Best set up for my Rover 4.6?

sidecar · Post by **sidecar** » Fri Nov 30, 2012 12:14 pm

kiwicar wrote: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.

Hi Mike,

It is interesting that you think that the poor atomisation of a 4 barrel allows it to 'appear' to be in tune when in reality it isn't. (That is if I have understood you correctly).

In some ways I would have thought that a mixture that was off the mark in terms of AFR AND was also poorly atomised would be less likely to burn than one that was off the AFR mark but at least it was atomsied well. Therefore if a 4 barrel carb does not atomise well it is more sensitive to getting the ratio right.

Please don't think that I'm having a go at you! I was really just interested in you thoughts on the subject.

I have heard the Holley carbs are much more sensitive to jetting than the Edelbrock carbs and I suspect that this is down to atomisation. Then again I have also read that there are many forms of Holley and some of the boosters are better than others. (In the same Vizard books that you read!)

I don't think that Eddy carbs are the be-all and end-all, I have just learnt about them because that was what was fitted to my car when I bought it. The fact that I can corner hard enough to make my engine misfire is annoying, the problem is down the the carb, I bet that they are not all that great off road too!

RealSteel do not like the Eddy carb due to the fact that you can plonk one on a RV8 and because it appears to run well people assume that the calibration is correct when in fact it is miles out. The result is that the bores get washed and the rings are trashed after a few thousand miles.

Cheers,

Pete

DaveEFI · Post by **DaveEFI** » Fri Nov 30, 2012 1:27 pm

It's interesting that both Rover and Rolls fitted SUs to their V-8s. And Daimler, come to that. SU was owned by BMC, so it's more understandable that most of their products used SU - but Rolls presumably had the choice of any with price not being much of a consideration?

kiwicar · Post by **kiwicar** » Fri Nov 30, 2012 3:51 pm

Hi Pete
I don't think you are having a go at all, though I probably deserve it

I as usual have stuck up a load of what are my opinions and deductions as facts with minimal back up, I must confess in the hope of soliciting a reaction, I am glad I have one

.
In your reply you have covered alot of what I view as the evidence for my statment, As a general rule 4 barrels are jetted way rich out the box, this coupled with poor atomisation generally means all the oxygen in the mixture is burnt, further owing to the large droplet size the oxygen tends to burn the fuel it is in contact with all the way through to CO2 because the combustion of any large fuel droplet tends to proceed like pealing the layers of an onion, the oxygen in the mixture tends only to "see" the fuel it can react with. net result hich co2, low co, high hydrocarbons in the exhaust, relativly good power out of an overly rich mixture and a tendency for the engine to be "flat" at the top end, because the combustion process proceeds more slowley.
Compare that with a system that atomises the fuel more compleetly here the fuel is more thoroughly mixed with the oxygen and offers more of a surface area of fuel droplets for a given AFR, in an excessivly rich mixture combustion happens far more rapidly and tends to burn to all the fuel to CO at once so no fuel is left in the mixture, then rather than all the CO burning to CO2 far more of the oxygen is used up and combustion process stops at the CO stage, this liberates far less of the energy (hudro carbon to CO is about a tenth as energetic as CO to CO2) and the engine is far more sensative to an over rich mixture. You get an exhaust low in hydrocarbons low in CO2 and high in CO.
Ultimatly you will get better power with better atomisation of the fuel but the correct tuning is more critical with the better atomisation, compare a webber 45 and a 4 barrel, basically the same fixed ventury carb, but the webber has a lot more emphasis on emulsifying the fuel before getting it to the jets and it produces a good atomisation of the fuel, it also has to have a far more sophisticated metering system and is far trickyer to get running right compared to a 4 barrel.
There are further clues as to what is going on, often with SUs and webbers, when everything is spot on fuel wise you can take out a couple of degrees of timing at the end and see a couple of extra bhp, further they will nearly always running at peak power with less timing than a 4 barrel, but they are more difficult to get the best out of.
Best regards
Mike

