how to gain 10-15 % hp on your R for $350 or more

[265 sleeper]

Here we go this setup is to make your 1989trx 250r go faster while keeping it a sleeper or close to . You can use this on a long rod crank or 4mm stroker crank running a trx250r 1986 piston and no spacer plate or a custom spacer plate depending on what build.

Ok, I have a 1989 trx250r with a 4mm stroker crank ,running a custom spacer plate 2mm thick instead of the 4-5 mm spacer plate , and a 1986 piston. this allows the piston to come out of the cylinder while keeping the rings below the cylinder deck height. The piston will stick up about 3mm. Then the head has to be machined to except the piston which is about 3.50 mm deep.


This is the measurements that I got with a not so good mic

2 Gaskets .020 each
Spacer plate .095
Head gasket .010 one
Cylinder head decked .150 deep
height piston sticking out of cylinder .100


This setup cost me 436 bucks and will still have it look close to stock

[265 sleeper]

Here's a pic of the head

[265 sleeper]

Originally posted by 265 sleeper
Here's a pic of the head

[derby]

Originally posted by 265 sleeper


If you have it setup with the right squish I am guessing you will probably have a 10cc dome there. It is kind of hard to tell if the dome even has an angle cut to it. I would measure your squish, angle and cc before you run that thing

[bobizzle]

squish clearance is measured for .035, and the angle is exact. the cc completed is 265. i have the exact same setup, and we ran over the numbers with him before and after dropping off heads. with the smaller spacer plate it allows you to deck the head enough so you dont have to run the bulky plate.

[265 sleeper]

What angle , rod angle or the angle on the head?

The machinist/motor builder/jet machanic has done heads for me before. He did my first one for a banshee. I ran a 4mm banshee with the spacer plate and then with out and WOW what a differance. The bike could lauch in 4th gear in the dirt with some yzf 450 tires running on pump gas

[machwon]

Originally posted by derby
If you have it setup with the right squish I am guessing you will probably have a 10cc dome there. It is kind of hard to tell if the dome even has an angle cut to it. I would measure your squish, angle and cc before you run that thing

I'm with derby here, that dome looks really small. Unless there was something wrong with the cylinder/head, you don't need to run the piston up that high. I done them in both stock cylinder and pro-x and they are always good for a 4HP gain. You can usually get a 10-15% gain just by getting any set up dyno tuned, sometimes more.

[hontrx265r]

I'm a alittle skeptical as well. Not that your not doing good.. but why? What is the difference between having a thin plate and a deep cylinder head vs. a thick plate and a normal cyl head? It seems to me all your doing is lowering the cylinder. I guess maybe changing the port timing a little?

[derby]

Originally posted by bobizzle
squish clearance is measured for .035, and the angle is exact. the cc completed is 265. i have the exact same setup, and we ran over the numbers with him before and after dropping off heads. with the smaller spacer plate it allows you to deck the head enough so you dont have to run the bulky plate.

I was referring to cc of the head not cc of the motor. In other words what is the trapped volume at tdc. The machine guy cut into the head, what 3.5mm is what you said. He made the dome really shallow. So the trapped volume when the piston is at the top of the stroke is going to be very small. Putting your compression not just high but really high just judging by the looks of the head especially if the squish is .035. He now needs to go back over the head and cut material out of the dome to obtain the correct trapped volume. The squish angle almost looks like it would work with a flat top piston. The angle on the head should be matched to the piston or cut on a radius. I am not knocking your setup just giving you some constructive feedback. I am afraid that if you run that you will be asking for problems.

