Rat vs. Mouse

When it comes to max power, it’s hard to beat a Rat motor. There are plenty of options for the big-block crowd, with the 454 the least expensive to build. This is the GM Performance Parts 502/502 that appeared in the Nov. ’01 issue before its cosmetic makeover. This motor ended up making 553 hp and 608 lb-ft of torque!

Cylinder heads dictate power potential from any engine, and it should come as no surprise that the Rat motor has this area covered with monstrous ports that can flow more air than a sewer pipe. Unfortunately, Rat heads are also very expensive.

Two big-block stroker packages mentioned in this story are based on a 496ci Rat, which is nothing more than a custom steel crank that bumps the stroke an additional quarter of an inch. This is a Crower 4340 steel crank and rod package for a 496 that we will be building in the near future.

Perhaps the most budget stroker package on the planet is a cast crank 3.75-inch stroke crank that drops into a 0.030-over 350 block to create a 383 small-block. Add a mild cam and decent heads, and 400 hp is a cinch.

Don’t be fooled by monster-sized carbs, even for a big-inch big-block. The Holley 750 and Demon 750 double-pumpers are both excellent carbs that can support well in excess of 600 hp without difficulty. They also can be employed on mild 375hp small-blocks.

Another excellent choice from GM is the 454 H.O. long-block that’s rated at 425 hp and 500 lb-ft of torque. Right out of the box, this oval port Rat offers tremendous potential. Stay tuned for future issues when we flog this Rat to see what it’s made of.

Tim Moore’s 422hp Hot-cammed 355ci has to be one of the more successful small-blocks that we’ve tested recently. This motor runs great on the street and yet offers an exceptionally smooth idle for everyday driving. We estimate that almost anybody could duplicate this engine from carb to pan for less than $3,200.

If you are seriously considering a Rat motor to replace that little Mouse, remember that you will need to change headers, the entire accessory drive, perhaps install a larger radiator, and possibly even stiffer front springs. All of these additions will drive up the cost of the conversion.

How’s this for a budget idea: Build a cast crank 383 using a set of iron Vortec heads. But before you start building, know that GM Performance Parts now offers the HT 383 outfitted just like this with a mild hydraulic cam. This motor is rated at 415 lb-ft at 3,500 with 325 hp at 4,500. Bolt in the Hot hydraulic roller cam, and you’d have a thumper 383. The engine is PN 12497317, and it sells for $3,895 through Scoggin-Dickey or any GM Performance Parts dealer.

While head porting is expensive, it’s one of the easiest ways to really pump up the power. A qualified cylinder head specialist can take a set of mediocre heads and create additional horsepower and torque.

This is Beck Racing’s blown 383ci small-block that, in its upgraded combination, makes 570 hp on 92-octane pump gas.

The Beck Racing 496ci can also make 564 hp on pump gas, and it doesn’t need a blower to do it. This Rat cranks!

More Power. The performance quest has always led horsepower junkies on a search not only for more power, but also for the least amount of coin. Anybody can throw money at a project and end up with an impressive engine that makes gobs of power. The art comes in when you can build an engine that makes serious power and do so for less than conventional wisdom dictates.

Years ago, CHP performed a heads-up contest pitting a 408ci Rat against a 408ci small-block (Rat Versus Mouse). Even with rules like iron heads and the same camshaft and header sizes, the Rat motor clearly won this shootout with 464 hp and 465 lb-ft of torque against the Mouse motor’s valiant but losing 423 hp and 443 lb-ft of torque.

We still receive letters about this contest, offering suggestions on how to make the comparison more even. Frankly, no matter what we do, the Rat motor always wins. Big-block heads have larger ports, the valves are larger, and flow is far superior. Over the years, CHP has performed more than 60 small- and big-block cylinder head flow tests. If you will accept the fact that higher flow bench numbers virtually guarantee more power, then it doesn’t take long to figure out that even a stone-stock, oval-port Rat head from an ancient 396 can flow more air than most hot aftermarket small-block heads.

For example, a stock production 049 oval port big-block iron head with stock valves starts life with a 253cc intake port and flows 232 cfm at 0.400-inch and 250 cfm at 0.500-inch valve lifts. To equal those numbers a small-block requires an aluminum aftermarket cylinder head like the Air Flow Research 180, Brodix -8 Pro, or a TFS 195cc head, all of which are more expensive cylinder heads with smaller 2.02/1.60-inch valves. Add in the larger 454 bore, and the big-block’s advantages just keep adding up. Since cylinder heads are the key to any performance endeavor, it’s clear that attempting to create a level playing field between a small-block and big-block is probably a waste of time. So we decided to look at the classic confrontation between the Rat and Mouse from a monetary perspective.

Ultimately, when you stomp on the throttle of any hot rod, it’s the power curve and the drivetrain that determine how well it runs. The more power you make, the quicker and faster your car will run. The old wheeze “power costs money—how fast do you want to go?” will always be true. If we were all rich, we’d probably all be driving gas-guzzling big-blocks. But because most of us have champagne tastes and soda budgets, the small-block is often the economical move. So we decided to look at these engines from a power-per-dollar standpoint. But before the big-block folks pull out their poison pens and accuse us of Mouse bias, let’s start by admitting that right out of the gate.

Yes, the small-block does have a distinct advantage >> in this category. However, we are not here to convert anyone from one camp to the other. We’re here to present the facts and let you decide on your engine of choice. Small-block parts are less expensive and plentiful due to basic economics. With a huge demand, manufacturers build large numbers of parts. Through economies of scale, they can afford to build these parts very inexpensively, which means they can pass those savings on to the consumer. That’s why a small-block crankshaft or cylinder head costs less than a big-block. There is more supply, so the cost comes down.

We’ve assembled several interesting viewpoints for evaluating big-blocks and small-blocks. The idea is to look at these different engine combinations from both the power and price standpoints. Sure, we’d all like to have a supercharged big-block that makes 1,000 hp and idles like a stocker, but then minor inconveniences like eating and rent intrude into our best horsepower daydreams. Yet despite the realities of life in the 21st century, there are ways to build a fun-to-drive engine that doesn’t cost a ton. It all depends on how much you’re willing to sacrifice to attain your goal.