V8 low power, and please check my work

Hi,


I apologise in advance for this long post.


I have had my 1987 V8 90 for about 6 months now and I have been teaching myself some basic mechanics while trying to improve it a little. It did run seemingly ok to start with but not knowing this engine I had no 'norm' to compare it to.


Anyway, although I cannot see the engine number due to the exhaust manifold having a link bar which blocks being able to see the number on the engine, I am fairly certain it is a low compression V8, and is the original engine fitted to the 90, with SU carbs.


The first thing I did was buy a compression tester and tested each cylinder, results are below;


8: 120 7: 115
6: 120 5: 120
4: 125 3: 129
2: 124 1: 120


I do not know if these results are too low or not, however since they are all quite similar they should be ok? maybe?


Next I removed the pulsair system as it looked very rusty and research online suggests this will not cause any issues to pass an MOT. While doing this I also removed the huge airbox / filter and elbows, and fitted some cone air filters on to the carbs. I was not too sure what to do with the pipes that had connected to various bits - the one connected from inlet manifold to airbox, I have but a mini crankcase breather filter on after the flametrap. The other pipe that used to connect at one end to a large, metal flametrap like item, then on to the 'T-junction' just before the air inlet joining each carb elbow, and the other end went to a '2-1' flametrap (which connected to both the left rocker-cover and the left carb), now does not go anywhere (at the end where it used to connect to the T-junction.
So, my first question, could I just change the '2-1' flametrap for the left crankcase to a '1-1' smaller one, like there is for the right-hand rocker-cover? This way I could just remove this extra pipe and large metal flametrap like item.


The sparkplugs looked ok on the first check (although read on for why they don't now), and the HT leads look ok, along with the distributor looking clean inside albeit with a little white mark on each of the metal pegs inside the cap. So ignition system seems fine to me.


When I changed to cone air filters, I noticed one carb seemed to suck in more air than the other, so I bought a carb balancer (which turned out to be a very cheap, basic tool which gave roughly accurate readings), disconnected the carb linkage and balanced the carbs. Since I was doing this I decided to tweek the mixture screws because under very hard acceleration, there was a misfire occasionally and I thought this would fix it (it did).

After doing this and noticing performance improvements, I next decided to tweak the timing by turning the distributor. (Yes I know now that I should have done this before playing with the carbs) I noticed that I could gain a good performance gain by 'advancing' the timing a little, although I was careful that because I do not know what 'pinking' sounds like I had to be careful with this. Due to a noise being heard when the engine was cool and under load, I turned this back to roughly where it was originally. In fact, I actually 'retarded' it past the original point as that was what it took to quieten down the noise to a level I was comfortable with.


Around this time, I noticed the engine had got louder than when I first bought it, and actually seemed to have less power than I remembered. After looking around under the car with it running, I noticed there was a hole in one of the down-pipes from the left exhaust manifold. Looking at replacements online, I found that my manifolds are not standard, but mild steel versions of what look like 'sports' manifolds (i.e. they look like the stainless steel sports option manifolds but obviously not stainless). Not wanting to buy a complete exhaust at this time, I bought an exhaust repair kit and paste, which seems to have worked (although the 'nice' sound I used to enjoy the V8 make now isn't there and it sounds rather quiet and average!).


Now the car is a lot quieter, I can hear other bits clearer. Under hard acceleration at low-ish revs, there is a 'fluttering' noise similar to the noise that used to come from the manifold, but slightly different. I guessed it may be due to a rich fuel mixture so have turned this down a little, but this has made no difference.
I have tried the 'lifting the pistons in the carbs 1mm' and see if the engine revs go up or down, and although the revs do rise a little, I am reluctant to lean the mixture any more because I feel I am starting to lose power at mid - full throttle compared to where the mixture was before. Although I assumed the mixture was too rich, for example the idle when warm is much smoother, it almost seems that it is the correct mixture for idle, but too lean for pulling well under load.
Questions 2 and 3 are, what could I do to solve this? As a side note, I have tried pulling the choke out while driving / accelerating and this makes no difference. In fact, when the engine is fully warm and the car is sat idling, if I pull the choke out approx. 10mm, the revs rise to about 2000rpm, but if I pull the choke out any more, the revs drop and the engine stutters and does a similar sound to the flutter I mentioned earlier, but much worse (this is what led me to think it was running rich at full throttle, which now doesn't seem to be the case). Is this what is supposed to happen when you pull the throttle out with a warm engine?


The latest thing I have done is re-check the sparkplugs. These now look a little more 'sooty' on the circular part the 90 degree angle is attached to, but then quite white / cream on the tip near to the electrode. I can only assume this means I was running too rich and now running correctly, or maybe a little lean during my experimenting with the mixture. I have also noticed that there is wet oil on the sparkplugs, mainly the threads and sat in the little 'ridge' of the hole the plug goes into. There was a tiny amount of oil on a couple of the plugs the first time I removed them, however now there appears to be more oil than before. What could this be due to?


