[Blued and Painted]

Have you tried vacuum advance disconnected and plugged.
May be we can narrow it down.
There will be no power loss at wide open throttle.

[steve25]

In terms of your spark plugs where is the color change over point on the electrode ground strap, about mid to 3/4s the way up from where it's welded to the main plug body , or closer to the weld?

[455rebel]

Found 2 of the stiffest dist springs I had and installed them, set initial at. 10 Btdc, drove 30 miles last night , no rattle, but it was 50deg outside. Going to bump to 12btdc today and go again.
Thanks

[tom s]

Remember you cant always hear detonation!The silent killer.Tom

[ta man]

Originally Posted by steve25

In terms of your spark plugs where is the color change over point on the electrode ground strap, about mid to 3/4s the way up from where it's welded to the main plug body , or closer to the weld?

Not meaning to hijack..but this is something I'm wondering about with my engine..When I use a set of NGK 7's my color change is close to the weld,when I use 8's I'm close to the tip..Neither is ideal..this is with the same timing.If in the center is ideal..I wonder just by adjusting timing slightly will this improve combustion?

[steve25]

When running the 7s bumping up the timing should move that color change point .

[455rebel]

Set at 12btdc drove 15 mile, no rattle but temp was in 50s.
Sure runs better with 12-14 initial on low rpm part throttle.
Going to buy some Oct boost and carry with and if rattle again add and c if it helps.
Ps if u can't always hear it, how do u check for it?
Thanks

[steve25]

In all the time you have spent battling this you could have pulled the timing cover and at least retarted the Cam 2 to 4 degrees and have been done with it untill you can afford to stuff in a bigger Cam with new lifters!

[WARPed]

also could had tried disconnecting the vacuum advance to see what happens. light throttle issues makes me want to look there

[ta man]

Originally Posted by steve25

When running the 7s bumping up the timing should move that color change point .

It would be the other way?Bump up the timing on the 8's lower the timing on the 7's?

[455rebel]

Got hot, got rattle at 10btdc, went to 8, no rattle hot.
Ordered timing cov gasket, going to retard cam this weekend, already got a 3 key crank gear.
Will do bef and after comp test.
Thanks
Ps- runs suprisingly well at 8btdc , just not as crisp at low rpm.

[455rebel]

Originally Posted by Blued and Painted

Have you tried vacuum advance disconnected and plugged.
May be we can narrow it down.
There will be no power loss at wide open throttle.

Yes still ratteled .
Changing to the stiff dist springs made the first noticable improvement .

[steve25]

From my 45 years of experience, sharp off idle and low speed throttle responce ( and fuel mileage ) is better had by being able to run a stought advance curve with some vacuum advance even if it's at the expense of 1/2 a point of compression .

The hp loss from peak rpm on a motor that is not fully built for racing is like 5!

You may loose 2mph at the track, but the car will still reach its greatest mph faster with a good advance curve!

[HWYSTR455]

Was trying to avoid commenting here, but couldn't help myself.

Ok, you can't just toss the stiffest springs in to prevent det, you have to actually know what the timing curve is. And just to say, there are other factors that cause det, not just timing. Like what temp you run at, static CR, rich/lean, final drive ratio, etc. (and cam as you just recently found out)

You need to plot your timing curve to start, determine the area, load, etc that the engine is experiencing det, and then target that area for changes. If you don't approach it methodically, you're just making matters worse.

Put a timing light on it, with the vacuum advance disconnected, and rev the engine from like idle to 3500, in increments of 500 RPM, and record the timing. That will give you a baseline.

Key tuning areas are initial, total, rate (curve), and vacuum, and you tune in that order.

So then take it for a drive, note at what RPM you experience det, and the conditions, and record that value. Then look at your baseline recordings for that RPM, and put springs in it that addresses that area.

I attached a chart from a 455 iron head combo I had that was very close to 10:1, and accelerating, and driving in top gear. Should give you an idea of the process. You can see the range where I was experiencing det, and how I targeted that area to control it.

Make sure you're not going lean. Try stepping up 2 or 4 jet sizes and see how it runs, and if it experiences det the same as before. Don't run higher than a 180 t-stat, and in extreme cases, you may want to run a 160 t-stat.

