Changing the heads on standard V6

[c2xejk]

Quote:

Originally Posted by lookin Why don't you make some intake port reducer inserts? I bet they would sell. Do I just overestimate their potential effectiveness?

On the intake side, it is a little tougher. There may well be some gain just by having a thin curved insert that follows the curvature of the port...

From my reading, such devices are often very effective at helping the air turn in the bowl... The problem would be how to mount them...

I haven't looked at something like this because my recent porting tests have had me bringing the cross-sectional area (CSA) back to stock...

I started by reducing the CSA, but the port design changes I made raised the CFM significantly. The velocity was getting way too high. So I have opened the port up to bring the velocity down to something more manageable. The result is a port that is higher and shaped differently, but with roughly the same CSA.

The air doesn't seem to have problems navigating the Short-Side Radius/bowl, so I haven't worried about an intake port insert.

[lookin]

What experts say:

Quote:

Originally Posted by c2xejk On the intake side, it is a little tougher. There may well be some gain just by having a thin curved insert that follows the curvature of the port... From my reading, such devices are often very effective at helping the air turn in the bowl... The problem would be how to mount them... I haven't looked at something like this because my recent porting tests have had me bringing the cross-sectional area (CSA) back to stock... I started by reducing the CSA, but the port design changes I made raised the CFM significantly. The velocity was getting way too high. So I have opened the port up to bring the velocity down to something more manageable. The result is a port that is higher and shaped differently, but with roughly the same CSA. The air doesn't seem to have problems navigating the Short-Side Radius/bowl, so I haven't worried about an intake port insert.

What dilettantes hear:

blah CFM blah blah short-side radi blah blah us blah ....

sigh

I'll take your word for it. Port reduction for 3.0s ..... bad ... .

[c2xejk]

Quote:

Originally Posted by lookin What experts say: What dilettantes hear: blah CFM blah blah short-side radi blah blah us blah .... sigh I'll take your word for it. Port reduction for 3.0s ..... bad ... .

Port reduction by itself is neither good nor bad. It is means to adjust other parameters... What you do with it depends on other factors, particularly velocity... Until I made some major gains recently, port reduction was a good thing. Now not so good, but it takes a flow bench to tell...

[phantomrt]

How about some bench flow numbers? Does anyone have them? 12 valve vs 24 valve.

[Ondonti]

the 24v's flow much better and always will.


but just because your heads flow more, doesnt mean things are going to be amazingly more powerful.

DOHC heads flow about 50% more then sohc 12v heads yet they only make about 10% more power (everything being stock)
Also as Ed pointed out. The SOHC 12v cams are way to small for the .24*valve diamter rule of thumb.
the dohc cams are probably larger then the rule.
Therefore the sohc heads power difference in stock form is probably 99.9% due to the cams.

both engines make peak power@5000 rpms (if you look at dyno sheets, not magazines or the intraweb benchracers websites)
With the proper cam (.430" lift or more and some decent duration) the sohc head wold be making almost the same power as the dohc engine.
If you dont like that, Im sorry.
The dohc 6g72 is NOT a honda tuned to make power @ 8000 rpms. Its a 5000 rpm torquey workhorse in stock form.

[c2xejk]

50% more, that would be ~275... So that would be more than I have achieved with a stock 12-v... 235 is my current max, but that was a little too biased towards high lift flow. The most important, but harder to quantify, gain would reduction in turbulence... On the bent my current round of heads has been much quieter than stock...

[Ondonti]

i was using a 170 stock flow to make up that statistic not 177 or whatever
I think the dohc heads flow 250+ stock but their flow drops off after .300" lift ......what do you think causes that (besides that you dont lift small displacement/valve dohc heads to .500" in real life).

[c2xejk]

On my bench stock 12v intake ports ~183 CFM... I think this is close to what Frank got (Steve M. ???)

Likely that the stock 24v port has some turbulence issues near the throat... Tends to be typical of stock ports. That limits the velocity through the throat. If the flow backs up from there or goes really turbulent I would look at bowl volume and seat shape. Once you start fixing some of the problems, other problems (like seat shape and bowl volume) start showing up...

[Ondonti]

and we measured a bad port @ 158 and the decent one @ 171

[c2xejk]

Flow benches can vary some. I have had one stock port that went turbulent at ~.4" and peak flow was off... The worse thing is flow at .4" was less than flow at .35"... That is very bad for hp even though a stock cam doesn't lift the valve that high...

[Ondonti]

the difference between those two ports was huge amount of casting flash on the short radius......thats why I tested both.
Obviously I didnt go very in depth though looking for velocities etc.