of 100.485 sq inches. It actually measures 14.5" X 8.25" but you have to subtract for the 12 grill bars which are 14.5" X .110" thick. These take away a little over 19 Sq " of the overall area. But that's not the only restriction and resistance to flow. The air has to make a severe 90 degree turn on both sides under the Grill into a smaller area which works out to an aggregate total effective area of 58 Sq, inches (including both sides)....Then...it makes another 90 degree turn and opens up into the two big holes in the engine compartment on the underside of the hood. These have an effective area of 139.50 sq. inches.    I hope this helps Ron.

I see that there are a lot of options if more air flow is needed. That restricted area (the 58 sq " area) could be modified and made bigger since I have dual carbs. and no center air cleaner in the way. this would probably add at least 33% and reduce the 90 degree turn/flow resistance as well.

You and Al have a good point about getting more air in thru that Grill so I'll be looking for possible ways to accomplish this. I guess It's just prudent to take this a step at a time. I really appreciate any input and Ideas any of you have out there.

Bruce

Bruce, I would think that theory would benefit the 911 style fan/shroud.

The stock air cooler sucks air in from the front (hence the 6" hole on the firewall in line with fan) but the 911 style would suck right from the grille right?

I run a 2110 w/911 shroud full flow, cooler yad yada yada and stay under 200 deg.

Thanks for your hard work and explanation as I'm still learning.

Excellent post !!!

It gets hot here in FL, so thank you for the info

Hey Bill, I had a 911 shroud on my first 'go around' with my IM.  I had to cut out a big chunk of the rain guard under the grill to clear the shroud, which worked great, until I got caught in a heavy rain storm.  The water leaked onto the big spinning fan and was thrown to all corners of the engine bay.  What a mess!

Here is a link to the post from May that Bruce mentioned a few posts back.  https://www.speedsterowners.com...4#387060361541533274

 Yes, I cut mine out as well. I try not to drive if there is rain forcasted but living on a tropical island we have our typical afternoon showers. 

Has any one tried to lay a piece of paper over the grille opening with the engine revving to see if the paper is held to the grille?  This would prove if the fan is pulling thru the grille. I think it pulls mostly thru the firewall hole. Bruces test shows that the grille opening alone is enough to feed the engine. Also, the engine fan pulls way more air into the compartment than the carbs are. Either way it is good to know that there is plenty of air getting in there.  

Frank- I think the paper over the grille may be held in place when the car is stopped and maybe at lower speeds (and higher rpm's), but at some point (40? 50? 60? 70?mph) the aerodynamics of the car (side profile is shaped somewhat like a wing) will overpower the fan's and carbs' abilities to draw enough air through the engine lid. Have a look at the size of the tube feeding the engine compartment of the vintage racer in my post above- I think it's not only to feed the fan and carbs, but to also create airflow through the engine compartment to whisk away heat through the grille. At higher speeds, above the engine lid is probably a low pressure area and I'll bet it takes that much air to make the high strung racing engine (7500? 8,000? rpm redline) last more than a weekend  or 2.

If the opening(s) under the grille are the same area as the grille itself (or more), then yes, there's more than enough air intake for most engines, but (as Ron and I have pointed out) not all these cars are built the same. The grille opening in my car is 8 1/4x14", or 115 sq. in. (and every one else's is a similar size), but the inner panel (which is part rain shield) has an opening on each side that don't total 15 sq. in., and it sounds like Ron's is similar. There's no way a fan that draws 1200-1400 cfm at 3500 and carbs that consume 600-1,000 cfm at full throttle are going to get enough air through those slots.

We have to introduce air into the engine compartment from somewhere else, or they won't last long. Gene Berg told a story of a conversation with a guy with a kit car (dont' know what it was) about engines not lasting very long in his car- the longest had lasted a little over 4,000 miles. Gene said that one look and he could see it was almost completely sealed and there was no air intake; how was the thing supposed to breathe and cool itself?

A 911 style shroud may be able to feed itself adequately through only the grille (if there's enough area), but I don't think a type 1 shroud (with the intake facing the front of the car) is going to be as efficient at higher speeds, and with in front of the firewall being a higher pressure zone (the higher the speed the higher the pressure differential), why not take advantage of the "natural path" into the fan and carbs?

