instead of "straight up"? What are the pros and cons? Thanks.

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Willie

Supercharged 1987 305 IROC-Z, Daily-Driver, Emissions-Legal.
Former Paxton (6-psig) with 50-hp nitrous: 12.043 @ 112.86 mph.
ATI D1SC (10-psig): 12.056 @ 116.62 mph.
All stats are altitude corrected for 3,100 feet using NHRA's Altitude Correction Table.

http://willie.camaro-firebird.org/

1987 "20th Anniversary Commemorative Edition" Z28 Convertible -- Super Chevy Show Class Winner, 1998.

 

If the cam is correctly ground, the other reason to change the installled intake centerline (the actual process of advancing or retarding involves changing the Intake cl), is to move the power band up or down. A 2 degree advance is said to move the power band down about 200 rpm.

 

Just another tuning device. You don't guess at where the cam timing should be. By advancing or retarding as mentioned above, you move the powerband around. Different cars in different types of racing require different adjustments.

Piston to valve clearance needs to be checked any time the cam timing is changed from straight up.

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Follow my racing progress on Stephen's racing page
and check out the race car

87 IROC-Z SuperPro ET Bracket Race Car
461 naturally aspirated Big Block (times are for the current engine)

Best ET on a time slip: 11.447 altitude corrected to 10.99
Best MPH on a time slip: 119.42 altitude corrected to 124.86
Altitude corrected rear wheel HP: 493
Best 60 foot: 1.586

Racing at 3500 feet elevation with a typical race day over 5000 feet density altitude!
Member of the Calgary Drag Racing Association

87 IROC bracket car, 91 454SS daily driver, 95 Homebuilt Harley

 

I asked the question because I've been playing around with Desktop Dyno. What's interesting is by retarding the cam by two degrees, I gain 11 hp (from 410 to 421). The torque increase is negligible (from 463 to 464). When I advance the timing two degree, my hp drops to 401 but torque remains the same. I've tried a couple of different cam configurations with similar results. Does this seem correct?

Willie

 

I dont find it surprising that DD2000 indicates that much difference, but in truth, its not likely to happen. For it to actually be that much of a difference the cam and intake would be somewhat missmatched.

Change it to 3 degrees and see what happens.

 

Change it to 3 degrees and see what happens.

Three degrees retarded:
424 hp
464 ft/lbs torque

Another three horsepower!! Torque's the same.

I don't know if this is relevant, but this is with 12 lbs boost.

Willie



[This message has been edited by Willie (edited October 27, 2001).]

 

You are looking at Peak hp and torque. That power you gain on the top end is lost at the bottom. You move the whole powerband up and down. Overall power gain is very, very minimal.

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350 with stealth intake, holley carb, 470 lift cam. 700r4 with .5 boost valve, vette servo, tci lock-up kit, B&M megashifter. Richmond 3.73 gears, powertrax locker, timkin bearings, synthetic lube. Custom 3 inch single into 2 2.5 pipes. 1 1/2 drop springs, 1 5/16 solid front sway bar, 1 inch rear bar, custom subframe connectors, custom LCA relocation brackets. Kobel ground FX, currant red metallic paint. Lots of other stuff...
82camaro

 

While using DD2000 and doing those changes, look to see where the peak is occuring. It should move around at different rpms.

By retarding it 2 degrees and picking up 11 hp 200 rpm higher than before doesn't help much if you never get the rpms up that high.

I've never tryed DD2000 yet. I don't know what kind of output it will give you. You may need to transfer the engine data to Dragstrip2000 to see what it will actually do for the car. If you have a TPI and changing the cam timing moves the peak powerband above 5500 rpm then you'll never reach that power etc.

Since you're playing with boost pressure, try trying different pressures at different cam timings as well. You should also try a blower grind to see what that does. The valves have different timing even though lift and duration may be the same to allow the forced air to enter better.

 

Willie,

You must have one big damn desk! I can barely fit a head on mine, let alone an entire dyno.

Either the authors have done a lot of homework and loaded a buttload of data points into the .dlls or they are just guessing at cam profies. The differences in valve timing will affect the power at a given RPM, but simply plugging in lifts, LSAs, and durations can't give very accurate results. The area under the curve of a cam is probably more important than the total lift, and the commonly quoted cam spec numbers don't often tell much about a cam profile.

For example, these cams would act vastly differently in an engine, but all have the same specs:



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Later,
Vader
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If you want to beat the World, it might reach up and pull you down...
Adobe Acrobat Reader

 

Sorry this has mothing to do with this topic but steven i was just wonder what size rims you are running front and back and what size wheels. Thanks A lot. Bobby.

 

That's why the Comp Cams Xtreme Energy cams are so popular. They offer a more aggressive cam profile with the same specs as other grinds. Trouble is that with a flat tappit cam there is only so much cam profile that can be fit under the lifter. With a roller cam the profile can be more aggressive because of how the roller lifter moves over the cam lobe.

All the specs for my car are on my web site.

 

As a rule, Regardless of size, duration shape, rate of lift;(all of which are important)advancing or retarding a camshaft
will favor the lower or higher part of the powerband of that engine.
It will not move the powerband up or down. Duration does that.
You're always going to trade a gain at one end of the band for a loss at the other.
For $39.95 Desk Top dyno does a good job of illustrating these trends. Only "on the dyno" and "at the track" testing will tell you if there is a benefit. So much for bench racing......
http://photos.yahoo.com/russ_q

[This message has been edited by F-BIRD'88 (edited October 28, 2001).]

[This message has been edited by F-BIRD'88 (edited October 28, 2001).]

[This message has been edited by F-BIRD'88 (edited October 28, 2001).]

 

if i remember it correctly advancing the cam will build more torque and retarding it will make more HP. all of the cams i've put in lately have been ground 2* to 4* advanced so they were installed straight up and the advance was alreadt there. always good idea to degree the cam and check piston to valve clearance.

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ICON Motorsports
1st & 3rd
MM Black Diamond 538 F&AM

 

It depends on what your interpretation of moving the power band is. Advancing the cam will cause the engine to produce more torque below the torque peak and less above the peak. Retarding does the opposite. Duration has a lot less to do with the where the power band resides than people think.

I have seen 500 cube motors make peak hp at 5000 rpm with 200 degrees of intake duration at 050. The peaks moved up less than 1000 rpm when a 250 degree cam was put in the same engine. Port volume is the main factor in the location of the hp and torque peaks. Not cam duration.

I think DD2000 is padding some of the results bc of the SC. Since SCs tend to make hp in higher rpms, the process of retarding the cam is reflecting that. If you tried the same test on a non SCed motor I don't think the results would be as significant.


[This message has been edited by jcb999 (edited October 28, 2001).]