Is it normal for a sbc to want over 40 degrees timing?

[steve cowan]

I was going to suggest coil or coil lead problem but it's running at the big end.
I just finished putting my 010 block 383 back together.
Small cast iron dart heads,tight quench 31"-32".
I redone the valve job myself and heads are 182cc from 165cc.
Measured 11.25:1 comp
220 psi hot cranking
Pump gas.
Have not been to track yet but has MSD dizzy with 6al programmable
Locked 32 idle,28 at rpm and 20 deg on cranking.
By the ground strap heat,the timing is very close, I have to recurved fuel but it's not bad.IIRC you have dart 180cc aluminium heads as I have a set as well going on my dart block.i find it unusual to need that much timing with that chamber,hopefully you did not deshroud to the max as I think that would cause problems??

[Circlotron]

There’s only 2 scenarios I can think of:
Either this inductive ignition needs a ton more timing, or the way I’ve altered the ssr has killed off a heap of swirl.

Hard to pinpoint when more than one thing has been changed.
Maybe simplest thing to do is temporarily go back to the old ignition and see if the problem persists.
I'm betting it's not the new ignition.

[1980RS]

A lot of factors go into timing an engine for sure. Here is what I found last year in testing, my peanut port 461 BBC liked 42-44° of timing and my little lol 406 with Vortec heads and more compression like only 31°of timing. I like others say give it what it wants, just keep an eye on the plugs that will tell you if things are going wrong. Yes the MSD boxes are great not over thinking stuff.

[CGT]

I wouldn't be shocked to see that engine needing 40° of timing for best ET.

Was the compression ratio increased by way of piston or milling?

Was the throat size increased along with the SSR work?

[rustbucket79]

What makes you think that jetting on the dyno is always perfect once in the car? Under hood air temperature, different headers amd exhaust, inertia, etc all affect fuel requirements.

[Walter R. Malik]

In the past I have built many SBC 9 to 1 race engines for oval track which needed 40+ degrees of ignition timing.
And a few very high compression engines which had a big dome piston crown in the chamber.

[dannobee]

This topic seems to come up every few years.

viewtopic.php?t=37995

I remember switching from "normal" sbc chambers to L31 heads in a lower division circle track car (before they were made illegal) and we needed to drop almost 15 degrees of timing (from 42 to 28). It's all about the shape of the chamber. The heart shaped chambers seem to require a lot less timing.

40 degrees doesn't surprise me at all. Especially if you inadvertently changed anything in the chamber.

[Biteme]

Look for Darin Morgan's videos on Youtube in reference to SSR, throat, and valve seat angles. He explains how it's easy to pick up flow at low and mid lift with the SSR on a flow bench (dry) but kill your wet flow. The fuel that used to turn easily into the throat is now slamming against the back of port wall and running down the wall into the chamber in big droplets. Big droplets need a longer burn time which is why it seems to want more timing. Anytime you have to increase spark advance to find best power, it's because the chamber is now less efficient than it was before.

Yes I think that’s exactly what’s happening. And I think the fuel is vortexing over the spark plug.

[Biteme]

I was going to suggest coil or coil lead problem but it's running at the big end.
I just finished putting my 010 block 383 back together.
Small cast iron dart heads,tight quench 31"-32".
I redone the valve job myself and heads are 182cc from 165cc.
Measured 11.25:1 comp
220 psi hot cranking
Pump gas.
Have not been to track yet but has MSD dizzy with 6al programmable
Locked 32 idle,28 at rpm and 20 deg on cranking.
By the ground strap heat,the timing is very close, I have to recurved fuel but it's not bad.IIRC you have dart 180cc aluminium heads as I have a set as well going on my dart block.i find it unusual to need that much timing with that chamber,hopefully you did not deshroud to the max as I think that would cause problems??

You’ve got a good memory!
Yes the ssr as factory was designed to work with low rpms. The port stalled at .500, so I layed the ssr back.
I’ve had these heads 15+ years so I figure they are good candidates to mess with and learn some stuff.
Previous to this they liked 33-36*.

[Biteme]

I wouldn't be shocked to see that engine needing 40° of timing for best ET.

Was the compression ratio increased by way of piston or milling?

Was the throat size increased along with the SSR work?

Was increased by new valves.
10.8 increased to 11.1
From cheap PBM to Ferrea 6000
The old pbm’s had had a few grinds and the margin was getting minimal.
Another thing I’m thinking is that the new valves having a nice think margin may be contributing to a bit of reversion.

[Biteme]

There’s only 2 scenarios I can think of:
Either this inductive ignition needs a ton more timing, or the way I’ve altered the ssr has killed off a heap of swirl.

Hard to pinpoint when more than one thing has been changed.
Maybe simplest thing to do is temporarily go back to the old ignition and see if the problem persists.
I'm betting it's not the new ignition.

Ain’t that the truth brother! I broke my own golden rule and made too many changes at once.
The old Msd digital 6 decided it was going to randomly switch off at inappropriate times lol.
I borrowed a mates Msd and ran the car down the road. No change, but I can only give this thing full throttle for a couple of seconds. Any more than that and I’d either kill myself or incur the wrath of our local constable!
Any proper testing I save for the dragstrip.

[Belgian1979]

In the past I have built many SBC 9 to 1 race engines for oval track which needed 40+ degrees of ignition timing.
And a few very high compression engines which had a big dome piston crown in the chamber.

I wonder about the piston dome as well. I remember reading more dome needs more timing.

[1980RS]

What makes you think that jetting on the dyno is always perfect once in the car? Under hood air temperature, different headers amd exhaust, inertia, etc all affect fuel requirements.

Bingo! we have a winner here. When you do dyno racing sometimes you go to the track and get a bad surprise.

[Biteme]

What makes you think that jetting on the dyno is always perfect once in the car? Under hood air temperature, different headers amd exhaust, inertia, etc all affect fuel requirements.

Bingo! we have a winner here. When you do dyno racing sometimes you go to the track and get a bad surprise.

You’re dead right there.
The guy that dynoed it though tunes a lot of engines that are raced all over the country, so have to perform at different tracks etc.

I trust him implicitly to have got the jetting correct for what I’m doing.

[MELWAY]

What makes you think that jetting on the dyno is always perfect once in the car? Under hood air temperature, different headers amd exhaust, inertia, etc all affect fuel requirements.

Bingo! we have a winner here. When you do dyno racing sometimes you go to the track and get a bad surprise.

You’re dead right there.
The guy that dynoed it though tunes a lot of engines that are raced all over the country, so have to perform at different tracks etc.

I trust him implicitly to have got the jetting correct for what I’m doing.

How much camshaft is in it and how much cranking cyl pressure?