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nogoodwithusernames
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Joined: November 10, 2014
Posts: 599
Location: CA, USA
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 Posted: Mon Mar 27, 2023 10:09 am Post subject: Re: type 4 fan peak airflow rpm |
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| raygreenwood wrote: |
Jake Raby noted that he was able....in his testing....to drill several vent holes in the tin on the back side/flywheel side of #3 to vent some of the static pressure at high rpms.....and straighten out a lot of the problem.
He also noted that for a while he also got an improvement by screwing down the oul cooler flap to make sure it was as flat as possible so the edge did not lift due to slop and static pressure....which further aided the ramp effect and rolling air motion.
I found the same issue with #3 back in 1999....by accident. I was drilling holes and testing with a hot wire anemometer. A couple of the holes I drilled helped #3 run cooler. I had no idea that was what helped.  . As I noted.....I found this by accident and he found it on purpose.
But.....these tweaks help at higher rpm.....but are not great at lower rpm and/or at various temperatures.
A lot of this information and R&D is what went into his work on designing the DTM to get rid of the turbulence and equalize the two sides of the engine for cooling air distribution.
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Ray,
Is there a diagram anywhere of where these holes were actually drilled? I've seen this mentioned before but never any actual information as to where/what size/how many holes.
In my Squareback with T4 I have HUGE running temp differences between around town and on the freeway. Nearly 200°. I think some of this is due the the turbulence and my thermocouple is on #3 spark plug so I would like to do some testing and see if I can bring that down at all. And obviously I am not concerned much for the around town driving as it is plenty cool already.
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71 Squareback, 1.7l T4 w/ crank trigger fuel and spark
(Conversion thread https://www.thesamba.com/vw/forum/viewtopic.php?t=732508&highlight= or https://shoptalkforums.com/viewtopic.php?f=1&t=151375&sid=f0542d44a322d290c29d6609fac7f215 )
74 914, 2.0L w/ D-Jet
-Derek |
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Vanapplebomb
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Joined: November 03, 2010
Posts: 5412
Location: Holland, MI
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| Posted: Mon Mar 27, 2023 10:33 am Post subject: Re: type 4 fan peak airflow rpm |
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Very interesting. I wonder how much difference the early vs late fan shroud makes. The 80-83 shrouds had no ducts for heater boxes like the 68-79 shrouds did. I have always assumed this would help, but have never gotten my hands on the late shrouds, so I never found out.
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1800 Type 4 Berrien 295
http://www.thesamba.com/vw/forum/viewtopic.php?t=487021 |
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Wildthings
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Joined: March 13, 2005
Posts: 50351
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| Posted: Mon Mar 27, 2023 3:50 pm Post subject: Re: type 4 fan peak airflow rpm |
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| Vanapplebomb wrote: |
| Very interesting. I wonder how much difference the fan shroud makes. The 80-83 shrouds had no ducts for heater boxes like the 68-79 shrouds did. I have always assumed this would help, but have never gotten my hands on the late shrouds, so I never found out. |
It might be interesting to check for any difference in the head-cylinder tins between a bay and a vanagon to see if they were in any way reshaped over time. The Bays used at least two different head-cylinder tins, one for carbed engines and one for FI engines, IIRC. |
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Alstrup
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Joined: July 12, 2007
Posts: 7216
Location: Videbaek Denmark
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| Posted: Mon Mar 27, 2023 3:59 pm Post subject: Re: type 4 fan peak airflow rpm |
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| Wildthings wrote: |
It might be interesting to check for any difference in the head-cylinder tins between a bay and a vanagon to see if they were in any way reshaped over time. The Bays used at least two different head-cylinder tins, one for carbed engines and one for FI engines, IIRC. |
Care to elaborate on that? I have never noticed a difference. That doesnt mean it is not there. I have just not seen it.
The later fan housing - is - slightly more efficient, and also equals the sides a little better. The only person I know who has real life data on that is Raby. I remember he did a comprehensive study on it back when he took over the DTM from Oregon Joe.
The velocity ring at the fan is interesting. How well it works is to be determined, by who ?? 
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https://www.thesamba.com/vw/forum/viewtopic.php?t=435993
Last edited by Alstrup on Mon Mar 27, 2023 4:16 pm; edited 1 time in total |
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Alstrup
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Joined: July 12, 2007
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Location: Videbaek Denmark
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| Posted: Mon Mar 27, 2023 4:14 pm Post subject: Re: type 4 fan peak airflow rpm |
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| SGKent wrote: |
and that is why Ray I pointed out that the SCCA FP 124 spider Fiat engines I used to build turned 10,000 RPM and they won championships. Len raced his 914-4 in SCCA FP and won races. He had to be turning a pretty damned high RPM to come close to lap records on some of the tracks (.13 second off at Barber from what I saw). When you are around true racing engines at road racing events, not just weekend drive by cones in a parking lot, you will see how much heat engines produce when racing because they combine a lot of air and fuel to go fast. I can not imagine Len lasting lap after lap if his type 4 engine was not cooling. Now maybe he was running DTM cooling, I don't know but he did have one fan explosion at RPM. The way these buses were built, they do OK cooling. The biggest issue is that they are a piece of plywood going down the freeway. If you get into a head wind in a bus, you WILL know it. This discussion is equal to debating with the other pilots what Orr could have possibly done to have the whore in Naples beating him over his head with a shoe. The answer is given in the end of the book. Because he paid her to so he could drive everyone else around him nuts trying to figure it out, sort of like the question in this thread.
