jets/props

[big blue]

What jets should a 4port Quadrajet have at 6000 ft? What pitch prop should work the best at 6000ft pushing a 26ft boat with a 350? Any suggestion would really help,or phone numbers!

 

[John Carpenter]

Re: jets/props

Can't help you with your carb problems and seriously question that you need to be trying to get 4800-5200 rpm out of that 350. Most that I've owned had a recommended rpm range of 4200-4600. If your engine seems to run OK then you clearly have too much prop...however you will only gain about 200 rpm for every inch of pitch you drop. Going to a 15X13 will get you up to 4200 rpm. I would also check the fuel and electrical systems to make sure you are not starving for gas or???<br /><br />If you are only turning 3800 at WOT then you are lugging the engine which is not good. My .02

 

[Boatist]

Re: jets/props

Big Blue<br />Two questions: Have you added a lot of weight to boat?? What is the condition of the hull, any hooks or moss on the bottom?? Has boat always ran at that RPM or is this something new??<br /><br />At 6000 feet you will need to advance the timing farther than the sea level spec. At 6000 feet will never have the power it has at sea level. I do not think any need to change the jets unless you made them smaller which would lower power normaly. Problem is have less air so with less air do not want more fuel. Kind like nascar at a restricter plate track. Only way I know to get more air at 6000 feet would be to change carburetor to a bigger bore or go from a two barrel to a four barrel and for this to work right may also have to change manifold and put in bigger valves. Should have some experts in your area if you are at 6000 feet.<br />I would check or change every plug and also make sure you are getting spark on all plugs. I also think normal WOT range should be 4200-4600 and if timing makes no difference then could go as low as a 11 or 12 pitch prop. Each inch change in pitch makes about a 200 RPM change.

 

[Bondo]

Re: jets/props

The posts above are Right On.. I Also question WHY you'd want to spin a sm. block 5200rpms.... It'll do it, But not for very long, or very efficently....<br />I'd start with a complete tune-up,+ engine survey... the plugs will tell you if the jetting is anywhere Near right.... Once you Know the engine is running properly, then Check the Hull, as Boatist says... Then, If nessesary, you can have your prop flattened out abit to get to 4200, to 4600rpms.....<br />At 6000', the ONLY Way to build any Real power, is with a Blower, or Turbo.....

 

[hydrabass]

Re: jets/props

the company i use to work for had high altitude set ups and when we had a boat that was going to a place at higher altitudes we knew to change to a different ratio outdrive and prop setup. the company that this viking came from may have a record of this setup