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Porsche 911 shroud pulley ratio (type 1)
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ottobevis
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PostPosted: Fri Mar 12, 2021 1:20 pm    Post subject: Porsche 911 shroud pulley ratio (type 1) Reply with quote

Hello everyone,
For all you 911 shroud users, what pulley ratio are you using? Or what diameter crank and alternator pulleys do you have? I am trying to figure out what the lowest ratio possible is to minimize HP loss while still maintaining adequate airflow and having the alternator light go off close to idle.

I know there are variables here (engine size, max engine RPM, how well the shroud is sealed, internal vain modifications to the shroud). Just trying to get a ballpark. I have a Bergmann shroud that I am fiber glassing internal vains to (I will post photos of that once completed. Basically I am dividing the air in to six sections, 3 sections on each side, capturing more airflow for the top of the cylinder heads, using custom made lower tin for the cylinders and heads). Will be testing the airflow under each part of the cylinder and heads to try and equalize them. Its going on a 2276, max RPM 6,500.

I know 911 shrouds have been discussed in detail and I understand their short comings. Reading through all the posts of various forums there is no mention on what pulley ratio people use. I contacted Bergmann and he suggested a 5.25" (133mm) to 5.75" (146mm) crank pulley. I have one of the older Bergmann kits that uses a V-belt. The alternator pulley diameter is 78mm (odd size, I guess it was custom made?). Using a 5.25" pulley this would give me a ratio of 1.7:1. This seems very high given most people agree that that a Porsche fan produces more air at a given RPM than a VW fan. It also seems high when comparing it against a real Porsche fan on a 911. The 1965-75 911 used a similar size 11 blade fan and used a ratio of 1.16:1. The 1980-89 which has considerably more HP than most type 1's used a ratio of 1.46:1. I know, the 911 has a lot more cooling surface area than a VW. It also has a lot more open area for the air to escape. Maybe I am missing something but wouldn't the 911 need more airflow than a VW? It makes more HP and has more space for the air to escape. Or maybe the greater cooling surface means it needs less airflow than a VW. So probably the real 911 ratios are irrelevant. Maybe I am limited to maximum airflow speed (mach 1) on a VW. If so how soon should this occur? Anything below max RPM would mean wasted HP (belt slipping). I think Bergmann suggests a high pulley ratio as a)it's safer than under sizing, covers small to big engines, b) the unmodified shroud has places that air escapes without cooling the heads, c) the lack of internal vains means pressure needs to be built at lower RPM's to help distribute the airflow.

Otto
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Maxpower
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PostPosted: Fri Mar 12, 2021 1:45 pm    Post subject: Re: Porsche 911 shroud pulley ratio (type 1) Reply with quote

Porsche did what they did because it was designed to do it. With an aftermarket shroud and a Porsche fan the consensus is stock is better you need all the air you can get unless you live somewhere very cold. The air deflectors will help a ton but there was a thread on here where someone spent lots of time and many variations to get something worthwhile. I want a 911 fan really bad but from what I've read not the best thing for the desert I live in. I'm sure people smarter then me will chime in and help you out.
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Wreck
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PostPosted: Fri Mar 12, 2021 3:42 pm    Post subject: Re: Porsche 911 shroud pulley ratio (type 1) Reply with quote

if you don't have a CHT gauge, I highly recommend a MGL TC-1 . another way is to get something like this

https://www.ebay.com.au/itm/Thermocouple-data-logg...Sw6bxZzTPY

Get 4 K thermocouples , pad type are good that can be secured near the spark plug with JB weld over them to hold them against the head and insulate them from the fan air flow . Then you are not guessing and can fit vanes in the shroud if needed and reduce the pulley ratio to suit how much cooling you need. No guess work .
spark plug ring type thermocouples could also be used but can be a pain to change spark plugs .
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King_vw61
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PostPosted: Fri Mar 12, 2021 4:59 pm    Post subject: Re: Porsche 911 shroud pulley ratio (type 1) Reply with quote

Innovate has a tc-4 for 102.00 and spark plug thermo for 38.00 from https://www.pegasusautoracing.com/productdetails.asp?RecID=7206

You could do all 4 cylinders if you wanted. I will be doing that once my heads are back, I will post head temps once I have the data. Mine is a little different but it is a 911 fan and the heads are going to be hotter than stock cast.
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ottobevis
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PostPosted: Fri Mar 12, 2021 5:32 pm    Post subject: Re: Porsche 911 shroud pulley ratio (type 1) Reply with quote

Maxpower, yes I did read stripped66 thread, "...an exercise of futility". The last thing he mentioned was that he had changed to a smaller dry sump pulley and CHT temperatures had increased 50 degrees. Unfortunately he did not mention the pulley diameters or ratios before/after.

