techg8

My 403 Olds is running strong after a re-ring and edelbrock cam/intake swap this past winter

I upgraded the exhaust with headers and a Pypes RacePro X kit - which I love.

I want to recurve the HEI distributor for response and power and am looking for advice from 403 owners who have done the same.

current stock specs:
18 degrees initial
17 degrees mechanical in by ~2250rpm
17 degrees of vacuum advance

I "get" the idea of advancing til just before pinging under load, but would like to hear form people what worked best for them etc.

Is there advantage to be had in a recurve or are the stock settings pretty much it?

Thanks

TripDeuces

Most V8 engines work best with about 36* total ignition timing give or take a degree or two either side of that. Right now you're at 35* total not counting vacuum advance. That is pretty ideal. Add in the fact you have all this timing in by 2250 rpm without the engine pinging and it sounds like you're doing great.

The only way to know if more or less timing is going to help you is by testing. Either on a dyno or at the track using your times as a gauge. I'm not a fan of adding more timing until it pings then backing off a few degrees. That's old school stuff (yes I've done it back in the day) that really only tells you you've put too much timing into the engine not necessarily the correct amount.

The way it sounds your car is driving now is a decent indicator that you're probably as close as you're going to get without further tools.

oldcutlass

Based on the numbers you gave it is set up right. As Trip stated, the only way to make it better is fine tuning at the track or dyno. Are you having any issues with the current set up?

DoubleV

Vacuum advance seems on the high side ( if you're running an EGR ) and your total timing is all in very early. Make absolutely sure you're not pinging in any situation ( going up hills, very hot days etc ). If your 403 still has the stock super low CR then you're probably fine though.

Also make sure you're not into your mechanical advance at idle. I say that because with your total coming in so early I assume you're using very light springs.

Octania

Starts easy, hot or cold?
Does not overheat at idle?
good seat of the pants response?

If so, hard to improve.
I can state that my 403, which ended up at about 9.7:1 compression, really really preferred the vacuum advance mechanically limited [adjustable unit] to 10-11* and hooked to manifold vacuum with static timing set back accordingly.

Easy enough to try and then undo if you don't like it.

techg8

I have no complaints at all about the engine's performance.

If I HAD to pick something to improve, I would like a little crisper throttle response at Lower rpms, part throttle around town

The car starts runs and drives great.

oldcutlass

Perhaps a new set of gears are in order.

captjim

What cam did you choose? Are the 4A heads on it?

Here is a "recipe" that has worked very well for me on 350s with mild cams. Get a recurve kit (Moroso, etc) with an adjustable vacuum can, if you don't already have one. Keeping the stock weights, replace the springs with one light and one medium. Make sure the shaft rotates smoothly and "springs" back, those things get gummed up. Set initial timing at 23 degrees and add in 12 degrees of vacuum. Fine tune as needed.

olds 307 and 403

That is near ideal in my books as is. I have ran near 50 at idle and almost 60 at cruise with vacuum advance with no pinging. Low compression Olds V8 run better with a lot of timing. As said gears are your best friend for peppy acceleration.

Octania

I have found that manifold vacuum to the distributor also gave better throttle response.

Again, so easy to try.

$20? vacuum canister
move the hose
re-set the timing
try it out....

DoubleV

I know you stated this in the past but I'm just not seeing how you can be running so much advance. You might want to check your balancer and/or timing mark to see if your readings are correct because 60* advance at cruise just seems out of line compared to what anybody else runs.

olds 307 and 403

Multiple motors, balancer off? Remember we are talking 8 to 1 or less compression. I can't run that in my 4x4 with the 8.5 to 1 Olds 350, low 40's at idle and 50's cruising. I blew out a head gasket from detenation, over tightened the knock sensor. Look at the late 80's swirl port 307 7.9 to 1 and over 60 degrees part throttle. I will be doing my head swap on my 350 in a couple of weeks, bringing it to 9.5 to 1 or slightly more. I willl be lucky if I can add 10 degrees vacuum advance even with premium fuel and really cold plugs. I use an Equess dial back timing light with the tach function.

techg8

Thanks for all the replies.

Its a stock 79 403 with 4A heads IIRC
Yes EGR

Edelbrock 3711 intake
3712 cam and lifter kit
Stock torque converter, B&M TH350

I changed the rear gear to 3.08 and have 255/60-R15s

I dont recall if I have vac adv on ported or manifold, but that is a good thought too

cutlassefi

Just a word of note for everyone. Don't always assume more and early is the best way, even if you don't "hear" detonation.
I just got done dynoing Edins 455. When we added more timing, we lost torque early in the pull but gained hp further up. That tells me it really wanted a slower curve, it was all in by 3400-3500rpm. And I never heard the first ping or knock, and I was standing right next to it. Just a word of caution.
They don't call it the silent killer for nothing.

olds 307 and 403

Mark that really makes sense on a more efficient, higher compression engine. What heads were used? The extra timing on my junk made it more responsive and just ran better. I added two extra degrees, 38 from 36 total not counting the ton of vacuum advance, was stronger on the street, slower at the track.

cutlassefi

Procomps, out of the box.
I don't want to steal Edins (70cutty) thunder but it made REAL good power.
And this isn't the first combo I've experienced this on. I did an EFI build a few months ago that responded the same way. Both applications had approx 10-10.25:1 compression.
If you have a lot of advance at light throttle it will respond well. But typically that doesn't equate to the best scenario under full throttle.

techg8

Thanks for all the replies!

