Best set up for my Rover 4.6?

[whelo]

Hi, i'm rebuilding my Defender with a Rover 4.6. I've read quite a few posts on here about setting up carbs & engines but wondered if they will work for my Defender, its not gonna b used on the race track, abit of off roading but nothing extreme as its a canvas top. Mainly for fun, she's not my everyday vehicle but would still like to get a decent MPG figure & yes i do know its a V8..

Here's what i've got, Rover 4.6 converted to dizzy. Its been completely stripped & checked with new rings, bearings the lot. Skimmed 20thou with composite gaskets, highlift cam, cant remember which one but think its piper torque max, currently running a weber 600, but noticed a few of you use the 500's which i have aswell. My ign is a standard lucas coil with magnecor leads & a 123 dizzy.
Any help with the jets for the carb, including which is better the 500 or 600, i understand every engine is different but alot of you have way more experience tuning these than i do & that speaks volumes..

[sidecar]

I also have a 4.6 stage III in a Cob replica, I have tried both the 500 and 600 carb, I have also thinned down a set of 500 boosters so that they flow the same CFM as a 600 carb. The 600 made around 20 ftlbs more torque at low RPM compared to the 500 carb but made the same peak BHP. The big problem I found with the 600 carb was a huge rich bog when braking hard. I tried the 600 primary boosters in a the 500 carb and that setup also bogged when braking. The 600 boosters have a different emulsion tube hole drilling pattern compared to the 500 boosters. This is why I them modified a set of 500 boosters so they flowed like a 600 set, that setup also bogged when braking. I know that it was not a float height issue because the 500 was fine and when I used that base part of the carb it was fine with the 500 boosters but no good with anything else.

In the end I gave up with the 600 and stuck with the 500. What I have also done on the 500 is drilled two holes in the secondary counter weight air valve so that it opens quicker. I made the holes too big to start with which caused a lean bog when the throttle was booted, I filled the holes with solder and re-drilled them smaller. The Thunder series carbs have an adjustable air valve but drilling the holes does work on the Performer carb.

Other things worth noting are that the carb does not like to be tipped forward at idle, it make the motor run rich, a wedge plate can sort this out.

With regards to jetting really the ONLY way to sort it out is with a lamba probe which is what I use but just for the record the following setup is very close to what my car and my mates 4.6 run....

Primaries...83, rods....65-47, piston springs...silver, secondaries...83.
pilots....2 turns out, accelerator pump arm....outer hole. (smallest pump shot). The counter weight holes are 7.5mm diameter.

I actually use homemade rods but the above setup is VERY close to my setup. The above setup will lean off the cruise mode 15.9% and the power step mode 0.2%

Having said all that there is no way of knowing if the above will work on your engine, it depends on too many other things.

With regards to ignition then something around 14 at tickover and 28 all in at around 2700-3000- RPM will work well, the standard is very retarded at low RPM. The vac Lucas vac advance does not work well with either carb, they feed the vac canister too much vacuum too early, the engine will kick back if you use it unless you back off the mechanical advance which then leads to poor WOT performance.

One way round this is to ditch the whole setup and go for something that is programable such as an MSD unit, that will cost big bucks though. Muscle Manta's 4.6 run this setup with a MAP sensor (He's the mate I mentioned), he got 27 MPG at motorway speeds out of his 4.6 Manta.

I also run an MSD but I don't run a MAP sensor due the fact that my idle vacuum is exactly the same as my cruise vacuum, this mean that the system would not know what state the engine was running in. I could probably work out a way round this if I was bothered about it.

[DaveEFI]

Surely any decent programmable system uses engine speed as well as vacuum?

[whelo]

Cheers for the replies, i think i can programme my 123 Dizzy with different curves to suit.

As regards the rods you mentioned i'll have a search online & get some.
I've been looking at LC1 probes & will get one after christmas, where did you drill the holes on the counter weight?

& lastly, the accelerator pump arm, is it worth extending it like i saw on one of your links? I'm not gonna be booting it alot, the truck isn't designed for it & the manual box isn't geared for acceleration, i like the torque of the 4.6.
Trying to get a good amount of power with fairly decent MPG, anything above 20mpg i'll be happy..

[sidecar]

Surely any decent programmable system uses engine speed as well as vacuum?

Yep and the MSD does detect RPM, in fact the RPM curve can be adjusted every 100 RPM and in 0.1 degree steps.

The vac curve is another independent curve from the RPM one. Like I said I could probably work something out if I could be bothered.

[sidecar]

Cheers for the replies, i think i can programme my 123 Dizzy with different curves to suit.

As regards the rods you mentioned i'll have a search online & get some.
I've been looking at LC1 probes & will get one after christmas, where did you drill the holes on the counter weight?