sidecar · Post by **sidecar** » Fri Nov 30, 2012 5:03 pm

kiwicar wrote:Hi Pete
I don't think you are having a go at all, though I probably deserve it I as usual have stuck up a load of what are my opinions and deductions as facts with minimal back up, I must confess in the hope of soliciting a reaction, I am glad I have one .
In your reply you have covered alot of what I view as the evidence for my statment, As a general rule 4 barrels are jetted way rich out the box, this coupled with poor atomisation generally means all the oxygen in the mixture is burnt, further owing to the large droplet size the oxygen tends to burn the fuel it is in contact with all the way through to CO2 because the combustion of any large fuel droplet tends to proceed like pealing the layers of an onion, the oxygen in the mixture tends only to "see" the fuel it can react with. net result hich co2, low co, high hydrocarbons in the exhaust, relativly good power out of an overly rich mixture and a tendency for the engine to be "flat" at the top end, because the combustion process proceeds more slowley.
Compare that with a system that atomises the fuel more compleetly here the fuel is more thoroughly mixed with the oxygen and offers more of a surface area of fuel droplets for a given AFR, in an excessivly rich mixture combustion happens far more rapidly and tends to burn to all the fuel to CO at once so no fuel is left in the mixture, then rather than all the CO burning to CO2 far more of the oxygen is used up and combustion process stops at the CO stage, this liberates far less of the energy (hudro carbon to CO is about a tenth as energetic as CO to CO2) and the engine is far more sensative to an over rich mixture. You get an exhaust low in hydrocarbons low in CO2 and high in CO.
Ultimatly you will get better power with better atomisation of the fuel but the correct tuning is more critical with the better atomisation, compare a webber 45 and a 4 barrel, basically the same fixed ventury carb, but the webber has a lot more emphasis on emulsifying the fuel before getting it to the jets and it produces a good atomisation of the fuel, it also has to have a far more sophisticated metering system and is far trickyer to get running right compared to a 4 barrel.
There are further clues as to what is going on, often with SUs and webbers, when everything is spot on fuel wise you can take out a couple of degrees of timing at the end and see a couple of extra bhp, further they will nearly always running at peak power with less timing than a 4 barrel, but they are more difficult to get the best out of.
Best regards
Mike

Hi Mike,

I'm only too keen to oblige when someone is soliciting a reaction!

As to your postings only being your opinions and deductions that's fine by me, really that is the only thing that anyone can ever post up.

Your explanation of how a 'blobby' rich mixture will burn is interesting and I can certainly vouch for the fact that the Eddy is way too rich for most Rover engines out of the box yet they do seem to run OK. (At least until the rings wear out!).

In fact your explanation of the whole burn process is very interesting!

At the end of the day I will stick with my 4 barrel for the moment, I guess any fueling system will have pros and cons, even EFI! One thing about SU's is that they must by their very nature create a throttling effect in order for the slide to lift, this must reduce the CFM that the engine can take in to a degree. Then again any carb must create some form of vacuum otherwise it won't deliver any fuel!

It's a shame that nobody makes a 4 barrel that is as sophisticated as a 'proper' Weber with regards to being able to setup all of the fueling circuits.

Cheers,

Pete

kiwicar · Post by **kiwicar** » Sat Dec 01, 2012 7:52 am

Hi Pete
you are correct, an SU does offer a restriction to flow, a large part of that is because of the floor below the piston is a series of of facets, the trouble here is that if you smooth them out you get a dramatic reduction in the fuel atomization

obviously as you say the lifting of the piston requires a small depression across the carb, though you can get a situation where you need very little.
The 4 barrel isn't all bad, they were designed to work pretty consistently even with US manufacturing standards and on a wide range f engines with a limited range of jetting options, this they do do really well. You can get after-market 4 barrels from the likes of Barry Grant that are made out of ally rather than zinc/ally alloys and made to decent tolerances, some have proper transition circuits that can be tuned, not just a slot in the wall of the venturi.
Best regards
Mike

bigaldart · Post by **bigaldart** » Sun Dec 02, 2012 12:58 pm

There is always the option of Weber style metering on a Holley.

http://www.tmpcarbs.net/products_home.html

Never had hands on one but uses all weber components, ie tubes and jets so the fuel curve should be totally mappable.

