New plugs, test hit on them, afr gauge read 13.4. Stroked 350 with twin turbos. Timing controlled with 6 btm.
Initial 14, total 35 , all in at 2400.
Pulling 1.5 degrees per 1 lb of boost .

Looks to me like a little tooo much timing. Also looks like 7, 5, 6 & 8 may be a little fat. So I’m thinking take 2 degrees of timing out & dropping some jet in the secondaries.
What do you plug readers think?




#ad
#ad
#ad
#ad
#ad
#ad

 

1. you don't give enough information. How much boost? How long was the load? How many minutes did the engine idle or run on those plugs? did you shut down the engine immediately after the boost run? What is compression ratio?

2. The A/F ratio needs to be more like 12:1 or 11.6:1 or 11.8:1 range. Anything over 12.5:1 is very risky in forced induction at any boost pressure.

3. The plugs need to come out looking all the same. You have some issue with #8 and perhaps another one or two. Its hard to tell but there is some issue which must be dealt with there. Either fuel distribution, spark quality, or something mechanically (leaking intake valve or something) or maybe something with the blow-by (ring related or PCV related perhaps).

4. Seems like when performing a true plug analysis you have to cut the metal part of the plug off.


I've never needed to go that far, you can almost just look down at the porcelain even with the threads in the way using a light. And really thats the part of the plug with the least useful information anyways, IMO simply match in car wideband with Dyno Wideband and then look at the plugs for evenness, no sign of abuse (no crackles, crinkles, cracks, severe discoloration, flakes or fleks of piston or aluminum material, melted or melty looking appearance, yellowing when not using leaded fuel, stuff that just looks wrong is usually obvious) and get high mileage from them. I will like to see 60k to 100k miles from an iridium NGK plug in an efficient engine like the LS or newer. There should also be a nice mostly unbroken black carbon ring around the outside circle diameter in my experience, but you don't hear much talk about that on the internet, its just something I noticed. Usually the only time I Pull a plug is while its on the dyno with a car for the first time just to be sure no sign of abuse on plugs after a nice pass or two. You keep timing pulled back as far as you can, I would max out the timing retard and only add just enough back to get it to the dyno where you find the minimum timing for being 10% to 12% near max torque with a smooth graph set to smoothing = 0
theres more but I dont wana fill the page with stuff unless you ask

 

Fill away my friend, fill away.
So I assume in reality, if the wideband readings are correct. I need to up the jet in primary as well as the secondary. Correct?

 

Its been over a decade since I messed with a carb. From what I remember the front jets are used by themselves until the rears kick in later, either by actuation (manually linkage) or pressure drop (spring/diaphragm). That tells me that your WOT air fuel ratio isn't mostly based on the front jets. You need to keep the fronts around 14.5:1 to 15:1 air fuel ratio for a steady state cruise to keep plugs clean and reduce carbon deposits. Cruising 13.5:1 and richer will gradually foul the plugs. Even 14.0 can eventually foul them. It is essential you manage to control the a/f using wideband to reach the goal of 14.6 to 15.2 ranges while cruising. Somehow.

The rear jets kick in when you start wanting WOT. If the car is for performance only, a manual linkage would seem to be the best since it has no delay. However, in reality and with EFI tuning as a comparison we see that a gradual enrichment is preferable to a sudden one. So manual linkages are probably not the best solution. A diaphragm which is set to provide the correct enrichment rate will offer superior performance. Here is a chart I recently made showing the desired air fuel ranges. Every six months to a year this comes up and I remake the same sort of chart. I probably have five copies of this post written slightly differently, perhaps slightly different a/f ranges as well, over the last ten years or more. Somebody should find them all and put them in one place
https://forum.hptuners.com/showthre...Tune-Criticism&p=678778&viewfull=1#post678778

Here is a guideline based on pressure, For engines using typical (8.5 to 9.9:1) forced induction compression ratios which double as daily drivers in reliability apps
For modern combustion chamber design (Nissan/Toyota after 1991 and in Chevrolet from 2001+)
Also this is for in-car wideband sensors, which tend to read a few points richer than a dynometer wideband. 10.8 In the car can be 11.2 on the dyno wideband.
So err on the side of richer and then confirm on the dyno that the fuel really is there IMO before trying to find tune any fuel out of a setup (not good to strongly rely on in-car wideband for fine tuning).


