Very very impressed with the Edelbrock 4-barell carb. Finally on the road. My only concern is it appears I only need 2 barrels! I get loads of power and acceleration from 0 to 50% throttle application. Above that the induction noise changes (sounds like a chug-clug really) and I suspect its heavy pinking as no more acceleration in fact the opposite!
Ignition is 123 electronic; set to 5deg 400-1000rpm, 22deg 2200rpm and 32deg 4800rpm. This worked well with twin SU’s and a quick google suggests it’s in the ballpark for a SD1 engine. I’ll mention here that you need to connect the vacuum hose to “inlet side” vacuum otherwise you get the 5degree advance at idle which my engine doesn’t like; it likes a little more advance at idle. It also means that the 123 distributors feature of detecting a gear-change works! I suspect this is normal?
http://123ignition.nl/downloads/manuals/Rover-8-R-V.pdf
I suspect lean running. The Edelbrock is stock apart from the rods which I changed before fitting the carb to 67-55 as this seems to be general consensus for 3.5l rover v8.
Cruise; pick-up and up to 50% throttle very good with this set-up. In fact if you had a throttle stop at 50% throttle opening I would be very happy!
Engine is pretty stock 3.5l; flowed heads (usual fair). Piper 270 cam I believe; 123 ignition system set to “F”. BP5E plugs (new). Carb stock apart from the 67-55rod change.
Any ideas? I don’t think the engine is modified enough to require so much extra fuel when the extra throttles open?
If it stays dry this afternoon I am going to put back the stock rods but I understood they don’t affect the secondaries?
It may of course by ignition advance; I can adjust the curve down; is 32deg at 4800 that high? I never run beyond 3-4k rpm to be honest so it’s a curve between 22 at 2.2k and 32 at 4.8k. The pain with the distributor is you need to remove it from the car to change the curves! The available curves are in the .pdf file.
I know without a wide-band lambda we are shooting in the dark but hopefully I can get acceptable running without. Your ideas are most welcome!
Edelbrock secondary opening causes pinking?
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Will Reeve
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If it really is pinking then maybe the VE of your engine is going up as the secondaries are opening and this is enough to send the peak cylinder pressure high enough to detonate the fuel.
Like you say the rods don't really effect the secondary settings but they must effect the overall mixture even when running at WOT because the primaries are contributing fuel all the time. The standard setup will richen your cruise and acceleration circuits and will therefore also richen the WOT to a small degree.
Like you say you are shooting in the dark without a wideband!
I used to 'bang on' about being able to transfer the carb setting from one engine to another, I've worked on loads more Eddy carbs now and I've changed my mind! You can use one setup as a starting point but that about it! I was working on a 3.9 lump the other day and that needed 104 jets in the secondaries in order to get the AFR to 12.5-12.8:1. They are the biggest jets I've ever had to use! If you think about it a smaller engine will pull less vacuum at WOT than a bigger engine so the depression across the fuel circuit will be less, this means that you may well need less restrictive (i.e bigger) secondary jets in order to get the right fuel ratio. Of course loads of other things come into this such as head flow, camshaft, exhaust system etc.
Like you say the rods don't really effect the secondary settings but they must effect the overall mixture even when running at WOT because the primaries are contributing fuel all the time. The standard setup will richen your cruise and acceleration circuits and will therefore also richen the WOT to a small degree.
Like you say you are shooting in the dark without a wideband!
I used to 'bang on' about being able to transfer the carb setting from one engine to another, I've worked on loads more Eddy carbs now and I've changed my mind! You can use one setup as a starting point but that about it! I was working on a 3.9 lump the other day and that needed 104 jets in the secondaries in order to get the AFR to 12.5-12.8:1. They are the biggest jets I've ever had to use! If you think about it a smaller engine will pull less vacuum at WOT than a bigger engine so the depression across the fuel circuit will be less, this means that you may well need less restrictive (i.e bigger) secondary jets in order to get the right fuel ratio. Of course loads of other things come into this such as head flow, camshaft, exhaust system etc.
