YZ250 Blaster Build Log

[best]

Thanks for the info!
The goal with the pipe is to keep it one piece and model it after the stock blaster pipe with the curves and it must mate to the stock style silencer. <SOME SNIPPED>

It was not possible for me to keep my pipe one piece and get it in and out of the Blaster frame. I suspect yours will work out the same way as well. The header flange has worked out well. They are available in several diameters, just slide it up the pipe and mark off where you need to cut. Header flanges are heavy 1/4" steel plate, with bolts and gasket add about 1 pound to the weight of the pipe. (just realized I had said the same thing to this thread months ago - please forgive my old age repetitive dementia)

Steve

 

[Tbrock77]

It was not possible for me to keep my pipe one piece and get it in and out of the Blaster frame. I suspect yours will work out the same way as well. The header flange has worked out well. They are available in several diameters, just slide it up the pipe and mark off where you need to cut. Header flanges are heavy 1/4" steel plate, with bolts and gasket add about 1 pound to the weight of the pipe. (just realized I had said the same thing to this thread months ago - please forgive my old age repetitive dementia)

Steve

I noticed with your set up that you have the radiator right in front of the motor where with my set up that will be open just like the stock blaster so I'm hoping with the extra room I can get the pipe to fit in and out with just one piece. If I can't I will definitely use one of the head flanges as you suggested.

 

[Tbrock77]

Still no major progress, but I'm not giving up!

Bought a set of used flat track tires from someone on Craigslist, looks pretty sweet with them on. Now it just needs to be a lot wider, which is already in the plans.

 

[best]

Any more progress on this?
I kinda like to keep mods and swaps as simple as possible.
One step at a time, sort of thing. Too much at once doesn't get completed.

Steve

 

[Tbrock77]

No progress made, just don't have anyone to weld the pipe.

Once I figure that out I should be able to finish it in a few days.

 

[Tbrock77]

Making some progress, buddy of mine is going to tack it together so I can bring it someplace to be properly welded. Keeping it one piece seems very possible but going to be tight getting it to mate to the stock style silencer.

 

[Tbrock77]

More progress. I'm looking for a damaged aftermarket stock style pipe. If anyone has one laying around please let me know, I really only need the last 8-12 inches of it, where it connects into the silencer.

 

[best]

Ah, the last 12" of a Blaster pipe? So it fits your muffler?

Sweet! Looking good!

A lot easier than my design to get the pipe in and out, but where are you going to put the radiator?

My son opted for a single rad on the right side for his DT200 powered Blaster:

He has no problem with overheating (especially in this weather).
The 15 extra hp that your YZ205 makes also generates a lot more heat.
You might want a rad on each side or in the front. Any plans?

 

[Tbrock77]

@best Yes, the last bit of a blaster pipe, I want it to mate to the stock silencer. The plan as of right now is to run a front mount radiator, I'm going to look into side mount radiators though.

 

[armengcorp]

Tbrock,
Been watching your progress. Great job! Best has been giving you good advice. One thing though:
I wouldn't suggest using a Blaster stinger. The outlet diameter to headpipe ratio is just way too small (should be about .6 x diameter of the headpipe. Less than that (and the blaster is way smaller than the YZ) and it creates too much backpressure and therefore too much heat. Best case, poor performance, worst a grenade-ed top end. I might have the last 8 inches of a 78 YZ pipe and the pro circuit stinger from a 94 laying around. I cut the pipe off close to the Stinger for another project but the two could be cobbled together. You'lll need to use both YZ radiators or a single large one like a YFZ .

 

[Tbrock77]

There didn't see to be too much of a difference between the outlet of the YZ pipe and the Blaster pipe. The pipe I'm currently using is a FMF YZ pipe, just cut to shape to fit in there. I'll measure the difference between the YZ outlet and the Blaster outlet when I get home but i believe it was only a small fraction of an inch. I won't be using the stock silencer because of the lack of airflow.

I might have the principles wrong but people are using stock style aftermarket pipes on 240 blasters, wouldn't that be constricting the airflow as much running a YZ250 through a blaster pipe outlet? if people running those pipes aren't having issues why would running 10cc cause an issue?

