Camshaft choice in a 3.9?

Background is that when I rebuilt the 110's engine (3.9V8, 9.35:1, hotwire injection) last year I ended up fitting a genuine parts 4.2 litre camshaft in the engine - I got it cheap and thought it worth a try.

Anyhow, having driven the 110 around for a while now, including to Italy and back earlier in the year, it seems to be lacking power from around

2,000rpm upwards - trying to keep 70mph on the flat in 5th (LT85 & 1.222:1 LT230, 3.54:1 diff and 265/75r16s) sees the vacuum gauge drop down to around 2" Hg and fuel consumption soar - you can tell the engine is really working hard. I don't think this can right - the 110 is heavy and unaerodynamic, but a 3.9 should be able to cope better than that (or am I being nieve...). Low-end is fine - she'll pull away happily in 2nd from idle and nips around town no problem.

I recently found the numbers for the 3.9 and 4.2 cams and it seems that the 4.2 cam has quite a bit shorter duration than the 3.9 cam - 285deg. for the 3.9, 272deg. for the 4.2. My understanding is that longer duration means more top-end power, shorter duration more low-end torque, which would tie-in with my feeling that the engine is lacking top (mid-) power. The shorter duration means the 4.2 cam also opens later and closes earlier, with peak being slightly later on the inlet and slightly earlier on the exhaust.

So, if I'm going to change the cam, what's the best option, bearing in mind the 110 is quite heavy and I'm aiming for (relative!) economy at cruising speeds rather than performance? I'm leaning to the standard

3.9i cam, but is there a better alternative?

Cheers,

AndyC.

Reply to
Andrew Cleland
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Well having read the above it appears you have already come to a sensible conclusion. 70mph is never going to be economical in a 110 though no matter what you put in it. We cruise Europe towing with the L322 TD6, 65 is fine but 56 is more sedate and much more economical and tbh doesn't make massive differences in time of arrival.. but then we are on holiday so its not a rush.

I'd be inclined to fit the correct parts when rebuilding, unless you really go to town on the maths. There was suggestion in the past that 3.9 Cams in a

3.5 were much better for the 3.5. The reality is more likely to be that a good 3.5 cam would be far better than a knackered one. I would imagine the same principle applies to the 4.2 in your 3.9.

I've been there when I fitted the XK engine in my SIIa. I fitted a carb manifold rather than EFi out of necessity rather than choice... I was never

100% happy with the end result and forever tweaking it. No I prefer to stick to the norm and be content with it running correctly rather than with issues.

Other option I guess would be a stroker kit to bring it up to 4.2l in the cc. Fitting a 3.9 cam sounds to be far less work mind.

Lee

Reply to
Lee_D

56mph? is that 90kph? and 65mph = ~100kph?
Reply to
GbH

Near enough 62mph is 100kph.

Handy site:

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Reply to
Dave Liquorice

Indeed, we tow quite a large twin axle caravan. The car will happily tow much faster though having swept up at a few RTC's I don't like to push my luck however confident I may feel in my ability theres always someone waiting to help us show our buttocks :0) These speeds I hasten to add are not ones in the UK... where of course I stick to the 60mph and slightly under.

Lee D

Reply to
Lee_D

Ah, I wondered what prompted such an obtuse collection. Makes sense now, sort of!

Reply to
GbH

Yep, for a carb 3.9 engine fit a Viper Hurricane cam and BAC needles. For a Hotwire engine fit a Viper Cyclone and set it up exactly as per instructions, no need for re-mapping or chipping. Both available from Real Steel. Anything more will need expensive re-mapping of the ECU by someone such as Mark Adams. Badger.

Reply to
Badger

Cheers Lee. You're right about 70mph not being economical, but what concerns me a bit is that the engine is *really* working hard to get there. I have a friend with a slightly older 200Tdi 110 which seems to be a lot less effort to get to that speed. It could just be me, as I think I'm too mechanically sympathetic and hate revving my engines (ok, with the exception of our Panda's 1.2 - small Fiat petrol engines are made to be revved).

The best bits of our trip to Italy earlier this year were done around

50mph - through the Black Forest and then Baveria and taking the old road over the Brenner Pass rather than motorway. Unfortunately however you get plan it, there is always an interminable amount of northern France or Belgium (and even though half my family are from there, it's still pretty dull going) to get through first and no obvious non-motorway routes.

I'll probably stick with the standard 3.9 cam or maybe the Viper Cyclone Badger recommends - price is pretty much of a muchness.

Cheers,

AndyC.

