Why is it when you go looking for an article in a magazine, you can NEVER find it???? LOL Anyways, somewhere I have an article that talks about the drawbacks of having too little backpressure. Why do you think a lot of drag racers now run mufflers (other than because some sanctions require them) instead of open headers? Unfortunately I can't remember the details of the article or I would enlighten you all to the theory, but a little backpressure can be a good thing.

Note I did say A LITTLE backpressure. Everyone knows most exhaust systems have to much, but none at all isn't neccessarily a good thing. From what I've read in the past it's a very fine line, and unless you have unlimited access to a dyno and parts warehouse (as well as a lot of time to kill) you'll never find that optimum combination.

IMO, the best thing you can do is follow your gut instinct, buy what you think is best (as we all do anyways), and keep your eyes and ears open to new testimonials so when it's time to replace your exhaust again, you're already informed and know what you want to go with.

TrailDawg
1993 F150 2WD
4.9L-Auto
Pro-Comp Stage-2 6" lift
Auburn Pro-Series Diff. w/4.56:1 gears
35x12.50x15 General Grabber MT's
http://www.geocities.com/ProjectTrailDawg

 

I am not sure about this engine, but I have something to say about backpressure. In a 96-99 Taurus SHO with the V-8 engine, some shops were selling a 3rd-cat bypass kit. For a little more top end power, they lost a lot of low end torque. Documented on a dyno. So backpressure does effect the engine.

-Chris
1980 F-250 4x2 LB
NP-435 4 sp. w/o OD
3.55 open rear end
200K Miles and going... and going... and going...

 

[font size="1" color="#FF0000"]LAST EDITED ON 09-Mar-01 AT 04:44 PM (EST)[/font][p]You're absolutely correct Traildawg, one can never get rid of all backpressure. It would be nice if somehow or way the whole idea behind backpressure could be solved. I have to back Traildawg when it comes to choosing what one wants. If it's your truck you make the desicion on what and how you want to do something. We are all here to add our 2 cents and experience. Happy truck'n guys!!!!


P.S. NO hard feelings Traildawg!!!!:P

1994 Ford F150
300-6
Highly Modified and more to come!

 

Well, looking into my trusty manual again, I find 13 causes of 'lack of power'.

1. Incorrect ignition timing ... the route of more evils than one imagines!

2. Problems with fuel or electrical systems. In an EFI engine, there are lots of little places for problems to creep up ... even something simple like clogged injectors.

3. Excessive play in the distributor shaft, damaged rotor, faulty distributor cap, plug wires, etc.

4. Faulty or incorrectly gapped spark plugs ... they should have a .044" gap.

5. Bad or maladjusted carb (although this won't apply to your EFI engine)

6. Faulty ignition coil.

7. Brakes binding.

8. Automatic trans fluid level incorrect.

9. Clutch slipping.

10. Clogged fuel filter or bad gas.

11. Clogged catalytic converters.

12. Using the wrong grade of fuel ... try a higher octane gas.

13. Low/uneven compression in the engine.

There ya go ... a big ol' fun list of possibilities! :Oo

Chris in Canada
74 Gran Torino Brougham
84 F150 2WD 300I6/NP435 no OD/3.08 open rear

 

Just to put in my 2 cents worth on the backpressure debate, I recently read an article on backpressure in a hotrod magazine(that I couldn't find again) about how when tracks started implementing muffler rules, E.T.s went down instead of up. They had a lot of test results through different mufflers, with technical explanations of how mild backpressure helped, however, these were all behind headers.. If any one could find where/when the article was I'd like to reread it just to find out their conclusions.

 

I was just considering an air intake system for my 88 six. I already have the exaust done. What is available for intakes and does it matter with this type of injection? I want to eliminate the stock air box and run two tubes with the K&N type filter.
Thanks

 

before you do anything, find aomeone who has the same engine/tranny set-up, but who has 4.10's or any gear that is above what you have.(i bet you have 3.08) i think you will find a big difference in the feel of the truck.

 

Holly Molly!!! I never thought i would get this kind of response. I have been meaning to check back on this site but havent had the time. Im not sure what the gearing is in my truck so i dont know what to say about the gears. But i have heard that on a 4x4 you have to change the gears in the back AND the front, sounds like it could get expensive. Everything thing else i have already done except for the timing and catalytic. But i have decided to take out the 300 and drop in a 351 switching from FI-Carb. I know that will give me more power and i already have the engine and all the extra goodies. All i need to do is take it in to be cleaned and bored and get to the rebuild. I also have a few things to buy for changing over but thats basically it. Anyone have any idea how much i could get out my 300 with the FI system, its got about 165,000. I will admit i have had no problems at all with the engine it just doesnt have enough power for my liking. Thanks guys.

 

[font size="1" color="#FF0000"]LAST EDITED ON 19-Mar-01 AT 11:32 AM (EST)[/font][p]black:

Yeah!!! GO for the K&N FIPK! It will make it easier for the engine to breath and you might gain some mpg. I did! Got a .5mpg increase and better acceleration. My 4.9L really seemed to like the easier breathing on the intake stroke, I also redid the exhaust and the engine really came alive. By the way I also have 4.10s and they really get the truck moving. Acceleration isn't really fast but man I can tow and haul anyting I want. Bad things is gas mileage with 4.10s is 12mpg on a EFI 4.9L!!!!

