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Discussion Starter #1
Looking to build a reliable pump gas 489ci Chevy that is reliable and faster than my near stock 454. I am going to be building this engine for pump gas at approx. 10:1 compression. Running the Dart iron eagle top end kit Dart 01120005 - Dart Iron Eagle Top-End Engine Kits for Chevy - Overview - SummitRacing.com something alont these lines for a cam COMP Cams CL11-314-4 - COMP Cams Xtreme Marine Cam and Lifter Kits - Overview - SummitRacing.com. Anyways now on with my question. Should I run an 850 cfm 1450 holley or a 950 cfm? Thanks for your help guys:)Unsure
 

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What rpm do you plan to run,, and are you going to cut down the impeller to be able to get to that rpm?
Totally green to making a jet boat fast. I was planning on going to a stainless impeller but other than that I'm not real sure on the rpm. will spend most of it's time around 3500 rpm but when I get after it I want it to move out pretty good. Just looking to build a performance engine not a race engine.
 

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Don't get the 950 because you ASSUME its bigger and flows more than the 850. It doesn't. The 950 is nothing more than a 750 main body screwed to a 850 throttle base. It has fantastic throttle response, and is the killer small block carb of all time. But IT IS NOT bigger than an 850. In fact it flows less than the same series Ultra HP 850.

the number one chioce if your buying a Holley, IMO, is the new Holley Ultra HP all alum carb. New over sized ALUM float bowls, anodized billet throttle body and metering plates, and
ALUM main body. There is no excuse for buying a pot metal/zink carb today except price. The price on the new carb is a little pricey, but it is a much better carb than the older zink carbs.
And its available as a 950 if thats what you think you want. And its availble in red, blue, and all black.:)sphss
LINK: Holley Ultra HP



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Pump gas and aluminum heads at 10 to 1 is fine. Pump gas and Iron heads with 10 to 1 not a good idea. You need to keep the combo down around 9 to 1. As many 496 combo I have spec'd for customer a good 950HP from QF or AED is your best bang for the buck.

I agree with Barry you need to select a max rpm range you want to turn the engine then build the combo around that. A 490" CID that is going to see a max of 5500 rpm needs a good 270 to 290 cc head. Same engine to 6000 around 300 to 310.
 

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Discussion Starter #7
Pump gas and aluminum heads at 10 to 1 is fine. Pump gas and Iron heads with 10 to 1 not a good idea. You need to keep the combo down around 9 to 1. As many 496 combo I have spec'd for customer a good 950HP from QF or AED is your best bang for the buck.

I agree with Barry you need to select a max rpm range you want to turn the engine then build the combo around that. A 490" CID that is going to see a max of 5500 rpm needs a good 270 to 290 cc head. Same engine to 6000 around 300 to 310.
obnoxious001 and we took it to pm's and talked it over. I will be more around 9.5-9.75:1 if I have to run a mix of a little race gas with it, it will not be that big of a deal. I can get fuel at a very discounted price due to my off road racing. I understand with my compression ratio that I will have to back the timing down if I run pump gas but most of the engines life will be spent at around 3200-3600 rpm.

I am not trying to sound like I know every thing as I don't when it comes to jet boats. I have built some fast race cars for drag racing (streetable muscle cars) but the whole jet boat experience and trying to go fast is a different story. That is why I ask the help from all of you guys that are knowledgable in this area. I am going to go with what I have planned and see where it goes. Thank you all for your help, it is very appreciated:3:
 
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