V8 camshaft choices - BEWARE!

Interesting info. So if you were going to rebuild my 3.9i Discovery engine for me, what cam would you put in, ie. genuine or other? Richard

Assuming the engine is actually fitted to a Disco, it'd get a standard

3.9EFI cam but if you wanted a little more oomph (10-15bhp at the top end) without turning it into something that needs revved hard or drinks excessive ammounts of petrol, I'd fit a Viper Cyclone, a cam specifically designed for the EFI engines that will also work ok with automatics and doesn't require any ECU mods specifically for the cam grind. RPI's RP4 is a similar grind but slightly more expensive. That is, of course, unless you specified a specific cam yourself for a given reason.

Badger.

That's some very detailed and good info, thanks a lot! Who sells the Viper Cyclone cams online?

Thanks!

Jens

No-one, unfortunately, at least not that I know of. They are Real Steel's own cam range, but bear with me for a week or so and I may have more info.

Badger.

Golden rule No.1 when buying spares. If a supplier lists two parts that appear to be the same - they are not. Pattern, and increasingly Genuine, manufacturers will go to great lengths to reduce stock levels by ascertaining if two parts are

*really* the same. If they list two (of the same brand), then there is a difference, and it does matter.

Richard

Hi Richard, I was prompted to write this after seeing an advert on ebay by a well known uk v8 engines firm. They were advertising a cam as being a standard direct replacement for either carb or efi, when the profiles are so obviously completely different. I coplained to them by email and mentioned that I may be tempted to contact trading standards re. false advertising, they then emailed me back stating that they would ammend the wording on the auction which they now have. They now claim that they have had this cam specially produced as a replacement that has been optimised to be a direct replacement for the OE cam in either efi or carb engines. I can smell s**te! For one, I doubt if they have the budget to specially develop individual camshafts for what are, lets face it, relatively low production runs. Two, almost every cam for rv8 application on the uk market can be cross-checked to another as being the same cam (Piper 270/2, Oselli RV8271 and Kent H180 for instance are all the same cam!) Three, rover spent a small fortune developing the cams for the later v8 engines to be an ideal compromise, if one cam had been suitable, they'd have done it, as you rightly say.

They (the sellers) still conveniently neglect to tell you that you will need to change carb needles etc to get it to run correctly through the whole rev range, that is how they sting you for extra money after you've bought the cam and call them to ask why it doesn't run right. I know people they've done it to!

Look at the completely different timing profiles and ask yourself how these

2 cams could possibly be "optimised" into one! Rover had the cam for the 3.5 EFI specifically designed and tuned for serious low rpm torque, to prevent any risk of the engine stalling when selecting D with the auto, and to assist a big heavy vehicle get off the line. Any other cam will undoubtedly give you more power (claims range from mild to wild depending on cam and advertiser!!) but you will loose this torque at low revs and you may experience stalling with an auto, even with relatively mild cams such as Piper 270/110 and 270/2, I have personal experience with them both and stalling autos!

Badger.

On or around Mon, 24 Jan 2005 16:40:30 +0000 (UTC), "Badger" enlightened us thusly:

Is there an easy way to tell which cam is likely to be in a given engine? I've a low mileage 3.9 cam in the shed, with a set of followers, and it'd be nice to know whether it'll suit the hotwire 3.5 in the disco. The exhaust system on the disco seems to be tuned for more power at higher revs - it's not all that torquey at low revs, but takes off quite nicely when the revs get to about 2500-3000

Austin, according to the parts book, the cam in the 3.5 hotwire (14CUX) is the same cam as the 3.5 "flapper type" (4CU), so if you fitted the spare 3.9 efi cam then you'd be relying on the airflow meter and ecu to correct the fuelling as the profiles are different. Now to confuse. Allegedly, some of the late 3.5 efi hotwires had the 3.9 cam, but I haven't found any reference to this anywhere official. Best to stick a degree wheel on the front of the crank, whip off a rocker cover and have a look-see what your timing figures are. Pull the rocker shaft ass'y out (offside is easiest obviously) and use the no. 6 piston as your reference, it'll give the same tdc as no. 1 would have. Use the pushrod, but check for movement with the rocker removed as the valve spring will hold the follower partly closed and give you false timing figures otherwise.

