grasshopper
New Member
Hi all,
In my quest to squeeze more horses out of the 3.9liter V8 in my recently assembled Defender 90, I fitted the engine with a Holley Truck Avenger 470 CFM carb, sitting on an Edelbrock intake maifold.
At first, despite my use of the agricultural 4-Speed gearbox in the D90, I was impressed with the performance boost from the new Holley carb, which delivered more robust acceleration than I had ever seen from a Rover V8 using either standard Stromberg twin carbs or any of the factory fuel injection systems I have tried over the years.
My grin faded in a matter of days though, when the engine started emitting ominous oil lifter tapping noises during a short test drive. Yanked the cylinder head covers off, and to my horror, SEVERAL valve springs, and one valve were snapped, all at once, on what was a newly rebuilt engine.
Now to my questions : Is a Holley carburettor with 470 CFM capacity simply too big for a Rover 3.9 V8 ?
Should I have chosen a smaller capacity carb to use with the 3.9v8, or can I retain this 470 CFM carb and prevent future damage by simply applying far less throttle when driving the D90 ?
Did my use of a 4-speed gearbox instead of a 5-speed have anything to do with the destruction of the engine valves when I test-ran the motor ? The rear diff in this D90 does seem to be geared rather low, causing me to shift gears up in rapid sequence, at what would be ridiculously slow speeds in any other vehicle.
Thanks for listening to my tale of woe, and I would be grateful for any advice that can be offered here.
In my quest to squeeze more horses out of the 3.9liter V8 in my recently assembled Defender 90, I fitted the engine with a Holley Truck Avenger 470 CFM carb, sitting on an Edelbrock intake maifold.
At first, despite my use of the agricultural 4-Speed gearbox in the D90, I was impressed with the performance boost from the new Holley carb, which delivered more robust acceleration than I had ever seen from a Rover V8 using either standard Stromberg twin carbs or any of the factory fuel injection systems I have tried over the years.
My grin faded in a matter of days though, when the engine started emitting ominous oil lifter tapping noises during a short test drive. Yanked the cylinder head covers off, and to my horror, SEVERAL valve springs, and one valve were snapped, all at once, on what was a newly rebuilt engine.
Now to my questions : Is a Holley carburettor with 470 CFM capacity simply too big for a Rover 3.9 V8 ?
Should I have chosen a smaller capacity carb to use with the 3.9v8, or can I retain this 470 CFM carb and prevent future damage by simply applying far less throttle when driving the D90 ?
Did my use of a 4-speed gearbox instead of a 5-speed have anything to do with the destruction of the engine valves when I test-ran the motor ? The rear diff in this D90 does seem to be geared rather low, causing me to shift gears up in rapid sequence, at what would be ridiculously slow speeds in any other vehicle.
Thanks for listening to my tale of woe, and I would be grateful for any advice that can be offered here.
