Steve Morris Posted January 9 Report Share Posted January 9 I’d be grateful for advice on the attached AFR curve from my RR session a few months back. It looks to me that the mixture is excessively lean towards the top of the rev range, given that it was a power run on WOT. One line is cyls 1-3 and the other wiggly line 4-6 as I have a fully twin system from the manifold back - soon to be changed to 6-3–1 single pipe. Since that session the throttle bodies have now been changed to Fred Millturn and the car is driving way better however at the back of my mind I am concerned about the leanness at WOT. Plugs look a good colour after a run but exhaust does smell a bit rich driving around town. According to this curve does the fueling need looking at or is it within the acceptable range? Thoughts appreciated folks. Quote Link to post Share on other sites
john.r.davies Posted January 9 Report Share Posted January 9 I'll look forward to the opinions of those with more knowledge, when I think that 15:1 is a good "economy" ratio, rather than dangerous. But I'd be more concerned by the grossly unstable ratio on your rear cylinders! Bad sensor, or waht? John Quote Link to post Share on other sites
andyhall Posted January 9 Report Share Posted January 9 Hi Steve, Have you got a lambda sensor boss on the exhaust? if not make sure you do on the system. Andy Quote Link to post Share on other sites
Steve Morris Posted January 9 Author Report Share Posted January 9 1 hour ago, john.r.davies said: I'll look forward to the opinions of those with more knowledge, when I think that 15:1 is a good "economy" ratio, rather than dangerous. But I'd be more concerned by the grossly unstable ratio on your rear cylinders! Bad sensor, or waht? John John, I’m not sure what was going on there! I had put the instability down to the old throttle linkages which have since been swapped out. I don’t have a sensor - they stuck separate probes in the 2 rear pipes. Quote Link to post Share on other sites
Steve Morris Posted January 9 Author Report Share Posted January 9 Andy, don’t currently have a boss but as I’m going with a TLE manifold I could ask them to fit one in the collector. Quote Link to post Share on other sites
john.r.davies Posted January 9 Report Share Posted January 9 1 hour ago, Steve Morris said: John, I’m not sure what was going on there! I had put the instability down to the old throttle linkages which have since been swapped out. I don’t have a sensor - they stuck separate probes in the 2 rear pipes. New test needed then! Quote Link to post Share on other sites
TRTOM2498PI Posted January 9 Report Share Posted January 9 2 hours ago, Steve Morris said: Andy, don’t currently have a boss but as I’m going with a TLE manifold I could ask them to fit one in the collector. Hi Steve, The 6-3-1 collector should come with sensor blanking plug as standard (mine did). I run one on mine, with AFR gauge in the cabin. Cheers. Quote Link to post Share on other sites
Waldi Posted January 9 Report Share Posted January 9 I agree with John. For a good assessment a new test is needed, it would be wrong to “average” the 2 curves, especially in the lower rpm range. For the upper part of the revs (say 3000-5000 rpm) the better adjusted TB’s would not make much difference since the butterflies will be further opened so the difference there is difficult to clarify. FWIW: My std PI runs with 12.5-13.5 AFR at idle and more towards 14.5-15 at cruising speed. I have one sensor only, in one of the 2 down pipes. When the engine is cold it shows leaner readings, likely due to wetting and poor combustion. Waldi Quote Link to post Share on other sites
roy53 Posted January 9 Report Share Posted January 9 what did sanspeed advise ? Quote Link to post Share on other sites
Peter Cobbold Posted January 9 Report Share Posted January 9 For max power the mixture should be rich, around AFR 13...12. Cylinders 4-6 look good. Cylinders 1-3 are leaning above 3000 rpm. AFR 15 is cruise/economy mixture, and will burn slower, needing more advance. The lean mxiture on 1-3 is therefore costing power. 1-3 have the longest PI hoses......that could explain the progressive leaning at higher rpm. For road driving peak torque and acceleration - the 'feel' - is aorund 3000-3500 rpm. and the AFrs on all six cylinders are nice and rich, AFR12-13 which is what we want at wot. I'd be quite happy with those curves, but I prefer to drive the torque not rpm. Peter Quote Link to post Share on other sites
Spit_2.5PI Posted January 9 Report Share Posted January 9 Steve, I had assumed that the smooth line was power, as it goes up nicely to 144 as stated at the top, but you're saying they're BOTH AFR??? Cheers, Richard Quote Link to post Share on other sites
Peter Cobbold Posted January 9 Report Share Posted January 9 12 minutes ago, Spit_2.5PI said: Steve, I had assumed that the smooth line was power, as it goes up nicely to 144 as stated at the top, but you're saying they're BOTH AFR??? Cheers, Richard Ah, yes. Top line looks very much like power. Peter Quote Link to post Share on other sites
Steve Morris Posted January 9 Author Report Share Posted January 9 (edited) Guys I think you might be right about the power line - hadn’t even occurred to me - just assumed they tested both sides. Schoolboy error. This is potentially very good news indeed and once more this forum has put me straight. looking forward to another test now! Massively appreciate all your input folks. Edited January 9 by Steve Morris Quote Link to post Share on other sites
