roulli Posted June 28, 2011 Share Posted June 28, 2011 Hello My triumph 6cyl 2.7l is running on triple Dcoe40 (151) My newly acquired AEM wideband system shows lamda values around 0,80 at 3000rpm steady state I reduced the mains from 120 to 115 without any noticeable effect My target was to run between 0.9 and 1 How can I achieve these values? Further reduce the mains? Changing the idle jets effects the lamda values greatly up to 2200 rpm But at >3000 rpm the engine should be running in the main circuit and after 10s an eventual squirt from the accel pump should be vanished in the lamda readings 30 venturies and180 air correctors.... Appart from that the engine runs fine and the plugs aren' black eather Any hint is welcome as I'll leave for Goodwood on Thursday Cheers Patrick Link to comment Share on other sites More sharing options...
DaveNotSoSideways Posted June 28, 2011 Share Posted June 28, 2011 Increase air corrector size to 190/200. Use a "thicker" / larger diameter emulsion tube. If plugs are good, don't worry? People always want to go too lean with these airfuel toys. A modified engine might want to be richer, you won't get a modified engine to run @ 14.7 and you don't want to. Link to comment Share on other sites More sharing options...
CHRIS211083 Posted June 28, 2011 Share Posted June 28, 2011 Max power WOT 12.6-13.2.......Economy 14.5-16.......idle 13-16......part throttle acceleration 14.5. Just to fill in the gaps, Also remember that there is always a compromise with carb's you can never get everything the way you want it. Chris. Link to comment Share on other sites More sharing options...
spitNL Posted June 28, 2011 Share Posted June 28, 2011 2.7Litre? Sounds like a tuned engine. Does it have a "fast road" camshaft? Could be the fuel is going into the exhaust at overlap. Lambda readings are not always showing what's going on in the engine. If you've got a friendly MOT station, they might let you hook it up on their 4-gas tester. Lambda 0.80 should be about 8.0% CO. Cheers, Frederick Link to comment Share on other sites More sharing options...
roulli Posted June 28, 2011 Author Share Posted June 28, 2011 Hi thanks for the feedback the engine is actually not heavily modified - but make your own judgement the engine had these big forged pistons inside, which were still immaculate. Since the bores were rather tight for forged piston, I could reuse them and simply had to re-hone and put in new rings. Regarding the cam I swapped the original 280 PI cam against a 260° Newman cam. This is very common in Deutschland. But GT calls it detune the engine. The only thing I did to the head was the short side radius according to ncoll's instructions Standard but stellited exhaust valves, standard inlet valves not backcut 2-angle job There was no room for un-shrouding, since I use the std. size Payen head gasket. compression ratio is 10,5 megajolted 1,5 kg removed from flywheel (early TR5 type) ballanced The new engine doesn't like as much advance as the old one (PI cam) Fuel into the exhaust at overlap? I am talking about steady state, in third gear, not downhill, at +3000 rpm. Overlap is when I release gas, isn't it? When I release gas it goes totally lean and it pops in the exhaust. Link to comment Share on other sites More sharing options...
spitNL Posted June 28, 2011 Share Posted June 28, 2011 (edited) No overlap isn't when you release the gas, that's overrun. Sorry for the confusion. I was talking about valve overlap or "Ventilüberschneidung" But that's not really a large camshaft, so I don't think you will have to worry too much about it. Edited June 29, 2011 by spitNL Link to comment Share on other sites More sharing options...
roulli Posted June 28, 2011 Author Share Posted June 28, 2011 No overlap isn't when you release the gas, that's overrun. Sorry for the confusion. I was talking about valve overlap or "Ventilüberschneidung" But that's not really a larhe camshaft, so I don't think you will have to worry too much about it. You mean, that unburnt mixture is getting directly from the inlet valve thorugh the exhaust valve. Yes, it looks like it. Another guy was reducing the mains to 105 on a TR6, and it didn't make a difference on the AFR. Always too rich. With my cam (20°-60°), this is weird Patrick Link to comment Share on other sites More sharing options...
