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-   -   .480" v. .512" GM valve lift HP & Torque test (http://s91730302.onlinehome.us/forums/showthread.php?t=681)

SedanMan 11-21-2006 08:35 AM

.480" v. .512" GM valve lift HP & Torque test
 
Ok engine guys, here's your chance to give me some input on the increased valve lift test I'm going to run on my GM car on a chassis dyno. Recently I measured valve lift on one valve and it read just under .480" at zero lash with 1.5 ratio rocker arms, so that will be the baseline test.

I have a limited budget and since this is going to be on my dime I have to limit my testing to a chassis dyno. Since we're looking for a relative horsepower difference between .480" and .512" valve lift when we leave everything else the same, I think chassis dyno results are just as good as engine dyno results. As nice as it would be to exclude drivetrain losses, engine dynos have their own inaccuracies.

With an engine dyno you typically can't use your car's exhaust. I've never seen car headers clear a water brake so "dyno headers" are usually used, not to mention that the rest of your exhaust pipes don't usually fit in a dyno cell. Also, dyno engines often use a dyno fuel pump, dyno ignition system, a remote water cooling system, and a different (if any) oil cooler than what's in your car. So, chassis dyno it is.

As willing as I am to share honest, accurate test results of the relative horsepower difference for .480" v. .512" valve lift on my GM engine, please don't ask to see the actual dyno sheets. After all, this isn't a development mule, this is my car. :)

I thought of the following test procedure but I'm open to suggestions to change it. Note that all of the dyno pulls will be done back to back, on the same day, on the same chassis dyno, without removing the car in between sets of pulls.

Data Gathering
1) Use race gas from the pump I always use at a local track.
2) Put enough fuel in the car to run all the tests without refueling.
3) Tie the car (with 1.5 ratio rockers) down onto the chassis dyno.
4) Warm up the car to operating temperature and record oil and water temps.
5) Verify that all valves have the desired hot valve lash.
6) Make 3 '.480 lift' dyno pulls and record the max hp, max torque, and air/fuel ratio for each pull.
7) Replace the 1.5 ratio rockers with 1.6 ratio rockers.
8) Adjust the hot valve lash for the 1.6 rockers to be the same as the 1.5 rockers in Step (5).
9) Warm up the car to the same temperatures as recorded in Step (4), or at least as close as possible.
10) Make 3 '.512 lift' dyno pulls and record the max hp, max torque, and air/fuel ratio for each pull.
11) If the air/fuel ratio is approx. the same as in Step (6) then go to Step (13).
12) If the air/fuel ratio is significantly different than recorded in Step (6), rejet the carb until the air/fuel ratio is the same. Record the required jet changes. Make 3 final '.512 lift' dyno pulls at the same engine temperatures as in Step (4), recording the max hp, max torque, and air/fuel ratio for each pull.
13) Replace the 1.6 ratio rockers with the original 1.5 ratio rockers.
14) Adjust the hot valve lash for the reinstalled 1.5 rockers to be the same as the lash was in Step (5).
15) If the jets had to be changed in Step (12) then change them back to the original jet sizes that were used for the '.480 lift' pulls in Step (6).
16) Warm up the car to the same temperatures as recorded in Step (4), or at least as close as possible.
17) Make another 3 '.480 lift' dyno pulls and record the max hp, max torque, and air/fuel ratio for each pull.

Data Reduction
A) Verify that the air/fuel ratios from the pulls in Steps (6), (10/12), and (17) were similar. Note any significant differences.
B) Average the 6 '.480 lift' hp and torque values recorded in Steps (6) and (17). Record the average '.480 lift' hp and torque values.
C) Compare the average '.512 lift' hp and torque values from Step (10/12) to the average hp and torque from Step (B). Calculate the percentage change.
D) Post the average hp and torque percentage change for .480" v. .512" valve lift on this Forum.

Whew, who said this would be simple......

Ok, if anyone has suggestions to change the procedure then please let me know. If not then this will be the plan and I'll make a dyno appointment as soon as I get my car. The results should be posted in about 4 weeks, hopefully sooner.

[Note: it would be nice to duplicate this test with another GM car so we'd have more data, however, I think even this one test will give us some real numbers that should be more accurate than some of the wild guessing that's been going on (from 3 to 35 hp). By the way, when the Ford folks were asking for more power to make up for the perceived GM chassis advantage a few years ago, was there this level of testing and were the results posted on the AS Forum before the membership, AdHoc, and CRB made their recommendations?]

