Sidedraft 40mm or 45mm or 48mm???

[73DATSON]

What are the difference in each one? What does the number means? I have 40mm with a canon intake, if I go with a 48mm do I need to changed the intake?

[Ratty260z]

The number is the size of the bore or of the choke, I can't remember for sure, but if you have a l20b or L16 48 weber would be pretty big, Most Z's don't even run that size, 40 should be pretty good for a mild L20, Otherwise all the different sizes will bolt up, the port size might be different depending on the intake.

[72240z]

40 is fine, 48 is way to big even for track only.

 

Your in NY? near nyc?

[ggzilla]

Its the bore size. The chokes on sidedrafts are tuning parts

 

40s are great for 1600/1800 engines

45s for 2-liters

48s for ultra high rpm racing

 

First step in tuning is to select an appropriate size choke (venturi)

[73DATSON]

40 is fine, 48 is way to big even for track only.

 

Your in NY? near nyc?

[73DATSON]

I'm queens

[73DATSON]

I'm thinking of going with 45mm. My 40mm are good but I'm looking for more power:-)) I did the head new cam lifter valve job just order MSD with a 2 step coil 2. THX for the infor.

[banzai510(hainz)]

48mm to big

[Silver04rs]

If you decide to part with your 40's shoot me a PM. I might be in the market for some soon

[72240z]

Bigger bores dont automatically equate into more power. Matter of fact you can loose power by going too big. I would say for a street l20, even worked, that 45's are too big.

 

I'm running a 11:1 comp l28 with a pretty aggressive cam and 40's are more then enough. The flow through the head is the bottle neck not the carb bore. You need to have a stroked motor and highly worked head to flow enough air to require 45+

 

I'm right by the GW, you ever break that dime out?

[Stoffregen Motorsports]

One thing to think about is velocity. As the bore from the opening of the carb opening to the bowl and then finally the valve seat eventually decreases, the air charge (ideally) is picking up velocity. This is the idea behind venturis (or chokes). Chokes are placed strategically to speed up the air charge around the spot where the fuel is picked up, so as to atomize the fuel.

 

When it comes to real world carb sizing, I have used mainly Mikuni/Solex carbs in my life, we always shied away from Webers because Mikunis were easier to tune ( I don't want to get into that debate). And not just race motors, I have built many street motors using dual carbs and 44's were usually the smallest we would go. I agree, 48's are too big for a street L20B, but 45's ought to work fine, assuming it has the right porting, the right cam and big enough valves. If it's a stock L20B, I wouldn't even run dual side drafts. Stick to the DGV.

[69srl311]

I'll go against conventional wisdom here a bit. I picked these up on Ebay for my roadster not realizing that they were 50's with 43mm venturis.

 

 

So I threw them on with the stock cam, it would scream at wide open throttle, but ran terrible at part throttle and had a big mid range bog. after installing a bigger cam, smoothing out the intake manifold and head ports and proper tuning (jets) it is very docile in normal daily driving while keeping it's fantastic top end.

[72240z]

I dont think anyone would say larger wouldnt work though you do sacrifice low rpm drive-ability and add tuning issues. Would bet the bog was disrupted a/f. You ran with 50's on a stock set up great but you didnt actually use them. There is no where near enough flow through that motor to use even close to that much carb. Beyond just keeping things usable the motor will make less power. That stock motor will make more power through the range with proper tuned 40's rather then 50's. There are many many dynos to prove it. The main reason to go so big is on the track staying high in the rpm range they allow the engine to breath better but as I said if the head cant flow enough whats the point? It's much better to size the carb correctly to the motor, just like you jet it.

 

I dont think your going against conventional wisdom your actually a good example of it. Dont think anyone could fault someone for buying 50's at a great deal either. I would and just choke them down until I had a motor that could actually use them properly.

[EricJB]

I'm jumping up to 48 DCOE's right now. With a cannon intake and sortmounts, you have to do a bit of work. Boring the softmounts and putting a small counterbore on the mani as a reference for the die grinder.

 

 

 

And then carving the hell out of the mani with a burr that looks like a pinion gear.

 

 

This is not a street set up. I have run 48 IDA's on a 2.0 VW bug motor on the street, with a .600lift/320 duration cam, it idled at 2200rpm and got 8mpg. It was my DD for about 6 months. Actualy ran pretty good. You could'nt hear the exhaust over the carbs.