1994 Ford F150
300-6
Highly Modified and more to come!

 

 

Yeah, I'm going to have to go with the catalytic converter being plugged or some other type of engine problem. My 1991 F-150 had a 300 with 200,000 miles on it an it honestly ran like new and had tons of low end torque even with the 3.08 gears. It would do at least 90MPH. The overdrive will make it seem like you are having to almost floor it to stay at 75MPH but after you turn the overdrive off it will take off. My dad just got rid of his 88 F-150 with a little over 300,000 miles on it and really had some pulling power with 3.55 gears and a 5 speed manual.

 

OK-

Like PaulG was saying, I don't wanna beat a dead horse, but too little back pressure is bad. Now from what I've seen, the main reason for this is because of the physics of how the exhaust works. After each cylinder fires, it obviously creates exhaust fumes and what not that run through the exhaust. (I know evryone knows that. hold on, i'm getting to the interesting part). Think about the amount of vacuum those "***** of exhaust" from each cylinder must create as they go flying down the pipes. This vacuum is what causes the next group to move through so quickly, and so on, and so on. Now, I agree wholeheartedly that stock stiffles the engines ability to breathe bc between the emissions stuff and the overall dimensions on the pipe, it just can't flow. But if you go to big and lose too much backpressure, you're basically doing more harm than good.

By they way, this is just what I was told. The guy might have been pulling my leg or just b-sing it, but it made sense. Course, how much stock can you put in a guy who stuck a 3.5" exhaust on a Honda 4-banger?

 

I don't want to start beating on a dead horse either, but, on a big engine like a 300, the headers probably make enough back pressure. My Headman dual exit headers have 1½" primaries, and, I can run open headers and not lose any back pressure, but they aren't too small either, as it will readily rev to 5000 rpm, the 300 doesn't need the big header tubes the 302 does, as it is a big low revving engine, and it's got a lot more in common with the 400(bore and stroke for one.)
Evan MacDonald
82 F100 FlareSide ex. 2wd
MAF MPFI HD 300-6
Hedman Hedder
NP435(6.69 low)
NP205
3.55 Geared ARB'd 9"
Dana 44 TTB
31x10.50/15 Goodyear M/T's

 

>OK-
>
> Like PaulG was
>saying, I don't wanna beat
>a dead horse, but too
>little back pressure is bad.
>Now from what I've seen,
>the main reason for this
>is because of the physics
>of how the exhaust works.
>After each cylinder fires, it
>obviously creates exhaust fumes and
>what not that run through
>the exhaust. (I know evryone
>knows that. hold on, i'm
>getting to the interesting part).
>Think about the amount of
>vacuum those "***** of exhaust"
>from each cylinder must create
>as they go flying down
>the pipes. This vacuum is
>what causes the next group
>to move through so quickly,
>and so on, and so
>on. Now, I agree wholeheartedly
>that stock stiffles the engines
>ability to breathe bc between
>the emissions stuff and the
>overall dimensions on the pipe,
>it just can't flow. But
>if you go to big
>and lose too much backpressure,
>you're basically doing more harm
>than good.
>

Well... when i bought my 93 F150 4x4 last month the entire stock exhaust system (from the manifold back) for the 4.9L I-6 had been removed and replaced with a pair of straight pipes exiting out the rear. Sounded mean as hell that way (actually got a few warnings from the police about it being too loud) but the poor truck had NO POWER AT ALL. Additionally the gas mileage was really bad (below 10mpg) so i had a local muffler shop remove the pipes and put in a new exhaust system (dual in/single out catalytic converter to a single muffler, exhaust pipe). The truck now runs better, mpg has improved, and it can hold 75 mph on the expressway (on level ground, whereas before it was straining to reach 70 going downhill). So, i'm definitely going to agree with the statement that you can go too big in the search for lower backpressure.

I'm also looking for more power out of this engine, so far (in addition to the new exhaust system) i've had the clutch replaced (got the truck cheap cause the slave cylinder was blown), the air filter has been replaced, and oil changed (last two were clearly well overdue from the look of it). What should i be looking at next? Tune-up? Something else?

Thanks.

 

[font size="1" color="#FF0000"]LAST EDITED ON 30-Mar-01 AT 10:41 PM (EST)[/font][p]Hey guys, I'm reading all your power increasing ideas and I think they are great and I know they work, but I have something you all seem to be overlooking. Let the exhaust flow sure, but let's force it to produce MORE exhaust than the little torquer ever thought possible. A turbo-4barrel combo will greatly increase power and is probably your cheapest and most effective
thing you could do. Kits come with a new intake and exhaust manifold with dual outlets. I have this combo with a performance cam and a ported and polished head and I smoke my buddies chevs in anything (mind you there stock). But just a turbo on a stock engine will give you the "best bang for your buck" eh?