Read some posts about iridium vs old style plugs for carb 308's. Some disputes, but since I have a modern ignition, is iridium a no brainier? What specific ones should I get? Going to change out the plugs because some idiot washed the engine and used a hose. It's cleaner but took a day to start the car. It's missing alot now. Did an Italian tune up for 15 miles, better, but still missing and backfires. Figure it's time to change plugs anyway. Thank Rick Jaffe
The other reason I want to change plugs is because hot starts are very hard. I have a high speed starter and it'd difficult to the point of not wanting to drive the car to go someplace because of the difficulty hot starting. Cold starts w The day or two after I drive it are fine and immediate. If I let it sit for a week or 10 days, cold start is bad, but not as hard as hot start. Read some posts that new plugs might help. I've noticed the problem has gotten alot worse or noticeable over the past couple years. So I'll start with the plugs. Also, seems to be a disput as to whether iridium plugs have to be gapped. What's the current thinking on that?
The manufacturer recommends not resetting/adjusting the gap because the small center electrode is very fragile -- these exotic high temperature metals are more like a ceramic (very brittle) than a common ductile metal. Just do a visual/non-contact inspection to ensure no obvious damage and that they are in the right ballpark.
so what iridium plugs do I get? the trip back from the airport was alot better, less popping and much less loss of power. but I still want to change out the plugs in the hopes it will help resolve the hot start problem.
NGK Part Number BPR6EIX (stock number 6637) would be a reasonable place to start IMO for street use (BPR7EIX is the "stock" equivalent, but, unless you are really flogging it, those are a little cold). Don't pay more than $6.39 each -- www.rockauto.com
Rick, the type of plugs depends on the type of ignition you have installed. Iridium (or Platinum) fine tip plugs lower the secondary voltage required for the spark creation considerably, so these are ideal for points and transistor (inductive) ignitions such as the original factory ignition setups in all 308s. Capacitive ignitions such as the MSD 6 series and original Dinoplex have a much higher secondary voltage than inductive ignitions, so they won't benefit from the fine tip plug design. For this ignition type, standard plugs such as the NGK BPR6ES are better suited, and cheaper too. Best, Adrian
Hey Rick The plugs might help a bit but its really todays gas that is the problem. I don't remember exactly, but it has something to do with the "evaporative rate?" (not the correct term) of modern gasoline. In the old days when everything was carbureted gas had a rate of 10 (just as an example). Todays gas has a rate of about 2. What this means is when your engine / engine bay is hot the gas in the carbs starts to warm up and vaporize in the carbs. This could also force the float jet to close as the fuel boils. Carbs are designed to pass liquid gas to the jets, not vapor. So when you go to start the hot car there is little or no gas in the carbs and the float jets could be closed not letting in any gas. Also as the carbs are hot any gas that does make it back into the carb will vaporize as well. I have an older 911 that had 2 triple choke Webbers that used to have the same problem. There was a fix that helped to alleviate the problem somewhat. It was a special guide and very small drill bit that you used to drill a small hole that would vent the float chamber into the intake runner. This would help prevent the vapor locked / empty carb problem. The other half of the fix was to turn the ignition on but not start the car for 30 - 60 seconds. This would allow the carb time to fill with gas. You could try waiting now to see if it helps. Barry
Put in the iridium plugs. Didn't check the gap because of some of the posts. Previously the day or two after I use it, it started immediately. Same today with the iridium. Let it sit for maybe a half hour (hot start time) and it started right up. That's the good news. Car feels Alittle but noticibly more powerful, but might be wishful thinking. Until 3k it runs normal, Now the bad news: over 4 k, alot of popping and some chirping, worse at 5 k. And also when I take my foot off the gas. Both popping and chirping and a small intermittent backfire. I'd say it runs rough. Ran it in the morning and the evening. Same both times, good until 3 k bad over 4 and foot off the gas. Alot worse than the old plugs, except for hot start. And the four plugs closest to the rear of the car looked bad, but but for hot start (which got worse in the past year or two) old plugs worked better Is the next step to check the gap? Is there anything else explaining symptoms. Maybe carbs have to be adjusted? That's beyond my skill set and I don't have anyone here in Houston I trust and is reasonable. So it's not a gap issue or something else i can tackle, I guess I'll have to go back to the old school plugs. Too bad, was hoping it would work out because of the modern crane ignition. Live and learn
The factory gap should be fine, gapping can be useful for race cars and tuned engines where you want to optimize ps and torque but the difference between a factory plug and a gapped plug in a street engine is typically less in performance gain than the difference between driving on a dry or a humid day. The symptoms you have most probably won't get fixed with gapped plugs if your engine does not run well with factory gapped plugs already. With a Crane XR ignition the iridium plugs are the better choice, with a MSD 6 series i would recommend BP or BPR ES plugs as setup. You said that the plugs on the back look worse, so if the banks behave differently i would have a look at the carbs setup, and in a two distributor setup also at the distributor managing the back bank. If it's the ignition or plugs which are the problem, then a possible issue should be apparent at both banks.
have the crane xr 700 ignition. what's got me stumped is that but for the apparent resolution of the hot start problem, the old plugs ran the car better. now at around 3800 rpm accelerating, get a constant popping an chirping; only variable is the plugs. connectors are all tight.
Interesting, the Iridium plugs should work nicely with a transistor ignition such as your Crane XR700. Do you know what coil/resistor you have installed?
I thought I had an MSD ignition, maybe that's the coil. it was done before I got the car. I'm going to look at the gap in a couple plugs. If that's not it. I guess I'll switch back to the regular ones. I will say. I don't seem to have any hot start problem. maybe it takes another crank or two, but nothing really.
bottom line is the but for the hot start, it ran pretty good before with the old plugs. some minor popping, but not too bad. changed them because of the hot start problem which made the car undrivable unless I was going to let it set whereever I went for a few hours. now I've got no hot start problems but the car runs like crap starting at around 3800 rpm, but it's fine and wonderful below that rpm.
Steve is dead-on. I ran the BPR6EIX in my '78 carbed 308 GTS with the Electromotive ignition system, and the car ran great. Highly recommend them. And as Steve says, shop around. You can find some very good pricing on them if you take the time to look.
More likely, with the old plugs, their "missing" was just more consistent (so didn't create burbs and farts ). You should ensure that the carbs and the advance mech in the distributors are working correctly as per Adrian's recommendation -- JMO...
so I changed the gap in the plugs: drove a couple miles to get on the highway to test them out (610 south loop at buffalo for houstonites); I was in the middle lane at the stop light. A old black panhandler looked familiar (I've took the same route a couple days ago with these plugs before I gapped them and the car ran bad). So the panhandler yells to me unsolicited. "hey your car's running better today, no backfiring or popping!" anyway: first thing I checked was the gap on the old plugs; most were around 35-36, a couple were 32. next, I checked the gaps on the iridiums. the first one had no gap. maybe I screwed it in too tight or something. The other plugs were all 25 or between 25 and 26. Changed the gap to 32. I think I still have one bad plug (the filament looks too short on the one which had no gap. will get another couple plugs for spares and to change out that one) bottom line, the car ran much better. no popping on acceleration through close to redline (as close as I get to redline). minor popping like before when I take my foot of the accelerator. but very minor. seems like it has more power or just peppier. you think if I go for 34 or 35 I might get rid of the minor popping when I take my foot off the gas? But the first thing I'll try is to change out the one plug. thanks for all the good advice. I think I got this resolved. lesson for me is when you change a component like ignition, you can't necessarily slavishly follow the OEM book.
