I used Vizard's teachings from this link:

http://www.gofastnews.com/board/tech...er-issues.html

and particularly the chart captioned: "Pinch Point Shape Variations"

I modeled my ports after example #4.

The $ 64 question is, what cross sectional area (CSA) do I want at the pushrod pinch point ?

But that is not such a simple question, since it is not the total surface area that really matters as much as the distribution of the surface area in the port opening. See in Vizard's link above, the port velocity map. It's most "busy" in the top half. Remove material there and you gain flow without losing bottom end Tq.

So, what CSA do I want ? I don't know, throw a dart perhaps, but it's also good to aim for a proper and effective air velocity in the port, and a number accepted by many as being good is mach 0.55. Courtesy of grumpyvette on another forum:

here’s a chart FROM THE BOOK,HOW TO BUILD BIG-INCH CHEVY SMALL BLOCKS with some common cross sectional port sizes
(measured at the smallest part of the ports)
...........................sq inches........port cc
edelbrock performer rpm ....1.43.............170
vortec......................1.66........ .....170
tfs195......................1.93........ .....195
afr 180.....................1.93............ .180
afr 195.....................1.98............ .195
afr 210.....................2.05............ .210
dart pro 200................2.06.............200
dart pro 215................2.14.............215
brodix track 1 .............2.30.............221
dart pro 1 230..............2.40.............230
edelbrock 23 high port .....2.53.............238
edelbrock 18 deg............2.71.............266
tfs 18 deg..................2.80.............25 0

Turns out that if I want max HP to occur at 5800 rpm, then my CSA needs to be about 2.07 which will give port velocity of mach 0.55 @ 5800 rpm, unless I've made a math error, but I checked it twice.

Problem is, the stock LT1 manifold, although heralded by many as being really good, is quite limiting. I measured a CSA in the ports on the manifold to be 1.8, which means I need to open it up if I want it to not be limiting to my heads once I've achieved them to be 2.07 CSA. And I can't lengthen the manifold ports vertically due to the injector bosses, so .125 will have to come off of each side wall.

Then I run a cam with an LS6 grind. LS6 has same rod/stroke ratio as LT1 and also compression is about same so that cam should be as matched as it gets.

I'm hoping it should be good for just over 400 ponies, and using an emissions-friendly cam with good manifold vacuum and economy and should have maybe just a little less Tq than an LS6, but with the added advantage of reverse cooling, including no sharp edges in the chambers, especially those incorrectly factory installed seats. The LT1 should be able to beat an LS6 when done properly because of the reverse cooling, if the limiting factors present in the stock configuration that un-did its benefits are remedied.

Anyone else ever get into Vizard's writings ? I read that stuff over and over !!

 

I read just about every Vizard article I could find, even got one of his books and borrowed a few of his other published writings from a friend, before I started work on my heads. I am especially intrigued by the 30* valve seats he uses, although I opted for the traditional 45* seats anyway because to make a 30* cut on my seats I would have had to have new seats installed to keep from setting the seat too deep and hurting flow with too much shrouding.

He's a good one to read. I'd also suggest looking for any of Lloyd's advice posts. He goes by nighttrain66 on here and several other forums, and he's ported more LT1 heads than I've even seen. He's another one who will offer good real-world helpful tips.

 

yeah, I like Lloyd's style alot too - no bones about it, although he does dance a bit around the fire whereas Vizard seems to be more revealing about numbers. Probably since Vizard has made enough cash from book publications and can't be financially harmed from releasing secrets whereas those still in business need to maintain some secrecy. Trouble with selling heads is that once you sell them, the market is free to measure dimensions and publish it - no trade secret or patent protection available. That's one competitive business I wouldn't want to be in but I respect those guys alot, especially Lloyd based on what I've come to understand about him from reading his works. thanks alot.

 

speedtalk.com, the pros all post there including Vizard himself. Dont think youll get your question answered here

Edit: shoot us a link to your thread to follow...

 

And this guy is a good one to talk to too...

 

YEP!!!!

