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Discussion Starter #1
I need help deciding which way to go. My main concern is having to tune on the rex to much. I know the Standard Bore 750 Kit is 11.5 to 1. What compression is the 840 Big Bore? What compression is the stock teryx? If the Big Bore is closer to stock compression it should be easier to dial-in and walk away. Assuming the high compression 750 is anything like a SB Chevy temperature changes affect how lean/rich you need to be. I live in Iowa so it could 100 f. and high humidity and 3 to 4 months later 20 f. I'd really like to go with the standard bore but if the 840 would be easier to tune and start I might go that route. I guess if the 840 is hi-comp as well I just wasted everyones time but the way the piston looks it must be lower. Thanks in advance for any help.
 

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This has been a big ugly debate here but the 840 is high compression too.

I prefer standard bore mostly for price and am happy with the additional power.


Forums tend to analyze things more than they should. Meaning if one vehicle had a 840 and one a standard bore and they raced and one was half a length ahead of the other every time the one that was half a length has to be the best and the way to go regardless of cost and any other issues that may arise.
 

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The FST standard bore is 11.5:1, the FST 840 is 11.0:1 and I beleive stock is around 8.8:1.
 

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I need help deciding which way to go. My main concern is having to tune on the rex to much. I know the Standard Bore 750 Kit is 11.5 to 1. What compression is the 840 Big Bore? What compression is the stock teryx? If the Big Bore is closer to stock compression it should be easier to dial-in and walk away. Assuming the high compression 750 is anything like a SB Chevy temperature changes affect how lean/rich you need to be. I live in Iowa so it could 100 f. and high humidity and 3 to 4 months later 20 f. I'd really like to go with the standard bore but if the 840 would be easier to tune and start I might go that route. I guess if the 840 is hi-comp as well I just wasted everyones time but the way the piston looks it must be lower. Thanks in advance for any help.
No different tuning either a standard bore or a big bore....

Half a length? Todd? lol It will be 2 lengths just out of the hole.
 

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Discussion Starter #5
Not trying to start a war here, just wanting to make the right decision. Thanks for the compression info X- Champ. I'm leaning real hard towards FSTs $599 standard bore deal. My question now is will I need to rejet from summer to winter or is there a happy medium? Would like to hear any opinions on why you like/dislike the standard bore kit. I think my driving abilities can overcome the two links outta the hole. :D
 

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Well it really depends on the money if you ask me if you can afford an 840 kit well thats what i would go with,and a 840 with make more power and torq.
 

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How would that kit work on an 08 with carburetors I think I've got a rod knocking in mind looks like it might be a good kit to get love your opinion new to these things thanks
 
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