911SC Mods/Engine Rebuild

[bones]

You can't build a hot Porsche engine on a budget but if you have to go to the expense of buying all new pistons and cylinders then go 3.2. This displacement coupled with HEs and a Triad exahaust will give you a substantial power increase with no other mods apart from resetting the fuel mixture. Read Bruce Anderson and Wayne Dempsey's books.

 

[bruceb]

SobeUK

I would take a second opinion on those two damaged barrels. When my SC engine was rebuilt the barrels were machined shorter by 0.5mm to increase the compression ratio.

Its very likely that the two damaged barrels could be salvaged if the decison was made to machine all six barrels. Speak to an engine builder who knows these porsche engines, Bob Watson did my rebuild work mine.

BTW my engine ended up at 235 bhp with just barrel machining, special 3 angle valve job and a custom pair of reprofiled 964 cams. All good whilst you in there upgrades.

 

[Guest]

Bruce

Thanks for your thoughts. At last I have successfully negotiated the purchase of two cylinders and piston sets. I looked at going 3.2, however when I saw the list of other mods that would be required to convert properly decided to either remain at 3.0 or use the Big Bore Max Moritz from Mahle in the USA. After successfully negotiating to buy the cylinders separately decided it is better to remain at 3.0.

With this all six cylinders will be machined down to ensure they are all equal. So at last we are moving forward.

I'll speak with the machine shop again on the cams point, as I was told the 964 cams are not a straight swap. Did you need to do any mods for the 964 cam to work correctly?

Cheers[8D]

 

[bruceb]

No mechanical modifications required for 964 profile cams. However if you do fit OEM 964 cams you need to machine off an auxilliary drive, which I think is for the power steering, 5 minute job for any machine shop.

To get the best from the cams, the CIS injection needs very carfull setting up. Without it you can easily loose all the potential gains. For example my engine was run in on a dyno, first run was 220bhp with a very unstable idle, mucho expert tweaking whilst still on the dyno got it up to 235bhp.

However my cams are modified 964 reprofiled to take the CIS to the limit of useability with further increases in duration, lift and overlap I still think a stock 964 cam would have these set up issues but probably less severe.

 

[Guest]

Bruce

Sounds interesting. I will have to look further into the 964 cams.

Apparently the bottom end is ready, so we are moving forward.

Cheers

 

[wblackw9]

Ye deffinately a good idea to have a pop off valve, i found out the hard way and installed one after detonation to my 2.7!!

 

[Gary C]

Could you explain the function of the pop off valve ?

Coming from Turbo cars where 'pop off' valves have a specific but often misunderstood purpose, im not certain I know what you mean in relation to a NA car.

 

[Guest]

Ouch that sounds expensive. I installed a Popoff nearly 2 years back. Worth it's weight in gold. Had a big back fire one day when starting from cold which blew the whole falve out. Had to seat it back in to start and was fine to get home when I re-glued it in. No issues since.

Cheers

 

[Guest]

Gary

Quoted from Pelican Parts:
Sometimes the CIS fuel system is prone to backfires. This can cause a small explosion within the CIS airbox. Without some type of pressure relief valve, this explosion can blow apart the entire airbox. Replacement airboxes are several hundreds of dollars. The work-around is to install a pop-off pressure relief valve in your CIS box. The process is quite easy, and it's very cheap insurance against costly backfires.

Check out this link for installation:
http://www.pelicanparts.com/techarticles/911_pop_off_valve/911_pop_off_valve.htm

Cheers

 

[Gary C]

Thanks for that, sounds like good insurance for a CIS car.

Sometimes its easy to forget how things have moved on in car electronics.

Not a problem for a 3.2 then with its system (Seems to be a K-jet hybrid with some sort of Motronic digital control)

 

[Guest]

Well at last the barrels and heads are nearing completio, however I have just been told the price for the machining of new cylinders and the three angle valve job. How much do you guys think is reasonable? The price currently is £1300.

Any thoughts?

 

[bruceb]

What are they quoting to do for 1300 ukp?

 

[Guest]

It would be the following

Machine the cylinders (they did 2 new and 4 old then had to do a further 4 new as it was established that the 4 old ones had to be replaced)
Three angle valve job

That's pretty much it. I am getting a breakdown now.

 

[wblackw9]

Ye i had only had my 2.7 about 3 months when it developed a hot start problem, unknown to me at the time was the problem caused when you keep trying to crank it and then a huge backfire and a dozen pieces of airbox over the engine bay! Luckily nothing had dropped inside the engine and i was able to do the work myself. Rebuilt the whole lot with new airbox, fuel accumulator, warm up reg and non return valve for the fuel pump, oh and of course lots og gaskets rubber bits etc. Once back together took it to the garage for a tune up and its run sweet since.
Engine looks lovely now.

 

[Guest]

Bruce

Just spoke with the machine shop. The basic list of what was done includes:

- Machine set of barrels (4 old and 2 new)
- Machine set of barrels (6 new - had to replace the 4 old as the pistons were buggered and so had to re-machine as the have to be machined as a set)
- Weld fault in head and machine to as new
- replace guides
- three angle cut valves
- Replace crank case studs
- New exhaust insert (required due to welding)
- New exhust valves
- 5 x exhaust studs and SS inserts

That's about all I know at present. Most of the additional cost will be in the re-machining.

Cheers

 

[bruceb]

I had six heads rebuilt with new guides, exh valves, and 3 angle seats with bit of polishing of the inlet ports, maching 6 barrels and face a flywheel for £1100.

Not quite as much work as you so, £1300 sound about right to me

 

[Guest]

Well the engine is all re-built. Just waiting on a couple of tinwear parts before puting her back together.

Here's a pic or two

 

[Guest]

And a second pic

 

[engleflick]

Looks really good you must be pleased. []

If you don't mind; what was the total cost for your rebuild?

 

[Guest]

Yeah pleased with the result thus far. As for the cost I have not finished adding up. we are looking at over £5000 so far and I have the labour to go yet. Once it's all done I will post a report here.