springersrolla Posted December 29, 2011 Report Share Posted December 29, 2011 Gday, struggling for choice with my options for intake on my 5k. Full 2" exhaust extractors, will be bolting on my worked head, o/s valves port work and will be chasing a suitable cam. Currently running a standard 3k carb. It seems to run out of legs around 5-5500rpm. I have sitting at home a gemini nikki carb modded sitting on k manifold, never tested. Twin SU's from a l20 datsun with k manifold Single 40mm dhla dellorto - no manifold but have found one Also found a 38/38 weber, and a 32/36 online Now, I've been looking at and comparing cfm's of all carbs, but what is too big, what will work well, what's easiest to tune, run and get resonable economy??? Also what is the best idea with running a 02 sensor, what type? And where's the best spot to place. I have seen altezzaclubs write up and I think ill stick to just one after the collector, but any idea how far down?? Any info would be tops, help me start getting me on my way Cheers Quote Link to comment Share on other sites More sharing options...
philbey Posted December 29, 2011 Report Share Posted December 29, 2011 I'd go the dell onto, have it jetted and choked to suit your motor. Probably 32mm chokes, perhaps 34. Sus would also be good but mani will be harder to find. 2 inch extractors at big but so be it. Is o2 necessary? Your running carbs, you can log data, pull over, adjust, drive again log, pull over? Seriously the money you spend on a good setup on a non efii motor will pay your dyno tuners bulls for 3 years. I spent 300 bucks tu ing my 5k and it ran fine for 2 years. Quote Link to comment Share on other sites More sharing options...
altezzaclub Posted December 29, 2011 Report Share Posted December 29, 2011 The oxy sensor setup would be good if you have the SUs on, then you can reshape your needles to suit the car exactly & do it all yourself. As Philbey said, the Dellorto would make sense as you could have one run on a dyno to get it jetted correctly and leave it at that. Check what it is like getting jets for the Dellorto, ideally a local tuning place with a box full. There's nothing worse than finding it is running rich so you buy a leaner jet set and find its still rich, so you buy another jet set... Quote Link to comment Share on other sites More sharing options...
springersrolla Posted December 29, 2011 Author Report Share Posted December 29, 2011 extractors aren't 2" sorry, but exhaust is. its pending difficult to find much info on a tuning a single 40mm to suit k series but i imagine it wouldn't be too bad i have a k series to suit su manifold here to suit the twin su's i have only reason i suggest an 02 sensor is i have a jaycar air fuel reader i wanna hook up. i did a bit of research and found cfms of carbs standard 150-160cfm 32/36 255-300cfm 40mm dellorto with 32mm chokes 336cfm 38 dgas 380 cfm single HS4 SU 142cfm each what sort of cfm should i be looking at getting? I'm guessing the biggest restriction would then be a manifold after the carb anyways. really I'm looking for something with ease of putting on and running, letting me get somewhere without needing trailer etc cheers Quote Link to comment Share on other sites More sharing options...
snot35 Posted December 29, 2011 Report Share Posted December 29, 2011 I reckon spring for a twin weber/dellorto manifold if you can. If you're going to take advantage of big valves and port work then you might as well let the thing breathe. The SU's would be a reasonable choice as well though and should make the car very drive able. I'd forget about anything that keeps the standard manifold as you're not going to be able to take full advantage of the head mods you have. I've owned all three manifolds and by far the best air flow path is provided by the twin manifold. The SU manifold is quite short and kinks a reasonable amount, as does the single manifold. My picks; twins if you can, SU's, single side draft. Quote Link to comment Share on other sites More sharing options...
springersrolla Posted December 29, 2011 Author Report Share Posted December 29, 2011 Cost is the biggest issue at the moment, I'd love twins, i've found twins on eBay for 1300, I'd rather the Su's as there free and sitting here at the moment. I just have to modify the Su linkage to suit. Guess there's no harm in trying and goin from there. Quote Link to comment Share on other sites More sharing options...
altezzaclub Posted December 29, 2011 Report Share Posted December 29, 2011 (edited) Work it out.. http://www.theformul...showtopic=11007 For a rough CFM use this formula: Engine Displacment * Max RPM / 3456 = CFM @ 100% Volume Efficiency 1500cc is roughly 90cu", and 90*7000/3456=182cfm I'd say maximum you need is 180cfm, I don't think you get anywhere near 100% efficiency. But check my maths! Side draught manifolds should be more efficient than downdraughts. The oxy sensor works when hot so just as the collectors join would do. Mine are in the downpipes, as you saw, great for twin carbs. Use the SUs!! I need someone to bounce ideas off!! :laff: Edited December 29, 2011 by altezzaclub Quote Link to comment Share on other sites More sharing options...
altezzaclub Posted December 29, 2011 Report Share Posted December 29, 2011 (edited) Just read your figures again- so the stock carb won't quite handle 7000rpm, but the others will easily. Did you get them from here? http://www.mgbmga.com/tech/mgb19.htm Now you can see how guys can overcarb their 4K quite easily! Twin Dellortos would be absolute overkill! Edited December 29, 2011 by altezzaclub Quote Link to comment Share on other sites More sharing options...
springersrolla Posted December 30, 2011 Author Report Share Posted December 30, 2011 pulled some of the info from here http://www.thesamba.com/vw/forum/archive/index.php/o-t--t-271444--start-380--index.html altezza what did you do for vacuum lines for the lynx manifold?? still struggling to decide what to do out of simplicity, su's appear to need some work, then will need a good clean up, and have to do all the checks, ill go over this dellorto and see how it looks in comparisson thanks for all your knowledge Quote Link to comment Share on other sites More sharing options...
altezzaclub Posted December 30, 2011 Report Share Posted December 30, 2011 One of the SUs has a port on it for vacuum, which I use for vac advance and the charcoal canister. The Su carbs do not pull much idle vacuum compared to 'normal' carbs. I have probably already tried running the vac advance on manifold vac via the brake booster but can't remember what the effect was. You get high vac advance at idle from the manifold, but I can't remember what effect it has as you open the throttle and it retards to get the car moving. Quote Link to comment Share on other sites More sharing options...
snot35 Posted December 30, 2011 Report Share Posted December 30, 2011 I'm not sure I'd say the side drafts are overkill, we're talking single choke per cylinder and they can be changed. I think the deciding factor will probably be the condition of the carbs. Do the pistons move freely, do they have any dings or anything like in the bore or on the piston? This will really make things difficult. Quote Link to comment Share on other sites More sharing options...
philbey Posted December 30, 2011 Report Share Posted December 30, 2011 Sus are easy to rebuild, you already have them also, big plus. Are they su or hitachi though? Hitachi I understand can be a little more difficult to get parts and tune. Heresay though. If you have the mani it's a done deal. I run twin 40 dells so I'm biased. I got them tuned by a dell guru, it was 2 years of problem free driving (with respect to the tune that is.... 2 starters, an alternator and a broken valve spring make for a different sentiment) Definitely go the su. Give them a rebuild, put them on, get needles and springs to suit. You will be able to get it running and driving, at least to take it to the dyno tuner. Get it tuned properly by a pro, the fiddle with your o2 from a professionally benchmarked level. Quote Link to comment Share on other sites More sharing options...
snot35 Posted December 30, 2011 Report Share Posted December 30, 2011 If they're from a Datsun they're Hitachi's. You can fit English SU needles though, so it's not a big deal. Quote Link to comment Share on other sites More sharing options...
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