Valve overlap
 

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.

Re: Valve overlap
 

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

Re: Valve overlap
 

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.

Re: Valve overlap
 

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.

Re: Valve overlap
 

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.

Re: Valve overlap
 

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.

Re: Valve overlap
 

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

Re: Valve overlap
 

OK. I read this revision as "Aluminum heads OK. No billet in modified classes except CS"

2017 revision:
Aftermarket aluminum cylinder heads permitted (no billet) except in CS.

I'll take the car to ETI in March and see. I'm beginning to not care any more.

Back to camshafts.

Re: Valve overlap
 

Dale,
The rule can be confusing.
What the rule change should say is that any aftermarket aluminum head, except billet heads are allowed.
Still, SS/CS class is NHRA approved cast iron cylinder heads only.

Prior to the current rule, it was required to run approved cylinder heads that had an OEM part number.

As applicable to your Mustang, would be the Ford N351 cast iron cylinder head casting.The N351 head, as cast, just with port matching, will outflow the AFR 165 heads by a mile.

Re: Valve overlap
 

Comp Cams Chart
http://www.compcams.com/Pages/413/ca...ion-angle.aspx
Might give you some added info

Re: Valve overlap
 

Adger I have been using that page a lot of great info there.The issue i am having now i think is in the black science of designing cams that is not printed. like when to open and close valves during the stroke, how much lift during overlap, lots of variables roller versus flat tappet cam, engine stroke. I am looking to improve what i have, I have identified an issue over a year ago and looking to solve it. So understanding valve overlap and a standard on what lift and if it is tappet or valve is important with the issue I have.

Dale one other thing about the new BOSS block is it has different size head bolts also.

Re: Valve overlap
 

James,

If you want make your life easier, I recommend this base software package:

http://www.controlledinduction.com/djrc.html

If you want to spend hours analyzing data, although spendy, this would be the software to use:

http://www.motionsoftware.com/Dynomation5.htm

Re: Valve overlap
 

Thanks Joe I knew you would chime in sooner or later, as always you have great leads to more knowledge. Congrats on retiring and moving some where warmer. you still have the same phone #? cant wait to see your car go down the track how much longer?

Re: Valve overlap
 

As always, glad to help James.
As regards to valve overlap, there is a lot in writing out there.
Nevertheless, there are other details and parameters that are not taken into account.

The Controlled Induction software package is easy to use and it has been used by Crower for many years. It provides great camshaft specification based on the inputs.

Dynamotion is a more complex software package that will require a lot more details of the engine and it provides a lot of data output. Also and it comes very close to actual dyno numbers. However, unless you are building engines for a living, it may be an overkill.

Just remember, if you input bad data, the program will give you bad results.

Yep, sort of enjoying the retirement; need to keep my brains busy, therefore, I am going to either be working for a smaller local company or consulting for my previous employer.

My wife and I are enjoying the move to Glendale, Arizona, although it was 27 degrees this morning!:eek::eek: At least, no snow and clear!

Race car is in progress and will be picking it up next month once Sean Cour is done squirting paint. Then will be busy finishing the car and getting it to the track.

Have the same number, feel free to call me anytime.

Re: Valve overlap
 

James: Bolt holes are no issue. I was going to drill out the heads Brian had to 1/2 inch. Water passages are another issue, though. Going to stick with my AFR heads and run bracket. I thought SS would be fun to build for but not so much.

Good luck on your quest for answers.