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Will Reeve
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I've just sneaked out between the rain with the standard rods; literally a few seconds of throttle on the straight and it seems better. It wasn't necessary WOT it was when opening the secondary throttle plates (again it feels like that as you could switch the effect on/off mid throttle). Trouble is with the original rods the off idle / light cruise (in the 30mph limit for instance) doesn't feel as responsive as with the 67-55. I'll have to drive both of them more to confirm!
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Will Reeve
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http://www.ebay.co.uk/itm/141277896341
expect some more questions later on!....and I said I was going to just fit and forget and not get sucked into tuning again!
expect some more questions later on!....and I said I was going to just fit and forget and not get sucked into tuning again!
Will Reeve wrote:http://www.ebay.co.uk/itm/141277896341
expect some more questions later on!....and I said I was going to just fit and forget and not get sucked into tuning again!
I take that you bought the wideband then!
Really this is by far the best approach, I think that it is better than a rolling road. (Although WOT testing on the road is not good for you driving license!)
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Will Reeve
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Yes sidecar, looks like it should be able to give me some readings to play with the carb from! WOT! I know I must be getting old but vary rarely use it; this might of course be that the WOT settings are so out! It pulls so well low down; if I could get it to keep that torque above 3k rpm I might change my mind!
I am interested to see the difference between the two rods I have at the moment. Stock seems better for larger throttle openings; the leaner ones better for small openings! But it's all seat of the pants at the moment; the wideband should put a little bit of science behind it!
I am interested to see the difference between the two rods I have at the moment. Stock seems better for larger throttle openings; the leaner ones better for small openings! But it's all seat of the pants at the moment; the wideband should put a little bit of science behind it!
Hi Will, I've done quite a few Eddy carbs now my basic procedure is as follows:-
1. Clean out the carb and set the float heights.
2. Run the engine up to temperature then with the idle screws set too rich I slowly turn each one in 1/4 of a turn at a time jumping from one screw to the other. I'm listening for the engines response, the revs may climb a few RPM but at some point the revs will just drop by a fraction, I go out 1/4 of a turn from that point on both screws and that seems to be a good setting for the idle screws. You may find that one screw is out 1/4 of a turn more than the other, if so I just set them both to the same setting. I adjust the idle speed with the tickover screw. Depending on your cam this might be quite a dirty setup, my AFR on idle is 12.2:1, If I lean it off just a fraction the engine goes lumpy!
3. I then set up the cruise, I keep going leaner on the cruise setup until the engine response goes bad whilst driving at 40-50MPH under a very light throttle, at that point I go one stage richer on the cruise setup and that's the correct setting. I find that the AFR will be 14.5-15:1, as soon as you start seing 15.5:1 flash up then you can feel that the engine is as flat as a fart!
4. I then then setup the acceleration circuit, you should not use more than 1/2 throttle as you don't want the secondaries opening and clouding the issue. You could even stick a block of wood under the throttle pedal so that the throttle stops just before the secondaries start to open. You need a vac gauge on the non-timed port, read off the vac level when accelerating as hard as you can on the primary side of the carb then select a set of rod springs that lift the rods at that level or at just slightly more vacuum. You want an AFR of 12-12.5:1, if the reading is not that then you need a rod and jet combo that keeps your cruise setting as is was but just changes the acceleration setting. This is where things get tricky! It can be a right pain working out all the jet and rod combinations so I now use a spreadsheet which will compare one setup against another and give a percentage difference for the cruise and acceleration circuits. In the past I've modified standard rods to get what I want but you have to be accurate to 0.001"
4. I then set the WOT using the secondary jets, you need to aim for 12.5-12.8:1 Running leaner than 13:1 in my experience kills off the top end BHP and shortens the rev range.
