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 Craig S
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 posted on September 12th, 2010 at 07:03 PM |
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The 5 speed overheating allegation
Around the traps I have heard some talk about the fact that aircooled VWs with 5 speeds can overheat. On the face of it, to a non-mechanical person
like me, this doesn't make sense. So I'd like to put forward why I think it doesn't make sense, and would then appreciate people's input as to
whether my thinking is right or wrong.
Please note that none of the engine speeds and such like here are meant to be real, but are just being used for the purposes of illustration.
Say I have a five speed that does the following speeds at the following rpm
4th gear @ 3,000rpm = 80km/h
4th gear @ 4,500rpm = 110km/h
5th gear @ 3,000rpm = 110km/h
According to some of what is said, the car may overheat in 5th, even though the engine rpm is much lower than it would be doing the same speed in
4th.
I have heard it said that it is because the fan is running slower, but surely this would mean that it is as likely to overheat doing 80km/h in 4th
because it is doing the same rpm. I would have thought if anything the engine would run slightly cooler because of the extra air flowing underneath
the car past the sump at the higher speed.
In terms of the engine working harder, certainly at a higher speed the car is doing more work in pushing air out of the way, but I would have thought
his was accounted for in the engine rpm.
I look forward to hearing your thoughts.
Cheers
Craig
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ibmoknegawsklov
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| posted on September 12th, 2010 at 07:15 PM |
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Due to torque multiplication with the lower 4th gear, effective engine load is less in 4th at 80kph than at 110kph in 5th.........not to mention
drag, it multiplies rapidly as speed increases. Now with a nice water cooled engine
your thermostat will keep your engine happily at correct temprature as long as your radiator cools eficiantly........A cylinder head temp gauge can be
a usefull addition for an air cooled motor if you want to be sure.
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 matberry
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| posted on September 12th, 2010 at 07:20 PM |
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A proper 5 speed conversion will give you closer ratios for a higher performance engine and 5th gear ratios will end up similar to what 4th gear was.
So in this case no probs.
But the cooling issue is valid, basically it will always require the same amount of energy (measured in Btu's) to push your car through the air at a
given speed, this energy cames from burning fuel, so at the same speed, it doesn't matter if it's a 1200cc stocker or a 2332 fire breather, the std
cooling should do the job. VW engineers designed the cooling system to function at a designed set of parameters, change these and things get
complicated. The way I see it, if you now lower the engine speed, the engines ability to make the same power changes as we may (for example) fall
below the power output of the engine that is required for that speed, also the cooling fan speed is reduced thus giving us a situation where the
engine is working harder but getting cooled less.....I think that makes sense  .
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pete wood
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| posted on September 12th, 2010 at 07:39 PM |
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there's a big write up on the Gene Berg website that covers this.
http://www.geneberg.com/cat.php?cPath=13_387
btw, matt, would a good oil cooling system be a way to sidestep this a little?
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Barnabie
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| posted on September 12th, 2010 at 07:40 PM |
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Thanks Matt, its not my thread, but that certainly answers questions I had 
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Craig S
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| posted on September 12th, 2010 at 07:46 PM |
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Fair enough, I think I sorta kinda understand, in my own simple way.
Essentially what you're saying then is that a water cooled engine would also be producing more heat in the same circumstances (i.e. 5th at 110km/h),
but the cooling system would step up to the job either through the fans coming on or due to the greater air flow through the radiator (by achieving
greater heat reduction), or a mixture of both.
Would I therefore be correct in suggesting that this is actually a shortcoming of the aircooled concept (if you consider having lower rpms at higher
speeds to be desireable (e.g. for noise, engine wear and fuel economy))? Or have I misunderstood and I'm wide of the mark 
Thanks for the replies.
1969 Beetle - June
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matberry
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| posted on September 12th, 2010 at 07:51 PM |
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Not in my opinion Pete, oil is aour secondary cooling, air is primary. A bigger oil cooler would help reduce the oil temp, but the problem would be
the actual heads, bigger fins (ie more cooling area) and/or more air would help but it's beyond me to advise on this one . Heaps of r&d required I'd say.
Matt Berry Motorsports...air cooled advice, repairs and mods Ph 0408 704 662
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Joel
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| posted on September 12th, 2010 at 08:09 PM |
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Agree with Matt, the oil temp can be as low u want but it wont effect head temp much, and head temp is what comes up when the engines under load
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bajachris88
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| posted on September 13th, 2010 at 08:33 AM |
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If you worried about fan speeds being slower... retrofit a smaller generator pulley to speed it up. Type 3 style tinwear under the cooling fins is
suppose to help markedly.
