match porting, intake, exhaust..., d-jet performance gains Options

[mattillac]

i plan on taking apart my 75 2.0 to see if the jugs and pistons and heads and valves, etc. are still good. if i'm feeling brave i'll try my hand at some port matching and maybe a polish if the heads are in good condition. does anyone have any experience in using an unadjusted d-jet with a mild match\port and polish? i dont know if i gots the skills to mess with the mps. has anyone used any resistance between the head temp sensor with any gains at all? maybe i'm going in the wrong direction with this one. that wouldnt suprise me. (IMG:style_emoticons/default/wacko.gif) i've also got an open element air filter. when i find a good local welder, i'll have my ricer muffler on there pretty soon.

[Bleyseng]

I did port matching especially on the intakes. The exhaust is where all the gains can be had porting, although its kinda thin so you don't take out much. Jake has a new cam that might be better to gain hp as it has a longer exhaust duration to get some real flow=hp.
After porting,tuning the djet I have dynoed 95 hp at the rear wheels which is about 110hp at the flywheel. Most stock 2.0l dyno about 80hp to give you an idea. I wouldn't just start hacking at the heads as you can ruin a set pretty damn fast!

Ask Jake for a cam change as thats money ahead.

Geoff

[Joe Ricard]

(IMG:style_emoticons/default/agree.gif) With what Geoff said.

A little here and there is OK. Port matching is good. Even just knocking off the sand cast marks will help on the exhaust. Going to smooth on the intake will cause more harm than good.

my 1.7L motor had a great big blob of aluminum (like a booger) from the casting sand imperfection. (IMG:style_emoticons/default/confused24.gif)

[Brett W]

Port matching doesn't do a as much as many people think it does. Inside of a tube (manifold) there is a boundary layer. This boundary layer runs along the walls. This layer has a thickness. How thick, will depend, on air speed. The manufacturing mis matches usually are not large enough to penetrate this boundary layer. Thus little benfit is gained by "port matching".
Another thing to think about is port cross section change. The more times the port cross section changes the more turbulence is generated. You do not want turbulence in the ports. This increase air friction and port efficency.
The area that can generate the most benefit are not at the port entrance (on our heads). The area .500 above and below the seats are in most cases the area where the most noticable gains are to be found. They are also the area that can be messed up the easiest with a simple slip of your porting tool.
Polishing the casting flash out of the ports can help a little but unless you have huge boogers like Joe recalled, I wouldn't waste my time.

There are more gains to be had through camshaft and fuel control than a simple buff of the ports.

[mattillac]

thanks for the tips. i don't plan on grinding too much out. just want to do the port match and smooth things down a little. why not polish the intake side? i've heard that fuel swirls/atomizes better if the intake side is a little rough? is that why?

[Joe Ricard]

why not polish the intake side? i've heard that fuel swirls/atomizes better if the intake side is a little rough? is that why?

Yup that's the idea

[Bleyseng]

cuz you are running FI which sprays the gas right at the back of the intake valve. If the incoming charge has a little swirl to it the gas mixes better. On a carb the gas and air are mixed way back up stream and then you want to keep the gas from falling out of the air traveling in the manifold. Thats also why the dual carbs run well on these motors, short manifolds.
Here is a shot of a exhaust port.