[Joe03400ex]

Hello all, My name is Joe i am From Central New Jersey.

I am currently Awaiting parts, but I am a little confused on what I should do with my upcoming project.


Currently the machine is bone stock with just a KN air filter with an outerwears sleeve over it... Quad started to burn some oil so here is my plan of action...

Wiseco top end rebuild kit .040 bore and 10:1 compression, all new gaskets and head studs, new cam gear and cam chain (keeping factory cam), rebuilding the head entirely hardware and seals. Kibble white stiffer valve springs, wiseco valves and all new hardware inside, going to add an ebc dirt racer clutch kit and completely rebuild the carb with factory jets.

The question I have is will I need to jet the carb and will I need to run a slip on exhaust? I like the stock sound on the bike it’s perfect for where we ride... I don’t want to change it if it is not necessary...

Any positive input would be greatly appreciated. Thanks in advance

 

[Austin92]

Building my own engine right now too. Here’s what I’ve learned since I’ve been on here that might help you. JE makes the lightest piston. The crf450r timing chain is an upgrade for our 400EX motors. Gt thunder head studs are the only ones that address them pulling the threads out of the jug.

I still haven’t decided what I want to do with my valves and springs though.


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[Joe03400ex]

I had listed the parts I have already ordered. Will I have an issue with new oem head studs. I’m not trying to go with a complete performance build looking to keep reliability and make it just a tad better than stock.

 

[Austin92]

I guess these 400’s are bad about blowing head gaskets and the gt thunder studs allow you to torque them a little tighter helping with the head gasket problem.

I would say you probably should’ve jetted with just the air filter, a larger bore will definitely need more fuel. These come from the factory lean.

I don’t think you’d NEED a slip on but it will make a difference in power. Dirt wheels magazine did an article on mufflers. Ct racing made the most power but you can change the disks out for different db levels. Stock is like 89db and the quietest the ct got was like 93db all the way up to like 101db. Louder settings made more power. Hmf has quiet core inserts for their mufflers too but wasn’t reviewed in that article. Something to think about


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[Joe03400ex]

I guess these 400’s are bad about blowing head gaskets and the gt thunder studs allow you to torque them a little tighter helping with the head gasket problem.

I would say you probably should’ve jetted with just the air filter, a larger bore will definitely need more fuel. These come from the factory lean.

I don’t think you’d NEED a slip on but it will make a difference in power. Dirt wheels magazine did an article on mufflers. Ct racing made the most power but you can change the disks out for different db levels. Stock is like 89db and the quietest the ct got was like 93db all the way up to like 101db. Louder settings made more power. Hmf has quiet core inserts for their mufflers too but wasn’t reviewed in that article. Something to think about


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What jet sizes would you recommend for the upcoming build? And when I drop everything off at the machine shop- should I just redo the head or should I have it ported and polished for the additional compression?

 

[XplicitRacing6]

Everyone has there own opinions, here’s mine.

GT head studs are a waste of money. Buy ARP Studs

Second, it’s hard too tell exactly what jetting you are going too need, it all depends on elevation, air temp, and all that good stuff


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[Austin92]

Depends on how you ride. Port and polish might kill your bottom end. Just a polish will help across the board though. When I was planning my build I was going to go with arp also but they use the same threads as stock. The gt thunders need drilled and retapped because they’re bigger so they’re less likely to pull out when you over torque them. More clamping force is less likely to blow the head gasket. But xplicit isn’t wrong. Arp makes quality stuff too


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[Joe03400ex]

I’d use ARP over anything... that’s what holds down my turbo diesel....

 

[Joe03400ex]

I’m in nj there’s no real elevation here... riding in say 50 to 80° weather sometimes colder...