Camshaft Thoughts for Rover V8 4.2 on Twin SUs.

Burbling · Post by **Burbling** » Mon Apr 06, 2015 10:15 am

Hi Guys,

I have a Rover 4.2 V8 which I am changing from its original Hotwire system to twin SUs - I am wondering about the factory camshaft being suitable for running on carbs?

I've searched the forum and have seen the info on 4.6 engines, but not quite what I'm doing.

It might be that the factory camshaft that produced 205bhp with the Hotwire would run on twin SUs but I am hearing conflicting opinions when asking about.

Has anyone done a change to carbs from injection? How does it run on carbs?

Any advice or experiences much appreciated!

DaveEFI · Post by **DaveEFI** » Mon Apr 06, 2015 10:39 am

IIRC, there never was a 4.2 fitted with SU carbs. They really went out with the 3.5. For comparison, an SD1 on SU carbs produces about 155 bhp - 190 on injection. Although the SD1 EFI has a higher compression ratio and some head mods.

If you're fitting carbs not designed for an engine, they will have to be properly set up for it. Choosing the correct needles etc isn't that easy.

If you must have a carb, might be better to get one properly specified for this engine.

But I'm not the one to ask, as I'd stick with injection.

stevieturbo · Post by **stevieturbo** » Mon Apr 06, 2015 11:24 am

As above, other than setting up the carbs for the engine, it will be fine.

By all means change the cam if you want to change it, but it certainly will not need changed.

Burbling · Post by **Burbling** » Mon Apr 06, 2015 8:02 pm

Cheers guys - cam stays in and I'll see how she runs.

Yes the engine came with Hotwire but the vehicle it's going into is a 1958 Series 1 Land Rover, so carbs seemed more fitting for the build - there's a guy in Australia who runs a 4.6 well on twin SUs and I'm starting with the needles and springs he runs, nice interesting project.

Hotwire's easy isn't it? It either runs or it doesn't, I grew up around carbs and am going to enjoy the fiddling about and cursing that's probably coming my way!

Seriously though, when she's all up and running the engine is going to be fitted with LPG which it'll run on most if not all of the time, with the petrol system disabled. That's the plan.

paul c · Post by **paul c** » Tue Apr 07, 2015 6:33 am

My 110 runs a 3.9 with a new factory cam and a new pair of solexs and has been running fine with that combo. The new 4.6 I am building will be running a new factory 4.2 cam and SU carbs.

DaveEFI · Post by **DaveEFI** » Tue Apr 07, 2015 8:39 am

As a matter of interest, is the transmission of a Series 1 going to be able to handle the torque of a 4.2?

MikB · Post by **MikB** » Wed Apr 08, 2015 12:14 pm

I would say NO - you'll need a LT95 if you want to stick with a manual, or a R380 if you insist on 5 gears

unstable load · Post by **unstable load** » Sat Apr 11, 2015 7:11 am

DaveEFI wrote:As a matter of interest, is the transmission of a Series 1 going to be able to handle the torque of a 4.2?

Not even maybe!

Burbling · Post by **Burbling** » Sat Apr 11, 2015 9:45 am

Absolutely not on a Series 1 box - you probably would get to 2nd gear before something wrenched itself to bits!

The wagon came to me with a Series II 2.25L petrol engine & gearbox. which I've sat to one side to be rebuilt at a later date. The V8 is being fitted to a rebuilt SIII gearbox, modified (shortened) rear props haft onto a Land Rover SIII Stage 1 V8 rear axle. Standard front axle on freewheeling hubs.

The Stage 1 was limited to 90bhp and I think I'll be at 140 to 150 max with the twin SUs and the planned exhaust system, but the brakes have also been updated to Stage 1 'train brakes' with a low ratio remote servo.

The engine will be setup for petrol as a standby, and running on LPG 99% of the time, variable ignition for cutting between fuels, which is where the power will also be limited down (EFi 4.2 on Hotwire was around 200bhp, way too much for this).

DaveEFI · Post by **DaveEFI** » Sat Apr 11, 2015 10:03 am

It's not the BHP you need to be concerned about as regards the transmission, but peak torque. And, in general, that is a function of engine size.