Has anyone ever used the sniffer tube assemblies to actually make mixture adjustments? The tubes were OEM apparently on some carb 308's. The idea presumably was test the mixture of each cylinder at idle. There is a bank of 4 that taps into each branch of the front exhaust manifold and terminate in a row somewhere near the top of the front head. Rear bank tubes are paired 1-2 and 3-4 to cover the rear bank. The tubes are blanked off with a plug, gasket, and lock tab when not actively being used for test purposes. When left in place and neglected, they apparently deteriorate and plug up or fracture. What did the dealers use to analyze the gas? Was the test just a CO mesurement at idle? Bill
I've wondered about that too. I still have the tubes on my GT4 (although on mine it is just plugs directly on the manifold, no tubes attached), and wondered if I could use them to get my mixture nicely even on all 8 throats...
I use the tubes to adjust the idle mixture on both my Alfa 1750 and my 308, in my opinion it is the best way to get the right idle mixture. regards jesper Image Unavailable, Please Login
Yes, its an old CO analyzer i found in the corner in the local Alfa Romeo shop and bought cheap. Today the all use a 4-gas tester, but for an old carb car its good enough. I set the level to ca. 4% CO, as standing in the workshop manual. For the synchronisation i have also attached small sniffer tubes in the inlet manifold, and I connect it to my mercury test device. Regards Jesper Image Unavailable, Please Login
Thanks Jesper. The owner's manual and vehicle emission control information plaque (affixed to the engine bay), for my 1978 USA GTB/S, specifies CO and HC levels at idle. I assume the Ferrari dealers at the time used at least a 2-gas analyzer. At each cylinder without air injection: CO 6%,+/-1%; HC MAX 300 PPM At exhaust tail pipes with air injection: CO MAX 1% HC MAX 200 PPM It appears the smog cars, like mine, were tuned a little richer at idle and relied on the emissions system to clean up the down stream exhaust. How often do you sample your idle mixtures and have you had any problems with the tubes plugging up? Thanks again, Bill
Single best thing they ever put on the cars for diagnostic work. Within min's every cylinder can be analyzed for efficiency and a problem pin pointed. I do not see them plugging but I see them breaking off. A bit of a pain to replace but worth the effort.
I've gotten 308's to run best after a careful check thru those tubes. I once thought I had a bad cylinder as I couldn't get CO to respond. It turned out to be a cracked and deteriorated sniffer tube. I wound up pulling the header, and EDM'ing out the rusted tubes, then putting in a new set. So glad to have those working again!
How often do you sample your idle mixtures and have you had any problems with the tubes plugging up? Thanks again, Bill[/QUOTE] It´s my first season with the license plates on the car, but I guess every second year or when needed because of poor running. Dont know if they plugs up, the originaltubes are made of steel and will rust away because of agressive exhaust acids ( was rusty on my first 76 ). On my second 76 the front bank tubes was missing, made new ones in 6 mm stainless steel. Very tough job from underneath the car with one arm. Regards Jesper Image Unavailable, Please Login Image Unavailable, Please Login
Exceptional workmanship Jesper! Fabrication like that DOES NOT happen by accident, very tough indeed! Keep an eye on the brass fittings in the header. I made stainless steel fittings as I was having aging problems with the brass after a number of years, just couldnt handle the heat in this application.
Jesper, I like what you've done. Do your tubes terminate at the factory location? I think this is somewhere near the 5-cylinder on the forward edge of the valve cover? The sampling ports on the headers of my 78 GTS, appear to have been welded shut in a most unworkmanship way in a previous life. Over time, I managed to find replacement tubes, some used, but in serviceable condition and a good set of used headers with good fitting bosses. Does anyone know what the header fitting thread specification is? I do have a new front bank tube assembly, but missing the attaching L-bracket and hardware. A collection bar fuses all tubes in a line at the sampling end. The tubes themselves appear to have been hand formed in an artistic manner, with great care exhibited by the uniform compound curves approaching each port axis. I saw one spall dent or tooling mark on the tube leading to the 8-cylinder. The tubes are fused together between the 5-6 and 6-7 cylinders and all four are fused together prior to termination at the valve cover collection bar. I state fused, but I suspect they were brazed. The whole assembly has a silver finish, maybe nickel plating or silver paint over mild steel tubing? I much prefer the all stainless approach. Some very high temp antisieze on stainless steel fittings and if necessary one has a good chance of taking them off, intact in the future. I'm running an XDI-2, programmable ignition system. Without the distributors in the way it may make more sense to plumb the termination point to the bell housing area, for better access. Any thoughts? Thanks, Bill
Dave, Been thinking about this a few days... Not trying to stir the pot, just trying to learn. On the injected cars, what can the sniffer tubes tell you besides whether an injector is a bit fat or a bit lean? Can you tell if there is a valve problem or weak spark?? Please elaborate... and thanks! Rick
Rick, Cam timing bank to bank. Plug wire/extender issues with high HC. Injector/fuel distributor issues with high or low CO. Cat issues with a simple and quick access to pre cat readings for a given bank. As Jesper showed, with a carb car, especially at our altitude, jetting and sync is a breeze. But just a few examples, Very valuable in time savings and the ability to do it correctly and accurately while eliminating guess work. Bill, I will measure them and let you know, 14 x 1.25 by memory. I was unable to locate a suitable top fitting and a correct lower fitting in stainless so we had them made. This was a joint effort with Troy at HyperFlow and myself as the TestaRossa sample tubes were NLA and he wanted to offer those... hence the design of the top fittings. Just one of those many projects waiting for the time to finish..... With the Beta testing now ongoing with 3x8/Mondial series cars and the Gold Connector kit, I had to fab up and finish them for a number of cars. Only someone that has been there can appriciate the workmanship shown in Jespers efforts! Image Unavailable, Please Login Image Unavailable, Please Login
Some very nice work there! My front bank ('79 308), is in fine shape but on the rear bank only one remains. I have been up in the air on whether to replace them or not. After reading this thread, I am thinking that maybe I should replace them! Thanks for the inspiration.
