I have a '28 roadster with a 283 SBC. I have an issue with my engine eating spark plugs at prolonged idle or slow cruise, as in the plugs are so black they short circuit. I have chased this issue with the idle and slow speed circuit (ICRs) on a Holley 4-barrel forever and finally gave up and installed a Holley Sniper in hope of getting better control of the slow speed mixture. It actually made things worse. I took the car to tuner who could run it on a rolling road. He had a heat camera and could see that at idle some of my header pipes are considerably cooler than others, which correponds with spark plugs photo. His theory is that my camshaft's overlap creates pulses in my intake that blocks some cylinder at low rpms. Also when some cylinders get no air, the fuel injection compensates the overall fuel to get a good average at the lambda sensor in the collectors, which floods the other cylinders. Maybe a single plane intake would help? He has limited V8 tuning experience and mostly with with turbo I4s I'm at my wits end... The intake is a Edelbrock Performer Air Gap. The cam is an Engle EP-22, 0.491"lift, 238°@0,050", 110° lobe separation. Right now a full Holley Sniper system, incl, distributor. Yes, it's not traditional but I have progressed from 4x97s through mechanical- and vacuum Holleys with the same issues. I tried running an RV cam one summer but the car became too boring.
When you say boring, are you talking about acceleration, steady speed, or the gotta sound like a wild thing in the parking lot? That cam is not easy to track down. I did find a 2010 catalog PDF that confirms it, though. 490 lift, 238 duration is a pretty big hyd cam for a small block and yours is the smaller cubic inch version. It will have fairly poor idle operation, and is tuned more for mid to high RPM. Same with that intake. Seems that you have spent a lot of time and money trying to tune for this. You can continue to try to get it to behave better, or swap the cam to a smaller lobe size. This one can be used, but it will require advancing the timing, bringing up the idle RPM, fine tuning the A/F and living with a pretty healthy lope. It will tend to foul plugs. I'd suggest bumping up the initial timing to at least 15 BTDC, probably more. This will require limiting mechanical advance. Idle speed of at least 900 RPM, probably closer to 1100. If this is too much and the RV cam was too little, here are some other suggestions to find that Goldilocks cam for your taste. https://www.jalopyjournal.com/forum/threads/283-chevy-cam-suggestions.1127978/ https://www.jalopyjournal.com/forum/threads/cam-choice-for-this-283.1073043/ https://www.jalopyjournal.com/forum/threads/help-me-pick-a-cam-for-283-cheby.627088/ EDIT: seems you have @Johnny Gee 's attention. He's got a LOT more experience in this than me. Listen to him!
LT1 Aluminum heads (not LT-1) Abt 10.5:1 CR with steel gasket. Timing is run throught the Sniper unit but essentially 25 degrees at idle, 34 at WOT, 44 at cruise.
The front 4 are rich, the rear 4 have 2 rich and 2 lean. Maybe a vacuum leak? Have you checked it with a vacuum gauge?
With the carb: Were the plugs exactly the same? Same rich/lean on the same cylinders? What was it like with the RV cam? Now with the FI: How long is the engine running for for you to have a bad idle? Is it ok from cold? Is it better hot? Are you running in closed loop all the time? Is it learning from cold? Where is your O2 sensor? Where is your temp sensor for the FI and have you confirmed it’s reading correctly?
Vacuum is around 10” and steady at idle. Yes a vacuum leak would cause this, but no leaks from the top side when spraying on it. And
The problem was the same with the carb, but not as different. It ate plugs but the difference was not as appearant so I did not pick up if specific cylinders were dead. I did not have this issue with the RV cam. The Engle cam will rev to the moon and makes the car fun to drive. I can live with the bad low end, but the plug issue makes it unusable. Right now with FI it will start misfiring from shorted plugs within a couple of miles. I have two lambda sensors, one in each collector, one to a gauge and the the other to the ECU. They both read the same, and within usable (programmed) range. The car will make your eyes tear on cold start in the garage. I have the temp sensor for the FI next to the thermostat in the intake and a mechanical gauge from one of the heads. They both read the same. The Sniper won’t go into learn until operating temp.
