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post #1 of (permalink) Old 09-06-2002, 05:17 PM Thread Starter
 
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Virtually NO back pressure

All right, here I need some suggestions. I've noticed a lack in low end power (and many of you may remember me posting on this). I finally got into the shop to ask about a x-over pipe to link my duals. The muffler guy (which everyone tells me, "knows his stuff") said that the power loss isn't from a lack of equalization, it was from a lack in back pressure (i.e. too high flow intake & exhaust). He told me I could either add backpressure (dumb) or I could build up the motor to use the high flow. He suggested power chip or cam. I WAS thinking in the future I may add headers, but I'm guessing here that would be a bad thing!... Anyway, I've looked at jet chips and hypertech chips - they all say I have to use 91 or better octane. I'm thinking not so good. I asked him on this and he said I could find some chips that didn't need higher octane gas. TO MAKE IT SHORT, can you make any suggestions on chips, or cams, or anything else? Thanks in advance!
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post #2 of (permalink) Old 09-06-2002, 05:26 PM
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Re: Virtually NO back pressure

Well, how's the top end? If you have minimal backpressure it should breathe quite nicely at say 3500 rpm +

I don't remember your previous post, did this problem begin after installing a new, larger exhaust system?

I know too little backpressure can and will kill low end torque. I actually had a buddy just recently w/a BMW have a new system installed w/something like 3" pipe. It killed his power off the line, and he took it back and had another sytem installed w/2.5" or 2.75".

I know nothing about equalization, sorry.
post #3 of (permalink) Old 09-06-2002, 08:36 PM
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Re: Virtually NO back pressure

i still dont buy the "backpressure helps torque" argument. having a pipe too big WILL kill low end power, but thats because you dont get the siphoning effect of the gases as they go down the tube because they arent packed in there tight enough to get suction. a cat or muffler will not help low end power, i dont think. to me, it seems that a 2" straight pipe should help the low-end torque tremendously, but at the cost of high rpm flow. a cat or muffler would restrict the high rpm flow (bad) but wouldnt add to the siphoning effect, so i think they are useless except for thier obvious uses. does that make sense? any exhaust experts on here to set me straight?
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post #4 of (permalink) Old 09-07-2002, 02:38 PM
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Re: Virtually NO back pressure

Looks like stock exhaust manifolds....
What size "duals" are you running, and what mufflers?
What arragement is coming out of the mufflers?
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post #5 of (permalink) Old 09-08-2002, 08:45 AM Thread Starter
 
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Re: Virtually NO back pressure

Starting at the intake...
K&N replacement filter
Helix throttle body spacer

Exhaust...
w/ Stock manifolds
and 2-1/2" pipe.
The only time they meet is at the O2 sensor.
2 high flow cats
2 "turbo" mufflers (don't know much about these, but they sound real nice)
2 2-1/2" exhaust tips at 45degrees.


I have NO power until 2100-2200 rpm. Then it takes off and is great until about 4000 rpm (except for pulling hills in OD, which is what I was trying to fix in the first place). It's the funniest thing, I can hold my foot at a spot on the gas pedal and it will creep up to 2100rpm then all of a sudden it gets louder/deeper and starts to accelerate at about twice (or more) than what it had been, all without me moving my foot a bit. Its almost like something "opens" up at that point. Also, flooring it at low rpm seems to hurt my acceleration more than it helps. Half throttle does better at that point. Man, when I got the bronco - it would suck you back in the chair, but had little top end.

Can anyone explain this, or tell me what I can upgrade to fix it? Thanks
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post #6 of (permalink) Old 09-08-2002, 12:07 PM
 
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Re: Virtually NO back pressure

Muddy, everybody that has posted is right. It is just a matter of scemantics. Call it back pressure, whatever, I like to think that what you are after is the proper size matchiing of the pipes, and other good components in good condition, that will yield the best results. In this case 2 2.5" pipes is too much for a stock 302 to develop good low end torque. Dual 2" or better yet a single 2.25 or 2.5" would work well.
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post #7 of (permalink) Old 09-08-2002, 12:23 PM
 
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Re: Virtually NO back pressure

I'm taking it that you have a mass air system. If so, my recommmendation for a cam would be a RV cam or Comp cams 4x4 extreme (not sure if they make one for the 302 though). Those cams would be your best bet for low end torque, but I don't know if they would be able to solve your problem by themselves.
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post #8 of (permalink) Old 09-08-2002, 05:30 PM Thread Starter
 
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Re: Virtually NO back pressure

Tell me more about these rv cams, please. Where do I go online to find/order them. About how much do they cost, and what all is required to install them? I know absolutly nothing about cams, except for the fact that I have one, right? Will this increase or decrease or not effect my gas mileage? I figure I'll go for the cam instead of downgrading my exhaust. And yes, I have the MAF system, which by now I figure is a good thing. Sorry for all the q's. And thanks for all the help!
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post #9 of (permalink) Old 09-09-2002, 11:43 AM
 
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Re: Virtually NO back pressure

I would talk with a reputable local shop about an rv cam. When I got my 302 stroked they slapped in a rv cam. I couldn't tell you anything about the specs except that it cost me $70, I should have asked for a spec sheet or something. A local shop should be able to help you choose a cam and then install it. All I did was tell them I wanted as much low end torque as possible and they hooked up the rv cam. Sorry, I don't have a part number or anything.
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post #10 of (permalink) Old 09-09-2002, 04:20 PM
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Re: Virtually NO back pressure

Have you tried removing the Helix throttle body spacer?
Never know.[img]images/icons/wink.gif[/img]
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