Adam Blackaby Posted May 16, 2021 Report Share Posted May 16, 2021 Why is Sunday afternoon the time for playing with the TR? Latest issue, decided today to undertake plugs, leads and coil change. As per Moss catalogue I had a set of NGK BP6HS plugs to hand. But, taking old ones out I discovered that they were 5HS versions. Looked on the web but I couldn't find any clear explanation of difference. (The old spare plugs in the boot were 6HS's) Unfortunately its p.....ng with rain so I can't take the car out for a test but it starts and revs fine with the new plugs in. Is there any difference between the two? Thanks in advance Quote Link to post Share on other sites
RobH Posted May 16, 2021 Report Share Posted May 16, 2021 That is the heat range Adam - i.e. how well the plug gets rid of heat. In the NGK system a lower number is a 'hotter' plug so your 5HS is a bit hotter plug than the 6HS. I think it's usual to use the 6 on a standard TR 4-pot engine. https://www.ngk.com/what-is-a-spark-plugs-heat-range-2 Quote Link to post Share on other sites
ctc77965o Posted May 17, 2021 Report Share Posted May 17, 2021 The hotter plug, (5HS) helps prevent fouling of plugs due to rich mixture (too much choke for instance), but theres more chance they cause preignition during extended hi-speed runs... the 6HS is less likely to cause pre-ignition but more likely to foul... if it runs nice with 5s, stick with 5s Quote Link to post Share on other sites
Lebro Posted May 17, 2021 Report Share Posted May 17, 2021 I ran with 5's up to my recent engine rebuild as the plugs were prone to fouling. I am now on 6's. Bob. Quote Link to post Share on other sites
Hamish Posted May 17, 2021 Report Share Posted May 17, 2021 2 hours ago, Lebro said: I ran with 5's up to my recent engine rebuild as the plugs were prone to fouling. I am now on 6's. Bob. i'm with bob - i also use 6's Quote Link to post Share on other sites
BlueTR3A-5EKT Posted May 17, 2021 Report Share Posted May 17, 2021 Adam. As stated. BP 6 HS is the most common figment. BP 5 ES get fitted if the engine is a bit of an oil burner and prone to fouling. Peter W PS was your green Bristol a 400 or 401? PJT and I are discussing it. I say 400 as it had lop sided SU carbs. Quote Link to post Share on other sites
Adam Blackaby Posted May 18, 2021 Author Report Share Posted May 18, 2021 Thanks Guy's. As expected, you had the answers. I'll see how it goes on the new plugs and revert to 5HS's if needed. I'm sure they they were fitted for a reason, previous owner had the car maintained by Glen at Protek. Quote Link to post Share on other sites
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