[73DATSON]

I LOVE IT!!! My car is not going to be Daily driver just for fun on WKENDS:-)) it runs strong now good power good tuning. I just love the BIGGER STACKS... I do want to put a bigger cam too. I bought a head from A1manchince, port and polish,valve job new lifter springs and a 287cam. But I want a MORE Aggressive cam!! Can anyone tell what a good size?

[73DATSON]

If you decide to part with your 40's shoot me a PM. I might be in the market for some soon

Sure I'll let you know.

[73DATSON]

Bigger bores dont automatically equate into more power. Matter of fact you can loose power by going too big. I would say for a street l20, even worked, that 45's are too big.

 

I'm running a 11:1 comp l28 with a pretty aggressive cam and 40's are more then enough. The flow through the head is the bottle neck not the carb bore. You need to have a stroked motor and highly worked head to flow enough air to require 45+

 

I'm right by the GW, you ever break that dime out?

GOOD TO KNOW I WILL HIT U UP:-)) I used to live on 172st ST. Nicholas

[72240z]

Nice port work I didnt even think there would be that much meat lol. I know my mikuni would never make it.

 

it been pretty laid out as far as the ups and downs of sizing for you to make your own choice. I wouldn't go bigger then 45s if your going to street it, daily or otherwise.

 

I am on the Jersey side but a member of the nyzcc we do fun runs, track days and meets. You should def come out sometime. There was a nice dime at the ctzcc meet in october. A bunch of us nyzcc guys had a mini fun run and went over for it.

[73DATSON]

Nice port work I didnt even think there would be that much meat lol. I know my mikuni would never make it.

 

it been pretty laid out as far as the ups and downs of sizing for you to make your own choice. I wouldn't go bigger then 45s if your going to street it, daily or otherwise.

 

I am on the Jersey side but a member of the nyzcc we do fun runs, track days and meets. You should def come out sometime. There was a nice dime at the ctzcc meet in october. A bunch of us nyzcc guys had a mini fun run and went over for it.

Yes keep me in mine ill show up.. Hey I just bought a ISKY cam 490-290-280:-))) I think I'm hold off the carb for now. And see how it runs with that BIG A.. CaM. I started a new post.

[ggzilla]

45 with the smallest venturis is milder than 40 with largest venturis.

 

It's the venturis that are important.

[72240z]

45 with the smallest venturis is milder than 40 with largest venturis.

 

It's the venturis that are important.

 

Yes that true velocity wise but its not the whole story. The butterfly being larger allows more air at the same throttle which can be a good or bad thing depending on the tune and flow capabilities of the engine. It's one of the many reasons people who run dcoe of just about any configuration deal with bog or dead spot issues somewhere in the range during tuning.

 

Yes keep me in mine ill show up.. Hey I just bought a ISKY cam 490-290-280:-))) I think I'm hold off the carb for now. And see how it runs with that BIG A.. CaM. I started a new post.

 

Sounds awesome.

 

Feel free to drop by http://www.nyzcc.com/ and introduce yourself. You can also drop by the NYZCC facebook page if your on there. Most of us are flat out datsun fans and always love to see whats in our area. Not many 510s....

[ggzilla]

Yes airflow is the thing. The Weber book says start with ventiuri selection and you can get it perfect, but if you have inappropriate venturis then no amount of tuning will get it to work smooth.

[EVILC]

Nice to see another dime in the NYC area. Would love to see it next season.

 

Visit us at NYZCC.COM

 

Any pics?

[73DATSON]

Nice to see another dime in the NYC area. Would love to see it next season.

 

Visit us at NYZCC.COM

I have pics but don't know how to post on the ratsun fourm??

Any pics?

[69srl311]

Quote "I dont think your going against conventional wisdom your actually a good example of it. Dont think anyone could fault someone for buying 50's at a great deal either. I would and just choke them down until I had a motor that could actually use them properly. "

 

I thought the same thing about the removable chokes. They came with 43mm and I purchased a set of 41mm. I didn't notice much difference in the lower rpm range but it definitely hampered the top end. Perhaps it is because of the cam I use. It also has an aluminum flywheel and a 4.88 posi.