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Messages - GT Jets

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Engine Mechanical / Electrical / Re: Piston cylinder clearance
« on: December 11, 2018, 01:23:24 pm »
Forged pistons, compression around 9.5 to 1. Using fresh water for cooling.
You don't need to go crazy.

The issue is that the block temperature will be dreadfully cold, especially cylinder number one and two whilst the pistons will be extremely hot under wot conditions.

When we build them, forged pistons will get an additional .001" over and above what the piston manufacturer recommends for an automotive application. If boosted (turbo, roots, centrifugal) we go as high as .002" over the OEM application.

The ring gaps should remain fairly snug, there are times we would order file to fit rings if the gaps on the stock rings end up wide (in all honesty, shouldn't).

I hope this helps.

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The No Wake Zone / Re: Current situation.... So this just happened.
« on: December 11, 2018, 12:21:20 pm »
Just had shoulder surgery two weeks ago. In the process of healing up, not fun. Good luck with surgery and your recovery. I'm up here in Redding so if you need a hand at some point when we're both back to full strength let me know.
How is your shoulder feeling? I'm actually a little shocked at how little I'm hurting.

I have 8 weeks of no active shoulder movement, but can passively (assisted) move all over the place with minimal pain.

I hope you're doing awesome. I'll be heading up in February and will hit you up to see if you want to head over to Woodys for some wings and a beer....


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Engine Mechanical / Electrical / Re: Piston cylinder clearance
« on: December 10, 2018, 04:58:14 pm »
In my 454 with speedpro pistons how much clearance should I have between cylinder and piston. My machine shop isn’t very familiar with marine applications and I need to know what to tell him.

Forged, cast, hyper?

What piston and what cooling system?

Also, compression ratio comes into play if in the low range.


The No Wake Zone / Re: Current situation.... So this just happened.
« on: December 01, 2018, 06:10:55 pm » made some progress! Keep after it bud. And good to see ya back on here. Hope your next surgery goes good and smooth.

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Thank you, should know by Tuesday if I it will be a success...


The No Wake Zone / Re: Current situation.... So this just happened.
« on: December 01, 2018, 06:09:50 pm »
Wow you must have been REALLY bored. So, has it been worth it? Or do you need us to talk you out of being bored next time?

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It's been good so far, honestly, getting some time with my dad has been the best part. It's getting a little exciting now, things will start going the other way now... Been coming up with design ideas and will begin building walls as soon as I'm able to lift my right arm again (rotator cuff repair)...

Go in on Monday at 5:30AM....  :screwy:


The No Wake Zone / Re: Current situation.... So this just happened.
« on: November 21, 2018, 01:43:15 pm »
Been busier than a cat covering crap.... haven't been around much at all.

Made some crazy headway on the Moose... With all the fires and whatnot, was difficult to get her moved.
Boat's moved to its new dry dock area, stripped down to the pontoons, major metal work done, pontoons pressure tested and coated.

Removed 4-1/2 tons of crap...  :o

Next items are engine and drive and so on, headed in for another surgery next month, so progress will suck for a couple months.

Hope you guys are doing awesome.


The No Wake Zone / Re: GoPro Hero4 Silver
« on: July 07, 2018, 04:57:54 pm »
Tell me what you want for it... I think I may need it, mine is being a glitchy bitch, you never know if it's going to work or not....

I'm not rich, but I gotta lotta money..  :sly:

Shoot me a PM with your best shot and let's make it happen... Need it to chronicle my Moose boat build..LOL


Thanks again i will be installing gate valve today... took a look and from jet it tees off 1 line each going to tee to block then tees off one each to block to ball valves one line each to top of tstat then bottom lines to dump....I have a separate ball valve off of intake to basset tee then to headers. Excited to test it out after gate valve is installed and hopefully have a worried free weekend at the lake.

This sounds correct.... Don't forget to update on how well she ran....


Thank you for the responses.. I believe it’s tee’d off at block I will check when I get back home later how it’s plumbed and take pics. Would it be easier to just install a pressure relief on jet and leave those valves open? Thanks again guys!!

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Those pressure relif valves are one of the dumbest things I have ever seen... Install a gate valve on the pump line, I use the Red and White 3/4" threaded valve and they typically end up about 1/2 open.

With the thermostat set up you have, you can literally just turn it closed until it warms up to above the thermostat value and open it back up one half turn... Leave it alone... Run a tie wrap through the handle so it doesn't get disturbed.

One thermostat line goes through the transom and the other to a tee control valve for the headers.