King Matt 11-21-2006 09:02 AM

The only comment I have is that changing rocker ratio also affects the effective duration of the camshaft, so you are changing more than one variable. But it will tell you if your engine can use more air flow, or more accurately, if there is any more air flow there for you to use.

Mark Allen 11-21-2006 09:06 AM

Bill, I think you've got a pretty sound plan there, I'm anxious for the results. Just for one final caution, are you sure that you won't have any clearance issues at .512" lift?

Mark

Dawson Motorsports 11-21-2006 09:25 AM

Bill, as mentioned make sure you have enough valve to piston clearance. I understand not wanting to share all the info, I think any percentage change will be sufficent, and Thanks.
Chuck

SedanMan 11-21-2006 09:25 AM

good question
 
Quote:

Originally Posted by Mark Allen
Bill, I think you've got a pretty sound plan there, I'm anxious for the results. Just for one final caution, are you sure that you won't have any clearance issues at .512" lift?

Mark

Good question Mark. I should be ok since I checked with my engine builder and he said that the pistons he chose had a fairly generous valve pocket depth. I really wish I knew for sure but I'll take his word for it as I don't have the time/money to take my engine apart.

If increasing max valve lift from .480" to .512" ends up to be a bone that is thrown to the GM guys to hopefully make more power, I'm not sure everyone else will be as lucky as I think I am. Someone has already posted in another thread that they would not be able to use their current pistons, which makes a seemingly simple change become much more expensive.

Time will tell what the hp increase is (if any) for the increased valve lift, at least with my engine.

SedanMan 11-21-2006 09:31 AM

actual hp increase number
 
Quote:

Originally Posted by Dawson Motorsports
Bill, as mentioned make sure you have enough valve to piston clearance. I understand not wanting to share all the info, I think any percentage change will be sufficent, and Thanks.
Chuck

Chuck, after I posted it I thought about the percentage change thing and perhaps I should just post the actual rear wheel horsepower change. I probably won't post the before and after hp numbers, but I will give the hp change in actual hp, not just the percentage. (who wants to know that it gained 1.21% hp?) :)

Dawson Motorsports 11-21-2006 09:33 AM

That's your call. Are you going to use "A's" or "R's"?

SedanMan 11-21-2006 10:16 AM

tires?
 
Quote:

Originally Posted by Dawson Motorsports
That's your call. Are you going to use "A's" or "R's"?

Are you talking about tire compounds? That's the only thing that comes to mind when you say A/R. I don't use Hoosiers so I don't have the A/R choice. I wish I did have an autocross compound for qualifying though.

jimwheeler 11-21-2006 10:48 AM

I think the percentage increase would be the most interesting to me. If it is, say, 2%, that would mean about 9.5 hp increase for Phil and about 6.8 hp for me.
wheel

KW78 11-21-2006 11:54 AM

Quote:

Originally Posted by jimwheeler
I think the percentage increase would be the most interesting to me. If it is, say, 2%, that would mean about 9.5 hp increase for Phil and about 6.8 hp for me.
wheel

:laughing: Jim, uncross those two plug wires and try again...

Bill,

I would suggest also...

If you have an oil temp gauge, take note of that and use it more than the water for consistency.

You make have to take something like 6 or 8 runs to warm everything up to get consistent to start (that is pretty typical on the dyno, drivetrain combos here regardless of car)

Crank the rear tires up in pressure, and they may change also every couple of runs a little, so you'll have to bleed them maybe (guys here often heat cycle there tires this way, not sure I agree)

Important!

On your first pair of rockers (say #1), pull that plug and the companion plug (say #6) and install the rockers at zero lash. Turn the motor over by hand, with a breaker bar not a ratchet, two revs and feel around at 30 deg BTDC or so to TDC on both strokes (especially exhaust stroke during valve overlap).

Turn your motor over again to where you adjust valves, and back off your adjuster to .050 lash and see what that takes (say 3/4 turn), then go back to zero, then go that 3/4 turn more to hold that valve open the .050. Turn the motor over again by hand, feel around on that exhaust stroke again. Also stick a feelers gauge in the valve spring at max lift and check for coil bind.

If everything is smooth, 95% chance it will be, then you should have good clearances for redline. It's a very easy check to do, and harder to explain than actually do.

Good Luck,

Kyle

BTW, is this on a dynojet? And midrange TQ differences would be interesting to hear about.


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