In general, it's a trial and error thing, but by just tossing the heaviest springs in there, you are impacting many areas of operation, and will most likely suffer in other areas.

.

[Cliff R]

The way I tune all street set-ups here is to forget about the vacuum advance and find the ideal initial timing, then total timing the engine wants combined with the most ideal advance curve.

Once you find settings that allow for hot restarts without "bucking" the starter, and a curve that's fast enough for best power and total timing without detonation, lock the distributor down and forget it.

Then start adding in vacuum advance to improve things in the "normal" driving range.

Most very well thought out engine combinations will like about 10-14 additional degrees from the advance at cruise. This will improved off idle power, throttle response at low throttle angles, fuel economy, engine cooling and allow for a leaner mixture from the carburetor w/o negatives. This also adds up to less carbon build up in the cylinder heads and exhaust system.

With higher compression engines and relatively small camshafts you'll find 9 times out of ten ported vacuum to the advance will be the best choice. Same thing with very well thought out engine combinations making great power, there will seldom, if ever be any need to run the timing clear off the scale at idle speed to make them happy.

If you do not have an adjustable advance (for how much timing is added), there are several methods to modify them. I use the MIG here, but a screw and a washer can be made to work equally as well. Use drill bits to measure the travel of the arm so you know how much timing is being added with each modification. .120" is around 5 degrees (10 at the crankshaft).

You can also custom modify the mechanical curve in a similar manner with a positive stop for the advance. HEI's are slightly different that points distributors, but same basic concept, you need to control the amount of movement of the rotor from idle to full advance.

I attached a couple of pics showing how I set them up here. This gives you the amount of advance added, when it comes it can be verified and adjusted on the distributor machine or engine with a marked balancer and or dial back timing light.....Cliff

PS: those aftermarket advance kits are completely HOPELESS for attaining the same results, and are complete JUNK, IMHO. They move the relationship of the cam/weights and make it nearly impossible to establish a smooth advance without some of it in at idle. I just toss all that crap in the trash can when factory distributors show up here with it, and install the factory parts for perfect results every time.....

[steve25]

Good info, but I think you also need to track the vacumm under ping conditions also if you want to tie in a possible lean condition ?

[HWYSTR455]

That's good advice Cliff, though I have used those aftermarket limiting cams with success. And the order is basically what I was suggesting too. Vacuum last.

And very true, most aftermarket weight/spring kits are junk. You can use the springs, but never use the weights. (only OE ones as you suggest)

Yes, you can take it a step further steve25, and monitor the vacuum during driving and det conditions, but in general, just by load and throttle position, you can kind of figure out what the vacuum is doing anyway.

One thing I do is put a hand vacuum pump on the advance can while running, slowly add a pump at a time, read the value, and the timing. You can chart a can the same way.

Most aftermarket adjustable cans have a limit of about 9 turns, if you go past that, and the screw comes out, it's next to impossible to reinstall it. (and you end up having to replace the can)

If you look at the Crane adjustable can kit, it comes with the limiting plate/cam:

https://www.summitracing.com/parts/c...00-1/overview/

Accel makes the cam separately, but I can't find the number right now.
.

[Cliff R]

I don't like or use the Crane adjustable advance. They make vacuum advances that you can insert an allen wrench in and control how much timing is added, quick and easy.

The cammed plate on the screw used with the Crane advance just isn't a good way to do that deal, IMHO.

We have vacuum advance units here that already start early (lighter spring tension), so all we have to do is modify how much timing they add and install them......Cliff

[TedRamAirII]

I have heavy springs, but my advance is all in at 2500. Do I need lighter weights? or where can I get stronger springs? I really need to get it stretched out as I'm already at the edge.

[Sun Tuned]

Ted if it's an HEI, the cam may need to be changed as it currently may be an aggressive advance cam. Meaning it operates rather quickly rate wise ( not a gradual cam lobe but more flat causing it advance quickly).

As far as springs, those generally have to be custom made but not always.

Don't forget you can clip a coil off yours and lay over the fresh loop to stiffen a spring if needed.