281 replies to this topic

[pablo83 TT Silver Member]

A number of people have asked me to start a thread on my NX650.  I know this is the XR forum, but the NX has the same engine as the XR650L and my NX probably has more XR parts on it than NX parts.  So here's my NX650 with a lot of work done to it:



The next step on the bike is installing a Garrett GT1544 turbo.  It will go right here:



This pic is taken with the forks fully compressed to show clearance.  The exhaust manifold will have to enter at an angle due to the tight space.

I'm saving money for a trip to the Mojave Dessert, so the build is on hold until March.

[HeadTrauma Get Help Now]

This is an XR forum, but anything with an XR engine is welcome.

I look forward to seeing the project progress. Are you going to keep it carbureted or go with EFI?

[pablo83 TT Silver Member]

The current plan is a blow thru carb with a low pressure fuel pump (from CBR600F) to keep fuel in the bowl.  According to my research, this setup will only be good for about 10 PSI boost.  I'd like to run much higher boost in the future, so FI may be in the distant future.

[HeadTrauma Get Help Now]

Well, you should be able to use a carb for whatever boost you want as long as the fuel pressure keeps up.

As I mentioned in another thread, I have a Garrett GT1544 just like yours. I just pressurized the wastegate and it releases tension on the puck right at 10psi. If you want more than that, what works well is a bleeder-type boost controller. It can even be controlled with a 12v valve to give two boost settings....like "stun" and "kill."

[pablo83 TT Silver Member]

HeadTrauma said:

Well, you should be able to use a carb for whatever boost you want as long as the fuel pressure keeps up.

As I mentioned in another thread, I have a Garrett GT1544 just like yours. I just pressurized the wastegate and it releases tension on the puck right at 10psi. If you want more than that, what works well is a bleeder-type boost controller. It can even be controlled with a 12v valve to give two boost settings....like "stun" and "kill."

My wastegate is an issue I still need to work out.  The dashpot is removed from the turbo right now.  With it installed it interferes with with front wheel.  I'd really like to use the internal waste gate since it has one, but I'll have to modify the dashpot placement to make it work.

[UncleBob TT Silver Member]

good to see other turbo fans. If I can help with your build any, let me know

[martinfan30]

I guess I don't understand certain parts of this mod, but how do keep the air filter from collapsing from either the vacuum or positive pressure?

[pablo83 TT Silver Member]

UncleBob said:

good to see other turbo fans. If I can help with your build any, let me know

Bob, are you the guy with the wheelie-poppin turbo DRZ video on YouTube?  Do you have a thread somewhere on your turbo build?  What turbo did you use?

[UncleBob TT Silver Member]

pablo83 said:

Bob, are you the guy with the wheelie-poppin turbo DRZ video on YouTube?  Do you have a thread somewhere on your turbo build?  What turbo did you use?

thats me.

the really big thread is on supermotojunkie.com:  http://www.supermoto...ead.php?t=23824


Using a GT12, although I dabbled a bit with a chinese version of a RHB3, didn't go too well though.  I'm sticking with the GT12

[pablo83 TT Silver Member]

UncleBob said:

thats me.

Using a GT12, although I dabbled a bit with a chinese version of a RHB3, didn't go too well though.  I'm sticking with the GT12

Great thread, Bob.  I'm only half way thru it.  The notes on the pitot tube are very good.  I've done a lot of turbo bike research and have never heard of this before, but it makes great since.  I'd love to see a pick of the tube if you have one.

I looked at a Chinese RHB52, but then this one poped up on eBay.  It needs a rebuild and maybe a new compressor fan, but that can all be done in the future.

[cleonard I ride therefore I am.]

It would seem that given the locations of everything a "proper" turbo location must be just about impossible.   If you put the turbo in front like that you will have an easy time routing the exhaust.  What are your plans for routing the intake piping?

