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About AK260

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  1. Thank you sir! Loving the body of knowledge on this forum! [emoji106] I need to read a lot more. Will likely buy his tune tips books to better understand the principles. (Even if I’m not running triples).
  2. So chaps, here’s a thought to chew over: The video I shared has gotten me thinking and yes it hurts ;) The intake velocity is high, the intake valve shuts rapidly, the energy of the intake air bounces against the back of the valve and sends a pressure wave back up the inlet tract. With the balance tube on the SU manifold, the shockwave not only affects the carb that was supplying but travels through the tube to the other carb which potentially disrupts the airflow of the other bank. On DCOEs, it spits harder through one inlet tract, say cyl 1, but cyl 5 starts to breath through an undisturbed tract. So would this be one good reason why DCOEs behave better at the top end beyond the sheer size of each carb feeding each cyl? Except for sacrificing low end smoothness what would happen if the balance tube was blocked? Surely that would be the same as The DCOE scenario? But without an idle circuit? Also I think I better understand why foam filters on carb mouths have been known to disintegrate under the shockwaves and / or even catch fire when the carb spits [emoji33]
  3. Utter genius!!! And so on point!!! [emoji1787][emoji1787][emoji106][emoji106]
  4. Thank you sir! That was a brilliant read and good food for thought. I definitely saw an increase in the dips after going to a more free flowing header / exhaust. It also seems there is hope to tune out, or at least minimise the dips. I do think I can get a few more ponies out across the mid range and the top end once the needlework is done. The torque curve quite consistently follows the AFR curve and drops off at the top as soon as the AFR starts to lean up (lean being relative - below 14 but above 12.8). Ordering needles today, so the weekend should prove to be interesting. In the interest of science, I plan to sort out the carb tuning to work well with the existing header, power run, then re-install old header / exhaust and do a power run to see the difference in the mid range and top end. It will cost me another 250GBP but as the man in Dirty Harry said (for those old enough to remember) - “I gots to know”, so it will be worth it! And for those not old enough to know it ...
  5. Thanks buddy, it’s quite fun experimenting and learning! That thread you shared is very interesting and certainly a testament to commitment and tenacity! [emoji106] I will read again in detail and absorb / learn from your experiences. On the hybridz there’s a thread that asked people to post their dyno sheets. That and goes if googling showed me that nearly all the “tuned” L series engines seem to have those exact two dips +/- 500 rpm from mine (I’m guessing cam timing dependent). https://forums.hybridz.org/topic/123487-compare-your-dyno-sheets-here/ So it seems it’s not a just a carb induced factor - having said that a wise man with 40+ ears of technical Z experience was just telling me about his experience of variations in inlet tract shape / length etc and the airbox / filter housing having a big effect on these conditions. For example (and let me quote very badly) open trumpets makes the inlet tracts hugely different due to the shape of the inner wing and the distance to the mouth. Then there is reflected pulses etc and the Helmholtz effect. Never-the-less (as you say) I believe we are blessed with this effect on our engines and what needs to be done is to spend time and effort in minimising it but I’m not certain we will ever eliminate it. My plan is to sort out the mix as best as I can then do a power run with existing header / exhaust and another with the old one for some back to back testing to see if the primary diameters can tune this out a little.
  6. Thanks chaps. Being in the UK the weather has been atrocious so the next video may be a while :(. Just had a month of rain in one day!! Yes the springs are indeed available here and I will definitely experiment. Some think of this as a bit of a faff but for me it’s an enjoyable part of my Z ownership journey. I love spirited driving and tinkering in equal measure! ;) Wow that is a serious mixer!!! I thought my 36 channel mixer was complex [emoji33]
  7. Thanks chaps and yes I will do a much better video / show full speed version - not sure why the sound didn’t work but this was a first trial run with the web cam. I need to shield the timing light pickup and cable as it is OK for tuning but clearly it suffers with noise when all the cable is under the bonnet. The VERY long version of what I’m doing is on the link below: https://zclub.net/community/index.php?threads/su-carbs-will-work-perfectly-on-my-modified-l28-and-give-dcoes-a-run-for-their-money.25839/ Suffice it to say it all started with not being happy with the RR tune and the modified SM needles so I started working things out for myself. I have two torque dips at 2.1-2.5 Krpm and 3.1-3.5 k rpm where the AFR heads into the 9s and 10s. I’ve been suspecting reversion of exhaust gasses combined with over rich needles at that point in the rev range. No stumbling, just bogging down before breathing fire and scaring the life out of modern performance cars between 3.5-6.5krpm! [emoji12] But I want to smooth out the power band as best as possible with needles. I’ve modelled what I am aiming for on a spreadsheet and have shortlist of two needles (DX and KD) that may improve the situation around the torque holes. Also the RR showed it gets lean over 6000 going from mid 11s and 12s to 13.8 on the AFR. So once I’ve dealt with the low-mid range I will be very slowly polishing the last few stations to get the very top rich enough for track days. Dotted line is the average of the two SM needles the tuner modified. The unmodified SM is on the chart for reference and judging how lean I want to be at cruise ... However, I wanted to get some “real” data on where the piston sits at various “cruise” RPMs as well as seeing evidence of reversion - hence the video. Like the idea of the washers, had similar thoughts on that [emoji106].
  8. So I got a little time to play and this happened. You can clearly see the reversion through the carbs!! [emoji33] Unfortunately the video quality reduced on the upload so you can’t see the piston markings on this version of the video clip. I may try stronger carb springs to increase intake velocity and see if that reduces it. Alternatively I can make some weights to securely sit on the top of the pistons ;) https://youtu.be/uedh4L32OkA Oh I just realised - I need to get a life!
  9. Just a teaser for now without much explanation but this could get very interesting! Will do a proper write up as to why and what when I finish the work ... 1/8” increments ... Webcam pointing into carb mouth Nice view ... Timing light with rev counter fixed in field of view for analysis, need to improve lighting ... Let the fun begin!! Ah, no! Children’s activities stopped play at the crucial moment! [emoji22]
  10. I took the advice and bought some banjo fittings and used 5mm clear pipe ...
  11. Ok dude, electric fans won’t stop fouling plugs. The first thing to look and adjust would be your mix. But before any of that, go for a drive with a pair of cloth gloves, towel and a spark plug remover socket in the car. Re-created the scenario. As soon as it happens, turn off engine, pull over, pop the bonnet, lay the towel on the wing and pull your plugs (which will be hot) and lay them on the towel. Now look at what the plugs look like and if the ones from the front and rear banks are different in any way. I also experienced similar symptoms but with fuel vaporisation as the header was heating up carbs and everything carrying fuel above them. A decent heat-shield works wonders. Good luck chap.
  12. I had that header on mine, it’s an absolute peach and will make your engine sing beautifully!!! It’s a very well balanced size and length of primaries. Ps. Keep the stock manifold - with prices shooting up for originality someone will pay good money for that one day! )
  13. This is what upsets me - I bought the Z as a hero halo car I can drive hard and enjoy, not as an asset that I worry about breaking. But having the “inferior” 260z I doubt I need to worry too much :p
  14. I have garage envy now!!!! [emoji106]
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