atually on #3) you should feel an increase of power regardless if it is plugged or not, that is why drag racers don't use any of that stuff just the headers...

 

I kind of disgree with the above statement. If the cat was clogged then you would make more power with the y-pipe unbolted. If the cat isn't clogged you will lose a ton of power because these trucks need exhaust velocity and back pressure to make power. I ran my truck with open exhaust from the manifolds back for a day or so waiting to get to the muffler shop and it was a complete dog, our trucks are nowhere near the power level of drag cars and trucks that run open headers. Just take your truck to an exhaust shop and they can tell you pretty quik if your cat is clogged

 

I wasn't saying that our trucks are at the same power level of drag cars, I was stating that it restricts the exhaust flow thus when it is diconnected it will increase power, that is why drag racers do that to get as much power as possible

 

I called a local exhaust shop and they charge $60 to check the catalytic converter. The ford dealer said that the OBD-I system would show a code if the cat was bad. If that's true I have a hard time spending another $60.

 

i had an 87 corvette that started to lose power going up a long hill in pasadena, ca.

no codes were thrown, checked engine with vacuum gauge, it dropped on acceleration.

took to muffler shop, put in new cats, car ran 300% better than it ever did. put on new muffs the next month, car ran another 200% better.

car never threw a code.

a computer is not always the answer.

 

Dave

I was wondering if you put a K&N in the original filter box and if so did you change your air intake to one from a F250 460 engine. The air intake is moved to beside the radiator and air flow is greatly impproved. I done this and it seemed to help my truck a bit the part was only 14.00 from the dealer. If you want the part number let me know. By the way Autozone will read your codes for free I would try that first to see if anything turns up..
Good Luck

 

That's just the way it works. The 302 likes high RPM. To maintain 70 on a slight incline it will drop down out of overdrive. Believe it or not the 300 6 will pull lot steeper grades at 70 without dropping down a gear than the 302. It's all about the torque curve of the engine. I'd say there is nothing wrong with your engine or transmission...Van

 

I tend to agree with the 302- 3.55gears and oversize tires=DOG. Mine does this too, same setup. 86 f150 2WD 302 AOD 3.55 31x10.50 tires. I gotta keep it up to over 70mph to keep it from down shifting out of OD. Also, I didn't pass my Calif. smog test and had to get new CATs. This made a little bit of difference in pulling power. I don't think clogged CATS will glow red hot. Mine didn't. They weren't heating up at all in fact.... just shot. They check the CATs with an infrared heat gun to see if they are up to temp. that way they know they are working. The 302 has good power, just not down in the lower RPMs.

 

Hey Fair 96 what is the part number for that F250 airbox? Will my stock F150 filter fit in it? Do I have to do anything special with the mass air flow sensor? Got any pics?

I test drove a coworkers 94 F150 302 with the same tires as mine and his shifted very similar to mine. He just had his tranny rebuilt so his shifts alot smoother than mine but its in about the same rpm range. I guess I am just stuck with it.

I do want to do a vew simple mods to help free up a few more horsepower. I would like to free up the intake and install an electric fan. I noticed a significant difference when I put an electric fan on my 300zxt. I ran a bottle of sea foam through my truck tonight too so maybe that will help a bit.

Thanks for all your help guys.
Dave

 

Dave

Here is the Ford part number # F3TZ-9A675-B Intake tube all you replace is the tube from the bottom of the air box to the radiator.. Everything else stays the same Filter and box and you do nothing with the mass air flow. Very easy and cheap mod.

 

Thanks for the info. I don't suppose anyone has done a dyno run to show improvments?

 

D Harry...there is a diffrence between a plugged cat and a bad cat. A plugged cat does not allow for much exhaust flow, and the hot exhaust gasses build up, potentially creating red hot temperatures, or more commonly, a stalled engine. By comparison, a bad cat is not plugged, but the catalyst material has failed to clean up the exhaust gasses for one reason or another. That is the reason why you failed the emissions test.

 

I agree with everyone who said the high gear ratio together with the high-revving 302 and bigger diameter tires are all taking away from low speed power and causing the acceleration and hillclimbing performance to be doggy. If the cat is a problem, then replace it, but I don't think you're ever going to be truely happy with that engine/gearing/tires combination.

If it is a 2wd truck, the gearing can be changed for cheaper than putting on a new exhaust/intake/chip and if it is a 4wd the cost will be a little more than the motor mods but the gear change will most likely give better results.

I had to switch from 3.55 gears with my F350 with 351 engine and 33" tires because the engine would dog out anytime the trans shifted into 3rd, especially if there was a hill involved. Switching to 4.56 gears brought that engine firmly up into it's powerband at lower vehicle speeds and the performance gain is like night and day. I would recommend 4.10 gears with your tires and engine since you likely have overdrive in the transmission. Without overdrive, 3.73 gears are a good compromise between power and mileage.

I have a Bronco with 3.50 gears and 31" tires with a 302 and it is geared too high. It lugs going up hill unless I downshift it or make a running start at the hill and keep my speed way up. At some point I will change to 4.10 gears in it, as well as swap in a granny gear 4-speed transmission (no OD) for better use off-road. That combination will work ok with the 31" tires that are on it now since I don't need to drive it fast on the highway, and allow me to eventually switch to 33" tires and still have enough gear to keep the engine happy.