So, a few weeks ago I bought an HEI dizzy to drop in my 302 to replace the old points one. I got it all hooked up, dialed in the timing and went about my business, I loved how much it improved startup and there seemed to be a little better performance but the more I drove the car the more I realized that there just wasn't the kick in the pants I was expecting. So i get home today for my lunch break and I go and fire it up like I do most days to keep things in good order so its fresh to go out on the weekends. I'm listening to the engine purr as im doing a few things in the garage and I decide to google "tuning hei distributor" to see what comes up... I read all of the goodies about the lighter and the heavier springs that I was already planning on putting in soon and how to properly set the timing, etc etc. Then the part about spark plug gapping comes up. hmmmmmmm, why didn't I think of that? I go from a stock points rig to 50K volt hei dizzy, and I forgot to open up the plug gap. I'm guessing thats where my "Lost power" was hiding. So, in a fury of excitement for my newfound fix for lagging dizzy syndrome I shut 'er down and start yanking plugs out.. hmm... I don't think an .030 plug gap was doing much favor for my ignition system, i crack em up to .050 to get that spark hot and get em all back in and whammo, she purrs even more than before, lightning fast startup, and unreal throttle response even just sitting in the garage revving 'er up. So, the moral of my story is... even if you are a card carrying ASE Certified (former) Mechanic, and you think you know all of the tricks, you may just very well be forgetting some of the basics while you are chasing those "gremlins"
Your absolutely right. As the old saying goes ,sometimes you cant see the forest through the trees.We probably all could tell stories about being burned by not checking the basics. Thanks for the reminder.
wow, I have abour 2500 miles on my motor with a HEI dist and I know that I forgot to open the sparkplug gap..... thanks for the reminder... bet it makes a difference.
You know what - I put an HEI in my 283 back in March, and I just realized NOW that I never did re-gap the plugs!!!!
yea, it made quite a difference, I haven't had the chance to test drive it yet, but the biggest improvment was the throttle response, just revving it in the garage I could tell a HUGE improvement. I'll probably have to go back through and set my timing and whatnot all over again now that its right, but golly. That extra .020 gap give that spark alot more power
I'll also add that I'm glad to know that I'm in good company, I hesitated on posting this because I felt like it was such a rookie mistake, but I'm glad to know that there others who also willfully admit their mistakes
Also ... you need to make sure the hot feed wire to the HEI is 12 volts ... not the old original wire. It had a voltage drop built it. Mine was about 8 volts ( via the meter ). Much improved when I replaced the entire wire ... and started getting the full 12 volts at the HEI . EDIT ... this is for GM vehicles originally equipped with a points type distributor. I have no knowledge of other makes and models.
hmmmm, i'll have to check that, i just replaced it yesterday from the firewall forward, never thought to check the voltage. Its in a '62 Fairlane, would it have still been 8v? Good call.
I learned the value of plug gaps when I bought my MSD 7AL-2 in the early nineties. It's amazing what .020" makes
Thx for the tip on the 12v wire and gaps. About to install an HEI this weekend on my 351W. Goodbye Duraspark II!
another tip that i've been told is to replace your plugs with platinum plugs, an HEI with a hot coil will start to burn up cheapos in a few months. thats my next step after making sure im getting 12v to the coil
I'm glad to see this as a topic, I have an MSD HEI distributor in my 351, and a 6AL2 I was told not to open the gap, to run the same gap as the block requires. I did a bit of research into this and that's the advice I was given, I never opened the gap so I am running a stock 351 W gap, I too seem to have a power lag that I cannot tune out, I assumed it was from not being able to get the jet kit for my Edelbrock AVS 800 carb. So you had no troubles with this? What plugs are you running? I also have a situation where I cannot hook up my PCV to the front of the carb and my valve covers, the engine starts howling, scares me so I disconnect it, has a big cam. The thing runs better and makes the same vacuum numbers with the PCV port disconnected from the front of the carb. I have to try this regap, maybe it will solve my troubles. Is 50 ideal?
a stock hei has a 35k volt coil, the reccommend gap is .040, the msd coil is 42k and it was reccommend to gap at .045. mine is a 50k coil so i went to .050 on reccommendation to go larger for the higher voltage coil. I would go by the voltage on your coil, given that you are running the MSD box, id go for .050. or maybe even a little more, but i'd start at .050 and see how it goes. on my 302, my PCV is hooked into a vaccuum port on the back of my intake behind the carb, there is some sort of adapter screwed into the manifold to allow for this, along with the trans modulator.
