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Zedyone_kenobi

Getting the urge to upgrade in size

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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.

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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. ;)

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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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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.

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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 by 240260280
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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 by moelk

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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 LOL 

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

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

I corrected my wrong.

Edited by moelk

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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.

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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. 

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Weber tuning update. 

 

I have not ordered DCOE 45's, but I would love to try.

However I have decided to get my setup even more dialed in. Again, I have run the same setup untouched for 4 years now.  Car starts and drives beautifully. I decided to keep my LM1 wideband out visible while driving lately and found out how incredibly pig rich I was at 3000 rpm 4th gear steady state cruising. I decided that this was a main jet issue not an idle jet issue (due to the rpm) and checked my settings.  My air corrector was a 170 and my main jet was a 130. This combo gave me a 11:1 AFR at 3000 rpm. Far too rich for normal cruising.  This was with whatever Etube that came with my 151 DCOE 40's. I forget, F9 I think.  

 

Anyway, I decided to go down to a 125 main jet and leave the air corrector alone.  Car feels fine, if not a bit more crisp.   At 3000 rpm in 4th gear I am getting 12.3-12.5 AFR. now.  I have a set of 120's I will try this week.  If I can get around 13:1 I will declare victory and call it done. I have a beautiful idle at 850-900 rpm at 13.4:1 AFR. 

 

The webers prove to be so tunable yet again.  If I get these dead set and running perfectly I will have no other choice but to order 45's and start from scratch again.

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You should be able to run stoich or even 15 to 1 at 3,000 rpm cruise with those carbs and proper tuning.  Literally, a well tuned set of Webers can almost equal fuel injection curves. Keep tuning. Maybe invest in a AFR gauge to mount permanently in car.  Gotta get the emulsion tubes bang on though...

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This is the setup I used to run to achieve 420 hp on a daily driven 1986 Camaro. Could pull 25 mpg on Highway and set record times at Hillclimb. Aircare ( emissions testing ) came out as clean as specs for an FI engine.  Fairly mild cam, good HP figures and broad Torque band. Engine went to 7,200 at Hillclimbs.

https://www.facebook.com/TMPCarbs/

https://www.youtube.com/watch?v=5tKBwAruqXU

 

Edited by Chickenman
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Zedy - Dave Rebello is finishing up dyno'n my engine this week that he built for me (hopefully it will ship the end of next week after the dyno).  I did step up to Mikuni 44's (Custom ported 38's venturi's from Dave) with a bigger header primary,  and moving to a larger exhaust as well.  Really excited wiht the complete increase airflow and horsepower.  Come on now........you know you want to do it!

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You get out of my head you evil man!

 

LOL

 

On a really cool note. I took the time to mess with my air correctors this weekend.  I swapped out my thermostat and while the engine was warm I had a chance to try out my sync tool.   All of them were close to flowing the same volume of air.  However cylinders number 2 and number 6 were flowing a tad bit less air.  Having never touched my air correctors since the 40's were new, I gave it a shot to see what I could do.  I lightly backed off the jam nut and opened up the screw. The air flow quickly came up to match cylinders 1 and 5 and now all 6 cylinders are dead nuts even at idle.  And speaking of idle, the engine smoothed out even more than it was and it seems to be snappier off idle now.  I guess I am a believer in the air corrector adjustment.

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