Denso Plugs/Jacobs Box?
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Denso Plugs/Jacobs Box?
I have posed this question on the Engines forum, but can't seem to get an answer. I have a '97 F150 w/4.6 & Manual trans. Besides the Jacobs box, I have Accel coil packs, K&N FIPK & (Useless) Poweraid. Is anyone using the Jacobs box w/the Denso plugs and if so, what are your results and what are you gapping them at?
Mark
PS: Right now, I'm using Autolite wires, but will upgrade to something better.
Mark
PS: Right now, I'm using Autolite wires, but will upgrade to something better.
Last edited by SundayNiagara61; Mar 12, 2004 at 11:33 AM.
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Joined: Mar 1998
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From: Virginia
Hi SN61,
The Engines section is generally where you should post that type of question - it isn't related to "Computer Chips." However, I do have a lot of experience with this, as we've specialized in modifying F-150's for more performance for 12 years, so I'll be happy to try to help you out here briefly.
In short - forget trying to run a significantly bigger-than- factory-spec plug gap on that truck, as that will *NOT* work well when the humidity level goes up and you have to use heavy throttle, especially in the higher gears where the load is higher & demand on the ignition system is highest. Sure, it will work OK at 50% humidity, but not when it hits 85% or higher humidity and you have to use heavy throttle - especially in the higher gears at higher rpms!
Aftermarket ignition systems generally do not allow you to run a "significantly" bigger plug gap in modern computer-controlled vehicles as a general rule - despite what the manufacturers tend to claim. They simply give you a hotter spark and a shorter saturation time for the coil - being able to run "significantly" larger than factory plug gap is something that really applies to older vehicles without fuel injection, whose factory plug gaps were like .028, 0.32, etc. - and a REALLY good electronic capacitive discharge system in such a vehicle might allow you to open those gaps up by .005 -.010 or so, etc., and still be able to pull cleanly all the way to redline in each gear even in 100% humidity.
You've got a nice setup there, those Accel coil packs do work really well, and the Denso Iridium plugs are the best performance plug you can get.
What I would do is to run no bigger than a .045 plug gap since you have OEM low-grade plug wires on there - then once you get a nice low-resistance set of plug wires (and I mean not higher than 200 ohms per foot - your current units have a resistance well over 1000 ohm per ft!) is to run a .050 plug gap.
Then the next time you get a chance to get that truck out in a day with like 85% or higher humidity (especially 95% or higher humidity) - take it out and wind it out hard in the higher gears - don't get a ticket, but if it's a manual, take it up all the way to redline in 3rd gear, and as high as you can in 4th (with an automatic, wind it all the way out in 2nd and as far as you can in 3rd, too)- and see if it pulls cleanly. Sometimes it will seem to pull cleanly with no obvious miss, but still lose a TON of power due to the high humidity causing the ignition system not to be able to fire the plug really well. At any rate, thats one way to test it - just don't take chances or get a big speeding ticket!
Better yet would be to put it on a dyno - though the load won't be as high as the load when actually driving that heavy truck on the road, that would at least allow you to wind it out in the higher gears - assuming you have a performance chip to take off the top speed limiter.
The very best thing would be to do some datalogging while winding it out, so yo can really see what the engine is actually doing - I can advise you on that, just give us a call.
Just as an aside (and at the risk of sounding like a sales-dude) - if you do not have a chip or performance tune yet, then at some point give us a call, as that is the single best bang for the buck. We can add well over 20 HP with a good custom tune and make that truck run better *everywhere*, all the time, at any throttle position or rpm, and get probably get a bit better fuel mileage in the process - as well as knock off the top speed limiter, etc.
If you have any questions on any of this, feel free to give us a call at our number listed below & good luck with your truck!
The Engines section is generally where you should post that type of question - it isn't related to "Computer Chips." However, I do have a lot of experience with this, as we've specialized in modifying F-150's for more performance for 12 years, so I'll be happy to try to help you out here briefly.