James Posted June 28, 2011 Share Posted June 28, 2011 I've heard of this odd practice of detuning the engine— it's bizarre and I dont understand it at all— especially when running performance carbs etc Can you enlighten us to the theory? Link to comment Share on other sites More sharing options...
roulli Posted June 29, 2011 Author Share Posted June 29, 2011 I've heard of this odd practice of detuning the engine— it's bizarre and I dont understand it at all— especially when running performance carbs etc Can you enlighten us to the theory? You're talking about the 260° Newman PH1 cam, with regard to "detuning" ? Well there is a German Triumph 6 cylinder Guru, who is very respected in the German Triumph scene, for road cars.. He's setting up 6 cylinders, mainly, PI and EFI conversions. Never ever heard a negative word on his engine building capabilities, only positive feedback. This guy recommends to use this specific cam - for a road car. If you don't want to use the 2,5l above 5500-6000rpm, you won't need a cam that outperorms the PH1 above this range. That's the story. Now I do have Webers, because the car came with them. I was told in this forum that the 280° PI cam and Webers was a missmatch (due to the low lift) That's why I thought to use the PH1, when rebuilding the engine I do not have the feeling that the rebuilt engine flattens beyond 4500rpm. Link to comment Share on other sites More sharing options...
DaveNotSoSideways Posted June 29, 2011 Share Posted June 29, 2011 Idle @ 13-16? Maybe on a modern car More like 11-12:1 on anything on carbs and with any form of modified cam. Chris's figures are just nonsense regarding anything bar a modern 4 valve or a BOG standard low compression worn out heap producing 6hp. Link to comment Share on other sites More sharing options...
James Posted June 29, 2011 Share Posted June 29, 2011 Idle should be around 13-14 - you want it richer or it'll stumble when you pull away. Those values are really for EFI so no idea how applicable to carbs. Link to comment Share on other sites More sharing options...
CHRIS211083 Posted June 29, 2011 Share Posted June 29, 2011 I Love it when some one says something is rubbish or can't be done especially when ive been doing it or have done it......My Su's were running the spec's I'd just shown with the last manifold on my 1300. Idle 14-15 depending on engine/air temp. Maybe not with Webbers(never tried them)but my Hs2's managed it fine. I also have a lean part throttle cruising at 15-16. The only bits I've not got at the mo is the 13.2-12.6 WOT top end. I'm currently at 13.5 at 2,500 increasing to 12 by 6,500rpm. My engine was rebuilt 6 months ago with a TR5 cam. However my compression is currently stock at 8.5. Cheers anyway Dave..... Chris. Link to comment Share on other sites More sharing options...
STIV62000 Posted June 30, 2011 Share Posted June 30, 2011 (edited) How many progression holes do the carbies have? take one progression plug out and look thru the hole closest to the engine. Now open the throttle ever so slightly...do u see the butterfly or is it a couple of mm away before it exposes the 1st progression hole? The type 152 45's are crap because of this reason on a road car. They run too lean with just a cracked open throttle regardless of what size idle jet you use because they are not exposing a progression hole until further down the throttle action. Mine always ran good at idle, way lean just off idle into progression, and after that ok cause i could play with jetting. i couldnt do a thing about the slight throttle cruise...always lean. Now on Dellortos and can get the AFR's i want across the range. And yes, engines on these carbies need more fuel than what you read as a requirement. Typically a point more i found. Edited June 30, 2011 by STIV62000 Link to comment Share on other sites More sharing options...
DaveNotSoSideways Posted June 30, 2011 Share Posted June 30, 2011 I like it when someone has worked on one engine and thinks they know everything. Link to comment Share on other sites More sharing options...
smithy Posted June 30, 2011 Share Posted June 30, 2011 Ah, how I love this site. Even when I haven't got a clue what anyone's on about. I want the popcorn franchise. Link to comment Share on other sites More sharing options...
