Desiding which engine to go for...

[Capri_84]

Hello all,

I've been scratching my head alot recently doing alot of research, trying to get an idea for the engine spec of my Capri I'm building.

All rust welding has been done, its been blasted and primed up with epoxy 121, and nearly all the filler is done. After another 2 coats of epoxy I'll be at the stage where I want to be doing welding modifications, to do this I need my engine and gearbox so I can do the mounts and so on, so I need to hurry up and get something sorted

I've come to the certain conclusion that its going to be a Rover V8 for weight reasons (handeling is a massive factor in the build)

So this is one for the Rover guys

I started out with the goal of 300hp, it soon became apprent that from a Rover V8 this was going to be abit tricky without alot of tuning work, so I've desided to settle for anything more than 225hp I can get really, this is with a 4.6 lump...

After doing some searching it appears that the 4.6 only came with GEMS management? and its a very hardcore if you like management system, with multiple computers all talking to each other doing different things. It sounds abit too heavy on wiring for me and I really want to be able to know this car inside out and work on it myself. If it had been one of the early types of management I may of stuck with it and learnt. But the idea of carb is very apealing for the reason I'll know the car very well, and it will be nice and simple. Not too mention how ridiculously easy it will be to wire it up and get it running (car did have a 2.0 Carb pinto in before)

So I now have the idea of removing everything on the ignition and fuel side of things and installing a Edelbrock 500 carb and megajolt... I like the idea of this alot because it still means I've got the 4.6, but its keeping things nice and simple and easy to live with. Then the loss of MPG it would suffer I've also found running a Edelbrock on LPG is fairly easy and has been done plenty. LPG was something I was considering from the start anyway.

Now what has me guessing though, is I hear the P38 4.6 lump has a very limited choice of cams to choose from... witch leads me to think would I get more and be better off with a 4.2... having more cam choices, and I think... the problem with the liners on the block would no longer be an isue as well with this engine? It seems the 4.2 will be abit easyer to tune up (not so much I have problems running on LPG) and theres alot more potencial and parts out there for it?

The level of tune I had in mind was a Edelbrock 500 carb, a good choice of cam best suited to the engine, rebuilt stage 1 heads skimmed to up the ratio (this would be ports matched, rough casting removed and a little bit of opening up and then the outlets polished and inlets surfaced with 80gritt media, good headers and system, and the megajolt... I was debating about a lightend flywheel as well, seem as though the engine is driving 1 ton less of weight.

Thanks for taking the time to read my very long post! any ideas very welcome

[kiwicar]

Hi
for the 225 BHP you are after I would go for the 4.2, you will need some higher CR pistons but that is doable ( ford Mod 3.7" jobbies, the ones Ian Stewart found) a real steel blower cam, set of stage 2 ported heads and a set of tubular manifolds and you should have a really nice engine. Personally I would go for efi and megasquirt as you already want to control the sparks properly and I hate 4 barrels but that is your choice.
Best regards
Mike

[ChrisJC]

Sounds like you want something similar to what I have in my Land Rover.

It is a 4.6, with 4.0 pistons to raise the CR, and ported heads. Piper 270 cam, megajolt lite ignition and twin 2" SU's. Standard Range Rover twin-outlet exhaust manifolds and a 2.5" straight through exhaust. Develops 250BHP. Also runs on LPG, and is pretty pokey on that too!

The Megajolt Lite can have two maps, so my ignition map automatically follows whatever fuel I am running on.

The P38 engine is better than the 4.2 because it has a crossbolted block, but they do suffer from cracking behind the liners so you want to be careful what you buy (or get a cheap cracked one and shell out £800 to have it top-hat linered).

The P38 came with either GEMS or Thor (Bosch Motronic), neither of which are straightforward to port to another application!

You shouldn't have any difficulty.

Chris.

[Capri_84]

Firstly thanks for the fast replies! very much appreciated!

I had a hard time trying to find someone with a 4.6 that wasnt on gems, so running a 4.6 on carbs is no isue then... good to hear. Is there a reason why your running twin su's rather than a 500?

The bore is the same with the 4.0 and 4.6 then they just changed the stroke?

Also how hi can I go with the CR till I will have problems running on LPG?

[martyn123]

Hi,


Don't ask me any tech questions as my knowledge is limited but i recently bought a 5.0 from v8d with a edelbrock and megajolt system as a complete unit,


Martyn....

