2.7RS vs. 2.7E

Hi all.

I am having built a new engine for my 1973 911E. Bought a 2.4E MFI system and a 2.4T (carburetor) engine. The original plan was to build a 2.4S spec with MFI.

Then I came across a dismantled engine with 2.7 nickies and JE 9.5:1 pistons, and the plan was upgraded to 2.7 RS specs. Now I am concidering to go for a 2.7E engine instead, simply because I will save more than 5,000 USD on not having to modify the MFI system and port the heads.

The big question is: Will I be satisfied with the performance and character of the engine?

I have driven a 2.0S and a 2.4S, and both are on my top three list of memorable rides.

A high compression 2.7E engine will have a power output somewhere in between a 2.4E and a 2.4S, but will it be as thrilling as an S?

I’ve had both of these in my car, albeit both with 40IDAs and both with 36mm ports. The E cammed 2.7 was the best auto X engine EVER. It was replaced by an S cammed 2.7. The S cammed motor just moved the power band up a little. It may have produced a little more who knows. It also may have sounded faster but the S cammed car was not quite as fast at the auto x. It just didn’t have the power lower in the curve.

E cam = punch. S = top end (but there is not nearly as much difference on a 2.7 as a 2.0).

You could split difference and use Solex. I would also port to 36mm regardless. It may start a flame war, but there is plenty of adjustment room in your pump to get pretty darned close with an S or Solex using your E pump space cam.

It seems pointless to go to a 2,7 cylinder without porting the heads as you would not get the airflow to match the cylinder capacity,
I just had a 73 engine done with 2.7 cylinders, ported heads, S cams and Weber carbs. It has a much more linear HP/RPM line than I expected compared to my 2.2 S.
To geneulm’s point, if you already have E cams, not sure S cam’s would be worth the expense.

Still not sure about this. My hypothesis is that the 911S, regardless of displacement, is so much fun to drive due to the torque rising so suddenly when the revs reach the level where the maximum power becomes available. An SC is definitely quicker, but the linear increase in power, proportional to the revs, makes it seem less brutal. I suspect that this will also be the case with a 911E cam profile.

I own a 250 ccm two stroke motorcycle with less than 50 HP, but the engine is really lively and gives a punch that four stroke bikes with three times the maximum power can't match.

You have gotten good advice from several of the previous posts. It all depends on what engine characteristics you want. Keep in mind that as you increase engine displacement the same cam gets smaller. I.E., An S cam in a 2.0L is much more radical than the same cam in a 2.7L. The 2.0L S will feel like a Turbo kicks in about 5,000 rpm. The 2.7S (i.e. Carrera RS) will have much more power throughout the rpm range but less kick at the upper end... and it will be much stronger overall than the 2.0L. It's the displacement that makes the difference...which is torque. Torque is what you feel. Old small racing engines produced their torque at very high rpms...7-8,000. That was OK because that is where they ran in races. On the street, even a high performance car will spend most of it's time at much lower rpms. So, if you are after a thrill at high rpms only...go with a wild cam. If you want overall power and performance throughout most of your rpm range go with more displacement and maybe an E or Solex cam. I love the S cam so don't get me wrong. I own a '73 2.4LS that I've raced for years. I love it's kick at 5,000 rpm. In the past I've also owned a '73S we rebuilt from a 2.4S to 2.7RS. My 2.4S is fast but the 2.7RS was noticeably faster. It didn't have the high end kick but it was stronger throughout the mid range and pulled very well at the top too. You need to decide how you want your car to perform. Then the decision on the engine build will be straightforward.

Calling Hugh Hodges, he has a 2.7 in his 73E with E cams from memory so give him a shout out.