In short - forget trying to run a significantly bigger-than- factory-spec plug gap on that truck, as that will *NOT* work well when the humidity level goes up and you have to use heavy throttle, especially in the higher gears where the load is higher & demand on the ignition system is highest. Sure, it will work OK at 50% humidity, but not when it hits 85% or higher humidity and you have to use heavy throttle - especially in the higher gears at higher rpms!
Aftermarket ignition systems generally do not allow you to run a "significantly" bigger plug gap in modern computer-controlled vehicles as a general rule - despite what the manufacturers tend to claim. They simply give you a hotter spark and a shorter saturation time for the coil - being able to run "significantly" larger than factory plug gap is something that really applies to older vehicles without fuel injection, whose factory plug gaps were like .028, 0.32, etc. - and a REALLY good electronic capacitive discharge system in such a vehicle might allow you to open those gaps up by .005 -.010 or so, etc., and still be able to pull cleanly all the way to redline in each gear even in 100% humidity.
You've got a nice setup there, those Accel coil packs do work really well, and the Denso Iridium plugs are the best performance plug you can get.
What I would do is to run no bigger than a .045 plug gap since you have OEM low-grade plug wires on there - then once you get a nice low-resistance set of plug wires (and I mean not higher than 200 ohms per foot - your current units have a resistance well over 1000 ohm per ft!) is to run a .050 plug gap.
Then the next time you get a chance to get that truck out in a day with like 85% or higher humidity (especially 95% or higher humidity) - take it out and wind it out hard in the higher gears - don't get a ticket, but if it's a manual, take it up all the way to redline in 3rd gear, and as high as you can in 4th (with an automatic, wind it all the way out in 2nd and as far as you can in 3rd, too)- and see if it pulls cleanly. Sometimes it will seem to pull cleanly with no obvious miss, but still lose a TON of power due to the high humidity causing the ignition system not to be able to fire the plug really well. At any rate, thats one way to test it - just don't take chances or get a big speeding ticket!
Better yet would be to put it on a dyno - though the load won't be as high as the load when actually driving that heavy truck on the road, that would at least allow you to wind it out in the higher gears - assuming you have a performance chip to take off the top speed limiter.
The very best thing would be to do some datalogging while winding it out, so yo can really see what the engine is actually doing - I can advise you on that, just give us a call.
Just as an aside (and at the risk of sounding like a sales-dude) - if you do not have a chip or performance tune yet, then at some point give us a call, as that is the single best bang for the buck. We can add well over 20 HP with a good custom tune and make that truck run better *everywhere*, all the time, at any throttle position or rpm, and get probably get a bit better fuel mileage in the process - as well as knock off the top speed limiter, etc.
If you have any questions on any of this, feel free to give us a call at our number listed below & good luck with your truck!
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The truck is NEVER driven hard and ran it's best with Autolite pugs/Holley wires, with the gap set at .064. This question was posted twice in the Engines section and no one replied and that's why I posted in this forum. Anyone else have experience?
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From: Virginia Beach, VA
SN61,
Just an opinion, as I haven't run the Denso's myself. Other than having less misfires, they should probably be gapped to whatever you have found optimum for your other plugs.
I have a Jacobs box/coil/wires on my '95 and have found little difference in gaps using various plugs. I found that on my truck the first indication of going too large on the gap was slightly "soggy" off idle performance, especially while the truck was still cool.
I had a problem with my box and due to nothing more than lack of time haven't worked it out yet. Living in a high humidity area as Mike noted I run stock gaps withouth the box (.053) and normally run .060 to .065 with the box.
Just an opinion, as I haven't run the Denso's myself. Other than having less misfires, they should probably be gapped to whatever you have found optimum for your other plugs.
I have a Jacobs box/coil/wires on my '95 and have found little difference in gaps using various plugs. I found that on my truck the first indication of going too large on the gap was slightly "soggy" off idle performance, especially while the truck was still cool.
I had a problem with my box and due to nothing more than lack of time haven't worked it out yet. Living in a high humidity area as Mike noted I run stock gaps withouth the box (.053) and normally run .060 to .065 with the box.