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Lash and compression relation, and other drivability stuff.
https://www.slantsix.org/forum/viewtopic.php?t=51800		 Page 3 of 3
Author:  DusterIdiot [ Sun Jun 02, 2013 2:41 pm ]
Post subject:  Dang.
Quote:
Last fall I purchased a Quick Fuel Technology 34-8 metering block. I did not install it because the brass tube connecting Holley’s metering block to accelerator pump has to be cut for the QF part to fit.
You have an older carb and this block will not work with it, that tube was typical of the late-70's-80's metering block setup, the late 90's and new carbs use the standard flat block common among the 4150/4160's. By cutting the tube, it won't seal correctly and you'll chase another issue (Did that with a Jeep 390 cfm with a bad metering block...not a good experiment but the carb was cheap...)

Another quick note, you'll have some mods to make as the numbers listed for that block indicate that it's primarily set up for use with a 600-750 cfm carbs, so they will have a fatter idle fuel passage than the 390/450 is used to.

FYI.

-D.Idiot
Author:  wjajr [ Mon Jun 03, 2013 1:20 pm ]
Post subject: 
Will this thing ever run right?????

Today's antics:

This morning’s compression test yielded nos.(1-6) 170, 165, 165, 155, 155, 155 psi. Some lashing evened out pressures: #1 @170; and nos. 2-6 @ 165psi.

I cracked open secondaries for a bit more idle air (could Holley made this adjustment any more difficult), idle mixture screws out about 1.5 turns from stop. Vacuum gage has settled down, vacuum in park 1000 rpm is 13â€￾ Hg, in gear idle at 500 to 650 rolling rpm around 11â€￾Hg with needle floating up and down an inch or so depending if mixture is rich or lean. Mixture is running mostly in 0.95- 0.65v range dropping out to 0.2 v for a revolution or two than back to 0.9v.

Two conditions I can’t make go away, one the rolling rpm at idle, second the rich to lean to rich to lean rolling air/fuel mixture at idle; and which condition is cause & effect.

Spark plugs all looked to have the same light tannish gray coloring of electrode, rim, and porcelain, number 3 plug has a bit of a slightly reddish hue to the above coloring. Exhaust pipes have lightened up from dusty soot black to a grayish black indicating more ideal average A/F mixture.
Author:  Doc [ Mon Jun 03, 2013 1:37 pm ]
Post subject: 
Quote:
...Will this thing ever run right?????...
You will have a better chance at getting it to run "right" when you swap-out the cam for something more "civilized".

Truth is... it's running pretty good for the "hot" cam that is in it.
DD
Author:  DusterIdiot [ Mon Jun 03, 2013 1:53 pm ]
Post subject:  X2
Quote:
You will have a better chance at getting it to run "right" when you swap-out the cam for something more "civilized".

Truth is... it's running pretty good for the "hot" cam that is in it.
I agree with Doc, the numbers you have and the rpm and bouncing are about as good as it gets for a fat cam and heavy overlap event...I know I have one of OCG's 549's in my engine but ordered it with a 109 LSA instead of the 106 it had stock...(smaller overlap necessary to keep the Hpak intake happy), compared to the Erson 280/270, i gave up about 3" of vacc. at high idle (that's 19" down to 16 if at 1200 rpm), and I don't expect it to be happy under 1000 rpm with a carburator.

Sounds like it's time to shop for a replacement cam for street use, your wallet and sanity will thank you.


:wink:

-D.Idiot
Author:  Rick Covalt [ Mon Jun 03, 2013 6:20 pm ]
Post subject: 
Quote:
Sounds like it's time to shop for a replacement cam for street use, your wallet and sanity will thank you.
A carb swap ( Edelbrock) may save some sanity as well, and would be a lot easier than a cam swap. Just a thought.

Rick
Author:  wjajr [ Mon Jul 15, 2013 12:22 pm ]
Post subject:  up date on jetting, and drivability
I made a Jet change in Holly 8007 back to #512. I ran #49 jet for about fifty miles, it produced too much lean surge too often, then a 50 jet for perhaps five hundred miles which gave better drivability but still a slight lean surge at selected throttle openings under some grade change conditions previous to this change.

This 512 jet is best for this engine at this time as far as I can see. Lean surge is gone, perfect transition between carburetor circuits under all conditions, and seems to produce best low end torque as judged by seat of pants.

Also I changed out purple secondary diaphragm spring to long yellow. This change lowered secondary throttle plate opening rpm threshold, and smartened up engine response at WOT. As soon as 4000 rpm comes up engine responds with a flat spot free solid rush of power, and pulls hard to 6000 rpm. It easily makes two good black marks on dry clean pavement from a stop.

The only thing left to do is crank up the dynamic compression this winter; it is still below 8:1 with this cam.
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