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SP250 Dwell angle

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Culbu
Posts: 220
Joined: Tue Nov 15, 2016 5:21 pm
Location: Deauville, FRANCE

SP250 Dwell angle

Post by Culbu »

Good evening guys,

Today in France, it was a sunny day ! A good time to have a ride with the SP250 currently into my workshop.

The ride was a real pleasure, the engine, recently and completely rebuilt, seems to run perfectly. Once back at my workshop, just by professional consciousness, I decided to check up the dynamic ignition timing and the Dwell angle. For that purpose, I use a Gunson G4123 Supastrobe Professional.

10°BTDC at 750 rev/mn : perfect. But concerning the Dwell angle, 98% !!! Can any engine run with a such Dwell angle ?!? The data given by the official handbook is 32% !! Should I incriminate my device or should I adjust my contact points gaps ?

Thank you,

Julian

Chris_R
Posts: 499
Joined: Wed Feb 10, 2016 12:48 pm
Location: Twickenham

Re: SP250 Dwell angle

Post by Chris_R »

Don't you halve the reading for an 8 cylinder engine?

Culbu
Posts: 220
Joined: Tue Nov 15, 2016 5:21 pm
Location: Deauville, FRANCE

Re: SP250 Dwell angle

Post by Culbu »

When the Dwell angle is given in %, no matter the number of cylinders. I think...

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heh101353
Posts: 55
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Location: Basel, Switzerland
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Re: SP250 Dwell angle

Post by heh101353 »

Just my 2c
  • dwell angle too small ==> ignition coil will not deliver it’s maximum power
  • dwell angel too big ==> ignition coil will overheat
The dwell angle depends indeed on how many cylinders an engine has.

For an eight cylinder engine the distributor needs to trigger eight sparks in one revolution of the distributor shaft.
This leaves a mere 45° degrees of revolution for each spark.
The dwell angle therefore should be at about 33°.

I guess the figure given in the handbook is correct

Hans
Owner since 2015 :mrgreen:
http://www.wyhe.ch/

Chris_R
Posts: 499
Joined: Wed Feb 10, 2016 12:48 pm
Location: Twickenham

Re: SP250 Dwell angle

Post by Chris_R »

Page 2 of the instructions.
For an 8 cylinder engine: Dwell % = Dwello / 0.45 assuming a single distributor and a single set of points.
The data sheet for my dwell angle meter quotes 31o- 37o for a Lucas 20D8 distributor on a Daimler V8. That would be 70% - 82%. Your gap is slightly off at about 44o. The gap needs to be increased slightly.
If all else fails, read the instructions!

Culbu
Posts: 220
Joined: Tue Nov 15, 2016 5:21 pm
Location: Deauville, FRANCE

Re: SP250 Dwell angle

Post by Culbu »

Chris,

Are you saying that the value of 32 given by my SP250 Handbook is a degrees and not a percentage ?

In this case, I would understand...

Julian

Chris_R
Posts: 499
Joined: Wed Feb 10, 2016 12:48 pm
Location: Twickenham

Re: SP250 Dwell angle

Post by Chris_R »

Yes.

Culbu
Posts: 220
Joined: Tue Nov 15, 2016 5:21 pm
Location: Deauville, FRANCE

Re: SP250 Dwell angle

Post by Culbu »

🤓

Big Col
Posts: 446
Joined: Tue Feb 16, 2016 12:45 pm
Location: Leeds

Re: SP250 Dwell angle

Post by Big Col »

Does the fact that there are two sets of points make a difference ?
Also how much wobble is in the shaft ? If it is considerable then it will exacerbate the findings.
That said if it is running sweet then leave it well alone.
Colin,
I may be slow but I’m rough as well !

Chris_R
Posts: 499
Joined: Wed Feb 10, 2016 12:48 pm
Location: Twickenham

Re: SP250 Dwell angle

Post by Chris_R »

If there are two sets of points each set is tested separately with no connection between them.

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