David Vizard's Porting School Articles

[1bolt]

http://www.gofastnews.com/board/technic ... l#post4254
That is part 1 of 7 (and more to come) the other 6 are on the first page of the forum currently.

That is a link to GFN (GoFastNews.com) some will recognize Vizard's name as a omnipresent and possibly pre-eminent authority on making cars go faster and telling you how to do it, in books and mags (Hot Rod, Car Craft, Pop hot rodding and every other one just about).

I'm impressed that he would post a series of articles on a free web forum, even if he is connected with GFN (I think he owns it or something).

[Alex22]

School's starting again soon so I'll read through them in a week or two, but just skimming through them quick (pictures only and captions) I can see one thing I don't agree with. I will read the last two articles on porting before I jump out and knock him. Most of the stuff does look like good info.

~Alex

[1bolt]

if you've got something to knock him for I hope you're carrying some pretty serious credentials yourself.

[John]

Vizards works is the basis for my chasing that 5th cycle and concerns for flow & velocity viewing the system as a hole. A most excellent article, http://www.stockcarracing.com/techartic ... index.html
John

[gradon]

Reading that makes me want to install bigger valves(I still want 1.97in and 1.6ex) or 1.7rrs and advance my cam 4*. I'm never gonna get that m3 if I keep modding the stroker(at least it's comparable--the 30s, ie 330 & 530, don't have nuttin on my 4.6, but I have yet to go up against a 3.2). So how are you gonna experiment with tuning the 5th cycle John(diameter, length)?

[dwg86]

According to that article ,our stokers would need a LCA of about 104. That seams really tight, and I don't think that would be enough vaccum for the computer controlled EFI. Interesting reading....

[dwg86]

Another thought...maybe thats why the Mopar 30AB cam makes good power(comparing desktop dyno numbers) to other cams. The Mopar 30AB cam uses smaller lift and duration than most other cams but makes about the same, if not more, HP and Torque than other cams with more lift and duration. The mopar cam has a 108 LCA, while most other cams use a 112LCA. The 108LCA is closer to the 104 that the chart says to use.

I think Gradon used a Mopar 30AB. YO Gradon...how is the cam working with computer controlled EFI?

[gradon]

It's working great. According to the PSC1-002, with the internal 2.5bar map, I'm pulling about 17"hg at idle, so it's a lil lopey, but sounds nice and wakes up about mid 2Ks and keeps pulling(I haven't gone above 5K yet). I never did get those results from flash that you got with the 30ab and 1.7rrs(did he advance it 4* also?). I still wish I would've had the $200 to buy those mopar ss tulip valves in the above sizes, but maybe sometime down the road. . . I too figured that we should have 104*lca according to that article and 106* if you have the 2.02"in.

[dwg86]

Well 17 hg at ilde sounds like plenty of vaccum. I don't know how much a stock cam has, or the computer needs to see. I am really confused about choosing a camshaft right now

[dwg86]

Just thinking...It seems as if the vaccum issue has to do with overlap and not LCA. If you use a smaller duration you can narrow the LCA and reduce valve overlap and not affect vaccum. The more duration you use, the lobes have to further apart, or have move LCA, to reduce overlap. Am I thinking correctly?

[gradon]

Well the early cams(87-95) have 270* advertised duration and 197*@.050(many use the @ .050" duration measurements which is lower than advertised, mopar never advertised the @.050#), .424" lift in/ex, 46* overlap, lobe separation angle 112*, intake centerline angle 120*. The 96-06 cams have 256*in, 260*ex, 188*@.050in, 192*@.050ex, .408"in lift, .414"ex lift, 43* o-lap, 107* lsa, 114* ica--this cam has lower in-lift than the ex-lift(still less than the earlier one) and the ex lift has a longer duration than the in-lift. Now the mopar 30ab has 256* in/ex duration, .45" lift, 40* o-lap(less o-lap means it builds more pressure cause the intake valve shuts earlier), and 108* lsa and ica. Dino has a good 4.0 cam comparo @ http://www.angelfire.com/my/fan/Jeep4.0Camshafts.htm . Most of those cams have >110* lsa and bigger o-laps. All the mopars have 108* lsa. Even if you couldn't get the 30, a 29 and even a 28 would be good(esp w/ the 24* o-lap--probably pretty torquey) and you could always use 1.7rrs to increase the lift more and they have the same wide lobes as the stock cam(you could use them too with the 1.7s). So yeah just because a cam has long duration, doesn't mean it has high lift, doesn't mean it has big o-lap, doesn't mean it has big lsas, etc. . and then you get into advancing--choose one wisely. I had no idea how mine would handle 10:1 SCR, 8.5-6:1 DCR, so I installed mine straight up. Now that I know it doesn't ping and keeps strong up to 5K, I'm curious how it would handle 4* of advance which would bring DCR up to 8.7:1 and move that powerband down some hundred RPMs.

[John]

Reading that makes me want to install bigger valves(I still want 1.97in and 1.6ex) or 1.7rrs and advance my cam 4*. I'm never gonna get that m3 if I keep modding the stroker(at least it's comparable--the 30s, ie 330 & 530, don't have nuttin on my 4.6, but I have yet to go up against a 3.2). So how are you gonna experiment with tuning the 5th cycle John(diameter, length)?

Take a good look at when valve shrouding really kicks in and starts a diminishing return on flows. Trace a pattern of a cylinder head, run a transfer punch down the valve guides to mark the centers. With simple drafting tools you can draw any size valve and get a feel for what needs done. Try sketching a intake valve of 1.960" and exhaust valve of 1.55". Much larger than that you will see the need to narrow the centers of your guides...
I am aggressive in tuning intake and exhaust flow characteristics, I do not have a good flow bench set up but had good teachers in the use of a manometer. A good infrared thermometer will give you more information about your exhaust system than most will consider. Cam selection is a important part ,yes, but only a part, To stuff much more fuel/air into the system by utilizing the timing events and the vacuum pulses of the exhaust to power it. We are improving the efficiency of the system. Significant gains are easily made by sizing selection, length of tubing, high flow cats, muffler choice. I think most are upgrading their intake system to improve flow volume and velocity, too many only consider the sound of a exhaust system. There is a good article on tuning a exhaust system. I will try to find it. For this motor I like to keep the header tubing small and do not increase the the collector size until I enter the 2.5 inch muffler with a adapter that is a inside fit to the muffler, reducing to allow the collector diameter to fit inside it. the inlet pipe fits very deep into the adapter to end with adapter and pipe ends both arriving at the inlet edge of the canister (muffler) entrance. Remember the step at the head exhaust manifold and why it is there. Here it is again.
John