| Quote: |
| Bare in mind this is NOT in a Bus but in a much lighter car. |
I stand by my answers. More, if I was building a lighter car with a T4 engine I would be over in performance and not here. I would be looking at gearing ratios on 914-4's, 411's and 412's - NOT buses. |
And Kent. The SCCA type 4´s (and super Vee´s for that matter) used a "toothless" fan, - meaning that every other or every third vane, I forget" was taken out in order to prevent the fan from exploding, but also to reduce drag and keep the fan effective at those rpms. One thing the 124 doesnt have to fight.
I agree that the 124´s were/are pretty efficient. I have worked with them too (not SCCA but similar) along with the other faster Italian brands. But the main reason to why the 124 and MGB´s are so relatively efficient in the FP is due to one little thing. - The rules. You can´t bring a 914 that much down in weight. That said the 124 was also laid out for more rpm off factory. That helps too. Porsche´s were almost never the fastest on the laps, but after 24 hours they were one of the few still standing.
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raygreenwood
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Joined: November 24, 2008
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Location: Oklahoma City
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| Posted: Mon Mar 27, 2023 7:54 pm Post subject: Re: type 4 fan peak airflow rpm |
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| Vanapplebomb wrote: |
| Very interesting. I wonder how much difference the early vs late fan shroud makes. The 80-83 shrouds had no ducts for heater boxes like the 68-79 shrouds did. I have always assumed this would help, but have never gotten my hands on the late shrouds, so I never found out. |
Going off memory so it may not be correct....but I think Jake mentioned that getting rid of the heater box feeds ....and plug the feed to the alternator were considerable improvements....mainly in static pressure.
nogoodwithusernames said:
| Quote: |
Ray,
Is there a diagram anywhere of where these holes were actually drilled? I've seen this mentioned before but never any actual information as to where/what size/how many holes.
In my Squareback with T4 I have HUGE running temp differences between around town and on the freeway. Nearly 200°. I think some of this is due the the turbulence and my thermocouple is on #3 spark plug so I would like to do some testing and see if I can bring that down at all. And obviously I am not concerned much for the around town driving as it is plenty cool already. |
No I do not remember that he posted a diagram or size. But, when I was drilling holes for testing, I was drilling 3/8" holes. I had one in the farthest back corner of the top sheet metal tin for 3/4 right before it turned downward io the crevice. I was trying to check the temp of the head fins there. I drilled one more about 2" further toward the case to try to check the cylinder fins.
Between those two 3/8" holes....I was plugging each after I used them.....with duct tape...but it came off on a drive....and I saw about a 50* drop in head temps on #3. I double taped it and repeated the route and the head temps went back up.
Ray |
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Abscate
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Joined: October 05, 2014
Posts: 22668
Location: NYC/Upstate/ROW
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| Posted: Tue Mar 28, 2023 2:36 am Post subject: Re: type 4 fan peak airflow rpm |
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| Abscate wrote: |
| Someone wrote a tome about this including stall speeds and the like. Maybe Robbie? |
Thanks for reminding us this was Jake Rabi, Ray. Apologies to Jake from me for the ghosting.
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oprn
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Joined: November 13, 2016
Posts: 12730
Location: Western Canada
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| Posted: Tue Mar 28, 2023 7:47 am Post subject: Re: type 4 fan peak airflow rpm |
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All interesting stuff, not often stock type 4 cooling systems are discussed!
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Wildthings
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Posts: 50351
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| Posted: Tue Mar 28, 2023 7:59 am Post subject: Re: type 4 fan peak airflow rpm |
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| Alstrup wrote: |
Care to elaborate on that? I have never noticed a difference. That doesnt mean it is not there. I have just not seen it. |
I don't have them in front of me to compare at this point in time, but should in a month or so. |
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oprn
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Location: Western Canada
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| Posted: Wed Mar 29, 2023 8:22 am Post subject: Re: type 4 fan peak airflow rpm |
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I just did some number crunching on a gear ratio calculator just to see how VW did the fan RPM vs highway speed thing in cars. Quite a variety I must say!
As Ray said the 412 at 3000 RPM is geared to do 60 mph.