 

[armengcorp]

The YZ pipe mockup looks really good! I had to cut the stinger off and make one other cut to curl mine through the frame. The important part is to measure the ID of the head pipe (the straight part before the expansion chamber) and the ID of the stinger (straight part just after the expansion chamber) and make sure the ratio is close to 0.6 if you're not using the YZ stinger. Also, if it can't be helped, try not to muck around with the length a bunch either. Believe it or not, a several hundredths of and inch in dia. will make a difference and .25 could easily cause overheating.
To attempt the 240 question w/o going too far down a rabbit hole....the pipe design (and silencer to a lesser extent) is motor specific because they are effected by bore, stroke, port size, port timing, compression, RPM, etc. (and the YZ power valve variably changes compression, exhaust port size and timing and throws a whole new monkey wrench in the mix). Even if the CC's are are exactly the same, pipe size and lenght is dramatically different. Just look at a Honda TRX250R and CR250 pipes for example. This is why the small difference in the variables between 240 Blaster and 200 Blaster are worlds different than a 240 Blaster and YZ250. Make sense?

 

[79 bronco]

The YZ pipe mockup looks really good! I had to cut the stinger off and make one other cut to curl mine through the frame. The important part is to measure the ID of the head pipe (the straight part before the expansion chamber) and the ID of the stinger (straight part just after the expansion chamber) and make sure the ratio is close to 0.6 if you're not using the YZ stinger. Also, if it can't be helped, try not to muck around with the length a bunch either. Believe it or not, a several hundredths of and inch in dia. will make a difference and .25 could easily cause overheating.
To attempt the 240 question w/o going too far down a rabbit hole....the pipe design (and silencer to a lesser extent) is motor specific because they are effected by bore, stroke, port size, port timing, compression, RPM, etc. (and the YZ power valve variably changes compression, exhaust port size and timing and throws a whole new monkey wrench in the mix). Even if the CC's are are exactly the same, pipe size and lenght is dramatically different. Just look at a Honda TRX250R and CR250 pipes for example. This is why the small difference in the variables between 240 Blaster and 200 Blaster are worlds different than a 240 Blaster and YZ250. Make sense?

People also dont realize that the 1/16" they lose from the bandsaw blade when cutting there pipe apart can make a difference, especially after they cut it apart in 5 difference places.
If your cylinder has booster exhaust ports or single exhaust port makes a difference.

 

[best]

Good advice from these guys. A 240 Blaster is no comparison to a modern MX engine. Much difference in port window area and rpm range. That is why we (Blasters) run a 26mm carb quite well, whereas a 250MX runs a 38mm. Good advice on pipe lengths too. The heavier quads typically need a slightly longer pipe, not shorter, and not by much. Stinger diameter is a very critical thing, length not so much. The advice these guys are giving you agrees with my experiences.

 

[Tbrock77]

I added a bit of length to the first segment of the pipe to compensate for cutting, not ideal but this pipe is going to be temporary, If I keep it long enough I'm going to get a proper pipe made for.

Thank you for explaining the reasoning behind the piping, it makes sense.

I took some measurements here they are
YZ250 exhaust port 1.655"
YZ250 FMF Pipe outlet 1.02"
Blaster Silencer Inlet .990"-.60"=.930"
So the original ratio is 1.02"/1.655"= .616
the New ratio is .930"/1.655"= .562
that's a difference of 9.6%, what do you guys think of that?

 

[armengcorp]

My fluid mechanics is rustier than the body of an early 90's F250, but I recall a decrease in pipe diameter increases pressure in the exhaust system geometrically. If the stinger accounts for most of the backpressure than a 10% decrease in dia. would produce much greater than 10% increase in backpressure. This would account for the precision that headpipe to stinger diameter ratio usually fall into and 56% is running on the edge. You're getting into drag quad territory. Can it work? Yes, might even give that older mill some umph (technical term), but I would really watch exhaust temps and make sure to use a quality free flowing silencer (first hand experience).

 

[Tbrock77]

The thought to run it without a silencer had crossed my mind, but it was quickly replaced with a very loud ringing in my ear. I have an infrared temperature gauge so I can accurately watch the exhaust temperatures, along with cylinder and head temperatures. It would probably be a good idea to add in a coolant temperature gauge.

 

[armengcorp]

Here's how I got the pipe to fit.

 

[Tbrock77]

A major goal of this build was to use the stock style blaster silencer. I'm going to do whatever I can do use it.

 

[Tooloose]

I see advantages and disadvantages there. Weight is lower, but far forward. Tho with the YZ should have enough powwa to lift the wheels.

Biggest drawback is rad cap will be lower than most of engine. Which will make "burping" the system impossible.
You'll need to add a tee, length of hose, and fitting with either a plug or cap so that it's the highest point of cooling system.

You could use a airlift device which can be purchased from any local tool trucks or advance auto, autozone, ect. It draws a vacumn on the whole system, removes all air then draws coolant back in without any air