Reply to
Andrew Cleland

Cheers Badger - I'll consider the Cyclone. Annoyingly I actually bought a cyclone when I was rebuilding the engine, but then went with the 4.2 cam as the cyclone didn't have the step in the cam end for the thrust plate (ERR5926) that I'd carefully fitted to the block & the local engineering company wanted stupid money to machine the end of the cam to fit. I then sold the cyclone on ebay - doh!

At the moment the engine has 14CUX injection, but my summer project is to fit a megasquirt ecu and EDIS - first to do just the spark, but assuming that goes OK, then to do fuelling as well. In the long term I'd like to use the megasquirt to do both petrol and LPG injection, maybe even sequential, and with a Thor manifold I picked up recently (although looking at it, fitting a Thor manifold is going to be quite involved with water hoses etc.).

Cheers,

AndyC.

Reply to
Andrew Cleland

Andy,

I guess the other option to consider is if there are any longer legs for the transfer box or a pair of custom Diffs but that would of course affect the whole range of gears.

Sounds like you are having fun with the V8, I love them , just can't afford to run one, though there is an argument on diesel / petrol and depreciation that actually it doesn't make alot of difference unless you stack up the miles. Especially now derv has overtaken petrol with pump prices.

Lee D

Reply to
Lee_D

Crap firm, it takes 10 minutes in a lathe, I do them all the time!

Good plan - the V8 will respond well to more advance at lower rpm's. You'll find a good bit more torque, but just watch out for detonation, especially on petrol if it's mapped for gas! Can you do dual-mapping with EDIS?

Brave man! many have tried and failed......

Yep, been there done that. Has to be modded on the front face to take a thermostat and housing, needs to be drilled and tapped for a coolant temp sensor for the gauge (Thor only has one sender, the gauge is ecu driven) and the manifold modifying at the rear to give clearance for the hotwire fuel rail and pressure regulator. more torque in the midrange, but it seems to run out of steam above 4000rpm, or at least that's what my 4.7 did with a Lund LE1 cam. Badger.

Reply to
Badger

Yup, funnily enough they've shut-up shop since then - they obviously weren't interested in doing the cam as the apprentice was sent out to see what I wanted, took the two cams (one with, one without grove) round the back and came back 5 minutes later - £300 to do the job. Unfortunately the cam is just a shade too long to fit into my old ML7 otherwise I'd have had a go myself.

Not with the EDIS itself, but the Megasquirt can have two maps, both for fuel and ignition. The LPG plan being to set one up for petrol and one for LPG - when I switch to LPG the petrol injectors are turned-off and LPG on along with ignition timings changing.

Yeah - mechanically I don't see it as too bad with the Megasquirt - 34+1 wheel on the crank and the old dizzy modified to send a pulse every cam revolution. The fun seems to be in getting the mapping sorted out, but it has been done for the RV8. I've read though that the gains in going sequential on the RV8 aren't really worth the effort involved.

In my innocence I'd hoped the Thor upper-manifold whould match up to the hotwire lower-manifold and I'd be away, but as you note, there's a lot more to it than that. Could you not though use the Thor standalone thermostat unit (PEM101130) rather than fitting one to the manifold?

Cheers,

Andrew.

Reply to
Andrew Cleland

Fits in my Super 7....... just! chucked on the front spigot, rear running in a short rotating centre, turned with a thin parting tool!

Cool.

I'm led to believe the difference between the two is maybe 3 or 4 bhp.

In theory, yes you could, but then you're back to stressing the engine thermally as there are, to my knowledge, no lower temp thermostat units of that type available. With that stat, the coolant will circulate in the block at 99 degrees c - not healthy for an RV8. Use the early style stat and get it down to 78 or 82. It's not that difficult a job - the front of the thor manifold has enough meat to modify it quite easily - just needs the hole behind the water pipe opening out a bit to each side to allow the stat to sit in and 2 holes drilling and tapping for the thermostat cover. It clears the dizzy, being virtually in the same place as an early style stat. I cheated, for the water temp gauge I welded a steel boss to the heater feed pipe coming out of the manifold next to the stat and I had no issues with that at all. You could also use the stat cover but then the gauge wouldn't read until the stat started to open. Badger.

Reply to
Badger

Hmm, I'll have to have another look. It could be that the only centres I have are quite long, maybe a shorter centre would do. It was very close.

Ah, I hadn't realised the only external units were stupid hot, which I think had more to do with all the RV8 problems than anything else.

I don't have the lower manifold yet to look at but it doesn't sound so bad then. I'll have to keep my eyes open on ebay/shows for the bits.

Cheers,

Andrew.

Reply to
Andrew Cleland

Might be one kicking around here if you want it? Make me an offer, plus postage of course. Badger.

Reply to
Badger

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