wanting to build a hi-torque 4.6 - recommendations please?

conrod · Post by **conrod** » Wed Mar 27, 2013 9:13 am

Hi all,

I am in the process of rebuilding a 4.6 GEMS engine, which will be fitted into my (don't laugh!) 1995 LDV 400 van, which I use to tow my race car. The aim is to produce a high torque engine, with reasonable fuel economy (current low comp 3.5 on SU carbs is quite thirsty)

It will retain the R5-150 5 speed gearbox (last evolution of the 2WD LT77) to which I have already fitted a taller fifth gear (0.72 from some Land Rover model?) and a taller diff ratio.

I have a Thor inlet manifold which I will fit, with corresponding injectors, and have a Pectel ECU which will also be fitted and tuned once built. Also to be fitted are the stainless 4.6 tubular exhaust manifolds, and I will make a large bore exhaust system.I will also fit an 80°C thermostat, to keep Des Hammill happy!

I plan to do some mild porting of the cylinder heads, nothing radical, just mainly cleaning up the rough area under the valve seat where the machining meets the cast finish, and maybe open them out a little. We have measured the bore sizes, and there is some wear present, so we will rebore to first oversize. Similarly, the camshaft is worn, and requires replacing.

So my questions to you are:
-what would be the most suitable camshaft for this engine?
- does anyone sell a higher compression ratio, oversize cast piston set (currently 9.35) that will go in without too much machining?

Bearing in mind this is not a race engine, so hp is not a high priority, rather I am looking for a lot of torque from 1500-5000 rpm.

Currently have around 200ft/lbs. and 145 hp with the 3.5 low comp. engine on SU's. Looking for 300+ ft/lbs, and hp will be what it will be. I read somewhere else about fitting 4.0 pistons to a 4.6, what is the difference in deck height? I was thinking 9.8-10.0:1 CR might help things a bit, seeing as I have to replace the pistons anyway.

I look forward to your suggestions:)

cheers Conrad

Wilts289 · Post by **Wilts289** » Wed Mar 27, 2013 7:20 pm

Hi, I have a 4.2l Rover and fitted the Crower Comp-U Pro Cam 50230 Rover V8 from V8 Tuner a couple of years ago and found that it pulls like a train right up 5500rpm, and I can still pull away in forth gear from stationary. Apart from a Weber 500 and and correct valve springs, engine is pretty well standard.

Boosted LS1 · Post by **Boosted LS1** » Wed Mar 27, 2013 8:07 pm

A tame cam and a single turbo will give you significant gains in torque.

conrod · Post by **conrod** » Wed Mar 27, 2013 8:12 pm

Boosted LS1 wrote:A tame cam and a single turbo will give you significant gains in torque.

its going into a van, lets not be silly!

Boosted LS1 · Post by **Boosted LS1** » Wed Mar 27, 2013 8:15 pm

Why is it silly? They stick turbo's on buses and dusbin lorries

You wanted torque? You have a mappable ecu so a 5psi blown set up would be a doddle.

conrod · Post by **conrod** » Wed Mar 27, 2013 8:25 pm

granted, but they are diesels, and need the turbo.

I have owned plenty of turbo cars, and don't get me wrong, I love them. But I do not want the added work of fabricating manifolds, exhaust, intercooler plumbing etc. I certainly do not have the time for all of that, it is a tow vehicle that is not used much. I am not sure there is room in the engine bay for a turbo anyway as it is very cramped. And if I start with 5 psi, soon it will become 10, then 15, and you know how it goes

Gearboxes, diffs.......... N/A will prevent stupidity from taking over.....

As I said earlier, it is just a tow vehicle. Just looking for a good cam choice for a 4.6 and higher comp. pistons. I think my torque target is easily achievable without resorting to a turbo setup.

Boosted LS1 · Post by **Boosted LS1** » Wed Mar 27, 2013 8:31 pm

Pah, tiz simple. Stick a single turbo onto one exhaust header and also feed into it with the other exhaust bank. Retain the rest of the exhaust system that you have. You don't need intercooling for 5 psi. You will need an oil feed to the turbo and oil drain to the sump. Oh and a rising rate fuel pressure regulator. You'll get appx 30% torque increase from 1500 rpm's without doing anything to the engine internals

.

Anyway good luck with it.

ChrisJC · Post by **ChrisJC** » Wed Mar 27, 2013 8:34 pm

To answer your questions....:
Pistons from the 4.0l when fitted to the 4.6 give a useful improvement in compression ratio.

Apart from that, fit an RPi Torquemax cam, and it will pull like a train.

You don't want to port it out much, because that will reduce low end torque!

Chris.

ChrisJC · Post by **ChrisJC** » Wed Mar 27, 2013 8:37 pm

Also, if you've ever seen under the bonnet of a V8 LDV, you'd see there ain't a lot of spare room for a turbo.

Chris.

conrod · Post by **conrod** » Wed Mar 27, 2013 8:38 pm

To give an idea of what I mean by cramped, here is the engine bay:

And a current dyno reading of the RWHP and torque:

Conrad

Robrover · Post by **Robrover** » Wed Mar 27, 2013 9:44 pm

What ChrisJP said. 4.0 pistons, mild head work to stage 1 (clean up the ports without opening them up, standard waisted stem valves, bit of relief work around the throats) and I suggest Kent H180 cam.

Much the same as a LR 4x4 engine which also needs to produce torque. Turner Engineering's 4.6 long motors are built pretty much to this spec.

conrod · Post by **conrod** » Wed Mar 27, 2013 10:40 pm

Awesome guys, thanks, thats what I was looking for

Conrad

DaveEFI · Post by **DaveEFI** » Wed Mar 27, 2013 11:23 pm

ChrisJC wrote:Also, if you've ever seen under the bonnet of a V8 LDV, you'd see there ain't a lot of spare room for a turbo.

Chris.

Quite. We had a fleet of V-8 Sherpas, and they suffered dreadfully from fuel evaporation in heavy town traffic. Ended up setting the idle at 1200 rpm to try and keep them cool. Gawd knows what the extra heat from a turbo would do.