I have played around with the timing a bit and really like the results.

first I bumped the initial setting up 4 degrees to 22. This was an improvement at WOT but the engine didnt seem to like it at idle (manifold vacuum advance). Not so much of an improvement part throttle around town etc....

So I pulled the vacuum can and opened up the "slot" a bit, adding about 10 degrees vac advance. The engine did not like this at idle on Manifold vacuum, so I teed into the egr ported vacuum line - this was the ticket.

The engine idles at 750 rpm 22degrees and smells, sounds and idles great!

just off idle the vacuum advance kicks in and really has enhanced the response of the car to throttle.

WOT runs are a blast, simply put.

I run 3.08 gears so around town I am not way up in the rpms. I am typically cruising at 1500-1750 when the vac advance is all the way in.

My one concern is how this setup will fare on the hiway for extended driving. Lets say I am at freeway speed, maybe 2500 rpm with mechanical advance all the way in and high vacuum cruise....66 degrees is a lot of timing. I wonder if it wont run overly hot or have some other issue. Time will tell.....

olds 307 and 403

Just listen really careful and keep an eye on your gauges. Olds needed a lot of timing on it's low compression V8's.

DoubleV

66 degrees is alot.....

techg8

I did take the Trans Am on a 40 minute each way hiway cruise to a car show Sunday.

I did notice the engine running hotter, but nothing abnormal (steady 190deg). If anything it was abnormally cool before the timing changes (never really got up to 190).

I had no issues whatsoever on the hiway. Accellerating up the on ramps and passing cars/trucks was smooth, responsive and powerful.

Cruise was just fine. No surging or over temp or noises.

WOT blasts from cruise were great.

The timing changes really woke the engine up. Very pleased with the results.

time will tell....

olds 307 and 403

190 is normal for a 403, especially in hot weather. I found my 403 liked similar timing. I had heating issues but the timing was NOT the reason.

techg8

burnout vid for fun:

oldcutlass

So what did you ultimately set your timing at?

techg8

22initial
17 machanical by 2250rpm
27 vacuum

it rocks.

DoubleV

What parts are you using to achieve those numbers? Are you certain you have zero mechanical advance at idle?

techg8

Stock everything with a slight modification to the vacuum can slot to add 10 degrees to its total.

Stock setting was
18 iinitial
17 mechanical by 2250rpm
17 vacuum

I rotated the distributor to bump up the initial at idle 4 degrees for the final setting of 22degrees initial.

Left the mechanical alone

increased the slot length in the vacuum can for an added 10 degrees over stovk.

Yes I am certain I am out of the advance curve at idle. Car idles dead even and the timing mark is stationary at idle.

oldcutlass

Your 66 total with vacuum is too high and needs to be around 50ish. Imho, I believe you will experience detonation at light cruise. Vacuum advance will not affect power, it's for burning the lean fuel mixture efficiently under light throttle. The 39 total, initial + mechanical is maybe a bit high as most shoot for 36, however if the engine is tolerating it. Remember that detonation is hard to hear sometimes and will destroy your engine.

Smitty275

I'd say he has it pretty close. That's about identical to what my 77 Custom Cruiser with 403 ran. Only time it ever pinged was if I got stuck running BP fuel. His fuel wasn't mentioned but that alone can make one heck of a difference. All 93 octane is not the same. Just brand to brand can be a big difference. Also if he lives 2000' above sea level he'll be able to run more than someone 250' above sea level. Come September and October when the cool dry days with high barometer set in is when he'll find out just how close he is to the edge of detonation.

techg8

I just thought I would update this thread, the 403 is still running strong with lots of timing.

I haven't touched it since I set it a couple years back and its running great.

No noticeable pinging.

olds 307 and 403

Great to hear Ken, I knew the 403 would like it. My little 260 currently in the 70 S is running a ridiculous amount timing as well, someone set it at 25ish at idle with a similar fast curve. Out of multiple HEI's, this the only one I have found with such a fast mechanical curve. The big cap HEI is coming out with the 260 and the Mallory Breakerless, running pink springs for a quick curve with the Mallory 6AL box will go in for a more stock appearance being a small cap distributor.

techg8

as an aside, I recently acquired a SUN 504 machine for the business, to provide distributior services. A handy piece of equipment to have around for my own purposes as well! Could have used it back when I was recurving the 403 dist!

http://everyday-performance.com/distributors.htm