My Piston Failure

[Dolly-Nut]

What star rated petrol was the Sprint spec'ed for? 95 RON being only 3 Star, is that safe even at std advance (unless one drives like a nun)?

Having lost a set of pistons to using premium unleaded on standard advance - bust the lands out -, I don't ever use less than 97 RON super, and prefer to use Tesco's 99 or shell's 100 RON super supers.

I don't remember which mark of 44D4 dizzy I had in it at the time, A, B, or C, and I'm told that makes a difference to whether you can use 95 RON safely. But I was also told to retard the ignition a few degrees as well.

Graham

Standard fuel rating was 4-star wasn't it? Equal to 98 octane?
Manufactures usually retard the timing from optimum for a safe margin.

[soe8m]

High octane it is then! I therefore recommend noone exceeds the factory recommend timing by more than a couple degrees!

I recommend no one does actually exceed the factory timing.

Jeroen

Do you not see a power gain by advancing the timing past standard from your engines Jeroen?
Mine made a significant amount more.

No, your mixture was probably bad and needed more advance. A 16 valve head and especially a sprint one with a central sparkplug is very efficient and does not need that much advance. A bad mixture what does not ignite very well does need a spark earlier than a good mixture. You can ignite a good mixture later. When you gain more bhp's after 32 degrees on a sprint there's something else wrong.

Jeroen

[GrahamFountain]

Standard fuel rating was 4-star wasn't it? Equal to 98 octane?
Manufactures usually retard the timing from optimum for a safe margin.

Oddly, I can't find it in my copy (issue 1) of the Dolomite Sprint Handbook, but the TR7 Sprint handbook says "minimum octaine rating of 97... 4 star rating".

How much you have to retard for 95 octane/RON depends on which version of 44D4 you have, because the mechanical advance profiles are different, and probably how worn your's is, because that will change the profile from std.

All I've got on the profiles is this note:



I assume it's all in degrees.

As I remember, I got this over the phone from Nick at MND Motorsport. But I don't know where he read it from. I could probably ask if it matters.

What happens if you mix the mech and vac advance bits from different types, I have no idea.

Graham.

[xvivalve]

Mine made a significant amount more.

...but not for long!