Perhaps due to lack of availability of stock belt drive setups, you might want to do a synchronous belt conversion and seam weld the vanes of the
fan.
The key way setup on the generator looks very similar to those of timing belt pulleys form your average toyota style DOHC engine. (i will check at
home for you).
and you can get vw pulleys that will bolt straight on the crank that are synchronous.
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ian.mezz
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| posted on September 13th, 2010 at 09:37 AM |
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If you want a 5 speed that runs good by a Hyundai
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Joel
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| posted on September 13th, 2010 at 09:46 AM |
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| Quote: | Originally
posted by bajachris88
Type 3 style tinwear under the cooling fins is suppose to help markedly.
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That ones an interwebz myth, and completely untrue
"cooltins" are for type3 pancake motors only and dont work properly on upright
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matberry
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| posted on September 13th, 2010 at 12:44 PM |
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| Quote: | Originally
posted by Joel
| Quote: | Originally
posted by bajachris88
Type 3 style tinwear under the cooling fins is suppose to help markedly.
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That ones an interwebz myth, and completely untrue
"cooltins" are for type3 pancake motors only and dont work properly on upright
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x2
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dangerous
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| posted on September 13th, 2010 at 01:10 PM |
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Daimo found his ran cooler and got better economy.
And that was with a 0.82 fifth and 3.88.(way taller than the stock L-Bug 0.93)
I agree though that if you went too far, there may be issues.
I thought Daimos was going to be too tall, but he said it is great.
Mind you it has twice the stock power too.
| Quote: | Originally
posted by westi
That's mad Alan.
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Joel
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| posted on September 13th, 2010 at 01:21 PM |
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After going for a spin in Daimos old bug last year, I gotta say that tranny is geared to perfection but Like Dave said his engine has the torque to
use it
expecting a stockish motor to run with the same setup would be kicking sqaure in the balls
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Phil74Camper
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| posted on September 13th, 2010 at 02:12 PM |
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| Quote: | Originally
posted by ian.mezz
If you want a 5 speed that runs good by a Hyundai
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You're kidding Ian. Do you wave at all the 5-speed VW Golfs that overtake you? What about the later 6-speed Golfs? Or the ones with the 7-speed
DSG?
I think this one is a myth. Following their train of thought - you put in a taller 5th gear. The engine is turning slower at the same speed. Therefore
the fan is turning slower too. Therefore the engine overheats!
What they forget is that the engine turning more slowly is doing less work. It's burning less fuel, both per distance and per time, so it isn't
making as much heat. VW engines produce their best torque at lower RPMs anyway. Think about it - imagine a stock Beetle travelling at say 80 km/h in
3rd. Leave it in third for 15 min. How hot does it get? Now shift to fourth. Same road speed, and now the fan is turning slower. But does it run
hotter still? Of course not.
The air-cooled VW/Porsche 914 came with a 5-speed as standard. VW/Porsche Austria used this gearbox in their rally Superbugs in the early 1970s.
http://www.rallybugs.com/
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dogo
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| posted on September 13th, 2010 at 02:29 PM |
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BOLLOCKS! Aircooled VW's have a 5th gear as standard but they call it 4th! Yes thats right, 4th gear is an overdrive. A taller final drive ratio
(diff) or taller tyres would create the same situation if it were true.
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hellbugged
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| posted on September 13th, 2010 at 02:40 PM |
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oh dear 
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Phil74Camper
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| posted on September 13th, 2010 at 02:45 PM |
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The fact that a Beetle's 4th gear is an overdrive is irrelevant. What has the ratio got to go with the number of speeds?? Anyway, it's only an
'overdrive' into the diff. To the wheels, you then multiply by the diff ratio. I suppose you know for example that the auto Kombi's 3rd (top) gear
is EXACTLY 1:1. So how many speeds does it have?
You can easily build a Rally Beetle 914 gearbox with all 5 gears above 1:1 - all close ratio speeds and NO overdrive. By your logic it isn't a
5-speed!
However you are right, you CAN create the same cooler situation at highway speeds with a taller diff, or taller tyres. VW did exactly that with their
diff ratio, which got taller over the years. Make the engine turn slower at a given speed and it runs cooler, not hotter.