Wreck, I was looking at that gauge, it looks really good. Another option was to buy four cheap LED single digital thermocouple K gauges. They are sold on Amazon/Ebay for about $10 each and supposedly adjust for ambient temperature, reading up to 999 degrees. I was thinking of drilling a hole in the fin above each plug hole and bolting a small ring type K thermocouple.

Ivkings4, thanks, I hadn't looked at this. I will do some more research. Do I need to buy software to extract the data from the TC-4?

I still would like to get feedback from anyone with a 911 shroud as to what ratios/diameter pulleys they are using? It would be just helpful as a starting point so I don't have to go and buy multiple size crank pulleys to experiment with (although there are not many options 5" and under) I am leaning towards getting a 4.5" Jaycee crank pulley. This would give me a ratio of 1.47:1. Gene Berg sell a 4.25" crank pulley. I would probably try 4.75" but haven't seen anything out there in this size. Bugpacks 5" dry sump pulley is out of stock. Then its 5.25" but I think this will be overkill.
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King_vw61
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PostPosted: Fri Mar 12, 2021 5:41 pm    Post subject: Re: Porsche 911 shroud pulley ratio (type 1) Reply with quote

Easiest thing to do is to run a laptop in the car, log works is free software from Innovate and you build your gauges on your laptop and you can record the data that way. Or you can buy a $50 pocket logger from Innovate and that has an SD card in it then you would play it on your computer through the log works software.
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ottobevis
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PostPosted: Fri Mar 12, 2021 6:52 pm    Post subject: Re: Porsche 911 shroud pulley ratio (type 1) Reply with quote

ivkings4, that sounds good. I will read up about the TC-4. If I can connect it to an Android maybe I can mount a small tablet or phone in the car.

Right now I am fiberglassing the shroud. There are four large gaps on the Bergmann shroud by the top outer case stud bolts. Basically the air just blows on to the valve cover. I am partially blocking these holes and diverting the air around the outside of the exhaust ports.

Another area that leaks air is the spark plug holes on the shroud. Last week I attempted to make some grommets out of silicone to cover these. I have always found that the rubber spark plug air covers that are supplied with leads go hard and become ineffective. Rubber cannot take the heat (I think most rubbers are rated up to 180f). Unfortunately I was unsuccessful, the angles of the shroud, proximity of the intake manifold and how far the spark sticks out means I need to use a thinner, more flexible silicone (silicone is more heat resistant than rubber). I am still looking for some silicone grommets (that seals on both the inside and outside of the shroud to prevent air leakage) which I can adapt to fit the spark plug leads.
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74 Thing
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PostPosted: Fri Mar 12, 2021 7:44 pm    Post subject: Re: Porsche 911 shroud pulley ratio (type 1) Reply with quote

I change out the spark plug seals to Porsche ones that are shaped like old lamp shades, and do not harden and are easy to maneuver past the manifolds.

The Porsche boots are part number 111905449A

I got mine from Pelican Parts
https://www.pelicanparts.com/More_Info/111905449A.htm?pn=111-905-449-A-M136
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ottobevis
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PostPosted: Fri Mar 12, 2021 9:12 pm    Post subject: Re: Porsche 911 shroud pulley ratio (type 1) Reply with quote

74 Thing - right, I saw these and thinking of trying them.
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Maxpower
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PostPosted: Fri Mar 12, 2021 11:03 pm    Post subject: Re: Porsche 911 shroud pulley ratio (type 1) Reply with quote

I was expecting more Porsche fan haters keep it up and show us some pictures. I'm interested to see what you do with the air deflectors. My brother bought a 911 shroud from Australia for a type 4 he hasn't had the chance to test it out its going to be about 3 liter should be interesting. The thread with the guy with the old school 911 shroud made from a car rim was pretty cool even though it's no help to you fun to read.
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66brm
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PostPosted: Sat Mar 13, 2021 3:30 am    Post subject: Re: Porsche 911 shroud pulley ratio (type 1) Reply with quote

Wreck wrote:
if you don't have a CHT gauge, I highly recommend a MGL TC-1 . another way is to get something like this

https://www.ebay.com.au/itm/Thermocouple-data-logg...Sw6bxZzTPY

Get 4 K thermocouples , pad type are good that can be secured near the spark plug with JB weld over them to hold them against the head and insulate them from the fan air flow . Then you are not guessing and can fit vanes in the shroud if needed and reduce the pulley ratio to suit how much cooling you need. No guess work .
spark plug ring type thermocouples could also be used but can be a pain to change spark plugs .

