I'm running a T78 w/ GT79 wheel and decided to open my ports up some more since my last motor was mildly ported for twins. Before I put her back together I wanted to ask for everyone's opinions. Any suggestions? I'll post my intake ports tomorrow.

If you look closely at the last pic, you'll notice that I have room to probably square up the top of the port. What are the advantages and disadvantages to doing this verses keeping more of a "D" shape?

 

Bueler?

anyone?

 

Looks neato!

 

Eric,
Thanks for bringing the dremel over last night. I'm going to knock the rear housing after I get off work. I just picked up some hylomar, rtv, and carb cleaner on my lunch break.

I'm really tempted to square it up a little more.

 

No sweat!

 

PM Rice Racing.

 

there's really no advantage in using that d shape. just square it off more to increase the area of the exhaust port.

 

I personally would leave it, just to leave a slight mismatch. Anything to help prevent gases from flowing the wrong way.

 

My intake ports look pretty mild in my opinion. Do you think I ought to open them up also?

Where am I going to see the largest gain with the large turbo? Opening up the exhaust more, intake, or both?

Basically, I'm asking if I leave my intake ports some what mild this exhaust port where are my gains going to be over the mild exhaust port I used to have?

 

are you're intake ports already ported or are they stock? if you have a mild street port on your intakes, you can still see a gain from cleaning up that exhaust port. all you really need is a light touch-up on the upper edge. the larger exhaust port should help spool up your turbo. if you wanna open up the intake just a touch, you can delay port closing of just the secondaries, and just leave the primaries alone. this way you still get good port velocity through the primaries for a little better low end. and you'll get that extra cfm through the secondaries, and by delaying the port closing instead having an earlier opening you get a little less overlap.

 

I'm not by any means experienced on porting, but I have talked to many people who have, Jim Downing's engineer, Roger Mandeville, and my Formula Mazda engineers and mechanics. What I picked up on exhaust ports is that the D shape is essential to providing the best flow for exiting, expanding gas, in other words less turbulence. Yeah, more of a "hole" that fdracer is suggesting seems logical, but there will be less efficiency in removing that exhaust gas from the chamber because with the D shape, it creates not only a straighter exit for the exhaust, but also pulls the exhaust out faster with vacuum (similar to a piston engine with and without headers, and different header configurations). If you think about the way the apex seal opens the chamber to the exhaust port, having a nearly flat opening creates the most efficient exit for the exhaust and as the next apex seal is closing the exhaust port, the D shape will cause the exhaust to converge toward the center of the apex seal and we all know that the combustion chamber tapers this way as well. So leave the D shape and I believe you'll have more power as well as faster exhaust flow which will equal quicker spool up. I apologize for not knowing more information myself to let you know some numbers, but I think you'll be taking a step backwards to just open the port bigger...

Richard

Where are the pics of the intake ports?

 

Thanks for all your replies. I didn't have time to take pics of the intake ports last night. Hopefully I'll be able to take a couple pics after work and post them late this afternoon. Here are a couple pics comparing what my new exhaust ports look like compared to how they were in my last build. My last build was based off a pettit port, except I slightly raised the top of the port. Amazing how small they look. I still have a housing with a pettit exhaust port and can post a pic of if anyone is interested.

I've actually cleaned up and slightly opened the new port at the bottom more than what is pictured. Here's a pic of the before and after.


Here's a pic of a stock port for comparison

 

Your exhaust looks good, the insert edge could be tapered to the rest of the port a bit, but other than that, it's a good shape/size. Good luck on the motor.

Richard

 

I thought, and this may be completely wrong, that if your intake ports are slightly larger than your exhaust port that it helps with low end tq. Is this right? Or was I just misinformed?

- Steiner