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matberry
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| posted on September 13th, 2010 at 02:54 PM |
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Matt Berry Motorsports...air cooled advice, repairs and mods Ph 0408 704 662
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hellbugged
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| posted on September 13th, 2010 at 07:01 PM |
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so all modern cars are geared to do cruising speed just above idle .........or is this debate about wether it's possible to OVER GEAR a vehicle reguardless of wether it has 3, 4, 5, 6 or even 36 forward speeds
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vlad01
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| posted on September 13th, 2010 at 07:04 PM |
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| Quote: | Originally
posted by pete wood
there's a big write up on the Gene Berg website that covers this.
http://www.geneberg.com/cat.php?cPath=13_387
btw, matt, would a good oil cooling system be a way to sidestep this a little?
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dam you bet me to it
yes a higher ratio final drive will make a 5 speed practical as 5 is the new 4 and 4 is the new 3.5 lol
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vlad01
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| posted on September 13th, 2010 at 07:11 PM |
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| Quote: | Originally
posted by hellbugged
so all modern cars are geared to do cruising speed just above idle
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Are you a vw person?
cars now are water pumpers and collect air into the rad by speeding through the air. Engine rpm is irrelevant in this instance.
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pete wood
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| posted on September 13th, 2010 at 09:00 PM |
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Vlad, do you realize who you are talking to? You might end up looking a little silly.
Daimo knows his stuff.
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matberry
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| posted on September 13th, 2010 at 09:19 PM |
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Well......Daimo.........Are you a VW person???
Matt Berry Motorsports...air cooled advice, repairs and mods Ph 0408 704 662
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Joel
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| posted on September 13th, 2010 at 09:28 PM |
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Priceless
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hellbugged
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| posted on September 13th, 2010 at 09:34 PM |
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 .......a very embarrased one now
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Keith Haeusler
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| posted on September 14th, 2010 at 12:42 AM |
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Hi all,
This is my real life experience with taller top gear in a bug. In the early 90`s good mate had 68 bug, 2165cc,8.6:1 ida etc. Ran awesome. Never over
heated oil or heads.
Changed to irs, stock L box, still good albeit lost a little bit of zippy-ness. Broke box, fitted .82 top with 3.88. Engine always ran hot in 4th gear
and felt lazy.
Swap back to .93 top and problem went away.
I think the VW engineers knew what the score was.
Again, this is just what we found with this combo.
Regards, Keith
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vlad01
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| posted on September 14th, 2010 at 07:53 AM |
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yes that about right.
71 notchback,
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Sides
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| posted on September 14th, 2010 at 09:40 AM |
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| Quote: | Originally
posted by hellbugged
.......a very embarrased one now
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Awww... someone's made Daimo blush !!!
Gotta say tho that the last few posts of this thread are gold...
As most everything else, it's all about the combo... VW stuffed around with gear ratios constantly, but they were all relatively minor changes... and
the revs in top gear never dropped a huge amount... presumably to keep it all balanced.
If I was going to build a 5 speed, I think I'd be keeping 5th fairly close to a stock L box (say 0.85 - 0.90 x 3.88) and then spacing all the others
to get a close ratio box that was still happy on the freeway. More fun, but still practical.
Daimo I know put a lot of thought into selecting his ratios, and all of that was AFTER he knew exactly how his engine behaved in the real world... and
yeah, he came up with what looks to be a bl@@dy good result.
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ttriebler
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| posted on September 14th, 2010 at 10:06 AM |
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Hey interesting discussion on final drive ratio guys.
I am about to start testing (and later on marketing) Subie 5 speeds for aircooled motors (fitted with my adaptor plate and flywheel combo to suit.)
I will most likely have to get a combination of gears and final drive ratios together that is 'one size fits all' for most aircooled customers
wanting to fit a 5 speed.
Given that most of these would be fairly hypo 2 litre motors with either BIG cams and twin carbs or a turbo kit, what are the thoughts about getting
the gearing where it needs to sit? Or is having a 'one size fits all' the impossible dream.....
Was thinking :
3.083 1st gear, 2.062 2nd gear, 1.545 3rd gear, 1.151 4th gear, 0.825 5th gear.
Final drive choice of 3.9, 4.1 or 4.4 ( I'm suggesting 3.9)
Other 5th gears available are : 0.972, 0.738, 0.78, 0.871.
Helical LSD
Reversed gears for Subaru transmissions.
Fit a Subaru 5 speed to your rear engined car
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