Performance issues.. need help/opinions!

A general, non-powerplant specific, discussion on airboat technology, ie., hulls, rigging, polymer, etc..
SthrnStyle3
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Performance issues.. need help/opinions!

Postby SthrnStyle3 » Thu Dec 08, 2016 12:38 pm

I guess I will start out by listing the problems and then listing things I think may be a possible issue, to see what y'all think. The description of my airboat is in my signature, if y'all have any other questions, please ask. I've never really been extremely pleased with the performance of my setup. It's still a night and day difference from a DD, but I feel it should be better. I originally thought I may have a freshly built motor (by me) that should be capable of 350-375 hp, but I feel I'm lucky if it's 300.. I'm only basing this off the fact that I'm spinning a 78" whispertip 2.0 two blade at 8 degrees (measured at the tip) 5000 rpms. I was really expecting more pitch lol.

The issues I'm currently facing are crappy idle (especially when it's not warmed up), dieseling when I shut it off (unless I let it idle for quite a while), runs warm at about +/-200ish in summer and 180-190 in this cooler weather and I have a 160 tstat, really bad gas mileage and a sputter when I stomp it to get up on a plane.

The dieseling and running warm have been an issue from early on, but the rest are fairly new..

Some possibilities that I am considering are: a vacuum leak, because the "S" shaped intake gasket in the back is sucked out pretty bad. I sprayed starting fluid on it and didn't notice a change in rpm though.., the idle air mixture needs to be adjusted (edelbrock) but why are there now symptoms..?, maybe I need to adjust the idle mixture in order to adjust the main idle screw to get the plates closed more to help stop the dieseling?, timing has been played with from day one and it was at around 36 and is now around 30-32. Maybe jets, needles and/or springs need changed in the carb.? Maybe vacuum advance might help cool the motor down at idle (only cools down at a fast idle/slow cruise, too slow and temps climb after a hard run).

I'm all ears to hear opinions and ideas to troubleshoot. Thanks in advance!
12' aluminum hull, 350 sbc w/ flattop Pistons and camel hump heads, side by side seating w/ double in front, 2:1 gearbox and a 78" whirlwind whispertip 2.0

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John Fenner
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Re: Performance issues.. need help/opinions!

Postby John Fenner » Thu Dec 08, 2016 1:34 pm

OK, flat top pistons and camel hump heads will have you at about 11/12:1 hope you are running high test, you might need to get some avgas to it too, this will curb the dieseling, as far as carbs go edelbrocks suck, I would suggest a Holley 600, any idea what cam is in it?
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SthrnStyle3
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Re: Performance issues.. need help/opinions!

Postby SthrnStyle3 » Thu Dec 08, 2016 2:18 pm

It's a mild cam from summit with an rpm range of 1200-5400, hydraulic flat tappet. I'd have to look up the specs when I get off work. When I tried to calculate the compression, using online calculators, everything came up with about 9.8:1. The Pistons have four valve reliefs. They're the Speed Pro brand from summit. The machine shop that did my block and heads also said the compression should be close to 10:1. But I do run 93 every single time.
12' aluminum hull, 350 sbc w/ flattop Pistons and camel hump heads, side by side seating w/ double in front, 2:1 gearbox and a 78" whirlwind whispertip 2.0

One Eyed Gator
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Re: Performance issues.. need help/opinions!

Postby One Eyed Gator » Thu Dec 08, 2016 2:20 pm

Pm Sent

jeepinocala1111
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Re: Performance issues.. need help/opinions!

Postby jeepinocala1111 » Thu Dec 08, 2016 2:28 pm

Do you have a gear box?

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scottyroll
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Re: Performance issues.. need help/opinions!

Postby scottyroll » Thu Dec 08, 2016 2:41 pm

jeepinocala1111 wrote:Do you have a gear box?


Per his signature, he has a 2:1.
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jeepinocala1111
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Re: Performance issues.. need help/opinions!

Postby jeepinocala1111 » Thu Dec 08, 2016 3:58 pm

scottyroll wrote:
jeepinocala1111 wrote:Do you have a gear box?


Per his signature, he has a 2:1.


Dam :violent1: ok I see :slap: what I missed, then that is pretty bad I am guessing he has a lot lower hp then.

SthrnStyle3
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Re: Performance issues.. need help/opinions!

Postby SthrnStyle3 » Thu Dec 08, 2016 7:04 pm

Jeep are you referring to the pitch I'm turning? I thought it may of been low too but I'm not sure what would be normal.. Im suprised my hp would be that low, even though I've done some stuff to the motor. Granted it wasn't the most expensive engine build, but still lol.
12' aluminum hull, 350 sbc w/ flattop Pistons and camel hump heads, side by side seating w/ double in front, 2:1 gearbox and a 78" whirlwind whispertip 2.0

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scottyroll
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Re: Performance issues.. need help/opinions!

Postby scottyroll » Thu Dec 08, 2016 7:34 pm

OP, I think you should be closer to 20* (2 mark) with your combo and build specs. All else I can say is you need a tune up to get it dialed in and I don't even know where to start because it could be a number of things but a reputable engine man should be able to figure it out in no time. Things like this remind me why I loved switching over to a junk yard vortec; even a dummy can run it and read any problems in plain english thru their phone lol. Good luck :salute:
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14ft Laser/6.0 LQ4/2.37 Rotator/3 Blade "K"


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