Locky1978

Active Member

• Jul 19, 2015

• #1

Hi all,

Got a quick question for those in the know. Ive always timed my 3.5 low comp at 6 degrees btdc. I've ran it at 12btdc before as well with no real difference.
Today I decided to see how far I could advance it before it starts pinking then just back it off a tad. Well I got to 28btdc and still no pinking. What gives? is it because its a low comp and it will be hard to get it to pink?
I would have thought with 28btdc at idle it would have back fired when I ran it up the road at full bore.

 

norseman

Well-Known Member

• Jul 21, 2015

• #2

Locky1978 said:

Hi all,

Got a quick question for those in the know. Ive always timed my 3.5 low comp at 6 degrees btdc. I've ran it at 12btdc before as well with no real difference.
Today I decided to see how far I could advance it before it starts pinking then just back it off a tad. Well I got to 28btdc and still no pinking. What gives? is it because its a low comp and it will be hard to get it to pink?
I would have thought with 28btdc at idle it would have back fired when I ran it up the road at full bore.

Click to expand...

 

norseman

Well-Known Member

• Jul 21, 2015

• #3

Year / carb or efi / manual or auto ?

 

Locky1978

Active Member

• Jul 23, 2015

• #4

Ah yeah sorry. All standard 1983 3.5 V8 on factory twin strombergs. Manual

 

norseman

Well-Known Member

• Jul 23, 2015

• #5

Sorry, I've only got the manuf. specs. for 1886
Both high & low comp. ratios are listed as 6 degrees BTDC @ 650-750 rpm with vac pipe off
Same specs. for both Europe & ROW
Hope that's of some help.

 

Locky1978

Active Member

• Jul 23, 2015

• #6

Thanks, I'm running 6 btdc now. I just wasn't sure why it could take so much static advance with no detonation. I guess it may be down to it being low comp. I might be sticking some P6 pistons in it soon so that will soon tell when I crank the advance up again.

 

norseman

Well-Known Member

• Jul 24, 2015

• #7

Some engines are like that. I remember having a '66 Humber super snipe many years ago & soon after purchase I got the local garage to check the timing (not having a 'stobe' myself). The mechanic asked me if the engine pinked, when I said no he looked surprised & said that it was so far advanced that had it been a Ford it probably wouldn't have run!

 

M

Murtle

Active Member

• Jul 27, 2015

• #8

One of the things you can do is check the engines emissions while adjusting your timing that will give a good indication of the correct timing, you need to monitor it's hydrocarbon output, as this dramaticly rises with advanced ignition timing.

 

cooltide

sheep fancier

• Jul 27, 2015

• #9

Probably worth confirming tdc is correct by removing spark plug no.1 and turning engine with some sort of probe down plug hole. Don't lose it in there though. Could also be knackered mechanical advance vacuum advance or all of the above. Wouldn't expect to get above 12 btdc on 95ron. When I ran my 4.6 on LPG it was happy at 18 but it is higher octane fuel

 

P

pete1987RRC

Well-Known Member

• Aug 9, 2015

• #10

Assume you did the setting vac off?
But as him above said the crank pulley is not always accurate, not the same but my 3.5 on lpg runs on the o of before sweet as a nut ant there is loads of adjustment to tbc and to E with no pinking