63mako

This seems to come up quite frequently so I thought I would post this.
To figure this you take the advertised intake duration and divide by 2.
Then you add the LSA to this number.
Then you subtract out the ground in advance.
Then you subtract 180
We will assume the cam we are installing is installed straight up.
This gives you an actual intake valve closing point to use in the DCR calculator.
Before someone jumps on this, I do realize that some manufacturers uses different lift points for advertised duration but almost all are figured at .004 or .006 lift. This is close enough to get you within a degree or two of the actual intake closing point.

63mako

Just refreshing this for those who need it.

Ralphbf

Thanks 63Mako

R~

MotorHead

63 Mako, nice easy explanation

As far a people "jumping" on posts they need to get a life and a job. I once had someone make a big deal when I called my engine a motor, they had to tell me "Last time I looked a motor was an electrical device" give me an f'ing break and go out for a walk.

I believe you are trying to help as I always have. Not trying to tell everyone how brilliant you are we are just trying to help those that may not know something.

I noticed that things get muddied when talking about building engines when it comes to what type of motor you are trying to build and what purpose the "motor" is going to be used for, this can vary from stock to pure race, this I believe is the sticking point.

Vortec heads have their place all the way to 245cc AFR heads, there's a huge difference between the two and I think this starts many misceptions, you, me, Gkull, Billa etc. have our own ideas and it is up to the person asking the questions to decide which advice to take.

This arguing and bickering who's dck is bigger should stop. State your opinion based on whatever info you have in your head and leave it at that.

This is what I have been trying to do for a decade but sometimes I hear things that are just plain wrong or not going to help and I try to state my opinion and in most cases I try and do it civilized and lately I just don't open the thread again. I was not even coming here for months, but now if I believe I have something to add to help someone I will do so as most of us do. Not reading threads and trying to pzz people off because they made a mistake

Ralphbf

63mako
I waded through this article and when I got to the end the link was gone.
Do you know anything about it?

http://www.motortecmagazine.net/article.asp?AID=4&AP=7

Ralph

63mako

I read 7 pages of David Vizard telling you how great he is and how his genius has generated this phemoninal new chart capable of choosing a cam that is 98% or better optimal in 15 seconds even if you have no clue how an internal combustion engine works and got sucked right in to the article. I was anticipating something groundbreaking and got nothing, nada, zero, zip other than the last page where he says he can choose you the best cam for your application with his propriatory program for $200 an hour. Sounds like a great deal. If it is that easy sign me up for 15 seconds of Vizards time on my next build. If you notice he also says in the text this infomation is in the most recent issue of 'How to Build Max Performance Small Block Chevy's on a Budget'. I have no doubt David Vizard is very competent in cam design but the article appears to be nothing but a commecial for his services or purchase of his new book and some serious ego stroking.

Ralphbf

He is very proud of himself isn't he.
It must be a tough life when everyone tells you how WONDERFUL you are.
Ralph

MotorHead

I have never read anything he has to say. There is one book I will vouch for and that is "How to build the small block Chevrolet" by SA books

Crepitus

Amen!
Mako thanks for sharing the equation.

63mako

For those that need this.

68post

Thank you, alot of cam co's don't list their valve events , or they list the .050 only.

No "cam sticky" ??

Maybe that's next !

gkull

I'm going to have to dig around and find my custom cam cards. I don't think that they have advertised duration, but I will look tomorrow. Do you have a formula bases on .050 duration?

Mako, I am just in the process of putting in a smaller motor in my Vette. I have to rebuild my Motown. It was an oil burner. I file fit all the rings to .018 and I measured a few and they had opened up to .028 -.030 But you can still see the cross hatch honing. So the block is getting the beater ***** and a hot tanking. All the bearings look nice for cleavite H's If anything slightly thinner on the tops of the rod bearings. Which could indicate too much timing and building excessive pressure. But I find that hard to believe using only 34 total and either 5 or 10 on the vacuum advance dial switch. Have you seen more ware on the surface coating on the tops of the rod big ends before?

63mako

You need the intake closing point to figure duration. With varying ramps duration @ .050 won't give you the info you need. This formula is not exact but real close. It assumes symetrical lobes. If you look at various cam cards you will see it is right there, close as you can get to figure DCR.
Pull apart a 1/4 mile SBC and you will have the same wear at the top of the bearings. You have a lot of compression and are not easy on it, I would call it expected wear. That is what sees the most pressure.
Are you putting your spare 383 in it?

resdoggie

Thanks 63mako for your simplified formula for calculating IVC point. I used this formula many, many times for different cams and DCR calculations. My new hrc is on its way and I can't wait for spring to arrive and try it out. Btw, what brand of rod/main bearings would you recommend for a 355, +450 hp build?

gkull

Yes, my 383 was a long block with intake manifold. All I have to put on it is my MSD E-Curve ignition, carb, and adjust the valves because I took the rocker stud girdle nuts off to relax the springs for storage. I Only had to run to summit racing and buy an new poly resin dizzy gear because the cam is a billet non sleeved screw job from Comp Cams.

I have to see if the poor little motor can handle .064 OD with 3.55 rear end It was kind of fun with 4.11. I have the cam card and all the specs at work if you would like them posted today.

63mako

I use King bearings now. Clevite is what I have always used in the past, Callies makes them now too but I haven't used them. GMPP has them and I am sure they are OEM type. I would say proper fit, sizing and clearances is the priority.

REELAV8R

At the risk of sounding like I'm defending him I think David Vizard is an individual who has enjoyed a great deal of success in his field of expertise. He has also had his share of failures. I think he uses his successes as examples and proof of what ever subject he is explaining. He also sites his failure as proof that he is not always right. He may appear to come off as arrogant to some. I interpret it as confident. He has achieved much in engine development and has by his own account done thousands of dyno test to prove various theories. Proving many of his theories as correct would warrant a high degree of confidence.
Much of his testing has lead to success in building engines that produce more power for less $$$ than many think possible. He then has written books to share some of this information so that others can benefit from some of the things he has learned or proved to work well.

I don't fault a guy for making a living sharing his experience to a large audience and commercializing it to expose a larger number of people to it in hopes of making money selling books. Many in the performance industry jealously guard whatever information they glean in order to have an edge on the other guy be it imagined or actual. Vizard also does not give away all his secrets.
We need guys like Vizard. None of us were born with the information on how to build or overhaul a chevy 350. We all had to learn it somehow. Learning everything from trial and error would not be feasible time wise or money wise.
So what's the problem with learning it from David Vizard, a guy could certainly do worse. There are many other books available to read. All are a good source of information, all had to sit down and take the time and effort to write and publish these books. That takes considerable effort. It's not something most of us are willing or able to do. So those that can, do, and the rest of us benefit from their experience.

63mako

He has a vast amount of experience. My comments above were based on this one article. Read it. You expect a great breakthrough and useable information and at the end it is only an advertisement for his serices and book with no charts, graphs, information virtually nothing for the guy building his own engine. As I said it is a David Vizard commercial, period. For those building a high end motor from scratch you might do well to pay him for his cam selection advice if you don't trust yourself or others. I have read and learned a lot from him over the years but this article is useless.
http://www.motortecmagazine.net/article.asp?AID=4&AP=7

REELAV8R

I know the article your talking about. I guess it was a teaser to get you to buy the book like you say. Too bad it doesn't tell you which book that is. I now know that the last page is in the book "How to build max performance chevy small blocks on a budget" Published by SA books

htown81vette

That is what I like about comp cams, they give you the angle ABDC which is what you need to calculate the DCR:



And any other cam maker should do the same (if you call them). I wouldn't buy from them if they did not supply this info cause its important...