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Old 05-04-2010, 10:20 PM
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New engine break-in & tuning

So, I just fired up my rebuilt Pontiac 400 last Friday. Second rebuild on the engine, but waited about 6 years this time around and took my time. Followed the Comp Cams break in procedure, used their break-in oil, monitored pressure w/ mech gauge, drained the oil and changed the filter after break in. How much metallic content is considered 'typical' in the break-in oil? I have broken in a few new engines before and noticed the oil can contain varying amounts of shiny iron particles (sticks to magnet). This always went away with the first oil change, but just curious of others' experience with this.

Also, took a crack at setting the timing. It didn't seem to like anything lower than 16 deg initial (vac adv disconnected) before it really fell on it's face at idle and became hard to start. I'm running a Comp 292H, 10:1, ported heads, 2.11/1.77, Torker II intake, Edel 750. Seems like a lot of advance, but I hear these cams like a lot more at idle. Does this seem reasonable? I know timing is very specific to the engine setup, but anybody else run a 292H and find the same thing?

Lastly, took a shot at idle mixture. Followed the procedure in the carb book which seemed to jive with what I have read on this forum. Seemed like I had to crank those screws out maybe 2-3 full turns before hitting peak vacuum (all the while adjusting the idle to keep it constant, of course). This thing has such a choppy idle even at 1000 rpm it is very difficult to monitor vacuum, and I'm trying to keep the idle down to about 750. Can I set the idle mixture at 1000rpm for max vacuum then just turn the idle down to 750?

I appreciate hearing if anybody else has some input with a similar setup.

Thanks!

Phil

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Old 05-04-2010, 11:18 PM
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A lot of what looks like metal in the break -in oil is often moly paste, did you use a moly based cam lube?

Your timing sounds in the ballpark, might like more initial yet. I know SBC's with the 292 comp cam like to be in the 20-24 initial range but you have to be careful with the total timing added by the mechanical advance, not more that 38 total. It ususally takes modifying the advance stop in the distributor to get a high initial timing without sending the total too high.

You are not likely to get the engine down to a 750 rpm idle with this cam, 900 should be doable however, maybe 850 rpm. More initial timing will really help this, as well as full manifold vacuum to the vacuum advance along with an adjustable advance can.

Increased initial timing will also allow you to close down the idle mixture needles some too.
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Old 05-05-2010, 12:59 AM
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Interesting

I use to have 6.6L 78 trans am and I decided to go all out like you did here lol. I didnt have these issues but I did have good amount of metalic dust in oil. The compression on mine was about 9.5:1.

Anyways when I build my most recent engine for my cousin (455) I got it up to 11.2:1 and I had funny chopy idle for a while. The engine also had a hard time starting. I got it started and kept it to about 1000rpms for a while. I was basically trying to let engine settle it. After a few try's the engine fired up on a dime then I was able to fine tune it.

JD
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Old 05-05-2010, 07:42 AM
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I used the CompCams moly lube that came with the cam. Perhaps that's what I'm seeing.

As far as timing, I rebuilt the HEI with an adjustable vacuum advance as well as a mechanical advance spring/weight kit. Of the three spring pairs I'm running the middle, and based on the chart that came with the kit it comes on around 1500 and in full around 3000. The lighter springs come in right around 1000rpm, which I figured was probably too soon. I don't have an adjustable timing light so I'm not sure what total timing is, the tab only goes to 24 or so (Rather than buy a new timing light I was thinking about marking the damper for reference. Either way the next step is to dial in total timing). Based on my calibrated eyeball it looked like I was in the mid 30's.

As far as running full manifold to vacuum advance, that makes sense since this cam makes much less vacuum at low rpms. Some coworkers have mentioned they have disabled vacuum and went mech only as long as the gap between initial and total can be handled by the mech advance. Any thoughts on this?

Thanks!
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Old 05-05-2010, 08:13 AM
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Use MAKE A TIMING TAPE for a temporary tape that you can also use to mark the damper w/the total timing for future reference.

You might find your Pontiac not needing quite as much timing as a SBC- somewhere around 34 max works well for most OEM Pontiac heads.

Initial timing is another thing altogether. Between the 292 cam and that Torker II intake, you're going to need a LOT of initial. I wouldn't lock the timing at full advance, unless absolutely necessary- which it isn't.

If I were going to change just one thing on this build, it would be to use an Edelbrock (or clone) RPM dual plane intake.

