912 Engine Makeover

[neilbardsley]

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.

Are you sold on twin spark Mark? I like the idea but once you drill the heads there is no going back and you have another set of wires and spark plugs pointing towards the ground to get dirt into? However, many John Benton etc love the extra power and better running you get from them.

[Kneeslider]

Reading all the comments with interest here.

My thing is engine tuning, specifically with motorcycle engines, more specifically Ducati 2 valve SOHC air cooled twins, but a lot of the skills learned here should be transferrable to Porsches.

Rule1 is normally make everything work as it should, as stock as possible. Because how can you know what effect the new shiny bits you have just bought have had, unless everything about your engine is performing optimally before you started?

Secondly, if you don't check your work, and this usually involves performance testing with a dyno, then how can you assume that it is perfect?

Most people are attracted to shiny things. Often some careful fitting and finishing will yield better results than the spending of £££ on a shiny thing.

My 900ss Ducati engine left the factory with about 75bhp, till the alternator nut worked loose on the crank at about 90mph, and trashed the sprag clutch and flywheel splines, so rebuild #1 saw the engine stripped down when I found a broken piston ring, so with the splines rewelded on the crank, and ground to size, a pair of new JE forged pistons from the USA cost less than a new ring set from Ducati.

By careful setting of the squish with plastiguages, cleaning up the ports, and setting the cam timing just so, with vernier pulleys, after a run in on the dyno it made 85bhp.

When the time comes with my SC motor, it will get the same sort of treatment. Just because the engine was made by Ducati, or Porsche, don't assume that it is as good as it could ever be out of the factory. All road engines are built to a price, and after measuring, a few extra % can usually be found quite easily, which normally improves both reliabilty and power and mpg.

[womble912]

Very valid points!

[neilbardsley]

Reading all the comments with interest here.

My thing is engine tuning, specifically with motorcycle engines, more specifically Ducati 2 valve SOHC air cooled twins, but a lot of the skills learned here should be transferrable to Porsches.

Rule1 is normally make everything work as it should, as stock as possible. Because how can you know what effect the new shiny bits you have just bought have had, unless everything about your engine is performing optimally before you started?

Secondly, if you don't check your work, and this usually involves performance testing with a dyno, then how can you assume that it is perfect?

Most people are attracted to shiny things. Often some careful fitting and finishing will yield better results than the spending of £££ on a shiny thing.

My 900ss Ducati engine left the factory with about 75bhp, till the alternator nut worked loose on the crank at about 90mph, and trashed the sprag clutch and flywheel splines, so rebuild #1 saw the engine stripped down when I found a broken piston ring, so with the splines rewelded on the crank, and ground to size, a pair of new JE forged pistons from the USA cost less than a new ring set from Ducati.

By careful setting of the squish with plastiguages, cleaning up the ports, and setting the cam timing just so, with vernier pulleys, after a run in on the dyno it made 85bhp.

When the time comes with my SC motor, it will get the same sort of treatment. Just because the engine was made by Ducati, or Porsche, don't assume that it is as good as it could ever be out of the factory. All road engines are built to a price, and after measuring, a few extra % can usually be found quite easily, which normally improves both reliabilty and power and mpg.

and this is the man for the job

http://wilshers-garages.com/contact.asp

He found an extra 20hp on Steve Wright's engine in about 90 mins!