Wide vs Narrow Band

[architect]

All,

I'm looking to tune my 32/36 DFEV carburetor (78 Fiat 1800 CC) with the handful of mods. I'm assuming my car is running lean.. and would like to get a metric for comparison.

Would a wide band be overkill compared to a narrow band? I'm not looking to get a decimal point reading, just a tune that's more accurate than.. guessing. The price point is pretty significant.. At the moment, I'm leaning towards wide.

Also, I read a few post about using the bung on Vick Auto header as a sensor spot. Any thoughts? or should I weld a bung after the collector (no cat on my setup).

[grrrdot]

A narrow band can get you in the ballpark of stoic but its still just guessing.

An engine can run fine over a large range of A/F ratio. I've read 12:1 - 14:1 for max power and 15:1 - 17:1 for maximum fuel economy.
Also the engines AF ratio is going to change with the load / rpm / temp / elevation etc etc. So an engine will rarely burn stoic for any period of time.
With a narrow band you are left guessing e.g. it shows lean in the transition but is it too lean? When I'm at WOT it shows rich but is that too rich?
With a wideband you see the current AF ratio and can dial in each jet. I landed my IDFs at a nice lean-ish cruise (~15:1) and rich WOT (~12.5:1).

I welded a new bung into the final collector on my Vicks header. I read on the internet that wideband sensors burn up when too close to the exhaust values, dunno if its true or not. I'm also running IDFs and I wanted to see across all the cylinders.

-G

[SteinOnkel]

Wideband. A narrowband is completely useless for tuning.

I would still strongly discourage from this approach. You will see just how crappy carburetors are at regulating fuel and if you're a perfectionist like me, it will drive you insane. *

What AFR your engine wants to be at depends heavily on a variety of factors. For a 40+ year old design I would suggest the following guidelines:

Do you want to not risk knock? Run it at 13:1 or richer @ WOT. Who cares if you're leaving a bit of torque and horsepower on the table, at least you won't grenade your engine. Stay away from anything over 14.7:1. Yes, modern engines can run at 17:1 at light cruising speeds, but this is with modern electronics that will enrichen just enough in a split second when you touch the throttle to overtake a semi. Your carburetor cannot do this and will lean out even more. Even my other project car (2001 engine, with modern open source fuel injection) does not like anything over 15.5:1. Shoot for 14:1 at idle, light load and 13:1 when you put the hammer down. This will be hard enough to achieve with a carburetor, in most cases it will be impossible. Which is why we have fuel injection in the first place.

*Try a Gunsen color tune glass spark plug first. This is what I use to setup my carburetors. You tune your idle circuit (which is the only thing you can tune, anyway) and leave the rest as is.

[architect]

Wow! Great feedback!!! Thanks for the education.. This is my first carburetor.. so I'm a bit of a novice.

I had the same fear as mentioned above.. being a perfectionist. (I'm an architect by trade.. so its in my blood). In the past I used wideband for data logging and turbo / FI applications... But honestly pan to never go WOT on this build. My restoration was intended to enjoy the slow neighborhood roads and I really don't plan cruising faster then 50mph around the lake.

I installed a new 32/36 DFEV from Redline, and haven't adjusted the tuning screws just yet. And like mentioned above.. I'm really only messing with the primary / secondary idle. Its my assumption Redline jetted it correctly based on the description of the application.

If I don't want to / or need to adjust the jets... its sounds like the glass viewer might be a good solution.. I have read reviews about it and it sounds promising.

[SteinOnkel]

"I had the same fear as mentioned above.. being a perfectionist. (I'm an architect by trade.. so its in my blood)."

Sounds like we've got more in common than just Fiats Landscape Architect here.

If this is an application specific aftermarket carburetor, I would bolt it up, set the mixture screws to 1.5 turns out and expect it to run almost perfectly. Perhaps a bit of tweaking with the lean best idle method (see also: http://www.redlineweber.com/html/Tech/c ... _best_.htm)

And that should be it. I would suspect that a wideband is overkill for this, but then again, we've had some really negative surprises with Redline. We avoid them now.

"But honestly pan to never go WOT on this build."

