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By DANIEL TINDER - 15 Years Ago
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J. Mummert stated in his Y-Block Porting articles that he does not like to relieve all the way to the gasket surface when unshrouding, as the "G" chamber overhangs the block least, thus not canceling the benefit over more open chamber models. It's a bit unclear if he was referring strictly to loss of compression by relieving all the way (which would obviously remove more material), or is there some other factor in play re: "block overhang" that I'm just not getting (assuming no material is removed outside the gasket line)?
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By John Mummert - 15 Years Ago
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Dan, you might be worrying needlessly about dynamic compression. According to the E-4 Isky I checked on the Cam Doctor the intake closing is considerably later than Isky claims. Its closer to 90 ABDC. To get to their claimed duration of 260 degrees and intake closing around 60 ABDC the lash would need to be .028". At .016" lash the seat to seat duration is nearly 290 degrees. If you're still concerned you could put your new valves, springs ect in a set of -113 heads. 73cc will put your static C/R at 9.25:1.
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By Butch Lawson - 15 Years Ago
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That's really good news. I have an engine similar to Daniel's and I have been following these posts pretty closely and trying to get all this straight in my head for a couple of days now. Thanks John for the "stress reliever". I can sleep tonight.
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By DANIEL TINDER - 15 Years Ago
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Ted,
Wow. 90 ABDC really drops the dynamic CR way down (using web formula program link). If final volume measurement proves all chambers within 2 CCs, I might not bother with any more grinding (though it is tempting since they are still laid out on the bench). Only inquired about relieving to gasket surface since none of the sectioned head photos demonstrated thickness of that particular part of chamber. While breaking through not likely, I DID read about cracking danger if thinned too much. A lot of meat quite accessible near the top if more material HAD to be removed to lower CR. Also, if more precise chamber uniformity might prove exceptionally beneficial (though not sure it would, if unnecessary lowering of CR resulted), damage to valves (final state of assembly) a lot less likely if grinder bit kept high.
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By DANIEL TINDER - 15 Years Ago
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Oops. Not Ted, but JOHN! (senility setting in).
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By DANIEL TINDER - 15 Years Ago
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John Mummert (5/26/2010) According to the E-4 Isky I checked on the Cam Doctor the intake closing is considerably later than Isky claims.
John,
A bit puzzling. Don't know enough about the manufacturing process to guess, but wonder if deviation from advertised specs. is consistent? If they are cranked out by hand/one-at-a-time, then set-up errors could be quite random. If made in larger lots, then date of manufacture might be a determining factor? What is your experience with other brands re: consistency? Is it common practice to double-check each cam and validate specs?
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By DANIEL TINDER - 15 Years Ago
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John,
P.S. Unless that was MY E4 you checked, it occurs that simplest way to insure peace-of-mind before heads are buttoned-up might be to just measure my intake closing point. Once a damper is bolted on and TDC verified, installing a pushrod and chalk-marking the point where dial indicator stops moving should allow (using tape measure & calculator) an accurate enough estimate to determine if dynamic CR is really under safe limit? Also optimistic (assuming intake closes significantly later than Isky specs.) smaller aluminum head CCs would not then present any future problem? Going over all the relevant alum. postings, I didn't notice a specific comparison guideline for DCR/pump gas limits for the new heads?
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By John Mummert - 15 Years Ago
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Dan, I checked a 505 Isky and it needs .036" lash to match the 290 degrees they call advertized duration. So they seem to be consistant. They may be figuring in deflection of the cam, pushrod, rocker shaft ect and coming up with a calculated running duration. Or, they might just be telling us what we want to hear. This is something that cam grinders often do since they know most of us have no way to check their work. The reason we got the Cam Doctor in the first place was I bought "284" degree cams from 3 different manufacturers and had them tested. They were radically different and would have behaved very different in an engine. I realized that we could not rely on the manufacturers for accurate information.
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By DANIEL TINDER - 15 Years Ago
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[quote][b]John Mummert (5/28/2010) "they might just be telling us what we want to hear".
John,
Confused. If "what we want to hear" is that the cam has MORE duration than it actually does, that would be the opposite of my problem, as more duration than advertised would then keep my DCR under the safe limit?
"most of us have no way to check their work".
