Spark Plugs

For Speed 20, Speed 25, 3.5 Litre and Crested Eagle cars
shaun matthews
Posts: 25
Joined: Mon May 21, 2012 9:30 am
Name: shaun matthews

Spark Plugs

Postby shaun matthews » Fri Apr 20, 2018 9:39 am

My Sp20 SC has 14mm plugs (I believe some run 18mm ). This are not directly in the combustion chamber but connect via a c5/16" dia flame tube. - I believe the head is speed 20 with square ports and high compression chambers

Although absolutely fine on a run, Its always suffered from plug fouling (particularly no's 2 and 6) if it spends too long ticking over or in thick traffic.

When I got it in 2010 it had ancient Champion J6's (Very short 3/8" reach) which are the most reliable plugs it has ever had - Since then we have tried NGK B6's and now Champion J6C's. - Both of these are readily available but both are absolute buggers for fouling - Pointing to plugs that are a grade too cold. However, as far as I can establish, no one makes a hotter 3/8" reach plug (both NGK and Champion only make 6's in this size). I can also lean the carbs but then starting and power both suffer.

My initial though was to fit NGK B5HS (1 grade hotter but 1/2" reach) along with a 3mm copper index washer but when I took a torch and vernier to the plug holes I found that the threads are 15mm long - i.e. if I clean the threads it will take 1/2" reach plugs with no fear of piston interference but with the electrode 1/8" closer to the flame tube throat. This would give access to the full range of plug heats including iridiums (which have cured all the issues on my '24 Sunbeam 350 racer)

Does anyone else run a 14mm plugged Speed 20 and if so what sparkplugs do you run? Are they 3/8 or 1/2" reach and do you have fouling issues?

Thanks in advance

Shaun

RichardWallach
Posts: 343
Joined: Mon May 21, 2012 10:14 am
Name: Richard Wallach
Location: Melbourne, Australia

Re: Spark Plugs

Postby RichardWallach » Fri Apr 20, 2018 2:35 pm

Shaun,

I was at the Alvis Car Club of Victoria meeting tonight and raised your questions. A knowledgeable member recommended Y gap plugs that have the projected nose with 1/2" reach. He mentioned a BY5HS. He didn't think that you would get any value from iridium plugs.

Hope this helps.


Richard
Melbourne
Last edited by RichardWallach on Fri Apr 20, 2018 11:45 pm, edited 1 time in total.

shaun matthews
Posts: 25
Joined: Mon May 21, 2012 9:30 am
Name: shaun matthews

Re: Spark Plugs

Postby shaun matthews » Fri Apr 20, 2018 4:54 pm

Richard

Thanks - Have run it today on B5HS and all seems well. I might try a multi electrode plug sometime when I find one that is right size and heat range - The NGK catalogue claims they are more foul resistant with modern European (i.e. crap) fuels.


Shaun

johnlayzell
Posts: 151
Joined: Mon May 21, 2012 2:44 pm
Name: John Layzell

Re: Spark Plugs

Postby johnlayzell » Fri Apr 20, 2018 10:29 pm

The SP25 runs OK on B5HS. I've also got a few Champion L90C as spares.

These and the attached may help:

Spark Plug sites

http://www.sparkplugs.co.uk/

http://www.dansmc.com/sparkplugs1.htm

http://dirtbike.off-road.com/dirtbike/a ... ?id=332655

http://www.strappe.com/plugs.html

Alvis spark plugs.jpg
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1925 SC12/50
1937 SP25 VDP Saloon
1970 Peking to Paris Rally VW Beetle


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