best freeway flyer options on a budget? (1600 engine)

[1938vw]

hey guys winter is fast approaching so its time to get some major jobs done to the bug!
i have a 1973 bug with a 1600 engine, i have 195 65 15 tyres that are almost identical height and circumference to original 165 sr15, i want to stay with that profile preferably lower and a 1200 trans.
with this set up i'm running around 4000rpm @70mph and it feels like its screaming!!


so here's the question:

what are my options for dropping the rpm at cruising speed?

i wanted to get a gt box till one went on ebay for £600!

cheers guys, dangerous.

[Hotrodvw]

Personally I would do one of a couple things (options):

Berg 5 speed (not a budget minded mod, but can achieve what you're after if ratios are selected properly)

Simply change the R&P to get you closer to the desired mph/rpm.

I run a 4:12 r&p (Stock '67 type 1 ratios and box) in my '67 sedan, and tach 3k at 65mph. I personally am not a fan of fwy flyer trans set ups. People forget that there's a sweet spot for rpm vs. effective cooling. I believe for a 1600, the sweet spot is 3200-3500 rpm. I usually run 70mph, stock dia crank pulley and full tins for cooling. Dropping the rpm via tall 4th gear does a couple of things. It makes your engine work a bit harder to maintain the same given mph, and also the cooling fan now turns slower, thus making your harder working engine run hotter than it did before. Now, obvioulsy the r&p you select can effect this as well. If you had more than a 1600, this theory would be altered a bit. Simply my opinion, it makes sense to me and has served me well thus far.

[Marc]

...i have a 1973 bug with a 1600 engine...and a 1200 trans...

So, it's a swingaxle? I don't know what gearing that would have, probably 4.375:1 R&P and .88 4th - that'd be around 3625 RPM (not 4000) @70MPH with 195/65-15 tires. BTW, those tires are about 3% shorter than the original 165-15...a 205/65 would be closer.

If the car is a `73 1600, it should be IRS with a codeletter AT transaxle - 3.875:1 R&P and .93:1 4th. ~3395 RPM @70MPH with 195/65-15 tires.
Late Karmann-Ghia transmissions (codeletter AO) had the 3.875 R&P but a .88 4th - compared to the AT, that's a 5½% change in the right direction without any surgery. If you can find a good used one, that'd be the cheapest change you could make to an IRS car. Works out to ~3210 RPM @70MPH with 195/65-15 tires.

We never got swingaxle `Ghias in the US after 1968, but I've heard that there were late model swingaxle `Ghias in other markets which also had the taller gearing.

[1938vw]

Cheers for the input guys.
Yeah sorry guys it's a swing axel 1200 box in a 73 1200 car with a 1600.

I've had no issue with cooling in fact according to my oil temp gage it's not even getting up to optimal temps!!

Would it be possible to fit a different r&p in the existing box or is this almost impossible for an average joe?

[1938vw]

According to most places I've looked (3 seperatle sites) AO is a 4.125. I've found one of these for sale. Would it help?

[Bruce2]

According to most places I've looked (3 seperatle sites) AO is a 4.125.

Any gearbox you find with those two characters at the front of the trans code will 99.9% be NOT what you think it is. That's because it will be an A0##### code. If the trans you find is swing axle, it's NOT an AO code.

The ideal gearbox for your car is what came in a 1500 Beetle. You want a 4.12 R&P with stock gears. Taller than this is too much for a 1600. Contrary to popular belief, a GT 'box is not taller than a 1500 'box when you're on the motorway in 4th gear.

[Bruce2]

Would it be possible to fit a different r&p in the existing box or is this almost impossible for an average joe?

That is not an easy task for a novice. Special tools, know-how, and a selection of shims are needed.

[1938vw]

Cheers buddy.

What code would be on a 1500 then?

[Marc]

The aerodynamics of a Beetle set the practical limit for a Type I cooling system - IMO, you shouldn't ever go taller than about a 3.4 final ratio with stock diameter tires unless the cooling fan ratio is altered. Because the 195/65-15s are slightly smaller, ~3.4 should be completely safe.
The most common "Freeway Flyer" combination uses a 4.125:1 R&P and substitutes the Bus 4th gear with a .82:1 ratio for an overall ratio of 3.38:1 - virtually identical to the late `Ghia's 3.41:1, but peppier around town due to the 6% shorter R&P. The price you pay for that is a little less overlap between 3rd & 4th, which isn't likely to be a problem unless you're in mountainous country.


The following applies to US-market, IRS cars - can't say how much, if any, is relevant to UK/swingaxle.

"AH" denotes a 4.125 R&P; depending upon the year, it could have a .89:1 4th (coarse-tooth 3rd & 4th) or a .88:1 4th (fine-tooth 3rd & 4th).
"AT" is a 3.875 with .93:1 4th - overall ratio in 4th gear is 1.9% taller than an early AH, or .7% taller than a late AH, a barely discernible difference (but a difference nonetheless).
Karmann-Ghias received the 3.875:1 R&P before Beetles did, and their 4th gear remained .88:1 - that's a 7½% difference compared to an early AH (and a 6% difference compared to a late AH), enough to be significant. This is the codeletter "AO" trans - note that's A, letter O - NOT A, zero.

[1938vw]

Oh dear I'm VERY confused now. I preciate you help I just need a little time to understand your reply

[Marc]

Without spending money on internal surgery to change 4th gear, I see three options. A stock 1500 swingaxle trans will make all 4 gears 6% taller than what you have now.
If there are 1600 swingaxle transmissions where you live with gearing comparable to the IRS AT, one of those would make 1st/2nd/3rd 12% taller but gain little over a 1500 trans in 4th - not exactly what you're looking for, but the R&P (and possibly 1st gear, depending upon the year) are going to be stronger.
If there exists over there a 1600 swingaxle `Ghia trans with the 3.875/.88 gearing, that'd be a bolt-in resulting in 12% taller gearing than you have now - but the way to do it around here would be to find a double-sideplate AO trans (from a `70-`72 IRS `Ghia) and convert it to swingaxle.

[1938vw]

Thank you, that's a perfect explanation.

[Dougy Dee]

Why not get an AH IRS trans and switch it over to Swing?
Use the diff and sidecovers from your 1200 trans. Should be an 8 bolt diff but 6 bolt can be redrilled...

[1938vw]

Please tell me more that sounds interesting!!!
It's was mentioned before but I didn't really understand.

[Marc]

AH = 4.125:1 R&P IRS. Same codeletter was used from `69 through `72, but there are at least three internal configurations which all bear the "AH" designation. Only the late `72 (large cross-shaft, stronger 1st) is especially desirable IMO; `71/early`72 would be second, and `69/`70 all but pointless. `70 cases have the bosses cast in for the late TOB guide tube, so they can be updated to the late clutch/TOB arrangement with a little effort (requires installing the `71/early`72 cross-shaft, also)...but I'd still rather have the late `72.
Bruce2 suggested that you find a 1500 swingaxle trans (also the first option on my low-budget list) - that would have the same 4.125:1 R&P and (for all intents and purposes) 4th gear ratio as an AH, and would be ready to bolt into your car. Sorry, Dougy Dee, but there's nothing to gain here from starting with an AH IRS box, just the extra work/expense of converting from IRS to Swingaxle. If you started with an AO IRS box it'd be worth the trouble in order to get the taller gearing. Even an AT would offer the benefit of the stronger 1st gear, although cruising RPM in 4th wouldn't be much lower than with an AH or 1500 swingaxle box...and that was the initial goal as I recall.