drag port specs for CR500

[rsss396]

I have a CR500 powered TRX quad that I sent to a shop out west that is very experienced in sand drag motors.

I won't name the company because I am not here to bash just want your opinion on the final porting specs.

I put my degree wheel on and this is my results:

The exhaust has been raised to 192 degrees open(stock is 180)
The transfers are stock at 122 degrees open

Compression is 13.5 to 1 (have not verified this, just the info that was given to me)

The motor pulls hard through mid range but is flat on top.

I have always ported my own motors but being the 500 was new to me I thought I would just save the headache and time experimenting to get the right port timing combo and went with a known builder.

So now that I am not happy with the performance I figured I would just finish this port job myself.

My experience on 265 motors was to take them to 130 degrees on the transfers when running 192 degrees of exhaust.

I thought trying 128 degrees on the transfers would be a good start then maybe a little more down the line if needed.

Any thoughts would be appreciated
thanks Dave

[FPMXer]

You will find your answers here www.cr500riders.com

[370banshee]

i;v never built a 500 but i;d suspect that a transfer of 126 would be best.. if a 33 blowdown is good on a cr500 like it is on other motors i've ported

[rsss396]

126 would be a safer bet and I could raise a little more if needed.

I have been told by the shop that set up my lectron that 192 is pretty mellow for a large bore motor like the 500 when drag racing it, and the transfers should be rasied but was hesatant to give any #'s.

I talked with the builder and he thinks the 35 degrees blow down is fine and thinks I should take it to a dyno to see where the pipe is making power.

I agree the dyno would be a step but the blow down just seems to long for my needs.

thanks
Dave

[flotek]

to me 192 exhaust isnt really a drag port sounds like something Ct racing or ftz racing would do .... i have opened them up as much as 200ex with 132 transfers (yes i know its tons of work ) ,but those are just simple specs... only a small part of the porting ...theres other key things that make or break the perofrmance that are just as important .I would shoot for a blowdown between 32-34 .the pipe and head design will really play a huge part on those 500 motors.coo lthing is you can safely get a ton of exhaust area on a cr500 and still have ring support .if the head is setup for loads of compression yo u can get away with running higher durations because the torque will be there .lots to consider

[ky 2stroker]

im no porting expert, but i've always heard of the 500 motors not really being the fast/ really high revving motors for drag racing. I guess another way you could look at makeing it a fast drag bike would be to port it for tons of all-around power but emphasizing on midrange and lowend torque. and then find the right tire size combo with a pretty tall gearing that jumps hard from the hole and runs each gear pretty good between shifting, using alot of the midrange rpms instead of revving its guts out on the topend.

do you got any pics of this trx500r monster you got? how bad is the vibration with the cr500 motor

[rsss396]

Thanks Evil, I have heard of real high exhaust port # on some 500's in the past but never seen them run, kind of curious if they were to peaky.
I run in the sand and tend to like motors with a little broader power band.
Going to raise the transfers to 128-130 and maybe raise the exhaust to 194.

ky2stroker,
Vibration is reasonable but it is rubber mounted with a cradle that ties the front and mid motor mounts together resting on a single rubber mount and the rear motor mount pivots on the swing arm bolt.
The handle bars have brass in the ends, foam grips and is mounted on a anti-vibration mount along with a custom rubber isolating steering stem.
It was allot of of fabrication to make this project happen and would never do it again or recommend it to anyone.
If I could have done it all over I would have done the Sabertooth expensive but allot less head ache and vibration.
Cr500 are bad ass in dirt bikes but really don't make all that much horsepower.
Factory rated them between 58-62hp at the flywheel depending on the year.
But I will stick with my project and work the bugs out as time passes.
I don't race competitively just play at the dunes so my 500 does alright.
My biggest problem as of now is starting the machine, I presently have a hand held starter to crank the motor which is a pain if you kill it.
I don't really have any pictures but I will make a point to get some here real soon and will post them.

[rsss396]

well, my final #'s came in at 196 on the exhaust and 130 on the transfers, took alot of time making the tops of the transfer flat but came out nice.
Took the bike out this weekend and I am very happy with its mid-top end power band.

Had problems with fuel foaming in the bowl a good part of the weekend, do the vibration of the motor.
So I will have to address somehow, I currently run a lectron 44 setup by Packard
along with there oversized bowl. Raising the float bowl level higher than recommended did help most of the problem but it still happens.
Any ideas how to solve this would be gratly appreciated

Dave

[flotek]

wel l Dave flat top transfers tend to be peaky due to the sudden drop of pressure as they open ...angled and staggered transfer heights widen and smooth a powerband .its a shame you had paid good money to have a pro do the work and had to re-port the cylinder to get the correct timing and performance

[rsss396]

Originally Posted by eviltwin

wel l Dave flat top transfers tend to be peaky due to the sudden drop of pressure as they open ...angled and staggered transfer heights widen and smooth a powerband .its a shame you had paid good money to have a pro do the work and had to re-port the cylinder to get the correct timing and performance

Ya I knew it would be a little peaky compared to an angle but my last motor (265) didn't seem to be allot different after only changing the roof tops from tapered to flat so I went ahead with the flat roofs.
But everything I have ever read tells you taper will make for a smoother hit.

I have come to realize that most performance shops will choose the milder option when you tell them what you want. They do this to protect themselves from dreamers with no clue how much more maintenance and tuning go into true race motors.
My exact words in my letter to them was the motor would be sand dragged 90% of the time and dune road 10%.
I like to ride my bike to the drag area of the dunes and maybe one trip around the park a day.
After my port changes I did just this and had no problems at all, I am sure the wider, larger ports are harder on rings but I don't mind changing pistons and rings before they fail.

I could have sent my cylinder back to them like they offered but choose to do it myself because of down time.

Only thing I really kind of ticks me off is they really didn't want to give me any port #'s when I told them I would change it myself because of the down time issue.
I look at it as I saved them allot of work changing it to what I wanted yet were not willing to help.

The shop is really not a bad shop they build some killer fast stuff, I just got thrown in with the typical kid that just wants to go faster not with the racer group.