2.7 engine upgrade

[tonizzos]

hi friends,

i have an 2.7S engine with webers.. the engine has been redone but with new CIS P&C it also has still the CIS cams... head were done to ...

now my question , if i want to upgrade to 2.7 RS specs.. what do i have to change appart of the 2.7 RS P&C set??
is there something else i have to change??

thanks for help

cheers
steve

[Grady Clay]

Steve,

A ‘73RS engine (type 911/83) is an MFI engine. If you could find the 2.4/2.7 MFI, that would be wonderful – however unlikely and expensive.
I assume you will retain the Webers.

To convert your 2.7CIS/Weber engine to “2.7 RS specs”, you will want the 2.7 RS Nikasil P&Cs and a pair of 2.4/2.7 ‘S spec’ cams.
Be careful if these are re-ground from something else. OE is far the best.
You will also want new or properly reconditioned rocker arms to match the new cam lobes.

Other than that, you will want the best rebuild as you want to reliably turn your up-rated engine 7300 rpm regularly.
That might include a later oil pump, confirm your case has the oil bypass mod, case inserts for the head studs and the 7R case is in good condition.
Have the crankshaft thoroughly inspected. Have the connecting rods inspected and reconditioned as necessary replacing the rod bolts & nuts.
Depending on your use, you might lighten the flywheel and use lightweight clutch components. You don’t need or want some ‘heavy duty’ clutch or race parts unless this is for ‘track-only’.

While the heads are apart to re-do the valves, seats and guides to ‘best possible’, you should weld closed the CIS ‘notch’ in the intake.

The 90 mm RS P&Cs come as 8.5:1 CR. With care (and slight machining) you can assemble the engine slightly above 9.0:1 CR while maintaining slightly less than 1.0 mm (say 0.95 mm) piston-to-head clearance – very desirable.
Every engine benefits from twin sparkplugs. If you do this, install 12 mm exhaust plugs. This helps with clearance to head nuts and can be enclosed under the exhaust valve covers.

What venturae are in your Webers? You will want to decide on something around 35 mm (±) depending on your use (+ for track, - or 0 for street). You will need to change idle, main and air jets accordingly. With ‘S’ cams, it would be appropriate to use F3 emulsion tubes.
Make sure the Weber throttle shafts are in good condition. If not, consider having them rebuilt now or exchange for new PMOs.

Be sure you use 1-3 insulating phenolic spacers between the heads and intake manifolds (match spacers and gaskets to the port size for smooth transition). Continue to use your original CIS fuel return so cold fuel passes by the carb fuel inlets.

This combination should produce something slightly above the 2.7 RS specified 210 hp and be very drivable. This should be comfortable on ‘pump’ premium fuel.

Best,
Grady

[tonizzos]

hi , thanks for this clear answer...

the case has been redone with the inserts and all the reliability modifications but not with the oil bypass mod..

i just have the webers as i bought the car like that..
i do not go for track , just using the car to go to work as often as possible depending on the weather....

so my idea was not to try to go from 175-180hp to 240... but i was looking for an engine that would be a little bit more agressive than the setup i have with the cis cams...

so i was wondering if going with the RS P&C and let's say e-cams or solex , i would have to change other components ...

as wrote before , it s realy a street car and i am not the high rev guy... just sometimes hahaha

thanks again
steve

[Grady Clay]

Steve,

Yes, ‘E’ cams or ‘Solex’ are far more streetable than ‘S’ cams and just as ‘fast’. The ‘S’ cam has the wonderful benefit of really ‘coming on the cam’ feel at about 4000 rpm and pulls strong to 7300 rpm.
For your street use, the ‘E’ cam is very suitable (almost ‘ideal’).
If you are cruising along at 3500 rpm and ‘punch it’, you will appreciate having headrests.

240 hp is an unreasonable expatiation unless you raise the CR very high and use leaded 114 octane race gasoline.
You can build the engine using the bolt-on 92 mm RSR Nikasil P&Cs (2808 cc) and get above 11:1 CR (perhaps closer to 12:1 CR).
In this configuration you must use twin plugs and always use race fuel – no exceptions.
I have several of these engines with MFI. They are wonderfully fast and comfortable on the street – IF you have access to the fuel (we have a few regular drive-up gas stations with 114 octane – at $8.00/Gal).

I recommend you settle for something around 200 hp with ‘E’ cams, twin plugs and 9.0:1+ CR.
This will make for a wonderfully fast and civil street 911 with only ‘pump’ premium fuel.
This will be far more fun and a lot more performance than your no-overlap CIS cams.

In every case, you need a good, full-fin front oil cooler with electric fan and turn the engine fan at 1.81:1 crank speed using a 245 mm 11-blade fan in warm weather.
This also makes the A/C and heaters work better.

I hope this helps.

Best,
Grady

[al lkosmal]

A 2.7 with Webers, E-cams, 9.5:1 JE pistons, SSI's and sport muffler makes a great street engine.

regards,
Al

[tonizzos]

Perfect, thanks to all of you..

Cheers from luxembourg
Steve

[Grady Clay]

Steve,

Al brings up an important point I neglected to ask: What exhaust do you have?
If you have the ’74 and earlier exhaust, and in good condition: Great.
If you have any of the ’75-’77 emissions exhaust, get the SSI.
I recommend an OEM ‘street’ muffler so you don’t attract unwanted attention from the Grand Ducal Police.


