bajardine
New member
I've finally gotten around to putting a set of SRX600 heads on my '03 Mountain Viper. I put the heads in a lathe and opened up the heads to the bore of the 700. I ran the sled for a couple days last weekend and it pulled better than my mono head that was opened up to 24cc across all domes.
Now I'm ready to cut the heads for a target squish gap measurement of .055". The question I have is how far away from the cylinder wall do I measure the gap? At the edge of the piston the squashed solder is measuring .075" and at 1/4 inch from the side it measures .079". Which should I use as the correct squish measurement? I just spent two hours reading every post I could on squish and couldn't find that bit of info. Seems like I remember at some time reading it should be taken around 1/4" from the cylinder wall.
I have the stock Viper head gasket on. I don't want to peel any layers since I have access to a lathe and would rather cut the heads and use the full gasket to eliminate any potential problems of having a bad seal.
Also, if I took two measurements for each piston, one on the PTO side of the piston and the other on the mag side, and they're a few thousanths different, should I use the lower of the two measurements or an average?
Now I'm ready to cut the heads for a target squish gap measurement of .055". The question I have is how far away from the cylinder wall do I measure the gap? At the edge of the piston the squashed solder is measuring .075" and at 1/4 inch from the side it measures .079". Which should I use as the correct squish measurement? I just spent two hours reading every post I could on squish and couldn't find that bit of info. Seems like I remember at some time reading it should be taken around 1/4" from the cylinder wall.
I have the stock Viper head gasket on. I don't want to peel any layers since I have access to a lathe and would rather cut the heads and use the full gasket to eliminate any potential problems of having a bad seal.
Also, if I took two measurements for each piston, one on the PTO side of the piston and the other on the mag side, and they're a few thousanths different, should I use the lower of the two measurements or an average?
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You would measure the squish at the outer edge of the piston, close to the cylinder wall, for your minimum squish clearance. Most times you want the cylinder head squish band angle to be on a 2 - 3 degree larger angle then the piston dome so the squish measurement slightly increases as you move away from the outer edge...not unlike what your measurements do now, increases from .075" -.079". Always use your minimum measurement for setting your squish clearance.
JM.02c
Bob
JM.02c
Bob
mopar1rules
Active member
be sure to double check the trapped volume, now that you have 600 heads on a 700, as the 600 srx heads were a few cc smaller to begin with than 700 heads. you don't want too high of a compression ratio for the fuel being used.
bajardine
New member
Okay, so I'll go with the measurement at the edge of the piston.
I'm planning on measuring the trapped volume before and after I'm done cutting the heads. What would be the highest compression ratio you would want to have using premium gasoline? I'll calculate it by (cylinder displacement+trapped volume)/trapped volume. In my area the highest octane at the pump is 91. I ride at 7,000 ft +.
I'm planning on measuring the trapped volume before and after I'm done cutting the heads. What would be the highest compression ratio you would want to have using premium gasoline? I'll calculate it by (cylinder displacement+trapped volume)/trapped volume. In my area the highest octane at the pump is 91. I ride at 7,000 ft +.
My Seadoos measure 150 LBS at Sea Level but only call for 89 Octane. Not sure why SRX calls for 91 Octane with 130 lbs. Maybe timing?
You may want to post on the Mountain site as they would be more in tune to what compression ratios you can run at the higher altitudes.
If you go on to Mountain Peformance's website it has volume recommendations for Peak heads that you may be able to apply.
Most guys are not going to want to give you specifics as it is a fine line on what you can run and what will result in engine damage.
As for cranking compression, it is not as relative as some may think because porting has a huge effect on cranking compression. You could have a 14:1 compression ratio engine with less cranking compression then a 11:1 engine because its all about the trapped compression or corrected compression ratio, the 14:1 engine could have a 6.7 corrected compression ratio and the 11.1 engine could have a 7:1 corrected comp ratio all depends on the exhaust port height.
If you go on to Mountain Peformance's website it has volume recommendations for Peak heads that you may be able to apply.
Most guys are not going to want to give you specifics as it is a fine line on what you can run and what will result in engine damage.
As for cranking compression, it is not as relative as some may think because porting has a huge effect on cranking compression. You could have a 14:1 compression ratio engine with less cranking compression then a 11:1 engine because its all about the trapped compression or corrected compression ratio, the 14:1 engine could have a 6.7 corrected compression ratio and the 11.1 engine could have a 7:1 corrected comp ratio all depends on the exhaust port height.
bufalobob
Member
when measuring squish you need to take 2 measurements @ the same time 180* opposite of each other @ the cylinder wall above the transfers. if you do 1 side @ a time there may be a certain amount of piston movement that will give you incorrect #'s. 12.5:1 is borderline premium pump gas.
bob
bob
bufalobob said:
I thought the reason you measured in line with the wrist pin (east/west rather than north/south) was to avoid incorrect numbers as Bob mentions above due to piston rocking. Seems it would be a jugling act trying get two solder pieces lined up and at the correct length, through the plug hole. Maybe not or maybe it's more accurate. I haven't done it in years but I seem to remember going to the 3 or 9 o'clock position for that reason.