[265 sleeper]

Originally posted by hontrx265r
I'm a alittle skeptical as well. Not that your not doing good.. but why? What is the difference between having a thin plate and a deep cylinder head vs. a thick plate and a normal cyl head? It seems to me all your doing is lowering the cylinder. I guess maybe changing the port timing a little?

the differance is port timing is UNcorrected with the 5mm
spacer plate and is off by like 2 and a half mm below transfer ports

The motor was clayed for the correct cc and squish clearance. The motor will be running at 170 to 180 psi. He don't like building high compreession bike. He like bikes to perform all around and last . I thought that it was to much he had to take out of the head but the machanist said it was ok. These pics were takin off my cr*p berry so you can't see it to well but there is an angle on the dome
Trapped volume is around 19cc dome or bigger the piston sticks out about .100 so giving me .060 clearance between the head and piston

[derby]

Originally posted by 265 sleeper
the differance is port timing is UNcorrected with the 5mm
spacer plate and is off by like 2 and a half mm below transfer ports

The motor was clayed for the correct cc and squish clearance. The motor will be running at 170 to 180 psi. He don't like building high compreession bike. He like bikes to perform all around and last . I thought that it was to much he had to take out of the head but the machanist said it was ok. These pics were takin off my cr*p berry so you can't see it to well but there is an angle on the dome
Trapped volume is around 19cc dome or bigger the piston sticks out about .100 so giving me .060 clearance between the head and piston

So previously you had a 72mm stroke .190 spacer plate, long rod, 86 piston. Then you put in a 4mm stroke now raising the piston height 2 more mm and then you dropped the cylinder nearly 2-3mm. Does not make sense to me. I am interested in your port timings now. If you will measure how far your piston sticks out the top of the cylinder(measure on the side right above the wrist pin) and the distance from the top of the cylinder down to the top of your exhaust port I will calculate your exhaust timing because I think you may be surprised unless you have some major work done with the porting.

Also at TDC I bet your exhaust port is open when it should be closed. You might check that as well.

[406Z26]

Something about this setup does not sit right with me. Especially how far the piston is out of the cylinder and that now the porting is way off.

[methyman]

I agree something is not correct. I had a 4mm with a 87-89 piston with out a spacer plate and the piston was .040 out of the hole. Are you sure the cylinder was decked from the bottom or possibly using a 87-89 piston. That piston is sticking out too far from you description of what you have as parts. It could be a 5mm stroker crank also.

[265 sleeper]

No porting done to port transfer timing just intake and exhuast. I had a 4mm from the start of owning a 250r just didn't know it because the guy I bought it from lied about a lot of stuff. I ran the big spacer plate running the piston even with the cylinder deck height. Same porting I was running port timings un corrected not knowing and then found this guy to do a banshee head for me and wow what a differance it made from the spacer to no spacer plate so. I rebuilt my 250r buying a 4mm it looked a lot like the crank I had before so I looked and they were crank pins same location. Ill look at the piston exhuast skirt to see if it passes the port

Its a 86 piston not the 87-89 piston

[bobizzle]

i just went go check my port timing, and my exhaust port is fully closed when tdc. i have the same setup as him, and the port timing is corrected with drooping the cylinder down with a smaller space plate and decking the head. the reason i did this is so i could keep mine as close to a sleeper. with this small plate it almost looks like a real thick gasket. for the head, we are not using the original pancake gasket, but running the single layer gasket to keep it from blowing.

[derby]

Originally posted by bobizzle
i just went go check my port timing, and my exhaust port is fully closed when tdc. i have the same setup as him, and the port timing is corrected with drooping the cylinder down with a smaller space plate and decking the head. the reason i did this is so i could keep mine as close to a sleeper. with this small plate it almost looks like a real thick gasket. for the head, we are not using the original pancake gasket, but running the single layer gasket to keep it from blowing.

Port timings will not be close to the same with that setup. I was just wanting to know how far off they were going to be.

An 86 piston measures less than 76mm from lower crown to the bottom of the skirt. So if you had a deck height of absolute zero it would barely cover the exhaust at top dead center. If you are pushing the piston out the top of the cylinder 3.5mm you are free porting the exhaust by probably 3mm. If you guys would have used a .190 your exhaust port timing should have only changed about 2 degrees while your transfers will change a little more.

[bobizzle]

tom i will go and take pics of bdc, and tdc, and show where it is out the head, and a better pic of the head.

[derby]

Originally posted by bobizzle
tom i will go and take pics of bdc, and tdc, and show where it is out the head, and a better pic of the head.

You must not have the same setup he does or your piston was not at TDC.

