2.7 RS Upgrade to 2.8 or?

[JScaramella]

From the forum past threads I have seen, I came up with the following possible upgrade. Any suggestions are appreciated


What I have:

72 911
2.7 RS spec motor
The Mag case has the time certs and racewear bolts.
2.7 Mahle 8.5-1 pistons
MFI
S Cams
Large front oil cooler
Fulls susp mods
Brembo big break kit F&R

What I want:

I thought about a simple 9.5 or 10.5 upgrade but than seems less cost effective as I will have the entire motor open anyway.
Also the suggested outcome is not lighting my fire.

From what I have read here I can upgrade to a 2.8 displacment and twin plug set up with this case. True? 2.9 seems like its a push?

I plan to use a crankfire system as the twin plug Dist. I have seen are very costly! 3-4k alone. Can that be right?

I would retain the MFI, assuming that this has more adjustability to compensate for the larger displacment.

Use either a Mahle 2.8 set up or J&E. I prefer the Mahle but $ will be the ultimate factor.

I also have the s cams which I'd like to keep. My mech. suggested a possible GE 60 but did perfer that I keep the S cams for the power band.

What can be expected in Bhp from that set up.

I assume, as I have no dyno info on the 2.7, that I have at least 170 RWH now?

Thanks guys

Happy Holidays

[Wayne 962]

'S' cams will work well for you on this engine.

The crankfire systems are about $1500 including everything from us.

The 2.8 set is nice, but you really need to make sure your case is done right...

-Wayne

[Eagledriver]

For what it's worth my G-tech says I have 195 RWP from the same engine you have. That doesn't inclued about 10hp for wind resistance on a 2nd gear pull. Is the engine worn out? If it's still running well and has life left I'd leave it alone. I think you'll find that a 2.8 conversion will be expensive and much less reliable with less longevity. If you must have more power I'd sell the motor or keep it as a spare and build a 3 litre or short stroke 3.2. You can probably do this for little more than upgrading your engine and have more power and longevity with less exotic mods.

-Andy

[Wayne 962]

Originally posted by Eagledriver
For what it's worth my G-tech says I have 195 RWP from the same engine you have.
-Andy

FYI, the G-Tech is really only useful for comparing changes on the same car - there are too many variables that can affect performance to compare them car-to-car.

I also have a section on this G-Tech unit in the Engine Rebuild book...

-Wayne

[Eagledriver]

Couldn't the same be said for a chassis dyno?

-Andy

[Wayne 962]

Originally posted by Eagledriver
Couldn't the same be said for a chassis dyno?

-Andy

Yes, I do say that about chassis dynos as well, however, there are many more variables with the G-Tech than with a chassis dyno. A few to mention:

- Guessing the weight of the car
- Mounting the unit absolutely vertical
- Repeating runs along the same stretch of road
- Repeating shift points (not required on a chassis dyno).

Many things to vary...

-Wayne

[Eagledriver]

Wayne,

Those are all true but have been controlled fairly well in my measurements.

-My car gets weighed after every race. I know the weight of the car at all times within 20 lbs for sure and more likely 10 lbs. This will give an error of 1 or 2 HP.

-The unit tells you when it's mounted horizontal with the g-meter inside it. Don't know how much error is available here but not much if your careful. The reading is within 1/100th of a G of horizontal.

-I do at least 3 runs and take an average. I use different directions and measure both the wind and temperature for later comparisons. My variations between runs are usually less than 4 HP.

-Shift points are irrelevant as long as the pulls are done past the peak HP rpm. I use moderate acceleration in first followed by a full throttle pull to redline in second. This ensures that the peak reading is during my second gear pull so I have the same wind resistance for each reading. I tried a first gear pull and indeed got higher numbers but the car is breaking loose the rears at times and the acceleration is "rough" which will decrease accuracy and repeatablility.

I've done 4 different sessions this way and have seen repeatable results. Granted I'm guessing the wind resistance HP and driveline losses if I try to calculate flywheel HP.

I would say that with careful control of the variables you could get within 10 HP of accurate rwhp.

-Andy