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Discussion Starter · #1 ·
So I'm going to be doing a plenum gasket here in the next couple of weeks, I got the hughes plate. I've been doing some research and I have seen that some people are cutting the runners in the intakes down in order for more power in the upper ranges. Anybody have any more information about this? My motor is stock, would cutting the runners help or hinder? Any links or actual information would be greatly appreciated. Thanks
 

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Cut mine back as far as possible,gasket matched ports and radiused injector wells for better shot at port. May have lost a little off idle BUT it really comes to life above 2000 rpm.
 

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From what I read when I was in this situation a few years ago, cutting much off the length reduces the off-idle torque to the detriment of drivability, so I just smoothed the walls on mine, cleaned up the ends of the runners, which are roughly cast, but easy to shape to a smooth trumpet, and smoothed the bosses around hwe injectors. Definitely felt more responsive afterwards, but then the new gasket may have been influencing that.
 

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I cut mine back last month based on this DTO thread about intakes and elk hunting and this DT thread. While I was at it I also changed the cap, rotor, wires, plugs (Autolite 3923), and thermostat (180 degree).

I cut back the divider as far as I could and 1.5" off the runners (at the back):


I hooked up my trailer for a trip and there's definately more pull in the 2,000 - 3,500 rpm range where I spend my time when towing.
 

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Discussion Starter · #5 ·
please define gasket matching ports? and where abouts to I smooth out for the injectors? Any detrimental after cutting the runners down? Less power between idle and 2000rpm but a lot more power after 2000rpm? Are you happy with the outcome of cutting the runners?
 

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Gasket matching -- using the intake manifold gastkets as a template, open up the port to match. Usually you do the intake and head for smooth flow.

The injectors spray down a straight port and some people (not me) flare out the port and clean up any flash.

There's no downside -- it idles fine and pulls better. Fuel economy is the same. I'm suffering from the death flash so the next step is a programmer to fix the timing.
 

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Discussion Starter · #7 ·
will my 99 have that egr wall in the intake? Did you use the cutting wheel to open up the ports to match the gasket or a grinding wheel in a dremel or something of the sort. Any guess on the amount of power gained from these mods? It just offers a more free intake to get the air and the fuel to the cylinders faster correct?
 

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The divider disappeared some time after 1998 but I don't know when. Cutting the runners lets the intake breathe better (it's a little constricted) and it effectively shortens the runners which moves the peak power to a higher RPM. Now the runner length matches what the rest of the engine is doing. I'd guess that all the mods -- intake, thermostat, plugs -- is good for 20 - 30 hp.

To cut off the runners I used a recipricating saw (e.g. Sawzall) with a 6" blade. A 14tpi wood/metal blade works pretty good with aluminum.

edit: my truck has a 318 and auto.
 
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