[kiwicar]

Hi
Twin 2" SUs are a better route than a 4 barrel as they offer far more acurate fuel metering, are made better, and can operate without modification in conditions other than that of horizontal and constant velocity. Hhris is an off roader so they are really the only choice for him appart from fuel injection.
Personally I think the 4.0/4.6 block is flawed, the cross bolting and larger diamiter bearings are really a step too far and are the cause of the block failures tht lead to slipped liners. the 4,6 motor is really designed around producing power for a 4x4 and produces an engine with a narrow power band.
The 3.9, 4.2 4.0 and 4.6 engines all have a 3.7" bore
Best regards
Mike

[ChrisJC]

As Mike says, my engine is in a Landie, so it needs SU's or similar, not a petrol-bucket like a 500!

I have a different opinion to Mike with respect to the bottom ends - the cross bolted blocks are the strongest. And all the 3.7" blocks can crack behind the liner, it's just most prevalent in the highest power / stress engines, i.e. the 4.6 litre P38A (@ 2.25 tonnes!) Top hat liners in a cross-bolt block is about as strong as you can get.

Indeed the 4.6 upshifts at 5500 in sport mode in my P38 (yes I have two 4.6 V8's), so it's not designed to spin any faster.

I also think it has a very wide powerband, particularly the engine in the Landie. It pulls hard from idle to 5000 where the upshift is set to. No noticeable surges as the speed picks up.

Highest comp is 4.0 pistons in 4.6 engine with standard parts. I think that gives a bit over 10:1 which is OK still for petrol (just!), and gives a useful boost for LPG.

Yes the 4.0 / 4.6 are the same apart from the crank & rods. The pistons have a different bowl size in the top but otherwise are interchangeable.

At one point I was running it at about 12.5:1 compression. It was fine on LPG, but ran on terribly on petrol!

Chris.

[dnb]

Might be worth taking a look at what TVR did, and what people have done to their TVRs after the fact.

I know there were no 4.6 engines, but the concept of using an intermediate serpentine timing cover (found on early GEMS cars I think) rather than the later sort with the short nose cam (like the THOR cars or maybe later GEMS?) opens up lots of cam choices. You can even use a dizzy & 4 twin DCOEs if it takes your fancy. (Carbs aren't my thing because I grew up with EFI and computers, so I might have got the names wrong!)

A well tuned 4.6 with H404 cam should make good power and be reasonably tractable as long as you don't intend to commute in it!

[poo slinger]

what about a supercharger?

that will get the power up there

[DaveEFI]

I'd consider an MS and EDIS even if you only use it for sparks. Gives you the option of going injection later. But I don't like four barrel carbs either. Fine for out and out power - but if you want that don't go for a RV8. For grunt, SUs or injection is better.

[Capri_84]

I'm going to add to this post as its been mentiond, rather than start another.

I'm trying to work out the ins and outs of the use of 4.0 pistons and things related...

The use of 4.0 pistons with 4.6 crank, rods and block increases the compression... this being because the bowl of the piston is shallower than the 4.6 pistons.

?This on its own (with no block decking or head skimming) achives the best and highest compression ratio for standard octane fuel, any higher standard octane fuel may be abit touch and go?

do the crowns of the 4.0 pistons need abit of resessing to avoid contact with the valves?

The bores were the same with the 4.0 and 4.6 was the stroke? I ask because this intrigues me...

http://www.landroversonly.com/forums/f1 ... ker-48135/

If the bore is the same where does this 4.6 crank,rod,piston and 4.0 block get you, surly the blocks are the same? If so that page is non sense?

Surly a "Stroker" would be achived with 4.0 pistons but 4.6 rods and crank... we're back to running 4.0 pistons as the blocks are the same...

[DEVONMAN]

The 4.0 and 4.6 blocks are the same except a 4.6 may have a thicker aluminium wall behind the cylinder liners due to factory selection methods.
So, putting a 4.6 crank etc in a 4.0 engine will be considered a stroker and using 4.0 pistons with a 4.6 crank will increase the compression ratio due to a smaller dish in the 4.0 piston.
If the 4.6 pistons didn't need valve cut outs then in the same engine the 4.0 pistons will not need cut outs.
Cheers
Denis