As for engine size, Pettis said "to be honest, Artis showed up with a 4.500-inch stroke KP crankshaft (Kellogg Performance) Henry ordered, so that is what we worked with for this combination. The conventional heads and this intake worked really well in feeding all those cubic inches. We normally don't run conventional heads on something this big but on the dyno this engine went to 8,800 rpm pretty easily and that was a pleasant surprise." He continued to tell us that the next common sizes up for crankshafts are 4.625 and 4.750 inches. Pettis explained that the piston speed increases dramatically with those sizes and it hurts the engine's ability to pull very high rpm-where he likes to run nitrous engines. "The higher we can keep the rpm, the more we stay away from the peak torque area on rpm drop-off at the shift. Peak torque is where cylinder pressure is highest and the chances of detonation are greatest. We make the engine push more rpm and ease the drop-off at the shift. 8,800 rpm might sound like a lot of rpm, but it is nothing when compared to a Pro Stock engine, so even 8,800 can still be easy on parts. This motor has the proper pieces to accomplish that," added Pettis.
Looking at the big-picture, the short-block is based on a Dart Big M iron block during a time when drag racers are desperately trying to shed weight and mostly turn to aluminum blocks. "The iron block definitely seals the walls better but it is harder to repair if you hurt the cylinders," said Pettis. He continued, "the car is in a class where you want more weight up front anyway. If we used an aluminum block, then the chassis would really require an additional 50 to 60 pounds to be hung up front. So in reality, the iron block is the way to go for this combination, especially considering where the Nova is going to race."
Our KP 4.500-inch stroker...
Our KP 4.500-inch stroker crankshaft is billet steel and was pendulum cut and lightened locally. However, it's important to note that KP Crankshaft's can accommodate any special custom orders to fit your needs.
Here is an area that has been...
Here is an area that has been trimmed to clear the crankshaft.
A little material was removed...
A little material was removed from the rods as well. Once the rods were modified, each was weighed so the crank can be balanced properly.
Moving to the rotating assembly, a KP crankshaft was employed along with GRP aluminum rods and JE pistons. The compression percolates at just 13.6:1, a number that is lower than other engines we've come across at this level. Pettis rightfully explained the reasons for the compression ratio, "on the nitrous stuff we tend to find that the higher compression makes the tune-up window smaller and too finicky. On several occasions we've reduced compression from 15:1 to 13:1 and it didn't result in slower e.t.'s at the track. Then we were able to get a little more aggressive with the nitrous tune and go even quicker with the lower compression. In naturally aspirated trim on the dyno, the higher compression numbers do reveal more power, but that isn't the case on the track." He continued, "We build the motor as if it is spec'd out for the power on nitrous. The cylinder pressure is going to be high with the nitrous so we dump the compression out of it. The cam and compression are mismatched in N/A trim but it comes together when the nitrous is engaged."
Next month, we'll finish up the big-inch mill and pull the pin on the engine dyno. Then it is off to the track in search of quicker times. Stay tuned!
Quick Notes
What We Did
Put together a big-inch doorslammer mill
Bottom Line
If you want to have a competitive nitrous car in the drag radial scene, then this build is for you
The lifter bores were enlarged...
The lifter bores were enlarged from 0.842-inch OD to 1-inch OD. This allows a bushing that supports a larger Jesel lifter with its bigger roller wheel. A large roller lifter will open the valve quicker as well as being a stronger unit.
Not only was the lifter bore...
Not only was the lifter bore enlarged, Pettis also moved it over 0.050-inch. This accomplishes a few things, first is that it allows room for a larger pushrod without having to ruin the heads. Secondly, the modification allows for a slightly straighter pushrod angle. Both are critical to running higher rpm levels while still maintaining valvetrain reliability.
"We found that when we add...
"We found that when we add a large-body lifter with the larger 55mm camshaft the oil flow to the lifters is affected. We modify the bushings to get ample oil flow to the lifter. The alternative is to modify a set of lifters, but who wants to do that to a brand-new set? This way you drop 'em in and forget about 'em," commented Pettis.
The JE piston is dropped into...
The JE piston is dropped into the hole for piston-to-valve clearance but first Pettis puts tape around it to simulate growth when the engine is warm. This prevents piston rock when the block and piston are cold.
A major process in the Pettis...
A major process in the Pettis book of engine building are the piston mods. Pettis ensures the domes fit properly in the combustion chambers and he marks it all with ink.
"We fix the valve pocket layout...
"We fix the valve pocket layout problems because piston companies don't have the engine in their hands so they can sometimes be a bit limited in how close everything will fit. We will have the pockets made really shallow so we can custom fit to each engine," commented Pettis.
Pettis was quick to tell us...
Pettis was quick to tell us that he makes the pistons square to match the valve perfectly. They also try to remove as little material as possible from the JE piston so the pocket depth doesn't get too close to the top ring and cc's are not wasted. This allows a shorter dome so that flame travel is improved. Keeping the dome thick also strengthens the piston and keeps heat away from the rings.
Total Seal rings were used...
Total Seal rings were used exclusively during this engine build.
The JE pistons are outfitted...
The JE pistons are outfitted with the Total Seal rings and the long 6.680-inch GRP aluminum rods are hung on the forged pistons.
Pettis checks the cylinder...
Pettis checks the cylinder volume so he can accurately calculate the proper compression ratio. The modified dome and the Edelbrock cylinder head combustion chamber (which was also measured by Pettis), combined with a copper head gasket, bring compression to 13.6:1.
One more test with the pistons...
One more test with the pistons is performed, Pettis checked the ring tension. He informed us that you want around 26-28 pounds of oil ring tension with a nitrous motor. A race-only naturally aspirated setup can go down to 8. But on a nitrous engine you want more so no oil passes into the combustion chamber, which can lead to unwanted detonation. You lose a little bit of power but the dry combustion chamber is worth the trade-off.
A Moroso oil pan is combined...
A Moroso oil pan is combined with a wet-sump oiling system. The oil pump is an external one from Moroso.
Finally, after what seems...
Finally, after what seems like half a dozen mock-ups the short-block is finally assembled for the final time. Next month, we will be covering the top-half of the engine, engine dyno results, and finally on-track performances from our new Pettis Performance 598ci bullet.