On the Edelbrock they are calling the one on the back for use with power brakes, the front one for pcv and a small port on the driver side for the trans vac. She runs like a raped ape if I uncap the pcv port and let her pull air. I'm afraid I may have too large of a carb on her, she is stroked out to 408 and has a set of Dart heads on her with a .540 .550 cam at 9.5-1. The AVS is a 800 cfm. They have the jet kit for this thing backordered for about a year. I sure would want to play with the jet springs before I come to the conclusion that the carb is too large. She was dyno'd with a Holley 750, It was not mine, I really should have gone that route. What kind of platinums are you gonna run? You must have a stock intake, I remember a little multi port vacuum fitting, I have a tapped fitting on the runner of my intake, not too sure what to do with that. No ports on the intake floor or out back of it.
my intake is an edelbrock performer 289, i have an edelbrock 600cfm carb, sounds like your motor is pretty well built. the only vaccuum line im using on the carb is the front drivers side, it goes to my vaccuum advance. I'll have to hook up my vaccuum gauge and see what kind of readings i get on all of the ports, even just out of curiosity. this is the way it was all hooked up when i got it, so no telling if its right or wrong, fords are all new to me. hope the plug gap trick helps for ya.
I Bought an engine that was barely running like that, for cheap. Guy just said get it out of his way, he had a Jasper engine coming Thought, no biggy i need to rebuild it, it sounded tired. cool. First thing i did once i got it home was pull all the plugs out..more than half of them were around .018!...some of them were almost closed? wtf? I put a set of new plugs in it , stuck it in my daily detroit hooptie and ran it for over 2 more years , sold it still running in that car. I think the guy was gapping the plugs like they were points? i have no idea. crazy..yet good for me.
This might be an"old wives tale" but I've heard that you can't just open the gap drastically; you need to start with a plug that is made for the big gap. Maybe internal resistance??? I don't know if this has any merit.
i was told to run a stock gap with my hei. is this true?? should i gap it? its a 350 with an rv cam if that makes a difference?
Don't need platinum plugs just because you have an HEI. I have a DUI HEI and use NGK or Denso U groove non-platinum plugs and they last a long time. Not sure about the parts store $1.25 crapo ones though. I don't put those an anything. Might want to check out the advance curve on your dist. You will get the best performance by having the combination of inital and total timing that your engine likes.
can't hurt to try, the larger the gap the more powerful the spark given that the coil can handle it. if your coil is of unknown origin i'd start at .040 and go from there in .005 incriments.
Thanks for sharing that! HEI's are great. Don't feel too bad. I know a guy that should have known better that ran a Hercules G1600under extremely lean conditions, doing a university R&D project searching out where the best fuel economy might be. He didn't bother to check spark gap and in the back of his mind wondered why he couldn't run as lean as that theory said he could. After the research was all done and he published his PhD dissertation he realized that he hadn't checked that one simple thing. The spark gap was around 0.015 - 0.020 when it could have been at least 0.040, 0.050 or even 0.060 (with an Altronic industrial magneto system [or was it capacitive discharge? -- I can't remember]). Fortunately, the results were still valid, but he could have had much better results had he optimized everything. (The guy was me).
Nice, thats a way cool story! I feel alot better about my oversight now, knowing so many others are in the same boat.
hmm what if you switch to a petronix(?) from points? I dont remember reading anything about the plug gap in the instuctions
Well, the last perfect guy that was around got his ass nailed to a cross. You are in good company, experience is surviving your mistakes.
the reason to only open a plug up.020 is alignment at one time .065 was GM stock opening and going smaller cut down mileage but that was back in carbureted days I run my 355SBC .070 with a pertronix module HOT item and a hot coil Accel which is not really a favorite but it works
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