912 Engine Makeover

[womble912]

Dear Friends,

I need some advice and your thoughts about undertaking some work to my 912 stock matching numbers car. I'd like a little bit more vroom so was thinking of having a big bore upgrade to 1720cc with new carbs and exhaust. This is costly but should give me 120-130BHP and new internal parts. The other option is having Carbs rebuilt and new exhaust. I have been doing some research and there is no guarantee the Solex's would work at 100% effeciency and the cost of refurb and new Webers is marginal. I must add the car runs very well and has been to Le Mans this year without any issues.

I would welcome your thoughts.

regards

Maz

[tjbates]

Maz,

I just upgraded my 912 to 1720cc and there is a definite improvement in performance (difficult to say whether this is due to the rebuild or not thou). From the research that I have done for my car, i elected to rebuild and clean my Solex carbs, as long as there are not worn out they won't need an expensive refurbish.

Have you got a copy of Duane Spencers book, The Complete Porsche 912 Guide? It has a lot about upgrading the engine and what I gleaned from reading was in order to get the 120-130HP you're looking for you will need to change the cam as well as the 1720cc upgrade and you'll need to get everything perfectly balanced (crank, rods, flywheel, heads, etc.) so that all the energy is honed to the wheels

If you have not got a copy of Duanes book it's well worth finding, buying and reading it before you begin work.

Hope this helps.

[womble912]

Hi,

Yes, I do have a copy and will read it again. Your advice is much appreciated.

M

[Timo]

Yep, I'd agree with tj, a 1720 big bore kit will likely add about 10 bhp and 10 ft ibs of torque to the factory output of 90bhp/90ft ibs so you should end up around the 100 bhp mark (mine produced 99 bhp when I had it rolling roaded) To get 120-130bhp you will definately need to fit a higher lift cam.

[womble912]

Thank u

I am getting a higher cam fitted.

[Timo]

Good stuff, you'll have to let us know how it compares to a stock setup once you've got it all up and running.

Have you decided which cam you're going for yet? Also make sure you get check your piston crown to valve clearances, 912s run pretty close here with a stock setup but when you add a higher lift cam you may need to provide additional clearance.

[neilbardsley]

Looks like Sanjay, and I, didn't talk you out of rebuilding your engine at the Christmas dinner

I think you need to have this discussion with the engine builder but getting more HP from a 912 engine can be a slippery slope. Once you decide to get a new cam then should you replace the rod and crank for the additional forces involved? Will you look at a full flow filter to look after the new engine?

Have a look at Steve Wrights 356 race car thread where they had been racing for the race for about 1.5 seasons then they found an extra 30+ hp (Sorry I can't remember the amount) on the rolling road by changing the input manifolds. This would suggest to me that before rebuilding the engine best bang for your buck is a couple of hours spend on a rolling road? You might just find another 10/20hp for a fraction of the cost of an engine rebuild.

[womble912]

Thank you Neil will investigate.

[silverfox]

I'm watching this knowing that it's getting close to decision time for my poor 912 engine. I am thinking about mothballing and transplanting a Type 4 that has had a bit of money and love thrown at it. Any experience on what involved?
Paul

[Timo]

Have a look at Steve Wrights 356 race car thread where they had been racing for the race for about 1.5 seasons then they found an extra 30+ hp (Sorry I can't remember the amount) on the rolling road by changing the input manifolds. This would suggest to me that before rebuilding the engine best bang for your buck is a couple of hours spend on a rolling road? You might just find another 10/20hp for a fraction of the cost of an engine rebuild.

That's very good advise Neil, I had a very similar experience with my car which prior to my ownership had been serviced by "porsche professionals". After purchasing it I drove it around for a while and all seemed fine but I couldn't help thinking it should have a bit more get up and go than it had. After inspection it turned out the weber carbs were jetted completely incorrectly. I took a trip to my local rolling road which revealed that there were timing issues too, after quite a bit of fettling they managed to find in the region of 30 bhp! (70 ish bhp when I arrived, 99 bhp when I left) The difference between the before and after was like night and day and the car now drives superbly. I can't recommend a decent rolling road setup enough. Of course if your engine is on its way out a rolling road session could be the final nail in its coffin!

[womble912]

Dear All

Decision made engine rebuild with big bore and new cams and carbs.

Maz

[neilbardsley]

Maz how about some pictures and updates?

[womble912]

Hi Amigos,

CT has the engine out and is currently getting external parts powder coated. FLM have refurbished the Solex's they look a treat! Parts from Neutek are here so hopefully mid May completion. I will post some pics if someone can advise on how to? Oh one other small item the wheels are being sent away to exelwheels to be chromed.

[neilbardsley]

Are you chroming or chrome painting the wheels? I need to do something about mine

[912uk]

Arrrr the engine talk.

Apart from the fact I've forgotten almost all the good stuff, the need to change rods and crank really only comes into play once you pass the 125-130 bhp era.

1720 shasta , newtec cam , reground crank , rod bearings, exhaust general rebuild with head work and balancing done right should see 115-122 bhp a very well set up car should get 125-128 once run in.

A number of people spoke about cars getting 130 after a build as like a given but I didn't see that, the most I knew about was 155-160 bhp from Stuarts race car it ran a competion cam and was in for rebuild after a one season of racing. A complete pig of a car to drive in traffic due to the cam. Made worse by the fly wheel.

To get 115bhp for an all round nice driving car with more poke. Would be a more sensible goal. This will also give an engine that is reliable as well. I'm sure Mike would back these

I was, before my er lack of interest. Heading for the mother of all 912 engine rebuilds. 1720 twin spark with carello rods and billet crank I have every thing apart from the crank at the moment.