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I posted this in another thread here, but someone who also peruses these forums suggested I should post this in its own thread. Hopefully someone will find the info useful or helpful.
I just wrapped up the 3rd dyno session on the 496 out of my Chevelle.
To get everyone up to speed--
I originally built this 496 back in 2006 (I stated 2008 elsewhere in error). The original build can be seen here.
The engine consisted of a 2 bolt block, Eagle 4130 external balance crank, SCAT H beam rods, Probe pistons, a Crane flat tappet cam & matching valve train, stock stamped steel rockers, and a 163 intake. The cylinder heads are 100% stock 291 castings (rectangle port closed chamber) with 2.19 and 1.72 valves. The oiling system consisted of an M77HV pump (mistake #1) and a factory A body oil pan (mistake #2).
The first dyno session was done @ George Montgomery's shop where we recorded 6 pulls. The first pull was using the un-cut 163 intake, a LIST 3910 780 vacuum secondary carb, and open 2 1/4" headers.
RPM------CBT-----CBP-----BSFC
3000------522------298------.507
3500------520------343------.491
4000------504------384------.513
4500------479------411------.532
5000------459------438------.541
5500------428------449------.564
6000------414------474------.580
Over the next series of pulls, the headers were swapped out for a set of 2" Hedmans, a 3' long 3" exhaust was added with the actual mufflers that would be used on the car, the 3910 was replaced with a 3418 carb, and finally the plenum divider was removed which resulted in the following figures (the gains from the previous pull are in parenthesis highlighting the change solely from the cut plenum):
RPM------CBT---------CBP----------BSFC
4000------546 (+12)---417 (+10)---.483
4500------544 (+20)---467 (+17)---.454
5000------531 (+27)---505 (+25)---.493
5500------488 (+34)---512 (+36)---.507
6000------467 (+30)---534 (+34)---.536
6500------417 (+32)---517 (+40)---.580
The engine exhibited unmistakable oil control issues on the dyno, so the oil pan was swapped out for a 6 quart Stef's before the engine went in the car.
There was also a nagging ring seal issue which I finally found the time to address last month, which led to this series of dyno tests. The engine came down, the block was re-honed and I replaced the Probe pistons with a custom set of Autotec units which dropped the compression from 11.2 down to 10.5.
Fast-forward to 7/1/14: George's schedule prohibited re-testing there, so I made arrangements to dyno at Kammer Racing in Huber Heights, Ohio. The engine was put back to the same basic configuration as it was during the initial series of testing on George's dyno (as close as I could get it).
Here's one of the baseline pulls:
As you can see the numbers are very comparable, so I consider this a valid baseline comparison.
Pull #4 was a water/oil temp test. Pull #5 saw a swap from the 3418 carb to a 4781, but the pull was aborted due to the choke slipping closed during the pull.
Pull #6 with the 4781:
There was a significant increase in power at higher rpm with the 4781, but note the brake specific numbers between it and the 3418--the 3418 is going very rich up top. I'll be recalibrating the 3418 further and re-testing it again somewhere down the road.
Pull #7 was an oil level test.
Pull #8 was a 2° bump in timing.
Pull #9 was a swap from the OEM points distributor to an MSD unit. The curves were similar and the total was the same.
Pull #10 was very surprising. The 3" collectors were removed from the headers and 3 1/2" collectors were installed. Both pairs of collectors were the same length, and both tests used respective 18" collector extensions.
The 3 1/2" collectors hurt power everywhere. The 3 1/2" collectors remained for all subsequent dyno pulls for the remainder of this session (to pull #25), but for pulls #26 through 30, the collectors were changed back to 3".
Pull #11 was another water/oil temp test.
Pull #12 saw another drop in water/oil temps, and power went up again.
Pull #13 saw the 163 intake swapped for a heavily ported Holley Strip Dominator intake.
Pull #15 saw a lash change on the exhaust valves only.
Pull #17 was the addition of a 1" open carb spacer.
Pull #18 saw the addition of a 14X3 air cleaner. I tried to install the OEM air cleaner but I forgot that the base won't clear the secondary pump lever on a double pumper carb, so I had to use a "generic" aftermarket base.
Pull #19 was a spark plug test between non-projected tips and projected tips, both of the same heat range.
NOTE: Despite the oil pan swap, there were still oil control issues present during this round of testing. Varying oil levels were tried, but pressure still began to drop above 5000 rpm.
