Oil Pump Failure On A 4.6 Again !

[Ppaulred96]

WHY?

More compression
The 4.6 crank 4.6 rods and 4.0 pistons combination gives you almost 11:1 compression ratio (I think right at 10.8:1 if you do the math). I took a chance with this built not knowing how the GEMs ECU would react or how long the oil pump without pins would hold up etc. All seems to have worked out well thus far - - No pinging & more power than standard 4.6.

 

[ptschram]

More compression

I doubt this. I compared one of each before I posted my question. The dishes are nearly identical, but if it runs OK, who am I to disagree?

 

[Ppaulred96]

Sorry you have doubts - - maybe someone else will chime in to confirm. THe 4.6 pistons appeared to me to have a much greater dish. Maybe just my circle of friends but I thought this was fairly common knowledge. Anyway as you say it runs strong. Truth - - I did not do the math - - but faithful sources gave me the advice. Jimmy - - have you discussed this engine mod with Drew before?

 

[ptschram]

Even if it did have shallower dishes, the knock sensors are going to retard the timing so far to avoid detonation that you would have no benefit. If you had a Lucas truck and could take advantage of the increased compression, then you'd have something.

I seriously doubt you're gaining anything as an engine with an 11:1 compression ratio is going to require very good gasoline to avoid detonation.

 

[92rrrandall]

I too recall that simply using 4.0 pistons with 4.6 crank/rods yeilds 11:1 CR. And I also recall that the difference between 4.0 and 4.6 pistons is the size of the dish. Will doulble check to make sure this is correct.

This is a common mod with people who are using a very aggressive camshaft on a 4.6 engine. Increasing the CR is good for torque at all rpms. But going higher than 10:1(on pump gas) may be asking for trouble unless the overlap of the camshaft lobes is increased as well.

Randall

 

[ptschram]

Could be, but without recognizing the detonation issue, there is probably little improvement in performance.

 

[jymmiejamz]

Sorry you have doubts - - maybe someone else will chime in to confirm. THe 4.6 pistons appeared to me to have a much greater dish. Maybe just my circle of friends but I thought this was fairly common knowledge. Anyway as you say it runs strong. Truth - - I did not do the math - - but faithful sources gave me the advice. Jimmy - - have you discussed this engine mod with Drew before?

He may have mentioned it before, I know he's done a lot to that one motor he's got now for the MGB GTV8 conversion. I think it should have close to 300 hp IIRC.

 

[Ppaulred96]

PT,
Here are the dish sizes differences as provided to me.
Piston dish volume: 4.0-litre, 13.23 cc. 4.6-litre, 22.29 cc.
Crankshaft and rods also play a big roll in the equation as it has been explained to me.
I have no pings or knocks with this truck - I run BP 93 octane gas with no additives. Other factors to note: the heads on the truck have never been decked and I am running a composite gasket both are factors which lower the compression just a bit. I do not pretend to be an expert but some of the folks who advised me on this build know their stuff.
All in all as you said it runs - - I am happy and that is the bottomline.

 

[ptschram]

You have no pings nor knocks because the EMS is detecting them and retarding the timing.

I have looked much more closely at the psitons and they do appear to have the same compression heights and as you provided, the dishes are much more shallow, but using a stock GEMS ECU and 93 octane fuel, you're not getting everything out of it you could with better fuel.

Back in the day, I ran an SBC with 11:1 compression. Unless I ran 110/100LL AVgas, it knocked something horrible (when you could hear it, open headers made it difficult). Anything less than 100 octane fuel wasn't worth running and probably did horrible damage.

Using Lucas EMS and only 9.35:1 compression ratios I have encountered horrible detonation with even 93 octane fuel unless I retard the ignition. My penchant for cheap fuel requires all of my trucks to be retarded Even at 9.35:1 compression, these trucks are really sensitive to timing and fuel quality. They do run slightly better advanced, but fuel economy and warm starts suffer.

 

[MontrealRR90]

There were claims that when the machinery was sold, some of it bore tags indicating the machinery had come out of GM's R&D lab and had dates of late 1950. Much of the tooling was also that old. When the problem was identified, supposedly, Rover made some tooling changes to regain control over the process and later engines were supposed to not be plagued by the same problems.

It's all supposition though as few know the truth and they aren't talking.

tks PT. Finally im gona rebuild one from a RR since its for the wife and i will be using
it for our tent trailor wich is 4,500lbs. I will also get them top hat from a new guy here that does that. So i dont get a nice sliped liner after all that. I already have had two sliped liners on my trucks and now this oil pump. Sometimes i think the rover gods are testing me !

 

[MontrealRR90]

If you put a new front cover and oil pump on you could have the same problem because the dowel pins are misaligned from the factory. I have wondered if you could just remove the dowel pins all together and just use the bolts to align it.

I purchased a RR4.6 and it came with no oil pump cover could i use one from any 4.6 or it has to be from a RR ?