Dynamic compression
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From: The Vieux Ford, Kansas
Dynamic compression
I have a 351C in my truck and I was thinking about upgrading to a roller cam. I am looking at a Comp Cams 260H, and my dynamic compression is coming out to about 8.318. Just wandering if this will work with pump gas? I don't mind running premium but don't want to mess with octane booster, this motor was built with a different purpose in mind but found it way into my truck when the 400 got tired, the current cam is too big.
-Johnboy
-Johnboy
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So i calculated your static cr around 9.8:1, how are you sure of this? what pistons are you running? did you measure your combustion chambers? are your pistons 0 decked?
Since the 351 has a shorter stroke than the 400 you may get away using 91 octane if you have iron closed chamber heads or aluminium heads with 0 decked pistons, if not you will need 93 or better.... also the 260h is a single pattern cam , stock 2v heads suffer from restrictive exaust ports, so you will benefit mre from a double pattern cam, its still a good cam..
Since the 351 has a shorter stroke than the 400 you may get away using 91 octane if you have iron closed chamber heads or aluminium heads with 0 decked pistons, if not you will need 93 or better.... also the 260h is a single pattern cam , stock 2v heads suffer from restrictive exaust ports, so you will benefit mre from a double pattern cam, its still a good cam..
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From: The Vieux Ford, Kansas
Yes the static is about 9.8:1, the pistons are zero deck flat tops 4.040, the heads were milled and chambers polished to get 74cc chambers on all cyls. The heads have extensive port work and bigger valves 2.11int/1.69exh. Like I said this engine was not built for a truck it was built for a fox mustang that I don't own any more. Just trying to get a general idea of what would be the smallest cam I can get away with. Heads are 2V D1AE-AA but I think they are so far from stock that the casting number doesn't matter too much any more.
-Johnboy
-Johnboy
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From: The Vieux Ford, Kansas
What do you mean by conservative tune? Less advance and mabey a little on the rich side? I do a lot of short trips with this tuck so I would rather run a little bigger cam and a 195 thermostat. Thanks for the help, I really haven't ever tried for the smallest cam I can get away with before.
-Johnboy
-Johnboy
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From: The Vieux Ford, Kansas
Just had another thought, if I advance the cam timing by 4 degrees I can get 8.138. I guess I am wandering what you guys thing would be low enough 8:1 or should I be shooting for something like 7.5:1?
-Johnboy
-Johnboy
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hey john wrong thought.... advancing it wil get you ,pinging... you could retard your cam by 4 degrees REALLY getting you intoo a 0 degrees setup. since most comp cams will get you now days 4 degrees advance.... I Had my cam custom designed for 0 degrees to do so....beleive me , just ask
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From: The Vieux Ford, Kansas
Well think I'm going to give it a try, really don't want to step up to a custom grind the roller conversion is expensive enough by itself. If its still a problem I'm just going to buy a quick fuel carb and run E85 to heck with detonation.
-Johnboy
-Johnboy
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Last post was a drunk post, sh$t I hate doing that, anyways I was drunk right, you could get one of those 3 way timming chains and retard your cam by 4 degrees making the Intake Lobe Centerline of the cam 110 which is straight up and thus lowering your DCR to almost 8:1 which is perfect for 91, as i said before that cam has a built in advance of 4 degrees....
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I'd call your cam mfgr. before blindly moving the cam timing around. They will be able to tell you whats going to happen before you do it, assuming it's been degreed in and you have actual figures to give them. I never put a cam in without degree it in. 4* either way is a big jump that could lead to big problems & just because it says 4* doesn't mean thats what you will end up with either.
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From: The Vieux Ford, Kansas
Thanks for all the help, just want to get this thing right. I will talk to Comp about this before I buy any thing, or I might look for something a little bigger. I would really like to find something with the 272H duration but the 260H lift.
-Johnboy
-Johnboy
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