Holley Truck Avenger 470 CFM Carburettor in a 3.9 V8

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.

did you exceed the rev limits?

Logic would say that it must be revs not carb size (if it was purely carb size, you would expect problems with piston rings etc.).

Quite possibly though, the power from the carbs has allowed you to push past sensible rev limits. I am no expert on the V8, but thinking about the design age of the engine, you have to think that going past 5000 revs for an extened period is chancing your arm.

I'd rebuild the engine as is, but fit a rev counter.

Robrennie and Fett I thank you for your replies both pointing to revs as the possible culprit. I am definitely going to fit a rev counter before I fire up that engine again, as playing it by ear obviously didn't work very well.

The reason I went for the 470 CFM carb was that I originally planned to acquire a 4.6 v8 for the D90, but later changed my mind after the 3.9V8 became available when I ditched the idea of fixing up an old armored Rangie that I picked up last year, and then swapped the just-rebuilt engine from that Rangie into the D90.

Looks like I'll need to be extra careful with that accelerator pedal when this engine is back together. Revs were never a concern with the old Stromberg carbs, and that made me a tad careless while test driving the D90.

I think a 390 is better for smaller V8s but to be honest an Edelbrock 500 is a better carb.

Was the lifter preload checked when the engine was built ? I'd be more worried about the springs being coil bound than too many revs. Back in the spring I had to deal with a similar situation where a well known "engine builder" had supplied a 3.9 v8 which promptly broke most of its valve springs.The deck faces of the block had been machined as had the head faces.The valve springs didnt have a chance.
Another point is the poor quality of many replacement parts now - where did all the bits come from ?

Tell me more about this armoured rangie

Eightinavee I am giving away my ignorance here, but I am not familiar with the lifter preload check you mention, but it sounds like an evaluation of the valve spring compressive strength. A lot of making do goes on here in the third world, and in a typical engine build, the used valve springs are often used. I may have to order new ones from the UK to get better life out of those springs the next time round, after this first fiasco.


Fett, the armored Rangie was one of those seemed-like-a-good-idea-at-the-time purchases that I made at a junkyard here. Its original owner was the British High Commission, and I bought it without an engine, with the hopes of building up a car-jacker proof ride.

Fitted the 3.9V8 and found it to be woefully underpowered for the nearly two-ton bulk of the truck, but I finally got rid of the truck because I became very claustrophobic when test driving it, just knowing that I was only be a door-lock failure away from geting trapped in the vehicle and then broiled like a lobster in the tropical heat.

Also the steel plate armor made that Rangie very top heavy and unstable in turns. Finally I decided I'd be in far more danger driving around that tank than I would in a regular vehicle that took turns better and from which I could quickly egress if need be.

it looks like an LSE? should have had a 4.2 in , a 3.9 on carbs would be about 100 bhp short

They did say they were very wobbly on the corners, one of the "special" guys I worked with said that they used to roll alot of them and they were normally scrapped after that.

its amazing really as the 100 inch ones only came with a 3.5 efi orginally, must have been gutless.

I am thinking of getting one for when the Pa***s start blowing stuff up again but the last one I saw was a 3.5 minter and it was £20k

Did you have the A/C working on yours, must have been a cooker out there otherwise!

What you out there for? dont take that the wrong way, anywhere is better than here the way things are headed! :doh:

fit a 5.7 and get the brakes and suspension sorted

nah , Hemi

Sadly I sold the armored Rangie to recyclers who removed the custom back doors, the armored side windows and the heavy steel plating in the roof and body, before giving the vehicle a new lease of life as a mini tow-truck. Will post pictures of of similar such conversions in the Classic Rangie forum sometime.

The airconditioner in the armored Rangie repeatedly failed despite pressure leak checks, coolant refills and "repairs". With immovable, hermetically sealed, two inch-thick glass fitted all around, opening the windows for air was never an option, so the tank had to go.

Contemplating the possibility of someone getting trapped in the nearly sound-proof confines of the truck where it sat gathering dust, I opted to dispose of it, while retaining the ahem "overhauled" 3.9V8 for the D90.

I work in a catfish hatchery here, returning stateside just often enough to retain most of my sanity.

I take it the money is good in the catfish business?

Its a shame it was not on the road, it would have been worth quite a bit back at home (uk)

Mind you shipping might have been hard :doh:

Put some pics in the classic boys bit mate, sounds good!

can you help. i have a 3.9 and a truck avenger 470. did you have to change the jets in this carb if so do you rember what sizes. thanks ted

does any one know if the truck avenger 470 will work straight out of the box with a 3.9 or will it need re jetting if so what sizes. thanks ted

this thread is a year old, I havnt heard of anyone else doing this conversion- PM the OP and let us know what he says

a 3.9 with carbs going to make more than 100hp lol

fett said:

it looks like an LSE? should have had a 4.2 in , a 3.9 on carbs would be about 100 bhp short

They did say they were very wobbly on the corners, one of the "special" guys I worked with said that they used to roll alot of them and they were normally scrapped after that.

its amazing really as the 100 inch ones only came with a 3.5 efi orginally, must have been gutless.

I am thinking of getting one for when the Pa***s start blowing stuff up again but the last one I saw was a 3.5 minter and it was £20k

Did you have the A/C working on yours, must have been a cooker out there otherwise!

What you out there for? dont take that the wrong way, anywhere is better than here the way things are headed! :doh:

Click to expand...

come on , a 3.5 on carbs can make 150

I think you are to something here 8NV - I have read about this sort of thing happening from preload not being adjusted and now I am thinking that's what happened.

eightinavee said:

Was the lifter preload checked when the engine was built ? I'd be more worried about the springs being coil bound than too many revs. Back in the spring I had to deal with a similar situation where a well known "engine builder" had supplied a 3.9 v8 which promptly broke most of its valve springs.The deck faces of the block had been machined as had the head faces.The valve springs didnt have a chance.
Another point is the poor quality of many replacement parts now - where did all the bits come from ?

Click to expand...