Read them all in preparation for my head rebuilt / port polish. In fact I ordered this last week - " How to Build and Modify Chevrolet Small-Block V-8 Cylinder Heads by David Vizard" It is supposed to have detailed info on porting the L98 heads....(got it for $39 used...have to watch it, it gets pricey)

 

that's money well-spent, you'll get far more than $ 39 of value out of that book. Once you know how to make the heads you want, you'll have a pair of heads that would have otherwise cost $ 2500 if you do it right and depending on your needs.

I think the most important thing to start with on any motor whose bottom end isn't going to be modified is the static compression ratio. Then, figure where you want your max HP to occur, which should be around 5800 rpm, determine the port CSA necessary for a good peak air velocit, then pick a cam that will give the highest DCR you can run based on cooling capacity (t-stat) and the fuel you'll be using.

In the heads pay careful attention to the exhaust valve, its seat, and all sharps in the chambers must be removed. Got to get that exh. valve to run as cool as possible to minimize preignition and I prefer to use a seat width on the wide side of the range. I want to run sodium filled exhaust valves but LT4 valves are a bi*ch to find at a reasonable price. Also, paying attention to the quench height is paramount, one trusted source shows a 7HP increase for every 0.010" reduction from above the max desirable. My piston-to deck clearance is about 25 thous and stock head gasket is about 50. When I go to the 26 thou thick gasket I should pick up about 15 ponies plus a little more from the compression increase. I wish I had a set of LT4 valves and am still looking. Fortunately I have the leisure to do this slowly. Details, details, details.

 

It is not nearly that simple.. I have designed heads as well as port them though have not in the last 19 years since i went into the efi biz.. Companies were wide and varied and all for racing including for GM.. Without knowing peak and mean airspeeds you really don't know anything at all.. BTW mach .53 is the critical pressure ratio where you don't flow any more.. It isall about getting the air speeds correct at the right locations in the port you do have to slow it down in the valve seat area and map piston speed / demand every degree of crank rotation and never go over mach .53 or the port will stall. I have tons of workbooks I wrote for Mathcad that work well and while not for sale all the math is available to anyone willing to look for it. You are right about the area thing it is the reason for raised port heads and high included valve angles.. If I were serious about building a tpi based engine the first thing i would try is 6 inch rods to get the peak flow lower and extend the rpm range. GM uses 5.7 because they always did starting with a 265 all the way as far as i know to the LSX series engines don't have any idea what they are though. Here is a big clue do a web search on MIT and Heywood and you will find more head design info that you can read in a week and it is all the real deal stuff pros seldom talk about..

 

Thanks. Do you by chance know what the air velocity is in stock LT1 heads on a stock-cammed motor ?

LSX rods aren't 5.7. There's a real strong reason in favor of using a 5.7 rod in 283-350 sized engines. I'm surprised you didn't mention it - it relates to forces on the wall and piston speed near TDC and BDC, and longevity.

Also, mach .53 is not a pressure ratio. Being a speed, its a ratio of distance over time. Pressure is typically measured in units of force per unit area.

Raised ports were used on LSX because initially it was believed that this would provide better mixture by spraying the fuel directly at the valve, but GM later changed its stance on that after figuring out it wasn't that critical after all.

"Without knowing peak and mean airspeeds you really don't know anything at all." - I wouldn't agree with that. Just a couple tidbits of what I do know is that the stock head port openings are too small for my wishes, and I also know what the CSA's of a bunch of heads out there being marketed by AFT, Dart etc. are. I'm not out to be Einstein on this, just having a little fun. If others think I'm clueless, I'm ok with that.

 

Dont think he meant to say youre clueless...
Think in general what he is saying is there is a science to porting, (every car and motor will want something a little different) much of it we will never hear of, the top ones out there will never part with the info, its just the way they are; wont find any of this out from most boards or any printed articles..maybe enough to give some good basics thats about it.
Believe me my mind is boggled when I speak to one porter/cylinder head designer in particular, it seems it would take a lifetime to become super good and they are still "always learning". Science of cams/valve timing?
Think thats why they see stuff about home porting and shake thier heads when they see guys using broken drill bits, files, S.A. kits from Summit, etc
Ive gotten my butt chewed out more than once from a "certain" pro from making noob mistakes. Thats how ya learn though