Is it Necessary to be running 2 valves open or one cracked and one closed? Worried about getting milky oil. Just changed t valve and going to run it close next time out... here is setup 460bbf

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Take those off and throw them away IMMEDIATELY.... Is there a tee on the block water inlets? Hard to tell from those shots...

Regulate the tee valve timing with a gate valve on the jet pump.


WarZone / Re: CF # question
« on: June 28, 2018, 04:35:25 pm »
Those would not pass in most of the places I go... I would say no... What you can do though, use block style in the numbers and flare or shadow them with that same font in a different color... Should fly as long as they contrast each other...


Engine Mechanical / Electrical / Re: Oil temp reading
« on: June 24, 2018, 11:36:01 pm »
9 qts in a 10qt pan, 500ish... Im in it between 3k-5200 rpms. They have the sender on a t, where my oil pressure gauge comes off the block. Not the greatest pictures but i hope it helps. It seems like its got to be after its been cooled. I know the pan is the best place, but is there any other ports on the zz502.?

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I am going to sound like a dick here, but hang with for a moment....

Lose that brass bullshit.... All those tees and fittings with the gauge and the pressure sender, make that shit go away....

I don't see a temp sender anywhere.... Is it reading the temp before or after the cooler?

The cooler should be plumbed like this crude diagram....

The No Wake Zone / Current situation.... So this just happened.
« on: June 21, 2018, 10:31:42 pm »
Got bored, went to a lien sale, spent some cash. LMAO

15X56 Moose... Permitted on Shasta Lake. Gonna be a busy few months.


Engine Mechanical / Electrical / Re: Oil temp reading
« on: June 21, 2018, 10:14:09 pm »
So my oil temp reading on my bost is in the range of 150-170, I have a Thermostatically controlled engine block adaptor thats suppose to bypass my oil cooler until 180 then opens fully. My question is why am I seeing 150-170*, My oil cooler is a 3x25 on my 502. Do I possibly have a bad sender? My sender is tapped in right at the remote oil filter?
Any help would will be greatly appreciated, ill get pictures of my setup tomorrow. TIA

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How much oil? How much HP? how hard did you run it? Is the oil cooler plumberd on the cold side, or the hot? (should be the hot side)…

What was the leaving water temp?


Engine Mechanical / Electrical / Re: Running and bogging out??
« on: May 24, 2018, 09:25:50 pm »
I have a 460 with Edelbrock carb. I’m having trouble with carb. once I hit wakes or it starts bouncing it loses power and starts bogging out I’m not to sure we’re to look. I’m getting fuel but like I said once it bounce it Boggs out???

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Depending on which carburetor, these things have two extremely small fuel filters in the carb top... Pull it and ditch those little bastards..


Engine Mechanical / Electrical / Re: Rebuild or replace?
« on: May 14, 2018, 09:10:44 pm »
Stock BBC out of a 78 truck, peanut ports, logs and snails, Performer 2.0 dual plane and a 750 CFM Edelbrock 1407 on top of a 1" open spacer, turning an "A" impeller.    It makes ~18 - 20Hg at idle and I figure ~225 HP.

You need the vacuum numbers at WOT... Closer to 0"hg the better.


Jet Pumps / Re: help with best impeller for my project
« on: May 13, 2018, 09:22:01 pm »
When serving USCG boating safety team in '68, '69, we would work the River between Laughlin and Havasu and there I fell in love with the Jet Boats...  Now 50 years later I finally own one...  While escaping the Montana winter at Pirate Cove I bought a 1968 Hallett 18' that others made few changes over the years, with exception of the pump...  Now has a 454 BBC and the engine runs sweet, the pump is not only worn out but still has a "B" impeller...  We look forward to cruising the river next several years and I just removed the pump and am about to order rebuild kit and am asking for experienced Jet Boat owners to suggest correct impeller...  My goal is to cruise 35 to 40 MPH at 2800 - 3000 RPM ...  My guess is the engine is at 300 HP and we will be two person boat and never plan on using to pull anyone out of the water, unless by throwing them a flotation device :-)   Looking at charts, looks like I should get an "A"  or  "AA" impeller...  Any input appreciated,  Thanks in advance,  bagsworth

Two things to take into consideration.

The first thing is the engine may need some RPM to make some HP, so you can drop it out of a decent curve real quick. I personally would go with an A cut. If you want a decent cruise speed at 3000 RPM, build a v drive.

A double A will simply pull more HP from the engine, it wont necessarily make it any faster at the same RPM as an A, if it did, it will be very slight (maybe 2 or 3 MPH).

Wish I had better news. You will be in the 3,500 to 4,000 RPM to see a decent cruise speed (thinking you are talking 35-40 MPH)..