One thing I hadn't thought of before- Bruce; again, I'm not disputing your test results, but I wonder what you would have found out if you'd driven the car on the highway for an hour (or 2) with the firewall hole blocked off, and not just your 8 mile jaunt. It's been my experience that (especially with higher hp VW engines) it sometimes takes a longer drive for a car's cooling shortcomings to show. Al

This is a great topic. I have always thought the engine compartment doesn't get enough air. Well you have somewhat proved me wrong. 

The other half of the issue regarding the air is the density and temperature. We all realize these air cooled motors run great earlier mornings or evenings. Why ? The air is cooler.keeping the heat out of the engine compartment or reducing it makes a difference.  Putting a thermal barrier between header and the body reduces the heat transfer. Ever notice how warm the engine compartment is after a drive or quick trip around the block? when you prop that lid you feel the heat. Think about it! Run hot air  thru the fan does not reduce temps and same with the carbs. 

Is a Manometer the same thing as a Petermeter?

One is in millimeters and the other is is inches.  Doesn't 152 mm sound better than 6 inches? 

This is an awesome thread.  Thanks a ton, Bruce.  By the way, are you the Bruce from Vancouver?

The problem with not getting enough air into my engine compartment for the fan and dual carbs (in my case throttle bodies) has bothered me for a while, so I'm adding two vents by the throttle body air cleaners to increase air flow.  In the past I've propped the engine hood open on long, hot, summer drives to help cool the engine compartment (which it does).  Maybe with the added vents I won't have to.

Here's a photo of my IM with the hood propped open 4 inches.  I'm surprise no one on the freeway has honked at me and yelled, "Hey buddy, your trunk lid is open!"

Wow! I didn't think this subject would get too many comments! Please remember that I didn't go over 68 MPH because of my break-in protocol so the next phase will be up to 100MPH for a period of time. It will be difficult to maintain this speed for any distance and the priority is to measure engine compartment vacuum not heat. Although I expect that they go hand in hand and are probably inversely proportional. So the final verdict is not in. I did (just in case) make sure to leave that 6 inch hole in my cool looking stainless steel engine-turned firewall. It's covered with a plate of the same material.

Al....My whole trip was not just an 8 mile run. It was 30 miles (one-way for me down to VS) The highest CHT was 349 F. degrees and that was in stop-and-go traffic. I'm happy that you ask these questions because it give me cause to consider other things which ma be going on that I hadn't thought of...Thanks

Ron O.......No...I'm not from Vancouver. I'm from Arcadia Ca (next to Pasadena Ca.) I understand that there was another Bruce Williams in this group though.

You have a beautiful car! With your hood open like it is in the photo, it almost looks like the spoiler on other Porsche's....Hmmmmm.....A double blade improvement ??

Future tests.....I think I will install some temperature monitoring devices in the engine compartment to see what's going on both on the road and at rest with engine on and off... "Heat soak", Latent heat, and running heat. Should be interesting....hopefully not devastating........Bruce

As Ron said, Bruce, this is a great thread! For those fairly new to aircooled engines and extracting more power from them, there's a lot of great info here. With each manufacturer building slightly different cars, what makes a hot rodded air cooled engine live is a little different in each car. Even the displacement and power output play a role in this. And copying what VW did is not enough, as what keeps a 50 or 60 hp 1600 alive long term isn't always enough for bigger, badder beasts. The engineers in Wolfsburg, Germany never envisioned what we do with these engines now, so we're the engineers in charge. Oh- gotta go to the neighbors and watch the hockey game- later. Al 

An air scoop should solve any cooling issues.

They probably think it's a Speedster with a whale tail!! 

Anthony, we're thinking along the same lines. Someone on the Samba (who I consider very knowledgable) suggested a remote thermometer in the engine compartment as a way of knowing when "everything is right" (I'm paraphrasing hugely here). The idea is that with proper air access to the fan and carbs and flow through the engine compartment so it isn't holding in huge amounts of heat and preheating cooling and carb intake air, air temperature should never be more than a few degrees above ambient. Get this right and the engine will not have such a discrepancy in power from cold to hot and it will last longer.

