rebuild questions
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Freshman User
Joined: Jul 2005
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rebuild questions
am getting ready to rebuild the 351w in my 88 f-250.never rebuilt an e.f.i. before(ought to be a real circus).can i bore it .30 over or will the computer get cranky?i am just building a basic stock engine for everyday use.also, i found a frayed wire on one of the injector plugs,can i replace just that plug or must i replace the whole harness?
Post Fiend
Joined: Oct 2003
Posts: 6,214
Likes: 13
From: New Jersey
The computer won't get cranky with a .030 overbore by itself.
What really freaks the speed density computers out is cam overlap, which makes the vacuum as lumpy as the cam. You can get away with a ton of lift, radical lobe ramps (assuming a roller rebuild), *if* you are careful not to overdo the overlap.
The o2 sensor will compensate for about a 3-5% increase in displacement, if you don't hit too close to redline. At WOT the computer uses tables, and of course they are for a slightly smaller engine, so you might run a tad lean. Usually that's not a problem because most people with trucks, don't redline them. The power is much lower in the RPM band anyway.
If the wire is frayed, you can twist it together, solder, then wrap with automotive tape or before soldering, slip over a piece of heat shrink tubing to seal it up after you solder it.
No need to replace the entire harness.
I have a friend with a 91 F150 and his wiring harness is mostly twist-on wire nuts dispite my smacking him on the head, often, for such an evil thing
What really freaks the speed density computers out is cam overlap, which makes the vacuum as lumpy as the cam. You can get away with a ton of lift, radical lobe ramps (assuming a roller rebuild), *if* you are careful not to overdo the overlap.
The o2 sensor will compensate for about a 3-5% increase in displacement, if you don't hit too close to redline. At WOT the computer uses tables, and of course they are for a slightly smaller engine, so you might run a tad lean. Usually that's not a problem because most people with trucks, don't redline them. The power is much lower in the RPM band anyway.
If the wire is frayed, you can twist it together, solder, then wrap with automotive tape or before soldering, slip over a piece of heat shrink tubing to seal it up after you solder it.
No need to replace the entire harness.
I have a friend with a 91 F150 and his wiring harness is mostly twist-on wire nuts dispite my smacking him on the head, often, for such an evil thing
Freshman User
Joined: Jan 2004
Posts: 34
Likes: 0
From: Worcester MA
I just had my 351w rebuilt this summer bored .030 over and put a mild cam on it. It ran like crap afterwards(idle all over the place), but after replacing the IAC and the TPS it ran a lot better. the mechanic had to mess around with an adjustable fuel pressure regulator to get the idle where it should be, A lot of people on this board have said that this is a bad trick though.3k miles on it so far and I love it. I can smoke my 33" mt's pretty easily, even with a 3.55 rear end. I would like to go to MAF eventually because I think I will see more gains from my mods(and future ones!!)
Hope my stupid story gives you some perspective or something...
Hope my stupid story gives you some perspective or something...