 

Here ya go dude:

http://speedtalk.com/forum/viewtopic...=184010#184010

 

Yeah, science. But a lot of art mixed in there too. People still argue about whether 3-angle valve jobs are really necessary. Its by mistakes that we learn allright. Some suggestions I heed, others I ignore, like all of us. I think its nice to receive constructive criticisms that just don't tell you that your're wrong, but rather provide an indication of why one is wrong and what the right answer is, instead of a blanket statement that "there's more to it". Of course there's more to it !!!!!!!! People write books on this stuff. Vizard wrote a couple dozen !! But, if I've missed any critical points within my control in my above writing, I'd sure appreciate knowing what they are, although I think I've now reached a point of comfort. I'll put the CSA where I think it needs to be, pop a cam in that baby and be done with it. Whether it could have been a little better, well, probably could always be better, but at least it should perform substantially better than stock, and I did it myself, whatever the outcome !! thanks alot for your pointers in your postings cuisinart.

 

 

Check out the exhaust valve and seat on the new Eliminator heads

 

Not to steal the thread - but..


Very interesting....I had some thoughts around quench and compression ratio -

The rest of my build is a FIRST intake, comp promag 1.6's and a Crane 114142, and headers (heddman or hooker).

Crane 114142 specs:
Basic Operating RPM Range 1,800-5,600
Intake Duration at 050 inch Lift 216
Exhaust Duration at 050 inch Lift 228
Duration at 050 inch Lift 216 int./228 exh.
Advertised Intake Duration 272
Advertised Exhaust Duration 284
Advertised Duration 272 int./284 exh.
Intake Valve Lift with Factory Rocker Arm Ratio 0.454 in.
Exhaust Valve Lift with Factory Rocker Arm Ratio 0.480 in.
Valve Lift with Factory Rocker Arm Ratio 0.454 int./0.480 exh. lift
Lobe Separation (degrees) 112

I was thinking of going with 0.28 head gaskets to finish it off -do you think that works with this cam? I am hoping for between 10 to 10.5 :1

 

Very true. My intent with my heads is to learn, and hopefully with the basic stuff ( no major re-shaping) clean them up with bowl blend ect. I am trying to avoid putting out the cash right now, and will buy GOOD heads when I get around to buying them (buy them once).

 

If you're not changing the pistons or the chamber volumes, I think you might want to consider determining what dynamic compression ratio to shoot for based on the fuel available and temperature the system runs at. See the Wizard's chart towards the end of this article and work backwards from it using your current static CR

http://www.popularhotrodding.com/tec...ech/index.html

and I think that will be helpful in enabling you to choose which cam is best. You can incorporate your gasket change into the equation easily. You might find the cam you mention is right for the job, or you might find its not, or that its not that far off. good luck !!

 

Very cool - will look that up. I already have the cam (got it for nearly free) and I know it is not the most ideal for making big power - but I have another constraint , and that is the car is an auto with 3.07 gears and stock stall (2200 I believe for an 86). I can't really go much bigger without changing gearing / converter. (only slightly larger than the recommended one for TPI's by Grumpyvette)

 

Grumpyvette = wisdom and experience

 

Without getting into a peeing match I am offering what really works.. trying to give you the shortcut to success from someone that has learned the hard way it is all in the math and not what looks or feels right. the 5.7 rod is for economy of manufacture on automated machinery and existing tooling. If an engineering decision why not increase rod length with stroke to keep the rod ratio the same and the geometry the same. They use the same rod in strokes from 3.0 to 3.8 inch.. No engineering there at all. Air speed has a pressure related to it, 'static pressure' it is how the speed is measured look at an airplane sometime. At mach .53 the static pressure in the port causes all sorts of problems that I don't have the time to go into and offered where to find the info. The short story is air goes from laminar to turbulent to compressible flow as the speed goes up and related to those changes. You should care about airspeeds both peak and mean it is how the engine works, it is all pressure differentials at the end of the day.

Here is a link for you this 'mechanic' wrote a few books and a zillion papers buy the one on fundementals and you will change all your thinking as to what is important and why.

http://meche.mit.edu/people/faculty/index.html?id=43