Technical What do you guys think of this plug?

I'm still working on trying to tune my new setup...GM 350/357 crate engine with a 2G 3x2 setup on it. The truck starts right up and idles pretty good. It runs ok but doesn't feel even close to the 357hp 407ft/lbs of torque when I get in it.

Center carb is the only one with an idle circuit and the linkage is progressive. All 3 carbs currently have 62 jets in them. These plugs have about 50 miles of local and highway mixed driving on them. Do they appear lean? After a 20 mile drive home today the engine ran on for a few seconds after I shut it down.
These pics are all the #1 plug but the rest look similar. On regular high test pump gas.

 

plugs don't color near as much as they used to in the old leaded gas days...so I would think it's either right, or lean. But not excessively rich.

 

I'm wondering if they're lean and causing an exhaust backfire I've been chasing on one side.
Weird part is I'm getting terrible mileage.....about 10mpg just cruising around with no WOT runs

 

Some guys add an AFR gauge so they can know for sure what's going on with fuel mixture...

Running on is usually related to high idle speed, but there are other things that can contribute to it.

 

Have to "curve" the fuel supply too, when tuning, it's possible to be excessively rich at idle yet lean upon acceleration, or too fat at cruise conditions, etc. In fact that's probably the norm versus the exception. There are several carburetor circuits, each one is tuned different, but they affect how the other circuits respond.

If highway economy or fuel consumption is way off the beam and the engine is otherwise in good shape tuning wise, then you probably need to look closer at jetting. Sounds like something else is going on maybe. Ignition timing will interfere with highway economy, without the vacuum advance, that alone will cause maybe a 15% hit.

 

Yeah GM states not to run vac advance on this engine so I haven't hooked it up. Probably them erring on the side of caution but I'd rather not find out the hard way.

 

What kind of advance are you running?

 

Mechanical....Pertronix distributor with their copper/silver spring curve and limited to 20 degrees....plus the initial 12 base

 

I actually found some 65 jets at the local PepBoys today that I'm going to try tomorrow in the center carb. I bumped my timing curve up about a week ago because the original only brought in 3* at 1500....this new one adds 10 at that speed and that's where most of my highway cruising has been. I would assume that's going to want a little more fuel now to keep it happy. I currently have 62s in it and had 63s on hand but didn't think 1 size would make enough of a difference.

 

Can you show the documentation, where GM says not to run vacuum advance?

Seems hard to understand this on a street engine, where you are not happy with fuel economy.

 

I think those plugs are too hot, as in heat range.

 

32 degrees total is NOT enough ignition timing!
Try 36* and bring it in "soon". ..like ALL in by 2000-2500RPM.
What type of heads are on that crate-engine?
If nothing special...AFR/Brodix etc. give it more timing. 38-42*.
With lotsa timing in early.......THEN start bumping up the jets.

Oh.....this ain't the 'good-old-days' where reading the plugs told the story.
This mumbo-jumbo crap added fuel just doesn't "read" like the old stuff +
It's new plugs.......no long idle time.......wide open throttle run.....cut ignition....
THEN read the plugs! That's how ya do it (or DID it!)
If you putted around town on the way to make a full bore run....then putted back home after the full bore run
to look at the plugs..........welp...that really don't tell ya nuth'in.
+ Figure in winter blend...summer blend...west coast blend....Naaaa them days are over.
6sally6

 

Not sure if it's too small or not but see #4 in the attached pic. Also after going back and reading the GM instructions again they actually state that the 4bbl they used to rate the HP had 65 primary jets so maybe I am in fact too lean. Still doesn't explain the terrible mileage right?

 

jet size for a 4bbl doesn't correlate to jet size for a 2GC on a 3x2 intake.

 

Agree with above post, , 4 barrel jet sizing and 2 barrel jet sizing will not be transferable.

You can't even transfer jet sizing across 4 barrel brands even, ...Holley jetting is not even close to the same a Rochester 4 barrel or Carter/Edelbrock 4 barrel jet sizing.

And the "no vacuum advance" directive from GM is strictly them covering their ass on warrantee claims.....by keeping it underperforming they will have fewer failures. They are idiot proofing it against morons overtiming it and blowing it up with too much or too early vacuum advance timing.
Setting up the vacuum advance limits and adjusting the diaphragm almost seems like voodoo to many people, so the company fix was to disconnect it.
Plus a good portion of purchasers of this package are going to be racing it, mostly circle track. They don't want it overtimed there.

I've seen vacuum advance give as much as 6 mpg, especially on hot street motors.

You want mileage, your Full-on ignition advance at cruise driving conditions needs to be in the 46-52° range for Initial + Mechanical added + Vacuum added = 46 to 52 degrees.

 

I was able to read #4 a couple times. I think they want vacuum advance disconnected during initial startup and 500 mile break-in period.
By then the owner should have the initial and mechanical advance setup per their specification. I'd think for longer term highway cruising you'd want to add vacuum advance.

@Ericnova72 above has many good points.

 

Your fuel mileage is directly related to you not having a vacuum advance. You will be amazed at the difference. That's really what vacuum advance if for; part throttle economy.

 

I will certainly try hooking it up to see how much of a difference it makes in mileage. Will that effect my jetting requirements at all? I know vac advance is generally only at part throttle so I'd assume not drastically.

 

You mis read #4, it just says to set timing all in at 32 (I think is low) at 4000 RPMs ( I think should be sooner) with the vacuum advance disconnected. Disconnecting and then plugging the line is standard thing to do. Even when setting base timing. Then when done, reconnect the vacuum line to the canister.

