2.7 RS spec power delivery
 

Hi

We have just rebuilt a 2.7 litre to RS specification. It has a competition valve job, the cases have been boat tailed, flywheel lightened, compression bumped to 9.3:1. Other than that it is faithful to the original '73 spec. However now it is run in I must say I'm mildly disappointed by the way it delivers the power.
It comes on really strong in the mid range but runs out of steam at the top end. At 2,500 - 3,000 rpm it has fantastic throttle response, lots of low down grunt. Coming out of the corners it is fantastic. However it tails off beyond 5000 rpm. Holding onto it beyond 5,500 seems pointless, better to change up and let the mid range torque do its work. Only trouble is I like engines that like to rev. Having not driven this type of engine before I am not familiar with the way it should drive.
So my question is are they all like this or should it pull like a train all the way to the red line? If the latter it might indicate a fault(s). If so any pointers as to what that might be please :confused:

Thanks,

Keith.

Wow, you should be getting some more pull all the way up.

I have a 73E rebuilt to 2.7, 9.5:1 compression and it pulls hard all the way up to 7 grand. You should start with the basics:

Timing? Is it advancing correctly? No rev limiter on your rotor?

Cams? You didn't mention but are they S spec? Timed right?

Fuel/air? You don't mention MFI? If so is the pump working right? Rebuilt to RS specs? Throttle bodies the right size?

Good luck, you should have a hell of an engine.

Yes, it should develop power past 5500. But then again, true RS Spec engines redlined at 6,300 RPM, I believe.

you mean 7300?

Thanks. The engine is a european 210 carrrera from 1974. This is exactly the same as the RS 1973 unit. So it has 'S' cams, MFI, correct throttle bodies, etc. The rev limiter is built into the rotor arm and is the RS unit.

Think I'll go through the basics. Just need to check out the way these should actually be so I'm not chasing a problem that does not exist.


Keith.

When I bought my car, way back when, it came with a 2.7RS spec motor. It had a power curve exactly as you stated. Great throttle response from the mechanical injection, but something was definitely missing from the top end. Not that it was slow, (I still remember pulling on one of those twin turbo Z's. The look on the guys face was priceless), but it was lacking a solid push above 5,500 RPM. It would just kind of rev in that range, not really come alive.

When it started to leak a larger than normal amount of oil due to a pulled head stud, I pulled it apart. I discovered the prior owner had taken a few short cuts to obtain "RS" spec. Apparently he just added the P/Cs and left everything else the original standard "E" spec of the core motor with the exception of "S" cams. The heads were not ported or fly cut and the injection system was standard "E".

I reasoned that was the source of my missing "spike" in the power curve above 5,500.

I have since moved on to a bigger motor, but I have all the pieces machined and waiting in the garage for assembly. I just have not had the time to confirm if my hypothesis is correct.

Tinker

I run a MFI 2.7 RS replica motor in my race car. It is exact including 8.5 compression ratio. I shift at 7300 RPM because I hit the rev limit not because it's not pulling. I wish I could take it to 7500 plus but I don't have race valve springs and I want the engine to last awhile.

Something is wrong with your engine.

-Andy

Thanks for your interest. I think I may have found the root of the problem. I checked the timing marks on the crankshaft pulley. They are marked as 30 and 32 degrees. According to Wayne's book it should be 38 @ 6000 rpm. 6 degrees retarded by the looks of it. This is probably where the power is going. I also checked the part number on the distributor. It is 0231 184 004. Will check that that is the correct item too.:eek:

I would suspect ignition or MFI pump timing.
We recently had an MFI engine that was making us crazy. We went through a plethora of engine tune up possibilities and then did it again without success.
After literally months of anguish we took the engine out to discover that the MFI drive pulley on the cam had come loose and the mounting holes had gotten oblong so the pump timing was constantly changing.
This engine had a high rpm miss but your problem (lack of high rpm power) may be pump timing.
Good luck

I think you're onto the source of the problem. I just tracked down a whole host of problems with my own car last year, and the solution: rebuild distributor. Putting a timing light on the distributor revealed spotty triggering of the spark - this wasn't apparent until the new one was in there, and was "spot-on" compared to the old one.

Also, be sure to check total advance. This is very important - if the weights in your distributor aren't advancing enough, you will rob yourself of power on the top end. I explain the procedure for timing and checking this in both the Engine Rebuild Book, and the 101 Projects Book...

Just from memory, 004 is the correct distributor. I think we sell Bosch factory rebuilt ones for $350 or somewhere in that range.

-Wayne

yes....there is something wrong
my RS spec 2.7 MFI always pulled hard to 7400-7500 with no issues
from 3000 on up, it was hold on and smile

Yep, they should pull hard well beyond 7k...

Was that engine in a different car? The car you have now has a 3.2? What happened to the RS spec 2.7?

especially in an 1890lb 911 ;)

Andy - where do you drive around Denver? Maybe we should do a trackday or mountain drive sometime :)

I'd hate someone to overlook this. Many engines are running around with the throttle linkage set up to deliver less than WOT. Check at pedal and at the throttle bodies.

Sherwood

Good thinking. Sometimes the best solution is the most obvious!

-Wayne