00 - 19KPA: 13.3 to 13.8:1 *do not run lean a/f ratios here due to tip in concerns and situations which peg these pressure values after high load
20 - 60KPA: 14.9 to 15.8:1 This is general idle/cruise range, run lean to save plugs and reduce carbon
60 - 70KPA: 14.2 to 14.4:1 Gently accelerating up a hill or something
70 - 80KPA: 13.3 to 14.1:1 Starting to demand torque so give it a little fuel for safety and torque
80 - 90KPA: 12.6 to 13.2:1 Pretty much nearly wot so start thinking about wot ratios and full torque adding
90-105KPA: 12.0 to 12.6:1 WOT for NA engine, I like 12.2 to 12.4 , if higher compression or 87 octane maybe 12.0 is warranted
105-150KPA: 11.6 to 12.2:1 Up to 7psi of boost, should not be much richer than 11.8, those factory 2L and 3L JDM Engines run up near 12.5 here at 8.5:1 compresion
155-215KPA: 10.9 to 11.5:1 For stock LS and JDM engines I prefer to see 10.8 to 11.0 at roughly 1 engine power doubling (215KPA) on the in-car wideband using gasoline
215-250KPA: 10.7 to 11.0:1 It is rare to move richer than 10.6:1 for traditional setups as we are discussing on gasoline

These numbers are for engines 3L to 7L with camshafts that will pull good vacuum at idle and using gasoline fuel E10. Alcohol fuels as methanol and ethanol are far superior to gasoline and you may find that mixtures much richer than 12:1 aren't needed as often. We record EGT and dyno output with richer mixtures to compare them as part of dyno-tuning while staying aware of the load the dynometer is placing on the setup and comparing that with how the vehicle is planned to be actually run on the street or track later. If the dyno run is but a small fraction of the abuse that will be placed on a setup then of course you opt for richer a/f and further reduced timing and increased EGT control features while giving up power and wasting energy in the hopes of preserving the engine and making it absolutely rock solid reliable no matter how bad conditions will get. On the other hand if the dyno represents a pretty good comparison to the actual racing event the engine will be used in, like drag racing from 0mph you can dyno from 0mph and sort of see the drag racing power chart the engine can put to the ground. Then your actual racing will resemble the dynometer run and you can more easily fine tune the setup on the dyno because the real racing is similar. Most Dynojet rollers are kind of a like a 3000lbs vehicle being accelerated. Heavy cars get tuned too sharply because its easier to accelerate the dynojet than it is the actual car, so the engine gets over loaded on the street at 4200lbs or whatever and it can blow head gaskets, break pistons and wear out rod bearings over time to be left like that. This is why we keep pulling timing to find the EGT Ramp.

#ad


Timing control represents a transfer function for taking the energy of fuel and putting some fraction of it to the tires. Spark can be used to send more energy into the exhaust and less to the tires if needed to protect the engine or transmission. For example torque management during a shift in my car pulls timing down to -20* btdc causing torque output to drop negative and the engine decelerates. All the while burning the fuel that went in and using almost all of it to heat up the exhaust (and subsequently the turbine, spooling the turbo harder helping to cause a boost spike during a shift). I give these examples so you can see how energy flow of fuel moving towards exhaust can be controlled with timing and how the final timing reflects the extraction fraction from fuel ingested in a paradoxical situation where the more energy we extract, the more efficient the engine becomes, the higher the compression ratio and combustion pressure gets and the closer to rod bearing and piston destruction and catastrophic failure things can get. And the fact that you can get close enough that it will still run while causing long term damage to bearings without the owner realizing it.

Dynotuning progression: You find the EGT ramp and look at the chart, daily drivers stay really close to it. The most reliable engine will be just a couple degrees away from the EGT ramp which provides the lowest combustion pressure in the best possible situation while extracting enough energy from the fuel that it does not excessively raise EGT. You only advance timing a little tiny bit from the EGT ramp after finding and verifying it multiple ways, you can usually feel the power difference that a couple degrees of timing as you come on and off the EGT ramp.
When the actual car is in the field 'working' the conditions will wander. As temperature increases, so does the rapid expansion and combustion of gasoline fuel chemical reactions, making the pressure higher than it was on the dyno. This will shift the EGT ramp away, suddenly you are now much farther from the EGT ramp than you were on the dyno that day. Now the car is 'perfectly tuned' for the super hot situation, the worst possible conditions a daily driver would encounter (sometimes, sitting in traffic in the mid-day sun for hours feels harder than racing around some track) and it will thrive.

 

Running a c&s carb.
Primary jets are 78
Sec jets are 86.
I’ll drop the primary 2 sizes & increase the sec 2 as well & see what happens. Sound about right

 

When you see that you are getting near the ideal a/f ratios I posted, put a set of new copper plugs NGK 7 or 8 heat range and then do what you did before, examine them after using them. If you already have the engine set to idle cruise near 15:1 they won't foul from idling them so you can just idle the engine and drive like normal etc... and check them whenever you feel like because proper tuning = the plug conditions will stay clean and maintained well for many years.

