The V8 Owners Forum -

If you are thinking of changing the cam timing for more mid range then you want to advance the cam not retard it. About 4 degrees is enough but since you are decreasing piston to valve clearance you will need to check it, try the cam in different positions now while the heads are not finally bolted down, take as many measurements as you can and make sure you have clearance then you can simply rephase the cam when you like to try the different options. Personally for torque I would advance 4 degrees, however some books have it the Rover already has the cam advanced 4 degrees anyway. Maybe find the true centreline and set that to the cam specs, then advance 4 degrees, it will make a big difference in peak cylinder pressure so you may get pinking on petrol. On gas though you will see a noticable benefit to mid range, however it will nose over a little sooner on top end.

Alan

Hi

Yes your right ADVANCE the timing lol (just read back my last post lol) The pistons are pocketed already, but I will get a lump of plactacine out though just to double check and get a definiative clearance. As it's all going in a LR disco, losing a little top end really isnt an issue. The 3.9 cam is a retimed (+4 deg) 3.5 cam but I might just add another +2 deg or do think thats not enough to make it worthwhile? I hardly ever run pertol, really only to start on and its there as an emergency (incase I cant get any gas) so detonation isnt a worry, plus with the megajolt I can set up a fairly retarded map for petrol.

Thanks

Brian

I would set it up and check clearance at 2,4,6,and 8 degrees advance. Then when its built compression test at each setting you can use. Best compression reading is where best torque is. Make sure the battery and everything else is even for the compression test. Quite a few serious engine builders do this to establish best cam position before they even fire the thing up.

Alan

bigaldart wrote:I would set it up and check clearance at 2,4,6,and 8 degrees advance. Then when its built compression test at each setting you can use. Best compression reading is where best torque is. Make sure the battery and everything else is even for the compression test. Quite a few serious engine builders do this to establish best cam position before they even fire the thing up.

Alan

cool idea.

That does make ALOT of sense! Quite a bit of work mind, altho not that much I guess.......

Might be an idea to run in the new cam first tho... altho I spose cranking speeds wont really hurt it????????

It won't do any harm at cranking speeds, use plenty of cam lube and it stays in place at that sort of rpm. Then relube it before fire up.

Alan

Cheers for that Alan, sounds like a plan! All I've got to do now is resist the current urge to hog out the ports on them heads I'm doing and spoil my well laid plans for sensible midrange gains lol