Emissions, fuel regulators, stand off
Discussion
Does anyone know if reducing the pressure of the fuel regulator will successfully reduce unburnt fuel to get through the mot when youre running a hot cam? I'm sure it wont work with SUs because fuel is held in the float chamber, but what about with a webber?
I think i'm getting fuel stand off with my SUs, evidenced by residue in the k&n pancake filters, again due to the cam. Ive got stub stacks but i'm wondering if 50mm ram pipes and socks would be better, to contain the stand off and maybe improve the torque, does anyone run long ram pipes with noticeable benefits? Are the socks any good? I might just go for a webber and i'm hoping to try one on the car over the weekend beacuse ive been told that fuel stand off can be a problem with SUs.
I think i'm getting fuel stand off with my SUs, evidenced by residue in the k&n pancake filters, again due to the cam. Ive got stub stacks but i'm wondering if 50mm ram pipes and socks would be better, to contain the stand off and maybe improve the torque, does anyone run long ram pipes with noticeable benefits? Are the socks any good? I might just go for a webber and i'm hoping to try one on the car over the weekend beacuse ive been told that fuel stand off can be a problem with SUs.
I don't think a reduction in fuel pressure will stop unburnt fuel being thrown back out of the carb intake at tickover if you use a very hot cam.
Once I built a 1963 Cooper 'S' 1071 with a 649 cam and 1.5 rockers. The fuel just used to run down over the manifold with the filters removed at tickover.
With SU's it's best to set the tickover up to about 1400 rpm for the MoT and weaken the mixture right off as much as you can. That usually does it and there was a document issued from the DfT stating that this was OK to do with SU's. I don't have the details, but my buddy with a Dolomite Sprint does have this, I believe, so if it's a problem I'll ask him. Just let me know. Alternatively I can ask my friend who does my MoT's as he is a Mini enthusiast as well.
Has your car actually failed its MoT over this?
Once I built a 1963 Cooper 'S' 1071 with a 649 cam and 1.5 rockers. The fuel just used to run down over the manifold with the filters removed at tickover.
With SU's it's best to set the tickover up to about 1400 rpm for the MoT and weaken the mixture right off as much as you can. That usually does it and there was a document issued from the DfT stating that this was OK to do with SU's. I don't have the details, but my buddy with a Dolomite Sprint does have this, I believe, so if it's a problem I'll ask him. Just let me know. Alternatively I can ask my friend who does my MoT's as he is a Mini enthusiast as well.
Has your car actually failed its MoT over this?
Peter,
It hasnt failed an mot yet, but i was just curious about the fuel regulator thing. My air filters cost about 5 bhp on the rollers and i was toying with the idea of using long ram pipes with socks to contain the fuel stand off as ive been told this can be a problem with SUs. I didnt try the webber at the weekend, instead we fiddled with my SUs and nows its running really well. A while back i spoke to you about the carbs going lean in a corner, which i cured after cleaning the dashpot pistons. However, after a rolling road session this problem came back. Going through it step by step at the weekend we found that the jets needed to come down 1/2 turn and now its spot on.
It hasnt failed an mot yet, but i was just curious about the fuel regulator thing. My air filters cost about 5 bhp on the rollers and i was toying with the idea of using long ram pipes with socks to contain the fuel stand off as ive been told this can be a problem with SUs. I didnt try the webber at the weekend, instead we fiddled with my SUs and nows its running really well. A while back i spoke to you about the carbs going lean in a corner, which i cured after cleaning the dashpot pistons. However, after a rolling road session this problem came back. Going through it step by step at the weekend we found that the jets needed to come down 1/2 turn and now its spot on.
The fuel throw-back is normally only a problem at tickover and low revs, although the 1071 'S' I built a few years ago with the 649 cam and 1.5 rockers would not pull below 3200 rpm, nor tickover below about 1300. It has a 286 now, but lives in California - I'll get to drive it again in October.
Ram pipes certainly seem to improve things, but the length is a problem with any decent air cleaner/filter. I use K & N on my rally 'S' with stub stacks. I matched the stub stacks to the carb intakes and polished the surface, as I thought they were badly finished as bought. In all honesty, I don't think I gained anything at the top end, maybe a bhp or 2, but the responsiveness is improved and tickover is a bit better, or so it seems (it's hard to be definitive about this).
If you are racing and induction noise plus the need for filtration are not important, maybe 3" long ram pipes are the answer. I just gave away some 2" long ones I've had for ages. If you put any sort of filter over the end it must reduce their effectiveness. Of course, with any rally car filtration is very important in view of the dust and grit on loose surface roads - especially when you catch the Subaru that started one minute ahead of you (just dreaming again!).
I hope this helps,
Peter
Ram pipes certainly seem to improve things, but the length is a problem with any decent air cleaner/filter. I use K & N on my rally 'S' with stub stacks. I matched the stub stacks to the carb intakes and polished the surface, as I thought they were badly finished as bought. In all honesty, I don't think I gained anything at the top end, maybe a bhp or 2, but the responsiveness is improved and tickover is a bit better, or so it seems (it's hard to be definitive about this).
If you are racing and induction noise plus the need for filtration are not important, maybe 3" long ram pipes are the answer. I just gave away some 2" long ones I've had for ages. If you put any sort of filter over the end it must reduce their effectiveness. Of course, with any rally car filtration is very important in view of the dust and grit on loose surface roads - especially when you catch the Subaru that started one minute ahead of you (just dreaming again!).
