I6 upgrades
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Senior User
Joined: Sep 2000
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From: Castine, ME
I6 upgrades
I've got a '86 F150 with a 300 and a three speed with overdrive. Now, I know these engines have a lot of power potential and I have heard the a 390 cfm 4bbl holley and a offy manifold along with a split header and dual exhaust really does the job. What kind of gain can I expect from that upgrade. I am looking to correct sluggish performance; I mean I hear some guys talk about going 80 on the highway while I can just keep it at 70 up hills with no chance of acceleration. Also, does a 60 000volt coil or side gapping the plugs make much difference?
Thanks,
Tim
Thanks,
Tim
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Joined: Aug 2000
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I6 upgrades
Worth every penny!!
I run a clifford water heated manifold with holley 350 cfm 2 barrel, blaster coil and split exhaust into 2.5" single out the side on a 77 F150 4x4. Stock cam. The torque improvements alone is worth it. This beast now climbs hills in 4th at 1200 rpm that I used to have to downshift for. I get on the freeway at 30 mph in 4th, give it just a touch of gas and it actually accelerates - never got this even with the 1 barrel wide open. I understand a 260-268 cam is a must have - next rebuild!
So far the consensus for all round performance is the 390 - depends if you add a cam and how big it is. I avg between 13-15 mpg.
Hope this helps
Ron
I run a clifford water heated manifold with holley 350 cfm 2 barrel, blaster coil and split exhaust into 2.5" single out the side on a 77 F150 4x4. Stock cam. The torque improvements alone is worth it. This beast now climbs hills in 4th at 1200 rpm that I used to have to downshift for. I get on the freeway at 30 mph in 4th, give it just a touch of gas and it actually accelerates - never got this even with the 1 barrel wide open. I understand a 260-268 cam is a must have - next rebuild!
So far the consensus for all round performance is the 390 - depends if you add a cam and how big it is. I avg between 13-15 mpg.
Hope this helps
Ron
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Joined: Jun 1999
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I6 upgrades
Don't know what difference a new intake or carb will make on your '86. But sidegapping your plugs will make a little bit of difference, better response and acceleration. I did this 3K miles ago on my '90 F150 with 300 I6 and it has boosted accleration/response and raised the mpg a little. I now get close to 18 mpg on the highway at 72 mph with the AC running, and close to 20 mpg when I'm not hurrying and without the AC on. I've heard that the big I6's need help breathing...anything you can do to open up the exhaust will help immensely, like the split headers and after cat high-flow mufflers. I tried the K&N drop in air filter and my truck breathes better, but didn't think it was worth the bucks. Yours might respond well to a high-flow filter once you get the intake and carb changed. Another post somewhere on this board mentioned having to alter the acclerator pump/linkage in order to eliminate bogging down after they put an intake and 4bbl carb on their I6.
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Joined: Sep 2000
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From: Castine, ME
I6 upgrades
thanks to both of you for your responses...I tried the side gapping tonight and it actually does accelerate a bit smoother. In the next few weeks I am going to start the upgrades; I think beginning with the exhaust...does anybody know weather to go with straight dual exhausts or cross over to equallize back pressure? Also, what is a good cat and muffler to use that would be suitable for towing. (I particularly like the low big block rumble)
Thanks again,
Tim
Thanks again,
Tim
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I6 upgrades
Running straight duels will probably work fine. Straight duels on my '65 F100 with 240 works real swell. I am running 26" glass packs, that is my preference. Turbo mufflers are frequently recomended. Or longer glass packs will give a nice low rumble too ( like 30" or so). It is a matter of opinion I guess.
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Joined: Apr 2000
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I6 upgrades
I put a 12" glasspack with a Y-pipe out to duals on my 300 and its not real loud, but it will get your attention. It also improved my seat-of-the-pants performance quite noticibly, it also helped that I put in a 3.55 rear end, instead of the 3.08. My .02.
Josh
Blue '91 F-150 Custom
300 I-6 Manual 5sp Transmission
31x10.50R15 Tires
Cat back duals with 12" Glasspack
Josh
Blue '91 F-150 Custom
300 I-6 Manual 5sp Transmission
31x10.50R15 Tires
Cat back duals with 12" Glasspack
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I6 upgrades
The Holleys on a clifford need the 50cc accel pump to remove the bog - just putting on bigger shooters and/or different pump cams does not work.
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From: Castine, ME
I6 upgrades
well, thanks again this will certainly make my project easier. Since i am fairly new to bulding up engines, I have noticed that all of these performance upgrades, most notibly the offy and clifford manifolds and all of the headers I have seen, are all street-illegal. I would be interested to hear from anyone in an emmissions tested state (I live in CT)what they do to pass. I would think that having two brand new high flow cats on a dual exhaust system would pass most any vehicle, but maybe I am wrong. i would guess that these upgrades would be emmissions illegal because they eliminate stuff like the thermactor air injection and the oxygen sensor.
Thanks,
Tim
Thanks,
Tim
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Post Fiend
Joined: Jan 2000
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From: Dryden, ON, Canada
I6 upgrades
The headers are emissions illegal on carbed trucks because in order to have an alternator, you must either have a HD 300's alt bracket(no air pump bracket), or cut your stock one in half and do a little grinding on the back of it so that it'll clear the #1 primary tube, and, you can't run an egr valve. If you don't run your air pump anyway, you can hack the bracket off just above the bolt hole for the alt, and do a little grinding where it will interfere with the header, I did this for my neighbour when I installed a header on his truck Sunday, mine just bolted on, the HD's alt. bracket is a little different, it's stamped steel, and it mounts the alt. lower than a LD's bracket.
Evan MacDonald
82 F100 FlareSide
HD 300-6, 240 head
NP435(6.69 low)
2.73 Geared 9"
Blue & Silver
Evan MacDonald
82 F100 FlareSide
HD 300-6, 240 head
NP435(6.69 low)
2.73 Geared 9"
Blue & Silver
Thread Starter
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Senior User
Joined: Sep 2000
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From: Castine, ME
I6 upgrades
[font size="1" color="#FF0000"]LAST EDITED ON 26-Sep-00 AT 11:05 AM (EST)[/font][p]thanks for the tips...I still am unsure if my truck will have a shot at passing emissions with the new mods though....also Evan- since you have a HD 300, how can you tell the difference between HD and LD?
thanks again
Tim
thanks again
Tim
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Joined: Sep 2000
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I6 upgrades
Hello. OK I admit I've never heard of sidegapping. How do you do it? I have a 1985 with the 300 6 and it gets a big fat 8 mpg with a new carb, egr valve, oxy sensor and full tuneup. On the HWY maybe 11mpg. Thanks Greg.
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From: Castine, ME
I6 upgrades
To the question about side gapping. I believe it was mentioned in an earlier post, but here is how I do it. Place the spark plug in a vice and saw off a small piece of the electrode bar the extends over the top of the plug. The desired ammount has the electrode just barley covering the tip or anode of the plug; instead of entirley covering like they are manufactured. You should see a bit more mpg's and smoother acceleration, but the plugs won't last as long.
Tim
Tim