Bruce, Great minds think alike!
Your ducting is almost identical to what I did! The only difference is that I was able to squeeze 6" duct in there.
Jerome
Within reason, size of the ducting isn't too important. What counts is ducting the cool air right up toward the fan inlet - this means that the fan's intake will be cool air instead of "mixed air" (in from the grill and heated by the engine tin, etc.)
The mixed air also contains hot air leaked out around the colling tin into the engine compartment; this is why it's important to carefully fit the engine tin for minimum leakage and best engine cooling. For an original 36 BHP VW this wasn't too important a factor, but with performance modified engines it becomes an issue (more heat).
Cool air ducted to each carburetor air cleaner is a good idea, too (the competition oriented Carreras did this via shelf-like surrounding ducts from carbs to the louvers on the rear decklid).
(Message Edited 8/26/2003 1:54:38 PM)
The mixed air also contains hot air leaked out around the colling tin into the engine compartment; this is why it's important to carefully fit the engine tin for minimum leakage and best engine cooling. For an original 36 BHP VW this wasn't too important a factor, but with performance modified engines it becomes an issue (more heat).
Cool air ducted to each carburetor air cleaner is a good idea, too (the competition oriented Carreras did this via shelf-like surrounding ducts from carbs to the louvers on the rear decklid).
(Message Edited 8/26/2003 1:54:38 PM)
I may be crazy or it could be wishful thinking but, it seems that the more miles I put on the engine the cooler it seems to run. Could this be part of the breaking in process?
Jerome
Jerome
Jerome, that's the way it works - break-in is a "wear-in" process and once completed there is less frictional loss and the engine should run a bit cooler.
Hey Bruce, thanks for posting the photos, and nice work.
What tires are you runnung? By the look of the tread they look pretty trick.
What tires are you runnung? By the look of the tread they look pretty trick.
I agree with the yarn test, the only way to know what's going on (vacum?) is to put yarn (2" pieces) taped all over the deck lid and have someone follow or go to a wind tunnel.
J-P
J-P
The tires are Toyo Proxes T1-S 195/50/15. They were a great value I got them for $125 each mounted then a few months later I saw them for $69 unmounted. They are Toyos ultra high performance offering. Last summer a few shops were blowing them out nothing else came close for the money.
As far as the yarn thing goes, you don
As far as the yarn thing goes, you don
You will need a very sensitive gauge to measure any pressure drop that may exist inside the engine compartment.
Turbulence disturbing flow into the grill is usualy not a problem on Porsche Speedster/"D" replicas unless you have the top up. Note that the original VW beetle convertibles had a problem with the top down - it bunched fairly large at the back of the car and acted like a wing that diverted air past the grill inlet holes.
Dual grills were fitted on the later 356's not so much because one grill was not an adequate cooling air supply but rather because owners persisted in mounting several car club and/or rally badges to the grills, which impeded air flow.
Many engines do not have their tin fitted closely enough or engine compartment sealed well enough around the edges of the compartment. In either case warm or hot air can be blown into the compartment to be reingested by the fan; obviously if enough hot air is "recycled' back into the cooling fan you will have an engine cooling problem.
Some type 1 engines have fans improperly fitted such that there are large gaps between the fan and shroud.
Beyond that, check the items in the "Knowledge" cooling article if you have cooling problems. Loose fan belts, vacuum leaks, improper carb jetting, improper ignition timing, low oil level, and restrictive exhaust systems (or some combination of them) are usually the reasons for overheating.
(Message Edited 8/27/2003 12:38:57 PM)
Turbulence disturbing flow into the grill is usualy not a problem on Porsche Speedster/"D" replicas unless you have the top up. Note that the original VW beetle convertibles had a problem with the top down - it bunched fairly large at the back of the car and acted like a wing that diverted air past the grill inlet holes.
Dual grills were fitted on the later 356's not so much because one grill was not an adequate cooling air supply but rather because owners persisted in mounting several car club and/or rally badges to the grills, which impeded air flow.
Many engines do not have their tin fitted closely enough or engine compartment sealed well enough around the edges of the compartment. In either case warm or hot air can be blown into the compartment to be reingested by the fan; obviously if enough hot air is "recycled' back into the cooling fan you will have an engine cooling problem.
Some type 1 engines have fans improperly fitted such that there are large gaps between the fan and shroud.
Beyond that, check the items in the "Knowledge" cooling article if you have cooling problems. Loose fan belts, vacuum leaks, improper carb jetting, improper ignition timing, low oil level, and restrictive exhaust systems (or some combination of them) are usually the reasons for overheating.
(Message Edited 8/27/2003 12:38:57 PM)
The yarn test is a tried and true old test of seeing what the airflow is doing. Yes your right in that with only one person driving you can't see a thing with the yarn however if you get a person to follow and see what's going on then you'll know.
A while back I put on a 356 fan pulley for the summer and so far the oil temps dropped about 15 deg. however the head temps almost stayed the same. Go figure?
Also an interesting note, after putting in mobile one 10/30 the oil temp went up over using the Kendall 20/50. Kendall is great oil as it has a high level of phosphur and zinc (lub. devices) and it has a high flash point, around 480. Anyway, I'm not sure synthetics are the way to go for Southern Cal. temps. One thing I did notice about the Mobile one is that after a certain point the oil temp. just wouldn't rise even though the air temp. keeps going up. Out here there's a big diff. from the beach to the dessert.\
One day we will figure all of this out.
J-P
A while back I put on a 356 fan pulley for the summer and so far the oil temps dropped about 15 deg. however the head temps almost stayed the same. Go figure?
Also an interesting note, after putting in mobile one 10/30 the oil temp went up over using the Kendall 20/50. Kendall is great oil as it has a high level of phosphur and zinc (lub. devices) and it has a high flash point, around 480. Anyway, I'm not sure synthetics are the way to go for Southern Cal. temps. One thing I did notice about the Mobile one is that after a certain point the oil temp. just wouldn't rise even though the air temp. keeps going up. Out here there's a big diff. from the beach to the dessert.\
One day we will figure all of this out.
J-P
It would be interesting to determine what benefits if any engine lid louvers add.
As far as noting what is going on with the yarn, for a passenger it should be a piece of cake to observe and take photos. On a windless day make note of what is going on at 10 miles-per-hour step increases.
I would be also interested in if the guys that added the rear wheel area intake air duct -- if they have head and oil temp gauges in their cars -- they close off the intake duct and take a 15 minute drive at consistent highway speeds and note oil and head temps, and then open the duct and take another 15 minute drive on the same stretch of road to compare the two sets of figures. Perhaps not scientific but should easily determine a baseline.
As far as noting what is going on with the yarn, for a passenger it should be a piece of cake to observe and take photos. On a windless day make note of what is going on at 10 miles-per-hour step increases.
I would be also interested in if the guys that added the rear wheel area intake air duct -- if they have head and oil temp gauges in their cars -- they close off the intake duct and take a 15 minute drive at consistent highway speeds and note oil and head temps, and then open the duct and take another 15 minute drive on the same stretch of road to compare the two sets of figures. Perhaps not scientific but should easily determine a baseline.