At nearly $200 AUD shipping I think I'll pass
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Wreck
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PostPosted: Sat Mar 13, 2021 4:38 am    Post subject: Re: Porsche 911 shroud pulley ratio (type 1) Reply with quote

66brm wrote:
Wreck wrote:
if you don't have a CHT gauge, I highly recommend a MGL TC-1 . another way is to get something like this

https://www.ebay.com.au/itm/Thermocouple-data-logg...Sw6bxZzTPY

Get 4 K thermocouples , pad type are good that can be secured near the spark plug with JB weld over them to hold them against the head and insulate them from the fan air flow . Then you are not guessing and can fit vanes in the shroud if needed and reduce the pulley ratio to suit how much cooling you need. No guess work .
spark plug ring type thermocouples could also be used but can be a pain to change spark plugs .

At nearly $200 AUD shipping I think I'll pass



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That was the result of me playing with a cooling system with out spending money on CHT data .The air doesn't go where you think it does . There are cheaper options like cheap multimeters but they don't give data logging .
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ottobevis
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PostPosted: Sat Mar 13, 2021 2:33 pm    Post subject: Re: Porsche 911 shroud pulley ratio (type 1) Reply with quote

Maxpower, I will post photo's and air flow results. As of now I am making sure all the gaps are sealed as best as possible. First I will split the airflow vertically, probably around 60:40 to take in to account for the air direction at the rear of the fan (the vain will have a gap between it and the fan) and to allow for airflow that gets blown under small gaps below the vain. On each side I will run two vains horizontally over the top ridge of each cylinder. So in effect three chambers per side. The idea is to even out the air flow and to ensure the airflow flows down over all the cylinder surface. The rear most chambers (cylinders 2 and 4) will be larger due to the a) the issue with the air having turn 90 degrees sharply after the fan b) extra air is needed as I am using the fresh air outlets on the shroud to feed two oil external oil coolers at the back of the car. I'm making a scoop above the cylinder head fins to push air down in to the heads. Going to finish it off with custom type 3 style lower tins. The engine is out of the car presently so I will use an anemometer to measure air flow (before putting the lower tin on) at various points around the bottom of the cylinders and heads. My aim is to equalize each side and ideally increase CFM at the heads versus the cylinders. I will measure this at various RPM's using a drill. Going this route as once the engine is installed it will be harder to remove shroud each time to make changes.
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veltror
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PostPosted: Mon Mar 15, 2021 5:21 pm    Post subject: Re: Porsche 911 shroud pulley ratio (type 1) Reply with quote

you may find this of interest..
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ottobevis
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PostPosted: Thu Mar 25, 2021 12:16 pm    Post subject: Re: Porsche 911 shroud pulley ratio (type 1) Reply with quote

I haven't posted for a couple of weeks but have been working on modifying the Bergmann shroud, fiber glassing every gap. I brought the shroud used and there was quite a bit of material already removed by the PO around the spark plugs. I have since rebuilt this area, with a 1/8" gap between the shroud and the head. I have filled in all the gaps around the top of the case, at the case end and head ends of the cylinders, the exhaust ports. I have also sanded smooth the inside of the shroud (it was un-sanded chopped fiberglass previously). I have taken on and off the shroud close to 100 times just to get to this stage. The shroud now fits very tight and requires quite a bit of bending to get on. It will be pretty much be impossible to remove once the engine is in the car. Personally I would rather have it this way knowing there are no gaps.

Now I am starting the modifications. Looking inside the shroud while mounted there was a large gap for air to escape over the top of the head, near each exhaust port. To stop the air simply blowing out over the top of the head I have added fiberglass (see attached photo, the yellow fiberglass). This should a) move more air down through the outer head fins and b) move air down on the outside of the exhaust port. I have also cleaned up the fins on the heads (CB 044 super magnum plus) and used a drill to open up the outer fin paths.

I will be starting the internal vains soon.
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