Proper cruising RPM.

[Skulptorchaz]

We had the buggy out yesterday for a GLORIOUS (but a bit wet at one point) ride. Man, I love this thing!!!!
Anyway, something came up that I wanted to throw out there. If I cruise at 60 mph, my temp holds good at about 220. Any higher than that, and it starts to climb. The rpms at 60 mph is 2400. Is there a correlation between rpm and mph that I can change to get a higher cruising speed or is it, what I have been told, a negative pressure that occurs going down the highway??
Thanks guys.

[Letterman7]

Wow... you're rpm's seem to be way down at that speed. Do you have a regeared transmission? Even with my "freeway flyer" (Superbeetle trans), I was turning around 3200 at 60mph. It sounds like you're pushing your envelope with the gearing.

[Dale M.]

Hmmm... My cruse speed at about 60 mph is just about 2900-3000rpm...

Dale
_________________
“Fear The Government That Wants To Take Your Guns" - Thomas Jefferson.

"Kellison Sand Piper Roadster" For Street & Show.
"Joe Pody Sandrover" Buggy with 2180 for Autocross (Sold)
============================================================
All suggestions and advice are purely my own opinion. You are free to ignore them if you wish ...

[Skulptorchaz]

Dang. I'm not sure what I can tell ya. I'm running 15 " wheels with T/A radials. 275/60's rears and 235/60's fronts. The speedo is pretty close - at least checking it against a buddy driving next to me. (I will confirm that.) And the trany is a Ghia IRS - AN 25 05 3.
The engine is a 1915 with SCAT Cam 20006 (C45, 298, 262) and seems to pull it along just fine.
I guess I just need to make sure of the MPH but, I think it is real close. Does this rpm to mph sound like my issue with the "heating"?
Thank for the help!

[clonebug]

Are you talking head temps or oil temps...????

I have 275/60-15 tires with 4.12 gearing and turn 3100 at 70 mph
It's about 2750 at 60 mph if I remember correctly...
If your oil temps are that high then you probably need to look at the cooling system instead of rpm and load.
_________________

[VOLKSWAGNUT]

60mph
2400 rpm
Approx Tire diameter 28 inches (275/60/15)



That sounds like it could be a .82 4th and a 4.125 ring and pinion??
By the math... that puts it in the correct RPM range for those combined tire size, final drive and 4th ratios (2435 RPM's )

or the tach is jacked up.. ..

Check the trans code..
It may be spot on for its configuration.


Note: A TRUE Freeway Flyer has a .82 and 3.875 ring and pinion..

If it has a true flyer ... at 60mph with Approx Tire diameter of 28 inches (275/60/15)
Engine RPM's would be lower and around 2300. (2280 Rpm's )

If the tach is off 100 rpms.. it will be a hard to distinguish which combinations it has.. ..



.
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aka Ken {o\!/o}
Its your vehicle- stop askin' for approval-do what YOU like for cryin' out loud
Better to roll em' how you want and wear em' out-than lettin' em' rot out
Its about the going not the showing
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[Skulptorchaz]

Oil temps. My sending unit is at the bottom of the case under the distributor.

[Skulptorchaz]

From this site -
http://www.volksworld.com/tech-guides/technical-information/volkswagen-gearbox-codes-9444 -
it looks like a 3.88. So it would be a Freeway Flyer.
But is that my problem?? I'd like to "stretch it's legs" a bit more on the freeway but she starts getting warm (oil temp).

I'm very interested in the philosophy that there is "negative pressure" causing it. I believe I can cure that - or at least I can try some things.
Thoughts??

[VOLKSWAGNUT]

Without X ray vision.. it's simple math and an educated guess as to what the ratio's are inside.. The case number prefix AN is only an ID at this point.
The RPM's are too low for a stock gear box.

The RPM's are within acceptable range of a True freeway flyer with the tire size it has..... as suspected... yes.. check... ...

So the story comes out.. the issue isnt cruse RPM... its oil temperatures... hmmm sounds familiar.


There is so much more to this equation that could be the cause.

Stock size pulleys?

What is the oil cooler setup?
Offset Dog house?
VW fan shroud or some aftermarket junk?
What oil viscosity and type ?

Oil temp climbs?
To what?

How new/fresh is the engine?

Over 235 is where most advise to start to back down...

