Need help to choose a cam in my Renault Engine

Hi, everyone. I'm Santiago and I'm from Argentina. I'm currently building my first engine, which is a Renault C2L (a stroked version of the C1J at 1.6l = 77mm diam, 84mm stroke). I want to build first a N/A version of this engine and then jump to a turbo version. The engine has 2 valves per cylinder and the cylinder head has a combustion chamber shaped like a wedge. Original RC is 9:1. The camshaft is on the side of the engine and the valves works with a rocker arm system (rocker arm lift theoretical x1.5). Original fuel system delivery works with one 2-barrel carb (32mm) but I'm switching to a MegaSquirt 2 V3.0 with a semi sequential fuel injection and DIS ignition system.

I need help choosing a cam. I already reduced the list to 3 different cams profiles provided by a local manufacturer (check image), but mostly I want to have opinions about the 117A and the M1 profiles. The cylinder head will be mostly stock and the original cam is 5.2mm max lift. I'm oriented to a street/drag build. Problem is if I should choose the one with more duration with less lift or the one with more lift and less duration.

Also I want to know if there is any rule to the LSA and the Speed Density/Alpha N fuel calculation with 108° and 110°.

Thanks!

I would stop thinking about the camshaft in terms of duration and LSA and start thinking about the individual valve events (intake open/close, exhaust open/close). The table you provided actually shows these events @ .01mm. The intake closing event (second number) is the most critical in setting because it has the most profound influence on the rpm range of the engine. If you want torque high in the rpm you close it later, the inverse is true. If you know the factory camshaft specifications this will help you get an idea of how much later you should close the intake valve (assuming you are increasing your maximum rpm).

You also need to think about your valvetrain as a complete system, not just lift vs duration etc etc. Do you know if the valve spring you are using was designed to work with either of these profiles. These lobes do not have the same velocity, acceleration, and jerk values, so you need to have an idea of the limitations of you valvetrain to determine which lobes are feasible by not causing harmonics that will lead to loss of control.

As I'm sure you can appreciate this is a complex subject, and one which I am not an expert on. The bottom line is focus on your intake valve closing, and you are already ahead of 90% of people. #7 has the earliest IVC of the bunch, and if you're not increasing maximum rpm this theoretically should give you the most response and area under the curve.

Note: I am not a professional, this is not professional advice, and I am not liable for any damages you or your engine sustain.

I'm afraid that street/drag combo ain't going to work on such a small engine. For street drivability you need torque at low and mid RPM range with small engine while for drag racing you want all the power (means torque) at the top RPM range so it's totally opposite and it's going to be very difficult to find a camshaft that would satisfy both needs. Since your stroke is very small you can rev the engine very high in order to make good power for drag racing so you need long duration cams that can help you with getting enough air to the cylinder up top. I would go with M1 camshaft. You can also bump up CR to 12:1 to compensate for loss of torque at low rpm but it will require high octane rating fuel, very good efficiency radiator and valve to piston clearance check. If all three requirements will be met you'll be able to have decent torque at low and mid RPM range and great power at top RPM (providing valves and valve seats are properly cut and valve springs have correct pressure rate).

Needless to say that na engines tuning highly depends on intake and exhaust systems proper length and diameter choice.

Thank you both for the answers! I'm aware that the valve springs must be changed and I need to check the valve/piston clearance. I'll probably go for the M1 after improving the cooling system (which is a normal problem for this engine). Also I'm planing to do a valve seat and guide change (which is kinda normal here for CNG conversion) to a bronze one, with a multiangle cut. I still need to check the volume of the piston and cylinder head as also the gasket thickness to be able to choose a CR. Fuel octane is pretty much ok at more than 98 RON (with at least 12% bioethanol) and is also kinda easy to get methanol (but thats other topic). I'll check and do some calculations on the intake and exhaust lengths and diameter.

What makes you want to choose the M1 grind?

Also if the engine is apart I would take the time to do some head work. You don’t need a flow bench, just basic measuring tools to get an idea of different cross sections, and familiarization with airspeed formulas. I have no idea about the cylinder head on your platform, but if I had everything apart I would spend a lot of time working on this. If it is your first time sourcing a spare head is worth it. Also valve seat angles are not something you cut willy nilly. Your objective is to turn the air gradually while also creating a good shearing mechanism that helps with your TKE. I don’t mean to bombard you with information, but in my opinion these are universal concepts that can be applied to any engine which separate decent engines from great ones. I think determining your compression and other dimensions such intake, exhaust cross sections and length is critical information to know.

I recently tried to explain to experienced people how to improve jz head, I even sent videos as a guide - they said it's too complicated. Do we really expect the guy working on his first engine ever to make perfect cylinder head from scratch? Common...)) I really wish he can succeed with that but I don't think we are being realistic here...

I lost track of the fact that this is his first project, so you may be right. However, I would say that there are some easy gains to be had that virtually anyone can do. I try to give people the benefit of the doubt.

Oh, there is no doubt in my mind about what you're saying - you are absolutely correct. But you need at least some experience in order to realize it and get going that far. You need to learn how to walk before trying to run as they say)