SWCDuke

I've copied Jerry's data from the other post into this new thread that should be easier to find when someone asks the question next week.

Thank-you very much, Jerry, for providing this data. The SAE correction factor makes the results comparable assuming both were not too far from unity even though they were done a few days apart.

Another issue in chassis dyno testing is to ensure that there is sufficient external cooling to keep the fan clutch from fully tightening. My data and calculations indicate this can reduce peak torque by about 10 lb-ft and peak power by up to 15.

Duke

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Originally Posted by jerrybramlett at https://www.corvetteforum.com/forums...-365-a-12.html


Here are the SAE corrected results ...l with the .023" lash setting:

RPM / HP / Torque

2000 / not recorded
2100 / 84 / 210
2500 / 109 / 229
3000 / 140 / 246
3500 / 161 / 241
4000 / 189 / 248
4500 / 219 / 255
5000 / 234 / 246
5500 / 246 / 235
6000 / 249 / 218
6500 / 238 / 192

Peak rear wheel horsepower was 251 (SAE corrected) at 5,750 rpm.

...

This engine and FI unit made 256 SAE corrected hp ... with the valves set between .032" and .036", ...
Here are the SAE corrected results of the dyno pull this morning with a .030" lash setting:

2000 / not recorded
2100 / not recorded
2200 / 98 / 233
2500 / 116 / 244
3000 / 147 / 258
3500 / 170 / 255
4000 / 198 / 260
4500 / 227 / 265
5000 / 244 / 256
5500 / 257 / 245
6000 / 256 / 224
6500 / 244 / 197

Peak rear wheel horsepower was 259 (SAE corrected) at 5800 rpm. Plenum vacuum at 850 rrpm was 10.5" today. Plenum vacuum at 850 rpm with .023" lash was 9" last week.

Today was 9 degrees cooler than when the .023" lash pulls were made last week. The humidity was also lower today, 13% vs. 23%.

Jerry Bramlett

SWCDuke

The results verify the typical SOTP feel that .023" lash reduces low end torque and measured idle vacuum, which I expected. What I did not expect was a reduction in top end power. I guess this shows that increasing duration slightly (due to the tighter lash) is beyond the point where more cam duration helps the top end because head flow is effectively choked, but the difference may be different with massaged heads.

My .023" cold lash recommendation is based on taking up lash at no more than clearance ramp velocity under all engine operating conditions to minimize valve train shock loading. At .023" cold lash all clearance is taken up at .00036 inches per cam degree, which is clearance ramp velocity. You can convert this to ft/sec, MPH or any velocity measurement by factoring in RPM with suitable conversion factors.

At .030" cold lash clearance is taken up at about .009 inches per cam degree, which is 2.5 times greater. Think about ramming your car into a solid wall at 12.5 MPH compared to 5 MPH. The damage difference is significant!

This higher the velocity at clearance take-up the great valve train shock loading is, especially at high revs and can be heard as "valve train clatter". At .023" lash you could almost be fooled into thinking it's a hydraulic cam given that there is so little valve train noise.

The higher velocity also increases the possibility of valve bounce on closing at high revs and reduces the RPM for incipient valve float.

At clearance take-up, jerk (the rate of acceleration change), which is associated with shock loading is about .0005 in. per cam degree cubed at .023" cold lash because acceleration is just beginning to increase from zero.

At .030" cold lash lash take-up jerk is about .0045, which is nine times greater!

So I think everyone now has enough performance data and understanding of valve train dynamics to pick whatever lash setting they think is best for them; .023" lash will reduce power across the range (with unmodified heads), but should improve valve train life. Your choice!

At either lash setting the optimum shift point for maximum acceleration performance is 6500. This is because revs drop revs to about 5000 with a CR four-speed where available power is about the same as at 6500, and this yields maximum average power through the gears.

Duke

Critter1

Duke,

I'm glad you finally understand and accept the things that a lot of folks have been trying to tell you for a long time.

wmf62

never happen...

Bill

PAmotorman

was this done with open or closed exhaust ??

jerrybramlett

Reproduction stock FI exhaust and mufflers.

tuxnharley

Seems like it reads pretty clearly in the first paragraph of his post........

wmf62

'wiggle' words from Post 2....

