Oldsmobile 455ci - Fortified 455

There are people that will tell you that the 455ci Oldsmobile Rocket motor makes a better street engine than a race motor. In truth, a stock 455 does have a couple of drawbacks that are detrimental to living life above 4,000 rpm for extended periods. The 455's Achilles' heel is a poor oil return system. The narrow passages from the stock heads do not allow oil in the valvetrain to return to the pan in an efficient manner. This condition can lead to instant death for a 455 that is run wide open for extended periods of time. As rpm increases, the oil goes to the top of the motor and stays there, draining the pan dry and starving the bottom end at the same time. It doesn't take long before the inevitable happens, and the dreaded screech of metal-to-metal contact bellows from the engine compartment, driving an Olds owner to tears. In the past, many people who have experienced a severe drop in oil pressure while running their Olds motor would immediately install a high-volume (HV) oil pump, which could worsen this condition. The fix that will allow your motor to survive extended high-rpm runs is to restrict the oiling system and install a larger-capacity oil pan.

Unfortunately, this lesson was learned after this Olds motor was rebuilt and put to use. Thankfully, Mondello Racing was contacted before any damage had occurred. After explaining to Lynn Welfriger at Mondello Performance Products that this 455 would live a high-rpm life (High for an Olds motor anyway!), he set us up with all the parts necessary to keep the motor from seizing. As soon as the UPS man dropped off the box of parts, we headed over to Maynard's Custom Cars and Trucks to have them work their engine building magic. Installation of the oil restriction system required the disassembly of the motor and sending the block to the machine shop to be cleaned. Since the motor had to come apart, we seized the opportunity to replace the nondescript, RV-grind camshaft with a new COMP Cams roller valvetrain. We also wanted to see how the motor would respond to having more fuel thrown at it. After dyno testing with the cam and ignition, a vintage Offenhauser tunnel-ram and a set of custom carburetor adapters were added to provide a home for a pair of 750-cfm Holley HP-series carbs, mounted sideways. All the performance gains were measured on Westech Performance Group's dyno in Mira Loma, California.

The oil restrictors let the motor rev freely to 5,500 rpm without fear of seizing. The increase in carburetion kept the motor happy on the top end and made a few extra ponies. Check out the accompanying photos and dyno numbers.

Our story begins with the...        read full caption Our story begins with the disassembly of our freshly rebuilt, but almost stock, motor. After removing the intake manifold, carb, distributor, and valve covers, we can clearly see the "turkey tray" metal intake manifold gasket. These are considered weak due to leakage concerns on this motor and will be replaced with a better cork gasket when the motor is reassembled.

This nifty tool grabs the...        read full caption This nifty tool grabs the insides of the lifters for easy removal. You'll also notice that the rocker arms and pushrods have already been removed.

After turning the motor upside...        read full caption After turning the motor upside down, the oil pan is unbolted and removed from the block for access to the oil pump and the rotating assembly. The marks on the connecting rods indicate that this motor was balanced the last time it was rebuilt.

After the pistons are removed,...        read full caption After the pistons are removed, the main caps can come off, and it's time to pull out the crank. The crank looked to be in good shape (it should have been, with very few miles on the rebuild), and it only needed a good micro-polishing before being put back into use.

The engine has now been stripped...        read full caption The engine has now been stripped down to just the bare block and is ready for our oiling system modifications. Note that the freeze plugs were popped out. This wasn't a necessity, we just wanted to ensure both parts were new and properly installed.

The fortification of our 455...        read full caption The fortification of our 455 will come from a restricted oiling system designed and marketed by Mondello Racing. The restriction will come in the form of oil-restricted cam bearings, main bearing oil galley restrictors, and lifter bore restrictors. The goal of the restrictors is to slow the flow of oil to the top end of the motor, giving the oil that is already there a chance to return to the pan. A new 10-quart oil pan provides a boost in oil supply versus the stock 4-quart pan. The new pan features a trap door and built-in windage tray. A new high-volume, high-flow oil pump with 7/8-inch-diameter pickup will also be installed.

The oil restrictors will be...        read full caption The oil restrictors will be installed in the No. 1, 2, 3, and 4 main bearing oil galleys. In preparation for installation, the restrictors are coated in blue Loctite(R).

The restrictors are then pushed...        read full caption The restrictors are then pushed into the oil galleys using a punch and hammer until they are under-flush with the opening of the galleys.

A new set of main bearings...        read full caption A new set of main bearings is then drilled out so that the holes align perfectly with the restricted oil galleys.

We then chamfered the edges...        read full caption We then chamfered the edges of the freshly drilled holes with a file. We don't want any sharp edges anywhere near the crank.

The new bearings are then...        read full caption The new bearings are then installed into the engine block. You can see in this photo how the oil hole is clearanced so that it aligns with the oil restrictor.

With the bottom end restrictors...        read full caption With the bottom end restrictors installed, we can now move up to the lifter galleys. The lifter bore oiling holes will receive restrictors next.

In order to install the restrictors,...        read full caption In order to install the restrictors, the small holes inside of the lifter bores are threaded using the tap provided with the kit.

Once all of the lifter bores...        read full caption Once all of the lifter bores are threaded, a blower attachment with shop air is used to clean out the bores. Again, blue Loctite(R) is applied to the oil restrictors prior to installation.