Continued.....
I just wrapped up the 3rd dyno session on the 496 out of my Chevelle.
To get everyone up to speed--
I originally built this 496 back in 2006 (I stated 2008 elsewhere in error). The original build can be seen here.
The engine consisted of a 2 bolt block, Eagle 4130 external balance crank, SCAT H beam rods, Probe pistons, a Crane flat tappet cam & matching valve train, stock stamped steel rockers, and a 163 intake. The cylinder heads are 100% stock 291 castings (rectangle port closed chamber) with 2.19 and 1.72 valves. The oiling system consisted of an M77HV pump (mistake #1) and a factory A body oil pan (mistake #2).
The first dyno session was done @ George Montgomery's shop where we recorded 6 pulls. The first pull was using the un-cut 163 intake, a LIST 3910 780 vacuum secondary carb, and open 2 1/4" headers.
RPM------CBT-----CBP-----BSFC
3000------522------298------.507
3500------520------343------.491
4000------504------384------.513
4500------479------411------.532
5000------459------438------.541
5500------428------449------.564
6000------414------474------.580
Over the next series of pulls, the headers were swapped out for a set of 2" Hedmans, a 3' long 3" exhaust was added with the actual mufflers that would be used on the car, the 3910 was replaced with a 3418 carb, and finally the plenum divider was removed which resulted in the following figures (the gains from the previous pull are in parenthesis highlighting the change solely from the cut plenum):
RPM------CBT---------CBP----------BSFC
4000------546 (+12)---417 (+10)---.483
4500------544 (+20)---467 (+17)---.454
5000------531 (+27)---505 (+25)---.493
5500------488 (+34)---512 (+36)---.507
6000------467 (+30)---534 (+34)---.536
6500------417 (+32)---517 (+40)---.580
The engine exhibited unmistakable oil control issues on the dyno, so the oil pan was swapped out for a 6 quart Stef's before the engine went in the car.
There was also a nagging ring seal issue which I finally found the time to address last month, which led to this series of dyno tests. The engine came down, the block was re-honed and I replaced the Probe pistons with a custom set of Autotec units which dropped the compression from 11.2 down to 10.5.
Fast-forward to 7/1/14: George's schedule prohibited re-testing there, so I made arrangements to dyno at Kammer Racing in Huber Heights, Ohio. The engine was put back to the same basic configuration as it was during the initial series of testing on George's dyno (as close as I could get it).
Here's one of the baseline pulls:
As you can see the numbers are very comparable, so I consider this a valid baseline comparison.
Pull #4 was a water/oil temp test. Pull #5 saw a swap from the 3418 carb to a 4781, but the pull was aborted due to the choke slipping closed during the pull.
Pull #6 with the 4781:
There was a significant increase in power at higher rpm with the 4781, but note the brake specific numbers between it and the 3418--the 3418 is going very rich up top. I'll be recalibrating the 3418 further and re-testing it again somewhere down the road.
Pull #7 was an oil level test.
Pull #8 was a 2° bump in timing.
Pull #9 was a swap from the OEM points distributor to an MSD unit. The curves were similar and the total was the same.
Pull #10 was very surprising. The 3" collectors were removed from the headers and 3 1/2" collectors were installed. Both pairs of collectors were the same length, and both tests used respective 18" collector extensions.
The 3 1/2" collectors hurt power everywhere. The 3 1/2" collectors remained for all subsequent dyno pulls for the remainder of this session (to pull #25), but for pulls #26 through 30, the collectors were changed back to 3".
Pull #11 was another water/oil temp test.
Pull #12 saw another drop in water/oil temps, and power went up again.
Pull #13 saw the 163 intake swapped for a heavily ported Holley Strip Dominator intake.
Pull #15 saw a lash change on the exhaust valves only.
Pull #17 was the addition of a 1" open carb spacer.
Pull #18 saw the addition of a 14X3 air cleaner. I tried to install the OEM air cleaner but I forgot that the base won't clear the secondary pump lever on a double pumper carb, so I had to use a "generic" aftermarket base.
Pull #19 was a spark plug test between non-projected tips and projected tips, both of the same heat range.
NOTE: Despite the oil pan swap, there were still oil control issues present during this round of testing. Varying oil levels were tried, but pressure still began to drop above 5000 rpm.
Continued.....