If you are going to all this work I say do a little more and go with fuel injection.  Something like the Megasquirt, or it's smaller packaged Microsquirt.  http://www.microsquirt.info/

[UncleBob TT Silver Member]

the placement of the turbo doesn't SEEM to have much effect on lag. More of an issue of turbo size, tuning and system design (as a general rule, draw thru creates a lot of problems)

I would definitely go for blow thru no matter where you decide to put the turbo.  But you need a quite large air box to get the most out of the system no matter where you mount the turbo (and no matter what fuel system you pick)

Fuel system wise, anything that can surpass the fuel pressure required for your psi (boost + 3psi is a good minimum for carbs)  and it is highly recommended that you have a boost-reference-capable, 3 port regulator.  The one I use is a Mallory 4307M (about $100)

carb works fine, no need to go to EFI unless you are looking for extra bragging points IMO.

[HeadTrauma Get Help Now]

Yeah, turbo placement and plumbing length is a topic that gets a lot of attention, but in practice it does not make a huge difference in lag nor performance. I plan on turbocharging a 600 in the future, but I will probably put the turbo where the airbox is and keep the stock header. It should make plumbing(and hiding the turbo) a bit easier.

martinfan30 said:

I guess I don't understand certain parts of this mod, but how do keep the air filter from collapsing from either the vacuum or positive pressure?

The air filter shouldn't be enough of a restriction to allow that to happen. If it does, then the filter is either clogged, poorly constructed, or too small. Having a restriction on the compressor inlet forces the turbo to operate at a higher pressure ratio and shaft speed which degrades performance in a big way.

[pablo83 TT Silver Member]

I've read that placing the turbo where the airbox is creates heat problems which can melt the seat and overheat the rear shock.  I've seen a thumper turbo (diesel KLR) installation where it was mounted behind the engine, but lower, next to the swingarm with good success:

[UncleBob TT Silver Member]

you can mount the turbo anywhere, as long as you have a large airbox, that picture is a great example.  Very large air box

Draw thu would be different of course.  I wouldn't even want to give advice on a draw thru system.  Waste of time IMO

[lateapex31 TT Bronze Member]

UncleBob said:

carb works fine, no need to go to EFI unless you are looking for extra bragging points IMO.

Carb works acceptably with a lot of fiddling (but not 'good'-especially during transients) for fueling but how will you handle ignition timing?  Increased cylinder pressures call for reduced ignition timing, not the 30+* all in by 3k RPMs of the factory CDI box.  It's not even close!  While I applaud your creativity I think you may need to put some more effort into engine management.  Air cooled engines are not very forgiving, especially with forced induction.  Having said that, you sir, are the man for boosting your NX!!

[pablo83 TT Silver Member]

lateapex31 said:

Carb works acceptably with a lot of fiddling (but not 'good'-especially during transients) for fueling but how will you handle ignition timing?  Increased cylinder pressures call for reduced ignition timing, not the 30+* all in by 3k RPMs of the factory CDI box.  It's not even close!  While I applaud your creativity I think you may need to put some more effort into engine management.  Air cooled engines are not very forgiving, especially with forced induction.  Having said that, you sir, are the man for boosting your NX!!

The two biggest reasons I've decided to boost this engine is the stock compression ratio (8.3:1) and the stock cam with only 10 deg of overlap.  With a compression ratio this low I should not run into pinging issues until I'm way over 10 psi boost, particularly at my elevation (8500 ft).  When I start pushing the boost above 10 psi I'll have a whole new set of issues to deal with and that will be a project for another winter.

[DRX350 TT Gold Member]

how'd you put the disc brake on the rear?  Awesome bike by the way!

[pablo83 TT Silver Member]

DRX350 said:

how'd you put the disc brake on the rear?  Awesome bike by the way!

Rear wheel / brakes
The rear wheel (17x3.50) and brakes are from an '87-'90 CBR600F "Hurricane". I've found a number of these bikes for less than $500 on Craigslist.  It was an easy conversion, but it required some welding. I cut the brake stay bracket off the CBR swingarm and welded it to the NX swingarm. I welded a mounting point for the master cylinder to the frame. I also modified the brake pedal (But I think you could use an XR650L pedal instead).

The rear brake is now a two pot caliper so the rear brakes work better than the front. This isn't a problem on asphalt, but on dirt it locks up too easily.  One of these days I'm hoping I'll end up with a parts bike in the shop with a 1 pot caliper that will fit on this bike.

[UncleBob TT Silver Member]

lateapex31 said:

Carb works acceptably with a lot of fiddling (but not 'good'-especially during transients)

My three turbo bikes disagree with you