After installing all of the...        read full caption After installing all of the oil restrictors, the block was sent to the machine shop to have the old cam bearings pressed out and the new Mondello oil-restricted cam bearings installed. While the block was there, we also had the cylinders honed for a new set of rings and had the block hot-tanked to remove any dirt or metal shavings. After threading the lifter bores, we wanted to make sure everything was clean and free of metal shavings prior to reassembly. While the block was gone, we also micro-polished the crank and chamfered the oil holes to further improve oil distribution across the bearings.

We chose ARP fasteners to...        read full caption We chose ARP fasteners to replace the stock main bearing cap bolts and rod bolts. In addition to being crafted of better-quality materials than our factory fasteners, ARP fasteners are also much more consistent in their manufacturing. What's the biggest reason we upgraded to ARP fasteners? They aren't 30 years old like our original bolts and offer cheap insurance.

Once all of the main caps...        read full caption Once all of the main caps were in place, they are sequentially torqued to 120 ft-lb. The pistons were then fitted with new rings and reinstalled. The rod bolts were torqued to 42 ft-lb.

Here is a shot of the new...        read full caption Here is a shot of the new Mondello PN SP-765 high-volume oil pump. This pump has a larger-than-stock, 7/8-inch-diameter pickup for improved flow under hard acceleration. The bottom end is now assembled and the timing chain and gear is installed. On a 455 Olds, this must be done prior to installing the oil pan.

Fel-Pro gaskets are used on...        read full caption Fel-Pro gaskets are used on the pan rails. The Mondello Racing 10-quart oil pan is installed using ARP 12-point bolts. The new pan features a built-in trap door to keep the oil near the pump pickup. A windage tray is also incorporated to prevent parasitic loss of power due to the crankshaft being soaked in oil.

The heads are the original...        read full caption The heads are the original '71 C-castings, which don't flow all that well compared to new cylinder heads feeding engines of similar dimension. They received a mild exhaust porting during the engine's previous buildup and remain unchanged. An Edelbrock Performer intake manifold was installed, then we hauled the Olds over to Westech Performance Group to see what kind of power it was making.

Steve Brule bolted the motor...        read full caption Steve Brule bolted the motor onto the dyno and installed a Demon 850-cfm carburetor, MSD-6AL ignition, and a set of Hooker headers for the dyno test. Three pulls were made on Westech's dyno, showing the near-stock 455 was making 403 hp at 4,500 rpm and 533 lb-ft of torque at 3,600 rpm. The most important aspect of the test was shown by the oil pressure. Throughout the dyno runs, with an oil pan full of 20W-50 Mobil 1 synthetic, we noted that the engine produced a steady 75 psi oil pressure and peaked at 90 psi. Prior to installing the oil restrictors, this 455 produced 50 psi at idle and 60 psi under hard acceleration. Under extended periods of hard acceleration, this would fall off considerably when the oil temperature rose. Typically, pressure would fall to barely 15 psi at idle. With the oil restrictors installed, the motor produced a minimum of 55 psi, even when the oil temp approached 240 degrees.

After establishing the baseline...        read full caption After establishing the baseline performance of the motor, we replaced the old cam with a COMP Cams Xtreme Energy 284 hydraulic flat-tappet camshaft. This cam will give .240/.246 lift and duration at 50 degrees, with a gross valve lift of .541 inch on the intake and .544 inch on the exhaust side. Lobe separation is 110 degrees. The new cam was ordered as part of a kit that contained a new true double-roller timing chain, new valvesprings, the correct valve locks, and retainers. In addition to the new cam, we also installed COMP's Magnum roller rockers, pushrods, and guideplates. The roller rockers are considerably lighter than the stock cast rocker arms and will reduce friction in the valvetrain.

Steve re-installed the old...        read full caption Steve re-installed the old intake manifold, carburetor, and distributor used in the initial dyno runs. A few more pulls on the dyno netted 438 hp at 5,300 rpm and 538 lb-ft of torque at 3,900 rpm. Again, the motor maintained 75 psi of oil pressure throughout the dyno tests.

Now, we come to really fun...        read full caption Now, we come to really fun part, installing the tunnel-ram and dual carbs. Offenhauser is the only company that makes a tunnel-ram for the 455 Olds, and it is designed to have a pair of carburetors mounted front to back. Because we decided to install a pair of 750-cfm Holley four-barrel carbs side-by-side, we had to have a special pair of carburetor adapters machined for the tunnel-ram. There isn't enough room for the 750s to be installed front-to-back, and the mounting pattern of the tunnel-ram didn't allow for the carbs to be mounted sideways, so we had a local machine shop mill the adapters out of 1-inch-thick billet aluminum. The completed assembly looks awesome and, hopefully, will perform just as good as it looks.

Once the Offenhauser tunnel-ram...        read full caption Once the Offenhauser tunnel-ram and dual Holley 750-cfm HP carbs were installed, the motor was ready for its final dyno runs. The final tally was 452 hp at 5,400 rpm and 541 lb-ft of torque at 3,700 rpm. While we did gain about 14 horsepower, it became apparent that we had run out of room with the stock heads, and they were now our limiting factor. Jetting the carbs and adjusting the timing did virtually nothing to affect the power output or running condition of the motor. It's clear that we wouldn't be able to take full advantage of the tunnel-rams potential without some radical cylinder head work. On the other hand, Edelbrock does offer aluminum heads for the Olds that put out some pretty impressive flow numbers. Maybe next time!