Effect of Cam Timing Changes on Torque and Horsepower

[Qikbbstang]

The old VariCam and Cam-A-Go (run by  Henderson Power Sports at Engine Masters) both in their old fashioned/primitive ways they changed cam timing to maximize low end torque and maximize top end horsepower. Any way to dial-in determine/produce optimum Tq & Hp via cam timing?
 The Ford Coyote 5.0 infinitely alters the cam overlap, cam timing, F:A, and Ign Timing simultaneously for optimum performance. No air-pump for the cats, it just alters overlap/cam positioning to add more air/0-2 into the exhaust

[rockittsled]

Found this on google along with an old post on the other forum by Qikbbstang while I was looking for info on the Varicam

http://nepis.epa.gov/Exe/ZyNET.exe/91006D4P.TXT?ZyActionD=ZyDocument&Client=EPA&Index=Prior+to+1976&Docs=&Query=&Time=&EndTime=&SearchMethod=1&TocRestrict=n&Toc=&TocEntry=&QField=&QFieldYear=&QFieldMonth=&QFieldDay=&IntQFieldOp=0&ExtQFieldOp=0&XmlQuery=&File=D%3A%5Czyfiles%5CIndex%20Data%5C70thru75%5CTxt%5C00000008%5C91006D4P.txt&User=ANONYMOUS&Password=anonymous&SortMethod=h%7C-&MaximumDocuments=1&FuzzyDegree=0&ImageQuality=r75g8/r75g8/x150y150g16/i425&Display=p%7Cf&DefSeekPage=x&SearchBack=ZyActionL&Back=ZyActionS&BackDesc=Results%20page&MaximumPages=1&ZyEntry=1&SeekPage=x&ZyPURL

[jayb]

Ran the test again today, with some help from my pal Steve P, and basically got the same results as before, despite the obvious timing change.  I had thought about what I should see after the discussion earlier in the thread, and figured that with the cam timing changing +/- 6 degrees, I ought to see the same change in the ignition timing.  I started off by running a baseline pull at the straight up 107 ICL position and 38 degrees total, then went to the +6 advance point of 101 ICL.  Warming up the engine after the timing change, I ran it up to 3000 RPM and sure enough, the timing light said 44 degrees total!  So, I dialed back the timing to 38 total, and ran the pull.  The only real change was that I didn't lose anything at all on the low end of the RPM scale, just on the high end.  After changing to 6 degrees retarded, 113 ICL, I saw 26 total with the timing light, which made sense because I had changed from 6 degrees advanced to 6 degrees retarded, while starting at 38 total.  Again I adjusted the ignition timing back to 38 total, and got basically the same results as before. 

Here is the data:







The curves are a little hard to follow at the higher RPM range, but I did an average calculation and from 5500 to 6000 RPM, the engine gained an average of 6 HP when the cam was retarded to a 113 ICL.  So, retarding the cam definitely gave more power at the top end.  I also ran one test to 6500 RPM with the cam at 113 ICL (fearing for the lives of my connecting rods LOL!), but right after 6000 RPM it appears that this engine has some valvetrain issues, because the power falls off and gets pretty choppy.  So, I didn't bother to run any more tests at a higher engine speed.

A/F numbers also looked the same as before.  Given how far off the timing was on my original test, I'm just a little surprised at these results, but in any case it appears that the original conclusions still hold.  And it felt really right to start the new year, hearing a good FE on the dyno 

[Joe-JDC]

The facts are that you still have a certain amount of lift, duration, and airflow that will only change to the average, not maximum.  Finding where the car accelerates best with a given camshaft is what that ability to adjust the timing events helps to find the very most from a given combination.  To gain more, a person will need to move up to more lift, duration, etc., to move the average airflow up the scale if you do not change heads or intakes.  It all comes down to what your parameters for finding horsepower limits you to.  Class racing, or bracket racing, or street/strip.  The fun is in finding out the trends, and maximizing them to beat similiar combinations.  Joe-JDC

[cjshaker]

While it may have only showed an average of 6hp difference across the upper range, it also was showing an average of 20-25 ft lbs torque difference across the bottom to mid range. That's fairly significant. And I'd have to agree with Joe, it's all about maximizing the combo. A careful evaluation of the data could also help tell you what the engine wants in terms of camshaft specs, helping a person to choose a different lift/duration spec to better suit the heads and intake. It could also help fine tune a combination where the drivetrain comes into play with tranny gearsets, rear ratios, traction issues etc.

