LSA Question
How in the world did my post turn into pro stock engines, 128 formulas of which I have no idea of what it all means and probably doesn't apply to my particular set of goals. I thought that I had asked a simple question concerning the lsa of cams for the street. I'm looking at Howard's cams and they have one that said it has very strong torque. I believe it's .479 / .494 x 255* / 261* duration at 0.050" is 204*/214*, lsa is 112*. I know that it's not much more than the factory 360, 318willrun did a 360 with similar specs and he got 12.80's from his 360. Any suggestions on a cam that's close to the 340 grind and that would help throttle response and low to midrange torque would be helpful and if a stall converter and gears are needed that's fine. I don't mean to sound disrespectful here or anything but my question blew up into something that I don't understand or even ever heard of. I hope that the rest of the comments will pertain to the question at hand. This is going to be nothing other than a street cruiser and no track time what so ever. I thank everyone for their help.
Dan, you asked a question. Part of the answer is to find the video from David Vizard on his Powertec 10 channel. He explains very well and simply in two separate videos; What the Cam Manufacturers Get Wrong and there is another that discusses the 128 formula. In his book How to Build Horsepower David goes through the formula. It is very easy to understand. Some on here have posted about IVC and its relation to cylinder pressure. To understand the valve event timing requires a lot more knowledge than what you appear to have. Now I am not intending to be insulting by that statement, only expressing what you appear to know and not know.
The formula is 128 - (displacement of one cylinder ÷ (intake valve head diameter × .91)). This breaks the starting point for LSA down to a simple choice to understand.
A number of years ago I called Engle Cams regarding a cam for a 351W for my 1980 full size wagon for strickly street driving and intended to try to increase fuel economy. I had been looking at the prevailing noise indicating going to a 112° LSA. The tech talked me through it and suggested they grind on a 109° LSA. This worked out very well.
210°/210° @ 0.050, 256°/256° seat timing and 0.472" lift on both, ground with 109° LSA and 4° advance. I eventually parked the car and a friend talked me into selling the car to another friend to use mechanicals for his 1948 Mercury truck. Only thing was the first friend was adamant to rebuild the engine which ran well and did not burn oil. I insisted to get the cam and lifters back. I have the lifters stored in a 2 x 4 labeled fon and rear so the lifters can go back on the same lobes.
So on the 351 with the 1.78 emission intake valves it works out like this;
128 - (43.875 ÷ (1.78 × .91)) = 128 - 27 indicates 101 LSA. Pretty tight.
Now let's try that on my 0.020 over 289 and installing LS 1.9/ 1.55 valves:
128 - (36.43 ÷ (1.9 × .91)) = 128 - 36.3 ÷ 1.73 = 128 - 21 = 107° LSA. Now that cam lifts the intake valve fairly quickly and with 1.72 :1 roller rockers definately is guick off the seat. According to David Vizard this allows to increase the LSA by about 1°. With a back cut on the intake valves we can increase it a bit more. I also plan to increase the CR to about 11:1. So now the LSA is looking to be close to optimal for the 289.
I hope this makes some sense out of this for you.
Billy Godbold's book on highperformance cams and valvetrains is informative, but much of it passes over my head. I need to read it a few more times. Through his extensive knowledge earned by being a leading engineer with Comp Cams, he approaches the topic from opening and closing events. Without that intense knowledge we are peeing into the wind.
David Vizard is a friend of Billy Godbold due to years interacting in the high performance industry and says he intends to read Billy's book when he can find time. I am interested to know his opinion. It would be interesting to here them discuss their thoughts on eachother's selection process.
