spdfrk125
New member
Hello,
I am wondering if someone can tell me how much I can lower my jugs and heads without creating problems. I bought three new cylinders on ebay and two were .75mm shorter than the third. I milled he third down to match the other two with the thinking that I can always use two or three base gaskets.
(.010 each) If you can answer this I would appreciate it.
Thanks
I am wondering if someone can tell me how much I can lower my jugs and heads without creating problems. I bought three new cylinders on ebay and two were .75mm shorter than the third. I milled he third down to match the other two with the thinking that I can always use two or three base gaskets.
(.010 each) If you can answer this I would appreciate it.
Thanks
Did you measure the distance betweenthe port and top of the jug to make sure that the port timing is all the same? A safe distance for clearance between the head and piston should .050" (1.27mm) in the squish area(outer edge area of the piston). T
spdfrk125
New member
head clearance
Yes I did check that the timing was the same. How do you measure the squish area? With modeling clay? If you were to mill the heads on a srx 700 how much can you take off?
Thank you for your reply!
Yes I did check that the timing was the same. How do you measure the squish area? With modeling clay? If you were to mill the heads on a srx 700 how much can you take off?
Thank you for your reply!
in my experience, my engine builder cut the heads on my 02 SRX .012 and the motor blew up. .012 off the heads gave it a 12.67:1 compression ratio which is too tight for even 93 octane pump gas.
00-02 heads are the same CC's 00-02 heads are also 4 cc's tighter then the 98-99 heads
00-02 heads are the same CC's 00-02 heads are also 4 cc's tighter then the 98-99 heads
spdfrk125
New member
Head clearance
Thank you for your valued input.
Thank you for your valued input.
My compression is at 11.08:1 or 6.2:1 REAL compression. I run 94 octane with no issues! I just cut .007" off and my cousins took off .005". So .013" Total.
Tomseal, did you have the squish modified? Or did you just cut it down and that's all?
Tomseal, did you have the squish modified? Or did you just cut it down and that's all?
the heads were flat cut down
mopar1rules
Active member
more can be taken off '98-'99 heads, than on '00-'02 heads, to get the cc volume of '98-'99 heads close to a '00-'02 head. remember you will still have to keep the squish clearance correct, for the application.
tomseal, what was your squish clearance, after your builder flat cutted them .012"? must have been around .050"-.053", if flat cutting a stock '00-'02 head.
spdfrk125, what year srx are you working with? you also want to know the tightest squish clearance that you can run. well, that can depend on a few things....the max rpm that the motor will run (higher rpm = larger clearance and vice versa) and the octane of fuel to be run. TSR software, Bi-Motion, and a few others, are great for this kind of thing. TSR will figure your MSV (maximum squish velocity). depending on how high this value is, can dictate how high of octane fuel you run. for your squish clearance measurements, just use some .080" diameter solder. when you measure the squish clearance, make sure you have the solder parallel to the wristpin. otherwise if you have the solder perpendicular to the wristpin, you will get false readings, as the piston will just be rocking/piviting on the wristpin. now that you have cut the cylinder bases .75mm (.0295"), you will need to add 3 base gaskets in addition to the stock 1, so 4 total now, to have the same port timing as stock, and same comp ratio as stock. alltho, you will be a little higher (on compression), if flat cutting the heads a few thousandths, but not as high as you would be if not adding any base gaskets to raise the cylinders back to their original height.
tomseal, what was your squish clearance, after your builder flat cutted them .012"? must have been around .050"-.053", if flat cutting a stock '00-'02 head.
spdfrk125, what year srx are you working with? you also want to know the tightest squish clearance that you can run. well, that can depend on a few things....the max rpm that the motor will run (higher rpm = larger clearance and vice versa) and the octane of fuel to be run. TSR software, Bi-Motion, and a few others, are great for this kind of thing. TSR will figure your MSV (maximum squish velocity). depending on how high this value is, can dictate how high of octane fuel you run. for your squish clearance measurements, just use some .080" diameter solder. when you measure the squish clearance, make sure you have the solder parallel to the wristpin. otherwise if you have the solder perpendicular to the wristpin, you will get false readings, as the piston will just be rocking/piviting on the wristpin. now that you have cut the cylinder bases .75mm (.0295"), you will need to add 3 base gaskets in addition to the stock 1, so 4 total now, to have the same port timing as stock, and same comp ratio as stock. alltho, you will be a little higher (on compression), if flat cutting the heads a few thousandths, but not as high as you would be if not adding any base gaskets to raise the cylinders back to their original height.
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didnt check the squish. me and a former TY member took the mag cylinder and head that wasnt blown up and CC'd it. 12.67:1 compression
Lesson learned, with todays pump gas, I would leave the heads alone.
spdfrk125, what are you trying to do with your sled? if your sled is a 98 or 99, I would go with a set of stock 00-02 heads, jet it to 01 specs and ride it.
also, there is the old trick on the 98-99 of adding an extra base gasket and cutting the 98 or 99 heads .030 poor mans port job
Lesson learned, with todays pump gas, I would leave the heads alone.
spdfrk125, what are you trying to do with your sled? if your sled is a 98 or 99, I would go with a set of stock 00-02 heads, jet it to 01 specs and ride it.
also, there is the old trick on the 98-99 of adding an extra base gasket and cutting the 98 or 99 heads .030 poor mans port job
I also wanted to mention that the only differnce between 98/99 cylinders and the 00-02 cylinders is a slight lip on the top of the exhaust ports on the 98/99 cylinders. On 00-02 cylinders, that lip was removed and is flat cut across the top. That is the only difference.
