Guest bastaad525 Posted October 29, 2002 Share Posted October 29, 2002 I mean side by side with a measuring tool. Just wondering what the measurements are and where/how/how much SM's differ from the stock needles. Quote Link to comment Share on other sites More sharing options...
johnc Posted October 29, 2002 Share Posted October 29, 2002 Years ago Erik Messley, Rich Maloney, and Javier Guiterrez (two ITS regional champs and an L6 engine builder) spent about a week with calipers and an engine dyno comparing every single type of SU needle and jet that would fit in the Hitachi SU. All three ended up agreeing on a certain profile to help mid-range torque and it wasn't any of the profiles available over the counter. They used to grind their own. Of the ones available over the counter I think they preferred the N47 - but I could have that number wrong. BTW... Anything over about 4,000 rpm and the needle is completely out of the jet. Quote Link to comment Share on other sites More sharing options...
DAW Posted October 29, 2002 Share Posted October 29, 2002 You said that you had the SU book I referenced. I think you should read it more closely because it tells you where to look for the info you want. It references the "SU Reference Catalogue" and the "SU Carburettor Needle Profile Chart" as where to find SU needle diameters at 1/8" increments for virtually all SU needles. Why would you seek out hearsay when factual data is readily available? BTW, the technique for needle profile modification is very specific and requires a drillpress to spin the needle while removing small amounts of material with fine sandpaper. You mention that you might try to do this using a dremel tool...I hope you don't mean you're going to apply the dremel to the needle. If you mean you want to chuck up the needle in the dremel, I think you'd be better off with an electric drill because of the rpm and because a lot of drlls have a trigger-hold mechanism that you could lock on while holding the drill in a vice so that everything is steady. Also, if you are setting out to custom profile your needles for your engine/altitude/rpm use-range, you might want to start with stock needles rather than something like an SM because you can remove more material (richen), but not less. If memory serves, I think the SMs were a little too rich at top end but too lean in mid-range for my engine so I was better off starting with needles too lean throughout in order to add richness anywhere I needed it. DAW Quote Link to comment Share on other sites More sharing options...
DAW Posted October 29, 2002 Share Posted October 29, 2002 OK, I searched and found the SU Needle book here: http://www.minimania.com/Search_Inventory.cfm DAW Quote Link to comment Share on other sites More sharing options...
Guest bastaad525 Posted October 29, 2002 Share Posted October 29, 2002 Hey DAW, I did skim thru the SU book I have and it does have a decent sized section on needles, however I didn't see specific measurements for N47's or SM's or any other designation i could recognize. Admittedly I did just skim thru the section so I may have missed it. And yeah I meant chucking the needle in the dremels tip. I've been thinking of buying a dremel anyways for various other things so that's why I was gonna use the dremel as opposed to a drill. I may try to borrow a drill to do this though. The reason I was asking specifics between the two needles is because it seems to be a pretty common oppinion that for high compression 2.8's or larger, that the stock needles would run good up to a certain point, but were too lean and would tend to starve the motor on the top end. SM's provide a richer top end, and also help out with the midrange pull, but tend to run too rich at idle. So I was thinking of doing a kind of combination, taking an N47 and richening it up from the midpoint to the tip by grinding this section to the SM's specs. Also, it was my understanding that, although the needle has reached the maximum point of it's travel at roughly 4-5k revs and can't adjust mixture anymore, it is NOT all the way out of the nozzle at this point, a small section of it, fractions of an inch, still extend down into the nozzle. Is this not the case? Quote Link to comment Share on other sites More sharing options...
johnc Posted October 30, 2002 Share Posted October 30, 2002 > Also, it was my understanding that, although > the needle has reached the maximum point of > it's travel at roughly 4-5k revs and can't > adjust mixture anymore, it is NOT all the way > out of the nozzle at this point, a small > section of it, fractions of an inch, still > extend down into the nozzle. Is this not the > case? I don't remember if that's true for a stock SU. I've seen a number of SUs prepared for ITS where the needle is all that way out of the jet, but those engines are run WOT almost all the time. Quote Link to comment Share on other sites More sharing options...
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