Contour Enthusiasts Group Archives Forums Modifications Duratec Performance Modifing a 2.5 non-SVT UIM

Was out at the junkyard today and picked up a non-SVT UIM for 10 bucks. I'm planning on porting the holes larger myself, but I'm not sure on how far to go. Talking with my cousin he said the best way to go is to gasket match the manifold for best air flow. I did a little searching but couldn't come up with exact numbers on how big they should be ported. And I don't have the money to pay $$$ to have it done. So if anyone could chime in the knowledge would be appreciated.

Your cousin is right. Gasket matching is a tried-and-true method that guys have been using for 50 years. Put a gasket on the surface, scribe a line to port to with the gasket as a stencil, and take out no more that that. Look at it this way- even if you took out more, if you used the same gasket, the flow would still be limited to the size of the gasket.

-BigC

this is good advise, follow it. unfortunately with the design of our upper intake manifolds without cutting and rewelding(ouch!) they cannot be fully ported with dremel tools, only Extrude Honed. this is what i know, others will probobly chime in.

Bad advice of every account and every statement thus far.

The UIM to LIM gasket is FAR LARGER then the ports on the LIM. Even a RLIM.

Gasket matching would be the epitome of STUPID because it would cause the LIM to lip into the airflow and the poorly ported UIM.
The LIM inlet port should be a hair larger then the UIM outlet port.

Also for that matter ON ANY VEHICLE gasket matching by itself is a joke. Matching the opposing port size is what you want to do. Matching to the gasket is pointless as it usually RUINS the flow and symmetry of the port shapes. PERIOD!

~~~

Also to answer the main question even though it's been answered 100 times already.

You are NOT going to make any real difference honing out the UIM. The UIM does not allow for the ability to accurate and completely enlarge the ports. This is why the Extrude Hone process was & is used on the manifold to increase it's volume, flow ability, and to make they flow ability uniform across each respective port.

I think what demon ment is that if I gasket match the UIM it will fudge up because the LIM with be much smaller thus creating a major retard in the air flow.

I was thinking about what demon said and I was wondering what if I port the primary larger on both the UIM and the LIM. Or would this still not have any effect???

Every case may be different. I have port matched many engines by matching the gaskets, but others I have done differently because it was obvious that the results would not be beneficial. You really need to critically inspect the pieces involved to make a determination. I have not tried to do so with the Duratec.

I believe that porting the intake by cutting it open for access then welding it shut when finished is doable, but the skill needed to port such long ports as well as the hassle and expense of properly welding everything back when finished is beyond the level of most nearly any entry level hot rodder. I have helped do it on a Ford 302 but it was so much work that I would not likely do it again. It really did wake up the 92 Thunderbird we did it to though. The Mustang manifold would not fit under the hood and the Thunderbird manifold was very restrictive before we started.

hmm I need to do some thinking on this and I come up with something tomorrow because I worked 12 hours today and i'm beat. oh and i'm off to work for 6 in the morning. So we can fight this out tomorrow guys lol

I already mentioned that I didn't know much about the Contour/Duratec. My argument was not about the Contour. Great information regardless.

More often than not, gasket-matching is glorified by its gains. It would not be listed in and explained by such large publications if it was such a "joke." Your speculations are just that- speculations. Your opinion is noted, and I'll stand by a method I have always been satisfied with. The struggle for extra power in a motor by car enthusiasts has led to lots of modifications that many view as frivolous. This modification has proven time and again to add horsepower and improve airflow on vehicles.

I never said that you "should always do it to every engine" either. You said, "Enlarging it to match the gasket when it alters the design & flow of the port is bad and will always be bad." That is one of the least intelligent statements I have ever read. It is common sense! Rough castings often restrict flow, and cause excessive amounts of pressure and resistance. By smoothing out said castings, better flow and increased velocity OFTEN result in HP gains. This is true often in intake manifolds, exhaust manifolds/ports, cylinder head ports, and even rough oil passages. Ever notice why aftermarket components such as these (aftermarket cylinder heads come to mind) often come with machined/polished/bigger surfaces/ports?

I can understand your arguments, but to say that this is a waste of time is a stupid comment. This porting and polishing by itself may not add huge HP gains, but the increased flow supplements other parts of the motor, and combined with bigger modifications, can make major differences in power. That's why people do it.