Getting the urge to upgrade in size

[Zedyone_kenobi]

I have issues with leaving things alone.  Blame it on a short attention span, or what ever you like, but I have an urge to try some 45 DCOE's on my Datsun Spirit L28 STR engine build.  My 40 DCOE's are doing well, but at times I wonder just how much I am leaving on the table on the top end. I changed out my chokes in my 40's to 32mm and it really woke up the top end.  I have read that driveability suffers from the larger opening on the low end.  My only point of comparison is my Roadster. It is 2 liters with 45 DCOE's on it.  It idles and runs VERY smoothly and revs to the moon.  Granted that is 0.5Liters/ per cylinder.  While my Z is .47 liters/ per cylinder.  I guess that is close enough. Anybody have any experience with this. AS it is a VERY expensive thing to just 'try' for shits and giggles LOL.

[gwri8]

I'm not a carb guy so my opinion may be worthless,  but isn't just owning/rebuilding these cars just for shits and giggles?  

Like any habit , cost is proportional to giggles IMO. 

[madkaw]

Why don't you just try some 34 or 36 chokes first? So you started at 30 chokes? I'd keep bumping up and see if you can maintain drivability that you can live with.
I know webers are easier to get parts for than the Mikunis. I was going to machine out my 32's to 34


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[Mike W]

Zedy,

I was going to make the same suggestion as Madkaw did.

Turns out that after I changed my manifold to the Harada, I tried a set of 34's and no matter what I did with the jetting my engine just didn't like them.  I could never get it to run properly and I had to use such large idle jets that it was always running way too rich.  I went back to 32's and it was very happy again so I am convinced, at least for my setup, that this is the correct configuration for me.

Now you are an l28 and I'm and l26 so you do have more displacement so your experience could be different, although I believe that we are both running mild / stage 2 cams.  If you would like to try my 34's I'd be happy to send them to you for a try.  If you like them you can get a set of your own.  If not just bring them with you when you come to ZCON. 

Let me know.

Mike.

[240260280]

Passini says that for the same choke size, the atomized gas can precipitate more on exit after the venturi in say a 45mm throat than in a 40mm throat. 

I think this would hit you more at the start of the mains coming in when the air flow is lower and the momentum of fuel picked up in the aux venturi is low. At higher rpms it is probably nil.  Be prepared to tune / optimize in the mid range.

Edited April 11, 2017 by 240260280

[moelk]

Zedy, I got 45s on my L28+1 mm.

Im not a carb oracle but here's my set up.

Dont know if my translation is correct but I guess you get it any way ; )

Low speed 55 F8

Main 155

Air 160

Emulsions F16

Acc 45

Choke 36

Iv dynoed the car and everything looked good, it was a bit rich therefor we went with 160 air instead of 155 that I had from the beginning.

I have the harada intake on mine.

 

Edited April 14, 2017 by moelk

[Zedyone_kenobi]

That is so strange. You were lean and went up on your air corrector form 155 to 160. I would have thought that would have made you more lean. Go figure.  

I am juggling a few projects around these days.  I may try the chockes as Mike suggested first.  When you have to buy 6 of something, It always gets expensive  

I have an urge to tinker with the carbs. When I do I usually end up back to nearly where I started.  Car runs great right now. My AFR at 3000 rpm cruise are too rich, but have some room to adjust that with my hypojet. I have not messed with my carbs in years, as the darn thing just scoots like a banshee when I give her the beans.  I have no transition hesitation of any kind, and she pulls to redline.  

 

Maybe I am overthinking this. LOLOL

[moelk]

Sorry, my bad. It was to get it leaner that we went to 160 instead of 155.

I corrected my wrong.

Edited April 14, 2017 by moelk

[Zedyone_kenobi]

Mike, I know you run the hypo jets....Well you use to.  Do you remember which hole you had it on 1,2,3 or 4 with one being the smallest?  

[240260280]

3 hours ago, Zedyone_kenobi said:

My AFR at 3000 rpm cruise are too rich, but have some room to adjust that with my hypojet.

 

 

I had this problem with 25mm fuel level on 40DCOE 151. I could not tune it out. I dropped the fuel level to 29mm and was then able to tune properly.

[Jason240z]

Do it, OER carbs are on offer at the minute.

[Chickenman]

On 4/11/2017 at 0:49 PM, 240260280 said:

Passini says that for the same choke size, the atomized gas can precipitate more on exit after the venturi in say a 45mm throat than in a 40mm throat. 

I think this would hit you more at the start of the mains coming in when the air flow is lower and the momentum of fuel picked up in the aux venturi is low. At higher rpms it is probably nil.  Be prepared to tune / optimize in the mid range.

^ Yep. Totally true. Stronger booster signal overall  on the 45's compared to the 40's with the same Choke size. Passini has very good info and charts.