Another point I have noticed is, when driving around normal 'A-roads' and 'B-roads' (30-40mph in 5th gear, approx. cruising along at ~1000rpm), when the engine is warm with no choke, when I stop, it now idles reasonably smoothly at 750-800rpm. After a reasonable motorway run however, when coming to a stop shortly after, e.g. a slip-road to roundabout, the revs idle much higher around 1000-1100rpm, for about 30 seconds, then very slowly return to normal 800rpm ish. Any thoughts on this?


Any answers to my questions or any thoughts on any of the points mentioned would be very much appreciated. In case I haven't specifically mentioned, the power loss is in the form of, lack of acceleration unless setting the fuel mixture seemingly rich at idle, and that it loses speed going up hills unless again, I set the fuel potentially rich.


MC

hi, i have a 3.9 efi defender, however the principles are the same, first of all, the white bits on metal contacts is corrosion, wont help with spark, so get a new cap and rotor, secondly i would set the timing to 10 deg advance, the standard is about 6/8 deg advance, however they run also better at 10-12 deg, i rev mine to about 5.8/6k and i dont get any pinking at all..... i cant help you with carb issue as i have no experiance.....the extra soot on the plugs to me sounds like your either not getting a good burn either spark or running rich....they should be a nice light brown colour, i would imagine the hot idle is due to the extra vapourisation caused by the engine running hot like the situations you described.....however if it was me id take it to a old school garage with bunch of old men and ask them to check and set the carbs up right....unfortuatley it is a dying art, ive read book after book and still dont think i could do it properly if i had too., hope some of this helps....

oh just forgot to say i took my car to a garage and they set the advance to 6 degrees as it says to do and found it was down on power especially mid -top end......set it to 10-12 degrees

Hi, thanks for the reply, I have not done much on the engine since this post, I have been painting and fitting new doors and some other bits. I have found a 'happy medium' at the moment on engine tuning, it pulls reasonably well at lower speeds / revs, and does have some acceleration at top end, but not as much as I would like, especially on hills.

Now the weather is a little warmer I am thinking of changing the camshaft to see if this helps at all, although I take the point raised regarding the distributor cap, and will change it, however I doubt it will give me any better performance. Are there any thoughts on changing a camshaft? I have read up on the process but is it easy enough for a novice to do realistically? I was thinking of a sportier camshaft but not many for sale these days that I can find, all old forum references are years out of date on the topic.

kent H180 is the best for a standard engine - you will have to fit new lifters and it is advisable to change the timing gear as well - you may have to raise the rocker arms slightly to ensure correct valve timing but the cam comes as a kit with the shims included and instructions for fitting.

This camshaft will give an extra 20 bhp and much better torque - it really is a lovely cam - piper torque max is good also.

Given you already have free-flow exhaust manifolds, your next-best option is to bin the SU carbs and fit a dual-plane inlet manifold and 4-barrel carb such as a holley 390 or edelbrock 500. This will add the same amount of grunt again as the cam and gives fantastic throttle response.

here is a website you may find very useful

Tuning the Rover V8

Great advice griff as usual, at the expense of ££££ as usual!

Mr Noisy said:

Great advice griff as usual, at the expense of ££££ as usual!

Click to expand...

Sorry!

Mr Noisy said:

Great advice griff as usual, at the expense of ££££ as usual!

Click to expand...

Sorry!

two sorrys lol.

Dont turners advise new valve springs for that cam as the lift is over the 0.43'' max the standard springs can cope with? he would then have to take the heads off too. tbh its not really worth messing with the low comp engine as its got no balls anyway unless he fitted hi comp pistons from an efi sd1 or the like. better off just fitting an sd1 motor for £200 off ebay if he wants to do lots of work.

if he doesnt want to do lots of work he can gain 15 horses by taking the restrictors off from behind the su carbs that they fitted to landies at the factory to stop them being as fast as the rover cars of the day

Thanks for the thoughts on this so far. I have seen the kent cam on a couple of sites and looks interesting, some say you need lots of new parts along with it, others say just lifters and maybe better timing chain. Why would I need to remove the heads?

As for the restrictors, I think mine may have been removed already because between each carb and the part on the manifold it bolts to, there is only one 'spacer' between them, and from other pictures I have seen, there should be more than this normally.

If I did change the cam, the only part I am unsure of is the part involving the shims and 'preload', reading through various things has not made this any clearer as of yet.

Finally, thanks for the web address link, I had already found that and read through most of it, and although I would like to try a reasonable amount engine improvements, I think swapping an engine is beyond my ability.

if using standard parts no real need to do the preload as is the case if using a cam with less than 0.43'' of lift

Ok so I will not need to do anything much with the rockers and things then? This area looks complicated and open to many mistakes for the inexperienced, i.e. me.

It seems there is some uncertainty and debate on if the kent H180 will fit without other major work, therefore, is there another cam which will give improved performance but be below the max allowed height?