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454 cam phasing

4K views 18 replies 3 participants last post by  ratlover 
#1 ·
I posted this question at chevelle.com but not much help there so far. Any advice from here would be welcome.

I have a 67 chevelle., 4 speed 3.55 rear 10.2:1 454,+.040, 049 heads with 11/32" stem 2.19/1.9 valves. total combustion chamber volume is 103cc with the speed pro domes and the iron heads, measured by burette.
I was running a xe268h as I was enjoying the tame idle and torque for a mostly street driven car, but detonation proved to be a problem and I popped the head gaskets on #2 and 7 cylinders. Blue fel pro permatorques and stock re-used head bolts may have been a mistake.
I am going to swap to a 282s comp solid flat tappet. I am wondering if I should retard the cam 4 degrees to reduce the bmep a little more.
With the 268h the intake closed at 60, producing a dynamic compression ratio of 8.48:1, but it rattled at about 2000-3000 rpm. limited the total timing to 34 degrees with a stop pin on the centrifigal and ran 94 octane.the bmep was peaking at 180 psi right at that rpm range according to desktop dyno. Wallace cranking calc says the cranking compression should have been 171, but it was closer to 175-180psi.
the 282s closes the intake at 67 which produces 8.04 dynamic, 160 psi cranking, and a bmep of 176-178 where it was 180 before with a peak of 180 at about 4000rpm.
I am wondering if I should retard the timing 4 degrees to close at 71
this would produce a dynamic of 7.79 with a cranking pressure of 154psi and a bmep of 174 where it was knocking with a peak of 176. would this be detrimental to performance?
thanks in advance for any input.
 
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#3 · (Edited)
I've used the Keith Black DCR calculator for years with good success. It requires the intake valve closing point at 0.050" tappet lift, plus 15 degrees.
Your 268H cam closes the intake valve at 35 degrees ABDC @0.050" and when plugged into the KB calculator, reveals a DCR of 9.004:1. With iron heads, it's no wonder the motor is spitting out the head gaskets. I won't recommend anything over 8.5 on the calc with iron heads and less than 9.0 with aluminum heads. I also always recommend a tight squish, 0.035" to 0.045".

The 282S closes the intake at 44 degrees ABDC @ 0.050" tappet lift and will produce a DCR of 8.531:1. If you installed it 2 degrees retarded, closing the intake valve at 46 degrees ABDC @0.050" tappet lift, the resulting DCR would be 8.416:1 and the motor should operate on pump gas without detonation. Of course, I still have no idea of your squish, so that will play into the equation also.

If it were mine and I had made the mistake of using iron heads with a 10.2:1 SCR, I would use a 2-piece timing cover when I went back together, along with drilling the cam sprocket for hollow dowels. That would make it easy to retard the cam another 2 degrees if you have detonation problems with the new cam.
http://www.summitracing.com/parts/clo-9-231/overview/

Drill the cam sprocket hole to 13/32" and use these bushings.....
http://www.summitracing.com/parts/cca-4760/overview/
It's very easy to get this wrong and advance the cam instead of retarding it. With the cam sprocket stationary, the cam itself should be rotated counter-clockwise to retard it, with the thinner part of the bushing on your left and the fatter part of the bushing on your right if you are changing the bushing with the cam pin straight up.

Here's the KB calculator.....
https://www.uempistons.com/index.php?main_page=calculators&type=comp2

.
 
#4 · (Edited)
I have a wideband 02 and it was consistent at 13:1 throughout the 2-6k rpm range. I have a aluminum crossflow and the temp never rose much above 180-190 f. Overheating was never an issue. I caught the head gasket early. I pulled the engine to get the headers recoated, and when I pulled the plugs there was a couple of wet ones. I paid close attention to the timing. I ran a silver and blue spring, put a stop pin to limit the advance and ran 8* direct port vac advance. Ignition timing was 16 initial and 34 total. It ran hard, but I was not sure if it was the weights on the centerforce clutch rattling a bit or detonation. Pistons show no signs of damage. Pulled them and checked the ring lands and rings all ok. plugs had no signs either.piston is about .008 down the hole with .040 thick gasket. could be a little tighter.Thanks for the replies by the way! I am surprised that the Wallace dynamic calculator would be that far off, but it calculates from intake closing point. I have a timing chain that has keyways cut for +4 or -4 so I am thinking it would be wise to try the -4 right out of the gate.
 
#6 ·
The following was copied from the website of Ken's Speed and Machine Shop, Inc.......