There appears to be two final drive ratios for the 914... if I am reading the chart right that is. 4.428 and 3.857.
The 4.428 at 3000 RPM would be 72.5 mph (1.7L ?)
The 3.857 at 3000 RPM would be 83 mph (2.0L, or 914/6 ?)
The 412 is heavier and more dirty aerodynamically than the 914. My Buggy is lighter than the 914 but I suspect more drag than the 412. So perhaps I should be somewhere between the two... say 3000 RPM at 70 mph? That would not be much of a change over what I am running now. With the swing axle and tires I had I was running about 65 mph at 3000 RPM. Not sure if that small of a change will really effect anything.
Looks like 225 75 15, 235 70 15 or 245 65 15 would all get me there.
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raygreenwood
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Joined: November 24, 2008
Posts: 21519
Location: Oklahoma City
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| Posted: Wed Mar 29, 2023 2:33 pm Post subject: Re: type 4 fan peak airflow rpm |
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| oprn wrote: |
I just did some number crunching on a gear ratio calculator just to see how VW did the fan RPM vs highway speed thing in cars. Quite a variety I must say!
As Ray said the 412 at 3000 RPM is geared to do 60 mph.
There appears to be two final drive ratios for the 914... if I am reading the chart right that is. 4.428 and 3.857.
The 4.428 at 3000 RPM would be 72.5 mph (1.7L ?)
The 3.857 at 3000 RPM would be 83 mph (2.0L, or 914/6 ?)
The 412 is heavier and more dirty aerodynamically than the 914. My Buggy is lighter than the 914 but I suspect more drag than the 412. So perhaps I should be somewhere between the two... say 3000 RPM at 70 mph? That would not be much of a change over what I am running now. With the swing axle and tires I had I was running about 65 mph at 3000 RPM. Not sure if that small of a change will really effect anything.
Looks like 225 75 15, 235 70 15 or 245 65 15 would all get me there. |
This is interesting.....just to add a little more accuracy.....the 412 with manual trans is 2822 rpm at 60 mph and ~3200 at 70 mph. So 3000 rpm is about 65mph.
Weight wise....the 1973 Porsche 914 is ~2139 lbs (according to Excellence magazine). My two door coupe is ~2250 lbs. So I out weigh the 914 by 111 lbs. Yes my 412 has a bit more drag but mot much. Its a pretty sleek car....but its height makes it very susceptible to cross winds.
Yep....I think with good tire selection you will be at 3000 rpm at 65-ish.
The other interesting question of these fans.....do you choose the domed aerodynamic version with the spinner cap....or the flat faced version with teh notch to drive the air pump? 
No definitive testing to say which one makes more air....but I have driven both and the spinner version is more quiet. Also...in all theory.....the spinner version has more surface area on the fan floor and should produce higher air acceleration/velocity....but that does not definitively mean more cfm. Ray |
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Vanapplebomb
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Joined: November 03, 2010
Posts: 5412
Location: Holland, MI
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| Posted: Wed Mar 29, 2023 5:21 pm Post subject: Re: type 4 fan peak airflow rpm |
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I always liked the idea of the early fans, but don’t know how much different it really flows, if at all, from the later ones. Also, ever time I come across an early fan, it is missing the center cap. Just my luck I guess.
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1800 Type 4 Berrien 295
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Wildthings
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Joined: March 13, 2005
Posts: 50351
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| Posted: Wed Mar 29, 2023 5:33 pm Post subject: Re: type 4 fan peak airflow rpm |
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| I would suspect if there was much on any difference in the flow of early and late fans, VW would have gone back to the earlier fan when they ditched the air pump. |
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raygreenwood
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Joined: November 24, 2008
Posts: 21519
Location: Oklahoma City
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| Posted: Wed Mar 29, 2023 7:52 pm Post subject: Re: type 4 fan peak airflow rpm |
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| Wildthings wrote: |
| I would suspect if there was much on any difference in the flow of early and late fans, VW would have gone back to the earlier fan when they ditched the air pump. |
They kind of did. I will have to look back at my fan posts and see where the info is.....but the early fans all the way through 1.7L 412 had the spinner fan.
Then we saw a few only Cali cars with the air pump notch. Then for the first couple years of the bus ... non cali....they had spinners again. By that time it was pretty much all bus anyway.
Even if it was say.... 100 cfm difference....on a 412 with highway rpms down between 2800 and 3200.....the bus with its higher highway rpms would make up the difference anyway.
Ray |
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oprn
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Posts: 12730
Location: Western Canada
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| Posted: Thu Mar 30, 2023 6:47 am Post subject: Re: type 4 fan peak airflow rpm |
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It would be pretty easy to make a center spinner to stick on a later fan but I think the results might be more cosmetic than practical. I just might do it when I get spare time. My fan is in the open and visible.
About how long is the stock VW one?
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