Valve overlap

[west coast]

OK going to try and make this simple. I have measured my cam on lift and degrees so i know what the lift is at during every degree of engine rotation. My question is at what lift point do you calculate valve overlap and if it is measured at the lifter lift or multiplied by the rocker ratio for valve lift.So at .050 or something else. i also used Wallace racing calculator but not sure where they measure theirs at and not sure if their calculator is a standard pattern or a roller pattern for the ramps. Not getting into what it should be yet just need to know first then talk about affects and what it should be.

[John Dinkel]

I found this on the internet.

Here's an example:
Comp Cams XE294H
Adv Dur: int 294º, exh 306º
110 LSA, 106 ILC (4º advance)
Valve timing @ .006"
Int opens @ 41º BTDC
Int closes @ 73º ABDC
Exh opens @ 87º BBDC
Exh closes @ 39º ATDC

Adding the int open and exh close times (41+39) the overlap is 80º

Using the formula above:
294+306=600
600/4=150
150-110=40
40*2=80
The overlap is 80º

[Larry Hill]

On one of my cams the ex. closes 15* atdc and intake opens 15* btdc for a total 30* of both valves being open at the same time based on .006 tappet lift. This my not be the answer to your question but this is how I understand it in my backyard. It's a good possibility that I am incorrect.

[FireSale]

There's a difference between engine math (which I understand) and it's effect on performance (which I don't always) and I think the performance part is what you are after. Lunati has a nice explanation of what it means in terms of performance on their tech site. Link below.

http://www.lunatipower.com/Tech/Cams/CamSpecTerms.aspx

BTW: Those block photos you sent Brian were helpful. Now I understand why I cant easily run stocker heads on my M6010 block.

[west coast]

So it looks like there is no real standard of what lift you should measure valve overlap. Since i have a comp cam i will kind of fallow them. It sounds like you should use the numbers for tappet lift done during advertised duration which is .006. i found the web page that had the formula's that John Dinkel posted on here which work if your cam card reads valve timing at advertised duration which mine doesn't it is at .050. So now on to understanding all the theory's behind all of this.

Dale hope my costly mistake will save you money. Its hard to explain the problem but a picture is worth a thousand words that will leave you speechless sometimes.

[FireSale]

Read the Duration section of this link. It explains a bit more about the effects of duration and why cam grinders use 0.050 lift. It's a bit too long to post.

http://www.austincc.edu/wkibbe/camtheory.htm

Also this from the HotRod network:
http://www.hotrod.com/articles/ccrp-...amshaft-power/

Also: I'm going to just keep my AFR 1399 heads with the 1.9/1.6 valves that they come with. No fit issues with the BOSS302 block. If I declare the car for SS/CS I can run the Combo legally. Aluminum heads any valve size 10.5 lbs/cid. The index sucks O2 (10.30) but I have thrown t he book at my car over the Winter.

[SSDiv6]

Originally Posted by FireSale

Read the Duration section of this link. It explains a bit more about the effects of duration and why cam grinders use 0.050 lift. It's a bit too long to post.

http://www.austincc.edu/wkibbe/camtheory.htm

Also this from the HotRod network:
http://www.hotrod.com/articles/ccrp-...amshaft-power/

Also: I'm going to just keep my AFR 1399 heads with the 1.9/1.6 valves that they come with. No fit issues with the BOSS302 block. If I declare the car for SS/CS I can run the Combo legally. Aluminum heads any valve size 10.5 lbs/cid. The index sucks O2 (10.30) but I have thrown t he book at my car over the Winter.

Sorry Dale, you cannot run aluminum cylinder heads in SS/CS class, only cast iron, inline/wedge heads only.