Thread: Flat spot caused by 3.5lt really a 3.9lt?!

Had a close look at the vacuum advance gizmo? they are prone to perforate and testing is relatively simple. - Take the hose off at the other end, suck strongly and use your tongue to 'seal' the hose end. Wait 30+ seconds and see if the vacuum 'disappears'.
It shouldn't.

Being a tiny bit OCD, I'd also suggest taking off the distributor cap and rotor button - VERY carefully /budget on a new one anyway! - and see if your sucking is actually moving the IGN 'advance' mechanism.
Good excuse to oil the dizzy shaft felt pad.

A future Ignition module upgrade from the Prince of Darkness (LUCAS) to the BOSCH BIM 024 is a good idea.

There is a FORD rotor button that can be substituted for the OEM one, the advantage being a wider 'business end electrode'. Rover v8's can be run with more timing advance than is specified... around and up to 6 degrees more. The wider end shortens the gap from rotor to inside the dissy cap points.
Heck, why stop there? Order a new distributor cap and may as well change the leads too....

Engine number prefix should clue you on the capacity and compression ratio of your motor

Thanks guys.
Forgot to mention cap rotor button and leads are new, and i just fitted a vacume advance and visusly checked it was working.

Reason for questioning the engine capacity is that being clearly labled a 3.5 on the engine, i have no way of knowing if they lengthened the stroke to 3.9 during the rebuild hence the crappy after market ecu. However I realise i could be barking up the wrong tree.

Further info... Idle is Very smooth, timing is at 6btdc at the mo. But i doubt that would account for the complete lack of acceleration at highway speeds. Especially given it pins you to your seat taking off from the lights.

A 3.5 is the same stroke as a 3.9. You can't easily "recondition" one into the other as the blocks are a different bore size. Read the first few digits of your engine number (next to the dip stick tube) and plug it into a LR engine number data base. The external accessories from a 3.5 will bolt on to any of the bigger capacity blocks so are no guide to capacity.

Rover V8 Engine Numbers

Check that your distributor has fully working mechanical advance. base timing can be raised to 10 degrees on low compression engines no probs.

Mixture wise you need an O2 sensor in the exhaust to get any idea of what is happening under load, there's all sorts of stuff out there if you're interested. Even a cheap narrow band sensor will tell you something with little more than a simple multi meter. 0V lean, 0.8V+ rich, look for transitions as you power up.

You can lever off the cover of the flapper and adjust the spring preload to change the mixture profile. Make sure you keep note of where you started from so you can go back there.

Thank you.
Will find out the engine number and take it from there.
I have a spare flapper, so can play with that one and not risk the other.

If its a 3.5 block its possibly been stroked which would explain the aftermarket ECU, so it could be 4.2 + capacity.

Is their any way to find out without dismantling part of the engine?

couldn't you verify the stoke and piston size by dropping the sump

seeya,
Shane L.