Al’s recommendation of JE pistons needs to be done with great care.
You need to have a set of cylinders available for Nikasil plating.
You then need the ‘right’ size (diameter) new pistons and rings from JE.
You then send everything to the Nikasil plating shop with instructions as to the desired piston-to cylinder clearance.

The plating process can deliver the exact clearance and shape of the cylinder you want.
You want ’as tight as possible but not so tight that they ever seize’. A difficult trade-off.
Another issue with the JE pistons in Mahle or Kobenschmidt cylinders is the differential rate of expansion is not as matched as the Mahle Nikasil sets.
Because of this slight mis-match, the JE pistons must use slightly greater piston-to-cylinder clearance than the Mahle RS set.
This extra clearance reduces the life-span of the JE set.

The advantage of the JE pistons is you can choose the exact compression ratio you want and match the piston cut-out to your valve size.
The Mahle Nikasil 2.7 RS set only comes as 8.5:1 CR and valve relief for your 2.7 valves.
With a careful rebuild and minor machining, you can set these just above 9.0:1 CR.

EDIT:
personally, I would opt for the more expensive Mahle Nikasil 2.7 RS set.
These will outlive several (many?) future engine rebuilds with only new rings.

Best,
Grady

[tonizzos]

Hi Grady

Yes, i have alredy the -73 exhaust systeme... i also have header ready...
But may be i didn't wrote my question right.... sorry for my english haha

I just wanted to now what else i have to change if i want to go for the 2.7RS P&C..

As written , i have a well running 2.7 Cis P&C with webers and Cis cams

My idea is to get the 2.7RS P&C, E cams and put that on my engine... but i am not sure if i have to change something else...dizzy, some sensore or something else.....

Thanks to all of you for your help

Ciao
Steve

[RWebb]

MFI will give you better cold start than carbs but costs more and weighs more

you could also use EFI...

you may want to align bore the Mg cased 2.7L motor

yes, you will want to recurve the distributor

[frankc]

Originally Posted by tonizzos

but i am not sure if i have to change something else...dizzy, some sensore or something else

When I rebuilt my 2.7 with RS P&C, 901 cams, Webers and SSIs, I also had the distributor re-curved (by Stoddard). Below is a graph showing the old (CIS) vs. new advance numbers.

Btw, I am reading this thread with interest because I am contemplating moving to a twin-plug with 10.5:1 JE Pistons, but Grady's comments on the longevity of JE pistons are causing me to pause. What is the highest CR I can safely run on 93 octane (US) fuel? Would 9.5:1 be a better choice? Note that I would also be installing an electronic ignition system (Electromotive XDi2) for the twin plug setup (this will also allow me to optimize the advance curve on a dyno), along with a knock sensor. And what HP can be expected from a 2.7 with this setup?

[frankc]

I should add that when the distributor was re-curved the vacuum mechanism was removed, so it is strictly a mechanical advance dizzy now.

Ciao,
Frank

[tonizzos]

Hi, i see that from a simple switch off cams and P&C ... I could end on the next space shuttle haha

[Charles Freeborn]

Also curious about this upgrade.
My back of the envelope quick math:
P&C - good used - $2-$3 k
Cams " " - $500 +-
Machine work on heads to convert from cis - $500 ?
Carbs (since I don't have, good used again) $2k after re-furb
Other misc parts (rings, gaskets, bearings, machine work, etc) $2k

Total falls in the $8k range to gain 25-35 hp.... vs $6kish to swap out to a 3.2....sure is a slippery slope we're playing on here...

[T77911S]

Originally Posted by Grady Clay

Al’s recommendation of JE pistons needs to be done with great care.

Another issue with the JE pistons in Mahle or Kobenschmidt cylinders is the differential rate of expansion is not as matched as the Mahle Nikasil sets.
Because of this slight mis-match, the JE pistons must use slightly greater piston-to-cylinder clearance than the Mahle RS set.
This extra clearance reduces the life-span of the JE set.

my porsche mechanic friend HATES JE pistons. due to above, but also, JE does not offset the pins like Mahle does.

from what he told me, the JE's can be very noisey until warmed up.
i am glad to see this confirmed with grady.

[T77911S]

Originally Posted by Charles Freeborn

Also curious about this upgrade.
My back of the envelope quick math:
P&C - good used - $2-$3 k
Cams " " - $500 +-
Machine work on heads to convert from cis - $500 ?
Carbs (since I don't have, good used again) $2k after re-furb
Other misc parts (rings, gaskets, bearings, machine work, etc) $2k

Total falls in the $8k range to gain 25-35 hp.... vs $6kish to swap out to a 3.2....sure is a slippery slope we're playing on here...

your machine work alone could run 3k+, if done right.

7300 RPM, you might consider "pining" the case.

[Charles Freeborn]

Originally Posted by T77911S

your machine work alone could run 3k+, if done right.

7300 RPM, you might consider "pining" the case.

True dat.

I forgot to mention the golden rule of restoration and custom work....

"Double the time and triple the money"

-C

[Charles Freeborn]

So this direction seems more to my liking, as I can retain the CIS:
Pelican Technical Article: Extracting Power from CIS 911s...
Do I understand correctly that should I use the JE pistons I would need to have them machined / matched to the cyl's?
To clarify - my use will be 99% street. Not building a race motor here.
Thx,
-C