I hope this helps,
Peter
Fuel pressure on a carb will not change the mixture at idle, unless excessive pressure is causing flooding.
With hot cam you need a lot of static advance to get the engine running cleanly, and with a basic distributor setup this can cause the timing to be over advanced at lower engine speeds. A 3D mapped igintion system certainly helps a good deal.
You can try opening up the valve clearances for the MOT, this effectively reduces valve overlap (and lift) and may be enough to nudge it through. Not good for the cam and followers if you open it up too much though.
With hot cam you need a lot of static advance to get the engine running cleanly, and with a basic distributor setup this can cause the timing to be over advanced at lower engine speeds. A 3D mapped igintion system certainly helps a good deal.
You can try opening up the valve clearances for the MOT, this effectively reduces valve overlap (and lift) and may be enough to nudge it through. Not good for the cam and followers if you open it up too much though.
In the end I switched to an Aldon custom-curved dizzy to get my rally 'S' to run properly. The problem with the standard 'Aldon Red' dizzy I had previously was that if advanced enough to run best at mid and top end, the advance was so high static that it would not turn over on the starter . A 510 Amp Cold Crank battery, plus a dizzy with an extra 4 deg of total mechanical advance sorted that out.
If we were allowed mapped 3D ignition I would use that as you can run to within 1 deg or so of detonation for optimum performance and mixture, as Mr2Mike so rightly says.
If we were allowed mapped 3D ignition I would use that as you can run to within 1 deg or so of detonation for optimum performance and mixture, as Mr2Mike so rightly says.
I now have a modified dizzy to suit the engine. I was just curious about the use of a regulator to reduce emmissions, i read that in one of the mini mags.
Peter, do you use spacers between the manifold and the carbs? I havent got any but i wondered if effectively increasing the manifold length and providing some insulation would be of benefit?
I'm also now using a vacuum advance to pull the timing up on part throttle. Will the back plate rattle around?
Peter, do you use spacers between the manifold and the carbs? I havent got any but i wondered if effectively increasing the manifold length and providing some insulation would be of benefit?
I'm also now using a vacuum advance to pull the timing up on part throttle. Will the back plate rattle around?
Ah ha, don't believe all you read in the mags.
All the fuel pressure regulator will do on a carb engine is ensure that sufficient fuel gets into the chamber without it over-pressurising the valve and causing leaks from the chamber. The fuel drawn into the carb will only be that demanded by the throttle position and manifold vacuum.
Any form of spacer which increases the inertial ramming down the manifold is, in principle, a good thing, so long as the bore is nicely matched up and of constant cross sectional area. Be careful the carb doesn't get too close to the bulkhead.
On my cars I have to use standard manifolds 'with no intermediary device' as the regulations say, so I can't put spacers in. Spacers do help to keep the charge as cool as possible - never use a water heated inlet manifold as it costs in terms of power.
The use of a vac advance control is not necessarily bad idea, but it's another possible source of unreliability and inaccuracy in actual timing at different rpm's. It does make for easier starting though.
I hope this answers some of your questions. Good luck with this.
Peter
All the fuel pressure regulator will do on a carb engine is ensure that sufficient fuel gets into the chamber without it over-pressurising the valve and causing leaks from the chamber. The fuel drawn into the carb will only be that demanded by the throttle position and manifold vacuum.
Any form of spacer which increases the inertial ramming down the manifold is, in principle, a good thing, so long as the bore is nicely matched up and of constant cross sectional area. Be careful the carb doesn't get too close to the bulkhead.
On my cars I have to use standard manifolds 'with no intermediary device' as the regulations say, so I can't put spacers in. Spacers do help to keep the charge as cool as possible - never use a water heated inlet manifold as it costs in terms of power.
The use of a vac advance control is not necessarily bad idea, but it's another possible source of unreliability and inaccuracy in actual timing at different rpm's. It does make for easier starting though.
I hope this answers some of your questions. Good luck with this.
Peter
Be carefull that the vacuum advance does not cause detonation. This can be a problem on tuned engines with high CR's. When running part throttle, you get lots of adcance dialed in for economy, but when you snap the throttle open, the vacuum advance mechanism will not instantly retard and it's possible to initiate detonation on an engine that is already running near the edge. Although the detonation should be of short duration, you may get many bursts of it around twisty roads where you are continuously backing off and opening the throttle.
Thanks for that advice. Again in the mini mags, there was an artical about dizzys that said higher compression engines dont 'need' a vac advance, it didnt say they shouldnt have one! I thought the vac advance would help reduce the cammyness but i'm not convinved it does much there. How do i remove it all together, in particular what do i need to do to make sure the back plate isnt causing scatter?
I've found Aldon Automotive very helpful. They have a guy called Rob there who is very clued up on all sorts of dizzys. When I had a big problem with my 'S' using an Aldon 'Red' dizzy I felt that the amount of available mech advance was insufficient. I gave him the full engine spec and sent an old 'S' dizzy for rebuilding. A week later I was £100 lighter, but had the best dizzy I've ever used. He gave me about 4 degrees more available mech advance and re-curved it spring-wise. I reckon I gained by being able to run higher advance at the top end, but it was also better at the bottom end and the starter would turn the engine over, even with my 11.1:1 C.R., when hot.
I seem to have lost their phone number, but check out their web site.
I seem to have lost their phone number, but check out their web site.
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