Which Spark Plug for Race 400EX high compression? 13:1 426 EX motor? - ATVConnection.com ATV Enthusiast Community

Honda Discussions about Honda ATVs.

Thread Tools Search this Thread
Old 08-16-2001, 12:41 AM
Range Rover
Thread Starter
Join Date: May 2000
Posts: 151

Will I have any problems with the stock dpr8z Honda plug as far as piston to plug clearance? and do I need to run a colder plug?
I have white brothers cam,porting,426 bore,dmc pipe,fcr carb and am fixing to crank it but I want to use the right plug.
Reply With Quote
Old 08-16-2001, 02:42 AM
Pro Rider
Join Date: Jul 2000
Posts: 1,155

i personally do not think you will have a problem with that plug. i am currently running the ngk dpr9z although i do not know if it made any difference or not. i just wanted to try it. i raced a friend of mine on the exact same bike and we were close up until the end of the race where i had more top end. my whole bike is stock except i am running that plug. my friends bike is totally stock also. the only thing different is that he had his spark arrestor off and i did not. i don't know why but i did have a top end advantage over him. that spark arrestor could of made that difference.
Reply With Quote
Old 08-16-2001, 02:36 PM
Pro Rider
Join Date: Jan 2001
Posts: 1,850

What fuel are you running? I was using a DPR9EA in my 250x on 110 octane. It is a big bore at 10.5:1. You must stay D (thread size). If you had an easy way to "bump" the engine over to check to see if the protruding tip (the P in the plug #) contacts the piston, which I doubt it will. I recommend staying resistor (the R) type with the 400 ignition. Heat range, good question. I usually say 1 point colder with every 1.0:1 increase in compression. However, I warm it up one point for every 5 octane increases. So, factory 9:1 compression to 13 raise plug number from 8 to 12 (They only go to 10, I know this is part of why you should raise compression). Since that motor will be burning at least 105 octane verses stock 89, lower it 3 points. So the 9 is right. The E is the ground electrode style. I am going to change to a V tonight. This is actually a reverse of the splitfire V. The A is the center electrode style. I personally like the G plug because the CANNOT be fouled. Had to try it, overly rich RM125 at 24:1 mix oil designed for 50:1, didn't foul. My switch though is going to go with an X. Just as important as plug is the gap. DON'T just pull it out of the box. Gap it at honda specs for gas. If this is going on alcohol, forget the information above and use the D9VX plug gapped at 18-20.
Hope this helps
P.S. You will LOVE that FCR (39mm?). If it has a flat spot at any rpm you can easily adjust it out. The huge accerator pump gives awesome response.
Reply With Quote
Old 08-16-2001, 08:38 PM
Pro Rider
Join Date: Jul 2001
Posts: 401

the stock plug will work just fine and the spitfire plug makes zero diff on the dyno .......
Reply With Quote

Related Topics
Thread Thread Starter Forum Replies Last Post
Kazuma Falcon 110-4SAR troublshoot (wont start) TegraQuad 1) Engine problems.. 13 11-26-2017 02:40 PM
2001 Yamaha Warrior Wiring Problem njrider64 Yamaha 5 07-04-2017 02:34 AM
predator 500 wont start! help! Hankey Pankey Polaris ATVs - Ask an Expert! 23 08-09-2015 09:30 AM
Lt230e oil in exhaust joshuafromny Suzuki 3 06-22-2015 06:30 PM
Answered: Splitfire Spark Plugs, Where Are They Now? ATVC Correspondent Ask the Editor 1 06-03-2015 05:16 PM

131 , 2001 , 400ex , 426ex , 91 , change , compression , gapping , high , honda , octane , plug , spark , spot , stock

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

All times are GMT -5. The time now is 12:49 AM.

We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites.
  • Ask a Question
    Get answers from community experts
Question Title:
Your question will be posted in: