2.7 cam options

trekkor · 03-02-2008, 09:24 PM

911/92 motor.

Will have Webers.

For track.

I want max power.

Thanks

Also, will my mech advance dizzy from my 2.0 fit in place of the vac advanced one?

KT

Steve@Rennsport · 03-02-2008, 10:35 PM

KT,

Cam decisions get based on vehicle gearing and weight. Remember, the more HP you want, the narrower the torque & HP range will be so that affects how difficult the car will be to drive (race).

The 2.7 uses a distributor with a 30mm shaft; your 2.0 has a 27mm one so that won't work. Your 2.7 distributor can be modified for centrifugal-only advance.

Of course, if you use twin-ignition, you'll use a much better unit anyway,....

trekkor · 03-02-2008, 10:41 PM

Thanks,

I am used to a 5000-7300 operating range with my MSX geared 901 box.

With a cam change am I limited do to valve to piston clearances?

KT

trekkor · 03-02-2008, 10:43 PM

Tell me more about the dizzy mod.

Sounds interesting.

KT

Steve@Rennsport · 03-02-2008, 10:53 PM

To be honest with you, a 5K to 7300 RPM power range is a street engine,...

Thats what "S" cams do in a 2.0 to 2.7 litre motor. If you need more HP (and thusly a higher RPM range with a narrower spread of HP), you will need a proper close-ratio gearset to keep the engine inside its torque & power range.

I cannot tell you what cams will work in your engine without knowing precisely whats inside and what configuration/specifications you currently have.

If you want HP you will need compression, headwork, to get more revs. That requires different pistons, more cam, and a whole host of mechanical upgrades and modifications to the oiling system to ensure that the engine will be reliable at those engine speeds.

Twin-ignition is a must for any high-power 911 race engine and that requires a special distributor for that. You can contact me directly for more information on that.

trekkor · 03-02-2008, 11:01 PM

Will my "S" cams from my 2.0 motor 'fit'?

My close ratio gear box is fantastic!

KT

trekkor · 03-02-2008, 11:18 PM

Also, why is there such a big difference in hp between the various 2.7 motors?

KT

Eagledriver · 03-03-2008, 07:42 AM

KT,

I ran a 2.7 RS spec motor in my Toyo cup car for several years. I had a 915 with 7:31RP in the car. I started out with a Solex grind cam profile and then rebuilt the motor with an "S" cam profile. I got more peak power out of the S cams but I would definitely say the Solex cams were better both on the track and street. Lap times were identical.

-Andy

trekkor · 03-03-2008, 07:58 AM

Would a 175hp target be reasonable?

"S" cams with Webers...

KT

Steve@Rennsport · 03-03-2008, 08:09 AM

KT,

Your "S" cams will fit the 2.7 but you need to have the right pistons (not CIS ones).

The HP differences between all the 2.7 engines is due to variations in port diameters, camshafts, intake systems, and exhaust systems.

trekkor · 03-03-2008, 08:19 AM

I guess I'll just run it 'as-is'.

I do not want to tear the motor down unless there is another cam option that will allow me to keep the stock pistons.

KT

Steve@Rennsport · 03-03-2008, 08:49 AM

The biggest cams that work with the CIS pistons are 964-grind ones.

You would need to have some 3-bearing cams reground or made since the newer 4-bearing (SC-3.6) cams will not work in your existing 3-bearing cam housings.

jpnovak · 11:27 AM

Steve, Can you confirm that a 964 cam will clear a stock 2.7 CIS piston? I was under the impression from previously posted information that the exhaust duration would cause the exhaust valve to contact the piston on the down stroke (chasing effect). I don't recall anyone stating for sure this would/would not work.

trekkor · 03-03-2008, 09:49 AM

Thanks for the good replies.

KT

Ray_G · Ray_G's Garage

I would be interested to know what cams will work with the stock cis pistons as well. I am going to be putting my 2.7 together soon and I am still up in the air about the cams. I have also been told the 964 can cause clearance problems.