Good luck and thank you for your service sir. If I may, what part of Montana? I spent some time with my dad and his high school buddy in Trout Creek/Mazula area and was in awe...


Engine Mechanical / Electrical / Re: Rebuild or replace?
« on: May 13, 2018, 09:14:33 pm »
Any suggestions on hole size(s)/spacing/location(s) for the counterweight holes?

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It is really a trial and error thing. First thing I would do is to get a Wide open throttle vacuum reading and run a Go Pro on the upper velocity plates to witness the plates opening angle. If the carburetor is under demanded (like on a big cammed BBC) they will be WFO, but a mild small block may need that help to lower the vacuum pressure.

What's the set up?


Random Boat Parts For Sale / Re: Chrome modular rims and new tires
« on: May 12, 2018, 10:33:48 pm »
Dammit! I was just in SoCal..... I need these.

 :banghead: :banghead: :banghead:


Engine Mechanical / Electrical / Re: Rebuild or replace?
« on: May 12, 2018, 10:31:44 pm »
I guess that makes sense with that goofy air door at the secondaries.  Any tips on hopping it up a little?  Don't have the scratch for a holley at the moment.

Buy the strip kit, jet them up a wee bit, go down one needle size, pull the tiny fuel filters and discard, drilling the counterweight on the velocity door gains some much needed top end and allows the vacuum levels to get lower, this in turn equals more HP if the jetting can be made to match.


Engine Mechanical / Electrical / Re: Rebuild or replace?
« on: May 11, 2018, 12:25:57 pm »

A jet boat engine thrives on high RPM torque and the AFB type carburetor limits how much air the motor can pull in. They can be made to work better, but never work great. You would be much better off with a mechanical secondary Holley type deal. You also have to be careful with some of the Edelbrocks because they can have these teeny tiny little fuel filters in the carb top that restrict fuel flow when they are even a little dirty, causes an extreme lean condition.


Engine Mechanical / Electrical / Re: Chevy TBI distributor
« on: May 09, 2018, 06:55:13 pm »
I say toss that and go to a hei

That is an HEI........

Get the marine module for it and it will work tits.


Engine Mechanical / Electrical / Re: Rebuild or replace?
« on: May 03, 2018, 11:49:43 am »
Big block for what you want todo.... it ain’t cheap tho lol.. as I’m sure you already know!

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If you can't pull a tube with a small block, that's one anemic ass mouse LOL...


Engine Mechanical / Electrical / Re: Rebuild or replace?
« on: May 03, 2018, 11:48:35 am »
Truck headers???

Scoggin Dickey L31, $2195 delivered. New, not a remanufactured or rebuilt engine.

Add a vortec style dual plane manifold, 750 Holley, and 1.6 rockers.

325+ hp...All day long.

Still curious about those truck headers, post a pic?

Schoenfeld Sprint car headers work pretty well for 'off the shelf' headers. ,(Down side up).,3488.html



That's good chit...

A fairly well built 454 will make about 375 horse, you will need everything... Intake, carburetor, mount, exhaust, fuel pump, crank pulley, flywheel, completely redo motor mount location, which is alignment, the electrical is a little different...

I'm not trying to talk you out of anything, but that mouse is the way to go.

Looking at your picture, you have the worst carburetor on the market for a boat, I sort of dig the redneck vibe of those headers though...LOL

If you want to get on the water quick and cheap, I would build the 350 you have with some good parts. shoot for 10:1 compression, I have a few suggestions on carburetor and camshaft, but need to know how the pump is built. You don't want to hang the doors if there are no walls....LOL


Engine Mechanical / Electrical / Re: Rebuild or replace?
« on: May 02, 2018, 11:25:54 pm »
I’m kind of stuck on this decision. My jet boat has a tired 4bolt main 350 in it. (Burns 2 qts of oil per 15ish gallons of fuel). I can’t decide rebuild the 350? Build a 383 stroker, LS swap it (I happen to have a truck 5.3 with an aluminum block) or trade the LS for a big block...
My boat is a 78. Challenger with a dominator pump.
Any input, advice, opinions, are appreciated thanks in advance!

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So, just to get this party started....

What do you use the boat for?

What are you looking for as far as performance?

Do you have the funds to be scaring up parts for an LS swap?

Do you have all the crap for a big block?

If you want to get on the water quick and on the cheap, build the mouse with 10:1 compression, proper cam and carburetor and let her buck. You are talking the difference of 10MPH (at the most) between the big block and the mouse and I could build that small block to 350hp for under a grand....JMHO...


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