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Discussion Starter · #1 ·
Ive been driving my 90' tbi 5.9 RC around for a while now getting used to, but one thing I cant stand is I get to around 60 or 65 and its like an invisible wall ! it just wont go any faster. I have a 98 5.9 1500 and i know it has more to give... Now granted I know the magnum flows better than the la series heads but is their any thing I can do short of a head swap ? maybe new intake , tbi spacer ? I don t really know anything about how these computers respond to mods. Any help is welcome , thanks
 

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Hello the mods thing depending on the laws. I think header seemed the best add on for mine. I`ve not had a tbi dodge heres what I`ve heard the intake manifold is restrictive and the computer do not like many changes like hipo camshafts.You should be able to do bout 75-80 before it falls flat you might want to check into a tune up.
 

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it should go faster than that.Before you toss money and parts at it, find out what's wrong. Could be a fuel delivery problem, restricted exhaust, or ignition problem. A good diagnosis is in order.
 

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What is your tire size?

Let's say it was a 33. Let's assume you have 3.21. Let's also assume you have overdrive.

With those figures, 60mph puts you at around 1300rpm.

With the same figures and speeds, 4.10s put you around 1700rpm @60.

You need 70-100hp to maintain speed and have some acceleration.

By simply raising your rpms, you get the intended effect w/o internal modification.

 

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Time for the aerodynamic nose?  ;D
 

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Nah, I meant the bullet nose someone was dreaming up a year or two ago here on RCC, lol.
 

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I thought the lowest possible gear for 9 1/4 was 4.56. maybe I'm behind the times but I have 4.56s and had to grind a tooth to get the pin to go back in the carrier.
 

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Discussion Starter · #14 ·
The same company that sells the 4:88 also sells a tapered pin so modifying isnt an issue i guess. would a 8 3/4 fit instead ? that would be easier , and better for gear selection .
 

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OK so everything i see so far in this thread says that you have something wrong or broke with your truck. I have an 87RC 4x4 stock 3.21 gears, 31" tires and it'll cruise fine at 70-80 all day long and still have power to pull.

If you add 4.56's to your current setup you'll find your wall has moved from 60mph to 45 or 50mph.

Is this a 4x4 or 4x2? When you are hitting your "wall" what is the rpm? Is it wound all the way out or have you just run out of power?

Check the following:

High RPM's = Transmission or drive line issue - check that your trans is actually in D and not 2 (not the little indicator on the dash that can be inaccurate as it is controlled by a little wire connected to the column lever) when engaging the gear it should be the third position in the pattern -R-N-D you should feel it go from R to N then N to D.

Just out of power = Engine is having a hard time breathing - Check that your air filter is not clogged and that the intake snorkel on the filter is not plugged. Second option is that the exhaust is completely plugged and not allowing the engine to breathe

This may also be an indicator that your transmission or torque converter is slipping and bleeding off a lot of power in high gear therefore not transmitting power to the ground. This will also create lots of heat in the trans.

What kind of gas milage are you getting? should be between 10 and 14 for a ball park average.
 

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restricted exhaust can do the same thing .
had a chevy that ran fine till about 55 and you could mash it to the floor with no more speed ,just a sick sound fromm the motor.
hold you hand to the exhaust pipe and feel the pressure against your hand .
then have someone revit up. if it has little increase in flow you could have a plugged up muffler or cat converter.
on that chevy i pulled the cat converter off and tokk a punch to knock the honeycomb crap out .
 

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Discussion Starter · #17 ·
yeah i think the exaust is the best bet right now. The new issue of engine builders mag was freshing up a 340 and they broke down power adders part by part on the dyno. pretty interesting to see what headers do by themselves, then cam , then new heads ! headers gain like 22 hp ,oddly enough in their dyno so do the heads !!
 

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Adding HP by changing heads is not a suprise.

the new head most likely did the following
Changed valve size - allowing for better fuel air charge and scavenging within the cylinder
Changed runner geometry, volume and flow - also allows better fuel air charge and scavenging
Changed rocker arm geometry - allowing for higher lift of valves
Changed volume of cylinder by increasing the quench -

Lower cylinder head volume = higher compression = same amount of bang in a smaller package

Headers will help with seat of the pants feel of the vehicle but i don't believe 22 hp.

I think your greatest issue is down stream of your manifolds, either the tube is squeezed or kinked, or your cat or muffler is blocked with soot and gunk.
 

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headers and a true dual 2.25 pipes 20hp I can see. The stock system on these trucks seem to be restrive from the factory. I would look under the truck check for any kinks or leaks. Make sure that your truck is in tune before you mod it 
 

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Elwenil said:
Time for the aerodynamic nose? ;D
Would be better off making a tapered tail cap for it, cleaning up the air coming off the rig and reduce drag, how you put the air back together is more important than how you take it apart lol David
 
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