In other words, plug 'reading' is only for when you are tuning the engine. Once the engine is tuned you check your work by installing a new set and then making sure they look fucking great after 10k miles or something.

Usually after about 5k to 10k of them looking perfect I switch to iridium. Never tune on iridium plugs because you just waste the expensive plug. I mean, its fine if you have unlimited funds I guess, theres nothing 'wrong' with it. But the final test is to keep a set of plugs looking amazing basically forever until they disintegrate from age or natural wear and you can't fix or clean plugs that have been through many tuning adjustments already. If the engine was untuned for just a short period the plugs will show that. Its like a history report.

 

You want to keep area jet area equal for distribution reasons. The primary will be the total of the jet, and the pvcr's. Same on the secondary if running a pv. Do yourself a favor, and search the blow thru carb section for accurate info, advise, and what works.

 

I was afraid you wouldn't see this carb thing. Do you actually have to calculate the mass of fuel that power valve enrichment supplies to know how to distribute the rear stuff? Isn't it common to have power valves in the primary only, and if so why don't those carbs need larger jets in the rear to compensate for power valveenrichment of the primary? I have no desire to get back into carbs but I'm curious about the distribution of fuel within an wet flow intake manifold. I know for part throttle and high vacuum situations there is no problem feeding 100% from primarys but I agree that when at wide open throttle it is very difficult to give every cylinder the same amount of fuel when its got so far to go and so many volume to occupy along the way and very little time to vaporize and such a large portion is connected to other cylinders, pulling and shaping the column of air that forms at high velocity/flow rate

 

A very basic rule of thumb is that the stock pvcr's are equal to about 10 jet sizes, so a carb with only a primary pv will have staggered jetting. The stagger obviously gets larger once you add more fuel through the pv.

 

Nice, so it is kinda calculated. It's starting to be familiar. I guess the pv enrich could enrich main jet circuit but it doesn't really matter how the fuel gets in, as long as it gets in. Well this is kinda critical information then. I can see the benefit of having a rear PV because you can gradually enrich and afaik the only way to achieve a reasonable cruise a/f ratio is mostly in the primary main jet size, without getting all fancy with drilling sanding filing epoxy type of mods to the block and carb

so what happens if it takes a 52 primary to get 15.5:1 for 31% throttle, and a 78 secondary to reach 11.8 for 18psi, will it send a fraction of the difference 52/78 = .66667 ratio so up to 33.3344% more fuel can reach the rear cylinders? You would need to make some holes bigger elsewhere besides just the jet? If it came down to it I would try to find a way to better mix the fuel going in, use a extension plate and higher velocity runners, shorter runners, specific manifold surface roughness, find a surface which promotes mixing and distribution of liquid fuel should which can control and evaporate fuel over time with a good distribution. This is the type of questions I Would ask if I ever have to use a wet flow manifold again. How do you make sure the jetted area is 'square' as I think you put it. Does such disparity would seem rare? How many times have you said this answer already online, thanks

 

Many times cruise rpm is a mix of the transfer, and main metering circuits so there's plenty to tune with. There's also high, and low speed air bleeds, and emulsion circuits that can be tuned to tailor the afr's. Certain engines, and manifolds are know for distribution issues, but it's a good place to be on any setup, especially forced inducted. I'm definitely no expert on the subject.

 

1 and 6 are on the edge of timing being a bit high for me. Specially for the heat range plug you are running.
I would pull a couple deg. until you know your fueling is good.
What is your jetting now?

 

Plugs were nkg ur5, so I guess I could put some nkg ur6 plugs in.
Primary 74,
Secondary 87.
Pulled couple degrees, but wideband read 13.6 & only dropped to 13.5 so I got out of it.
Pulled the wideband sensor & tested it, it's garbage. New sensor in tomorrow. Hopefully this help with tuning

 

I use these AEM widebands alot
https://www.ebay.com/itm/303081183840?epid=23050788516&hash=item46910bda60:g:MJsAAOSwRZZgnEg5

It is superior to anything else in that price range.
If using normal gasoline/alcohol and installed correctly they will last 5 to 10 years, 50k to 100k miles perhaps more.
I am surprised you had a WB failure and would suggest you try one of these type of widebands which I know will last so many years.
The response is also superior to anything < $500

 

I've

The one I have is the aem 30-0300 wideband, had it for 10+ yrs