Blue printing the 98/99 cylinders to match the 00-02 cylinders would be no different then adding a base gasket and cutting the heads or if you really really wanted the extra 5-6 HP, you could also install 00-02 top end.
Blue printing the 98/99 cylinders to match the 00-02 cylinders would be no different then adding a base gasket and cutting the heads or if you really really wanted the extra 5-6 HP, you could also install 00-02 top end.
spdfrk125
New member
Thank you! Your information is very helpfull. I'm working on a 99 srx 700 with a 2000 stator and electronics as well as 2000 cdi,carbs. It has a cold air kit and clutching. Bought new pistons(99) cylinders(99) and 99 heads. Can I use only three gaskets and still run the pump gas with these cylinders?
What gaskets are you talking about?
Theres some not so accurate info given out here, first off, you set up the heads to match porting, the higher you make the exh port the more you must machine off the head to regain LOST compression from the bigger exh port. ((Compression doesnt start till the exh port is closed)). The simple check as tomseal6 did is not accurate as to the whole picture, he merely checked cylinder volume by the head volume, well that doesnt tell you what the engine has for a real corrected compression ratio. Yamaha uses the same corrected compression ratio as I do, this is because its the most accurate way. The longer the exh port is open the LESS compression you have, 12.67:1 uncorrected is just fine with porting and using real 93-94 premium octane fuel, theres 100's of these same sled engines on this site alone running that. It matters as to fuel quality, you do need the octane to prevent detonation, if your using 87 octane it will detonate. If your in a area where they have used alot of ethanol to cut the fuel youll also have problems because youll need more of it to get the same octane level. Alcohol needs more volume, (bigger jets) then gasoline does. There were ALOT of problems last year with fuel quality and even bone stock sleds having burn downs.
If your gonna cut the heads on a srx do it the right way and set it up for the fuel quality youll use all the time.
More compression is more power but theres a ceiling, and fuel octane will dictate that. Theres also ways to run more compression and not have large octane levels, this involves changing the squish angle of the heads, so it traps less heat at the edge, this where all the detonation will focus on, the edge of the exh side of the piston and sometimes all around under the squishband to edge of piston.
By adding base gaskets your adding deck clearance and no matter how much you cut the heads you cant remove the deck clearance. This will ruin the way the heads operate, youll now then have a space around the top edge of the piston crown and the closer to the top of the cylinder the ring is, the better the seal. If you add 2 extra base gaskets youve added another .020" deck clearance. Stock a srx has right around .010-.012" deck clearance. So all together youd have .032" deck clearance, meaning at TDC, the piston will now be down inside the bore by this much. The other down side is the piston crown edge will now not be timed with the floor of the exh port.,hampering the return pulse wave from the pipe. The best set up is exactly flush at BDC, and a flat exh floor in the cylinder will yield the best power results.
Also, the 98-99 cylinders are NOT the same, they have differnt port timing, not "just a lip", the exh. port is differnt as are the transfer port timing. I actually prefer to use the 98-99 cylinders when building a mod motor for the better (lower)transfer port timing, the exh port is just changed to the desired timing.
If your gonna cut the heads on a srx do it the right way and set it up for the fuel quality youll use all the time.
More compression is more power but theres a ceiling, and fuel octane will dictate that. Theres also ways to run more compression and not have large octane levels, this involves changing the squish angle of the heads, so it traps less heat at the edge, this where all the detonation will focus on, the edge of the exh side of the piston and sometimes all around under the squishband to edge of piston.
By adding base gaskets your adding deck clearance and no matter how much you cut the heads you cant remove the deck clearance. This will ruin the way the heads operate, youll now then have a space around the top edge of the piston crown and the closer to the top of the cylinder the ring is, the better the seal. If you add 2 extra base gaskets youve added another .020" deck clearance. Stock a srx has right around .010-.012" deck clearance. So all together youd have .032" deck clearance, meaning at TDC, the piston will now be down inside the bore by this much. The other down side is the piston crown edge will now not be timed with the floor of the exh port.,hampering the return pulse wave from the pipe. The best set up is exactly flush at BDC, and a flat exh floor in the cylinder will yield the best power results.
Also, the 98-99 cylinders are NOT the same, they have differnt port timing, not "just a lip", the exh. port is differnt as are the transfer port timing. I actually prefer to use the 98-99 cylinders when building a mod motor for the better (lower)transfer port timing, the exh port is just changed to the desired timing.
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mulderdad
New member
Had to read your reply three times mrv!lol!
Always did like a good info session.
Always did like a good info session.