Reducing compression
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Seasoned HDF Member
Joined: Dec 2012
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From: Orange County
Reducing compression
I'm thinking of changing to the Andrews 26G cam, so I need to drop my 10:1 compression. It's a 98ci; can anyone recommend which pistons/kit to get? Should I just buy the stock pistons for a 98ci?
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Joined: Mar 2010
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From: Poolville
At 10:1 you can run the 26G cam with the 35* ivc and should be at 195 ccp which is doable.... If your running a .030" head gasket then all you need is a .045" head gasket and that would put you right at 9.8:1 and 189 ccp @sealevel...
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Seasoned HDF Member
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From: Orange County
Well, from what I had read, it didn't seem like porting was absolutely necessary. Really what I'm after is lower end pull. These cams pull ok, but it's up over 3k rpm.
Road Master
Joined: Nov 2012
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From: Centerville, ohio
Your pistons are only 2 years old from Jims. He uses CP and it would have a 3cc dome. It's possible they are in tolerance and can be reused, just remove the dome. Deglaze the cylinders and install new rings. Otherwise you need a flat top piston. I would have Scott do the heads and pistons.
HDF Community Team
Joined: Jun 2006
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From: san antonio
Nothing we do to these vtwin motors is "necessary" but head work is a worthwhile upgrade. You could have the heads worked and the porter could pick up a couple of ccs in the chambers by dropping the valves, etc. and you could keep a .030" head gasket and run the 26 cams at 9.8 that way. Replacing the pistons just isn't necessary to achieve your goal. Even if you went so far as to pull the pistons, you could simply have the dome shaved to lower compression.
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Seasoned HDF Member
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From: Orange County
Yes, that is correct - 3cc pistons. I spoke with Jim and he told me I probably do not need to change pistons. The 26 should work. I may give it a go.
On the the other hand, It was mentioned in another post, that my exhaust was too free flowing for my setup. If things work out, I may change the exhaust to DD Fat Cat and see how it performs. Then, decide if I want to try the 26.
On the the other hand, It was mentioned in another post, that my exhaust was too free flowing for my setup. If things work out, I may change the exhaust to DD Fat Cat and see how it performs. Then, decide if I want to try the 26.
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HDF Community Team
Joined: Jun 2006
Posts: 12,774
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From: san antonio
Yes, that is correct - 3cc pistons. I spoke with Jim and he told me I probably do not need to change pistons. The 26 should work. I may give it a go.
On the the other hand, It was mentioned in another post, that my exhaust was too free flowing for my setup. If things work out, I may change the exhaust to DD Fat Cat and see how it performs. Then, decide if I want to try the 26.
On the the other hand, It was mentioned in another post, that my exhaust was too free flowing for my setup. If things work out, I may change the exhaust to DD Fat Cat and see how it performs. Then, decide if I want to try the 26.
Now you are off on your exhaust.
What exhaust are you running? There are aftermarket baffles, torque cones, etc. and other ways to increase exhaust back pressure rather than drop $700-$800 on new exhaust. A cam change would be much cheaper. Focus.
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From: Orange County
Money must be burning a hole in you pocket. Now you are off on your exhaust. What exhaust are you running? There are aftermarket baffles, torque cones, etc. and other ways to increase exhaust back pressure rather than drop $700-$800 on new exhaust. A cam change would be much cheaper. Focus.
Now you are off on your exhaust. What exhaust are you running? There are aftermarket baffles, torque cones, etc. and other ways to increase exhaust back pressure rather than drop $700-$800 on new exhaust. A cam change would be much cheaper. Focus.What the heck - it's only money.
