I'm really glad to see that turbo springs are being allowed!!!!

One item not listed is the cold start idle systems that were discussed before the rule change period opened. I would still like to see clarification of this. Can we delete the venturi and idle control valve to simplify the vacuum system?

These items only are for cold starts and provide no running benefits. The removal costs nothing. Removing the idle control valve also simplifies things when mixing early and late harnesses and electronics.

As for the low compress vs. high compression pistons...

I've done a lot of work with this topic this season. Almost everyone in the region is now running a 88 motor or a shaved low compression motor. There is one racer that is still running a unmodified 83 motor, and he can't keep up with the rest of us. With the exception of the two racers, the other cars seem very close on power. Besides the one with the low on power 83, we have one race that has a "magic motor". This motor seems to make significantly more power than the rest of the field. I got a chance to do some back to back testing in a few low compression, saved to minimum cars at Eagles Canyon a few weeks ago. Here's what I found.

Car 1: (Mine) 1983 Block, Crank, Rods, Pistons (Over 175k on rings and mains). Late Cam and Head (min thickness, this season rebuild). 83 Electronics.

Car 2: 1986 Block, Crank, Rods, Pitsons (Low hours since rebuild). Late Cam and Head (min thickness, low hours since rebuild). 83 Electronics.

Car 3: 1987 Block, Crank, Roads, Pistons (Over 100k on Rings and Mains). Late Cam and Head (min thickness, unknown mileage since last valve job). 1987 Electronics.

Car 1 & 2 make near identical power after having the mixture richened up. The low end torque is a little lacking, but the car pulls hard to redline. Car 2, a customer's car, was just redone to minimum thickness. The owner notes that now he can pass miatas on the straits, where before he could not.

Car 3 is the "magic motor" car. It makes much more torque on the low end and the midrange power band is much fatter.

I have no explanation for the performance on this car. All three cars are timed identically and all were built by me. The only difference is the electronics and possibly fuel mixture. I know this #3 car is running very rich, but it does not have an A/F meter installed.

I hope to do a little more testing and possibly get these cars on a dyno.

Honestly, I think it probably has to do with timing. I know that not all of the cams, cranks, and flywheels are indexed 100% the same. These little differences add up to some big differences in timing. I have confirmed this with Lindsey Racing. They have seen cars timed perfectly by the markings be off by 5 degrees when measured. This would make an argument for adjustable timing gears. But before I would make this request, I think more data needs to be compiled.

-bj

Hey BJ are we talking about cars with over 140 RWHP?
And what about the TQ numbers. Most cars I have seen are pretty squared. HP and TQ are very close to each other. We should look at the relationship of HP/TQ and A/F ratio.
It would be nice to know what is actually making these bigger numbers.
It could well be that the cam timing is dead on. According to Milledge Porsche used the optimal cam timing. Anything off of stock produced lower HP.
My experience at Miller in 09 was that my car made more HP when I made it richer on the dyno there. The difference was about 2 peak HP. I was expecting to lean out the motor due to altitude.
If it turns out that there is a reasonable HP gain just by tuning on the dyno then we may be able to help the low compression cars get closer.
I dont know if there is any real gains from the front mounted air intake. the dyno will not show us that data. But one option would be to disallow a front air intake for cars with 88 pistons if that proves to be a factor.
I suspect that the best cars with 88 pistons have been dyno tuned. I know mine was though I did not go to great lengths doing it. I did not swap AFM, throttle body or any sensors. I did swap a DME but nothig was found there. The biggest gain was using the fuel selector switch and mixing 100 octane and 91 octane. Total gains were 3 HP.

cbuzzetti wrote:


I won't know until I get them on the dyno. The I don't suspect that the "magic motor" car will make any more peak power. It is in the low to mid-range where is seems to shine. When I get time, I'm going to pull the DME and ensure it is running a stock tune. It was purchased as a built car, so there's no telling...


cbuzzetti wrote:


I agree. As I can, I want to compile as much data as possible. Dyno, different part combinations, etc. I'm planning on pulling the maps off of early, late, and 88 chips for comparison, too.

All the cars I've done with low compression pistons, I have set the timing marks in the closest position to stock. This mean retarding the cam timing. This explains why these cars pull all the way to redline and seem to loose low end torque.

What I haven't tried is advancing the timing a tooth--with the minimum thickness head one tooth is actually less than a full tooth. I'd like to get dynos for each configuration.


-bj

BJ

-Thanks for the reminder, we'll work on hashing that out.

Get those cars on a dyno!

I'm curious to see how your max shaved head turns out.

I had a max shave earlier 6R head, and while it put down great TQ (141 ft. lbs), peak power was only average (132 HP), and high RPM 6,000+ HP was down relative to the high -compression motors. I did not have time to dyno-tune it, though.

One of the other things we'll be looking into is the 6R head, vs. the 8R head.

Sounds like a good plan Eric.

Sterling Doc wrote:


I need to look at the stampings to make sure we are talking about the same things, but I would guess that the 6R, or early head, will never make the power of the 8R head because the intake ports are so much smaller. I think when I measured them, the early head had a intake port volume of 10cc less than the 8R. When you shave the head and leave the timing in the closest to stock setting, it retards the cam timing. This would move the powerband and peak power higher. My guess is that the 6R head can't get enough air to make peak power that high.

-bj