Measuring the intake closing point now would seem to be worthwhile insurance. Murphy's Law dictates my E4 will likely be one of the few that IS close to advertised specs.! Just need to figure out how to remove complications of lash, valve train slack, etc. so that when the lifter stops moving, I can interpret/translate that crank degree data to the Isky spec. sheet #s, since those measurements likely relate to a fully assembled motor? Would hate to lower static CR now just to be safe, only to discover later on I have ended up with unnecessarily low DCR, and thrown away power/torque.
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By charliemccraney - 15 Years Ago
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I think your idea of using the crank can work if you degreed your cam so that you know where it is in relation to the crank, and you have positively located tdc on the damper.
Keep in mind, the cam turns half the speed of the crank. If you forget that, you will come up with some really weird numbers.
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By DANIEL TINDER - 15 Years Ago
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charliemccraney (5/29/2010)
I think your idea of using the crank can work if you degreed your cam so that you know where it is in relation to the crank, and you have positively located tdc on the damper.
Keep in mind, the cam turns half the speed of the crank. If you forget that, you will come up with some really weird numbers.
Charlie,
Cam WAS degreed, and reportedly installed "straight up". But, that would seem irrelevant, since isn't intake closing point in relation to crank TDC (ABDC) what needs to be determined for accurate calculation of DCR? Also, as measurement only relates to intake cycle, and cam specs. stated in crank degrees (?), turning ratios shouldn't apply. Will definitely need to put on my thinking cap for this one.
BTW: Rereading instructions for finding TDC reminds me that I usually forget to maintain thumb pressure on piston (to take up bearing clearance). As a result, will have to repeat piston-to-deck measurements made earlier
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By charliemccraney - 15 Years Ago
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Brain fart! You're right. For some reason, I was picturing the degree wheel on the cam. Ignore my previous post.
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By John Mummert - 15 Years Ago
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Dan, the specs Isky is quoting for the E4 will be found .020" tappet movement. 260 crankshaft degrees from .020" tappet lift on the opening side to .020" lift on the closing side. Intake closing should be close to 60 ABDC when the indicator reads .020" on the closing side. This should be true for all E-4's, not just yours. Most cam grinders quote advertised duration and opening/closing events @ .020" tappet lift. Schneider and Clay Smith use lower lift numbers which means that a 280 degree cam from either of them will have less seat to seat timing than say an Isky or a Comp Cam will.
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By John Mummert - 15 Years Ago
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Dan, I just went on Wallace Racing's website to figure your DCR and things look favorable. The E4 shows an intake closing of 84 degrees at .016" lash. 3.820 bore, 3.47 stroke, 6.200 rod, 10.1:1 static compression, guessed at 500 ft elevation. http://www.wallaceracing.com/dynamic-cr.php
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By DANIEL TINDER - 15 Years Ago
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Thanks John,
Now I'm thoroughly confused. The DCR calculator program doesn't specify which measurement height/cam specs. to use.
So you are saying then, that actual Isky cams specs. (vs. advertised specs. of the same E4 model) measure consistently from one to another? AND, the 84 degree spec. you listed is what you got when YOU measured one? If your measuring height is the same one as the cam spec. determination method the DCR calculator was designed to use, then THAT DCR is plenty low/safe for most pump gas with my current chamber CCs.
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By DANIEL TINDER - 15 Years Ago
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charliemccraney (5/29/2010)
I think your idea of using the crank can work if you degreed your cam so that you know where it is in relation to the crank, and you have positively located tdc on the damper.
Keep in mind, the cam turns half the speed of the crank. If you forget that, you will come up with some really weird numbers.
Charlie,
I think YOU are right after all. Cam spec. sheet diagram/#s look to be degrees of CAMSHAFT rotation. Likely should double those #s to find ABDC crank position.
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By DANIEL TINDER - 15 Years Ago
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charliemccraney (5/29/2010)
Brain fart!
Cerebral flatulence must be catching. If you stare at that circular cam spec. diagram long enough, it's like the pinwheel they use to hypnotize people. (was led astray since the "two revolutions" caption at the bottom in such ultra-small print).
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By DANIEL TINDER - 15 Years Ago
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John Mummert (5/29/2010)
The E4 shows an intake closing of 84 degrees at .016" lash.
John,
Checked E4 specs. in my shortblock (#1 cyl.). Will repeat measurements to verify, but though finding precise crank degrees at .020" lifter rise difficult, it appears that specs. are very close to advertised. If anything, duration on both lobes measures 7 degrees short. Opening points are right on the nose (as expected with cam installed straight-up), but shorter closing would demonstrate a bit of built-in advance (unbalanced overlap). Disregarding heat expansion, it's hard to fathom how 51 degrees ABDC (.020" lifter rise) intake closing could end up being 84 degrees at .016" lash?
