madzx2
Member
YAMMIEGOD3:16 said:
ok so is there any measurement i could take to find out and idea of what i have exactly. i messaged mark and he remembers my sled. he gave me a good direction to go in. he said basically the same thing you said.
dyno time!!
- Thread starter madzx2
- Start date
ok so is there any measurement i could take to find out and idea of what i have exactly. i messaged mark and he remembers my sled. he gave me a good direction to go in. he said basically the same thing you said.
madzx2 said:
simply pull the head off and measure from the top of the cylinder to the topedge of the exh port. You cant run those stock pipes anywhere near 9000+ rpm and make any power.
madzx2
Member
i will take that measurement tonight and post it here. thanks.
madzx2
Member
my exhaust port is 29.5mm from the top of the cylinder.
madzx2
Member
whats my next step?
03viperguy
Moderator
wait for mrviper to tell you more lol!
madzx2
Member
yea im just really curious as what to do and what i really have. i been in contact with the builder and he says it sound like the motor is right on track but the pipes need to be shortened or use different pipes all together.
YAMMIEGOD3:16
Active member
YOU TRAIL RIDE THIS SLED ? SOUND LIKE YOUR GETTING UP THERE IN RACE FUEL COUNTY . YOU MIGHT NEED RACE PIPES MAN. 3:16 (yammie tony)
madzx2
Member
ive trail ridden it for 2 seasons now and i always run 92 pump gas. ive always clutched for 8500. its got .055" squish, 120 psi across all 3 cylinders. squish band is 7.7mm wide. i have some rough port measurements just waiting to see if anyone has an idea of what rpm they think it should run.
madzx2
Member
i was told by a couple people that i could have 3/8" taken off the head pipes so the pipes and porting would match rpm wise. im not sure in my case though what rpms exactly it should be running, the guy who did the motor say 9200, it made power at 8800 on the dyno.
I'll add my .02c . lol..I'll probably get blasted!
The designed RPM band of the pipes you are using is more critical then the optimum RPM the eng is ported to. Although they obviouslly should be matched for optimum performance!
I would run your engine at 8500RPM with the stock pipes and stock ignition.
IMO: Your sled ended up very close to the HP I had guessed it would and it made awesome hp for a trail safe rideable 700!!! Don't get to caught up in the numbers as there is so much inaccurate, assumed, anticipated, speculated hp numbers out there. I have built and raced a few sleds and I have yet to see a stock piped SRX out there that performs at a level much above about 150hp.
I still have a piped + ported 800 VMAX4 and I have to tell you when you ride it on the hard pack you really get a sense of what 175+ hp really feels like let alone the 200+hp Mod 866 10200RPM 480lb VMAX4 I built!
JM.02c
Bob
The designed RPM band of the pipes you are using is more critical then the optimum RPM the eng is ported to. Although they obviouslly should be matched for optimum performance!
I would run your engine at 8500RPM with the stock pipes and stock ignition.
IMO: Your sled ended up very close to the HP I had guessed it would and it made awesome hp for a trail safe rideable 700!!! Don't get to caught up in the numbers as there is so much inaccurate, assumed, anticipated, speculated hp numbers out there. I have built and raced a few sleds and I have yet to see a stock piped SRX out there that performs at a level much above about 150hp.
I still have a piped + ported 800 VMAX4 and I have to tell you when you ride it on the hard pack you really get a sense of what 175+ hp really feels like let alone the 200+hp Mod 866 10200RPM 480lb VMAX4 I built!
JM.02c
Bob
madzx2
Member
sideshowBob said:
im not here to blast anyone. i appreciate all that i learn from everyone on this site. i am starting to understand better whats going on with my motor. it would just be nice to know exactly what was done to it or a good idea of what it is. i also agree that the power @8500 looks really good. mark does too but he said their is a few more details that need to be addressed.
madzx2 said:
That (engine)will definitely make power at 8800rpm and then some over rev with that exh port, but your stock pipes wont do much good over 8600/8650, so you have a mismatch there in my opinion. That exh port would be like a aggressive lake race type port job, but should also have alot of compression to go along with the port. I dont personally see how you could make any good power at all at 9200rpm with stock pipes and the cdi, would be so far retarded it would be a real slug, youd have no heat at all in the pistons at that kind of rpm(rich running).
I also would suspect its a lower type compression engine thats why it wants to peak alot higher rpm then 8500rpm. More compression makes more low/midrange power with a LOWER peak rpm. the exact opposite with lower compression.
Looking at the dyno sheets, I see it kinda bouncing all over the place dropping a few then picking up a couple more within 150 some rpm in places, thats kinda bogus, and I suspect its likely dyno error.
shortening the pipes, yes, you can gain a slight bit of rpm, you will stretch out the pipes power range but youll also need to add timing to get power from over rev. The timing is fine up top for the over rev as its needed because the cdi box retrds the timing but may cause you problems down lower for a trail engine, this is NOT something I would do for a trail engine. ((Added ign. timing puts heat in the pistons, retarded timing puts heat in the pipes.))
a 150-155hp is easily doable on a trail port srx engine with pumpgas but the porting,compression,piston mod and headwork must all walk hand in hand. The head work is critical!! just a flat cut of the heads is not going to do it, they will need rechambered set up with the angles and the correct radius.
03viperguy
Moderator
as usual, a very good answer from a smart guy 
told you the next step was getting an answer from Don!
told you the next step was getting an answer from Don!3g racing
New member
mr viper, what kinda money do you get for a good port job with it set up for 500' grass and 660'ice I got a 01 srx with a pretty good trail stock set up for grass want to add some horsepower for this up coming season but keep it trailable,needed to rering anyways this year so was thinking a mr viper port job would be good so I read on here
madzx2
Member
its starting to make sense now. so what would my next step be? mrviper could i send you a cylinder and a head, could you take measurements and find out exactly what i have. this would give me an idea of what if anything motor wise would need to be changed, like head work.
madzx2
Member
so would more compression make more power at 8500 with the stock pipes and cdi?
madzx2
Member
i cc'ed my heads today and they are 24cc with the plug installed. i also pulled a cylinder off and remeasured my ports. the exhaust port is 30.1mm. so my compression ratio would be, 10.66 uncorrected or 5.97 corrected. does this sound right?
Last edited:
madzx2 said:
Is that 24cc with the head installed? You loose about 4 cc with the head installed which would be @ 20cc that works out to approx 12.6 : 1.
That exhaust port height[30mm] is pretty typical for a porting spec on these engines gives you approx 198 degrees exhaust duration.
You will need to provide a squish measurement, squish band width, + squish band angle as well for the "Gurus" to help you out. There is a lot of science in the head specs.
Again I must state the HP numbers you dynoed at were very respectable for a stock piped trail 700.
JM.02c
Bob