Alan

whelo · Post by **whelo** » Wed Dec 05, 2012 8:06 pm

Cheers for all the help guys, but i think i'll stick with me weber..

Jason

DaviesDJ · Post by **DaviesDJ** » Thu Dec 06, 2012 2:26 am

I run a 5.0 land rover with an eddy 600 and off road needles - it will be on the front of land rover monthly feb edition, its not perfect off road but as long as you keep moving your fine. I was suprised that in standard form it was actually running lean on hard acceleration, with AFR going into 14s, jetting it up to what i originally thought would be far too rich has made a real difference. my plugs actually testify that this was the case. now i am at work and its 0200 so dont have the needle and jet sizes to hand but they are among the richest configurationssupplied with the jetting kit i prurchased, with silver needles. I run stage 3 heads and a H404 cam, hi rev lifters etc, and now 50- shot of nos which slips the clutch with its poke. The point i wanted to make was at the begining pre-instalation of my AFR meter i was all ready for it to be 'pig rich' - but in fact it was lean when giving it the gun (well not optimal anyway). Cheers - Dave

whelo · Post by **whelo** » Thu Dec 06, 2012 12:06 pm

Nice, let me know what sizes you went for, i'm gonna try the sizes sidecar uses & see what differences it makes.
I'm gonna get myself a AFR meter after christmas to i can get her tuned up properly..

What air filter you using with the carb?

Jason

sidecar · Post by **sidecar** » Thu Dec 06, 2012 6:20 pm

The settings that for the 500 are going to be different to what is needed for the 600.

The 600 comes from the factory with two setups, one is leaner than the other.

When I was messing about with a 600 I was running a 95 primary and a 65-37 rod. This setup was 6% leaner than the standard setup on cruise and 1.7% leaner on the power step. This set the AFR figures to be around 14.5:1 on cruise and 12.5:1 on the power step.

DaviesDJ 5.0 lump must be using different settings if his power step is richer than the base setup. (Assuming his base setup was the same as my carb)

With regards to filter you need to be careful, it is mega important that the lid of the filter is not too close to the top of the carb, it really messing things up when it gets too close! I run a 3x14 holley filter, it is on a drop base but the lid is still around 3 inches from the top of the carb due to the cone shaped filter lid.

whelo · Post by **whelo** » Thu Dec 06, 2012 7:41 pm

I got ya, I'll probably convert my Eddy pancake so i can use the snorkel, looks to be the easiest option..

Jason

DaviesDJ · Post by **DaviesDJ** » Tue Dec 11, 2012 10:45 pm

Have just finished a run of nights do will post my net sizes, AFR I am getting now seems. Consistent with plug readings, I think these engines run so much nicer a tad rich;-) certainly feel that way

whelo · Post by **whelo** » Mon Dec 24, 2012 11:14 am

DaviesDJ wrote:I run a 5.0 land rover with an eddy 600 and off road needles - it will be on the front of land rover monthly feb edition

That's your Orange 90 on LRM? Nice truck, mag got delivered this morning just intime for Christmas..

Jason

Quagmire · Post by **Quagmire** » Mon Dec 24, 2012 12:12 pm

Threads like these make me love my Megasquirt all the more, couple of taps on the keyboard and your done!

sidecar · Post by **sidecar** » Mon Dec 24, 2012 1:47 pm

Quagmire wrote:Threads like these make me love my Megasquirt all the more, couple of taps on the keyboard and your done!

Plenty of threads kicking about along the lines of my "EFI hotwire mega flapper single multi point injector" system is not working as it should be though!