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goodtogo 06-26-2020 02:44 AM

1976 2.7 - Supercharger sir?
I have come by a really quite original 1976 CA 911s (smog pump, CSI, thermal reactors and air con) with original engine and trans that had a recorded total engine rebuild 5k miles ago (all be it in 2004) which runs smooth as a sewing machine and I'm looking at the engine bay and I'm thinking, thinking....

To get more power from the current, original set up, first off I'm considering binning the thermal reactors and heat providing headers and installing an SSI + sports exhaust, to let her breathe properly (smog pump already gone). I read that this engine is really quite special when stripped of the incumbrances and runs nice and cool with a carrera oil cooler set up, esp with ribbed oil tubes and then has that 'rasp' we all covet.

I'm looking at the air con setup and I'm thinking that to get more power, rather than strip the engine down again and breathe on it (Lots of money?), could it be an idea, to simply replace the air con pump with a supercharger, which could then easily be removed in the future to put the engine back to stock?

I know Paxton's have been fitted to 3.2's before, but a 2.7? well, why not? I'm also thinking Eaton superchargers which can be had second hand from small Mercedes engines. cheap as chips over here in the UK ($200).

I guess I'm really considering Bangs for Bucks

Any thoughts anyone please?

Rodsrsr 06-26-2020 10:03 AM

I don't think I would recommend that on a 2.7....pretty sure those are prone to pulling head suds normally aspirated. Others may chime in...

tx996tt 06-29-2020 03:46 PM

Not sure about the 2.7 but here is a data point regarding HP potential:

3.0 SC with Paxton SN2000HO- custom built kit not from SOK
964 Cams
Haltech stand alone efi
Custom fab intake using 70mm Ford throttle body
8.9:1 static compression - custom JE pistons with ductile rings
ARP head studs and rod bolts
Long tube headers and custom exhaust

270whp at .61 bar (9 psi) blowing thru a modified 930 intercooler. This was a serpentine belt set set up using Ford belt tensioner and idler pulley.

We converted to turbo so removed from car. I still have the Paxton head unit, stainless mounting bracket to get it on the motor and the tensioners. All other parts to complete are not available.

Willing to sell for $600. PM if you have interest.
Note: you will need to have a serpentine crank pulley machined, A/C pulley modified for serpentine belt, plus get it plumb to the throttle body.

cmcfaul 06-30-2020 01:18 PM

On the rebuild sheet did they add case savers? There like timecerts that hold the head studs more securely into the block. As mentioned earlier, the 2.7 weakness was a propensity to pull the head studs from the case or to break them, particularly if they are Delvar. It's standard procedure to replace Delvar during a rebuild with steel. If the head studs were not replace and case savers not used, no way I would put any more stress on this engine. Heat cycles associated with the thermal reactors make the magnesium more brittle. Taking all that stuff off (Thermal reactor, air pump, ac (if not working)) is a great place to start.

73 E 2.4

angelny911 06-30-2020 05:29 PM

I have a sok setup for a 3.0 motor

matthepcat 06-30-2020 05:31 PM

Depends on what you want out of the driving experience. Might be a better path to lighten the car and optimize the motor in N/A form. There have been some turbo 2.7 set ups done successfully. Never seen a supercharged one.

goodtogo 07-02-2020 12:02 PM

SC'd 2.7
Thanks for the feedback.

I've found these 2 articles which makes interesting reading:

I'm pretty confident I could make up the necessary parts but if I need an EFI and ECU then its going to start getting quite expensive, plus the additional unknown of whether a 2.7 mag case will be able to handle that extra power once its all done.

Another thought, if I'm looking at an already wheezy 2.7, I wonder whether I need all the cost of 4 or 6 rib drive belts and pulleys and tensioners. Would using just a simple standard v belt with the drive taken off the existing air con pulley, with no tensioners, work (with a suitable ratio pulley on the S.C.)?

If the belt did start to slip at higher rpm then this may be a bonus in preventing the S.C from generating too much boost at higher revs.

cmcfaul 07-03-2020 05:08 AM

The 2.7 is the worst engine to put forced injection on. Will need major mods to the case. One with a thermal reactor on it for so long makes me think it just won't hold. Too many heat cycles in a weak mag case. The SC is a much better engine to start with.

tx996tt 07-03-2020 07:25 AM

The 2.7 is not the best base to modify. That said, a V belt set-up will limit boost to around 4 psi. The effective compression ratio (CR at peak boost) will be 10.8:1 assuming your static CR is still factory 8.5. For comparison, the effective CR on my SC is 17.8:1 at 1 bar.

At 4 psi, consider if it is worth the effort/cost/risk. Estimate 20% power gain (5% per 1 lb boost). Considering a stock 76 made 165hp, estimate 200-205 flywheel hp SC with improved torque. Increase weight will mitigate the power gain. The Paxton head unit and mounting bracket weigh 28 lbs plus add in the weight or a tea tray wing. I would be concerned with the look of the the tea tray spoiler if you have less than SC flares. I changed the rubber to 3.2 Carrera to help with the proportion. If it was me, I would build a hotter 2.7 NA motor and take weight out of the car as previously suggested.

goodtogo 07-03-2020 10:48 AM

76 s.c
All good points, a lot to think about.

Thanks to everyone who has input.

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