Technical How Much Timing Do You Have ?

Thanks Lippy

 

On a SBC ?
If so, care to post its’ particulars ?
Just re-read, you set timing w/vacuum hooked up ?

 

Beautiful car and set up. I don’t know if your question was rhetorical, or serious, but either way I don’t know about flatheads enough to offer an opinion. I was just stating what I had read from a post made by Jim.

 

Thank you for the compliment.
No, it wasn’t really a question but a statement.....as soon as the weather clears I’m going to drop my timing to 23 total advance and see if my butt dyno can feel a difference. I can’t imagining it being any stronger, but you never know. I went from 27 degrees to 25 last year and that may have been my “magic” drop.
Flatheads don’t need/want timing as high as most V8s do.

 

What makes it tough to dyno a non-import, not OB2 engine, is finding a place that will actually let you inside the area and make a change to something.
There’s a place in my town that has a dyno. I don’t recall the cost, but they don’t do old school stuff. So I would have to go in, have them run it. Go home, make a change and take it it back, pay again, rinse and repeat.
Might be different in other areas, but for a working guy, you’d kinda like to get it done in a day.
I’d suspect that is why many of folks like me just “go by what others have with a similar set up” and have to feel good about it, then later on maybe make a tweak or two. I’d sure like to find someplace within a close drive that would let me in, bring a box of parts and let me make changes in the shop.

 

If you have a dragstrip,
MPH is a good
indicator of HP

 

I read in an old Ign. Book by (Jacob's Electronics), that you can't feel much under 10% by the seat of your pants, but then I'm not too sure that's correct.

I sort of proved my point when I chassis dyno'd my car, but then I've had a LOT of seat time in that car.

 

Are you using ported vacuum for the vac. advance mechanism?

 

A few things that most people never consider in the equation of Ign. timing are:

1) rod length to stroke ratio,
2) rod length to crank pin angle @ 90*,
3) how far down the hole in degrees is the piston at max. cyl. pressure,
4) bore to stroke ratio,
5) compression ratio,
6) cranking compression,
7) combustion chamber and piston dome design,
8) which determines mixture swirl,
9) which determines flame propagation and burn speed,
10) which determines which fuel to use,
11) air-fuel mixture ratio,
12) engine load, aerodynamics, gear ratio, vehicle weight, etc.
13) port flow to valve lift ratio,
14) quench area between the head and deck height,
15) cam timing (duration, overlap, LSA, lift, intake closing in degrees, etc.)
16) RPM range,
17) aluminum or iron heads,
18) intake charge temperature and density,
19) intake reversion,
20) port velocity
21) spark plug design, placement and heat range,
22) spark induction shape, and rise rate of the current flow
23) exhaust port design, header diameter and length,
24) boost flow and pressure,
25) intake manifold vacuum,
26) air density, (altitude / temperature / humidity)
27) I'm sure I must have forgotten something...

As you can see, there's more to Ign. timing than just stabbing a distributor!

 

I consider each of those things every time I pull out my timing light.....yeah right!

 

how to set timing with this set up on 350 Chevy?

 

Lots of good info here. As others said depends on head design as much as anything else. So a SBC I would expect anything from about 32 to 36 degrees BTC. Just want to point out that a lot of street driven hot rods are overfueled so not unusual to see 38 or 40. I like all in by 1800 or so although depends somewhat on gearing.

 

Yes, you can over fuel to "quench" detonation and therefore safely, over add timing, but the power will be down a little.

You can also under fuel to space out the fuel molecules (lean slow burn) and have to add timing to make it fire on time, but under great load and high mixture velocity, that combination results in disaster!

We used to say in drag racing,
"Before they blow, they really go, don't ask me, how I know!"

 

Same answer to same ? you posted in vacuum Advance poll.


Jenkins Competition
Time it till it spark knocks
and back off one or two

YESTERDAY AT 6:11 PM EDIT DELETE !REPORT!

 

38* all in @ 1800

 

SBF,16° initial, 36° total in by 2200 rpm. Tuned carb in at those settings.