Question about adjusable cam gears

[erioshi]

I'm new here and while reading through the CCR, I did not find a provision for cam gears or other forms of altering a car's mechanical timing (as opposed to ignition timing). Is this an oversite, or is mechanical timing a 0 point change?

 

I realize that altering mechanical timing usually just allows the power band to moved up or down the RPM range slightly (trading torque for HP or visa-versa), but altering the cam to cam relationship on a twin cam engine can change turbo spool and other parameters. The dyno testing I have done (with a 400+ crank HP Evo) generally show the changes to be within 2-3% of a car's unaltered HP.

 

My main reason for asking is that if I understand the CCR correctly, if I wanted to run TT and an "unapproved" modification was found, then I can be DQ'd. Given that cam gears are very common, I was looking for a clarification.

[Greg G.]

Welcome, and thank you for being so conscientious. You are correct in your assessment that if a modification is not listed, it is illegal. In this case, it could legally be considered a non-OEM camshaft since the functional change is the same (although, granted, not as beneficial as actually changing out the camshaft for one with changed lobes, etc.)

 

A 2-3% increase on a 400 hp engine is 8-12 hp, which is worth, in general, about 2-6 modification points, depending on the efficiency of the modifications. For now, let's assume it is a +4 modification (non-OEM camshaft). I will look into it further and determine if we declare it as a separate modification or not for less points.

[erioshi]

For reference, the 2% figure above would be a more reliable gain than the 3% figure.

 

I suppose it's worth mention that in my example case, the gears are being used with non-OEM camshafts. Another point worth considering is that in my case, I have also changed the timing of both cams individually and altered the timing relationship between the cams - that would not be possible on SOHC engines, to achive that result you would need a different camshaft. Also smaller grind camsafts (like OEM units) would probably produce noticeably smaller improvements from cam gears. I have not dyno tested gears on stock cams, but I would expect results more in the 0-1% range, if there was any gain at all.

 

The main reason I brought all this up is that the car I will probably be running at NASA events this year is a 91 Toyota MR2 (non-turbo) that is currently receiving an engine swap. As part of that process, I'm considering changing the OEM cam timing slightly to move the HP and torque curves up the RPM band. The OEM power curves were fine for the donor car (a '96 Toyota Avalon with a 3.0 v6 and an automatic), but it feels very un-sporting to have an MR2 where the power goes flat well before red line.

 

I will provide a requst to have the engine swap approved once I have tracked down all the info that NASA requests.

[Greg G.]

Thanks.

 

If you are already using non-OEM cams, I'm not sure that you need to take any other assessment, because I imagine that someone could machine the cams to do basically the same thing that you are talking about. So, they would only take the +4 for cams?