[vwracerdave]

Let me start by saying there is no such thing as a "Freeway Flyer" transaxle. VW never gave a name to any transaxle. The term was used in flashy magazine ads by a company went bankrupt, and it has no official meaning of any gear ratios. There is also no such thing as a "Super Beetle" transaxle.

AN code Ghia transaxles came with a 3.88 R&P and a .89 4th gear.

Normal cruising speeds for a VW are 3000-3500 RPM's. 220* oil temps are not too hot to be concerned with. There can not be any negative pressure on a Dunebuggy with an exposed engine. It only happens on vehicle with enclosed engine compartments.

If you want to experiment put the 235's on the rear and some stock rims up front and see what happens.
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2010 Sportsman ET Champion - Mid-America Dragway - Arkansas City, KS
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Featured in Dec. 2001 HOT VW's Magazine page 63

Watch my racing video's http://www.youtube.com/user/okvwracer/videos

[VOLKSWAGNUT]

[Skulptorchaz]

I never knew the term "freeway flyer" to be any more specific than just a high geared drive train, in any car, that goes down the freeway at low rpm. As opposed to a 1/4 miler that has a low gear drive train. It's used that way all the time in the Hot Rod and drag world. I don't think there is any need to worry about semantics here.
The transaxle is stock geared.
In answer to other questions,
Pulleys are stock (size)
Stock oil cooler, dog house and fan shroud other than cleaned up and powder coated.
Oil is 10-30 Brad Penn.
Engine has about 4000, or so, miles on it.

But the interesting part is that at 60 mph, she runs between maybe 210 and 220, beautifully. Then, if i pick it up to 65 mph, she immediately starts to climb. How far?? Sorry, I don't want to find out the hard way but, yeah, I have seen 235 or more.
It just seems like something happens at 60 mph. That is why I thought it made sense that at that speed a negative pressure could occur. But hell, I don't know. That is why I am asking. I have been playing and building cars and bikes since I was 16 (40 years ago) but VW's are a bit of a new creature for me. And I know "air" can do some strange things.

Thank you all for your input and any more that you care to share!!!!!! The reason I am concerned about this is because not only do i try to drive this everyday that is humanly possible (Yeah, I am THAT bitten!) but, I am looking at "possibly" driving it to So. Cal. (my old stomping grounds) either next year or the year after. I will post more questions about tips and tricks of doing that in the future but, for now, I'd like to get a bit more freeway speed. It will help me on my trips to the city's (Indy and Cincy) and for sure when I make the trek out west. OH, and the St.Louis run!
Thanks again!!!!!!!!!!!

[VOLKSWAGNUT]

Still more to consider...


In reality.... the VW air cooled engine has 2 cooling systems..
Oil and Air.. but yes... both requiring air.. so I understand the air flow question.

Your body configuration is a wide open air engine typical Buggy then, (orange one in your Gallery?) I doubt its an aero issue..

What is the oil pressure?
Does it happen to have any oil pressure boost springs or fairly high oil pressure?
Large pump?

If the oil pressure main relief spring keeps oil pressure too high.. the oil will continue to be dumped back to the sump and will bypass the cooler too long building heat.
The oil cooling system is designed so that when the oil pressure is LOWER than relief valve spring.. it is then routed to the cooler (as well as the bearings).
Too high oil pressure and the relief valve just dumps and dumps bypassing the cooler.
Path of least resistance prevails as always.. ..

Bypassing can be found sometimes by simply feeling (or IR Thermo) the cooler.. if its cooler than expected and the oil is hot.. the oil is bypassing the cooler.

Better in depth explanation and oil flow and data is here.. http://www.thesamba.com/vw/forum/viewtopic.php?t=280293

No pressure boost springs..???
Believe it or not.. it may be as simple as using 5w30 or lighter oil instead..


Carbueration?
Distributor?
Timing?
Fuel used?

^ Most of those effect head temps first... but the oil also picks up some heat from the heads .. so cant rule them out as well.



