easy carb question- Is smaller ok???
09-24-11, 03:21 PM
#1
car setter on firer
Thread Starter
easy carb question- Is smaller ok???
a 30 minute search on this site revealed little (it was only supposed to be a three hour tour.). i'd like to know how small of a diameter i can get away with when selecting a sidedraft carby for my stock 12a. Racing beat sells them in 48 and 45mm. i can't afford one of those right now... even used. but i have found numerous DCOE's in 40mm. can i run my little 12a on this? will it flow enough air? I also live at about 3400 ft. so i know that will toy with my A/F ratio.
any help is appreciated. i don't care if i dont gain HP or TQ, but i wouldn't want to lose power. i notice holley sells a 600CFM carb for this motor. is that for a stock 12a , or ported?
any help is appreciated. i don't care if i dont gain HP or TQ, but i wouldn't want to lose power. i notice holley sells a 600CFM carb for this motor. is that for a stock 12a , or ported?
09-24-11, 08:10 PM
#5
A great way to go would be a sterling nikki. Just a modded and stripped down version of the stock carb. I haven't run one myself, but I know a lot of people do with great success. Or you could just rebuild the stock nikki, strip it down and convert to mechanical secondaries. That'll free it up a lot. Seems like a waste of money to go with a holley or weber if you aren't really looking to gain much.
09-24-11, 08:28 PM
#6
car setter on firer
Thread Starter
I'm not after gains, rather its simplicity I'm looking for. Nikki carb is waaaaay too complex. Not to mention there are hardly any *accurate* diy nikki how-to for my sprcific carb. I know my way around webers. So thats what I'm shooting for
09-24-11, 08:55 PM
#7
love the braaaap
Best place to start would be finding out how much the 40 DCOE will flow. Stock nikki I think is around 390cfm (possibly a bit less), which doesn't quite choke the engine at high RPM with stock exhaust and of course stock ports. It won't get much past 7000rpm though, so its pretty much on the limit. As mentioned, the 40 will probably do with no other mods to the engine or exhaust. I think the 45 is considered optimal for the 12A with an opened up exhaust with the 48 being a bit on the large side but still doable.
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09-24-11, 09:09 PM
#8
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Stock Nikki is typically quoted as 313 CFM at 1.5" Hg.
I'm not sure on flowrates for the 40 DCOE, but even a 45 DCOE only flows 400-ish CFM with 36mm venturis. I'm sure the 40 DCOE would work, but it'd definitely be restrictive, especially if you upgrade the exhaust.
Larger carbs will always give you more power, but going too large will hurt low end. At some point the top-end gains aren't worth the tradeoff, but a stock 12A does okay with a 48 IDA, which is near or above 600 CFM depending on venturis.
I'm not sure on flowrates for the 40 DCOE, but even a 45 DCOE only flows 400-ish CFM with 36mm venturis. I'm sure the 40 DCOE would work, but it'd definitely be restrictive, especially if you upgrade the exhaust.
Larger carbs will always give you more power, but going too large will hurt low end. At some point the top-end gains aren't worth the tradeoff, but a stock 12A does okay with a 48 IDA, which is near or above 600 CFM depending on venturis.
09-24-11, 10:55 PM
#9
Junior Member
what he is talking about is that his nikki is on a '80 SA. lol
09-25-11, 02:51 AM
#10
There is heaps of info around about Nikki's... Stripping them down for simplicity is easy.
09-25-11, 11:06 AM
#11
car setter on firer
Thread Starter
i did find one, but it wasn't for my SA22c chassis. the pdf i DL'd is for the newer 83-85(?) nikki. mine does not have a whole lot of the components said to remove. not only that, i just really dont like the nikki carb in general. i hate downdrafts with a passion. not to mention one that was built for OEM smog equipped cars in early 1980... my datsuns were terrible for smog. I always rip that stuff out and do it right. a nice sidedraft (like every japanese car should have) 
thanks for the flow rating guys, i'll do my homework. i MAY not even have this car much longer if someone buys is from me. *WINK*WINK*
thanks for the flow rating guys, i'll do my homework. i MAY not even have this car much longer if someone buys is from me. *WINK*WINK*
09-25-11, 12:43 PM
#12
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what size venturi's fit in a 40 dcoe? a stock 12A will want something like 38's i'm not sure that'll fit in a 40dcoe...
although if you find a lake cities manifold it might work, the lake cities is short, and comes straight off the engine, instead of wrapping around the top. since the lake cities is so short, and has no bends, you can do a smaller carb
although if you find a lake cities manifold it might work, the lake cities is short, and comes straight off the engine, instead of wrapping around the top. since the lake cities is so short, and has no bends, you can do a smaller carb
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