Porting head: What to do about the "humps" in the exhaust port?

[dsm-onster]

Yep my 1000cc injectors from FIC have several (5 or so) holes for the fuel to exit. I've see the spray pattern first hand for 390s 450s 650s and the 1000s. Let's just say that I wish pure water injected out of my water/meth injection nozzles came out in that fine of a mist.

. . . However, the other side of the coin for me. . . Is it really worth it to take the time to get such a good finish. Honestly, the rough work I'm doing now feels much smoother than the casting. As long as the cut is smooth enough to take away the casting imperfections and blend in the lip, does a very small amount of HP increase merit the time it takes to get a really pretty finish? I'm not so bored as to spend hours getting 2 horsepower. Are the increases from polishing that minute?

 

[Freerevving]

. . . However, the other side of the coin for me. . . Is it really worth it to take the time to get such a good finish.

no not really

Honestly, the rough work I'm doing now feels much smoother than the casting.

A lot of people don't realize how much smoother it is after a rough cut. It's much much smoother although it doesn't always look that way.

does a very small amount of HP increase merit the time it takes to get a really pretty finish? I'm not so bored as to spend hours getting 2 horsepower. Are the increases from polishing that minute?

It probably isn't worth the time... but most people actually go back and do a uniform rough finish after their final cuts. This is actually more difficult than just polishing, since polishing could probably be done blindfolded.

IMO polishing is advantageous in three ways: 1) it's easier than going back and doing an attractive rough cut. 2) It prevents carbon/oil buildup in the intake, and 4g63's are notorious for this. But the main thing is 3) Polishing can actually be used as a tool between touch-up cuts because the reflective surface will expose low spots, flaws, and irregularities... You might add a fourth benefit of a couple/few more horses, but to me polishing just makes it easier to have a high-quality result.

 

[mach4g63t]

Your third reason is really good!!

I've done that many times on things I've ported; seen the low/high spots in the material and gone back to working on that section a little bit more, polishing again, and getting everything uniform. Then again, I'm really meticulous when it comes to porting things out. I would be the idiot who polishes his intake for the shine (and the prevention of build up, that's the whole reason I do it on the exhaust)

 

[dsm-onster]

Thanx freervving! great information!

 

[gixrman]

How rough is the finish on a CNC head? Do they go back and "rough" it up. Also does the finish matter on a pressurized motor compared to a N/A since a N/A motor uses vacuum to draw in the air fuel charge. The added heat and pressure must change flow and atomization.

 

[mach4g63t]

Get any further? Any new pics, info to pass along?

 

[dsm-onster]

I have a blog about it, I'm bored and I have a minigrinder. Hmmm. . . . I will be porting the intake side next: just blending the seats and portmatching to the intake manifold. I havn't had a chance to do the intake ports yet. I will be posting up the difference in volume flow via dsmlink logs (the rest fo the setup will be identical).

 

[assault187]

Sorry to bring this back although it is very informative, but I didnt want to start a new thread about head porting. I looked at my head (ported) and noticed that on the Intake side, who ever did the porting flushed the valve guides with the flow surface....Is this normal practice? I was confused because the exhaust side (also ported) still has 100% valve guide protruding from the flow surface.

 

[Zex4g63]

Sorry to bring this back although it is very informative, but I didnt want to start a new thread about head porting. I looked at my head (ported) and noticed that on the Intake side, who ever did the porting flushed the valve guides with the flow surface....Is this normal practice? I was confused because the exhaust side (also ported) still has 100% valve guide protruding from the flow surface.

It's a way to add flow but is hard on the guides. I don't recommend it for a street car or anything that requires endurance. I usually turn the guide down in a lathe but keep the length. I know you posted about valve guide clearance and if your intakes valves have more side to side than the exhausts....this is why.

 

[Freerevving]

I wouldn't shorten the intake guides much. I especially wouldn't make them flush with the roof, if the roof is ported... they're already quite a bit shorter than the exhaust guides. Exhaust valve guides can be shortened successfully.

I'm a "better safe than sorry" person and rather use tapered bronze guides.... or leave the guides alone. I've successfully shortened steel exhaust guides with no problems, but I've since decided that I'd better leave the engineering to the engineers.

 

[all_motor_mike]

like mentioned above........... cutting the guides flush with the roof will gain u flow (i think of it as the cheater way to get cfm) but there is the posibility that it will cause excelerated guide wear, valve wobble, etc (especially int he higher rpms) and even broken valves. i have done a few heads this and i have warned the buyers in advance but the still wanted the head done that way and they have yet to have problems but there is still the chance that something could go wrong because of it. so basically u gain flow but "loose" longevity.


mike

 

[mach4g63t]

One more question about valve guides...

For those of you who have experience porting heads... is it okay to do so while the valve guides are removed? I see some of the pictures where they are still installed and get scrapped up... I'm sure that's not a big deal. I'm interested in creating thorough and continuous form throughout the head and I can already foresee the valve guides hindering my ability to get at the roof around/behind where it protrudes. Does this area really matter? Throw me some input, please.