Sanford
ECF
- Location
- Freeride capital of the world
This is a weird one that I and several others haven't been able to figure out.
My rebuilt 701 motor that I've been working on for my SuperJet is your average limited setup. FP B-pipe, 37cc head, OEM twin 38mm (135/75/1.5/95g), stock 62T cases, V-Force 2 reeds, MSD Enhancer, 12/17 Freeride prop, .75mm Pro-X pistons, 61X cylinder with only port matched transfers and VERY mild exhaust port widening (top/bottom exhaust port has not been raised or lowered).
Symptom: (at sea level)
With stock head = 150psi compression.
With billet Blowsion and 37cc domes = between 195 and 210 psi (average between 5 different gauges - Snap-On was 210psi)
I first used the 35cc domes and it raised my compression by 7 to 10 psi when compared to the 37cc domes. Technically, on paper I should see close to 170psi with the 37cc domes and 180-185psi with the 35cc domes.
Mechanicals:
Squish is right at .052" (35cc or 37cc domes), cylinder deck height has not been altered, case deck has not been altered, crankshaft is within spec, N&S are not leaking, motor holds 8psi leak-down test, all new OEM gaskets. Supposedly, this is the first time this motor had been rebuilt (STD core parts).
Items to blame:
Head - I can't see the head is the cause because I tried it with 2 different size dome and both show unusually high compression. After talking with Blowsion, they say this is an isolated case and they don't see these high compression numbers on similar setups.
Cylinder or cases- If the cylinder or cases have been decked, I would see a much closer squish band (mine is .052"). Besides, if I put a stock head back on it its right at 150psi all day long.
Solution:
I don't have one and would love to know what the solution is. I certainly don't want to run race gas for a freeride ski and at times, I plan to run it at WOT. The "work around" solution would be to custom cut a set of domes but this really isn't the proper solution since this shouldn't be happening in the first place.
Ideas? (besides the basics)
My rebuilt 701 motor that I've been working on for my SuperJet is your average limited setup. FP B-pipe, 37cc head, OEM twin 38mm (135/75/1.5/95g), stock 62T cases, V-Force 2 reeds, MSD Enhancer, 12/17 Freeride prop, .75mm Pro-X pistons, 61X cylinder with only port matched transfers and VERY mild exhaust port widening (top/bottom exhaust port has not been raised or lowered).
Symptom: (at sea level)
With stock head = 150psi compression.
With billet Blowsion and 37cc domes = between 195 and 210 psi (average between 5 different gauges - Snap-On was 210psi)
I first used the 35cc domes and it raised my compression by 7 to 10 psi when compared to the 37cc domes. Technically, on paper I should see close to 170psi with the 37cc domes and 180-185psi with the 35cc domes.
Mechanicals:
Squish is right at .052" (35cc or 37cc domes), cylinder deck height has not been altered, case deck has not been altered, crankshaft is within spec, N&S are not leaking, motor holds 8psi leak-down test, all new OEM gaskets. Supposedly, this is the first time this motor had been rebuilt (STD core parts).
Items to blame:
Head - I can't see the head is the cause because I tried it with 2 different size dome and both show unusually high compression. After talking with Blowsion, they say this is an isolated case and they don't see these high compression numbers on similar setups.
Cylinder or cases- If the cylinder or cases have been decked, I would see a much closer squish band (mine is .052"). Besides, if I put a stock head back on it its right at 150psi all day long.
Solution:
I don't have one and would love to know what the solution is. I certainly don't want to run race gas for a freeride ski and at times, I plan to run it at WOT. The "work around" solution would be to custom cut a set of domes but this really isn't the proper solution since this shouldn't be happening in the first place.
Ideas? (besides the basics)
