[VintageMusclecar]

Just a quick follow-up if anyone's interested;


I got the 572 for Yeti on the dyno a week or so back. It did better than I'd expected actually in regards to HP, but due to the fact that I couldn't install the headers the engine needed on the dyno due to space constraints, we wound up leaving quite a bit of low end torque on the table. Past dyno experience assures me the power is indeed there with the correct exhaust, I just don't have a dyno sheet saying so.


I got hung up waiting on a new carb from Holley, so the dyno shop made an initial pull with their dyno mule modified 750 which was WAY too small for this application. It made over 600 lb.ft from 3500-4900 peaking at 630 @ 4300 and 563 HP @ 5000 when the pull was stopped.



I finally got the new Holley in, plus I pulled the 1000HP I built for the 496 in my Chevelle and took it with me to the dyno. With nothing more than the swap to my 1000HP, power increased dramatically everywhere. The #'s from that pull are shown below. The 1000HP was running pretty lean at roughly 14-1 @ WOT, so there was still quite a bit of power to be had there as well.


Next was my new 870 Holley, but it was deep into the 14-1 range at roll-in out of the box, so we aborted the pull and took lunch. I bumped the jetting up 5 sizes all the way around which brought air/fuel ratios down to the mid 13's which was still lean, but safe. We did 2 more pulls experimenting with timing, finding a touch of power dropping timing down from an initial 34°, then 36°, then finally at 32°. Next I removed the 1.8 intake rockers and swapped on some 1.7's which cost a few HP up top but picked up a little power down low, which was the entire focus of this project.


BTW, we tried to tug the engine down into the 2000 RPM range but the dyno couldn't pull it down any lower than 3400 and hold it there.



If you'll notice the "sag" in torque at the hit, that's 100% the result of not having the correct size headers & collectors in place. I am 100% confident with the correct exhaust on it the engine will make 700+ lb.ft. torque--I don't really care about peak HP, but since it's already at nearly 600 @ 5200, that should be ample. I was only anticipating 525-550 HP. The engine only has 8.8-1 compression and all testing was done on 89 octane pump gas, and the engine will idle with a pleasant but mild lope at 750 rpm.


Yeti is currently in the shop getting the howling 4.10 gears removed and replaced with a new set of 3.54 gears and a Lock-Rite differential. Hopefully I'll be able to get the 572 in the truck sooner than later as the existing 454 is running OK but has alarmingly low oil pressure.


That should be enough to be able to haul anything I need to tow.