P.S. Total cam lift also comes up shorter than advertised (.244") Should be .283".
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By pegleg - 15 Years Ago
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Dan, do you have the 1.54 rockers? Although it wouldn't make THAT much difference, total should only be roughly 6%. (.283 x 94% = .266)
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By John Mummert - 15 Years Ago
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Dan, when you use Isky's specs you are looking at the cam lobe only. In that case the tappet gets down to .020" off the base circle at 60 degrees ABDC. They call this intake closing but it is at the TAPPET. The DCR programs use VALVE EVENTS with rocker arms and valve lash. This is what the running engine actually sees. In this case your intake closing is actually 83 degrees ABDC. As far as .244" lobe lift, either your indicator was not properly zeroed or it was not firmly attached. I would not be surprised if the actual lobe lift was a few 1/1000's less than advertised .283". That's another gimmick that cam grinders do to make their life easier but costs us a small amount of lift. Basically, when they grind a cam they leave a few 1/1000's clearance between the lobe master and the follower to make sure the base circle has no runout. But if the master has .283" lift and they leave .003" clearance your cam will have .280" lift.
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By DANIEL TINDER - 15 Years Ago
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John,
Good guess. Inaccurate readings due to sloppy set-up. I went back and did it right (more solid support for the pushrod, much shorter indicator stand arm, etc.). Intake lobe right on the money (closes 58 degrees min. ABDC). Total lobe lift still 4-5 thousands shorter than advertised, but that's assuming my modestly priced dial indicator is accurate.
You would think the DCR program calculator should specify needed specs. are valve event. How many people likely bought the wrong cam or pistons after running that program, thinking the calculator data required was manufacturer lobe specs?!!
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By DANIEL TINDER - 15 Years Ago
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pegleg (5/31/2010)
Dan, do you have the 1.54 rockers?
Frank,
Supposed to be 1.54:1.
Re: the Isky spec. sheet, they supply valve lift calculated at 1.5:1 using their lobe lift figures (@ .020" lifter rise) in amongst the recommended lash (.015"H/.017"C). Not surprising confusion often follows, as they don't provide any hints re: actual "valve event" specs.
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By DANIEL TINDER - 15 Years Ago
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John Mummert (5/29/2010)
Dan, I just went on Wallace Racing's website to figure your DCR and things look favorable.
John,
While some specifics still fuzzy (volumes of .150" cut Probe dome/out-of-the-hole portions & thicker Best gasket, E4 lobe profile, etc.), after rereading all the data and running various DCR program calculations, looks like even if rocker geometry/ratio is maximized I should be able to increase lash up to the point where noise is a concern, and still be just under the pump gas DCR limit.
Still a bit curious about variations in recommended lash by cam manufacturers. Aside from the relationship between advertised duration & running valve events, can only assume lash is calculated to minimize wear according to specific model ramp design?
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By John Mummert - 15 Years Ago
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Dan, tightening the lash will lower the dynamic compression, looser will raise it. More lash, fewer degrees off the seat, earlier intake closing Lash ramp designs vary considerably. Typically, we figure maximum safe lash to be where the valve side of rocker is moving @ .002" per degree of crankshaft rotation. Above that, tip wear on the rocker and valve stem will happen much sooner and it will get pretty LOUD. Most cam grinders will recommend something a little lower to keep things quiet. For the E4 with 1.54:1 rocker this occurs at .028" lash. At .016" lash the valve side of the rocker is only moving .0008" per crank degree. You should be able to run the lash between .014 and .024" without damaging anything. I would try between .018 and .022" and see how it runs and if valve clatter is objectionable.
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By DANIEL TINDER - 15 Years Ago
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John Mummert (6/2/2010)
I would try between .018 and .022" and see how it runs and if valve clatter is objectionable.
I emailed Isky to see if they could provide an E4 ramp/lobe graph. Might be able to then calculate exact lash:degrees ABDC intake close. Guessing .020"-.021" will bring DCR to around 8:1.
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By John Mummert - 15 Years Ago
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Dan, .021" lash shold give you an intake closing of 70ABDC. .020" will be 72.5 ABDC
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