2.7 cam choices

[jpnovak]

How much cam can you put in a stock 2.7 CIS piston? Suppose I need options for a regular and S piston with CIS dome shape.

Lets assume induction is not a limiting factor and it will have an early exhaust or headers.

Basically I am looking to wake up a CIS 2.7 by swapping cams for something more fun. Plan is to run on Webers for now.

I have built other engines with bigger cams but they always have replaced stock pistons with JE or equivalent such that there is valve clearance. I have never measured or experimented with valve clearance on a stock piston.

[IAMDJGO]

Hi Jamie!
I can't speak too much for the S pistons but for the Stock CIS domed Pistons, the SC cam was a good upgrade for the CIS 2.7 engine I built a while back. 964 cams require reliefs in the pistons so those were out for me as well.

[mikedsilva]

What about the Webcam 464/465? Their website states it is a good upgrade for a 2.7? I don't understand cams at all.. looking at the duration specs and lobe sep angle, I would have thought the CIS would hate this cam, but it seems to be recommended.

[911 SLANT]

I ran 964 cams with my stock 2.7 CIS pistons. No relief needed.

[IAMDJGO]

Interesting!
Where did you time your cams? I didn’t like the clearances I saw with the 964s.

[jpnovak]

I was also under the impression that 964 cams would not clear. I suppose if the timing is sufficiently advanced this would help with clearance.

Mike, those cams would work great on a 2.7 RS. This has a very different piston shape with a lot more cleerance compared with a stock CIS dome.

I am just trying to figure out what clears without taking the engine apart and replacing stuff.

[Trackrash]

Interesting that no one seems to know what cam can work in a CIS 2,7!

I wonder if John the camgrinder would know?

It might be worth checking what clearance you have now. You know, every 10* screw in your valve adjuster and record the valve to piston clearance. Then knowing the lift of the stock 2,7 cam you could compare to a 3,0 and 964? Could that work?

[jpnovak]

Yes, Gordon. This could work and what I had planned. Unfortunately I do not have my hands on the car just yet. Planning phases on a SWB build for a friend.

right now just trying to see what other experiences are out there. And yes, Most people will not swap cams but jump to a 3.0 or 3.2 as a replacement for the 2.7. One of the goals of this build is lightweight so mag case is key. Plus there is already a well running 2.7 to be used. No point in scrapping good parts.

[911 SLANT]

I dont know what the cam timing was set at with my 964 cams.. But I had no clearance issues. 2.7 ran strong with 40 TIN carbs. Ported heads 40 intake 35 Exhaust

[icarp]

Jamie, I'm running a Cam designed by William Knight and Melissa from Web cams , It is called the Melissa , in her honor . I have an 80 sc motor ,small ports, CIS pistons , Measured comp ratio of 8.3, CIS, pulls 7k in 4th gear and 6700 in 5th
Ian

[jpnovak]

Ian,

Thanks. I know what specs I would like. I am concerned about exhaust side clearance. And of course, exhaust side duration is where all the fun happens.

[Nux]

Webcam 21/20 should work with stock cis.

SC cams of course

964 if you advance them a bit.

DC20 if you advance them to 1.8 (standard is 2.2-2.4).

Maybe even 993ss could clear the cis domes?

I'll second those cams from William Knight. The best out there.

[KNIGHTRACE]

This cam is the best version I have ever run in a cis motor. It outdates the 20/21 and 993 SS, I will not share the specs because we put way too much work in these for another cam grinder to start knocking them off and calling them their invention I have them in about 11 motors. In a 3.0 euro CIS motor they made 16 hp over a 964 cam at the wheels. They also reduce the potential for predetnation in the lower RPM's caused by the ethanol in our fuel.. The cam is called the "Melissa Cam" It is the best cam you can run in a CIS piston motor. My email is KNIGHTRACE@MAC.COM if you would like to purchase a set. Thanks, William Knight

[jpnovak]

I appreciate the suggestions William. Sounds like a great cam. But, will it clear in a 2.7? The smaller diameter 2.7 has a steeper dome angle on the CIS "bump" and generally less exhaust valve clearance.

the engine will not use CIS. It is currently running webers I am looking to maximize the 2.7 with stock pistons. Owner does not want to tear down and replace PC set at this time. The engine is currently installed in a SWB. Meaning, the shorter gears and lighter weight favor a higher rpm torque curve.

Ideally, I would build a new engine and spec everything to match but that is not going to happen right now.

[KNIGHTRACE]

I have not run them in a 2.7 but I think they would work, on the 9.8:1 euro piston we have about 80 thousandths clearance on top dead center overlap, but you can change the timing around to get more clearance. Of course these would be better than the other choices that work with CIS pistons on carbs. These cams were designed around the CIS piston so it is highly likely they will clear.

[faapgar]

This morning I installed 3.2 cams on an 82 CIS engine.At overlap TDC there was 60 thousandth clearance.So I retarded the cam a little and got 80.This engine was 9.3 to 1.The Mellisa cam sounds good.Fred

[KNIGHTRACE]

I have had a few clients gain around 20 hp at the rear wheels. It is as good as you can do on CIS in my opinion. Thanks Fred. William

[mikedsilva]

Still learning at this stage...
My understanding is that the CIS pistons have a unique dome shape to help promote a better spread of the intake charge...
If changing to an aftermarket piston with higher compression, I assume none of them have that same cis-piston dome shape.. is there any downside to this? ie, is the potential gain from the compression increase, offset by the less than ideal swirling and mixing of the intake charge?

[KNIGHTRACE]

If memory serves me correctly... The shape was more of a design for emissions and helped the idle, changing to an aftermarket piston like CP, it will have to idle about 70 rpm more.

[rgofast]

Loose the CIS. pistons if your running carbs. Elgin Modified S cams are nice for this engine. You’ve got to get the compression up to at least 9 to 1