@tunglegubbin Change Intake , Look into Torker or Team G , Reprogrammed distributor, More timing Needed 20ish or so of initial ,BTDC With about 15 degs of advance. What Plug are you using ? Heat Range ? NGK's Stick or Auto , idle 1,000 -1,2000 rpms If auto 2,500 - 2,800 rpm converter minimal. Witch Sniper ? Also Lap Top tunning Needed . Self Learn Just gets you going & base.
I think the problem with the carb was that you likely had the ****erflies open so far to maintain a steady idle that you were into the transfer slots. I think the problem with the Sniper is that it’s trying to learn when it’s running badly and it just ends up in a cycle of ****ness, you are going to need to set up the mixture yourself and not use the learning cycle. I think some more advance at idle will also help and run it down a bit when it moves away from idle.
Yes with carb ,, Off/p*** the transfer slot more likely, "off Idle Circuit", The cam is big for 283 , its going to want To come alive over 3,500 rpms . Open plane much better choice LT1 heads ? Like 1970 2.02 283 will pull over 6,500 with correct tune parts & gearing , But not going to be like a 327 or 350
With the carb back on...(I doubt you will ever get the FI to play nice with that much duration and LSA) PILE THE TIMING ON !!! Try limiting the total timing to 38-40* Light advance springs so it will get to Total advance pretty quickly. ( IF the starter/battery system is up to it maybe try a locked ...full advance all the time...ignition set-up) With A LOT of advance in it ...the idle will 'sharpen-up'.. (meaning you will need to slow down the curb idle on the carb...getting the carb OUT OF THE TRANSFER SLOTS and back into the idle circuit) Don't even worry with the vacuum advance...cap it off. I would 'guess' idle speed of 1000RPM if you're lucky... Maybe play with some hotter heat range plugs. Hope you have an MSD box (or equivalent) ignition...something with A LOT of spark Good spark plug wires and the best hi octane fuel you can get. The joys of tuning a HOT ROD engine ! 6sally6
If Later Snipper 1 or 2 ,it can support that cam shaft , "Lap Top tunning" required not supported by the handheld. On this Combo , The Handheld will get up & running , IT'S Not "" Totally self learn""....., Only Around 40 % running Quality... Intake is wrong needs Open plenum NOT "dual plane " Carb or Efi . If Op doe's not want to change intake Play with different heat range plugs in Front 4 cylinder Hotter , If auto train Converter Needed !! If Op wants to reinstall the carb Bigger Air Bleeds Needed Or Drill holes in front Throttle blades.. Or adjust rear blades open more. To get Front throttle blades below transfer slots..
Probably too little LSA coupled with small displacement. Need a different cam and/or open loop tuning at idle. The Holley can inhibit going into closed loop at idle, so you might want to see if its entering closed loop or not. Probably wouldn't be as problematic with a larger displacement engine. Many of these aftermarket EFI systems are limited in their ability to work properly if the LSA is too narrow. Might call Holleys tech line and ask their opinion. They also have weekend cl***es in Bowling Green Ky that help people learn how to optimize their systems. Its not every weekend, they have a schedule.
I can't say which is wrong. It just feels to me like the cam and intake don't belong on the same engine! I can't help with EFI either. That stuff has my brain behaving like a bouncer at a lefty bar seeing Nazi regalia walk in: Out you go! But I can see a 283 cammed like that. You'd just need to use it accordingly, live with its constraints, because you're that seriously committed.
On Snipper witch sounds like the typical 600 hp all 4 injector spray fuel Even without opening the back barrels/ ****erflies. even with a Carb if you where to put 8 Egt you will see the imbalance of Afr From Idle to 3/4 way threw Wot, This is why when serious about keeping all the cylinders happy staggered jets & other tricks .
Soooo, I changed the intake to a borrowed Weiand 7546 (X-type) No difference whatsoever. As an example, number 1 cylinder runs at 300F at idle, cylinder 3 runs at 500F. See pic. So, new cam. If my 110 LSA is the thing getting me in trouble. What should I do?
Did you Lap Top TUNE or still using Hand held ? The hand held is not going to get you what engine needs to run correct . I see you took vehicle to a tuner, If tunner can tune a turbo combo Should beable to tune a NA , But there is a diffrents in injector In runner Vs INJECTORS IN TBI & I can not remember stick or automatic? Who set up the IAC , TPS , ****erflies, Fuel ,& Timing as in phased distributor plus Timing features ?
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