[atvmxr]

i dont understand what all the fuss is about...
Im old school and thought the best setup TRX was 87-89 crank w/ 86 piston and spacer plate. recently learned that these days that is considered inferior setup, it lowers the crank pressure, and its better to not have spacer plate.

how is this not the same application? reducing the spacer plate for a 4mm equals more crank pressure and better performance? also my LRD national setup-circa 1995 and one hell of a motor, has the bottom of the cylinder cut down and head clearanced. I think there is something to be found by making the cylinder set lower in regards to port timings...

discuss... :D

[bobizzle]

i just looked at it, i wish i could show you now, but cam is dead. don't wanna take a phone pic and going to work now.

[derby]

Originally posted by atvmxr
i dont understand what all the fuss is about...
Im old school and thought the best setup TRX was 87-89 crank w/ 86 piston and spacer plate. recently learned that these days that is considered inferior setup, it lowers the crank pressure, and its better to not have spacer plate.

how is this not the same application? reducing the spacer plate for a 4mm equals more crank pressure and better performance? also my LRD national setup-circa 1995 and one hell of a motor, has the bottom of the cylinder cut down and head clearanced. I think there is something to be found by making the cylinder set lower in regards to port timings...

discuss... :D

If you have ever setup a stroker crank yourself, done your own porting, or cut your own head you would realize that there is a problem. I had some free time on my hands so I setup a similar setup in my garage. I used a 2mm spacer plate, 86 piston, 86 unported cylinder, and a 4mm crank in a set of empty cases. The top ring on the piston will nearly pops out the top of the cylinder. Put the degree wheel on there and came up with 170 degrees of exhaust. It gets worse as you will have 112 degrees on the transfers. Exhaust is uncovered at TDC.

Who told you guys to go with a 2mm spacer anyways?

[machwon]

sounds like the cylinder still might be usable, but likely not the head.

[bobizzle]

both are still usable, but the head just needs to be shave to the clearance you need.

[bobizzle]

no one told us to run this setup. it was a setup we had been talking about for a wile, not knowing that we would have the problems we are having now. i know about the 4 mil spacer plate, but i knew it also lowered crank pressure, so i decided to try 2mil, and i found out why it wont work now.

just trying to build a bad *** motor. it looked good, until we put the cylinder on top and seen the bottom of the skirt.

[derby]

Originally posted by bobizzle
no one told us to run this setup. it was a setup we had been talking about for a wile, not knowing that we would have the problems we are having now. i know about the 4 mil spacer plate, but i knew it also lowered crank pressure, so i decided to try 2mil, and i found out why it wont work now.

just trying to build a bad *** motor. it looked good, until we put the cylinder on top and seen the bottom of the skirt.

If you are really that worried about crank case pressure and volume you should run case stuffers.

[bobizzle]

what are case stuffers, and do you have pics of them.

[derby]

Originally posted by bobizzle
what are case stuffers, and do you have pics of them.

It is a composite piece that looks similar to plastic. Basically you put them down on top of the cases and the cylinder bolts over the top of them. I cant find a picture of them but I have a set somewhere in my garage. They basically fill the void underneath the cylinder. So they sit in between the top of the cases and the bottom of the cylinder. I got mine from dave moore racing about 10 years ago when he was pushing they idea about lower crank case pressure.

[bobizzle]

do ya remember roughly how much ya paid for em, also, if ya get a chance can ya look for em and take a pic so i can see what exactly your talkin about, i get the jist, but i know its hard to explain in words.

[derby]

Originally posted by bobizzle
do ya remember roughly how much ya paid for em, also, if ya get a chance can ya look for em and take a pic so i can see what exactly your talkin about, i get the jist, but i know its hard to explain in words.

Let me look this weekend and if I find them I will get back to you. Cant remember what I paid. You might give dave a call. Look him up at www.davemooreracing.com

[All250R]

Originally posted by atvmxr
i dont understand what all the fuss is about...
Im old school and thought the best setup TRX was 87-89 crank w/ 86 piston and spacer plate. recently learned that these days that is considered inferior setup, it lowers the crank pressure, and its better to not have spacer plate.

You might be thinking of a long rod setup where the stroke is still 72mm. It's easy to get confused at first with a longer rod and more stroke. They are not the same thing - completely different.