[scott70]

Just curious what combo you have in your MSD dist. I run the 8528 RTR in my 70 gto ,455 4 speed. I run the black bushing (18 degrees) with about 16 initial. Hard to tell because the factory timing marks dont go that high and ends with 34 total. Using their silver heavy and silver light it totals out around 3100 according to my tach. At full temp it does not buck on the starter at all. I was thinking about trying the purple bushing (19 degrees) and the light springs which is supposed to total out around 2750 rpms according to the chart but Im wondering if Im wasting my time. Wondering what other people are using for optimal performance in a street car set up.

[Kenth]

Here are the factory specs for a 1970 455.

My 1970 455 with #96 heads and #744 camshaft has never ran as good as it does with these.
I have found that earlier timing coming in faster held my engine back from it´s full potential, especially with today fuels. Learnt that feeding the engine with proper amounts of combustible air/fuel mixture for best performance. Ignite a too lean mixture with a mountain of timing does not work if you want max performance.

FWIW

[Formulajones]

I always use the black bushing because I tend to be tuning cars with a bit of camshaft that like more initial (idle timing)

In fact the 598 crate engine I just set up wanted more so I machined my own bushing. The black one is .375" so I made a .405" which is as big as you can go that fits in the distributor without rubbing the shaft. Every .030" gives you about 4 degrees additional initial or you can look at it like 4 degrees less of centrifugal.

So that one ended up with 22 initial and 36 total (14 degrees centrifugal) all in by 2600. Cranks and starts fine. In fact it starts better at this setting than it did with the black bushing at 18 initial and 36 total.


Every car is a bit different but I always tend to use the black bushing. Especially on engines that make peak power with low total timing. Something like 32 total would only give you 14 degrees of initial anyway with the black bushing, and even less if you lowered total timing.

[AG]

I use one silver and one blue spring with the black bushing.

[PunchT37]

I forget the bushings and springs but it is all in at 3000 with 14 down south. 246 cam with t2 manifold. 463 cubes. It rips.

[scott70]

I used to run the next set of lighter springs with the black bushing and it totaled out at around 2500-2600 rpm’s. I put the next heavier set of springs which ended up around 3-3100 rpm’s and it didn’t seem to make much difference in the 1/8th mile. I thought of maybe trying the purple bushing which would put my initial around 14 with about 20 mechanical. With light springs it would total around 2800 but now I’m thinking it’s probably a waste of time.

[Formulajones]

The all in total really won't make too much difference at the track simply because while racing the engine won't spend any time below that rpm anyway.
You could have total all in at 2500 or 3100 but as soon as you whack the throttle and go through the gears the engine stays above that, even during a shift when rpm drops.

The benefit you see with where the total comes in is street driving along with vacuum advance mixed in. If the total comes in way out in the rpm range you give up quite a bit of mpg and part throttle drivability. This is where you have to play with it to find a good balance without detonation on today's gas. Every car is different there, not just engine combo but car weight, gearing, how hot you want to run it etc....
The factory curves were lazy and on top of that most had partially working vacuum advance with tcs and the like so these cars sucked the gas as a result when new.

[77 TRASHCAN]

Originally Posted by Formulajones

I always use the black bushing because I tend to be tuning cars with a bit of camshaft that like more initial (idle timing)

In fact the 598 crate engine I just set up wanted more so I machined my own bushing. The black one is .375" so I made a .405" which is as big as you can go that fits in the distributor without rubbing the shaft. Every .030" gives you about 4 degrees additional initial or you can look at it like 4 degrees less of centrifugal.

So that one ended up with 22 initial and 36 total (14 degrees centrifugal) all in by 2600. Cranks and starts fine. In fact it starts better at this setting than it did with the black bushing at 18 initial and 36 total.


Every car is a bit different but I always tend to use the black bushing. Especially on engines that make peak power with low total timing. Something like 32 total would only give you 14 degrees of initial anyway with the black bushing, and even less if you lowered total timing.

Tell us more about the 598 and its vehicle!!!

I, I want to know!!!

[scott70]

Originally Posted by Formulajones

The all in total really won't make too much difference at the track simply because while racing the engine won't spend any time below that rpm anyway.
You could have total all in at 2500 or 3100 but as soon as you whack the throttle and go through the gears the engine stays above that, even during a shift when rpm drops.

The benefit you see with where the total comes in is street driving along with vacuum advance mixed in. If the total comes in way out in the rpm range you give up quite a bit of mpg and part throttle drivability. This is where you have to play with it to find a good balance without detonation on today's gas. Every car is different there, not just engine combo but car weight, gearing, how hot you want to run it etc....
The factory curves were lazy and on top of that most had partially working vacuum advance with tcs and the like so these cars sucked the gas as a result when new.

I have a accel adjustable vac can. I have it hooked up to full manifold but took the allen wrench and have it adjusted so at idle the initial timing is the same whether the vac hose is hooked up or not. As you slowly rev the car with the vac hooked up the timing goes up and if I remember right it stops around 45 degrees. What it does while driving I have no idea. My carb doesnt have ported vaccuum. Driving with or without vaccuum going to the distributor I really cant feel any difference.
Yeah Im sure thats completely wrong for how the vac advance is supposed to work,,,lol.

[Formulajones]

Sounds like you tightened up the spring in the vacuum advance with the Allen wrench. That basically adjusts how much vacuum it takes to start moving the actuator and also shortens or lengthens the duration at which it reaches peak.