Please note, the reference above that I made to ecu swapping for rangie/vittesse applies to flapper type only.

Badger.

On or around Tue, 25 Jan 2005 11:29:15 +0000 (UTC), "Badger" enlightened us thusly:

well, This one certainly hasn't got rafts of low-rev torque. There again, it's a non-standard stainless exhaust (make unknown, except that it don't look like super-high quality) which may well be tuned for more revs and less torque, if the exhaust can make that much difference to a 3.5... Sounds nice at full-ish chat, mind, above 3K revs there's a nice rasp to it...

'ere, 'nother thing you might know... Some hotwires are fitted with lambda sensors, and some ain't. can the ones without have them added, or is it a different ECU? I wouldn't mind putting lambda sensors on it so I could upgrade the gas system to closed loop - it's a bit thirsty on open loop, typically about 13 mpg if I'm lucky and don't floor it too often. It'd be neat, in a way, if the same lambdas could also talk to the petrol ECU.

"Austin Shackles" schreef in bericht news: snipped-for-privacy@4ax.com

I'm lurking in this thread with great interest... :-) My ruster has a Rimmer Bros. SS exhaust (with tubular manifolds). You guy's don't happen to know how these Rimmer exhausts are tuned? It's fitted to an ex-SD1 vitesse 3.5V8 with Stromberg carbs on top and fueled with LPG. Pretty good torque below 3k revs (to my knowledge, as this is my first V8) but above 3k it doesn't change for the better anymore. BTW, I can tow just about anything* anywhere without exceeding 2500 rpm, so it is good for me.

*With exception of the Eiffel Tower.

This is getting too confusing now. Perhaps I should just use a standard cam. Richard

You need to fit an efi harness with the lambda wiring in it, they don't all have it!, and the lambda probes themselves, obviously, then fit the correct tune resistor (located in the harness next to the ecu) to utilise the correct mapping in the ecu. The rangie factory manual lists the tune resistors somewhere, I'll dig 'em out later if I get a chance. Bear in mind that the landy lambda probes aren't the basic common 0-1volt types, they are some weird 5-0v inverse reading probes or summat like and hence dearer! Fit an AEB Leonardo control unit for your gas, weld a boss into one of your downpipes, fit a std 0-1v probe, get a lead (£50) and software (Normally free, talk to me if any probs) and set it up using a laptop, or pc if you can get close enough. You'll probably be cheaper than mucking about with the efi system, and you'd still need a gas controller that can read lambda. Try a bunch called Autogas Worldwide, they're in your part of the world somewhere I think. Badger.

On or around Tue, 25 Jan 2005 15:47:12 GMT, "Richard" enlightened us thusly:

if you use the right one for your engine config, you'll not go far wrong. I rather doubt that *just* changing the cam ever has that much effect. You also need to do the whole engine tuning thing, bigger carbs, different jets, free-flow exhaust, gasflow the heads, up the compression... 's a big list. Granted, at the end of the tunnel is a 200BHP engine, or somesuch, or more, depending on how you set it up. Then again, do you *really* want a race-tuned engine that does sod-all under 3000 rpm in yer rangie?

While granting that *if* you find an expert, I daresay they can build an engine that allows you to lug treestumps out of the ground at tickover. Such engine probably has modest peak power and revs out at about 4500, though.

On or around Tue, 25 Jan 2005 17:56:04 +0000 (UTC), "Badger" enlightened us thusly:

heh. trust LR...

that's probably the way to go, as and when - it'd only be worth doing the petrol bit if I were going to run a lot on petrol or it was easy and required no extra effort.

Still, I might yet get to build the transit-LR hybrid, and then all bets are off anyway, on the current one, as I'd most likely have to sell it.