22 replies to this topic

[jime17]

Soooo. If my 99HE21 auto engine was 10.3:1 CR (which i think it is??) would the advance curve of the distributor be too badly out for a 9.6:1 engine?

[Spider]

The 99HE21 was also 9.6:1. The engines are very similar in fact, only the Auto Engine from your Mini was factory fitted with a HS4, which is what you say you have.

 

You may wish to consider swapping the heads over, the only reason I suggest this is because the head from the 99HE should be unleaded suitable.

 

Distributor wise, curiously, the curves were different.

 

the 99HE21;-

 

(On deceleration)

 

18 deg at 4800 RPM

15 deg at 3700 RPM

8 deg at 2000 RPM
0 deg at 400 ROM

 

the 99H907B;-

 

22 deg at 4800 RPM

16 deg at 2800 RPM

12 deg at 1500 RPM

1 deg at 600 RPM

0 deg at 400 RPM.

 

You'd possibly get away with the distributor from the 99HE21, but it wouldn't be ideal at all.

[jime17]

Thanks a million MS. You certainly have loads of info to hand.

I was going to change the head because as you said it's definitely unleaded. I can't be sure of the one I'm using now until I remove it and the valves...

I will see how I get on with the current distributor but I could always get it re curved.... I assume that isnt a diy job?

Edit... Hope this isn't a daft question but why would two engines with the same displacement, CR and carb size and presumably the same cam require different advance curves?

I'd guess with my limited knowledge that it would be because of the fact one was made with unleaded fuel in mind and the demands of an automatic transmission and different final drive require different advance curves. I'd be interested to know the actual answer though.

Edited by jime17, 19 December 2018 - 09:10 PM.

[Spider]

 You certainly have loads of info to hand.

 

I often wish it was 'to hand' but probably 70%+ of what I do have (like this stuff) is still on micro-fiche - YUK !!!!!

 

 

Edit... Hope this isn't a daft question but why would two engines with the same displacement, CR and carb size and presumably the same cam require different advance curves?

I'd guess with my limited knowledge that it would be because of the fact one was made with unleaded fuel in mind and the demands of an automatic transmission and different final drive require different advance curves. I'd be interested to know the actual answer though.

 

Without studying it, off hand, I'd say it's due to one being set up for Leaded Fuels and the other for Unleaded. They do burn quite differently.

[jime17]

I often wish it was 'to hand' but probably 70%+ of what I do have (like this stuff) is still on micro-fiche -

Well then I really thank you for trawling through that. I do appreciate it.

Edited by jime17, 19 December 2018 - 09:44 PM.

[jime17]

Without studying it, off hand, I'd say it's due to one being set up for Leaded Fuels and the other for Unleaded. They do burn quite differently.

So thinking about what you said. if I'm using the distributor from my auto with the same CR which was curved for unleaded fuel then it should actually be curved correctly no?

Edited by jime17, 19 December 2018 - 09:54 PM.

[Spider]

 

Without studying it, off hand, I'd say it's due to one being set up for Leaded Fuels and the other for Unleaded. They do burn quite differently.

So thinking about what you said. if I'm using the distributor from my auto with the same CR which was curved for unleaded fuel then it should actually be curved correctly no?

 

 

I think you're trying to pull my finger nails out one by one here,,,,,,,

 

OK the Camshafts between the engines have different Timing and this would be the most likely reason for the different advance curves.

 

The 99HE21;-

 

In Opens    5 deg BTDC

In Closes    45 deg ABDC
Ex Opens   40 deg BBDC

Ex Closes   10 deg ATDC

 

The 99H907B;-

 

In Opens    9 deg BTDC

In Closes    41 deg ABDC
Ex Opens   49 deg BBDC

Ex Closes   11 deg ATDC

[jime17]

I think you're trying to pull my finger nails out one by one here,,,,,,,

Oops. Sorry its probably more a case of me trying to understand more than I should given my overall knowledge of the subject. I also suspect I'm trying to delve too deep when I'm just looking for a drivable weekend car rather than trying to eek every last horse out of it.

Especially as you can't just cut and paste from microfiche!

I can see now why the dizzy curve might not be optimum and leave it at that. Sincerely thank you for all the effort you've gone to Moke. You've answered a lot of my questions.

Thank you to all the other contributors too.

Edited by jime17, 20 December 2018 - 08:53 AM.