What kind of a build is that Seriously though, it needs to also work at this load range. You might not be driving the car, it could be an emergency situation etc.

Cheers
Steiny

[architect]

Ha! Fellow architect, nice’

Well these bumpers are good for about 5mph.. so I’ll be keeping it easy!



Would you mind sharing a few of your Redline surprises? I actually reached out to the seller for the sizes.. he declined to mention it, claiming it’s a trade secret (huh!!) and Redlines hotline email just get rejected when sending a message. Hmm!!? Guess if I have further problems, I’ll start pulling them out to see the sizes.

I’m assuming the jets work with my setup, however my car is far from stock (no emissions, Vick exhaust, Allison ignitionless, etc).

About to order the glass viewer...14mm. Wish you could keep them in permanently, they look kinda cool!

[SteinOnkel]

I think the glass viewers can't handle the added pressure and heat of anything above a few thousand rpm.

This was on a different car, but basically bought a set of brand new Weber 44 IDFs. They came assembled wrong (I kid thee not, venturis were upside down!), spraying fuel out of the engine. Then we opened them up to discover they were full of crusted old fuel remains. Nice. Had to basically rebuild them right out of the box. Redline told us "oh that's from testing". I don't care if it's from the assembly line worker in Spain spilling his Sangria over it - clean that out before you send it to the customer

This was about two years ago. The carbs/manifold etc cost in excess of $1400 and that's the junk you get. From the rest of your post it seems like they haven't gotten any better. Personally I just throw a rack of motorcycle carbs on the cars now. Knock together a quick and dirty manifold real quick, slap it all together, done. Same power gains, none of the hassle. But I digress.

[architect]

Long story short, turns out my jetting was wrong.

It could be from such along list of mods.. but for those who are interested, please find my thread here. The digital AF gauge is awesome and provides a little peace of mind.

http://www.fiatspider.com/f15/viewtopic ... 5&start=15


- Installed AEM wideband with clamp on 02 sensor. Pretty straight forward.. used a 2 1/2" clamp from Shiftglow (Amazon), drilled a hole right after the Vick Auto header (2" downstream from collector). and plumbed up thru the firewall.
- Swapped a few series of jets. 55/45 seems to be the sweet spot. NO MORE WHITE SMOKE! And the car smells more normal (even without a Cat Convertor).
- Mix screw is 1 3/4 turn out
- Idle sounds very cool!
- Let the car run for about 30 mins, temp stayed around 180 on the dot. Not sure if my thermostat opened up.. I will need to burp the system next time (Allison alum radiator and all cooling replaced)
- Cranked the car several times through-out the day, no hesitation at all.

[joelittel]

I’ve been using bosche wide band sensors with mine and every 12 months or so the sensor fails.

I’ve used the bung location that came with the headers and a second location I put further down the line... both failed over time.

What sensor are you guys using?

[SteinOnkel]

Bosch LSU 4.9

Had it for...oh...6 years now. Been running on single carbs, dual, bike carbs and for 2.5 years now efi. They usually go for 100k+ miles.

[joelittel]

Huh... time to figure out what I’m doing incorrectly then.

I had been messing with my tune for quite some time. I wonder if I’d get more out of the sensor now that I’m not bouncing between lean and rich every other weekend...

[SteinOnkel]

I highly doubt that is the case. For years my sensor saw anywhere from 10-19:1. That doesn't hurt them much.

You didn't try to clean it with brake cleaner or the like? That kills them almost immediately. What controller are you running? Maybe the heater is never on/always on.

[joelittel]

At the moment I cannot recall what controller I have, but I remember it being a very common brand that used to get mentioned from time to time on this site.
Innovate or something like that I believe.

I never tried cleaning the sensor, but I did buy the heat sink adapter thinking it would help. Which it did, for a bit...

I’ve used this sensor and controller on two different headers and had the same issue. Heat may very well be my problem but I cannot find a solution that lasts.

[joelittel]

According to my controller the heater is only on for a short period right after I turn the ignition on.

Maybe I’ll try another controller altogether...

[SteinOnkel]

Innovate Widebands are not know for being particularly good.