Ported Dart pro 1 pre platinum

[randy331]

The valve job for the sunk port #1 2.08" 40 / 45 / 60 / 75. Thanks, Charlie

Those seat angles should work well if your staying 45* seat. I'd want the top angle (40*) to show all the way around the valve.
And, I'd stay with a 2.08" valve in that head and 45* seat choice.
It takes .200"-250" to make a good transition through the throat and out through the window.
.225" less than 2.08" will give you a throat CSA of 2.61" with stem area removed. That's already bigger than your MCSA.
Staying a little conservative on port size, valve size, cam size, intake size, has always been the better running stuff from what I've seen.

And I disagree that sinking valves hurts flow, at least high lift flow.
I'm the process of re doing the valve job on heads that had new guides put in. They are sunk some more getting the angles all back, and every one of them has picked up high lift flow from before, 10cfm average, but the usual trade off, it's adding cc to the chambers. That will require milling to reduce cc, which may hurt air flow some.

But in general I agree with Knight, it's when you get into the top angle that hurts flow, that's why angle mill only. It disturbs the seat angles less.

Randy

[groberts101]

It's all a balancing act.. only so much you can do with the surrounding material and existing volumes.

Higher compression ratios(less combustion space) also helps to improve pressure recovery rate on a running engine because its all based on volume differentials. Due to the intake valves close proximity to the deck, no big surprise that 23° heads are usually kinda crapped out for pressure recovery on that side of the valve anyways. One of the great things about rotating the valve angles is that it stands the valve up/sinks the valves short side deeper into the chamber which enables improved recovery on that side of the valve curtain.

The bigger issue with sinking the valves larger amounts(not what Tony meant) is its affect on the short turns shape requirement. Some heads don't have very long throat sections to begin with and not all that much extra material to work with as the valve job gets closer to the short sides apex. Typically the further you go in with the valve seat, the more asymmetrical the throat layback will have to become. Opening the cross section up beyond optimum will reattach/quiet it back down but velocity will usually suffer during the porters continued effort to further trick air around the valve.

One change brings about the requirement for another. Then let's not forget about the fact that it's usually never considered optimum, for a couple reasons, to have the intake valve sitting much lower than the exhaust either. Optimize one part of the equation and sometimes another part begins to move towards sub-par spec's. A flow bench will often lie to you too.. a good cylinder head is all about balancing out the shortfalls for each specific application. Big bowls with well defined straight chokes work well on almost anything rpm/flow related. Maybe I'm off too far into left field though, cause I also prefer 75 - 84° bowl hogs too. lol

Personally, I'd like to see an angle milled version of both these ports with sunk seats/complimentary valve seat and chamber mod's. Even if that meant welding the chambers up to improve SCR/DCR. Cumulative results from almost every angle. Pun intended.

[Amilcar]

Randy,

Care to comment why wouldn`t you go 50*/52* on these heads?

[randy331]

Randy,

Care to comment why wouldn`t you go 50*/52* on these heads?

I didn't say I (as in ME) wouldn't but most don't seem comfortable getting away from 45*, so I was just saying if carnut is staying 45*, those angles he posted should work well.

If I was doing them they'd get a 50* intake and 52*-55* ex seats, and 2.08 valve, but I'm constantly in the minority so often I should qualify for affirmative action racing programs.

Randy

[JoePorting]

Nothing kills flow numbers like milling. Expect to lose around 3 CFM per .010" milled across each flow level.

Would that be because of pressure recovery out the short side?
Possible one of the reasons sinking the seat a tad helps?

Exactly. I would sink the valve until the top 35 - 40 degree top angle is all the way in. That should be your ideal valve/chamber setup.

[Carnut1]

0123171915b.jpg

Hard to get a decent pic of bowls and vj. Sunk both. 40/45/60/75 intake and 40/45/60/70 exhaust. I did do a bit of blending and polishing on ssr's after recutting.

[Carnut1]

0123172011.jpg

Sunk vj. Flowsheet with swirl.

[Carnut1]

0123172032.jpg

Sunk vj. Flowbench program. Exhaust lost noisy turbulence but also lost mid lift flow. I believe this is better than higher flow with noisey turbulence but not 100% sure. Still solid numbers intake and exhaust. Thanks for the help, Charlie

[Carnut1]

0123172034.jpg

stock flow vs. Last flow sheet. Exhaust curve looks like a chunk taken out.

[KnightEngines]

Nice!

[Carnut1]

Thanks Tony, you are one of the many who had a hand in giving these heads a chance to make 700.

[Carnut1]

0124171648.jpg

I am glad to be rid of the noisy turbulence but the flow dip in the exhaust curve bugs me. I decided to flow with 1 7/8" pipe and see if it gets noisy with the pipe. Sounded good.

[Carnut1]

0124171659.jpg

D.V. flowbench program adding 1 7/8" pipe to exhaust

[Carnut1]

0124171702.jpg

D.V. flowbench program after adding 1 7/8" pipe to exhaust. The flowloss dip is there but not as pronounced. Some input to the efficiency and potential of these is appreciated. Thanks, Charlie

[Biteme]

Impressive effort Charlie.
Interesting to see that sinking the seats made quite a difference.
What ss radius' did you end up using?
Did you stick with the radically laid back one on the intake?