.
_________________
aka Ken {o\!/o}
Its your vehicle- stop askin' for approval-do what YOU like for cryin' out loud
Better to roll em' how you want and wear em' out-than lettin' em' rot out
Its about the going not the showing
Rebuilt to drive not decorate
WANTED: Local Eatin' Joints, Triple D for TheSamba contributions here http://www.thesamba.com/vw/forum/viewtopic.php?t=570510
Search "VOLKSWAGNUT" on YouTube since you cant watch a "certain" BELT change video round here
Usually and often edited

[Skulptorchaz]

Thanks NUT! I am aware of these things but I doubt they have much to do with the significance of exactly when and how it heats up. It is very distinctive. Anything above 60 and she takes off.
Timing I can re-check but was set by my VW guru. It's a 009.
Dual 40 HPMX EMPI Carbs
Best fuel I can get - at the pump. Aviation fuel is bit too costly for my road vehicles. Carbs have been set up with synchrometer and plugs burn a little rich (black).
Oil pressure is 20 going down the highway. Don't know about boost springs.
I have an IR Thermo. I can check that. It seems plausible if at that rpm/speed that if the oil was "dumping" it could allow it to heat up. (???) But "something" after 60 mph happens to allow it to heat up. I will check your link but, it would be tough to check the cooler with the IR going down the road. lol
Thanks for the help and ideas!!

[VOLKSWAGNUT]

Is the doghouse cooler sealed and any hot air flowing properly away from the fan?
Hoover bit added?

It also seems you have an altered fan shroud just verify it's a real genuine VW shroud?
Lots of shrouds out there with no vanes..

Im still leaning on the cooler bypass so be sure to read up on it..

[wythac]

Try a shorter fan/gen belt on your engine. I think you can run 1/2' to 1" shorter and still use the stock pulley set up. This will push more air thru the tin as it increases fan speed.

Stock thermostat set ups help with cooling and timely warm ups too.

Keep in mind that stock VWs had a much more restricted path for the air to find the fan inlet. I have a battery access "door" in my package tray deck and when I have driven the car with that off, the airflow from that spot just in front of the fan inlet is POSITIVE...that is, it flows from the engine area into the cabin. Now all I can really deduce from that is that the pressure in the cabin area is less than the pressure in the engine area, but it gives you the basic idea that pressure is higher in that more confined space behind your rear firewall.

When it is hot, or steep, or both, the right foot works well as a thermostat on my car.

Keep driving it, you'll figure it out. With only 4K on it, you might also be having a little extra break in heat to contend with.

[wythac]

One other thought, if you reeeallly want to confirm or disprove a theory about fan intake pressure values at a given speed:

Attach a GoPro looking at the fan inlet. Tape or glue some (short) strings near the inlet. Set the GoPro to record, setting a timer on your smart phone at the same time.

Drive, using graduated speeds over time to achieve the temp values you are worried about, noting the time on your phone when each temperature value occurs.

Stop the car, stop recording, stop the timer on your phone. Then when you look at the video, compare what you see the strings doing near the fan intake at each speed/temp value you noted on your phone.

A lotta work, but no guesswork or speculation, which is the arena you are playing in now.

[vwracerdave]

You have a gearing problem. With a 3.875 R&P gear and the .89 - 4th gear running 28" tires the engine is working too hard above 60 MPH and causing the temps to go up.

You may also be over cam'd with the SCAT C45 (20006) What are all the engine specs? Tell me everything you know about the heads.
_________________
2017 Street Comp Champion - Thunder Valley Raceway Park - Noble, OK
2010 Sportsman ET Champion - Mid-America Dragway - Arkansas City, KS
1997 Sportsman ET Champion - Thunder Valley Raceway Park - Noble ,OK
Featured in Dec. 2001 HOT VW's Magazine page 63

Watch my racing video's http://www.youtube.com/user/okvwracer/videos

[slalombuggy]

I can tell you first hand, it is not an air flow problem. I'm with Dave in his diagnosis. Your gearing and tall tires is the problem. The engine isn't turning fast enough to cool the motor and when you try to go faster the engine is working hard and can't get enough air to cool it.

I have a 3.88/.82 transaxle in my Beetle with 26" tires and no problems. I had the same setup in my buggy and no issues at all.

brad

[VOLKSWAGNUT]

I do understand the whole lugging with tall gearing.. and load issues.. on stock and under powered engines...
I dont know if that's an issue with this combination.
..
The buggy is lighter, the 1915 is stronger.. I don't think it would be struggling to push it along..

I do agree at 2400 rpm's at 60 the fan speed is about 300-400 rpms lower than it normally would be...with stock Ghia size tires.
But as speed increases, fan speed increases... .. but then again.. so does the aero load..

A quick test to prove or disprove that...... is as Dave recommended..