Discovery 2 4.6 v8 build help!

[Tony22593]

Hi all, fairly new to v8's but now I am achieving one of my dreams by building one and dropping it into one of my favourite cars, a discovery 2. At the minute I have an all stock Bosch motronic 4.0 apart from a piper torque max cam. I'm looking to build a 4.6 cross bolted top hat block with 4.0 Pistons to increase compression. What heads and cam would you guys recommend? Obviously looking for torque more than horse power. Closer to 300 hp would be good. I know the Thor inlet is restrictive for horse power so making everything else flow better I'm thinking may be a waste unless that is improved also. Any help would be appreciated!

Tony

[Tony22593]

I would rather get it all laid out before i start so I can choose parts that all work together. How much torque could be obtained from a n/a 4.6? 320 ft lb 330?

[garrycol]

Obviously looking for torque more than horse power. Closer to 300 hp would be good. I know the Thor inlet is restrictive for horse power so making everything else flow better I'm thinking may be a waste unless that is improved also. Any help would be appreciated!

Tony

you say you are looking for torque but then to go on to explain you are actually looking for HP. If you are looking for torque then the Thor manifold is good for this bit you are correct - it sacrifices a little top end HP. If you are going to race at near max revs, then yes look for something else but the Thor maybe more practicable for everyday use.

Of course if you want to go away from a Landrover inlet manifold then all bets are off.

Garry

[Tony22593]

I see what your saying. I just threw 300hp out there as it seems to be a good benchmark for a 4.6 n/a rover. What I was getting at was improving the breathing I know will improve more for horsepower than for torque. I just want to spend my money in the right places! Is there anything that can be done to the Thor manifold? I read a lot about extrude honing?

Thanks for the reply!

[unstable load]

For a daily driver, the standard cam and intake will do you fine and save you a bomb of money.
I'd get the heads mildly ported with concentration on the area around the bend where it opens to the back of the valve to de-restrict the flow there, bullet the guides and generally clean-up the tracts.
The main issues with breathing are the path for air to enter the engine, the filter medium's condition and the exhaust. Filter medium is obvious, keep it clean by regular servicing and for a Disco, maybe look at a snorkel to get around the need to suck air in from around the front wheel area.

Exhausts... depends on your legislation around emissions... I'd toss the cat converters, get aftermarket headers and go big bore to get the gases out the engine ASAP, BUT you probably won't be allowed to toss the cats, so higher flow cats and bigger bore pipe to go with your new headers.

Extrude honing looks interesting, but also expensive. I'd buy a cheap USB borescope and have a look down the tracts of the intake first to see if there is a lot of seam material to be removed before going that route, but even if there was, it says that it's effectively a polishing process, so it won't remove a lot of material if there are big seams.

[Tony22593]

The cam isn't an expense I don't think as I have a piper torque max that I could swap out of my 4.0. It's only been in there around 800 miles. Don't mind spending some money on some nice heads of it will help. What sort of torque figures would this set up achieve?

[Tony22593]

Oh and it seems all Land Rover made products have rough castings on them. Obviously it's the long runners in the manifold that give the torque. Would opening them out increase torque power? Or would it increase horsepower and not do anything for torque?

[Tony22593]

Something else I've been looking into is compression ratio. Using 4.0 piston on a 4.6 bottom end with normal 27 cc Land Rover heads the compression ratio comes out a 12.6 to 1. I think I'm doing some thing wrong as 12.6 is way to high for normal petrol. I know there meant to be 9.35 to 1 standard. Only thing I can think off is that tdc is below deck height and that is where I have gone wrong. I'm thinking 10.5 to 1 is the highest I should go on normal unleaded 95 Ron.
Any help would be appreciated !

i calculated it off of these details.
94mm bore
82mm stroke
13 cc dish in 4.0 Pistons
27cc chamber in cylinder head
1mm composite head gasket.
I must be missing something.

[ChrisJC]

There are a few threads on this from memory. I seem to recall you'll get about 11:1 with the 4.0 pistons on 4.6 rods. I did this for an LPG engine and it was fine. It ran on a bit on petrol though.....

Chris.

[Tony22593]

Ok as mine is petrol only I need to lower that a bit. I need bigger chambers then. Could I get earlier rover heads and skim them to get 10.5 to 1? Or I've heard good things about
Merlin heads and they come with a 32 cc chamber. Any one have any other ideas?

[ChrisJC]

I am pretty sure that if you get an earlier head and skim it for composite gaskets (i.e. get the valve gear in the same position relative to the camshaft), you end up with a later head.

Chris.

[SimpleSimon]

Well unless you have your pistons at zero deck they wont be unless the block as previously been decked, if so I make your CR to be around 10.8/11.1 CR you could unshroud the intake valves if you need to lower this further compo head gasket are around 1.2mm unless yours are different

[garrycol]

I have 4.0 Low comp pistons in my 4.6 and the compression ratio comes out at about 9.2:1.

Also note that 4.0 pistons have gudgeons that have a thinner wall than 4.6 pistons so you would be advised to change these over from the 4.6 pistons for your build.

Garry

[unstable load]

Oh and it seems all Land Rover made products have rough castings on them. Obviously it's the long runners in the manifold that give the torque. Would opening them out increase torque power? Or would it increase horsepower and not do anything for torque?

I'm not that clued up as to the effects of opening the runners and the effect it will have, but I do know that runners and ports need a rough-ish surface to work well. A smooth surface isn't advisable.

[SimpleSimon]

I have 4.0 Low comp pistons in my 4.6 and the compression ratio comes out at about 9.2:1.

Also note that 4.0 pistons have gudgeons that have a thinner wall than 4.6 pistons so you would be advised to change these over from the 4.6 pistons for your build.

Garry

Most factory stock 4.6 although stamped at 9.35 CR often CC at less than 9.1 CR some as low at high 8's my stock intermediate serp 4.0/3.9 came out at less than 9 also stamped at 9.35CR