If I were given two changes, it would be the intake and cam, IF the heads are not either ported RA IV or Edelbrock, etc. aftermarket heads. I've yet to see that cam (or the 305) work as expected w/D-port OEM heads on a 400 Pontiac engine.
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Old 05-05-2010, 09:29 AM
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Thanks for the input Cobalt. I just found the article on "Distributor Tuning and Theory", very informative, may answer most of my questions about spark timing. The timing tape instruction is pretty good. I was thinking of setting the damper mark at 10 and using my friend Mr. Sharpie to mark a line at 0, but the masking tape will probably work a little slicker.

As far as head/intake/carb combo, heads are #46 small chamber d-ports (1969 castings, off of a 389 GTO), 2.11/1.77 Manley Race, bowl blended and ported. On the bench they flowed BIG TIME below .300 (can't recall the numbers, they were stored in a DesktopDyno file on a computer that has since kicked the bucket) and seemed to flatten out above .400. That's why I picked a cam with more duration rather than more lift. Figured the Torker II might give a flatter torque curve within the 292H's powerband. I was afraid an RPM might be slightly mismatched and fizzle out around 5500-6000. Understandably I gave up some of the bottom end, but we'll see how the trade-off worked. I used to have an Offy dual plane but I sold it years ago (MISTAKE). Ran it on this same engine but with a 230/230 @ .050 .480 lift and it ran like a raped ape from 2k-6k.
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Old 05-05-2010, 10:31 AM
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Quote:
Originally Posted by PontiacPhil
That's why I picked a cam with more duration rather than more lift.
I'm glad to see that you've gone into this w/an eye on this being a Pontiac, not a "big SBC"- as is often the case. I don't believe the high rise RPM-type dual plane would hurt the 400, but you know their out there if you need it.

Maybe I'm more conservative than I realize- I used Rhodes lifters on the intake side of a cam w/less duration than your cam, and this was on a 455 w/ported 6x-4 heads and FT's! lol Pulled like a mother ****er, though. Mid 12's in an all-steel (plus full OEM glass, interior, radio, etc.) '81 Camaro w/3.31's. 12.7 w/3.08's, shifting at 4900 RPM. Had a lot more in it, but got offered a ridiculous price for it to install it into a 4WD '78 Blazer, of all things.

Oh, and it never had a bigger carb and intake than a 4777 Holley (650 DP) on a Performer (not RPM, they weren't yet made).

Good luck.
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Old 05-13-2010, 08:42 PM
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So I took some time to sit down and study the article on distributor timing. All I have to say is... WOW! I wish I had read that years ago.

Update on my timing struggles:

Had the base at 16 with medium springs and noticed it was a dog below 2000, then WHAM! The motor would break loose and scream up to 5k. Got the timing light out and noticed that the timing was not so much of a curve as it was a step. It would stay at about 16-20* BTDC until 2k-2.5k rpm then it would go all in and the engine would take off. Took apart the dizzy and noticed the weights were floating up and down on the shafts, and the bushings were not very well toleranced, lots of slop between the pins, bushings and weights. (Recall I installed a Mr. Gasket advance kit which came with new weights, bushings & spring kit).

So I put the lighter springs in and checked again. Now the timing was all over the place, jumping from 16 to 24 erratically. Thoroughly irritated, I removed the Mr Crap-it advance kit, put the original cam and weights through the wire brush wheel and put them back on. Installed the medium springs from the kit and fired it up. Set the base timing at 20* and she SCREAMS to life, topping out at about 38* BTDC around 3k. I can't get my hand off the throttle quick enough to keep from hitting redline! Checked the timing on the vacuum advance and it kicks in about an extra 18-20, which I plan on backing off to probably 16. Might back the initial down to 16 to keep it around 34 all in, based on Cobalt's suggestions.

After looking at the Mr Gasket advance kit I should have known it was trouble. The parts were all stamped so they had sharp edges that catch on the cam, and the bushings do not fit snug to the shafts on the dizzy and the OD is too small for the weights, so everything tends to move around and bind up. That's what I get for buying an $8 mechanical advance kit.

Thanks for all the info guys. And that article was excellent.
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Old 05-13-2010, 10:14 PM
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Good job getting it dialed in, ya done good!
You have found out what other guys have, about those advance kits. The springs are the best part by far, of the whole kit.

AFA determining the optimum total timing, the way I've set that when there wasn't anything to go by, was to go for the best MPH in the quarter mile- using the same gas you'll be running on the street. You'll find a place where adding to the total timing will no longer add any MPH, I'll go back 2 from there and call it good.

In your case, you know it'll be in the area of 32-38. I'd start at 32 and work my way up from there.
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