I've said this before, but I think it bears mentioning again; I think the firewall is a great place to source air from, as the trans side is a high pressure zone. If it doesn't seem to be doing anything in your car, it's not being fully utilized and looking for ways of getting air out of the engine compartment (and removing radiated heat from the shroud/sheetmetal so it's not preheating the cooling and carburetor air) will bring benefits.

Mitch- Is your oil cooler/fan assembly above the transaxle? I've wondered about just what you've reported, and have been thinking that in the wheelwell may be a better place for it as well. Was oil temps that changed? How much? 

For those that haven't thought about it- the temperature of the incoming air makes a big difference as to how much heat it can absorb, and Bruce's observation of a 20' difference in ambient air temp resulting in an 11' difference on the gauge (oil temp?) is in line with what you can expect. If the air at the fan intake is 40 or 50' hotter then it will be removing that much less heat.... 

Al, we agree about almost everything. This thing, however, not so much. 

I really don't ant to get into a fight over this, but I've got 4000 mi of "seat-of-the-pants" data that says two 8" holes in the firewall did nothing for the temps. 

Propping the hood is good for 15 deg, but the holes with the lid down didn't do anything for me. Propping the lid with no holes accomplished the same thing, so I can only surmise that the area above the transaxle is not as great a high-pressure zone as I thought it was. NACA vents would work well, and ducting something from a big high-pressure zone up front would work as well, but the aerodynamics back there are funky.

It's a pity, because I did a LOT of really cool looking stuff to make my firewall vents work. They just don't.

I found this all very interesting. To me perhaps it is a lot of mental *********ion. I have a 1915cc with dual Webers and and 1x4 ratio lifters. Perhaps a rather tame set up. However i have driven for over an hour in 105 degree weather in the NV desert at 75mph and my temp gauge never reached the red zone. I had the same experience driving up Kingsbury grade to Lake Tahoe, a climb of over 3000ft in 5 miles. I have an temp controlled external oil cooler with a fan,  so maybe that is the difference

I have done this a standard VW's before and the red pressure light would flicker and the mechanical fuel pump would always vapor lock after a stop. I was young and stupid then of course. Now I am old and stupid. 

Vince, meet Noel. Noel, Vince.

I'm glad you have no issues. Ron O'Black couldn't drive his car in Vancouver because it ran so hot. Knowledge is power. If you aren't getting anything out of this one, there are other threads.

Stan, do you have your external oil cooler in the space in front of the firewall?

The problem is real for those who can't get engine temps down under all conditions.  It happened to me with a CB 2110 in a VS wide body, when ambient temps were high, as in SoCal summer weather.

The difficulty, as I see it, is that we are the engineers who have to analyze and fix the problem.  Porsche/VW engineers did a creditable job of cooling the engines of the day, but they have moved on to the successors of the 356 platform, namely the modern 911 in all its iterations, including water-cooled.  Today's replicas are producing about 3 times the waste heat of original 356's, since we now have engines capable of producing almost 3 times the HP.  Carrera GT's had HP ratings of 110, but most 1957 356's had HP ratings of about 60, with a low of 44 and a high of 75 for the 1600S.  356 rear deck lids went through design changes as HP increased, but it never reached the levels of today's Type 1 & 4 hot VW's.

Do some rudimentary research on NACA ducts, if you need a humility adjustment.  I was a pretty good student, but only marginal in the sciences.  Air movement in and around a moving vehicle is really complicated science.  If it was simple to figure out, someone in the hobby, including the talented manufacturers we have, would have done so.  We can't even seem to determine which openings are for air inlet and which for air outlet.  That doesn't mean we aren't clever, it means the problem is complicated.  

