2.4 race engine ideas/questions

[jmz]

Hi,
Considering putting together a 2.4 race motor out of spare parts laying around.

Any thoughs on RSR sprint cams on a high compression 2.4 with 46 IDA carbs?

The other possible option is a set of Solex cams I have laying around. ...third option I suppose is selling some stuff and getting an optimized cam.

Anyone have thougs on RSR sprint cam on a 2.4 big port twin plug heads with 46 webers?

Thanks,

JZ

[Classic 911]

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[colingreene]

I would not use the solex cams with high compression. unless running on strictly race fuel and even then thats iffy.

[jmz]

Race engine yes, Race fuel.

[colingreene]

I still think that the solex cams are a poor fit for a race motor not only because of the power band but because they build a ton of cyl pressure through the midrange causing the motor to knock.
Addionally because other better more modern cams are available.
Unless its that you are planning on building this out of your parts inventory and those are your only two choices?

[jmz]

@colinggreene, understood. Likely if Solex cams I would run less compression and I have the option of 40 IDA carbs as well. I do not have pistons/cyliders as of yet.

really, I'm looking for guidance on the 3.0RSR sprint cams on a 2.4 litre with 41-ish intake ports and 39-ish d-shaped exhaust ports and 46 IDA carbs. That is what I've thought I might assemble knowing that that the 3.0 RSR sprint cams are generally used on larger displacement motors. (came from an old 2.8 race motor we had) I am hoping some experience here from our experts might offer some thoughts on the spare parts combo….

[rennzeit]

In Elgin's old catalog, he described the 310/296 grind as
"2.4-2.9 litre 4500 rpms and up 11-1 c/r, more power than 906 and sprint"

All grinds wilder than that are described as for >2.8L.
The 310/296 duration puts it halfway between a GE60 and GE80.
RSR sprint has even more intake and exhaust duration than GE80.

[jmz]

Originally Posted by rennzeit

In Elgin's old catalog, he described the 310/296 grind as
"2.4-2.9 litre 4500 rpms and up 11-1 c/r, more power than 906 and sprint"

All grinds wilder than that are described as for >2.8L.
The 310/296 duration puts it halfway between a GE60 and GE80.
RSR sprint has even more intake and exhaust duration than GE80.

Thank you.

[stownsen914]

While I have no direct experience to share, a factory RSR grind was rated to make peak hp at 8000 RPM in 3.0L, so one would expect it to peak a little higher in a 2.4L set up as you describe. Worth considering how high you want to rev the motor to take advantage of that grind. You might be able to push peak hp RPM a little lower by advancing the cam timing a few degrees. Would make a fun engine for sure.

[Rosco_NZ]

I’d be a bit worried about revving a long stroke 2.4 that high for the same reasons the long stroke 2.5 and 2.8RSR had problems with crank bolts backing out. I’d be using strong aftermarket bolts, thread locking them in and torqueing them up as high as possible.

[Geneulm]

You don't want to turn a standard crank over 7800. The harmonics will cause it to shed the flywheel eventually. Needs an Rsr crank or a stroked 2.0/2.2 crank + stretched SC rod combo. I would use a sandcast alum case.

[jmz]

Thanks. I have a long rod trick race motor on sandcastle case at present. This is just a spare parts build. Will likely source a different cam.