CRF450 vs GX390

get the 450 don't worry about the 250 with your weight

the big thumpers have all the torque needed to pull that kind of weight with no problem I have out ran one of the best if not the best BRC150's in the nation while giving it 100#'s with the thumper I have...... they got grunt!
 
What do you do with the 450's for a clutch? Do you have to gut the transmissions? Im also curious as to whats all involved in the switch from a bike to a kart.
 
Wes Snow said:
I am Matthews friend that he is referring to. Matthew is asking for advice on what all is needed to put a 450 on a kart, and letting you all know he has never tried putting an engine like this on a kart before. Also, you all should know that Matthew is a big man and he comes across the scales at approximately 440 lbs with a animal motor and no lead, so he requires more power just to be equal to the competition. I also think that the extra weight will help him plant the extra power of the 450. He has been running an open animal in the RWYB class.
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Wes tell him I will sell mine.
 
Gentlemen,
Let's not present our opinion and our experience as Biblical fact.
The Biblical fact is, any of the present big displacement engines, BUILT right, will give the other big displacement engines a very competitive race.
It's the other factors, which determine winners usually.
 
A stock 450 with the tranny will put out in the neighborhood of 60 horse all day long at 10,000rpm. Honda recommends 10 hours between oil changes and 40 hours between rings and freshen. Doing a little math. We race maybe 20 min a night. Thats 3 races an hour so about 30 races per oil change. And 120 races between rebuilds. In most UAS division that would be 10 years of run time or more. Run an industrial motor built to 60 horse 1 hour between oil changes and let me know how things turn out. Run that same motor 10 hours between freshen and let us know how that all goes. Keep the tranny. Gear to match the bike original gearing. Use the shifter. Paste a smile on your face that you won't get rid of for a month.
Lets not forget other maintenance like your clutch and flushing alcohol.


QRC makes mounts. Mount your radiator. Extend kicker past body to start it. Clutch handle on steering shaft. Build shifter where its comfy. Normal kart fuel pump from pulse source. Little tid bits of mounting like cdi, throttle cable and stuff. You got a runner!!!
 
i have 16 race days on my 390 thats about 48 races total heats and features . i keep oil changed , stay on top of valve lash . compression test results were great so was leakedown .
no problems and dont plan on cracking it open anytime soon , no reason to :)
 
I have no idea of the weight of a 390. But I think my 450 is about 60#. Its an 07 and not a scuff that's able to be felt in the cylinder. Stock valves, just lapped a few times. New kipplewhite springs with Ti hardware which really pepped her up to compliment bigger cam. I did cook it pretty good at the big o when my fan switch broke and it gaulded the rod on wrist pin slightly so a 500 kit is the obvious fix. No replacement for displacementas they say. Most of the hours on it were from being on the quad and that bwas a lot more harsh conditions then any kart race.
 
The basic GX390 is listed as ~69-70lbs, but that's with an iron flywheel and chunky muffler.

I would rather use an engine designed to make 60hp.

Logan said:
Stock valves, just lapped a few times.
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Stock titanium valves? Lapping Ti valves is a huge no-no. It removes the hard coating and embeds abrasive in the titanium.

Jimbo925 said:
A stock 450 with the tranny will put out in the neighborhood of 60 horse all day long at 10,000rpm. Honda recommends 10 hours between oil changes and 40 hours between rings and freshen.
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I'm looking at a 2007 CRF450 owner's manual and it says 15 hours on the oil, piston and rings. Most user recommendations I see are for more frequent oil changes and longer intervals on the top end. Either way, using a CRF450 for competition purposes is going to incur a demanding maintenance schedule.
 
Run one for a season or two and get back to us on the maintenace they require. Im sure you will find it is next to none besides changing oil and keeping a clean air filter on it. As far as Ti valves and lapping, I've had no problem and there's a lot of 450 guys that do the same in the quad world.but then again there is a whole bunch of people who don't believe in lapping at all. Bluing don't lie nor does a leakdown test.
 
Which is better is purely a matter of opinion and setup, driving, and all the rest. Either is capable of winning big races.
Personally I'll take the 390 or other engine of that type.....rightly built.
 
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