davePorsche

Hi All,

curious, if you found a car with a rebuilt 912 with 1750 cylinders and a larger header.. what type of HP would you expect to get above a stock setup ?

and as a bonus question....

For doing vintage racing how much HP do you need in a 912 to not just look silly...

David

Mr Michael B

My 1750 with Weber 40's & aftermarket pipe is 111 HP on the chassis dyno. Accounting for drivetrain loss that works out to approx 130 at the crank.

How much HP do you need not to look silly? Well I race a Spec Miata with similar HP to my 912. It turns better laps then Lambos, Ferraris Vipers and many more. I have a pal who races a Fiat 500 with a 650cc two cylinder. Its fast - with him driving.

Moral of the story = Its not the HP, its the momentum. You wont look silly if you drive the damn thing. Floor it and throw out the brake pedal (its just added weight).

davePorsche

Thank you for the information MB !

The vintage racing rule book is a bit daunting for a newby..

I think the advice i need is a list of the minimum amount of things to do to a 912 to start the training and get into it.. (I drove a scca ITA class years ago - VW GTI) so i know a bit about driving but not a 912 and not vintage..

my goal is to do some DE's this year and maybe do some additional training while i get the car sorted and maybe try for a racing license in 2014..

Thoughts on things to do or not do to the 912 ? advice on sites that might have suggestions ?

Right now the car is pretty much stock with a recent rebuild on the engine and brakes ..

Mr Michael B

You know what they say...

Its more fun to drive a low power car quickly then a high power car slowly.

Things to do? Well your in luck. The 912 is nearly a perfect balance of power, brakes & handling right out of the box. They are a very good match for a vintage racer, as they are reliable, fun to drive & have a super respected shape & lineage.

Bolt on a set of six inch wide rims, some Hoosiers, high performance brake pads, unload any extras that may be considered a weight penalty, lower the ride height and off you go. With a 1750 you may dominate the small bore class.

As far as other 912 sites, pelican has a good following, as does 912bbs.org. But for vintage racing I would stay focused on sites for the vintage racer w/ any style of vehicle.

GTgears

If your 912 is a 4spd (many were) you will want to convert it to a 5spd, which is fairly straight forward.

Early 5spd aluminum case 901s will generally be geared AFMSX, which is acceptable, but not optimized for the track. If you can find a '69 only 912 gearbox it will have a shorter 6:29 ring and pinion and a better individual gear stack. It is very well suited to the 912's powerband. The downside is the 6:29 is non-standard in size and if you later wanted to add an LSD or TBD to it, you can't. You are stuck with an open diff. and on a Porsche an LSD is good for seconds (pl) a lap.

Many people will stick with the stock 7:31 ring and pinion for that reason and then build a new gearstack, often putting S in 5th position since that's about the top speed you will hit if you have a slightly raised rev limiter when you build your motor. If you don't raise your redline, then you will be looking for more something like a T or a U 5th, both of which have become slightly rare.

I'll leave it at that for now. Obviously, I could ramble on regarding gearing and the time to be gained in working with the gearbox, but am not going to smother you in the stuff as you are just starting to look at it all and think about it. Plus, depending on class, you may only be allowed to run the AFMSX ratios and then your only upgrade option to get more time would be the LSD.

jcslocum

MB, thanks for posting this info. I have a 66 912 that I'm looking to upgrade to 1720 and was hoping it would make a decent diff. I plan on running a rebult set of Solex split shaft carbs instead of the Webers.

What compression ratio is your motor at?? I plan to be only street driving it with maybe 1 DE a year with my daughter.

Mr Michael B

The 1750 P/C kit (86mm is called 1720/1750) listed it as 8.5:1, but when all was said & done with machine work etc it was rated at 9.0:1. This build was a real anomaly. Its super strong (built it 15 years ago). That is almost enough compression to blow the spark out, so you will want at the least a Bosch blue coil if not an upgrade from that. You go too far with spark & you will have to run a colder plug. Head temps are known to be high on big-bore motors but the 1750 is really tame. I had a 1915 (69mm stock stroke x 94mm cylinder bore) too and even it ran pretty cool but was not a barn burner power wise. Best to date? 2110 with Dellardos - felt like a V8!

raspritz

I am not sure that six-inch rims are legal for vintage racing a 912; check your eligibility rules. In any case, at the moment Hoosier has long-term backordered their Vintage tires that fit 912 rims, so you may need to find something close and petition your vintage racing organization for special rules dispensation before you buy.

butzip

I would upgrade to a full flow oil system and CD ignition. Makes for much more consistent running/tuning

MemoryLane

You wont look silly if you drive the damn thing.




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