I don't have the engine heat problem on my speedster. But if I did I would keep it simple make a rear engine prop to allow the deck lid to be open on hot days. I also would install an oil temp gauge or the simple candy thermometer in the dip stick hole to check oil temp on hot days so you have some idea of how the engine is doing. Other then that, just drive it and enjoy the drive..
^^THAT^^
And if you’re going to the trouble of monitoring your engine temperature on hot days under different conditions with a dipstick thermometer (which I highly recommend), make a mental note of where the needle is on your dash gauge at “normal” runs and then at the hottest temp you see so you’ll have a better idea from then on. It’s a simple thing to do.
You could even place a small piece of tape or something on the gauge that tells you; “Don’t let it run higher than THIS!”
I think I’ll try a Derale 16 in the original area and some scoops. Maybe I’ll ask Greg about scoops.
Oh, I ran across my notes from a conversation with Pat Downs. He said our 2332 VMC engines are 9.5:1, not 8.2:1 as the VMC literature indicates. I will correct that above.
I think I tested that void area in front of the firewall and it indicated a negative pressure at 65mph as well. I plugged up the VS firewall hole on my Speedster when I made sure that the engine compartment was totally sealed.
I then had 4 oil temp sending units plugged into my engine so I could monitor the oil temps simultaneously. I used a rotary switch to quickly cycle thru all the temps. (so I didn't have to buy 4 gauges) One on the inlet and outlet of the stock oil cooler, one on the outlet of the aux. oil cooler out in the fender well and the last one directly in the oil sump near the pick-up tube..
The reason I did all this was because I could tell that my engine was running hot and I wanted to know why and where. I used a very accurate thermocouple probe down the dipstick tube to verify this.
After reading about all the methods tried by many of you members here, I decided that the best method was to seal off the engine compartment like the VW/Porsche engineers intended. They obviously went thru great pains to do this so that is what I did. My logic dictated that the modified engines we now use in these cars will and do generate more heat, Hence, an external oil cooler in the left-rear fender well in addition the stock cooler. By doing what I did, I solved my engine cooling problem. About this time I was curious if the grill was a restriction because All the air for the engine now had to come thru the grill. Alas, I measured a negative pressure ! For me, I had already eliminated my cooling issue but perhaps I could get my temps down even further by eliminating this air flow restriction. I mentioned different methods in my previous post but what I did was remove the most material I could on the rain guard under my hood. I found these photos of what I was looking at. I borrowed this hood and rain guard from Greg. Please note that most of the actual rain guard that covers the distributor had been removed. This was OK because I was more interested in the restrictions on either side and that is what I measured.
The end result is that I removed a lot of the rain guard on the right and left sides , leaving the center part over the distributor. This eliminated the negative pressure and slightly lowered the oil temp. Only around 3 f in the sump.
An interesting note and surprising to me was that the stock oil cooler only had a difference of 4 degrees F. between the inlet and its outlet. It's a very high volume flow but I didn't expect that kind of number and still don';t really know why or how it cools the engine at all. Even on a stock engine. ............BRUCE
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@aircooled- I was hoping you'd run a hose up into the 'void' to see if that would pressurize the area (and feed the engine compartment) but by then you were done. Do you remember what weight oil you were running in that engine?
Al.........I believe I was using Brad Penn 10w/30. I think I did put a hose in there and I think I posted it on here but don't know how to find it..........Bruce
Thermodynamics ... I have a degree in that, and spent most of my career cyphering on those principles, albeit with emphasis on what happens at Mach-alot. All this back-yard engineering and scientific experimentation at subsonic speeds is completely on point. Very good work. As to negative pressure in the engine compartment, that really does sound about right given the design of the fan mounted in the shroud, sucking air in to the tins at a high rate. That said, if one could increase the ambient pressure inside the engine bay, and decrease the resistance to air flowing from outside to inside, that fan will push more air. I will invest in an engine lid prop -- that can't be too hard. and will use it if/when required, and see if it helps.
Alb.......Wow ! Did I do all that ? hmmmm ! I was wrong in my recollection of the area in front of the firewall. It appears that there was a positive pressure in there, not negative. Thanks for posting those.......Bruce
@El Frazoo posted:Thermodynamics ... I have a degree in that, and spent most of my career cyphering on those principles, albeit with emphasis on what happens at Mach-alot.