& lastly, the accelerator pump arm, is it worth extending it like i saw on one of your links? I'm not gonna be booting it alot, the truck isn't designed for it & the manual box isn't geared for acceleration, i like the torque of the 4.6.
Trying to get a good amount of power with fairly decent MPG, anything above 20mpg i'll be happy..

I've never managed to post a picture up on this forum so it is hard to explain where to drill the holes but basically you need to drill a hole in the counter weights which close the secondary air valve so that it takes less vacuum to open it. I think you can only do this mod on the bigger Rv8 lumps, it would probably cause a lean bog on a 3.5 lump.

I think that the pump shot maybe a bit too much on a 3.5 but the leanest shot is Ok on a 4.6 so you probably do not need to extend the arm.

With an LC1 you could check this out by booting the throttle and checking whether the mixture goes lean or rich for a second or so. I think you need just enough pump-shot to stop a lean out, any more than that is wasting fuel and possibly washing the bores if it is a massive pump shot.

The following book is worth a read, it explains how these carbs work very well, it also describes cutting lumps off the counter weights...

http://www.ebay.co.uk/itm/How-to-Rebuil ... 27b90a5f68


This book is crap...

http://www.ebay.co.uk/itm/Rebuild-Power ... 19d6fe174b

[whelo]

Brilliant, thank you.

[ChrisJC]

I have a Series IIA SWB with a 4.6V8.

It has twin 2" SU's, and a MegaJolt ignition system.

Pertinent points are:

SU's work well at crazy angles, unlike a lot of these yank-style carbs.
I had the ignition mapped to suit my engine, which makes for a far better result than faffing around with a distributor! And it means you can keep the short front end on the engine.

1 3/4 SU's are a tad small for a tuned 4.6. The 2" SU's are fine.

I run a Piper 270 cam, ported heads (around the valves only), and it develops about 250BHP.

Chris.

[whelo]

I changed to the weber when i had my 3.9, at the time i was told they're alot better than the SU's. I didn't have any problem off roading but admit i didn't go to any extremes, i'm too afraid of rolling the truck.
Seems the MegaJolt system seems the be the weapon of choice of many, I'll take a look at it once christmas is out of the way, dont mind spending the money, just want the engine & truck built right 1st time, saves alot of hassle afterward..

Jason

[ChrisJC]

I changed to the weber when i had my 3.9, at the time i was told they're alot better than the SU's

I think that's a matter of opinion rather than fact! A well set up pair of SU's is just as good as a weber. Probably better in fact as you can 'map' it better if you can be bothered.

Chris.

[whelo]

Any idea's the best place to get jets & rods for my 500?
Been on real steel's web site & its hard to sift through, rang them up & must have spoken to the work experience boy, he wasn't very helpful..

Jason

[SimpleSimon]

I changed to the weber when i had my 3.9, at the time i was told they're alot better than the SU's

I think that's a matter of opinion rather than fact! A well set up pair of SU's is just as good as a weber. Probably better in fact as you can 'map' it better if you can be bothered.

Chris.

CV carbs are considered the next best thing to EFI they atomize fuel very efficiently including the supply on demand principle and should be more fuel miser than fixed jet carburation type's

[kiwicar]

4 barrel carbs are inferior to SU's and stromburgs for part throttle use and Sus are far more stable/consistant with time and throttle progression. Mechanical secondary 4 Barrels generally will flow more air for a given choke area, however their fuel atomisation is pretty poor, this makes them seem to have a wider range of "in tune" settings, they generally work nearly as well out the box as they do after a day on the rolling road. this is even more the case with vaceuum scondary 4 barrel carbs that tend to favour the primary barrel metering by keeping the velocity through these barrels more consistant however this is at the expence of the secondary barrel conditions that tend to be even more prone to meter fuel "like a leaky bucket"
The biggest problem for the SU is it likes to see many small pulses in the flow rather than a fer big ones, experiments by David Vizard in the early '80s showed that SUs worked very well on "tunnel ram" style manifolds where many carbs were shared across many cylinders.
Best regards
Mike

[sidecar]

SU's may be good carbs but you need a good manifold as well and that 'could' be an issue. The Eddy Performer manifold is very good, other 4 barrel manifolds may either be good or crap depending on what they are.


Muscle Manta on this forum can get you jets and rods, you could buy a calibration kit but in my opinion only about 5% of what's in it is any use.

Do bear in mind what I said about the setup that I use working on my car, your engine is quite different to mine!

[whelo]

I understand they're different, I forgot to mention mine is slightly ported & polished, i had a go myself with a mate who used to build rally engines in the good old days, he helped so not exactly stage 3 but it'll do..

& PM 'd Muscle manta..

I'll give the settings u gave me a go & c how she does..
I think i have plenty of potching to do before its finished..

Jason