Page 1 of 1

345 timing

Posted: Fri May 17, 2019 9:19 pm
by ShaunT
Hi all... the manual says timing for 345 should be 10 deg BTDC but bunch of posts on binder planet say say set at TDC. I have petronix ignition set up... what say you?

Re: 345 timing

Posted: Fri May 17, 2019 10:07 pm
by Big John
Start to time it at 5 degrees before top dead center. Then adjust from there. Seems they run best around 8 to 10 degrees.

Re: 345 timing

Posted: Sat May 18, 2019 6:44 am
by Tim Potter
nor sure what manual you're referring to, I've never seen 10° btdc in any of mine. 0° btdc is shown for base timing quite a lot for many years and for many distributor configurations though, which may be why you see it as the recommended setting on BP. however, there's this thing about the FSM that needs to be considered as well. it is a collection of excerpts really, so the tune up specs for a 345 in a Scout maanual, for example, are the same as would be found in the manual for a dump truck or bus of the same vintage. 0 is for what IH calls medium duty applications in my opinion. Similarly, spark plug gap of .030 is for those vehicles, while in Scouts the same plugs should be gapped to .035.
As to timing, I usually recommend 6° btdc as a good place to start; however, that can vary depending on altitude: higher altitude needs more timing, something like 1-2°/4000' ish. I'd call it a "feel" setting, which is to say, give it to her till she feels good. You can apply the same technique at sea level and be fine but, again there are variants at work that need to be considered such as fuel quality and the load that'll be put on the engine during operation. For example, my 345/DUI runs like a top on regular gas around town and on the highway at 12° btdc, it runs better at 15° btdc, but if i try pushing it up over grapevine or cajon at 15° on regular gas itll ping where with premium, it won't. Higher octane fuel burns slower; more complete burn equals more energy, probably better milage to.
Having ssid all that, my "opinion" on how to set the timing for your 345/pertronix is to start at 6°. Then set it at 35° "all in". Itll take 36, but no need to push it that far. Whatever that comes back to at idle, is what it is. If you want to back it down a degree or two from there, that's fine. The other way is to just give as much as itll take under heavy load until it doesn't ping. That's kinda what your after anyway, no ping, running balls out. Just keep in mind its a Scout, not a street racer.

Re: 345 timing

Posted: Sat May 18, 2019 7:46 am
by gorilla snot
Sage Advice!

Re: 345 timing

Posted: Sat May 18, 2019 11:28 am
by ShaunT
So does 35 deg ALL IN means at full throttle is that correct?

Re: 345 timing

Posted: Sat May 18, 2019 6:48 pm
by Joe V
I put petronix in my 345 before ihwr and it got set to Big Johns recommendation. So far so good.

Re: 345 timing

Posted: Sat May 18, 2019 8:58 pm
by Tim Potter
not exactly full throttle, more like 2000-2500 rpm. all in means all the advance the distributor is capable of giving. where it reaches all in depends on the cintrifigul advance curve built into the distributor. whats different about this method than setting base timing is while base timing is typically set with no vacuum signal to the advance can and rpm low enough, 500 rpm or so, that no cintrifigul advance is added by the distributor, all in is setting maximum advance at high rpm, or "high" for an IH SV anyway.

Re: 345 timing

Posted: Sun May 19, 2019 8:52 pm
by ShaunT
Thanks for the feedback. I messed around with it going from zero to 10 on the advance but could not notice any difference other than the RPM changing. I did not notice any pinging but then again that could be just lack of experience on my part. I split the difference and set it at 7 advance and she seems to be driving pretty good at this time.