Great, you’re just the person to run this by, I was going to post it yesterday and got distracted:
When I was “doing my own research” wrt my Spyder getting really hot driving at consistent high revs (freeway) or pulling a long grade, and finding out about the Cooled Thing repro shroud I read something that seemed a bit fantastical. I can’t remember if it was in the Concept1 sales lit, Jake Raby’s endless cooling thread on the Samba, or just some random forum post, but someone postulated that you can actually have TOO MUCH airflow over a cooler, that as the temperature of the vanes goes down past a certain point, so does the heat transfer. Seemed like mumbo jumbo to me. Is there any validity to that?
dlearl476......Very good question !...........Bruce
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Randy, sorry I didn't realize you have a Pat Downs 2332 in a recent VMC build.
Before attempting anything on your own, why not just talk to Pat directly about this issue?
No one knows more about keeping these engines running cool than he does. He lives in the central valley and has been building VW engines here for over 20 years. I'd guess he'd be willing to spend a few minutes on the phone with you as he built your engine and has a pretty good reputation for wanting to keep customers happy.
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@aircooled posted:
...An interesting note and surprising to me was that the stock oil cooler only had a difference of 4 degrees F. between the inlet and its outlet. It's a very high volume flow but I didn't expect that kind of number and still don';t really know why or how it cools the engine at all. Even on a stock engine. ............BRUCE
Bruce just to be sure: was your stock oil cooler's "exhaust" ducted to a spot under the tins? Asking because, on my Spyder build with the DTM shroud, the fan put a good amount of air through the stock cooler.
Ed.....Yes the complete ducting to make the air on the outlet side of the oil cooler go down (an if I recall) and out in front of the tin that blocks off around the bell housing. The cooler was the large HD unit that bolts to the adaptor which is fastened to the crankcase. Both of the temp. sending units were installed in that adaptor. One in the inlet and one in the outlet. I welded bungs into that adaptor such that the temp senders, when installed, did not restrict the oil flow. There is a tremendous amount of air flow thru that cooler. You can feel how much if you happen to be around it when an engine is on a dyno !..........Bruce
@dlearl476, as to the physics, generally speaking, film cooling over a flat surface always increases with bulk air speed. The engineering issue is usually centered around is the flow laminar or turbulent. Laminar flow occurs under very restrictive conditions and is characterized by lower fluid speeds and hence lower heat transfer rate than if the flow is turbulent. I had some situations with hardware where we purposely introduced tiny obstructions in the flow channel to purposely trip the flow from laminar to turbulent. I can't see how the air flow induced by the engine fan is anything but turbulent, especially at higher engine speeds. So likely we would see ever more heat transferred the higher the velocity through the cooler's fins. Turbulent flow generally requires higher pressure differences in order to achieve a certain bulk flow through a passage and the relationship is non-linear . All of that said the design could reach a point where the turbulence is so great that ever more action by the fan (higher engine speeds and also higher heat generated) might not result in much increase in bulk air flow. At such a point the actual air flow through the cooler fins would not go up in direct proportion to the fan speed and the increase in engine heat output would not be accommodated by the cooler, basically being choked out for flow rate. At high revs, the engine fan might be beating the air to death, but the cooler fins are just not letting enough air through to match the increase in heat load. And a centrifugal fan like we have on these engines does have a performance curve showing output vs rpm at one atmosphere ambient, and I'm betting that CFM falls off at higher rpms, and does not just keep going up the faster it spins. Just a theory.
I could not find a performance curve for centrifugal fans when spun too fast. Did find some data that shows the operating curve for a fan (CFM vs RPM) is not quite linear. So I'm going to hold to my claim that if a given fan is spun too fast, the actual output in CFM could go down, or at least level off. I'm going to say that these fans have a CFM vs RPM curve that peaks at some speed beyond its proper design point. I think at some point the faster the fan spins the flow over the fan impellers will separate off the trailing edge and form a recirculation eddy off that trailing edge, and this will spoil the back pressure and CFM will decrease with increasing RPM. That makes sense to me.
FWIW, boat propellers can spin so fast that the pressure along the blade falls below the vapor pressure of the water and water vapor (or dissolved gas) bubbles form -- called cavitation. When these bubbles collapse, they can do so with explosive force, and in some cases can erode the propeller. Even absent actual damage, cavitation greatly reduces the efficiency of the propeller and the thrust it delivers will go way down.