MG-Cars.net

Welcome to our resource for MG Car Information.

Recommendations

Parts

TR parts and Triumph parts, TR bits, Triumph Car Spares and accessories are available for TR2, TR3, TR3A, TR4, TR4A, TR5, TR6, TR7, TR8, Spitfire and Stag and other TR models are available from British car spares and parts company LBCarCo.

Triumph TR6 - timing for octane (or lack there of)

This is a subject that I don't quite get due to the fact that timing and detonation are activities happening inside my engine where I can't see them...I can bolt stuff on and off but that don't make me a mechanic.
I've been led to believe that with todays lower octane fuels one would not run their idle spark at spec (4 degrees ATDC). I've heard timing in the range of, say, 5 to 25 degrees BTDC will help a fellows' car run better with todays gasoline.
Now, I'm looking at the manual of my way old Ford truck (1970), which specifies 6 B.T.C. and a footnote on the spec page states "If the individual requirements of the vehicle and/or sub-standard fuels dictate the initial timing may have to be RETARDED from the "normal" seting to eliminate detonation. If retarding is necessary it should be done progressively and not to exceed 2 degrees BTC."
Now this seems like changing the timing the wrong direction from what you would do to your Triumph. Would not timing corrections be the same for any internal combustion engine suffering from "sub-standard" fuel?
I query. Thanks in advance for any enlightenment!

Chris
c.a.e. emenhiser

First of all I don't think that the fuel today is "substandard" Engine ping or spark knock is caused by premature detonation as a result of higher compresion. "octane rating provides a rsistance to detination" accomplished by the use of lead at one time, now other additives sutch as manganese provide octane rating. Retarding your timing ensures that the spark plugs ignite air fuel mixture first. Before you start to make adjustments to your timing check compression ratio and look at pump rating.
M SIDDALL

Also forgot if your car has points check your dwell first (do not use feeler guages on points) as a change in dwell will affect timing.
M SIDDALL

Chris - this article probably gives you more than you you want to know, but there is a table in there which may be what you're after.

http://www.faqs.org/faqs/autos/gasoline-faq/part3/section-1.html
Roger H

I wouldn't go too much by spec. Play around with the timing a bit, drive it, if it pings (pinks?) or knocks under load, it's been advanced too far. I see guys saying that they disconnect (and plug, I'm sure) the vacuum retard hose. The only way retard makes sense is to think about emissions, which I assume is the reason (some?) TR6's had it. Anyway, don't be afraid to play around with it a bit. Someone with far more actual experience with TR6's will add to or correct this, I'm sure.
Tom

Yes, well we already have some differing TIMING THEORIES. M Siddall, what's inferred by substandard fuels is a lower octane than what the maker states to be used. In this case FORD says to use (in 1970) 94 octane but if a lower octane must be used then tetard the timing...I think the lead had to do more with lubing the valve seats than boosting the octane. Same with regards to the use of manganese.
ROGER, thanks, that's quite in depth and a lot to chew on. I will reread several more times...I want to grasp this new term "stoichiometry". This author seems to corraborate the practice of retarding the timing for lower octane and has a lot of science to back it up. I like the idea of timing it by ear, going back if it starts to ping...as Tom states. I'm just confused when a major manufacturer and gasoline scientist/ researchers, whatever, state contrary techniques.

Grasping,
Chris
c.a.e. emenhiser

I just set my car to 4' ADTC per the book and I had to back my idle screws all the way out to get it to idle at 850 rpm. They are just touching the lobe.That seems wrong to me as I can only speed up my idle adjustment wise. The car however runs great at these settings, I think I'll do what Tom suggests and start trying different settings.

Charlie
Charlie B.

I am curious....Does not everybody use SHELLs high octane 94 gasoline?

Lead...octane booster...news to me.

The interesting thing is that this subject has been discussed before and timing setting (degrees) seems to be all over the map. Charlie is on spec. at 4*ATDC. Do what Tom says.
Rick C
Rick Crawford

The lead was in the form of tetraethyl lead (rather nasty stuff too). It's the ROH groups attached to the lead that do the trick.
SteveP

Stoichiometry, I guess 14/1 air/fuel was the standard stoichiometric ratio. Now they can make it a little leaner with computers and fuel injection. And constantly adjust timing electronically.

We have to use our ears and other senses. I would like to experiment some time with an oxygen sensor added to the exhaust to get a better sense of mixture at all times. Is there a way to add a guage telling us just what the timing is at all times?
Tom

Chris, there is some confusion in the octane rating systems; you cannot equate an octane number from 1970, derived by the Research Octane Number method with a current octane rating which is a blend of the RON and MON (Motor Octane Number) method.
Generally there will be a difference of about 5, the old rating being higher.
If you look at the small squinty print on the oump you will see a confirmation of this.
Complicating the matter further is the fact that different petroleum companies use slightly different calculations to derive the motor octane number. I recventky did a lot of research into this as the basis of an article in the Toronto Triumph Club Ragtop magazine, but assuming you don't have that take a kook at "How stuff works" on the internet or do a search, that's how I wrote the article.
Finally, my experience has been to retard the timing to prevent detonation, and make sure the cooling system is working as it should.
Simon.
Simon

I might be on spec Rick but it's short lived....I really see a relationship between timing and idle screws !!!.....the more ATDC the less I have in idle adjustment and when I go BTDC it's more adjustment.
I agree there is way too many settings with different cars when I read the threads and archives..it's confusing...I'm thinking that some must be hiding the wrong idle adjustments.
I disc.and plugged the retard, adjusted my BTDC to compensate..I did notice an improved idle but felt it did not have the same power off the line.
I know my carbs are in sync and everything is good
So I'm going to check my timing with # 1 at TDC and make sure it sparks at that point then take it from there.
Due to the almost perfect idle I had for a bit I know I'm on the right track..it's just getting the right combo
Lottsa fun !
Charlie
Charlie B.

This thread was discussed between 17/04/2005 and 21/04/2005

Triumph TR6 index

This thread is from the archive. The Live Triumph TR6 BBS is active now.