High and low pressure areas, boundary layers, and the correct placement and shape of Naca ducts are all elements of the problem.  As in all things automotive, the law of unintended consequences applies.  Modify the car body so that air now enters at point A, and is routed to point B.  However, that new air flow has now taken air away from the previous boundary layer pattern that supported down force, and helped the wheels stay sticky.  Now, at speed, the car wants to wander.  Porsche engineers not only have the science education and experience, they have those great tools, like smoke machines and wind tunnels, and lots of sacrificial bodies they can modify. 

As I'm sure many have noticed, Porsche, along with few other makers, has adopted fender vents to help cool the big HP engines of the modern 911's.  But, oh man, the thought of taking a jig saw or router to the body of one of our replicas sends chills up my spine.

Stan first if you actually read my post you would perhaps noticed it was done with a sense of humor, something you are apparently missing. Second if you wish to insult me please become supporting member otherwise fxxx off.

Well, that escalated quickly...

I'm going to get the leftover Hallowe'en candy and a rum beverage; this should be good....

Ah, major, jack down. Stan's words of wisdom are worth the price of admission for the rest of us.

Rich- What the h*ll are you doing? It was just getting good!!!

Noel,

I did read your post, just like I read everybody else's. I read where you insulted the discussion and equated the collective worth of this entire thread with a vulgar slur. What I don't understand is why guys who have no interest in the more technical aspects of these cars insist on insulting people who do. This is, after all, the "tech" portion of the forum. Vince Manto did it for years and I never understood it. It's not like every single thread is going to interest every single owner.

Yep. I'm a humorless idiot. The thing is, I like to learn stuff so I'm not so ignorant any more. There are people here posting real data, exchanging information regarding how to keep their cars cool under all circumstances. I've got enough invested in my engines, that I'd like to know how to best preserve them.

I'm truly glad your car doesn't seem to have any issues running too hot-- although I'm wondering if you really know for sure, since you seem to be relying on a Chinese oil temperature gauge with no numbers on it to let you know what's going on inside your engine. Knowing how dead reliable the tach, speedometer, and fuel gauges all are-- I'd suggest you might be putting a bit much faith in something with at least the possibility of being less than reliable, but what do I know (I'm the humorless idiot, right?).

I drove my car across the country this summer. I was 100% fine for 3000 mi, across the plains, the continental divide, on US40 across Nevada, over and through the Sierra Nevadas for 2 days, down to Monterrey, down Highway 1, and across Mojave Desert... right until Barstow. From there to Las Vegas, nothing short of popping the lid and slowing down would solve my temperature problem. My 9.5:1 2110 hit a wall at about 80 mph and 100* O/A temp-- I had reached the limitations of my set-up.

Jim Kelly hit the nail on the head-- some of us just want to be completely sure that we can drive these cars anywhere, any time, at any speed. That's not possible for more than a few engine combinations. Sharing as much data and real world experience as possible makes for a more informed collective. There are very, very few people who care. But most of them are here, posting.

I'm sorry you aren't one of them. There are threads I don't participate in because I'm not interested. I'm not out of line to suggest you do the same.

Vulgar Slur! What planet are you from? That is an expression I have used in many "C" level meetings in my career. By most definitions a vulgar slur would involve someones's mother and their ethnicity. 

Further my response was heavily self discounted and in no way presented with any authority than my own personal experience. This was done for the benefit of other simple enthusiasts like myself that attempt to learn from others on the site. When you "scientists" go beyond our diminutive comprehension it can be exasperating. Until you pay up and become a contributing member you have no right to complain about anything or anyone. Others may respect your input as do I, but keep you personal insults to yourself. 

Major, you do realize you're speaking with royalty here, no?

You might also note that many of the more astute members here are non-contributing. I think they get some slack cut since their contributions are much more valuable than just bloviating. 

I love engineers and have the utmost respect for them! Were it not for them I would never had been able to achieve the level of success I did in my career. I spent 35 years in technology and without people to invent products I would have nothing to sell. You will note that engineers never run companies. They do not understand the real world nor do they want to. Companies are run by operational or marketing types unless they are in financial trouble and then the CFO take over. Again by his own admission Stan has no sense of humor. I appreciate his contributions, but again it seems the technical folks feel no need to contribute to this great forum financially. I guess there mere presence is contribution enough for the rest of us pathetic souls.