Ignition advance and fuel type?

Dave Bilyk · 04-14-04, 08:17 AM

My car has a Marine type 302 with a Holley 4Barrel. I dont think it is any more than standard. I checked the timing and it is about 10deg at 1000rpm, maxes out at 38deg about 4500rpm. I think the relatively high rpm is to do with the marine distributor. The previous owner said he used Lead Replacement Petrol, but that it would be ok on unleaded. I am running on unleaded, but do I need to adjust timing to suit? I have searched and found some threads, and 34 to 37 was the suggested range. Do I need to come lower down in to this range? Can anyone tell me any ball park relationships between ignition advance and fuel type for a standard 302? Also, would there be an advantage in changing the distributor advance weights / springs to a road characteristic?
thanks in advance -- pun intended [img]/ubbthreads/images/graemlins/grin.gif[/img]

Dave Bilyk · 04-16-04, 08:15 AM

Hi everyone, just reposting this in case anyone who can answer hasn't seen this post yet. I'm driving the car tomorrow would like some confidence that I wont fry anything. [img]/ubbthreads/images/graemlins/blush.gif[/img]
regards
Dave

Kevin M · 04-16-04, 10:05 AM

34 deg. all in by 3,500 RPM is a safe "Rule of Thumb" standard for most engines on pump gas. You certainly won't loose much power, if any, by droping it to that. That said, you haven't mentioned the two most important things: What is the compression ratio, and what is the Octane number of the fuel? Without that everything is a guess.

Kevin

Dave Bilyk · 04-16-04, 01:12 PM

Kevin, thanks, I know so little about the small block engine, I think mine is a standard marine engine, so the comp ratio will not be high. Unleaded pump gas here is available in premium 95 RON Octane or Super 98 RON Octane.
Regards
Dave

Kevin M · 04-16-04, 01:47 PM

Those are higher Octane numbers than we see over here (92 to 93 is our best). You should be fine with 34 or 36 deg. all in by 3,000 to 3,500 RPM. Beyond that, temperatures go up but usually power does not, so no reason to run more. The final answer is to find a chassis dyno and have the ignition and carb tuned on that. That will get you the optimum settings.

Have Fun,

Kevin

Dave Bilyk · 04-16-04, 02:37 PM

Opened up distributor to check, find that the rotor arm spring (In centre of rotor arm, making contact with HT feed from coil) is in one half, engine still seems to run fine though.I didnt break it, the other half is nowhere to be seen, I took the breaker plate out to see if it was among the springs and weights, no sign of it! The half that is left lies in the groove in the centre of the rotor arm. How the spark is being distributed with it like this I dont know. Didnt think to look before I buttoned it up and started the engine. Is this a common thing? Any comments?
regards
Dave

BenL · 04-16-04, 03:14 PM

[ QUOTE ]
Those are higher Octane numbers than we see over here (92 to 93 is our best).

[/ QUOTE ]

The numbers for the octane rating in Europe and the US are calculated differently. In Europe, they use RON (Research Octane Number). In the US, it's the average of RON and MON (Motor Octane Number), which is usually a lower value.

Dave Bilyk · 04-16-04, 06:06 PM

I found a web page with number comparisons, for RON MON and PON (average of RON & MON)Octane number comparisons
according to this, Americas 92 Octane is similar to UK's 96 Octane, and 93 to 97.
I retarded the ignition a couple of degrees, seemed ok at first, but on the way back home got some popping and banging at around 3/4 throttle. Maybe the engine wasn't quite up to temperature, I don't know. It could be the temperature, timing, dwell or the rotor arm problem. It didn't do it before so I returned to the original timing, and will investigate and check tomorrow.
regards
Dave

Howard Jones · 04-19-04, 10:23 AM

Here's mine 2 cents.

Ford SVO X head alum 302 @ 9.5 to 1 comp ratio, B303 cam.
34 Degrees total advance all in at 3000 RPMS. This comes out to about 10 degrees static advance at 900 RPMS.

We have 91 octain gas here in Calif. This is possibly the worst gas available to any of us on the forum.

I also am running a 750 Holley doublepumper, jetted 1 mainjet size smaller than the way it came from Holley, on Eldenbrock RPM performer intake. The Distributor is a MSD billit without vacume advance and a 6AL box.

My exaust is the GTD Non crossover header running through a pair of muffers that are a baffeled type that have VERY little restriction. I would guess that they are less that 25% as restictive as the GTD muffler.

Dave Bilyk · 04-19-04, 12:58 PM

Thanks Howard, I found that the spring blade on the rotor arm was broken, so I may as well coorrect the other things at the same time. So I intend to change weights and springs to bring max advance rpm down from 4500 to 3500rpm, if I can't I will replace the distributor. I would guess that your comp ratio is higher than mine since it is a standard marine engine AFAIK.

regards
Dave