Ahhh... I had been thinking single hole as opposed to whole motor. Thanks Dave! Had a pep talk with our boy last night... Rick
Back in the day when it was insisted these cars were tuned to the cutting edge, THESE sample tubes were the answer. Single cylinder, bank to bank and the engine as a whole, they offered what was needed. Captain Tinfoil..... Set to rule the world. Got the funniest voice message I have ever heard from him this morning.... Bill, Correction, 12 x 1.25 header boss. RKL, I sure would consider it. Time spent now is saved many times over as Jesper has shown. Image Unavailable, Please Login
Exceptional workmanship Jesper! Fabrication like that DOES NOT happen by accident, very tough indeed! Thanks, only possible with my thin spaghettiarms, but a hard job with no space. Keep an eye on the brass fittings in the header. I made stainless steel fittings as I was having aging problems with the brass after a number of years, just couldnt handle the heat in this application. Dave, I think you are right about the brass fittings, the rear bank fittings go loose over time. On the front bank I think the fittings is secured by the tubes, have to secure the rear bank. One word to the stainless fittings: Stainless steel against stainless steel and heat, can stick so hard together and sometimes gets impossible to take apart again without damaging the threads. Think normal steel would be better here. Bill308. I think the tubes terminates about the same place as from factory, they were missing so hard to tell exactly. Regards Jesper
Thanks Dave and Jesper. I need to re-enable the sampling feature on my 308GTS. A little research on McMaster-Carr web site suggests stainless fittings of this type are good for 1200F. With the cap removed, can someone characterize the minimum gas flow coming out of a good condition tube and what size the tube is? I have a simple Gunson gas tester (CO based meter) and I'd like to assess whether it will get enough gas flow to work porperly. Do you think failure of these tubes due to primarily to fatigue or corrosion or asked another way, if there were no corrosion would they still break in 10-years due to fatigue? Dave, Can you tell me a little more about your fittings? Based upon your description of the thread form, it appears that the manifold fitting can be described as an m12 x 1.25 bubble flare? I assume the longer fitting is the termination end. How does this attach to the stainless tube and then to the analyzer? Do you look at 5-gases when hooked up to an individual tube? Thanks again guys. Bill
The tube size is not important as it will just change the sample refresh rate. I believe I used 1/4" OD by memory. Ferrari used mild steel as Tex stated for the lines and a Naval Brass for the fittings. That worked well for many years but neither material was well suited for the application. Upside is the brass fittings used allow for them to be drilled out far easier than a steel that would end up heat hardened over time. I use a 2500* Antiseize with the stainless and have not had any problem removing them from the manifolds after a dozen years or so but in all reality, there is little reason to remove them once installed. Yes, I believe that is correct, 12 x 1.25 bubble, I measured them when I posted the correction. Yes the long fitting is for the hose of the tester to slide over. We made these to reproduce what used on the TR sample tubes utilizing a brass acorn nut and a ball to seal the sample ends. This style of sealing the end proved better than the 6mm screw which often seized and resulted in twisted off sample tubes on both the 3x8's and TR's. Usually its the old reliable 4 gas hooked up to these cars and the 5 gas is saved for the lean burn Motronic cars. With 4 gases looked at on each cylinder of that engine individually, there is nothing that can hide. It really is a wonderful tool Ferrari gave us.
There's a possibility of an uneven mix coming from a CIS fuel distributor in need of rebuilding. When I had my "make it right" service on my 328, once they reinstalled the mill, the shop sampled each of the sniffer tubes to make sure everything was as it should be.
I need to swap out my front header. What's the best way to do this? Any significant danger in breaking off an exhaust port stud? Bill