I am surprised somewhat that the timing didn't make more of a difference. The more modern heads probably helped there. An old set of iron heads would probably have shown a bigger difference. Still good stuff. Thanks for all the effort, and posting it, Jay.

[blykins]

So the A/F ratio went rich again with the advanced cam timing?

[jayb]

While it may have only showed an average of 6hp difference across the upper range, it also was showing an average of 20-25 ft lbs torque difference across the bottom to mid range. That's fairly significant. And I'd have to agree with Joe, it's all about maximizing the combo. A careful evaluation of the data could also help tell you what the engine wants in terms of camshaft specs, helping a person to choose a different lift/duration spec to better suit the heads and intake. It could also help fine tune a combination where the drivetrain comes into play with tranny gearsets, rear ratios, traction issues etc.

I am surprised somewhat that the timing didn't make more of a difference. The more modern heads probably helped there. An old set of iron heads would probably have shown a bigger difference. Still good stuff. Thanks for all the effort, and posting it, Jay.

I agree, retarding the cam caused a BIG drop in low end and mid range power.  You sure wouldn't want to run that way unless you were only concerned about 5500 RPM and up.

Also, the engine has factory Cobra Jet heads, with a very minor porting job.

[jayb]

So the A/F ratio went rich again with the advanced cam timing?

Yep, rich again from 5000 RPM to 5700 RPM with advance, and then once again it spikes lean at the end of the pull.

[KMcCullah]

The old "boot heel" combustion chamber doesn't seem to care too much about ignition timing. Good stuff here Jay. Now we need a heart shaped combustion chamber to compare to. Wait a minute.... Didn't Blair just do something like this?  Lol

[Qikbbstang]

Boom-Zing it dawned on me that naturally an OHV motor valvetrain tries to retard its cam. The big problem with the VariCam and Cam-A-Go were they offered no way to adjust the ignition timing that was dictated by the cam/distributor and they were being backed off by the variable cam. The BINGO is a crank trigger eliminates the ignition timing being carried along by the variable cam timing unit.
Studying the VariCam I have to wonder if the "spring" that allows for the cam to retard by greater forces of RPM upon it, is subject to bouncing under the tremendous forces of driving a camshaft?
 

[WerbyFord]

Very helpful data thanks Jay.
I ran these 3 in the Gonkulator, a couple guesses to dial in the base engine, then the Gonk said

107 ICL, 3 advance
Torq 487 at 4100
Powr 444 at 5400

101 ICL 9 advance
Torq 482 at 4000 down 5
Powr 425 at 5300 down 19

113 ICL 3 retard
Torq 467 at 4200 down 20
Powr 442 at 5500 down 2

Pretty close to what you saw except the Gonkulator didn't like the retard even at the top end.
I do find in the Gonkulator that the generalities hold in general, but as noted each combo responds differently.
I also find that 4 advanced is almost always optimum if the cam is well matched to the heads/manifolds.
If the cam is way too small, 0 advance or even a slight retard can work better. Just depends.

[ScotiaFE]

You have that 428 mule pretty much figgered out.
As always Jay, thanks for all the effort.

Any chance of a head shoot out? Felony vs BBM...

[jayb]

I'd love to do the head shoot-out, Howie, but I don't have either cylinder head.  Now, if I were to receive a donation...

[bn69stang]

Diddo on what lovehamr said , reading these posts and your book and following your knowledge , along with everyone else s has helped in so many ways . I learn more every day , many many MANY  thanks to you JAY . And for that matter everyone else as well .. Bud