351w rebuild question
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From: Chattanooga, TN
351w rebuild question
I'm fixing to pull the 351w out of my '93 F-250 for a rebuild and I was hoping to change the cam, heads, and possibly intake to get a little better performance out of the truck. This will be the first build that I have ever done on my own and I'm not really sure what my options are. I'd like to stay with the stock fuel system if I can, but that may not be an option. The truck also has to pass emissions. Just for clarification, I'm not looking to make this a 400hp monster, I would just like a little more power if I can get it.
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From: Ottawa, Ontario
Just put a cam in it, and if your are looking for a little more port the factory heads. With a free flowing exhaust the motor will come alive.... lots more power over stock. My 351 is happy with the factory fuel system and easilly passes emissions.
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From: Chattanooga, TN
What cam are you running? I've been shopping around and I honestly have no idea which one is going to work best. This is going to be pretty much a stock rebuild, but I would like a good lope at idle and a little more mid-range power. After drooling over the $1,300 Trick Flow heads, I think I may just send mine off to get ported. My pockets dont run that deep. As far as exhaust, I already have a 2.5" manifold-back exhaust system with hi-flow cat and flowmaster mufflers. I will be going with standard length headers over the factory manifolds.
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From: Ottawa, Ontario
Originally Posted by Mr_Woodrow
What cam are you running? I've been shopping around and I honestly have no idea which one is going to work best. This is going to be pretty much a stock rebuild, but I would like a good lope at idle and a little more mid-range power.
Stock heads with pocket porting and cleaned up exhaust ports will support 300hp, and that's about the limits of the factory fuel system as well. It's pretty much useless to install aftermarket heads unless you also upgrade the intake and fuel system, so that's when things really start to get expensive.
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From: Chattanooga, TN
I've been reading a little more into it today and kinda got that impression. I've looked at heads and intakes, but I think I'm just going to have mine ported. At least for now.
Thanks for your help. I'm going to look into the two cams you suggested and see which one is going to work best for me.
Thanks for your help. I'm going to look into the two cams you suggested and see which one is going to work best for me.
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From: Topsfield, MA
You might be able to pick up a better set of heads or used heads for about the same money you'd spend in porting/polishing.
I know the GT-40Y heads like I have are a cheap marginal upgrade. They are aluminum instead of iron and save about 50lbs. They also allow for more timing before detonation because they're aluminum.
They cost me $700 new...which is about the cost of a full port/valve job. I'm sure you could get a set cheaper or a better used set if you search around...but its up to you.
I know the GT-40Y heads like I have are a cheap marginal upgrade. They are aluminum instead of iron and save about 50lbs. They also allow for more timing before detonation because they're aluminum.
They cost me $700 new...which is about the cost of a full port/valve job. I'm sure you could get a set cheaper or a better used set if you search around...but its up to you.
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From: Chattanooga, TN
Originally Posted by MustangGT221
You might be able to pick up a better set of heads or used heads for about the same money you'd spend in porting/polishing.
I know the GT-40Y heads like I have are a cheap marginal upgrade. They are aluminum instead of iron and save about 50lbs. They also allow for more timing before detonation because they're aluminum.
They cost me $700 new...which is about the cost of a full port/valve job. I'm sure you could get a set cheaper or a better used set if you search around...but its up to you.
I know the GT-40Y heads like I have are a cheap marginal upgrade. They are aluminum instead of iron and save about 50lbs. They also allow for more timing before detonation because they're aluminum.
They cost me $700 new...which is about the cost of a full port/valve job. I'm sure you could get a set cheaper or a better used set if you search around...but its up to you.
I know that this is probably going to be a stupid question, but I'm still a noob when it comes to this stuff. After yall did these modifications, was it a big hassle to get the computer tuned right or was the factory tune able to support it?
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From: Ottawa, Ontario
Originally Posted by Mr_Woodrow
After yall did these modifications, was it a big hassle to get the computer tuned right or was the factory tune able to support it?
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Post Fiend
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From: Topsfield, MA
A 302 MAF computer is capable of running just about anything...but the problem is under factory tune it isn't perfect. Conanski, have you ever run that with a wideband o2 sensor?
There are still parameters that may not be right when using a stock 302 MAF system on a different engine combo. Remember, in wide open throttle, cold start, and other times when the computer is running in open loop and not closed loop...is when you'll be relying on the base computer tables. The computer will not trim out the fuel curve when in open loop because it isn't looking at the o2 sensor input.
You might be running lean/rich and not know it unless you've analysed it. You can run dangerously lean but still have the engine run and sound right...
The right modifications can be made with the stock 351 computer and it'll be ok, but switching it over to a 302 MAF system is the better option. I'm going to be doing a write-up on how to do this soon, I wired it myself w/o a conversion kit.
When you make important changes, it should be analysed with a wideband o2 sensor to make sure there are no lean spots during operation.
There are still parameters that may not be right when using a stock 302 MAF system on a different engine combo. Remember, in wide open throttle, cold start, and other times when the computer is running in open loop and not closed loop...is when you'll be relying on the base computer tables. The computer will not trim out the fuel curve when in open loop because it isn't looking at the o2 sensor input.
You might be running lean/rich and not know it unless you've analysed it. You can run dangerously lean but still have the engine run and sound right...
The right modifications can be made with the stock 351 computer and it'll be ok, but switching it over to a 302 MAF system is the better option. I'm going to be doing a write-up on how to do this soon, I wired it myself w/o a conversion kit.
When you make important changes, it should be analysed with a wideband o2 sensor to make sure there are no lean spots during operation.
Last edited by MustangGT221; Apr 18, 2007 at 10:36 AM.
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So how hard is it for a novice to do the swap? I would like to take the truck to a professional tuner when I get it put back together and have a custom chip flashed. I had that done to my old S-10 years ago, but I dont know if that is possible with the computer in my truck now. Is that an option, or should I consider something else?
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From: Ottawa, Ontario
Originally Posted by MustangGT221
A 302 MAF computer is capable of running just about anything...but the problem is under factory tune it isn't perfect. Conanski, have you ever run that with a wideband o2 sensor?
There are still parameters that may not be right when using a stock 302 MAF system on a different engine combo. Remember, in wide open throttle, cold start, and other times when the computer is running in open loop and not closed loop...is when you'll be relying on the base computer tables. The computer will not trim out the fuel curve when in open loop because it isn't looking at the o2 sensor input.
There are still parameters that may not be right when using a stock 302 MAF system on a different engine combo. Remember, in wide open throttle, cold start, and other times when the computer is running in open loop and not closed loop...is when you'll be relying on the base computer tables. The computer will not trim out the fuel curve when in open loop because it isn't looking at the o2 sensor input.
Post Fiend
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From: Topsfield, MA
Originally Posted by Mr_Woodrow
So how hard is it for a novice to do the swap? I would like to take the truck to a professional tuner when I get it put back together and have a custom chip flashed. I had that done to my old S-10 years ago, but I dont know if that is possible with the computer in my truck now. Is that an option, or should I consider something else?
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