KJZ78701 wrote:


Agree with your last sentence 100%!

We have a lot of disparate dynos (different chassis, different dynos, different exhausts)on HC and LC motors but none that I am aware of that were done for the express purpose of comparing the motors while controlling most (but definitely not all) variables, specifically driveline loss and variations between two different dynos.

What I would like to do is get a baseline reading from a fresh HC build, then swap in a fresh LC build, get a baseline, then adjust the cam timing as or if necessary to get it to HC numbers.

The main benefit would be to see if the 2 degree key currently allowed is enough to get the power numbers to match, and, if not, determine how much of a timing advance is needed.

I know a lot of experienced racers like Dan Pina and Tim Comeau believe the 2 degree key is correct to equalize the engines and my money is on them being right. However, without at least a quasi-scientific comparison there is still doubt in a lot of racer's minds.

This doubt leads to guys only wanting HC pistons, the proportion of HC to LC pistons available is low, not impossible to find but more difficult, this leads to the allowance of aftermarket pistons being an item consistently submitted year after year as a rule change.

Over the years I have seen this discussion in particular can get pretty spirited as those on both sides of the piston issue both see their position as keeping cost down and competition/performance tight and I can see both sides of the argument.

If we can figure out how much advance is actually needed to equalize the engines we can take this particular discussion of the table forever and go back to arguing over aftermarket wheels.

The dyno cap rules were written by Eric Kuhn, who took his brand new HC motor to a dyno with my car, which had his 3 year old LC motor. He tested both motors trying everything to vary dyno results, including but not limited to: Hanksville Y Pipe vs stock, Oil viscosity changes, full length exhaust vs shorty, muffler vs no muffler, various restrictor plates, early vs late AFMs, early vs late DMEs, Air-Fuel tuning, etc.
What amazed both of us was that once properly tuned only changing the AF ratio (using a simple AF gauge) my older much cheaper built early motor made (at its peak run) 139 hp and 140.5 tq as compared to his 141 hp and 138 tq fresh late motor. I added a restrictor and used thicker 20 50 from there on out. This motor lasted 7 racing seasons, with only replacing rod bearings and t-belt preventatively every 2 seasons.
Once this LC motor finally died this season, I bought a used HC motor from Neal. It needs freshening too, but I didnt have time for another solution. I can tell you honestly, I'll be keeping and rebuilding both motors. I truly dont believe there's enough of a difference between the 2 motors to make or break a car. I won 2 regional championships and a national championship on a very used LC motor, and this was a very moderate rebuild.
My biggest issue is dyno variance. At every national I've dyno'd the numbers have jumped as much as 8hp in either direction. This is a big bummer, but a reality of using dyno procedures to verify power. I HIGHLY encourage all of you to dyno tune your car during your regular season, and send the results to your regional director and or me- your national director.
I'll remind you all, this rule was put in place to keep the cars at parody, and discourage folks from over-spending on engine builds. Our goal isnt to DQ cars, but to get every car as close in performance as possible.

I agree, can we just talk about the use of aftermarket wheels? Lol!

No issue with aftermarket wheels as long as the direct replacement is specified and same weight as the cookie cutters. Also, no issue with a 3 piece cross member other than previously stated safety concerns. Seems like a nice to have with no advantage other than bearing replacement ease.

dpRacing Dan wrote:


Didn't realize there had already been a pretty exhaustive comparison.

My memory (though after looking through the forum I can't find the thread) was that the general consensus was a LC engine with the same the compression ratio as the HC engine was at a disadvantage due to the change in timing because of the shorter distance between the cam and crank pulleys resulting from the decked head. This is why the 2 degree cam key was written into the rules.

Was the 2 degree cam key tested, too? I think the crux of the issue is that the 2 degree key allowance gives the appearance that the LC engine is down on power without being proven to equalize.

Dan, Brian should have just opened your eyes. Where is all of the data and who is working with it?

I hope you look at my suggested rules changes again. The clarity is required to get more racers to help you with the data. Also, look at the early dyno sheets that Joe P. has up on Rennlist from ten years ago and study how the curves have changed, not just moved up. I still see development room there and your (HP+TQ)/2 is too simplistic.

Brian, do a little math. If cam gear has 40 teeth then you have 9 degrees per tooth. What is the distance from tooth to tooth on the belt? I believe it's about 10mm, so at max head shaving, you would end up with under one degree of timing change on the 9.5 compared to the 10.2. So, 2 degree modification is overkill.

But please educate me. Does the cam gear turn CW? If so, a head shave should be retarding the cam timing which would shift the power toward the higher RPMs, which is a good thing. Why try to defeat that?

I would have to double check on the 2 degree cam offset key- but I'm 99% sure it was in-place for the testing.