 

There is a lot of debate online about these instructions. They say the engine is designed for only mechanical advance and to leave it disconnected. Many people have posted that they run the vac advance as well and haven't had issues. I agree with some of the above posts that it's probably just CYA techniques for the warranty department.

 

Crate engine supposed to have 4v carb? What cfm?

 

Is this the motor?
https://www.karlkustoms.com/product...evy Small-Block V-8 Displacement (cu in): 350

I assume the plugs are AC. They don't read very easy. They always look white unless there is something really wrong. My experience with SBC's, is they like Autolite and they're easy to read, even with this so-called bad gas. The insulator will come out tan to chocolate color when it's jetted right.

My first opinion on reading those plugs from a distance is it might be a little lean, it has a few degrees too much timing and it might be one heat range too hot to read. I can't see the fuel ring down in the core from those pictures, so I can't tell if it's too lean or not.

That motor doesn't come with a distributor, so you have to start from the ground up with a timing curve. I like Pertronix II or III, they're easy to tune and perform well with practically NO maintenance and they live long. That motor would probably like about 12-15* initial, 12-15* mechanical and about 8-12* vacuum advance (manifold vacuum). Vacuum advance will make gas mileage at part throttle.

That motor has mild 9:1 CR, 64cc iron heads with 1.94 intake valves and 1.5 exhaust valves and there is nothing exotic in this recipe. It only makes 357 hp and 407 tq. with their recommended carb and intake. I know they look good, but I don't think 3 deuces will do any better than that.

Chevrolet Performance hydraulic roller camshafts have a certain lobe pattern for balanced intake and exhaust flow, which isn't ideal for power. The camshaft is mild at 215* in. / 223* ex. and only .473 lift with 1.5 rockers, and has a 108* LSA.

I would recommend an aftermarket roller cam with 218* in. / 224* ex. and .510" lift or so, with 110* LSA and 1.6 rockers. That will give better torque and mileage and have a nice hot rod sound. You would have to check for coil bind, valve retainer to guide clearance and valve to piston clearance to make sure they don't hit. Make it fit and it will serve you well.

Over all, that recipe would give you about 375 hp / 425 tq. and 18-20 mpg, depending on gear ratio and tire diameter. Send me a PM if you like. I'm always up to talking about this stuff...

 

Montana1 thanks for the reply. That is the engine I'm running. After further research I almost wish I'd gone with the next step up....I believe it's the Fastburn 385 but it was substantially more for just 30hp. However it seems the 385 may be a more streetable combo from what I've now read.

As for swapping cams I'm not sure I want to get that involved yet on this....I know the Vortec heads may require additional work with more lift amongst other things. The NV3500 trans is also a limiting factor with adding more power...I'm already beyond its rated limits but don't plan to beat on this combo.

I'm currently at the 12* initial that GM specs and I'm adding another 20* mechanical in by 2500. I have to look but I believe I have straps to limit total mechanical to 16 if I am in fact using too much. I'll be honest I'm way better at making things look great than tuning a carb so I'd have to look up the process of adjusting the total vac advance....though I'm sure I could do it.
I'm going to swap the 65 jets in today to see what the seat of the pants difference may be whether it's an improvement or feels more sluggish. I know when I had 58s in it the engine wasn't happy and going back to 62s made it a little happier.

 

Put the 65s in it this morning and went for a ride. Seemed to pull slightly better at part throttle but plugs look like I'm too rich now I believe.....see attached of the 1 and 5 plugs. I have 63s that may be a good happy medium. However I still don't get any real kick in the seat of the pants when I floor it. Both end carbs are currently set up with 62s as well. I always heard tuning tri power setups could be frustrating....seems to be true. Truck idles well though and has good response....just doesn't feel like all the power is there. In a truck that weighs as much as a go cart I'd expect WOT even with 350hp to be hairy.
I don't have an advance style timing light to get an actual measurement but the mechanical advance is working....I can see my timing mark move as I rev it up.

 

I installed one of these, so I could see total advance (initial plus mechanical):
https://www.summitracing.com/search/part-type/harmonic-balancer-covers

Along with a pointer:
https://www.summitracing.com/search...ding&keyword=Timing pointer&kr=Timing pointer

Works fine with old fashioned timing light.

 

I'm enjoying the discussions regarding timing and fuel jetting but was talking with a young bloke who's just finished his mechanics apprenticeship. He was looking at the triple SU carbs on my HA/GR and didn't know what they were or how they worked. Apparently they don't teach carburettors or distributors at trade school anymore. So sad.
On a bright note, he was keen to learn about them.

 

Yeah, make sure you're running the stock heat range plugs before trying to look at jetting. Don't ask me what "stock" heat range is on a performance engine.

Reading the sheet does sort of sound like that it is a performance only engine, there is no need for vacuum advance whatsoever in a drag racing engine.

Vacuum advance helps keep engine temperatures down quite a bit at idle, as well as at cruise. Most any OHV engine since the 1950s is tuned from the factory to run 50+ degrees of ignition advance when running on flat ground. Retarded ignition timing will tend to run hot and kill fuel economy. Usually you're going to see a scenario where jetting down is necessary to the right cruise AFR, and then go back in maybe and fatten up the accelerator circuit or power circuit if required.

This way the engine AFR is richened up where it needs it, and leaned out where it can be. Out of the box everything will be buggered up, as mentioned they don't want any warranty returns.

 

Is your back fire occurring when you let off of the throttle? If so, is usually caused by combo of unburned fuel and air leaking into the exhaust system usually a leaking exhaust flange.

 

... shameless...

 

Yes only when I let off. I had a flange leak but its since been fixed and still backfires