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

[rebelyell]

if you have an elastomer damper, perhaps the outer ring has slipped (as well as its TDC groove)?

[Biteme]

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?

Solid flat tappet 260/264@0.050
190psi

[Biteme]

if you have an elastomer damper, perhaps the outer ring has slipped (as well as its TDC groove)?

Yeah that’s pretty much the first thing I chased.
It’s acting like it’s retarded 10*
Verified tdc when I assembled it.
I tried locking out the dizzy and even with timing set at 36 it started like a taxi. No kick back at all.
I should probably track down a piston stop and check it again, but I doubt the balancer moved between assembly and start up.

[1980RS]

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?

Solid flat tappet 260/264@0.050
190psi

That's about the same cam I had in my 9:1 comp 358 and that engine with some mild ported Sportsman II's likes 40° or more to run the best at the track.

[rustbucket79]

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.

If the dome design shrouds the spark plug that may well be the case, but it isn’t an absolute. I dynoed 2 different variations of a 406 in my younger years, same iron Bow tie heads but short block 1 was a flat top, 259/266 solid flat tappet combo, the other was over 14:1 dome, 276/284 solid roller combo. Both made best power with 34 to 35 degrees (locked) timing.

[novafornow]

Just my experience, but a 23 degree that likes 40 or more is very common. There are a lot of factors. Dome, chamber, cooling passages, etc. Give it what it wants. I have ran small cube combos at 45 - 48 because it ran best there. Randy really knows the 23 degree stuff, maybe he will speak up.

[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?

Flat top piston.
Increase came via new valves and a head gasket with slightly less diameter.

Didn’t touch the throat.
2.02 valve, 90% throat

[steve cowan]

You have to get that ignition box on a distributor machine and see how much timing you have because the box will retard with RPM. Until you figure how much retard you have and where it starts you have no idea what the timing really is.

Also, depending on the heads you may need 40 total. If you are using timing to clean up the plugs Id take some jet out of it and clean the plugs up that way. Sounds like it’s rich too.

When motor was dyno’d a few years ago the jetting was set.
It’s making more power now so I doubt it’ll need less fuel

This might surprise you but if the engine is making more power and the induction system is more efficient you might have to take fuel out or recurve the fuel,I am going through the same thing with my 383 at the moment.it has more compression, same heads but more efficient I hope,ported intake,bigger solid roller cam than the SFT I ran before and by the AFR and spark plugs it needs fuel taken out,no dyno or verification at the track yet.maybe with you increasing timing and mph increase because its rich and needs more timing,sooted plugs can happen fast if idle and transfer jetting is way rich.
I will be first to admit pumpgas is a pain to tune due to it being inconsistent batches.
My opinion with the spark plug being discoulored due to wetting I think most engines suffer from it more than people want to admit especially in a 23 degree head and pumpgas.

[Biteme]

I’m pretty cagey about taking fuel out at this stage.
If it’s getting fuel pooling then the mixture will already be lean.

I’m thinking I’ll keep sneaking the timing up 1 or 2 degrees at a time until I stop seeing an improvement, then back it off a couple of degrees, then put a fresh set of plugs in and see how they look after 1 run with no idling etc.

Then maybe start looking at valve lash.

Hopefully I have this thing dialed in before the end of the decade

[steve cowan]

Thats a fair call.
Do you mind sharing what car and combo
At 126-127 mph 10.6s ?? Or so
I won't be far off finishing my Dart 180s including new valve job,I will put some photos up when they are done

[Biteme]

LX Torana
372 sbc
5200 converter
TH350
4.11 gears
26” tyre

Yes did 10.6 @ 127 full weight with no head or tail wind.

Has gone 10.4 @ 128.9 but that was with less weight in car and a howling tail wind.

Best it went full weight previously was I think 10.70@ 125.

Things are looking up but man apart from a 350 I had with smog heads I ain’t been into the 40’s with the timing on this thing.
It’s like going into Apache country lol.

[Biteme]

PM sent Steve

[rustbucket79]

So if you’re nervous about lean, make a rip then jet up. If it gains, continue, if it loses, jet down.

[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.

If the dome design shrouds the spark plug that may well be the case, but it isn’t an absolute. I dynoed 2 different variations of a 406 in my younger years, same iron Bow tie heads but short block 1 was a flat top, 259/266 solid flat tappet combo, the other was over 14:1 dome, 276/284 solid roller combo. Both made best power with 34 to 35 degrees (locked) timing.

Yes, I believe that is correct. It will depend on a lot of things, like dome shape, rounded of edges and so on. Remember reading an old D. Vizard book in which he mentioned the effect of rounding off edges on the dome. I kept my timing conservative and I might have lost some power, but with added reliability.

[My427stang]

In general, lean mixtures want more timing, why are you guys recommending leaning? Not accusing, or correcting, just asking

In my opinion, big cam, 4 inch bore, unless it has a very good chamber, 40 is reasonable, maybe the last time 36 was the mistake of a bad light, etc?. MPH is going up each time, so it's making more power

I may have missed the a/f numbers, but if it's making power, and isn't too lean, I'd go for it. If it is on the lean side, I think I'd want to put it on a safe side and maybe the total will come down a little, if it doesn't, then it's just how the chamber is working now with the combo