5. Finally I setup the accelerator pump, you want to use the least 'amount' of pump whilst avoiding a lean bog. drive at 40MPH in 3rd or 4th then boot the throttle to the floor for a couple of seconds, the AFR does not want to go leaner than 12:1 and not richer than 10:1 (The engine will actually rich bog mis-fire at 10:1). The Eddy pump system is quite crude, you can make an extension to the pump arm if it still causes a rich bog when using the leanest (outer) hole.
Doing the above can take a day or more and that's if you have a load of jets and rods to hand! Also reading an AFR gauge whilst doing the above is a nightmare, its better to have a passenger reading the gauges and writing the figures down in a notebook.
1. Clean out the carb and set the float heights.
2. Run the engine up to temperature then with the idle screws set too rich I slowly turn each one in 1/4 of a turn at a time jumping from one screw to the other. I'm listening for the engines response, the revs may climb a few RPM but at some point the revs will just drop by a fraction, I go out 1/4 of a turn from that point on both screws and that seems to be a good setting for the idle screws. You may find that one screw is out 1/4 of a turn more than the other, if so I just set them both to the same setting. I adjust the idle speed with the tickover screw. Depending on your cam this might be quite a dirty setup, my AFR on idle is 12.2:1, If I lean it off just a fraction the engine goes lumpy!
3. I then set up the cruise, I keep going leaner on the cruise setup until the engine response goes bad whilst driving at 40-50MPH under a very light throttle, at that point I go one stage richer on the cruise setup and that's the correct setting. I find that the AFR will be 14.5-15:1, as soon as you start seing 15.5:1 flash up then you can feel that the engine is as flat as a fart!
4. I then then setup the acceleration circuit, you should not use more than 1/2 throttle as you don't want the secondaries opening and clouding the issue. You could even stick a block of wood under the throttle pedal so that the throttle stops just before the secondaries start to open. You need a vac gauge on the non-timed port, read off the vac level when accelerating as hard as you can on the primary side of the carb then select a set of rod springs that lift the rods at that level or at just slightly more vacuum. You want an AFR of 12-12.5:1, if the reading is not that then you need a rod and jet combo that keeps your cruise setting as is was but just changes the acceleration setting. This is where things get tricky! It can be a right pain working out all the jet and rod combinations so I now use a spreadsheet which will compare one setup against another and give a percentage difference for the cruise and acceleration circuits. In the past I've modified standard rods to get what I want but you have to be accurate to 0.001"
4. I then set the WOT using the secondary jets, you need to aim for 12.5-12.8:1 Running leaner than 13:1 in my experience kills off the top end BHP and shortens the rev range.
5. Finally I setup the accelerator pump, you want to use the least 'amount' of pump whilst avoiding a lean bog. drive at 40MPH in 3rd or 4th then boot the throttle to the floor for a couple of seconds, the AFR does not want to go leaner than 12:1 and not richer than 10:1 (The engine will actually rich bog mis-fire at 10:1). The Eddy pump system is quite crude, you can make an extension to the pump arm if it still causes a rich bog when using the leanest (outer) hole.
Doing the above can take a day or more and that's if you have a load of jets and rods to hand! Also reading an AFR gauge whilst doing the above is a nightmare, its better to have a passenger reading the gauges and writing the figures down in a notebook.
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Will Reeve
- Getting There
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- Joined: Fri Jun 04, 2010 8:22 am
Thanks. You’ve prompted me that using a MAP sensor would be a good idea. I made a MAP to MAF interface many moons ago so should have a couple kicking around. Thinking outloud it should be possible to use a linear potentiometer to measure throttle position quite easily. The wide-band sensor I’ve sourced from eBay has rpm input and 2 analogue inputs so can measure MAP, rpm, AFR, throttle position simultaneously and graph them after a run. That should provide some interesting data for us all; if you don’t mind me boring the forum with some posts!
By the way what do you set your idle to. Currently 600rpm is a little lumpy but I've not really optimised the mixture like you suggest!
By the way what do you set your idle to. Currently 600rpm is a little lumpy but I've not really optimised the mixture like you suggest!