I use the adjustable units on everything I tune. I weld the slots to limit arm travel to about .200" which typically gives me 10-12 degrees at the crank additional, then adjust the spring tension to something favorable for the particular engine it's on. That's something you have to play with. These mods basically makes the vacuum canister work like the popular b cans that came on the hotter muscle cars of the day with some adjustability.

[Formulajones]

Originally Posted by 77 TRASHCAN

Tell us more about the 598 and its vehicle!!!

I, I want to know!!!

It's an engine I bought from blueprint. So far a great package, very responsive and loads of torque everywhere. Very happy with it so far. I dropped it in my Chevelle.

[Formulajones]

Originally Posted by scott70

I have a accel adjustable vac can. I have it hooked up to full manifold but took the allen wrench and have it adjusted so at idle the initial timing is the same whether the vac hose is hooked up or not. As you slowly rev the car with the vac hooked up the timing goes up and if I remember right it stops around 45 degrees. What it does while driving I have no idea. My carb doesnt have ported vaccuum. Driving with or without vaccuum going to the distributor I really cant feel any difference.
Yeah Im sure thats completely wrong for how the vac advance is supposed to work,,,lol.

Also forgot, I always use manifold vacuum and as you described you can adjust that spring to give you as much or nothing at idle. Depends on how much vacuum your engine makes. I typically will add some to idle timing just because I've found some benefits with around town slow cruise and idle situations with most cars. Guys tuning EFI cars with electronic control do it all the time on a timing table, the vacuum advance can be made to do very similar in an antiquated way.
Example, you have 16 initial and 34 total. That's 18 degrees of centrifugal with black bushing. About all your EFI cars have a timing table where they idle with say 25 degrees but initial is 10 for example. They crank nice but idle with more timing.
You can do the same and add some with vacuum advance. That's a number you'll have to play with but I find the more radical the camshaft the more idle timing they like. Especially tight LSA cams which is something most here on the board don't mess with. This method improves drivability and mpg and makes some of the more rowdy engines very streetable and make more vacuum as a result.
I'm setting up a distributor for a guy now with a 396 Chevelle. Stock appearing but had a shop build the engine with a fairly lumpy cam. He's trying to run factory timing curve and it's not happy there. Hardly makes vacuum and complaining the car runs 230 degrees all the time.
Yeah 8 degrees initial and no vacuum advance ain't goona work in that scenario, lol.
When I'm done that cam will sound more like a mild cam and we'll see how much it improves temps before I dive in further. It's always the first thing I'll do before even touching the carb or anything else. 9 times out of 10 timing issues are the cause of multiple complaints.

[scott70]

Originally Posted by Formulajones

Also forgot, I always use manifold vacuum and as you described you can adjust that spring to give you as much or nothing at idle. Depends on how much vacuum your engine makes. I typically will add some to idle timing just because I've found some benefits with around town slow cruise and idle situations with most cars. Guys tuning EFI cars with electronic control do it all the time on a timing table, the vacuum advance can be made to do very similar in an antiquated way.
Example, you have 16 initial and 34 total. That's 18 degrees of centrifugal with black bushing. About all your EFI cars have a timing table where they idle with say 25 degrees but initial is 10 for example. They crank nice but idle with more timing.
You can do the same and add some with vacuum advance. That's a number you'll have to play with but I find the more radical the camshaft the more idle timing they like. Especially tight LSA cams which is something most here on the board don't mess with. This method improves drivability and mpg and makes some of the more rowdy engines very streetable and make more vacuum as a result.
I'm setting up a distributor for a guy now with a 396 Chevelle. Stock appearing but had a shop build the engine with a fairly lumpy cam. He's trying to run factory timing curve and it's not happy there. Hardly makes vacuum and complaining the car runs 230 degrees all the time.
Yeah 8 degrees initial and no vacuum advance ain't goona work in that scenario, lol.
When I'm done that cam will sound more like a mild cam and we'll see how much it improves temps before I dive in further. It's always the first thing I'll do before even touching the carb or anything else. 9 times out of 10 timing issues are the cause of multiple complaints.

I run a ra4 sized cam with roads vmax lifters,, idles with a little lope. I adjusted the vac can to where it’s right on the edge of adding idle timing . Mine totals at 34 but hooked up vac is around 45 so it sounds like it’s adding around 11 degrees which sounds about right. I guess I’ve got it about where it all should be,, as far as bushings go I guess I’ll leave the black one and having it come all in at 2500 or 3000 rpm’s I guess I’m better off leaving it at 3k and just leave it all alone. I might try adjusting the can to add a little idle timing and see if it helps.Thanks

[srmmmm]

MSD 8528 Distributor:

>Green bushing for 22 degrees mechanical
>Two blue springs for mechanical in at 3200rpm
>12 degrees initial

Comp XE287HR cam, 6X-4 heads, 350 block bored .060, 4.25" crank

[chiphead]

400 with 62 heads and 2802 cam, 3.25 gears, loose converter

16* base, 19* purple bushing
heavy silver spring, blue spring
11* of vacuum advance at 10" of vacuum, ported vacuum

35* of timing by 3500 RPM, 46* at part throttle cruise
93 octane
RPM intake and 750 double pumper

Runs really well, stays at 180*F. Converter is loose, so its not heavily loaded below 3000 RPM. May try one heavy silver and one light silver spring to get a little more MPG at cruise. It runs so well I'm hesitant to mess with it.