Port size on 2.7rs spec rebuild.

[whackit]

here's the motor i currently have the parts to rebuild (and please keep the discussion within these as I am not planning on getting other parts).

2.7 with rs euro pistons (8.5:1)
e cams
pmo's
ssis

I am looking for smooth wide band power, not really concerned with squeaking every ounce of power out of the motor as it's replacing a 2.2t and will be a significant upgrade regardless. I currently have 2.7 cis heads (and a set of 2.2t heads if need be but would like to keep that motor intact).

Just wondering whether I should port the heads or stick with stock (46/40 valve and 32mm ports) I may have access to a decent set of S heads (35mm ports). Please advise.

[J P Stein]

Originally Posted by whackit

Just wondering whether I should port the heads or stick with stock (46/40 valve and 32mm ports) I may have access to a decent set of S heads (35mm ports). Please advise.

I'd get the 35mm port heads. I opened up the intakes to 36mm, but it's not required for a good running engine. The 32s will choke the engine off it's potential power....IMO.

[Eagledriver]

Either get the S heads or port yours to 36mm. You will have a marvelous engine when you are done.

-Andy

[jluetjen]

I know a guy who has a 2.7 (MFI) with E cams. Even though the HP is "only" 185, it makes an awesome autocross car. It's making over 160 lb-ft of torque from 2400 RPM through 5800 RPM. It starts to run out of air at 5100 RPM because of the limited lift of the E cams. If you look at the data that I posted on this thread, you'll see that if you take the normal S cam used in 2.7RS's for example, it lifts to .455 inches with the S in the graph heads maxing out at .5 inches. If you're using E cams which have a lift of .405 inches on the other hand, and 36 mm intake ports, you'll have a lot of unused flow in the ports -- which means decreased intake velocity, reduced turbulence and poorer off-cam performance. Looking at the intake velocities, at the max torque engine speed, you'll be pulling about 61 m/s, which is comparable to a '70 S or a 906 -- neither car of which was renowned for it's off-cam performance. Looking at the intake velocity at the max HP engine speed, and it's a fairly meager 80 m/s, when most 911 motors are pulling 85 to 100 m/s, so you'll be leaving a lot of port flow unused.


On the other hand 32 mm looks a little small. I'd go for something in the middle like 34 mm, which will keep the intake velocities in a similar range to E's and T's, and should promote good mixing and smooth performance. Your engine will work with 32 mm ports, but the peak HP may be one or two ponies down on 34 mm ports. 35's will would make the velocity at the peak torque engine speed 65 m/s, and 85 m/s at the peak HP engine speed.

So my recommendation would be 34 mm unless you're going to use S cams, in which case you should go with 36 mms. That being said, my friend's engine uses 36 mm intake ports.

[J P Stein]

Read Bruce Anderson's book. In there he builds a 2.7L hot rod motor identical to what you describe...with 36mm ports..complete with dyno graph, carb jetting is even there and it works....

The only thing I would add to your list is a hot ignition set up.

[whackit]

in brice andersons motor he has bumped it to a 2.9. I'm basically building the same motor with the original 2.7 displ.

I am going to add pertronix /msd to the motor.

[J P Stein]

Originally Posted by whackit

in brice andersons motor he has bumped it to a 2.9. I'm basically building the same motor with the original 2.7 displ.

I am going to add pertronix /msd to the motor.

Upper graph pg 140.....latest edition.

The lower graph is confusing. I don't know of any 95mm PCs that will fit on a 2.7 case....a typo? I wouldn't use the 93mms.