DaveNotSoSideways Posted June 30, 2011 Share Posted June 30, 2011 I am pretty sure this thread mentioned Webers didn't it? See STIV understands, you'll be lucky to get a set of 152's to idle at all, let alone get the rancid things to idle at any sort of exceptable AFR ratio or get clean plugs, maybe try getting them to pickup without backfiring so bad they burst into flames at anything above 13:1 in any situation. Combine that with the typical 6cyl manifold garbage and a duff worn out linkage, best set them up at 12.5:1 almost constant or they spit, hiss, pulse and annoy you endlessly. You might just have a chance to use 14:1 on some 6 hole dellortos if you're engine is faultlessly prepared..... I don't even want my Dellortos/Webers to reach 16:1 on OVER-RUN. NEVER, cause then the exhaust pops and bangs making your car sound like a nail. Link to comment Share on other sites More sharing options...
STIV62000 Posted July 1, 2011 Share Posted July 1, 2011 Im only base my post on what ive seen with 3 sets of type 152 webers now. One set on my Fiat twin cam engine, 2 others on Alfa Nord twincams . No experience with other engines and these carbies. I know the Alfa guys are getting an extra hole drilled for progression under the throttle plate, and others chamfering the actual throttle plates to get them to sit closer to the 1st prog hole at idle. This in my opinion is a hit and miss affair...why bother when Dellortos dont have this problem. Type 152G webers have an extra hole, and they are even available in 5 hole now for 16V engines. All DHLA types ive seen have their 1st progression hole right under the butterfly, crack it open, and your drawing in extra A/F mixture- the engine isnt waiting for more throttle before it gets the right amount of fuel. Running the engine ridiculously rich at idle to compensate is wrong. In the above cases i know of even doing so did not fix the progression. Link to comment Share on other sites More sharing options...
roulli Posted July 6, 2011 Author Share Posted July 6, 2011 Hi, I was in Goodwood, so I didn't follow up the thread... STIV62000's description makes sense. The DCOE 45- 152 being the big Spanish brother of the DCOE 40 -151. My carbs do have 3 progression holes, and I was already thinking of them being at the wrong place, as the behavior is exactly as STIV... describes. Too weak at very small throttle openings. And if one wants to get rid of this weak spot, I need to over-richen the the idle circuit, to compensate... So adding a progression hole, just behind the throttle plate and/or filing the throttle plate should be the the road to go. What diameter are these progression holes actually? How does one drill a sub 1mm hole, without breaking the drill, by just looking at it? Dremel or stationary drill machine By the way, the eve prior leaving for Goodwood, I was still tweaking the Webers and I found that the mixture is still affected by the idle circuit at higher revs than expected. The AFR is highly impacted by the slightest idle mixture screw adjustments, I mean 1/8th of a turn (and the 151 does not have the coarse thread!) Cheers, Patrick Link to comment Share on other sites More sharing options...
STIV62000 Posted July 8, 2011 Share Posted July 8, 2011 I too looked at drilling an extra progression hole but when i considered the precision it needs to be done with...forget it! You will need a milling machine and an accurate set up to go this path. Dont attempt it with a hand drill or dremel.If just one hole is not exactly aligned with the other 3 then good luck getting it to idle properly...even with airbleed compensation they would be impossible to get perfect. Best solution is to get rid of them and get some nice Dellortos with 4 or 5 or 6 progression holes. If they run too rich in progression, then block off one hole with epoxy and test. If no good, then very easy to drill out the epoxy by hand. Actually i stumbled upon a youtube video by fiatnutz. He runs Costa Messa R and D in the US. If you search his VDO's you will see he has a set that he modifies for exactly the same reason. In the UK, i know there is a place that does them also, but cant think off the top of my head. Alternatively, Kinsler fuel injection was offering new throttle plates for these DCOE's that are cut at a different angle, to get the butterfly closer to the progression holes. You may want to try them. Search the Alfaholics website forum. Search weber dcoe 45 type 152 and you will see a whole discussion there as well as suggestions on where to drill the extra hole etc... Like i said though, for me...Dellorto's were the way to go. i sold the webers, bought Dellortos rebuilt them, set them up and had $200 left over! And i have a much superior set up as far as drivability and economy goes. At full throttle they are just tubes of a given diameter and flow according to size, but in progression and transition they are very different. Good luck Link to comment Share on other sites More sharing options...
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