a little insite? please - sbc porting

[sheppard00]

I'm fairly new to porting first off and totaly new to the board.
I have around 5 years and 20 sets of heads under my belt but still do not feel too confident about how "proper or correct" my portwork is. I would like to get any opinions or tips I can to help me improve on my techniques...

I have a thread on a local forum to my area with some of my work with pics.. flow #'s ect...

I'm interested in any opinions good or bad..

thank you mark sheppard

[sheppard00]

maybe i need to post a little more info... I use a makita (sp?) electric grinder with one cone, a ball nose, and a 6in ball nose cyld.. carbide bits... I also have a small pencil air grinder for getting in the small places that I use stones in... I finish my ports with 80 grit..

I know I said chevy but these are just random pics

ford TF TW 279cfm @ .600


E7TE 254 @ .550


186 DH 220 @ .500


ask me some ? I want to learn

[larrycavan]

Hi Mark,

I looked at your photos here and on the link you posted. In general, I'm a motorcycle guy and only do car heads for friends and relatives when I get involved in building their engines..... Here are just a couple of things I think are important to any porting project....

In general, low spots in the runners kill the flow.

I've found through my own experience that the size of the opening of the port exit, just below the valve seat will determine most of the flow volume overall.

I always think water when I'm porting. How the port aims the flow is every bit as important as how much it flows. Think about how the port runners can help induce a swirl pattern and the how the shape of the port exit will continue to guide the pattern being setup by the runners as the air enters the cylinder.

Just making volume happen isn't always the correct thing to be doing. If you kill a good delivery pattern while making more volume possible, the result may look good on the bench but the engine might think otherwise. How much you notice that depends on the state of tune of the engine before you ported the head.


If you haven't already done so, I highly suggest you look at


Best Regards,
Larry C.

[larrycavan]

Ooops..wrong link...try this one

[SWB]

David Vizard has a number of books on this SBC and I recommend them all.

Otherwise come straight along the outside wall and port as close to the stud hole as you can (there are sleeving kits with special studs for this) before curving back toward the bowl area. You need to widen around the short turn and on either side of the guide as well as deepen the bowl on either side of the guide, favoring the long wall (outside wall) side.

Do not lower the short side turn, but get as large a radius as you can there.

Check the cross sectional area at the throat and try to set it around 90% of the valve head area. All the areas upstreem of this should technically be larger, especially over the short side turn itself where you need the increased area to slow down the mixture as it makes the turn to the back of the valve.

Exhaust ports are simply cleaned up and detail the guide. Don't deepen on either side of the guide for most heads, it won't help.

Ford head looks good.

SWB

[68Corvette]

I have also done only about 30 heads so i am only starting to learn.

Here are couple of pictures about my sbc #291 2.02" that went 246cmf @ 28" (flowed with 32" depression).
SSR blended, more bias, roof raised to the limit, throat matched to fel pro.. more imrovement could be gained by largenin bowl a little on the cylinder side, but i wanted to keep swirl good.








This made 149hp & 130NM from the rear wheel at '93 GSXR 1100 (home made "all show no go" exchaust, stock valvesprings, stock valves, torque cam)
Head flowed 210cmf.








btw.. i have been thinkin about going to the flowbench place with my own calibration plate because my new "out of the box" Dart Pro1 200cc flowed 213cmf @ 28" @ .7"lift in his bench..
after i ported them they flowed 265cmf @ .7"

[cboggs]

Mark,

It looks like you're one the right track, .. keep at it, .. and asking questions.
Get your hands on some pro ported heads and try to look at everything.

There's a bunch to highly modified cylinder head for race applications, ..
and the first thing you should do is get a set of inside calipers so you can
measure cross section and figure cross sectional area of a port.

Once you map the area of a port from gasket to valve, .. it becomes
fairly clear where you need to work.

On another note, .. it's nice that you quoted my tech article from my web site
on your web site, .. but a credit to the author of the article might be nice

Cheers,

Curtis

[sheppard00]

Curtis sorry I didn't realize that I didn't put your name down... I have fixed it now.

a couple questions at what point does the intake runner size become a problem?

I ported a set of 302 heads for a friend of mine the final #'s on it were

--------Stock flow---ported flow
--------In.---Ex.----In.----Ex
.200---113---62----150---126
.300---140---98----190---140
.400---153---108---200---160
.500---152---110---217---167
.600---154---108---235---169

the intake runner volume was only 137cc I thought that this would be good in his 9.1 306ci engine because he isn't wanting to spend it past 6000 he is running an E303 cam 220@ .050 and .512 lift and a rpm air gap intake 650holley 3.73 gears

my thinking on this is to get as much air as I can through the ports and keep the air speed up even at low rpms on the street engine how small is too small for a specific amount of cfm.... or will this just make a mean little street engine with a broad power band?

[sheppard00]

oh yea and 68corvette what lift is that 246 cfm at your seat approach looks quite agresive... looks like a high lift head judging by your pics

[68Corvette]

[color=#000000]Yes i sacrifaced some low lift to gain up some, but it avaraged better:

[code]
lift "

[cboggs]

[68Corvette]

How does radiused intake seat lower your dyno numbers?
Does it effect peak or mostly area?

i have seen 150hp / 130NM per liter in car engines with these seats.

Do you have any angle seat vs radius seat dyno plots to share?

[sheppard00]

on the ford heads that flow 235 the mca is 1.35 as far as I can measure

[cboggs]

[sheppard00]

I use these to formulas to help guide me

Max power rpm
formula for hp rpm peak through a given cylinder head
(Min Cross Section x 185,000) / (Stroke x Bore ^2) = HP RPM Peak

forumla for airspeed through min. cross sectional area of a given head

(.00353 x RPM x stroke x bore^2)/min cross sectional area = Max Port