"So I think everyone now has enough performance data and understanding of valve train dynamics to pick whatever lash setting they think is best for them; .023" lash will reduce power across the range (with unmodified heads), but should improve valve train life. Your choice!
"

not sure that the sale of 30 - 30 cams has, or will be, affected by that profundity....


Bill

tuxnharley

I wonder how many 30-30 cams are sold at all these days, what with all the newer better alternatives available?

Are we bordering on a discussion like the best way to tune a Rhone rotary engine?

wmf62

so far this whole cam 'discussion' has been like 'painting yourself into a corner and then waiting for the paint to dry so you can get out'....

this has been a case where the paint hasn't dried, and may never, so the 'painter' is stuck in the corner....

BUT, a discussion of the intrinsics of the Rhone rotary engine might be a refreshing 'new coat of paint'....



Bill

PAmotorman

try it with close lash with open pipes because these cam were designed to be used in race cars with open exhaust. back when these cams were designed you had to race with stock cams but you were allowed open exhaust. .

63 340HP

What is an acceptable lifter acceleration rate for a gen 1 SBC, with an expected ten year service life between overhauls (considering the vehicle is unlikely to experience more than 25,000 miles in that ten year period)?

If there is published data, what rpm does that acceleration rate become a concern with the 0.030 lash?

MikeM

That wasn't the issue.

PAmotorman

why not the dyno sheets show less HP with tighter lash with closed exhaust. how do you know the engine would not make more HP with tighter lash with open exhaust ??? remember one corvette cam GM told you to run .004 closer lash for use in as they said competition.

wmf62

we had 'apples to apples', and the issue is settled.. with the exception of different days and slightly different conditions, the test mule was the same

someone else can take up the baton and run with it, Jerry has gone out of his way (and spent HIS money) to satisfy the curiosity of the forum. if 'inquiring minds' want to know, let them run the tests.

Bill

MikeM

As I told you on another forum, I suggested to one of the posters in this thread 7-8 years ago the tighter lash might be beneficial using headers. I was told at that time that headers were not beneficial on a mid year Corvette due to the superior design of the OEM exhaust system. That he had done some kind of back pressure tests...........................

Somewhere in the other thread currently running, same subject, same participants, I suggested it would be great to run the tests with open headers. So, I don't know but suspect what the results would be. I've suggested this over the years but it's never gained any traction because most owners here that piddle in their driveways don't have headers. Many do have headers and super duper cams though.

Read the other thread to get a feel for this one.

SWCDuke

The LT-1 cam is both newer and better. If you've read the Hinckley-Williams valve adjustment paper you should know that the inlet lobe is from the L-72 cam (on a smaller base circle) indexed at 110 deg ATC, and the exhaust lobe is the 30-30 lobe indexed four degrees earlier at 122 deg. BTC, which yields a LSA of 116 deg.

The L-72 lobe has about 10 degrees less effective inlet duration than the 30-30 and combined with the wide LSA, effective overlap is about the same as the Duntov cam, which is a lot less than the 30-30. This improves low end torque with about the same top end power compared to the 30-30.

Jerry's data indicates that you can't just keep increasing inlet duration to increase top end power. It starts out as diminishing returns and eventually turns negative.

Shortly after the LT-1 cam was released to service parts circa 1970 the 30-30 was discontinued and the LT-1 cam was called out for all prior 30-30 cam applications.

Draw your own conclusion.

Duke

SWCDuke

Telling me what? I've always stated that tighter lash would decrease low end torque and degrade idle quality. I also expected more top end power based on SOTP anecdotal reports from owners, including JohnZ, who reported that tighter lash on his DZ engine (he set them at .026" based on my initial recommendations) resulted in a smoother, more free revving engine.

Duke

PAmotorman

right from gm

Critter1

But you still kept recommending your tighter lash because you told everyone that it increased power at higher RPM. You've been telling that story for many years. Now you're story is changing. You finally admit (somewhat) that there is no higher RPM power increase. Over at that other board you recommended that lash to everyone and several believed your nonsense. Now that it's proven that it doesn't work, I hope you will let it go.

So, because you're recommended .023" lash doesn't do anything positive, in any RPM range, is there any logical reason why any one should even consider using it?

My guess is that it was you, not John Hinckley that decided that such a setting was of any value, at all.

You were wrong from the start. Just give it up, Duke.

And you STILL owe me lunch for two from that wager that you suggested several years ago.