Steve Morris Posted January 9 Author Report Share Posted January 9 2 hours ago, roy53 said: what did sanspeed advise ? Roy, Sanspeed were happy to do another power run but said they would prefer to see the AFR lower at WOT max revs. They weren’t able/free to do adjustments to the MU. Quote Link to post Share on other sites
Steve Morris Posted January 9 Author Report Share Posted January 9 Just to confirm, the straight line is definitely power - see below torque/power graph from same run. feeling a bit stupid now… Quote Link to post Share on other sites
DRD Posted January 9 Report Share Posted January 9 5 hours ago, Peter Cobbold said: Ah, yes. Top line looks very much like power. Peter Yes I thought that initially and the afr looked good to me. Quote Link to post Share on other sites
andyhall Posted January 10 Report Share Posted January 10 Hi Steve, I don't think there are many out there who can adjust a MU, certainly on a rolling road, hard enough to fine someone who can do Webers! anyway that's a pretty good power/torque graph, the new TLE will help and does come with a boss in 3-1 collector. Andy Quote Link to post Share on other sites
kiwican Posted January 10 Report Share Posted January 10 This might a silly question, and I could probably find then answer by doing a search, but are these RR test done in 4th gear? Does it matter what gear it is in when doing these RR sessions? Thanks Simon Quote Link to post Share on other sites
Steve Morris Posted January 10 Author Report Share Posted January 10 8 hours ago, andyhall said: Hi Steve, I don't think there are many out there who can adjust a MU, certainly on a rolling road, hard enough to fine someone who can do Webers! anyway that's a pretty good power/torque graph, the new TLE will help and does come with a boss in 3-1 collector. Andy That’s encouraging to hear Andy - thanks. Went for a blast this afternoon and all good. Looking forward to getting a decent manifold on there! Quote Link to post Share on other sites
Steve Morris Posted January 10 Author Report Share Posted January 10 1 hour ago, kiwican said: This might a silly question, and I could probably find then answer by doing a search, but are these RR test done in 4th gear? Does it matter what gear it is in when doing these RR sessions? Thanks Simon Not sure what the standard is Simon. but I think mine was done in 4th. Quote Link to post Share on other sites
john.r.davies Posted January 10 Report Share Posted January 10 On 1/9/2025 at 7:12 PM, Steve Morris said: Just to confirm, the straight line is definitely power - see below torque/power graph from same run. feeling a bit stupid now… Because of the way that the units are defined, the torque and power curves ALWAYS cross at 5500 revs. If you didn't want to rev any higher, fair enough, the standard TR6 engine reaches its strength limit at a little over 6K, but there is a little more nearer that limit. John Quote Link to post Share on other sites
Steve Morris Posted January 10 Author Report Share Posted January 10 26 minutes ago, john.r.davies said: Because of the way that the units are defined, the torque and power curves ALWAYS cross at 5500 revs. If you didn't want to rev any higher, fair enough, the standard TR6 engine reaches its strength limit at a little over 6K, but there is a little more nearer that limit. John Thanks John - so what would the likely theoretical max power be on my engine, looking at the graph? Quote Link to post Share on other sites
john.r.davies Posted January 10 Report Share Posted January 10 With the chart in front of you it's easier to 'extrapolate' the line of the graph. But I'd guess at about 150bhp at 5500. It'll go on flattening out, so above that as torque continues to fall, may never get to 160. John Quote Link to post Share on other sites
DRD Posted January 10 Report Share Posted January 10 2 hours ago, john.r.davies said: Because of the way that the units are defined, the torque and power curves ALWAYS cross at 5500 revs. If you didn't want to rev any higher, fair enough, the standard TR6 engine reaches its strength limit at a little over 6K, but there is a little more nearer that limit. John I thought they should cross at 5252rpm as power = torque/5252 Quote Link to post Share on other sites
Schnippel Posted January 11 Report Share Posted January 11 On 9.1.2025 at 12:03, Steve Morris said: Für Hinweise zur beigefügten AFR-Kurve aus meiner RR-Sitzung vor einigen Monaten wäre ich dankbar. Es sieht für mich so aus, als wäre das Gemisch im oberen Drehzahlbereich zu mager, da es sich um einen Powerrun mit Volllast handelte. Eine Leitung umfasst die Zylinder 1–3 und die andere Wellenleitung umfasst die Zylinder 4–6, da ich vom Verteiler nach hinten ein reines Doppelsystem habe, das bald auf ein 6-3–1-Einzelrohr umgestellt wird. Seit dieser Sitzung wurden die Drosselklappen durch Fred Millturn ersetzt und das Auto fährt sich viel besser, aber insgeheim mache ich mir Sorgen wegen der Magerkeit bei Volllast. Die Zündkerzen haben nach einer Fahrt eine gute Farbe, aber der Auspuff riecht beim Fahren in der Stadt etwas stark. Muss die Betankung anhand dieser Kurve überprüft werden oder liegt sie im akzeptablen Bereich? Gedanken sind willkommen, Leute. Hello, if there are demonstrable deviations between cylinders 1-3 and 4-6. Then it can be assumed that the dosing unit is defective. There is an aysymmetry of the shuttle due to wear. I've noticed this very often with newly overhauled dosing units!!! There are no more new rotors for the dosing unit. So the shuttles are reground. Unfortunately, this only works very, very rarely. And the hardness is gone and the shuttle wears out even faster. Without new rotors the problem will occur more and more often. Best Regards Ralf Quote Link to post Share on other sites
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.