Which engine for a V8 conversion?

THis is really really great info.

I am not really going to want to tune this for big power - I have been in a word of pain with my imrpreza on that score (running 480 reliably now but the additional upgrades have taken a long time and cost a small fortune!).

My impression of using a bigger block like the 4.6 is that I can get a reasonable amount or grunt without stressing the engine - again another reason for going auto.

I tried to find a few 3.5's and they are few and far between - however the 4.6s seem to be everywhere.

finally - am thinking along the wrong track by assuming a newer donor engine will give me less issue? If money was no object - I would have an engine built from scratch to my spec - but I woudl prefer a turnkey donor.

Still excited! You could spedn a lot of hours planning this stuff couldnt you!

there are shed loads of 3.5's just look on ebay. agreed they dont have crazy power but they shouldnt mechanicaly fail as often as the 4.6, which is the most unreliable of the lot for cracked/porous block, slipped liner and head gasket failure. so stressed engine or not they go wrong - a lot and its big money to put those breakdowns right- thousands for a lot of it. thats whay the p76 4.4 is so good- especailly for landys as its 280 ftbls of torque as standard and that was in 1973!

Tell us your budget and we could make suggestions accordingly

Hi guys

Yeah I know the 4.0 is the same as the 3.9 basically, just that there seems to be lots more 4.0 disco 2 and p38s blowing the tops than there is 3.9 discos and classics, although they all do it more than 3.5, which basically doesn't have problems.

Ok ok start from the start with a 4.6, lots of grunt, semi-rebuild it and you might get a yet or so without trouble.

I suppose I'm biased because my v8 hasn't had its heads off in 20 years (definitely not the last 15 anyway cos it's got history) so I'd say that's pretty reliable.

You could slap a load of hard work into a big bore engine and it might just keep spitting it's dummy out. Do it with a small bore and it'll work well for a long time, but it won't have the grunt of the 4.6 in the short, mid or long term.

In a 90 however, you might find a nice 180bhp 3.5 is sufficient. A 240bhp 4.6 would be even better, until it starts giving you hassle!

Agreed with fett the long stroke p76 makes it a torquey motor for its capacity. Bore makes horsepower and stroke makes torque.

A small bore strokey motor suites the land rover better than the bigger bore short stroke of the 3.9 for instance.

well said noisy, the fact that several re-builders are now saying that the top hat liner for the 4.6 doesnt always cure the liner/block/hgf issues and the fact that process costs thousands would put me right of the large bore engines.

I know one re-builder siad on here that he used irontite after the re-build as the top hat liner process couldnt be the whole answer to the problem worries me more!

BTW there is a you tube vid with some guy who has tuned his p76 v8 for torque and got 600 ftlbs lol, only 160 horse with that set up btw lol, or maybe it just the rev band it generated max torque was very differnt from the max hp band

just one more thing, pretty sure james martin on here who seems to know his stuff said when he worked rebuilding the warranty larger bore engine LR told them they had added extra metal around the bore to beef up what was taken away by effectivly over boring the orginal 3.5 block, but when he looked there was no extra metal

James, correct me if I am wrong especially about the bit where I said you know your stuff ha ha lol

hehe, no it was true ,biggest part of reason 3.5 s dont crack bores and 3.9 on do apart from poor bl;ock aligning when boring to fit liners,cut a few open to prove the point

hehe, no it was true ,biggest part of reason 3.5 s dont crack bores and 3.9 on do apart from poor block aligning when boring to fit liners,cut a few open to prove the point

good to know I remember summit mate lol

Oh yes on the alignment,some one said they looked at one an it was only 3mm thick?

Wowsers ... I may get flamed for this but would the Chevy and BMW blocks fit?

Definitely want reliability as the scoob has had 3 engines in the last 4 years and I can't take any more!

well if you are spending thousands (as you would on 4.6 at some point) you may as well go yank or german. you would need fabrication skills to make both fit and also with the german as opposed to basic yank stuff you would need some fairly serious wiring skills.

the basic and cheapest chevy 350 with simple carbs and exhaust is about 300hp.

I wanted to put a bmw v8 in mine before I became to concerned with keeping things orginal as mine is a 72 year and the values have gone crazy high recently

The 4.6 is more prone to hg problems because of the car they are fitted to. As the p38 has to run so hot for the emissions. If the engine was fitted to another vehicle and it had a decent cooling system it would be as good as any other Rover v8. The cooling system on my 4.2 is well sorted and never gets hot. It's all down to maintenance and cooling.

I think that is part of it mate, but only about 10 percent of why the bigger bore engines go wrong in that respect.

I am guessing your 4.2 is not an every day car either? I would say the other big bore engines also may not show signs of overheating untill they fail as it isnt overheating you would see on the guage per say that caused by the lean/lambda etc issues you refer to.

i would still say stay clear of the bigger bore engines, for all the resons my self, jamesmartin and noisy have outlined.

OK - this is probably another daft question.. but are you including the newer big bore engines also - I have seen a few 4.6s less than 8 years old with less than 50k on the clock... I thought if I bought newer I would have less issues... there are loads of modern ranges with 4.6s in - are they all doomed?

My budget would be around the 5k mark but I am only just researching.

NorthernGit said:

OK - this is probably another daft question.. but are you including the newer big bore engines also - I have seen a few 4.6s less than 8 years old with less than 50k on the clock... I thought if I bought newer I would have less issues... there are loads of modern ranges with 4.6s in - are they all doomed?

My budget would be around the 5k mark but I am only just researching.

Click to expand...

not all doomed ,but how can you tell , in some ,they cracked leaving the show room others with some mileage others only after fault in cooling system eg rad not cooling over entire surface ,if you overheate a 4.6 chances are you will crack block ,3.5 under similar circumstances will need head gaskets

Oh I see!

Also I think as the tooling for making them was getting knackered the later they are made by LR

I am thinking the following options.
A TVR V8 (Chimaera or even better from a Griffith 500) is a good choice. Usually these engines have very low mileage and are strong as a freight train. They are basically Rover engines. Another good idea is a V8 from an M5 (E39 M5 BMW) The engine code is S62. These engines make 410bhp but their ecu are very difficult to unlock. There is a guy that can unlock the ecu in Germany but he charges 2200 euros to do so. I do not like American engines because those are very old and very thirsty for gas (still on carbs).

not sure the tvr engine is more reliable than the other big bore rover v8's. that m5 engine is excellent but would be a lot of work and money to buy and fit and what would you do with the drivtrain to make it take 410 bhp that would be thousands more