Andy Bettencourt
Super Moderator
What is the point in limiting cam profiles at all?
Some Proposed STL Rules Changes
- Thread starter Greg Amy
- Start date
Is that a trick question...?
Cam lift limitations limit maximum airflow, with the assumption that all other components would flow more with a larger cam*. Remember, in STU/L car weights are based on displacement, not on rated power using stock camshafts; short of using inlet restrictors**, it's the second-easiest way of limiting airflow and thus, ultimate power potential.
Roundy-rounders have been doing that for years, placing limits on cam and displacement. They have the added benefit of choke size on carbs, too. But in the end different engines will respond differently to the mods, and as we've seen in our favorite category with the disparity of designs there's no real easy way to predict it...
GA
* In a perfect world, the .425 cam limit would be the power limiter versus hitting throttle body, intake manifold, and/or head flow limits first. Yes, I recognize it's not a perfect assumption, but given most engines it's a pretty decent number. Witness Type R - YO! - cams versus GSR, the former having head flow rates similar to the GSR, and the limitation of the GSR intake which would not work well even with the Type R - YO! - cams - and maybe not even the .425 exhaust cams (intake is already there, and maybe actually be the basis for that chosen number, to limit the growth potential of the B18C1 engine...)
** Please...no...please let's not go there.
mossaidis
New member
(Partly off-topic)
The more compliant half of me says: in extreme cases where time and money are not an object, you are correct.
The more stubborn part of me says: Admit that a 9/10th GT-1 build is far expensive than 9/10th SSC build regardless of popularity and competition. Most of us in the IT will eventually build a 8 or 9/10ths car. Yes there are times when modifying to more restrictive rules is more expensive to do when compared to building to the more expansive rules, i.e. stock flywheel cut down to min thickness (viewed by some as a legal gain in IT ~ $350) vs buying a new flywheel (STx ~ $250). Yet in this case, I can argue that the suggestive rules which will involve TB/IM & control arm purchases, installation and testing (dyno time) costs will be more expensive than the keeping and legally modding these parts within the current STL.... even in the 10/10th world.
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>> Admit that a 9/10th GT-1 build is far expensive than 9/10th SSC build regardless of popularity and competition. ...
That has nothing to do with anything. I figured it was self-evident that i was talking about within a given class. But that said, back in the day, a top-flight SSGT Pontiac V8 cost more than a GT1 version of the same engine.
My point was that there is no way that specific STL rules can keep someone from spending money. They can force the diminishing returns curve to come into play at lower spending levels but a person who wants to spend $100K/year to run up front in STL will be better equipped to win than somene spending $10K/year trying to do the same thing. It's about expectations and if the rationale for any given allowance is based on limiting $$ spent, it WILL eventually be a disappointment if the class gets popular and competitive.
K
That has nothing to do with anything. I figured it was self-evident that i was talking about within a given class. But that said, back in the day, a top-flight SSGT Pontiac V8 cost more than a GT1 version of the same engine.
My point was that there is no way that specific STL rules can keep someone from spending money. They can force the diminishing returns curve to come into play at lower spending levels but a person who wants to spend $100K/year to run up front in STL will be better equipped to win than somene spending $10K/year trying to do the same thing. It's about expectations and if the rationale for any given allowance is based on limiting $$ spent, it WILL eventually be a disappointment if the class gets popular and competitive.
K
Andy Bettencourt
Super Moderator
You hit on my point. If the rules mandate factory intake manifilds and throttle bodies, why impose a rule that drastically limits engine choices or makes you 'back-engineer' them?
Gotta be a line in the sand somewhere, right...? 
They chose .600 for STO/STU, and variants of .4xx for STL dependent on head design. I suppose that number's as good as any, and was probably chosen based on investigation of what engines already have (I personally suspect that the GSR engine's .423 intake lift had a lot to do with it, as a way to limit that engine's possibilities. Purely speculation on my part, no evidence of any kind to support that assertion).
On the other hand, many many modern engines have cam lifts higher than .425? We've identified the K20A2 (but not the rest of the USDM K20 family), someone above mentioned a higher-output Toyota engine, and of course we know the Type R and likely the S2000 F20 engine. Are there many others?
GA
They chose .600 for STO/STU, and variants of .4xx for STL dependent on head design. I suppose that number's as good as any, and was probably chosen based on investigation of what engines already have (I personally suspect that the GSR engine's .423 intake lift had a lot to do with it, as a way to limit that engine's possibilities. Purely speculation on my part, no evidence of any kind to support that assertion).On the other hand, many many modern engines have cam lifts higher than .425? We've identified the K20A2 (but not the rest of the USDM K20 family), someone above mentioned a higher-output Toyota engine, and of course we know the Type R and likely the S2000 F20 engine. Are there many others?
GA
lateapex911
Super Moderator
Good thread, and great letter Chip42. Too bad it wasn't 8 letters, LOL.
mossaidis
New member
Ah yes argee. Yes I am dense sometimes.
that's just an excerpt - it could have been 20 letters
. the rules from the august fastrack are horribly redundant, self contradictory, and full of holes. plus theres some thigns I want to see changed like the brakes, alt material arms, and engine country of origin rules.agreed, though - thanks to tGA for setting up the subforum to hash this out. I just hope Mr. Childs et al are listening.