13 5.3L BigBore Stroker + 2.9L Crusher = Awesome!

Alternative Auto has built several 5.3L BigBore-Stroker modular’s in the last few years. These are centered around the FRP iron BOSS-5.0 modular block. This block is capable of supporting 323 cubic inches when combined with a 3.750” stroker crank.

We just want to give an up-to-date review of what this 5.3L short block is capable of when combined with a moderate to high amount of boost (about 21psi) when supplied by a modern Whipple 2.9L crusher kit in a 2004 Cobra with an Automatic trans conversion using a 4R70W.

This combo uses “off-the-shelf” Crower Stage 2 blower cams, un-ported (but freshened up) stock 32v heads with a spring change to go with the cams. Compression on this one is 9.25 due to the planed higher levels of boost from the big 2.9L Whipple. Most of our shortblocks are 10.25+ to 1.

Fuel delivery consist of 80lbs injectors, and a “return” converted fuel system fed by a “Big-Bosch” external fuel pump. Also, this car is tuned for, and burns 110 leaded Turbo Blue Race fuel. It has large Kooks headers, and a full 2.5” exhaust system ending with Magnaflow mufflers. The rest of the power train consists of a 4R70W automatic trans and a straight axle conversion with 3.73 gears.

This combo could have most likely done very well on unleaded 93 octane, but it’s also going to see about a 100+ shot of NOS on top of the boost. We’ve decided to run it on 110 leaded racing fuels for maximum protection for the motor both with and w/o the NOS on top of the boost.

Please excuse the lack of a TQ and RPM reading on the graph at this time. Our Dyno’s tach input lead/ignition pick-up was broken during the testing, so we were only able to graph Rear Wheel Horsepower and tire Mile-Per-Hour. These RWHP numbers are still legit DynoJet numbers, just no torque unfortunately.

With what we feel is a tune that will never “burn-it-down” on 21.5psi of boost, we’ve managed 736rwhp and with approximately a 100 shot of NOS, we got 800rwhp. It can handle much more spray, but we’ve choosing to keep it very safe at this time.

This combo is easy to achieve and may seem somewhat exotic, but it’s all rather simple with entirely off the shelf components. This combo is not over thought and over built as most people would do while trying to achieve these levels of power reliably out of this combo. The ignition system is totally stock, no enhancers at all, just a very tight spark plug gap. The cooling system is stock with the exception of a 180 degree thermostat. It also doesn’t have or need the over hyped internet fad known as the “rear cylinder head coolant mod”. We’ve found over the years that this mod is useless and does nothing to protect the motor or cooling system. Alternative Auto builds and modifies countless 32v applications and we never see any need for this over blown and hyped mod!