Classic 3.5 to 4.6 Liter Engine Upgrade

Dave Brown's 4.6 Installation
Photo: Dave's 4.6 Engine before stock Air Flow Meter was replaced.

Far left rear is a small bracket holding the wires away from the headers,

and another holding the RPI fuel pressure regulator.

Dave Brown's 87 RR suffered warped cylinder heads at 100K miles when it lost coolant and severely overheated (a non functioning temperature gauge sensor gave no warning and by the time the engine started losing power on the hills it was too late). Checking out the problem, Dave noticed water dumping out of the exhaust pipe during cranking -- a sure sign of expensive damage. He decided to take the opportunity to boost power output with an engine transplant.


After reviewing the options, Dave obtained a new 4.6L Rover short block for about $1900 from RPI Engineering (UK). The new 4.0/4.6 block design is greatly strengthened, and has cross-bolted main bearing caps (similar benefit to a “4-bolt main”). It also eliminates the bottom row of head bolts that tended to pull on the top of the heads and blow the head gaskets. The 3.5L heads can be reused, leaving the bottom row of bolt holes empty. Dave's were shaved .017" to restore flatness, and ported by a local performance shop for better flow. Composite head gaskets helped compensate for the shaving and gave a superior seal. A moderate Piper RP1 cam, lifters, and Cloyes True Roller timing chain and gears were added, with different keyways allowing 3 degrees advance or retard. Dave chose 0 degrees for maximum torque, rather than top end horsepower. Hedman headers and a Flowmaster muffler were added.

Photo: Bottom of engine showing O2 sensor and exhaust work to connect the headers.

Dave had been warned that not supplying the larger engine with adequate fuel could make it run lean and eventually destroy it. A variable fuel pressure regulator was supplied by RPI to meet this need using the existing ECU. However its installation was delayed, and without it there was no significant performance increase. To make doubly certain the new engine would be well fed and timed, Dave installed the Haltech F9a engine computer, having its settings adjusted by a local dyno shop.


The overall result was almost "race car" performance. Dyno test numbers showed maximum torque occurring early, with the power band flat over a wide range. Average fuel consumption declined from 14 to 13 mpg, no doubt partly due to the temptation of using the newfound horsepower.

Bottom of Engine
Photo: Bottom of Engine - Note the headers (extractors) and "Mean Green" high torque starter.




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Page revised February 1, 2012