2.7 MFI rebuild
 

Hi Guys
I'm about to have my stock 2.7 MFI (210 bhp) engine rebuilt and this may give me an oppertunity to add to it!
What can you suggest? I drive the car everyday so it can't be full race spec and undrivable in the city.

?increase capacity to 2.8
?increase air flow ? using RSR stacks.

As you can tell I'm not that mechanically minded but would like your suggestions to take to the engine rebuilders

Thanks in advance!

Andrew
NZ

My suggestion would be higher CR pistons. This will make the torque curve even "fatter" with more torque across the rev range. Increasing air flow only helps in the 6500 + RPM rev range, and how much time do most of us spend with our engines spun that high???

I would go with...

a bump in compression if gas in NZ is good.

36 mm ports
38 mm throttle bodies
plastic stacks ported to 38/46
re-calibrate pump(or dyno tune if you can get away with it.

Twin plug if you have the budget for it....either way it will be a fun motor.

Thanks for your input John and Aaron

Your advice raised a few more questions -

What increases in BHP and torque can I expect (bang for buck)
Which higher CR pistons would you suggest.
Would the MFI be difficult to recalibrate?!

Thanks again
Andrew

From what I,ve heard(no experience), around 230 hp with only compression raised to around 9.5:1. Thats a pretty good bump!

pump calibration should be done by a profesional. Btw, that MFI system is worth quite a bit here in the states.

Andrew,

You won’t have to recalibrate your MFI pump, these changes are well within the range of the pump. Prior to your rebuild you should thoroughly go through the MFI and ignition (CMA) and get everything perfect as you can. You don’t want to be troubleshooting a fresh engine on startup.

The compression ratio (CR) is limited by your access to high octane fuel. Here in Colorado we can drive up and pump 114 octane, tax paid. Some people buy race fuel in 55 gal. drums.

The 92 mm P&Cs will bolt right up to your case and heads but great care must be taken with piston-to-head and piston-to-valve clearance. The Mahle Nikasil 2.8 RSR pistons will be about 11.5:1 CR on your heads if unmodified. Bruce Anderson’s Porsche 911 Performance Handbook, 2nd Ed. available from our host has lots of good info.

Twin plugs reduce the octane requirement slightly. If done properly, the real advantage is better running at light throttle lean mixture. Of course it puts out more power at WOT, particularly at very high CR.

Keeping the heads and cylinders cool is critical. The 1.82:1 fan ratio helps a lot. So will a later fan assisted Carrera front cooler. High CR generates more heat and detonation is temperature dependent.

How many miles (KM) on your 2.7? Are there any mechanical issues?

Best,
Grady

Andrew

If its a genuine 2.7 74 Carrera why would you do this, the cars to valuable

Neven

1st - what's your rebuild budget?

2nd - what parts of the engine are out of spec?

3rd - intended use?

when i specced the 2.7 for my race car (eg. MFI, 10.5:1, GE80 cams, Ti retainers etc etc) i couldn't justify a 3.7% capacity increase for the cost of 2.8 pistons and cyl's so i just went for high comp 2.7 pistons (my cylinders were fine) however, even if i had to buy barrels as well it would have been a tough choice.

twin plugging is also very expensive (my new 12 lead distr goes in next week...) but, with the timing retarded, my car runs ok on the "premium" pump gas we get in australia.

ps. i wouldn't worry about modding the engine on a 74 carrera as a. they aren't THAT rare/valuable and b. a strong engine rebuild is unlikely to devalue the car so long as you retain the case and MFI

My RS engine was in need of a rebuild, but during the tear down we discovered a previous owner had upped the displacement to 2.9L using a set of Arias (sp?) P/C. We made the decision to keep it at 2.9L but found a new set of Mahle P/C instead. It will have a higher CR that should make about 230 hp on pump gas. Of course I have no intension on tracking the car, you may have different ideas about your Carrera.

so true ... ask me how i know...

Agreed. Take the engine out and put it in a corner of your garage. Then get yourself an aluminum block engine (early or late) and build up the largest engine you can (3.2 / 3.4). The costs are about the same, why leave HP on the table?

-Wayne

Hi guys
Sorry about not getting back to you sooner, but things became interesting (and in many ways clearer) when we took the engine apart.

I had intended to go down the route suggested and use Mahle RSR Pistons to increase CR to 10.5:1 - but not go the twin spark route as this would have been too complex and costly.

I thought that this mild increase in torque and power would be enough for my use of the car (daily driver / very occasional track day).

However!

The previous rebuild (carried out in 1995) was an absolute shambles! And the bottom line is that I’m very pleased to have had the engine rebuild so expertly by Jon Warring at Rennsport here in Christchurch.

We found such things as.......
• The case had been machined and the original crank and pistons kept, but unusual (certainly not Porsche OE) spacers had been used to lengthen the barrels to stop the pistons hitting the valves.
• The engine case and pistons etc were original but the cylinder heads were from 1969! At some point there must have been a big bang and all new head replacements had been needed. When we read the previous owner’s garage bills from 1995, it turned out that he had paid for an additional 81 hours labour after the garage's “misassembly” had damaged the engine after its rebuild. We can’t be sure but we think that this is where the new heads came from as they don’t look that old. I’m tempted to give the previous owner a ring (he had the car for 22 years) to find out exactly what happened. What do you think?!
• The “carrera” tensioners and chain guides were installed wrongly and not working.

All in all John had his work cut out to get the engine back to spec – which it now is apart from an mild increase in compression. This came about because, after looking at Bruce Anderson’s Porsche 911 Performance Handbook, we decided to machine out the ports rather than replace the heads. After machining, John painstakingly buretted each head and found that they were 64 mls - slightly less than spec 66-70mls. This reduction increases the CR to 9.4:1!

The engine is just being re installed so I’ll give you another mail when we have had it running.

Cheers

Andrew

Wow! What a basket case of an engine. How many miles or kms were on the engine before this teardown?

andrew

if you can spare the dollars, go for the GE80 cams - they are great. however, they are high lift and thus Ti valve retainers are also recommended to lighten up the valve train.

i've heard good things about jw from a kiwi mate that he did work for - you're in good hands

I was going to suggest DC40 cams, but the GE80s would be sweet as well!

I would not use the GE 80 cams unless you are willing to rev the engine to 8000 RPM. You'll be faster on the track with GE40 or 60 at the normal rev limits.

-Andy