Pre-ignition/Detonation:
The porcelain shows up pre-ignition and detonation (timing/octane). It will not accurately reveal jetting/air/fuel ratios. To look for the first/beginning signs of detonation, search the white porcelain for tiny black specks or shiny specks of aluminum that have fused to the porcelain. When detonation occurs, part of the air/fuel mixture explodes instead of burning, the explosion is heard as a "metallic knock", this audible knock is the result of a sound shock-wave, and this shock wave travels back and forth across the clearance volume "disrupting" the cooler boundary layer gases that cover the entire clearance volume area. This disruption allows "more" heat to be transferred into parts, especially, domes/piston tops, along with the very rapid rise in pressure like a hammer blow, pistons can get torched with melted sides and holes!!! With the early signs of detonation, the shock-wave will also rattle rings causing the tiny amounts of oil that now gets by rings, to be fused to the white porcelain as tiny black specks, also fused as specks are soot that was clinging to clearance volume surfaces in the relatively "still-air" of the boundary layer. One step beyond the black specks, will be tiny specks/balls of aluminum coming off the pistons that will be fused to white porcelain,....the next step to be reached is occasional pieces of the porcelain being broken-off as detonation gets worse, etc. Soon after that are holes, blown head gaskets, broken connecting rods, etc.

"I am surprised that the Wallace dynamic calculator would be that far off, but it calculates from intake closing point.
So does the KB calculator, but it uses 0.050" closing instead of whatever number the Wallace calculator uses.
 
#7 ·
deck height is .008 down the hole. I wanted to zero deck the block but the machine shop owner said it was a bad idea. I guess he meant well and assumed that it was a gamble decking the block any more than necessary, as I was having the block bored at the same time and had not fit the crank and pistons to the block yet, even though I had the crank and pistons in for balancing..yeah whatever(the machine shop is a couple hundred miles round trip, wanted to get it done in one trip) I figure .048 quench is tolerable. spent $2k in machining and balancing and headwork. heads were planed as well.
 
#9 ·
I will post some pics of the piston tops and plugs... let me know what you think. Only got a few hundred miles on the motor, maybe a couple dozen real hard flat out runs. Thanks for your assistance. I got the machining done in Nanaimo. They did nice work, but it was pricey as there are not many shops on the island That was for new guides and hardened seats on the heads as well.
 
#16 ·
anything on the 10x scope to look for on the pistons or rings? They seemed to be ok on inspection, but so did the plugs before a closer look. I thank you for your experience. No replacement for that! I was thinking of stepping up to the 294s instead o the 282s, but I still want to maintain power braking and drivability. The 294 close the intake at 73, so I am thinking the 4 degree retard may be the safe way to go closing the intake at 71. That will put me at 8.29 which should still be a streetable compression. The lift on that cam is still conservative at.561, which I hope will contribute to longevity of the cam lobes. I am also springing for the edm lifters and the nitriding of the cam as well. Thanks again for all the help.
 
#18 ·
thanks for the pointers. Those old posts were when I was running forged flat tops. and your right the vac advance was waaaay tooo much then, but it was kind of a crutch for the low compression. I run 94 always. I actually run at 12.5-12.7 afr. the carb seems to stay consistent throughout. its an 800 cfm spreadbore. I have a crane adj vac advance now and its limited to 8*. I tried unplugging it and it made no diff to the spark knock, so I left it for fuel economy. I measured the combustion chamber by filling the chamber with light oil and the piston at tdc with a burette. it was 103cc. Plugged that figure into desktop dyno and that's what it told me, so I assume it was correct. what do you think it is?
 
#19 · (Edited)
OK.. finally got the 282s cam. dialing it in. not adding up. could use some advice...Is it me or did comp send me the wrong cam?
Lifters lashed at .020" as per cam card. ICL verified at 107.5 (should be 106 timing chain installed straight up dots line up perfectly)

Here's what I got:
IVO@ .015- 23 btdc should be 35
IVC@.015- 62 abdc should be 67
EVO@.015- 62 BBDC should be 75
EVC@.015-19 atdc should be 27

IVC @ .050 49 abdc should be 43
IVO @.050 11BTDC should be 11?
EVO@.050 51 bbdc should be 51?
EVC @ .050 8 atdc should be 3

what the heck? checked the tdc several times, it's within a half a degree.

cam only has .540 lift supposed to be .561

AM I crazy? or is this cam not exactly as advertised?
 
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