midias

I was thinking about buying this and installing over the winter to tune the carb in the spring.

https://www.amazon.com/dp/B00N3VGPYS/

Anyone see any reason why I should not?

Orr89RocZ

iTrader: (20)

They work good. Every performance motor should have a wideband

midias

It has been on the list for a while I just wanted to make sure I was not missing anything when I picked one out. I will install it this winter and finally tune my carb right

skinny z

Couldn't agree more.
Add to that a vacuum gauge as well.
I've had the AEM gauge installed for years now. Works very well. Keep in mind that the sensors don't last forever.

midias

Any suggestions for A/F ratio at Idle, cruise, part throttle and WOT?

350 +30 9.9:1 185CC vortec heads 2.02 1.6, XE274 Cam 1.5 Rockers, RPM performer manifold. 1_5/8 headers with 2.5 - 3" Y pipe and 3" exhaust.

I was thinking slightly rich maybe around 13.5 to start?

skinny z

WOT is about 13:1. That will be a combination of the secondaries and the power valve channel restriction.
Cruise is something I always target to be as lean as possible. Cruise is also relative. In my case, 75 MPH = 2600 RPM and about 13-14" of vacuum. I like to see 15:1 + under these conditions.
By part throttle, do you mean part throttle acceleration? What you get here is dependent on how much part throttle you apply. The mixture should go very rich once you've engaged the power valve. At vacuum levels above the PV setting, anything in and around stoichiometric (14.7) will get the job done. With the PV as part of the circuit, provided you haven't gotten into the secondaries, you should be approaching 13:1.
As for idle AFRs, the wide band gauge isn't used for that. Idle tuning is done with a vacuum gauge and you're looking for the highest vacuum possible with the minimum idle speed acceptable. You'll end up somewhere in the 13-14.5:1 range depending on your setup and the weather of the day.

A few things that I consider when I'm tuning:
I know what's in the carb. Power valve set point, power valve channel restriction (PVCR), idle feed restrictor and to a lesser degree, the high speed air bleeds (HSAB) and the low speed air bleeds (LSAB). Of course the primary and secondary jet sizes should also be known.
Be sure the transfer slots in the carb are properly set. As should be the accelerator pump.
Timing is very important. Be sure you've got what the engine needs.

You'll find that your idle settings will affect your cruise AFRs so there's a little back and forth.
General accepted procedure is after the idle is sorted out, tune the WOT.
The PVCR has the greatest impact here. It has to pass enough fuel as well as come on at the right time. Of course it will be open at WOT . That's why the PVCR should be known and modified if needed. Secondary jetting will come after. As will the vacuum secondary adjustment if you have a VS carb.
Cruise is the last thing to work on. In a simple case, a tweak to the primary jetting will bring things in line. If cruise AFRs are different at one end of the cruise range than the other, the work with the HSABs is in order. Seeing as a lot of carbs don't have adjustable air bleeds, that part of the tune gets overlooked.

FWIW: My latest go round at tuning with my new top end package has been both fortunate and excellent. My carb was setup with my previous build and admittedly I never worked it as I was disappointed with the engine package. The new heads and cam have played right into the existing carb spec. Result is WOT of about 12.5:1 (a little rich and adjusted by pulling some secondary jet. The PVCR is a large as it can be in this carb.), cruise AFRs are at the top end of 15:1, with 16:1 values appearing now and again. That nets almost 21 U.S. MPG in a 288 cammed 355. Lots of ignition advance here too. Probably in excess of 40 degrees at 2600 RPM.

Yours is an excellent engine/driveline combination. The Vortec and the 274 should give great idle vacuum, produce a strong booster signal and gives excellent highway mileage. The overdrive and 3.42 rear gear will keep the cruise RPMs down. If you're not at 23-24 MPG on the highway by the time you're done, then somethings not quite right.

Be sure to get a vacuum gauge and leave it hooked up next to your wideband gauge. The two go hand in hand.

midias

Thanks for the info, I already use a vacuum gauge to tune and it is how I set my idle and chose my step up springs. I am getting about 13-14" at idle. I have never tried a wide band for a carb but I am sick of reading plugs on hot motors and some of the guess work so I am going to learn it. Again thanks for the info, it at least gives me some numbers to try out.

Total timing seems to be spot on with my current mixture although I am going to try some lighter springs to see how the motor likes getting to max advance faster.

skinny z

Don't neglect your vacuum advance. It's massively important to your cruise economy as well as general driveability. Properly set, it'll help your idle vacuum as too. I'm in the process of changing this engine to full manifold vacuum from ported. It's difficult with a larger cam. The 274 will respond very well to full vacuum if you are on ported vacuum now. It may require some tuning though.
I've spent hours on the highway, checking out the gauge and learning what effects a change in the AFRs. That's why the vacuum gauge is so important.
Good luck and be sure to post your experiences and results.

midias

Thanks I am using full time vacuum for the advance and have tuned my idle with it active. I found it runs much better than ported. I have also tried a few different advance canisters although it currently escapes me what one I am using. I know I went a bit to aggressive and has some idle and cruising issues so I backed off one step. I am running the MSD 8360.

I used this as a reference

http://www.crankshaftcoalition.com/w...ance_Specs.pdf

skinny z

Excellent technical paper. I've read it more that once.
My past tuning experiences have supported what it has to say. Full vacuum advance all in about 2" below idle vacuum. Idle vacuum goes up, idle temps go down, driveability is enhanced.
Presently I'm running 16 degrees of initial timing and have 16 degrees of vacuum advance. The problem is in my case, I can't get the full vacuum deployed at idle as my idle vacuum is too low. With the help of that paper and several other internet postings, I've narrowed it down to only one vacuum advance canister that will do the job. And it's availability is slowly disappearing it would seem. Advance starts at 3-5" and the 16 degrees is all in by 7". Not even my adjustable vacuum cans can do that.