Torque curve tinkering

[SIVAllan]

I finished reading Bill Carroll's Ford Cobra Guide (1964 Sports Car Press). Toward the end, an interview with Ken Miles is presented with Miles discussing a few tricks of the trade in tuning engines.

Specifically he mentions moving the torque curve up or down by changing the timing and valve lash.

He also mentions that this won't necessarily make a big difference but it made me wonder about tuning our v6 engines. A small positive change can make a difference in both performance and overall satisfaction with the engine.

So this is deep water to me but I thought to ask - has anyone experimented with v6 timing and valve lash purposefully to seek performance gain?

What - how much - gain was achieved?

If my cam makes most torque too high for my preferences - can any substantial movement down the curve be achieved by experimenting with valve lash and timing?

How much movement could be expected?

Thanks in advance,

 

[260Alpine]

Allan, You have to be careful on advancing a cam. At around 10 degrees advance the intake valve is closest to the piston. At 10 degrees retarded the exhaust valve is. A lot of cams have built in advance. We talked about offset keys and multiple keyway gears in an earlier thread. If a cam is too big you can advance to lower the curve and if a little too low a power band, retard to move up. You have to watch your Dynamic compression/Octane requirement too. Valve lash setting can affect lift and duration also. Here's a couple of articles that explain it better than I can:

http://victorylibrary.com/mopar/cam-adj-c.htm

http://www.hotrod.com/articles/ccrp-0211-changing-valve-lash/

 

[husky drvr]

Allan,

I've got a book on building high performance Chevy "gen I" small block V8's by David Vizard. In the section on cams and valve trains he states: "If the cam's LCA (lobe centerline angle) has been selected to optimize power, then timing it into the engine optimally becomes more critical. If we had a cam of 116 degrees LCA retarded from optimum by 6 degrees, it may loose 5 foot-pounds at 4000 RPM."

To answer your question more directly, if a high level v8 with about double the 2800's displacement only looses less than 10 ft.-lbs. ( probably 2-3%) of torque with what is a fairly large 6 degree cam timing change, then the effects of that type of tuning is small.

HTH

 

[SIVAllan]

Thanks,

Miles mentioned small, incremental changes, such as .002 for valves and only a few degrees for timing, not to add or subtract power but to move it.

But move it how much?

For example, if a hypothetical cam builds peak torque at 4500 RPM, could it be moved down to ... 4000?

 

[Barry]

Based purely on personal seat-of-the-pants experience, I think advancing cam timing does more for the bottom end than retarding cam timing does for the top end.

 

[260Alpine]

On the 350 Buick V8, 8 degrees advance was around 500RPM's difference. So 4 degrees about 250RPM. I made a chart for Bruce on what his 2.8 V6 cam would be at 4 degrees advance. Peak HP went down from 6000RPM to 5500RPM. TQ peak was still at 4500RPM but was noticeably higher from 2000RPM to the peak. Another trick is to add lift with a higher rocker ratio.

 

[260Alpine]

Pics of offset key and multi keyway cam gear:

 

[Charles Johns]

I am an old Chevy/Ford small block drag racer in a 1940 Ford coupe. For a street driven car messing with cam timing is a waste of time, for any practical gain. Start the engine build with a desire in mind...for example: I raced in the late 60's but got the bug to help MPG and daily driving after the 73 gas crunch. With an Autolite 2100 two barrel (annular atomization), adapted to an aluminum intake, hot ignition, cast-iron headers, standard 3-angle valve job, and a cam used in the 289 installed in trucks/vans (made torque down low), I got 250 HP and 25 MPG in a hot rod. The key was a 303 full syncro 3 speed to get into high gear as soon as possible, and using a big car heavier flywheel. With 2.79 rear gears and 29" tall rear radials, the cam was in the sweet spot at 70 MPH (1850 RPM). At the time 70 was the interstate highway speed. For practical building, START with the right parts and design. I am not building a V6 but love the little engine. We had a 1975 Pinto with one and loved it...and NO we did not sell the Pinto to avoid a fire. The wife loved the new 77 LTD, so we traded. Weekend racers may gain something with the small gains with timing changes, but be careful of too much change, and know when the intake valve closes. Static timing can do much to help daily driving, but again, gas octane is important. If you advance to the max and get low octane gas at a Mom & Pop gas station like I did, you may fry/break a ring. My #6 in a 65 Mustang SIX required a .060" overbore to clean it up.

 

[260Alpine]

Charles, I agree with everything you say. Pick the right cam first and you won't need to mess with cam timing. For those that have too big a cam advancing it does lower the power/torque curve. Look for a street performance cam that is good in the 1500-5500 range ideally. Usually this means under 220 duration@.050 and under 480 lift. In a smaller engine a little less and a larger engine a little more. On static ignition timing you will usually be about 10-12 and total 32-34 by 3000RPM. Just a basic guide.